Recent studies have successfully demonstrated high-Tc superconductivity in bilayer nickelate La3Ni2O7.However,research on modulating the structural and transport characteristics of La3Ni2O7 films by applying“chemical...Recent studies have successfully demonstrated high-Tc superconductivity in bilayer nickelate La3Ni2O7.However,research on modulating the structural and transport characteristics of La3Ni2O7 films by applying“chemical”compressive pressure through cation substitution is still limited.Here,we address this issue in the La_(3−x)Nd_(x)Ni_(2)O_(7)(x=0,1.0,1.5,2.0,and 2.5)thin film samples.It was found that using Nd3+with a smaller radius instead of La3+can reduce the c-axis lattice constant and shift the metal-insulator transition(MIT)temperature TMIT.To probe the origin of the MIT at cryogenic temperatures,experimental measurements of magnetoresistance were conducted,and theoretical analysis was carried out using the Kondo model,Hikami-Larkin-Nagaoka equation,and other methods.The results indicate that as Nd doping rises,the contributions of the Kondo effect and two-dimensional weak localization(WL)first decrease and then increase.The total contribution of WL and the Kondo effect in the mid-doped La_(1.5)Nd_(1.5)Ni_(2)O_(7)sample was the smallest,which to some extent explains the changes in TMIT.The Kondo effect dominates in other La_(3−x)Nd_(x)Ni_(2)O_(7)(x=0,1.0,2.0,and 2.5)samples.This work demonstrates that cation doping has a significant impact on bilayer nickelates,providing experimental evidence for understanding the physical mechanism of the MIT in bilayer nickelates.展开更多
While the metal to insulator transition(MIT)of d-band correlated perovskite nickelates(RENiO_(3))are widely adjustable via their rare-earth composition,the roles of potential valence variabilities associated with the ...While the metal to insulator transition(MIT)of d-band correlated perovskite nickelates(RENiO_(3))are widely adjustable via their rare-earth composition,the roles of potential valence variabilities associated with the rare-earth elements were rarely concerned.Herein,we demonstrate the material synthesis and MIT properties of RENiO_(3) containing valence variable rare-earth compositions,such as Ce,Pr,Sm,Eu and Tb.The metastable perovskite structure of SmNiO_(3) and EuNiO_(3) with a rare-earth valence states variable towards+2 can be effectively synthesized under high oxygen pressures as it is necessary to reduce their formation free energies.This is in contrast to Ce and Tb,in which situations the variable rare-earth valence state towards+4 reduces their ionic radius and prohibits their occupation or co-occupation of the rare-earth site within the perovskite structured RENiO_(3).Nevertheless,PrNiO_(3) with MIT properties can be effectively synthesized at lower oxygen pressures,owing to the higher stability to form a fully occupied 6s orbit associated Pr3+compared to the half-filled one related to Pr4+.The present work provides guidance for regulating the MIT properties of RENiO_(3).展开更多
The discovery of nickelate superconductors,including doped infinite-layer(IL)nickelates RNiO2(R=La,Pr,Nd),layered square-planar nickelate Nd6Ni5O12,and the Ruddlesden–Popper(RP)phase La3Ni2O7,has spurred immense inte...The discovery of nickelate superconductors,including doped infinite-layer(IL)nickelates RNiO2(R=La,Pr,Nd),layered square-planar nickelate Nd6Ni5O12,and the Ruddlesden–Popper(RP)phase La3Ni2O7,has spurred immense interest in fundamental research and potential applications.Scanning transmission electron microscopy(STEM)has proven crucial for understanding structure–property correlations in these diverse nickelate superconducting systems.In this review,we summarize the key findings from various modes of STEM,elucidating the mechanism of different nickelate superconductors.We also discuss future perspectives on emerging STEM techniques for unraveling the pairing mechanism in the“nickel age”of superconductivity.展开更多
The chemical and electrochemical stability of lanthanide nickelates La2 NiO4+δ(LNO),Pr2 NiO4+δ(PNO)and their mixed compounds La(2-x)PrxNiO4+δ(LPNOs)with x=0.5,1 or 1.5 is reported.The aim is to promote these materi...The chemical and electrochemical stability of lanthanide nickelates La2 NiO4+δ(LNO),Pr2 NiO4+δ(PNO)and their mixed compounds La(2-x)PrxNiO4+δ(LPNOs)with x=0.5,1 or 1.5 is reported.The aim is to promote these materials as efficient electrodes for solid oxide fuel cell(SOFC)and/or solid oxide electrolysis cell(SOEC).La2 NiO4+δand La1.5Pr0.5NiO4+δcompounds are chemically very stable as powders over one month in the temperature range 600-800℃,while the other materials rich in praseodymium progressively decompose into various perovskite-deriving components with additional Pr6 O11.Despite their uneven properties,all these materials are quite efficient and sustainable as electrodes on top of gadolinium doped ceria(GDCBL)//yttrium doped zirconia(8 YSZ)electrolyte,for one month at 700℃without polarization.Under polarization(300 mA·cm-2),the electrochemical performances of LNO,PNO and La1.5Pr0.5NiO4+δ(LP5 NO)quickly degrade in SOFC mode,i.e.for the oxygen reduction reaction,while they show durability in SOEC mode,i.e.for the oxide oxidation reaction.展开更多
The rare-earth nickelates(RENiO_(3)) exhibit an exceptional complex electronic phase diagram and multiple electronic phase transitions that enrich promising applications in correlated electronic devices beyond convent...The rare-earth nickelates(RENiO_(3)) exhibit an exceptional complex electronic phase diagram and multiple electronic phase transitions that enrich promising applications in correlated electronic devices beyond conventional semiconductors.Nevertheless,the practical applications of RENiO_(3) are challenged by their intrinsic thermodynamic metastability in material synthesis and high material cost.Therefore,developing an economical strategy to achieve the batch synthesis of RENiO_(3) is of vital importance.In this work,we enlarged the synthesis amount of RENiO_(3) up to 20 g per batch using chloride(KCI) assisted molten salt reaction.By optimizing the reaction conditions,the powder of RENiO_(3) with the cubic shape and average size of ~2μm was effectively synthesized,while their phase purity exceeded 95%.In addition,the cost to synthesize RENiO_(3) was further reduced by using rare-earth extraction intermediate products as the raw materials,instead of using the pure rare-earth precursors.It also achieved wide adjustments in the metal-to-insulator-transition temperature from160 to 420 K without significantly reducing the transition sharpness.By enlarging the synthesis amount and the reducing the cost,it paves the way to the device application of RENiO_(3).展开更多
Although the thermistor and metal to insulator transition bi-functionalities were discovered for rareearth nickelates(RENiO3),the electronic stability in their correlated transports under impulse voltage or magnetic f...Although the thermistor and metal to insulator transition bi-functionalities were discovered for rareearth nickelates(RENiO3),the electronic stability in their correlated transports under impulse voltage or magnetic field remain as open questions.Herein,we demonstrate the thermistor transportations of the electron correlated rare-earth nickelates under impulse direct current voltage and in magnetic environment.The insulating phase of RENiO3 shows zero crossing linear I-V characters,indicating their stable electronic resistance is independent of the imparted voltage up to 10 V and pulse width down to1 us,in spite of their sensitive electronic structures to polarizations.In addition,the high electronic stability associated with the thermistor transportation of RENiO3 is also demonstrated in magnetic fields up to 9 T(i.e.,MR<0.2%).The high electronic stability further paves the way to applying RENiO3 as a broad temperature range thermistor in temperature sensing or circuit protections for correlated electronics.展开更多
The multiple quantum transitions within d-band correlation oxides such as rare-earth nickelates(RENiO_(3))triggered by critical temperatures and/or hydrogenation opened up a new paradigm for correlated electronics app...The multiple quantum transitions within d-band correlation oxides such as rare-earth nickelates(RENiO_(3))triggered by critical temperatures and/or hydrogenation opened up a new paradigm for correlated electronics applications,e.g.ocean electric field sensor,bio-sensor,and neuron synapse logical devices.Nevertheless,these applications are obstructed by the present ineffectiveness in the thin film growth of the metastable RENiO_(3)with flexibly adjustable rare-earth compositions and electronic structures.Herein,we demonstrate a metal-organic decompositions(MOD)approach that can effectively grow metastable RENiO_(3)covering a large variety of the rare-earth composition without introducing any vacuum process.Unlike the previous chemical growths for RENiO_(3)relying on strict interfacial coherency that limit the film thickness,the MOD growth using reactive isooctanoate percussors is tolerant to lattice defects and therefore achieves comparable film thickness to vacuum depositions.Further indicated by positron annihilation spectroscopy,the RENiO_(3)grown by MOD exhibit large amount of lattice defects that improves their hydrogen incorporation amount and electron transfers,as demonstrated by the resonant nuclear reaction analysis and near edge X-ray absorption fine structure analysis.This effectively enlarges the magnitude in the resistance regulations in particular for RENiO_(3)with lighter RE,shedding a light on the extrinsic regulation of the hydrogen induced quantum transitions for correlated oxides semiconductors kinetically via defect engineering.展开更多
Although the metal to insulator transition(MIT)observed in d-band correlated metal oxides enables promising applications(e.g.,correlated logical devices and Mottronic devices),its present recognition is mainly limited...Although the metal to insulator transition(MIT)observed in d-band correlated metal oxides enables promising applications(e.g.,correlated logical devices and Mottronic devices),its present recognition is mainly limited on the direct current(DC)electrical transports.Up to date,the MIT from the perspective of alternation current(AC)transport and its potential electronic applications remains yet unclear.Herein,we demonstrate the frequency(f_(AC))dependence in the impedance(Z=Z’+iZ″)of typical MIT materials,such as thin film rare-earth nickelates(Re NiO_(3)),across the critical MIT temperature(T_(MIT)).Apart from the abrupt change in the impedance modulus(|Z|)across the critical temperature(T_(MIT))similar to the DC transport,the MIT also triggers non-continuous variation in the impedance phase(θ),and this enables the f_(AC)-regulations in the Z’-T tendencies(Z’=|Z|cosθ).At the critical f_(AC) range(e.g.,104-106 Hz),the con-versing variations in|Z|-T and cosθ-T across T_(MIT) result in non-monotonic delta-shape Z’-T tendency in Sm_(x) Nd_(1-x) NiO_(3),the full width half maximum of which is effectively narrowed compared to the situation with the absence of MIT.Further imparting lower or higher f_(AC) elevate the domination in|Z|-T and cosθ-T,respectively,but also enables abrupt Z’-T tendencies across T_(MIT) showing negative temperature coefficient of resistance(NTCR)or positive temperature coefficient of resistance(PTCR).By introducing f_(AC) as a new freedom,the MIT behavior can be more comprehensively regulated electronically,and this extends the vision in exploring the new electronic applications based on the correlated MIT materials from the AC perspective.展开更多
The discovery of superconductivity in Sr/Ca-doped infinite-layer nickelates Nd(La)NiO_(2)thin films inspired extensive experimental and theoretical research.However,research on the possibilities of enhanced critical t...The discovery of superconductivity in Sr/Ca-doped infinite-layer nickelates Nd(La)NiO_(2)thin films inspired extensive experimental and theoretical research.However,research on the possibilities of enhanced critical temperature by interface heterostructure is still lacking.Due to the similarities of the crystal structure and band structure of infinite-layer nickelate La NiO_(2)and cuprate CaCuO_(2),we investigate the crystal,electronic and magnetic properties of La NiO_(2):CaCuO_(2)heterostructure using density functional theory and dynamical mean-field theory.Our theoretical results demonstrate that,even a very weak inter-layer z-direction bond is formed,an intrinsic charge transfer between Cu-3d_(x^(2)-y^(2))and Ni-3d_((x^(2)-y^(2)))orbitals is obtained.The weak interlayer hopping between Cu and Ni leaves a parallel band contributed by Ni/Cu-3d_((x^(2)-y^(2)))orbitals near the Fermi energy.Such an infinite-layer heterostructure with negligible interlayer interaction and robust charge transfer opens a new way for interface engineering and nickelate superconductors.展开更多
The recent discovery of superconductivity in doped rare-earth infinite-layer nickelates RNiO_(2),R=Nd,Pr as a new family of unconventional superconductors has inspired extensive research on their intriguing properties...The recent discovery of superconductivity in doped rare-earth infinite-layer nickelates RNiO_(2),R=Nd,Pr as a new family of unconventional superconductors has inspired extensive research on their intriguing properties.One of the major motivation to explore the nickelate superconductors originated from their similarities with and differences from the cuprate superconductors,which have been extensively studied over the last decades but are still lack of the thorough understanding.In this short review,we summarized our recent investigation of the relevance of Ni/Cu-3d multiplet structure on the hole doped spin states in cuprate and recently discovered nickelate superconductors via an impurity model incorporating all the 3d orbitals.Further plausible explorations to be conducted are outlined as well.Our presented work provides an insightful framework for the investigation of the strongly correlated electronic systems in terms of the multiplet structure of transition metal compounds.展开更多
Based on the two-band tight-binding model composed of the 3d orbital of Ni and the 5d orbital of R(=La),we used the random-phase-approximation method to study the pairing symmetry of the nickelate superconductors.It i...Based on the two-band tight-binding model composed of the 3d orbital of Ni and the 5d orbital of R(=La),we used the random-phase-approximation method to study the pairing symmetry of the nickelate superconductors.It is found that even without considering the coupling between the R and Ni orbitals,neither the antiferromagnetic spin-fluctuation pattern nor the doping-dependent behavior of the robust dx^(2)−y^(2)-wave pairing state obtained in our calculations will be obviously influenced.Our results suggest the dominating role of the Ni 3d orbital in determining the low lying physics of the system.Furthermore,our results reveal a dome-shaped doping dependence of the superconducting transition temperature Tc,which is consistent with recent experiments.展开更多
We report an improved method for the preparation of highly dense nickelate ceramics at relatively low temperature. It is found that the introduction of appropriate additives during the ball-milling process facilitates...We report an improved method for the preparation of highly dense nickelate ceramics at relatively low temperature. It is found that the introduction of appropriate additives during the ball-milling process facilitates the formation of nickelate phase through solid state reaction. Moreover, although high-purity nickelate powders can only be obtained by calcining the mixture of starting materials at temperature higher than 1100 ℃. The adoption of powders calcined at 1000 ℃, rather than those calcined at higher temperature, is conductive to the low-temperature densification of nickelate ceramics, which is attributed to the small and dispersive particles, and the solid state reaction of the residual starting materials during sintering. Compared with the conventional process, the improved method can reduce the sintering temperature of nickelate ceramics by about 100 ℃ and decrease the grain size of the obtained ceramics, and therefore makes nickelate meet the fabrication requirements of multi-layer ceramic capacitors（MLCC）.展开更多
In the current work, LaNiO3 perovskite was synthesized using the polymeric precursor method. The materials were thermally treated at 300°C for 2 hours, subsequently supported on alumina or zirconia and finally ca...In the current work, LaNiO3 perovskite was synthesized using the polymeric precursor method. The materials were thermally treated at 300°C for 2 hours, subsequently supported on alumina or zirconia and finally calcined at 800°C for 4 hours. The resulting samples were characterized by X-ray diffraction, thermogravimetry, BET surface area and thermo-programmed reduction. Steam reforming reactions were carried out at 750°C and 6 bar during 4 hours using a pilot reactor under a H2O:CH4 ratio of 2.5. The mass of catalysts was about 5.7 g. X-ray diffraction patterns confirmed the formation of the perovskite structure in all samples prepared. The results also showed that lanthanum nickelate was more efficient when supported on alumina than zirconia. Finally, it was observed that the methane conversion was approximately 94% and the selectivity to hydrogen was about 70%. In all cases low selectivity to CO and CO2 was verified.展开更多
In addition to the pressurized high-temperature superconductivity,bilayer and trilayer nickelate superconductors La_(n+1)Ni_(n)O_(3n+1)(n=2 and 3)exhibit many intriguing properties at ambient pressure,such as orbital-...In addition to the pressurized high-temperature superconductivity,bilayer and trilayer nickelate superconductors La_(n+1)Ni_(n)O_(3n+1)(n=2 and 3)exhibit many intriguing properties at ambient pressure,such as orbital-dependent electronic correlation,non-Fermi liquid behavior,and density-wave transitions.Here,using ultrafast reflectivity measurement,we observe a drastic difference between the ultrafast dynamics of the bilayer and trilayer nickelates at ambient pressure.We observe a coherent phonon mode in La_(4)Ni_(3)O_(10)involving the collective vibration of La,Ni,and O atoms,which is absent in La_(3)Ni_(2)O_(7).Temperature-dependent relaxation time diverges near the density-wave transition temperature of La_(4)Ni_(3)O_(10),while it is inversely proportional to the temperature in La_(3)Ni_(2)O_(7)above~150 K,suggesting a non-Fermi liquid behavior of La_(3)Ni_(2)O_(7).Moreover,we estimate the electron–phonon coupling constants to be 0.05–0.07 and 0.12–0.16 for La_(3)Ni_(2)O_(7)and La_(4)Ni_(3)O_(10),respectively,suggesting a relatively minor role of electron–phonon coupling in the electronic properties of La_(n+1)Ni_(n)O_(3n+1)at ambient pressure.The relevant microscopic interaction and dynamic information are essential for further studying the interplay between superconductivity and density-wave transitions in nickelate superconductors.展开更多
Recently,a signature of high-temperature superconductivity above the liquid nitrogen temperature(77 K)was reported for La_(3)Ni_(2)O_(7−δ) under pressure.This finding immediately stimulated intense interest in the po...Recently,a signature of high-temperature superconductivity above the liquid nitrogen temperature(77 K)was reported for La_(3)Ni_(2)O_(7−δ) under pressure.This finding immediately stimulated intense interest in the possible mechanism of high-Tc superconductivity in double-layer nickelates.Notably,the pressure-dependent phase diagram inferred from transport measurements indicates that the superconductivity under high pressure emerges from the suppression of density-wave-like order at ambient pressure,which is similar to high-temperature superconductors.Therefore,clarifying the exact nature of the density-wave-like transition is important for determining the superconducting mechanism in double-layer nickelates.Here,nuclear magnetic resonance(NMR)spectroscopy of 139La nuclei was performed to study the density-wave-like transition in a single crystal of La_(3)Ni_(2)O_(7−δ.)At high temperatures,two sets of sharp 139La NMR peaks are clearly distinguishable from a broad background signals,which are ascribed to La(1)sites from two bilayer Ruddlesden-Popper phases with different oxygen vacancyδ.As the temperature decreases,the temperature-dependent^(139)La NMR spectra and nuclear spin-lattice relaxation rate(1/T_(1))for both La(1)sites provide evidence of spin-density-wave(SDW)ordering below the transition temperature(T_(SDW)),which is approximately 150 K.The anisotropic splitting in the NMR spectra suggests the formation of a possible double spin stripe with magnetic moments aligned along the c-axis.Furthermore,we studied the pressure-dependent SDW transition up to∼2.7 GPa.Surprisingly,the TSDW inferred from NMR measurements of both La(1)sites increases with increasing pressure,which is opposite to the results from previous transport measurements under pressure and suggests an intriguing phase diagram between superconductivity and SDW.In contrast,the present^(139)La NMR is insensitive to the possible charge-density-wave(CDW)order in the Ni-O planes.All these results will be helpful for building a connection between superconductivity and magnetic interactions in double-layer nickelates.展开更多
Trilayer Ruddlesden-Popper phase La_(4)Ni_(3)O_(10) has been observed with T_(c) of~30 K at high pressure in a recent experiment,which further expanded the family of nickelate superconductors.In this study,we explored...Trilayer Ruddlesden-Popper phase La_(4)Ni_(3)O_(10) has been observed with T_(c) of~30 K at high pressure in a recent experiment,which further expanded the family of nickelate superconductors.In this study,we explored the effects of electronic correlations in La_(4)Ni_(3)O_(10) using density functional theory plus dynamical mean-field theory at ambient and high pressures.Our derived spectral functions and Fermi surface of the ambient pressure phase are nicely consistent with the experimental results by angleresolved photoemission spectroscopy,which emphasized the importance of electronic correlations in La_(4)Ni_(3)O_(10).We also found the electronic correlations in pressurized La_(4)Ni_(3)O_(10) are both orbital-dependent and layer-dependent due to the presence of Hund’s rule coupling.There is a competition between the Hund’s rule coupling and the crystal-field splitting,and therefore,the Ni-O layers with weaker crystal-field splitting energy would have stronger electronic correlations.展开更多
Recently, a bulk nickelate superconductor La_(3)Ni_(2)O_(7) is discovered at pressures with a remarkable high transition temperature T_(c)~ 80 K. Here, we study a Hubbard model with tight-binding parameters derived fr...Recently, a bulk nickelate superconductor La_(3)Ni_(2)O_(7) is discovered at pressures with a remarkable high transition temperature T_(c)~ 80 K. Here, we study a Hubbard model with tight-binding parameters derived from ab initio calculations of La_(3)Ni_(2)O_(7),by employing large scale determinant quantum Monte Carlo and cellular dynamical mean-field theory. Our result suggests that the superexchange couplings in this system are comparable to that of cuprates. The system is a charge transfer insulator as the hole concentration becomes four per site at large Hubbard U. Upon hole doping, two low-energy spin-singlet bands emerge in the system exhibiting distinct correlation properties: while the one composed of the out-of-plane Ni-d_(3z^(2)-r^(2)) and O-p_(z) orbitals demonstrates strong antiferromagnetic correlations and narrow effective bandwidth, the in-plane singlet band consisting of the Ni-d_(x^(2)-y^(2)) and O-p_(x)/p_(y) orbitals is in general more itinerant. Over a broad range of hole doping, the doped holes occupy primarily the d_(x^(2)-y^(2)) and p_(x)/p_(y) orbitals, whereas the d_(3z^(2)-r^(2)) and p_(z) orbitals retain underdoped. We propose an effective t-J model to capture the relevant physics and discuss the implications of our result for comprehending the La_(3)Ni_(2)O_(7) superconductivity.展开更多
The discovery of nickelates superconductor creates exciting opportunities to unconventional superconductivity. However, its synthesis is challenging and only a few groups worldwide can obtain samples with zero-resista...The discovery of nickelates superconductor creates exciting opportunities to unconventional superconductivity. However, its synthesis is challenging and only a few groups worldwide can obtain samples with zero-resistance. This problem becomes the major barrier for this field. From plume dynamics perspective, we found the synthesis of superconducting nickelates is a complex process and the challenge is twofold, i.e., how to stabilize an ideal infinite-layer structure Nd_(0.8)Sr_(0.2)NiO_(2), and then how to make Nd_(0.8)Sr_(0.2)NiO_(2) superconducting? The competition between perovskite Nd_(0.8)Sr_(0.2)NiO_(3) and Ruddlesden−Popper defect phase is crucial for obtaining infinite-layer structure. Due to inequivalent angular distributions of condensate during laser ablation, the laser energy density is critical to obtain phase-pure Nd_(0.8)Sr_(0.2)NiO_(3). However, for obtaining superconductivity, both laser energy density and substrate temperature are very important. We also demonstrate the superconducting Nd_(0.8)Sr_(0.2)NiO_(2) epitaxial film is very stable in ambient conditions up to 512 days. Our results provide important insights for fabrication of superconducting infinite-layer nickelates towards future device applications.展开更多
The recent discovery of high T_(c) superconductivity under pressure in a bilayer Ruddlesden-Popper-type nickelate La_(3)Ni_(2)O_(7)[1] has attracted great interest both experimentally and theoretically.Indeed,followin...The recent discovery of high T_(c) superconductivity under pressure in a bilayer Ruddlesden-Popper-type nickelate La_(3)Ni_(2)O_(7)[1] has attracted great interest both experimentally and theoretically.Indeed,following this discovery,superconductivity in a trilayer nickelate La_(4)Ni_(3)O_(10) has also been discovered[2,3].These findings have confirmed the arrival of the nickel age of superconductivity[4],kicked off by the discovery of superconductivity in the thin films of infinite layer nickelates[5].展开更多
The discovery of high-temperature superconductivity in bilayer nickelate La_(3)Ni_(2)O_(7)under high-pressure conditions has spurred extensive efforts to stabilize superconductivity at ambient pressure.Recently,the re...The discovery of high-temperature superconductivity in bilayer nickelate La_(3)Ni_(2)O_(7)under high-pressure conditions has spurred extensive efforts to stabilize superconductivity at ambient pressure.Recently,the realization of superconductivity in compressively strained La_(3)Ni_(2)O_(7)thin films grown on the SrLaAlO_(4)substrates,with a T_(c)exceeding 40 K,represents a significant step toward this goal.Here,we investigate the influence of film thickness and carrier doping on the electronic structure of La_(3)Ni_(2)O_(7)thin films,ranging from 0.5 to 3 unit cells,using first-principles calculations.For a 2 unit-cell film with an optimal doping concentration of 0.3 hole per formula unit(0.15 hole/Ni),the Ni-d_(z^(2))interlayer bonding state crosses the Fermi level,resulting in the formation ofγpockets at the Fermi surface.These findings align with angle-resolved photoemission spectroscopy experimental data.Our results provide theoretical validation for the recent experimental discovery of ambient-pressure superconductivity in La_(3)Ni_(2)O_(7)thin films and underscore the significant impact of film thickness and carrier doping on electronic property modulation.展开更多
基金supported by the Natural Science Foundation of Guangdong Province of China(Grant No.2025A1515011071)the National Natural Science Foundation of China(Grant Nos.92065110,11974048,and 12074334)the Beijing Municipal Natural Science Foundation Key Research Topics(Grant No.Z230006)。
文摘Recent studies have successfully demonstrated high-Tc superconductivity in bilayer nickelate La3Ni2O7.However,research on modulating the structural and transport characteristics of La3Ni2O7 films by applying“chemical”compressive pressure through cation substitution is still limited.Here,we address this issue in the La_(3−x)Nd_(x)Ni_(2)O_(7)(x=0,1.0,1.5,2.0,and 2.5)thin film samples.It was found that using Nd3+with a smaller radius instead of La3+can reduce the c-axis lattice constant and shift the metal-insulator transition(MIT)temperature TMIT.To probe the origin of the MIT at cryogenic temperatures,experimental measurements of magnetoresistance were conducted,and theoretical analysis was carried out using the Kondo model,Hikami-Larkin-Nagaoka equation,and other methods.The results indicate that as Nd doping rises,the contributions of the Kondo effect and two-dimensional weak localization(WL)first decrease and then increase.The total contribution of WL and the Kondo effect in the mid-doped La_(1.5)Nd_(1.5)Ni_(2)O_(7)sample was the smallest,which to some extent explains the changes in TMIT.The Kondo effect dominates in other La_(3−x)Nd_(x)Ni_(2)O_(7)(x=0,1.0,2.0,and 2.5)samples.This work demonstrates that cation doping has a significant impact on bilayer nickelates,providing experimental evidence for understanding the physical mechanism of the MIT in bilayer nickelates.
基金Project supported by the National Key Research and Development Program of China(2021YFA0718900)the National Natural Science Foundation of China(62074014,52073090)。
文摘While the metal to insulator transition(MIT)of d-band correlated perovskite nickelates(RENiO_(3))are widely adjustable via their rare-earth composition,the roles of potential valence variabilities associated with the rare-earth elements were rarely concerned.Herein,we demonstrate the material synthesis and MIT properties of RENiO_(3) containing valence variable rare-earth compositions,such as Ce,Pr,Sm,Eu and Tb.The metastable perovskite structure of SmNiO_(3) and EuNiO_(3) with a rare-earth valence states variable towards+2 can be effectively synthesized under high oxygen pressures as it is necessary to reduce their formation free energies.This is in contrast to Ce and Tb,in which situations the variable rare-earth valence state towards+4 reduces their ionic radius and prohibits their occupation or co-occupation of the rare-earth site within the perovskite structured RENiO_(3).Nevertheless,PrNiO_(3) with MIT properties can be effectively synthesized at lower oxygen pressures,owing to the higher stability to form a fully occupied 6s orbit associated Pr3+compared to the half-filled one related to Pr4+.The present work provides guidance for regulating the MIT properties of RENiO_(3).
基金the insightful discussions with Prof.Dongsheng Song.Project supported by the National Natural Science Foundation of China(Grant No.52172115)the Guangdong Provincial Key Laboratory Program from the Department of Science and Technology of Guangdong Province(Grant No.2021B1212040001)+2 种基金Guangdong Basic and Applied Basic Research Foundation(Grant No.2022A1515012434)Shenzhen Science and Technology Program(Grant No.20231121093057002)Natural Science Foundation of Guangdong Province,China(Grant No.2022A1515010762).
文摘The discovery of nickelate superconductors,including doped infinite-layer(IL)nickelates RNiO2(R=La,Pr,Nd),layered square-planar nickelate Nd6Ni5O12,and the Ruddlesden–Popper(RP)phase La3Ni2O7,has spurred immense interest in fundamental research and potential applications.Scanning transmission electron microscopy(STEM)has proven crucial for understanding structure–property correlations in these diverse nickelate superconducting systems.In this review,we summarize the key findings from various modes of STEM,elucidating the mechanism of different nickelate superconductors.We also discuss future perspectives on emerging STEM techniques for unraveling the pairing mechanism in the“nickel age”of superconductivity.
基金PEREN project(reference:ANR-2011-PREG-016–05)the ECOREVE project(reference:ANR-18-CE05-0036-01)the Agence Nationale de la Recherche(A.N.R.,France)for supporting these scientific works and for the financial support。
文摘The chemical and electrochemical stability of lanthanide nickelates La2 NiO4+δ(LNO),Pr2 NiO4+δ(PNO)and their mixed compounds La(2-x)PrxNiO4+δ(LPNOs)with x=0.5,1 or 1.5 is reported.The aim is to promote these materials as efficient electrodes for solid oxide fuel cell(SOFC)and/or solid oxide electrolysis cell(SOEC).La2 NiO4+δand La1.5Pr0.5NiO4+δcompounds are chemically very stable as powders over one month in the temperature range 600-800℃,while the other materials rich in praseodymium progressively decompose into various perovskite-deriving components with additional Pr6 O11.Despite their uneven properties,all these materials are quite efficient and sustainable as electrodes on top of gadolinium doped ceria(GDCBL)//yttrium doped zirconia(8 YSZ)electrolyte,for one month at 700℃without polarization.Under polarization(300 mA·cm-2),the electrochemical performances of LNO,PNO and La1.5Pr0.5NiO4+δ(LP5 NO)quickly degrade in SOFC mode,i.e.for the oxygen reduction reaction,while they show durability in SOEC mode,i.e.for the oxide oxidation reaction.
基金financially supported by the National Key Research and Development Program of China (No. 2021YFA0718900)the National Natural Science Foundation of China (Nos.52073090 and 62074014)+1 种基金the Fundamental Research Funds for the Central Universities (No.FRF-TP-19-023A3Z)Beijing New-star Plan of Science and Technology (No. Z191100001119071)。
文摘The rare-earth nickelates(RENiO_(3)) exhibit an exceptional complex electronic phase diagram and multiple electronic phase transitions that enrich promising applications in correlated electronic devices beyond conventional semiconductors.Nevertheless,the practical applications of RENiO_(3) are challenged by their intrinsic thermodynamic metastability in material synthesis and high material cost.Therefore,developing an economical strategy to achieve the batch synthesis of RENiO_(3) is of vital importance.In this work,we enlarged the synthesis amount of RENiO_(3) up to 20 g per batch using chloride(KCI) assisted molten salt reaction.By optimizing the reaction conditions,the powder of RENiO_(3) with the cubic shape and average size of ~2μm was effectively synthesized,while their phase purity exceeded 95%.In addition,the cost to synthesize RENiO_(3) was further reduced by using rare-earth extraction intermediate products as the raw materials,instead of using the pure rare-earth precursors.It also achieved wide adjustments in the metal-to-insulator-transition temperature from160 to 420 K without significantly reducing the transition sharpness.By enlarging the synthesis amount and the reducing the cost,it paves the way to the device application of RENiO_(3).
基金National Natural Science Foundation of China(61674013)Beijing New-star Plan of Science and Technology(Z191100001119071)the Fundamental Research Funds for the Central Universities(FRF-TP-19-023A3Z)。
文摘Although the thermistor and metal to insulator transition bi-functionalities were discovered for rareearth nickelates(RENiO3),the electronic stability in their correlated transports under impulse voltage or magnetic field remain as open questions.Herein,we demonstrate the thermistor transportations of the electron correlated rare-earth nickelates under impulse direct current voltage and in magnetic environment.The insulating phase of RENiO3 shows zero crossing linear I-V characters,indicating their stable electronic resistance is independent of the imparted voltage up to 10 V and pulse width down to1 us,in spite of their sensitive electronic structures to polarizations.In addition,the high electronic stability associated with the thermistor transportation of RENiO3 is also demonstrated in magnetic fields up to 9 T(i.e.,MR<0.2%).The high electronic stability further paves the way to applying RENiO3 as a broad temperature range thermistor in temperature sensing or circuit protections for correlated electronics.
基金financially supported by the National Key Research and Development Program of China(No.2021YFA0718900)National Natural Science Foundation of China(Nos.62074014,52073090,and 52103284)。
文摘The multiple quantum transitions within d-band correlation oxides such as rare-earth nickelates(RENiO_(3))triggered by critical temperatures and/or hydrogenation opened up a new paradigm for correlated electronics applications,e.g.ocean electric field sensor,bio-sensor,and neuron synapse logical devices.Nevertheless,these applications are obstructed by the present ineffectiveness in the thin film growth of the metastable RENiO_(3)with flexibly adjustable rare-earth compositions and electronic structures.Herein,we demonstrate a metal-organic decompositions(MOD)approach that can effectively grow metastable RENiO_(3)covering a large variety of the rare-earth composition without introducing any vacuum process.Unlike the previous chemical growths for RENiO_(3)relying on strict interfacial coherency that limit the film thickness,the MOD growth using reactive isooctanoate percussors is tolerant to lattice defects and therefore achieves comparable film thickness to vacuum depositions.Further indicated by positron annihilation spectroscopy,the RENiO_(3)grown by MOD exhibit large amount of lattice defects that improves their hydrogen incorporation amount and electron transfers,as demonstrated by the resonant nuclear reaction analysis and near edge X-ray absorption fine structure analysis.This effectively enlarges the magnitude in the resistance regulations in particular for RENiO_(3)with lighter RE,shedding a light on the extrinsic regulation of the hydrogen induced quantum transitions for correlated oxides semiconductors kinetically via defect engineering.
基金financially supported by the National Key Re-search and Development Program of China(No.2021YFA0718900)the National Natural Science Foundation of China(Nos.62074014 and 52073090)the Beijing New-star Plan of Science and Tech-nology(No.Z191100001119071).
文摘Although the metal to insulator transition(MIT)observed in d-band correlated metal oxides enables promising applications(e.g.,correlated logical devices and Mottronic devices),its present recognition is mainly limited on the direct current(DC)electrical transports.Up to date,the MIT from the perspective of alternation current(AC)transport and its potential electronic applications remains yet unclear.Herein,we demonstrate the frequency(f_(AC))dependence in the impedance(Z=Z’+iZ″)of typical MIT materials,such as thin film rare-earth nickelates(Re NiO_(3)),across the critical MIT temperature(T_(MIT)).Apart from the abrupt change in the impedance modulus(|Z|)across the critical temperature(T_(MIT))similar to the DC transport,the MIT also triggers non-continuous variation in the impedance phase(θ),and this enables the f_(AC)-regulations in the Z’-T tendencies(Z’=|Z|cosθ).At the critical f_(AC) range(e.g.,104-106 Hz),the con-versing variations in|Z|-T and cosθ-T across T_(MIT) result in non-monotonic delta-shape Z’-T tendency in Sm_(x) Nd_(1-x) NiO_(3),the full width half maximum of which is effectively narrowed compared to the situation with the absence of MIT.Further imparting lower or higher f_(AC) elevate the domination in|Z|-T and cosθ-T,respectively,but also enables abrupt Z’-T tendencies across T_(MIT) showing negative temperature coefficient of resistance(NTCR)or positive temperature coefficient of resistance(PTCR).By introducing f_(AC) as a new freedom,the MIT behavior can be more comprehensively regulated electronically,and this extends the vision in exploring the new electronic applications based on the correlated MIT materials from the AC perspective.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2021YFA0718900and 2022YFA1403000)the Key Research Program of Frontier Sciences of CAS(Grant No.ZDBS-LY-SLH008)+2 种基金the National Natural Science Foundation of China(Grant Nos.11974365,12004400,and 51931011)the Science Center of the National Natural Science Foundation of China(Grant No.52088101)the K.C.Wong Education Foundation(Grant No.GJTD-2020-11)。
文摘The discovery of superconductivity in Sr/Ca-doped infinite-layer nickelates Nd(La)NiO_(2)thin films inspired extensive experimental and theoretical research.However,research on the possibilities of enhanced critical temperature by interface heterostructure is still lacking.Due to the similarities of the crystal structure and band structure of infinite-layer nickelate La NiO_(2)and cuprate CaCuO_(2),we investigate the crystal,electronic and magnetic properties of La NiO_(2):CaCuO_(2)heterostructure using density functional theory and dynamical mean-field theory.Our theoretical results demonstrate that,even a very weak inter-layer z-direction bond is formed,an intrinsic charge transfer between Cu-3d_(x^(2)-y^(2))and Ni-3d_((x^(2)-y^(2)))orbitals is obtained.The weak interlayer hopping between Cu and Ni leaves a parallel band contributed by Ni/Cu-3d_((x^(2)-y^(2)))orbitals near the Fermi energy.Such an infinite-layer heterostructure with negligible interlayer interaction and robust charge transfer opens a new way for interface engineering and nickelate superconductors.
基金supported by the startup fund from Soochow Universitythe Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions
文摘The recent discovery of superconductivity in doped rare-earth infinite-layer nickelates RNiO_(2),R=Nd,Pr as a new family of unconventional superconductors has inspired extensive research on their intriguing properties.One of the major motivation to explore the nickelate superconductors originated from their similarities with and differences from the cuprate superconductors,which have been extensively studied over the last decades but are still lack of the thorough understanding.In this short review,we summarized our recent investigation of the relevance of Ni/Cu-3d multiplet structure on the hole doped spin states in cuprate and recently discovered nickelate superconductors via an impurity model incorporating all the 3d orbitals.Further plausible explorations to be conducted are outlined as well.Our presented work provides an insightful framework for the investigation of the strongly correlated electronic systems in terms of the multiplet structure of transition metal compounds.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074031,11674025,and 11774019).
文摘Based on the two-band tight-binding model composed of the 3d orbital of Ni and the 5d orbital of R(=La),we used the random-phase-approximation method to study the pairing symmetry of the nickelate superconductors.It is found that even without considering the coupling between the R and Ni orbitals,neither the antiferromagnetic spin-fluctuation pattern nor the doping-dependent behavior of the robust dx^(2)−y^(2)-wave pairing state obtained in our calculations will be obviously influenced.Our results suggest the dominating role of the Ni 3d orbital in determining the low lying physics of the system.Furthermore,our results reveal a dome-shaped doping dependence of the superconducting transition temperature Tc,which is consistent with recent experiments.
基金supported by the Natural Science Foundation of Fujian Province(2015j01231)the Chunmiao Project of Haixi Institute of Chinese Academy of Sciences(CMZX-2014-005)the National Key Research and Development Program of China(2016YFB0701003)
文摘We report an improved method for the preparation of highly dense nickelate ceramics at relatively low temperature. It is found that the introduction of appropriate additives during the ball-milling process facilitates the formation of nickelate phase through solid state reaction. Moreover, although high-purity nickelate powders can only be obtained by calcining the mixture of starting materials at temperature higher than 1100 ℃. The adoption of powders calcined at 1000 ℃, rather than those calcined at higher temperature, is conductive to the low-temperature densification of nickelate ceramics, which is attributed to the small and dispersive particles, and the solid state reaction of the residual starting materials during sintering. Compared with the conventional process, the improved method can reduce the sintering temperature of nickelate ceramics by about 100 ℃ and decrease the grain size of the obtained ceramics, and therefore makes nickelate meet the fabrication requirements of multi-layer ceramic capacitors（MLCC）.
基金The authors wish to acknowledge RECAT-Petrobras,Rede de Hidrogenio-MCTANP for their financial support and scholarship grants.
文摘In the current work, LaNiO3 perovskite was synthesized using the polymeric precursor method. The materials were thermally treated at 300°C for 2 hours, subsequently supported on alumina or zirconia and finally calcined at 800°C for 4 hours. The resulting samples were characterized by X-ray diffraction, thermogravimetry, BET surface area and thermo-programmed reduction. Steam reforming reactions were carried out at 750°C and 6 bar during 4 hours using a pilot reactor under a H2O:CH4 ratio of 2.5. The mass of catalysts was about 5.7 g. X-ray diffraction patterns confirmed the formation of the perovskite structure in all samples prepared. The results also showed that lanthanum nickelate was more efficient when supported on alumina than zirconia. Finally, it was observed that the methane conversion was approximately 94% and the selectivity to hydrogen was about 70%. In all cases low selectivity to CO and CO2 was verified.
基金funded by the National Key R&D Program of China(2022YFA1403100,2022YFA1403201,and 2022YFA1402703)the National Natural Science Foundation of China(12274251,92365204,12004270,52272265,12361141826,and 12074212)+3 种基金the Guangdong Basic and Applied Basic Research Foundation(2022B1515120020)Lexian Yang acknowledges support from the Tsinghua University Initiative Scientific Research Program and the Fund of Science and Technology on Surface Physics and Chemistry Laboratory(XKFZ202102)Gang Li acknowledges the support of 2021-Fundamental Research Area 21JC1404700,and Sino-German Mobility program(M-0006)Luyi Yang acknowledges the support of the Beijing Natural Science Foundation(Z240006)。
文摘In addition to the pressurized high-temperature superconductivity,bilayer and trilayer nickelate superconductors La_(n+1)Ni_(n)O_(3n+1)(n=2 and 3)exhibit many intriguing properties at ambient pressure,such as orbital-dependent electronic correlation,non-Fermi liquid behavior,and density-wave transitions.Here,using ultrafast reflectivity measurement,we observe a drastic difference between the ultrafast dynamics of the bilayer and trilayer nickelates at ambient pressure.We observe a coherent phonon mode in La_(4)Ni_(3)O_(10)involving the collective vibration of La,Ni,and O atoms,which is absent in La_(3)Ni_(2)O_(7).Temperature-dependent relaxation time diverges near the density-wave transition temperature of La_(4)Ni_(3)O_(10),while it is inversely proportional to the temperature in La_(3)Ni_(2)O_(7)above~150 K,suggesting a non-Fermi liquid behavior of La_(3)Ni_(2)O_(7).Moreover,we estimate the electron–phonon coupling constants to be 0.05–0.07 and 0.12–0.16 for La_(3)Ni_(2)O_(7)and La_(4)Ni_(3)O_(10),respectively,suggesting a relatively minor role of electron–phonon coupling in the electronic properties of La_(n+1)Ni_(n)O_(3n+1)at ambient pressure.The relevant microscopic interaction and dynamic information are essential for further studying the interplay between superconductivity and density-wave transitions in nickelate superconductors.
基金support from the National Natural Science Foundation of China(523B2061)National Innovative Talents Program(GG2090007001)University of Science and Technology of China Startup Program(KY2090000044).
文摘Recently,a signature of high-temperature superconductivity above the liquid nitrogen temperature(77 K)was reported for La_(3)Ni_(2)O_(7−δ) under pressure.This finding immediately stimulated intense interest in the possible mechanism of high-Tc superconductivity in double-layer nickelates.Notably,the pressure-dependent phase diagram inferred from transport measurements indicates that the superconductivity under high pressure emerges from the suppression of density-wave-like order at ambient pressure,which is similar to high-temperature superconductors.Therefore,clarifying the exact nature of the density-wave-like transition is important for determining the superconducting mechanism in double-layer nickelates.Here,nuclear magnetic resonance(NMR)spectroscopy of 139La nuclei was performed to study the density-wave-like transition in a single crystal of La_(3)Ni_(2)O_(7−δ.)At high temperatures,two sets of sharp 139La NMR peaks are clearly distinguishable from a broad background signals,which are ascribed to La(1)sites from two bilayer Ruddlesden-Popper phases with different oxygen vacancyδ.As the temperature decreases,the temperature-dependent^(139)La NMR spectra and nuclear spin-lattice relaxation rate(1/T_(1))for both La(1)sites provide evidence of spin-density-wave(SDW)ordering below the transition temperature(T_(SDW)),which is approximately 150 K.The anisotropic splitting in the NMR spectra suggests the formation of a possible double spin stripe with magnetic moments aligned along the c-axis.Furthermore,we studied the pressure-dependent SDW transition up to∼2.7 GPa.Surprisingly,the TSDW inferred from NMR measurements of both La(1)sites increases with increasing pressure,which is opposite to the results from previous transport measurements under pressure and suggests an intriguing phase diagram between superconductivity and SDW.In contrast,the present^(139)La NMR is insensitive to the possible charge-density-wave(CDW)order in the Ni-O planes.All these results will be helpful for building a connection between superconductivity and magnetic interactions in double-layer nickelates.
基金supported by the National Natural Science Foundation of China(Grant Nos.12122405,52072188,and 12274169)the National Key R&D Program of China(Grant Nos.2022YFA1402304,and 2023YFA1406200)+1 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.xzy022023011,and xhj032021014-04)the Program for Science and Technology Innovation Team in Zhejiang(Grant No.2021R01004).
文摘Trilayer Ruddlesden-Popper phase La_(4)Ni_(3)O_(10) has been observed with T_(c) of~30 K at high pressure in a recent experiment,which further expanded the family of nickelate superconductors.In this study,we explored the effects of electronic correlations in La_(4)Ni_(3)O_(10) using density functional theory plus dynamical mean-field theory at ambient and high pressures.Our derived spectral functions and Fermi surface of the ambient pressure phase are nicely consistent with the experimental results by angleresolved photoemission spectroscopy,which emphasized the importance of electronic correlations in La_(4)Ni_(3)O_(10).We also found the electronic correlations in pressurized La_(4)Ni_(3)O_(10) are both orbital-dependent and layer-dependent due to the presence of Hund’s rule coupling.There is a competition between the Hund’s rule coupling and the crystal-field splitting,and therefore,the Ni-O layers with weaker crystal-field splitting energy would have stronger electronic correlations.
基金supported by the National Natural Science Foundation of China (Grant Nos. 12274472, 92165204, 12174454, and 11974432)the National Key Research and Development Program of China (Grant Nos. 2022YFA1402802, and 2018YFA0306001)+4 种基金the Guangdong Basic and Applied Basic Research Foundation (Grant Nos. 2022A1515011618, and 2021B1515120015)the Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices (Grant No. 2022B1212010008)the Shenzhen International Quantum Academy (Grant No. SIQA202102)the Leading Talent Program of Guangdong Special Projects (Grant No. 201626003)the support from GuangZhou National Supercomputing Center (Tianhe-Ⅱ)。
文摘Recently, a bulk nickelate superconductor La_(3)Ni_(2)O_(7) is discovered at pressures with a remarkable high transition temperature T_(c)~ 80 K. Here, we study a Hubbard model with tight-binding parameters derived from ab initio calculations of La_(3)Ni_(2)O_(7),by employing large scale determinant quantum Monte Carlo and cellular dynamical mean-field theory. Our result suggests that the superexchange couplings in this system are comparable to that of cuprates. The system is a charge transfer insulator as the hole concentration becomes four per site at large Hubbard U. Upon hole doping, two low-energy spin-singlet bands emerge in the system exhibiting distinct correlation properties: while the one composed of the out-of-plane Ni-d_(3z^(2)-r^(2)) and O-p_(z) orbitals demonstrates strong antiferromagnetic correlations and narrow effective bandwidth, the in-plane singlet band consisting of the Ni-d_(x^(2)-y^(2)) and O-p_(x)/p_(y) orbitals is in general more itinerant. Over a broad range of hole doping, the doped holes occupy primarily the d_(x^(2)-y^(2)) and p_(x)/p_(y) orbitals, whereas the d_(3z^(2)-r^(2)) and p_(z) orbitals retain underdoped. We propose an effective t-J model to capture the relevant physics and discuss the implications of our result for comprehending the La_(3)Ni_(2)O_(7) superconductivity.
基金the National Natural Science Foundation of China(Grant Nos.12274061,52072059,and 11774044)the Science and Technology Department of Sichuan Province(Grant Nos.2021JDJQ0015 and 2022ZYD0014)B.H.acknowledges the support by the National Natural Science Foundation of China(No.2230402).
文摘The discovery of nickelates superconductor creates exciting opportunities to unconventional superconductivity. However, its synthesis is challenging and only a few groups worldwide can obtain samples with zero-resistance. This problem becomes the major barrier for this field. From plume dynamics perspective, we found the synthesis of superconducting nickelates is a complex process and the challenge is twofold, i.e., how to stabilize an ideal infinite-layer structure Nd_(0.8)Sr_(0.2)NiO_(2), and then how to make Nd_(0.8)Sr_(0.2)NiO_(2) superconducting? The competition between perovskite Nd_(0.8)Sr_(0.2)NiO_(3) and Ruddlesden−Popper defect phase is crucial for obtaining infinite-layer structure. Due to inequivalent angular distributions of condensate during laser ablation, the laser energy density is critical to obtain phase-pure Nd_(0.8)Sr_(0.2)NiO_(3). However, for obtaining superconductivity, both laser energy density and substrate temperature are very important. We also demonstrate the superconducting Nd_(0.8)Sr_(0.2)NiO_(2) epitaxial film is very stable in ambient conditions up to 512 days. Our results provide important insights for fabrication of superconducting infinite-layer nickelates towards future device applications.
文摘The recent discovery of high T_(c) superconductivity under pressure in a bilayer Ruddlesden-Popper-type nickelate La_(3)Ni_(2)O_(7)[1] has attracted great interest both experimentally and theoretically.Indeed,following this discovery,superconductivity in a trilayer nickelate La_(4)Ni_(3)O_(10) has also been discovered[2,3].These findings have confirmed the arrival of the nickel age of superconductivity[4],kicked off by the discovery of superconductivity in the thin films of infinite layer nickelates[5].
基金supported by the National Key R&D Program of China(Gran Nos.2022YFA1402304 and 2022YFA1402802)the National Natural Science Foundation of China(Grant Nos.12494591,12122405,12274169,and 92165204)+4 种基金Program for Science and Technology Innovation Team in Zhejiang(Grant No.2021R01004)Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices(Grant No.2022B1212010008)Guangdong Fundamental Research Center for Magnetoelectric Physics(2024B0303390001)Guangdong Provincial Quantum Science Strategic Initiative(Grant No.GDZX2401010)the Fundamental Research Funds for the Central Universities。
文摘The discovery of high-temperature superconductivity in bilayer nickelate La_(3)Ni_(2)O_(7)under high-pressure conditions has spurred extensive efforts to stabilize superconductivity at ambient pressure.Recently,the realization of superconductivity in compressively strained La_(3)Ni_(2)O_(7)thin films grown on the SrLaAlO_(4)substrates,with a T_(c)exceeding 40 K,represents a significant step toward this goal.Here,we investigate the influence of film thickness and carrier doping on the electronic structure of La_(3)Ni_(2)O_(7)thin films,ranging from 0.5 to 3 unit cells,using first-principles calculations.For a 2 unit-cell film with an optimal doping concentration of 0.3 hole per formula unit(0.15 hole/Ni),the Ni-d_(z^(2))interlayer bonding state crosses the Fermi level,resulting in the formation ofγpockets at the Fermi surface.These findings align with angle-resolved photoemission spectroscopy experimental data.Our results provide theoretical validation for the recent experimental discovery of ambient-pressure superconductivity in La_(3)Ni_(2)O_(7)thin films and underscore the significant impact of film thickness and carrier doping on electronic property modulation.
