We discuss the general interplay between the uncertainty principle and the onset of dissipationless transport phenomena such as superconductivity and superfluidity. We argue that these phenomena are possible because o...We discuss the general interplay between the uncertainty principle and the onset of dissipationless transport phenomena such as superconductivity and superfluidity. We argue that these phenomena are possible because of the robustness of many-body quantum states with respect to the external environment, which is directly related to the uncertainty principle as applied to coordinates and momenta of the carriers. In the case of superconductors, this implies relationships between macroscopic quantities such as critical temperature and critical magnetic field, and microscopic quantities such as the amount of spatial squeezing of a Cooper pair and its correlation time. In the case of ultracold atomic Fermi gases, this should be paralleled by a connection between the critical temperature for the onset of superfluidity and the corresponding critical velocity. Tests of this conjecture are finally sketched with particular regard to the understanding of the behaviour of superconductors under external pressures or mesoscopic superconductors, and the possibility to mimic these effects in ultracold atomic Fermi gases using Feshbach resonances and atomic squeezed states.展开更多
It is shown that both super phenomena-superconductivity and superfluidity are based on the same mechanism of streamline of zero-point oscillations. Proof of this is the agreement of obtained theoretical estimations wi...It is shown that both super phenomena-superconductivity and superfluidity are based on the same mechanism of streamline of zero-point oscillations. Proof of this is the agreement of obtained theoretical estimations with measured data.展开更多
In recent years,the research on superconductivity in one-dimensional(1D)materials has been attracting increasing attention due to its potential applications in low-dimensional nanodevices.However,the critical temperat...In recent years,the research on superconductivity in one-dimensional(1D)materials has been attracting increasing attention due to its potential applications in low-dimensional nanodevices.However,the critical temperature(T_(c))of 1D superconductors is low.In this work,we theoretically investigate the possible high T_(c) superconductivity of(5,5)carbon nanotube(CNT).The pristine(5,5)CNT is a Dirac semimetal and can be modulated into a semiconductor by full hydrogenation.Interestingly,by further hole doping,it can be regulated into a metallic state with the sp3-hybridized𝜎electrons metalized,and a giant Kohn anomaly appears in the optical phonons.The two factors together enhance the electron–phonon coupling,and lead to high-T_(c) superconductivity.When the hole doping concentration of hydrogenated-(5,5)CNT is 2.5 hole/cell,the calculated T_(c) is 82.3 K,exceeding the boiling point of liquid nitrogen.Therefore,the predicted hole-doped hydrogenated-(5,5)CNT provides a new platform for 1D high-T_(c) superconductivity and may have potential applications in 1D nanodevices.展开更多
Interfacial superconductivity(IS)has been a topic of intense interest in condensed matter physics,due to its unique properties and exotic photoelectrical performance.However,there are few reports about IS systems cons...Interfacial superconductivity(IS)has been a topic of intense interest in condensed matter physics,due to its unique properties and exotic photoelectrical performance.However,there are few reports about IS systems consisting of two insulators.Here,motivated by the emergence of an insulator-metal transition in type-Ⅲ heterostructures and the superconductivity in some“special”two-dimensional(2D)semiconductors via electron doping,we predict that the 2D heterostructure SnSe_(2)/PtTe_(2) is a model system for realizing IS by using firstprinciples calculations.Our results show that due to slight but crucial interlayer charge transfer,SnSe_(2)/PtTe_(2) turns to be a type-Ⅲ heterostructure with metallic properties and shows a superconducting transition with the critical temperature(T_(c))of 3.73 K.Similar to the enhanced electron–phonon coupling(EPC)in the electrondoped SnSe_(2) monolayer,the IS in the SnSe_(2)/PtTe_(2) heterostructure mainly originates from the metallized SnSe_(2) layer.Furthermore,we find that its superconductivity is sensitive to tensile lattice strain,forming a domeshaped superconducting phase diagram.Remarkably,at 7%biaxial tensile strain,the superconducting T_(c) can increase more than twofold(8.80 K),resulting from softened acoustic phonons at the𝑀point and enhanced EPC strength.Our study provides a concrete example for realizing IS in type-Ⅲ heterostructures,which waits for future experimental verification.展开更多
High-pressure electrides,characterized by the presence of interstitial quasi-atoms(ISQs),possess unique electronic structures and physical properties,such as diverse dimensions of electride states exhibiting different...High-pressure electrides,characterized by the presence of interstitial quasi-atoms(ISQs),possess unique electronic structures and physical properties,such as diverse dimensions of electride states exhibiting different superconductivity,which has attracted significant attention.Here,we report a new electron-deficient type of electride Li_(4)Al and identify its phase transition progress with pressurization,where the internal driving force behind phase transitions,bonding characteristics,and superconducting behaviors have been revealed based on first-principles density functional theory.Through analysis of the bonding properties of electride Li_(4)Al,we demonstrate that the ISQs exhibiting increasingly covalent characteristics between Al ions play a critical role in driving the phase transition.Our electron–phonon coupling calculations indicate that all phases exhibit superconducting behaviors.Importantly,we prove that the ISQs behave as free electrons and demonstrate that the factor governing T_(c) is primarily derived from Li-p-hybridized electronic states with ISQ compositions.These electronic states are scattered by low-frequency phonons arising from mixed vibrations of Li and Al affected by ISQs to enhance electron–phonon coupling.Our study largely expands the research scope of electrides,provides new insight for understanding phase transitions,and elucidates the effects of ISQs on superconducting behavior.展开更多
We report a theoretical investigation into superconductivity within the MAXH_(6) quaternary hydride system using first-principles calculations,where M and A denote alkali and alkaline earth elements,respectively,and X...We report a theoretical investigation into superconductivity within the MAXH_(6) quaternary hydride system using first-principles calculations,where M and A denote alkali and alkaline earth elements,respectively,and X represents transition metal elements.Systematic analysis of electronic band structures,phonon dispersions,and electron-phonon coupling reveals that substitution of MA binary metal combinations and X metal atoms can create favorable conditions for superconductivity.Mapping of superconducting critical temperatures,combined with dynamical stability analysis through phonon calculations,identifies ten superconducting candidates at ambient pressure.Among these,LiNaAgH_(6) exhibits nearly-free-electron behavior reminiscent of monovalent electron superconductors.It demonstrates exceptional superconducting properties with electron–phonon coupling λ=2.707,which yields a superconducting transition temperature T_(c) of 206.4 K using the Allen–Dynes formula.Its structural analogs MgNaPdH_(6),LiMgPdH_(6),LiMgAgH_(6),LiMgAuH_(6) all exhibit superconducting transition temperatures above 110 K.These findings advance our fundamental understanding of superconductivity in quaternary hydrides and provide guidance for rational design of new high-temperature superconducting materials.展开更多
A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform for exploring Majorana bound states.Trigonal γ-PtBi_(2),a superconductor,is a promising candidate,as both surface supercond...A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform for exploring Majorana bound states.Trigonal γ-PtBi_(2),a superconductor,is a promising candidate,as both surface superconducting gaps and topological surface states have been observed.However,the simultaneous presence of bulk and surface superconductivity has remained unresolved.In this study,we directly visualize coexisting bulk and surface superconducting gaps in trigonal PtBi2 using ultra-low-temperature scanning tunneling microscopy/spectroscopy.The bulk gap,Δ,is∼0.053 meV,with a critical temperature(T_(c))of∼0.5K and a critical field below 0.01 T,accompanied by a vortex lattice and vortex bound states and yielding a coherence length of∼200 nm.Remarkably,certain surface regions exhibit a much larger gap(Δ)of∼0.42 meV,persisting up to a T_(c)value of∼3K and surviving magnetic fields of up to 2 T,yet lacking a static vortex lattice.This coexistence of robust surface and bulk superconductivity establishes γ-PtBi_(2)as a unique platform for exploring the interplay between bulk and surface Cooper pairings in topological superconductors.展开更多
Signatures of superconductivity near 80 K have recently been discovered in single crystals of La_(3)Ni_(2)O_(7)under pressure,which makes it a new candidate for high-temperature superconductors dominated by 3d transit...Signatures of superconductivity near 80 K have recently been discovered in single crystals of La_(3)Ni_(2)O_(7)under pressure,which makes it a new candidate for high-temperature superconductors dominated by 3d transition elements,following the cuprate and iron-pnictide superconductors.However,there are several critical questions that have been perplexing the scientificommunity:(1)What factors contribute to the inconsistent reproducibility of the experimental results?(2)What is the fundamental nature of pressure-induced superconductivity:bulk or nonbulk(filamentary-like)(3)Where is the superconducting phase located within the sample if it is filamentary-like(4)Is the oxygen content important for the development and stabilization of superconductivity?In this study,we employ comprehensive high-pressure techniques to address these questions.Through our modulated ac susceptibility measurements,we are the firs to fin that the superconductivity in this nickelate is filamentary-like Our scanning transmission electron microscopy investigations suggest that the filamentary-lik superconductivity most likely emerges at the interface between La_(3)Ni_(2)O_(7)and La_(4)Ni_(3)O_(10)phases.By tuning the oxygen content of polycrystalline La_(3)Ni_(2)O_(7),we also fin that it plays vital role in the development and stabilization of superconductivity in this material.The upper and lower bounds on the oxygen content are 7.35 and 6.89,respectively.Our results provide not only new insights into the puzzling issues regarding this material,but also significan information that will enable a better understanding of its superconductivity.展开更多
The discovery of pressure-induced superconducting electrides has sparked a intense wave of interest in novel superconductors.However,opinions vary regarding the relationship between non-nuclear attractors(NNAs)and sup...The discovery of pressure-induced superconducting electrides has sparked a intense wave of interest in novel superconductors.However,opinions vary regarding the relationship between non-nuclear attractors(NNAs)and superconductivity,with two opposing views currently represented by the materials Li_(6)P and Li_(6)C.Here,we choose the ternary Li–C–P as a model system and reveal the underlying mechanism by which NNAs contribute to superconductivity.The loosely bound NNAs in the superlithide Li_(14)CP covalently bond with Li and form unique satellite interstitial electrons(SIEs)around Li near the Fermi level,dominating the superconductivity.First-principles calculations show that the SIEs progressively increase in number and couple strongly with phonons at high pressure.Moreover,the Fermi surface nesting associated with SIEs induces phonon softening,further enhancing the electron–phonon coupling and giving the superlithide Li_(14)CP a T_(c)of 10.6 K at 300 GPa.The leading role of SIEs in superconductivity is a general one and is also relevant to the recently predicted Li_(6)P and Li_(6)C.Our work presented here reshapes the understanding of NNA-dominated superconductivity and holds promise for guiding future discoveries and designs of novel high-temperature superconductors.展开更多
Ising superconductivity has garnered much attention in recent years due to its extremely high in-plane upper critical field (B_(c2)).Here,we fabricated 14 multilayer Pb_(1-x)Bi_(x) (0%≤x≤40%) thin films on Si (111)-...Ising superconductivity has garnered much attention in recent years due to its extremely high in-plane upper critical field (B_(c2)).Here,we fabricated 14 multilayer Pb_(1-x)Bi_(x) (0%≤x≤40%) thin films on Si (111)-7×7 reconstructed surface by molecular beam epitaxy.Large B_(c2) beyond the Pauli limit is observed in all the Pb_(1-x)Bi_(x) films,indicating that they may exhibit characteristics of Ising superconductivity.Moreover,the introduction of Bi doping can significantly enhance and effectively tune the in-plane B_(c2) of Pb_(1-x)Bi_(x) films,which will help us better understand Ising superconductivity and provide a new platform for the development of tunable Ising superconductors.展开更多
We report the fabrication of freestanding La_(2)CuO_(4)/La_(1.55)Sr_(0.45)CuO_(4)(LCO/LSCO)heterostructure membranes,which were fabricated by selectively etching water-soluble Sr_(3)Al_(2)O_(6)sacrificial layers from ...We report the fabrication of freestanding La_(2)CuO_(4)/La_(1.55)Sr_(0.45)CuO_(4)(LCO/LSCO)heterostructure membranes,which were fabricated by selectively etching water-soluble Sr_(3)Al_(2)O_(6)sacrificial layers from pulsed-laser-deposited heterostructures on SrTiO_(3) substrates.Transport measurements reveal that these membranes exhibit superconducting behavior with an onset temperature of approximately 19 K.Comprehensive structural characterization using x-ray diffraction and scanning transmission electron microscopy demonstrates that the membranes retain excellent crystalline quality after release.The superconducting properties remain stable following mild post-annealing treatment under vacuum.This work establishes LCO/LSCO as a promising platform for developing flexible high-temperature superconducting interfaces,opening new possibilities for the development of flexible devices.展开更多
We used a highly sensitive AC magnetic susceptibility technique to probe superconductivity in elemental titanium(Ti)under extreme pressures to 120 GPa in a diamond anvil cell(DAC).The measurements reveal that the crit...We used a highly sensitive AC magnetic susceptibility technique to probe superconductivity in elemental titanium(Ti)under extreme pressures to 120 GPa in a diamond anvil cell(DAC).The measurements reveal that the critical temperature(Tc)of Ti rises monotonically with increasing pressure,reaching 6.1 K at 120 GPa.Our results confirm the bulk nature of the superconductivity in Ti,as evidenced by a robust diamagnetic response in the AC magnetic susceptibility.Our work provides a routine technique to probe Meissner effect of elemental superconductors at megabar pressures.展开更多
Ytterbium polyhydrides were synthesized through in-situ high pressure laser heating techniques utilizing a diamond anvil cell.The temperature dependence of resistance measurement at high pressure demonstrates that the...Ytterbium polyhydrides were synthesized through in-situ high pressure laser heating techniques utilizing a diamond anvil cell.The temperature dependence of resistance measurement at high pressure demonstrates that the sample undergoes a superconducting transition at 11.5 K at 180 GPa.展开更多
Nickel-based superconductors have attracted great attention due to the finding of the Ruddlesden-Popper(R-P)bilayer nickelate La_(3)Ni_(2)O_(7)with superconducting critical temperature(T_(c))of 80 K at pressure above ...Nickel-based superconductors have attracted great attention due to the finding of the Ruddlesden-Popper(R-P)bilayer nickelate La_(3)Ni_(2)O_(7)with superconducting critical temperature(T_(c))of 80 K at pressure above 14 GPa.Recent efforts have been devoted to the study of La_(2)PrNi_(2)O_(7),while the detailed structure remains unclear.In this work,we explore the stability and physical properties of such an interesting system by using density functional theory and the U parameter simulation method implemented in VASP.The results show that the enthalpy of La_(2)PrNi_(2)O_(7)is slightly larger than its parent material bilayer R-P nickelate La_(3)Ni_(2)O_(7).The electronic structure analysis indicates that near the Fermi level,the eg orbit of Ni dominates and strongly hybridizes with the 2p orbit of O,thereby forming a significant van Hove singularity that is conducive to superconductivity.The Amam phase to the I4/mmm phase occurs,accompanied by an increase in the bandwidth of Ni 3d_(z)_(2) and an enhancement of the bonding-antibonding splitting(from about 0.5 eV to 1.5 eV),which leads to an increase in the density of states at the Fermi level.Our findings provide insights into the preparation and superconductivity of R-P bilayer nickelate.展开更多
Obtaining room-temperature superconductors has long been a research hotspot in the field of condensed matter physics.Previous studies have shown that doping strategies can effectively enhance the superconducting prope...Obtaining room-temperature superconductors has long been a research hotspot in the field of condensed matter physics.Previous studies have shown that doping strategies can effectively enhance the superconducting properties of materials.In this work,we employed first-principles calculations combined with the particle swarm optimization method to explore the structural possibilities of the Ca-doped As-H ternary system and to calculate the electronic and superconducting properties of the newly identified structures.Two thermodynamically stable hydrides were found under high pressure.The P4/nmm-Ca_(2)AsH_(4)phase remains thermodynamically stable within the pressure range of 90-200 GPa,while the Cc-Ca_(2)AsH_(6)phase exhibits stability over a broader range of 79-200 GPa.Electron-phonon coupling analysis indicates that the superconducting critical temperatures(Tc)of P4/nmm-Ca_(2)AsH_(4)and Cc-Ca_(2)AsH_(6)are 11 K and 16 K at 100 GPa,respectively.The incorporation of Ca significantly reduces the thermodynamic stability pressure of As-H compounds with higher hydrogen content,thereby improving their synthetic accessibility.展开更多
Two-dimensional(2D)superconductors have attracted significant research interest due to their promising potential applications in optoelectronic and microelectronic devices.Herein,we employ first-principles calculation...Two-dimensional(2D)superconductors have attracted significant research interest due to their promising potential applications in optoelectronic and microelectronic devices.Herein,we employ first-principles calculations to predicted a new 2D conventional superconductor,Tc_(2)B_(2),demonstrating its stable structural configuration.Remarkably,under biaxial strain,the superconducting transition temperature(T_(c))of Tc_(2)B_(2)demonstrates a significant enhancement,achieving 19.5 K under 3%compressive strain and 9.2 K under 11%tensile strain.Our study reveals that strain-induced modifications in Fermi surface topology significantly enhance the Fermi surface nesting effect,which amplifies electron–phonon coupling interactions and consequently elevates Tc.Additionally,the presence of the Lifshitz transition results in a more pronounced rise in Tc under compressive strain compared to tensile strain.These insights offer important theoretical guidance for designing 2D superconductors with high-Tc through strain modulation.展开更多
The emergence of high-temperature superconductivity in hydrogen-rich compounds has opened up promising avenues for investigating unique hydrogen motifs that exhibit exceptional superconducting properties.Nevertheless,...The emergence of high-temperature superconductivity in hydrogen-rich compounds has opened up promising avenues for investigating unique hydrogen motifs that exhibit exceptional superconducting properties.Nevertheless,the requirement for extremely high synthesis pressures poses significant barriers to experimentally probing potential physical properties.Here,we have designed a structure wherein NH_(3)tetrahedra are intercalated into the body-centered cubic lattice of Yb,resulting in the formation of Yb(NH_(3))_(4).Our first-principles calculations reveal that metallic behavior emerges from the ionization of sp^(3)-hybridized s-bonds in NH_(3),which is enabled by electron transfer from ytterbium orbitals to NH_(3)anti-bonding s-orbitals.A distinctive feature of this structure is the Fermi surface nesting,which leads to optical phonon softening and consequently enhances electron-phonon coupling.The subsequent density-functional theory(DFT)calculations demonstrate that this I-43m phase of Yb(NH_(3))4 exhibits a superconducting critical temperature(T_(c))of 17.32 K under a modest pressure of 10 GPa.Our investigation presents perspectives on achieving phonon-mediated superconductivity at relatively low pressures,thereby opening up extensive possibilities for the attainment of high-temperature superconductivity in hydrogen-based superconducting systems with specific ionized molecular groups.展开更多
The particle swarm optimization algorithm has predicted a series of binary cadmium hydrides that could be dynamically stable at pressures between 100 GPa and 300 GPa.These low-energy phases are composed of both Cd ato...The particle swarm optimization algorithm has predicted a series of binary cadmium hydrides that could be dynamically stable at pressures between 100 GPa and 300 GPa.These low-energy phases are composed of both Cd atoms and H_(2)molecules.Here,we propose a hitherto unknown metastable Cmcm-CdH_(6)phase,consisting of one-dimensional zigzag graphite-like hydrogenic H_(6)chains,quasimolecular H_(2)units and Cd atoms,which is metallic above 290 GPa.Due to H_(2)s→Cd d donation and Cd d→H_(2)σ^(*)back-donation,the electrons occupy antibonding orbitals for both types of hydrogen atoms.This results in weakened chemical bonds in the Cmcm-CdH_(6)phase via a Kubas-like mechanism,promoting the emergence of high superconductivity,which is estimated to be up to~60 K at 290 GPa.This work will inspire the search for superconductivity in materials based on group IIB hydrides under pressure.展开更多
Lead chalcogenides represent a significant class of materials that exhibit intriguing physical phenomena,including remarkable thermoelectric properties and superconductivity.In this study,we present a comprehensive in...Lead chalcogenides represent a significant class of materials that exhibit intriguing physical phenomena,including remarkable thermoelectric properties and superconductivity.In this study,we present a comprehensive investigation on the superconductivity of PbSe single crystal under high pressure.The signature of superconducting(SC)transition starts to appear at 7.2 K under 16.5 GPa.Upon further compression,the SC temperature(T_(c))decreases,and it is reduced to 3.5 K at 45.0 GPa.The negative pressure dependent behavior of T_(c)is consistent with the trend of T_(c)-P relations observed in other lead chalcogenides.The highest T_(c)is 8.0 K observed at 20.5 GPa during decompression process,which is also the highest record among all other PbSe derivatives,such as doped samples,superlattices,and so on.The phase boundaries of the structural and electronic transitions are well defined by Raman spectroscopy,and then phase diagrams are plotted for both compression and decompression processes.This work corrects the previous claim of positive pressure dependence of T_(c)in PbSe and provides clear phase diagrams for intrinsic superconductivity in PbSe under pressure.展开更多
文摘We discuss the general interplay between the uncertainty principle and the onset of dissipationless transport phenomena such as superconductivity and superfluidity. We argue that these phenomena are possible because of the robustness of many-body quantum states with respect to the external environment, which is directly related to the uncertainty principle as applied to coordinates and momenta of the carriers. In the case of superconductors, this implies relationships between macroscopic quantities such as critical temperature and critical magnetic field, and microscopic quantities such as the amount of spatial squeezing of a Cooper pair and its correlation time. In the case of ultracold atomic Fermi gases, this should be paralleled by a connection between the critical temperature for the onset of superfluidity and the corresponding critical velocity. Tests of this conjecture are finally sketched with particular regard to the understanding of the behaviour of superconductors under external pressures or mesoscopic superconductors, and the possibility to mimic these effects in ultracold atomic Fermi gases using Feshbach resonances and atomic squeezed states.
文摘It is shown that both super phenomena-superconductivity and superfluidity are based on the same mechanism of streamline of zero-point oscillations. Proof of this is the agreement of obtained theoretical estimations with measured data.
基金supported by the National Natural Science Foundation of China (Grant Nos.12074213 and 11574108)the Major Basic Program of Natural Science Foundation of Shandong Province (Grant No.ZR2021ZD01)the Natural Science Foundation of Shandong Province (Grant No.ZR2023MA082)。
文摘In recent years,the research on superconductivity in one-dimensional(1D)materials has been attracting increasing attention due to its potential applications in low-dimensional nanodevices.However,the critical temperature(T_(c))of 1D superconductors is low.In this work,we theoretically investigate the possible high T_(c) superconductivity of(5,5)carbon nanotube(CNT).The pristine(5,5)CNT is a Dirac semimetal and can be modulated into a semiconductor by full hydrogenation.Interestingly,by further hole doping,it can be regulated into a metallic state with the sp3-hybridized𝜎electrons metalized,and a giant Kohn anomaly appears in the optical phonons.The two factors together enhance the electron–phonon coupling,and lead to high-T_(c) superconductivity.When the hole doping concentration of hydrogenated-(5,5)CNT is 2.5 hole/cell,the calculated T_(c) is 82.3 K,exceeding the boiling point of liquid nitrogen.Therefore,the predicted hole-doped hydrogenated-(5,5)CNT provides a new platform for 1D high-T_(c) superconductivity and may have potential applications in 1D nanodevices.
基金supported by the National Key R&D Program of China (Grant Nos.2022YFA1403103 and 2019YFA0308603)the National Natural Science Foundation of China (Grant No.12304167)the Shandong Provincial Natural Science Foundation of China (Grant No.ZR2023QA020)。
文摘Interfacial superconductivity(IS)has been a topic of intense interest in condensed matter physics,due to its unique properties and exotic photoelectrical performance.However,there are few reports about IS systems consisting of two insulators.Here,motivated by the emergence of an insulator-metal transition in type-Ⅲ heterostructures and the superconductivity in some“special”two-dimensional(2D)semiconductors via electron doping,we predict that the 2D heterostructure SnSe_(2)/PtTe_(2) is a model system for realizing IS by using firstprinciples calculations.Our results show that due to slight but crucial interlayer charge transfer,SnSe_(2)/PtTe_(2) turns to be a type-Ⅲ heterostructure with metallic properties and shows a superconducting transition with the critical temperature(T_(c))of 3.73 K.Similar to the enhanced electron–phonon coupling(EPC)in the electrondoped SnSe_(2) monolayer,the IS in the SnSe_(2)/PtTe_(2) heterostructure mainly originates from the metallized SnSe_(2) layer.Furthermore,we find that its superconductivity is sensitive to tensile lattice strain,forming a domeshaped superconducting phase diagram.Remarkably,at 7%biaxial tensile strain,the superconducting T_(c) can increase more than twofold(8.80 K),resulting from softened acoustic phonons at the𝑀point and enhanced EPC strength.Our study provides a concrete example for realizing IS in type-Ⅲ heterostructures,which waits for future experimental verification.
基金supported by the National Key Research and Development Program of China (Grant Nos.2023YFA1406200 and 2022YFA-1405500)the National Natural Science Foundation of China (Grant Nos.12304021 and 52072188)+3 种基金Zhejiang Provincial Natural Science Foundation of China (Grant Nos.LQ23A040004 and MS26A040028)Natural Science Foundation of Ningbo (Grant Nos.2022J091 and ZX2025001430)the Program for Science and Technology Innovation Team in Zhejiang (Grant No.2021R01004)the Program for Changjiang Scholars and Innovative Research Team in University (Grant No.IRT_15R23)。
文摘High-pressure electrides,characterized by the presence of interstitial quasi-atoms(ISQs),possess unique electronic structures and physical properties,such as diverse dimensions of electride states exhibiting different superconductivity,which has attracted significant attention.Here,we report a new electron-deficient type of electride Li_(4)Al and identify its phase transition progress with pressurization,where the internal driving force behind phase transitions,bonding characteristics,and superconducting behaviors have been revealed based on first-principles density functional theory.Through analysis of the bonding properties of electride Li_(4)Al,we demonstrate that the ISQs exhibiting increasingly covalent characteristics between Al ions play a critical role in driving the phase transition.Our electron–phonon coupling calculations indicate that all phases exhibit superconducting behaviors.Importantly,we prove that the ISQs behave as free electrons and demonstrate that the factor governing T_(c) is primarily derived from Li-p-hybridized electronic states with ISQ compositions.These electronic states are scattered by low-frequency phonons arising from mixed vibrations of Li and Al affected by ISQs to enhance electron–phonon coupling.Our study largely expands the research scope of electrides,provides new insight for understanding phase transitions,and elucidates the effects of ISQs on superconducting behavior.
基金supported by the National Key R&D Program of China (Grant No.2022YFA1403201)the National Natural Science Foundation of China (Grant Nos.12125404,T2495231,123B2049,and 12204138)+9 种基金the Advanced MaterialsNational Science and Technology Major Project (Grant No.2024ZD0607000)the Natural Science Foundation of Jiangsu Province (Grant Nos.BK20233001 and BK20253009)the Jiangsu Funding Program for Excellent Postdoctoral Talent (Grant No.2024ZB002)the China Postdoctoral Science Foundation (Grant No.2025M773331)the Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of Chinathe AI&AI for Science program of Nanjing UniversityArtificial Intelligence and Quantum physics (AIQ) program of Nanjing Universitythe Fundamental Research Funds for the Central Universitiesthe Natural Science Foundation of Nanjing University of Posts and Telecommunications(Grant Nos.NY224165,NY220038,and NY219087)the Hua Li Talents Program of Nanjing University of Posts and Telecommunications。
文摘We report a theoretical investigation into superconductivity within the MAXH_(6) quaternary hydride system using first-principles calculations,where M and A denote alkali and alkaline earth elements,respectively,and X represents transition metal elements.Systematic analysis of electronic band structures,phonon dispersions,and electron-phonon coupling reveals that substitution of MA binary metal combinations and X metal atoms can create favorable conditions for superconductivity.Mapping of superconducting critical temperatures,combined with dynamical stability analysis through phonon calculations,identifies ten superconducting candidates at ambient pressure.Among these,LiNaAgH_(6) exhibits nearly-free-electron behavior reminiscent of monovalent electron superconductors.It demonstrates exceptional superconducting properties with electron–phonon coupling λ=2.707,which yields a superconducting transition temperature T_(c) of 206.4 K using the Allen–Dynes formula.Its structural analogs MgNaPdH_(6),LiMgPdH_(6),LiMgAgH_(6),LiMgAuH_(6) all exhibit superconducting transition temperatures above 110 K.These findings advance our fundamental understanding of superconductivity in quaternary hydrides and provide guidance for rational design of new high-temperature superconducting materials.
基金supported by the National Natural Science Foundation of China(Grant No.62488201)the National Key Research and Development Projects of China(Grant Nos.2022YFA1204100 and 2023YFA1607400)+1 种基金the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-003)the Innovation Program of Quantum Science and Technology(Grant No.2021ZD0302700)。
文摘A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform for exploring Majorana bound states.Trigonal γ-PtBi_(2),a superconductor,is a promising candidate,as both surface superconducting gaps and topological surface states have been observed.However,the simultaneous presence of bulk and surface superconductivity has remained unresolved.In this study,we directly visualize coexisting bulk and surface superconducting gaps in trigonal PtBi2 using ultra-low-temperature scanning tunneling microscopy/spectroscopy.The bulk gap,Δ,is∼0.053 meV,with a critical temperature(T_(c))of∼0.5K and a critical field below 0.01 T,accompanied by a vortex lattice and vortex bound states and yielding a coherence length of∼200 nm.Remarkably,certain surface regions exhibit a much larger gap(Δ)of∼0.42 meV,persisting up to a T_(c)value of∼3K and surviving magnetic fields of up to 2 T,yet lacking a static vortex lattice.This coexistence of robust surface and bulk superconductivity establishes γ-PtBi_(2)as a unique platform for exploring the interplay between bulk and surface Cooper pairings in topological superconductors.
基金supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1403900 and 2021YFA1401800)the NSF of China(Grant Nos.U2032214,12122414,12104487,and 12004419)+2 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB25000000)support from the Youth Innovation Promotion Association of the CAS(2019008)supported by the Synergetic Extreme Condition User Facility(SECUF)。
文摘Signatures of superconductivity near 80 K have recently been discovered in single crystals of La_(3)Ni_(2)O_(7)under pressure,which makes it a new candidate for high-temperature superconductors dominated by 3d transition elements,following the cuprate and iron-pnictide superconductors.However,there are several critical questions that have been perplexing the scientificommunity:(1)What factors contribute to the inconsistent reproducibility of the experimental results?(2)What is the fundamental nature of pressure-induced superconductivity:bulk or nonbulk(filamentary-like)(3)Where is the superconducting phase located within the sample if it is filamentary-like(4)Is the oxygen content important for the development and stabilization of superconductivity?In this study,we employ comprehensive high-pressure techniques to address these questions.Through our modulated ac susceptibility measurements,we are the firs to fin that the superconductivity in this nickelate is filamentary-like Our scanning transmission electron microscopy investigations suggest that the filamentary-lik superconductivity most likely emerges at the interface between La_(3)Ni_(2)O_(7)and La_(4)Ni_(3)O_(10)phases.By tuning the oxygen content of polycrystalline La_(3)Ni_(2)O_(7),we also fin that it plays vital role in the development and stabilization of superconductivity in this material.The upper and lower bounds on the oxygen content are 7.35 and 6.89,respectively.Our results provide not only new insights into the puzzling issues regarding this material,but also significan information that will enable a better understanding of its superconductivity.
基金supported by the National Key R&D Program of China(Grant No.2023YFA1406200)the National Natural Science Foundation of China(Grant Nos.12374004 and 12174141)the High Performance Computing Center of Jilin University,China。
文摘The discovery of pressure-induced superconducting electrides has sparked a intense wave of interest in novel superconductors.However,opinions vary regarding the relationship between non-nuclear attractors(NNAs)and superconductivity,with two opposing views currently represented by the materials Li_(6)P and Li_(6)C.Here,we choose the ternary Li–C–P as a model system and reveal the underlying mechanism by which NNAs contribute to superconductivity.The loosely bound NNAs in the superlithide Li_(14)CP covalently bond with Li and form unique satellite interstitial electrons(SIEs)around Li near the Fermi level,dominating the superconductivity.First-principles calculations show that the SIEs progressively increase in number and couple strongly with phonons at high pressure.Moreover,the Fermi surface nesting associated with SIEs induces phonon softening,further enhancing the electron–phonon coupling and giving the superlithide Li_(14)CP a T_(c)of 10.6 K at 300 GPa.The leading role of SIEs in superconductivity is a general one and is also relevant to the recently predicted Li_(6)P and Li_(6)C.Our work presented here reshapes the understanding of NNA-dominated superconductivity and holds promise for guiding future discoveries and designs of novel high-temperature superconductors.
基金supported by the National Natural Science Foundation of China (Grant Nos. 12374196, 92165201, and 11634011)the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302800)+2 种基金the Chinese Academy of Sciences Project for Young Scientists in Basic Research (Grant No. YSBR-046)the Fundamental Research Funds for the Central Universities (Grant Nos. WK3510000006 and WK3430000003)Anhui Initiative in Quantum Information Technologies (Grant No. AHY170000)。
文摘Ising superconductivity has garnered much attention in recent years due to its extremely high in-plane upper critical field (B_(c2)).Here,we fabricated 14 multilayer Pb_(1-x)Bi_(x) (0%≤x≤40%) thin films on Si (111)-7×7 reconstructed surface by molecular beam epitaxy.Large B_(c2) beyond the Pauli limit is observed in all the Pb_(1-x)Bi_(x) films,indicating that they may exhibit characteristics of Ising superconductivity.Moreover,the introduction of Bi doping can significantly enhance and effectively tune the in-plane B_(c2) of Pb_(1-x)Bi_(x) films,which will help us better understand Ising superconductivity and provide a new platform for the development of tunable Ising superconductors.
基金supported by the National Natural Science Foundation of China(Grant Nos.12325402 and 12074334)the National Key R&D Program of China(Grant No.2023YFA1406400)。
文摘We report the fabrication of freestanding La_(2)CuO_(4)/La_(1.55)Sr_(0.45)CuO_(4)(LCO/LSCO)heterostructure membranes,which were fabricated by selectively etching water-soluble Sr_(3)Al_(2)O_(6)sacrificial layers from pulsed-laser-deposited heterostructures on SrTiO_(3) substrates.Transport measurements reveal that these membranes exhibit superconducting behavior with an onset temperature of approximately 19 K.Comprehensive structural characterization using x-ray diffraction and scanning transmission electron microscopy demonstrates that the membranes retain excellent crystalline quality after release.The superconducting properties remain stable following mild post-annealing treatment under vacuum.This work establishes LCO/LSCO as a promising platform for developing flexible high-temperature superconducting interfaces,opening new possibilities for the development of flexible devices.
基金Project supported by the National Key Research and Development Program of China(Grant No.2023YFA1406000)the National Natural Science Foundation of China(Grant No.12204514).
文摘We used a highly sensitive AC magnetic susceptibility technique to probe superconductivity in elemental titanium(Ti)under extreme pressures to 120 GPa in a diamond anvil cell(DAC).The measurements reveal that the critical temperature(Tc)of Ti rises monotonically with increasing pressure,reaching 6.1 K at 120 GPa.Our results confirm the bulk nature of the superconductivity in Ti,as evidenced by a robust diamagnetic response in the AC magnetic susceptibility.Our work provides a routine technique to probe Meissner effect of elemental superconductors at megabar pressures.
基金supported by the National Key R&D Program of China under Grants Nos.2023YFA1406001,2024YFA1408000,2021YFA1401800,2023YFA1608902,and 2022YFA1402301the financial support from Shanghai Key Laboratory of MFree,China(No.22dz2260800)Shanghai Science and Technology Committee,China(No.22JC1410300)。
文摘Ytterbium polyhydrides were synthesized through in-situ high pressure laser heating techniques utilizing a diamond anvil cell.The temperature dependence of resistance measurement at high pressure demonstrates that the sample undergoes a superconducting transition at 11.5 K at 180 GPa.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFA1406103)the Education Department of Jilin Province,and Science and Technology Plan(Grant No.JJKH20211042KJ).
文摘Nickel-based superconductors have attracted great attention due to the finding of the Ruddlesden-Popper(R-P)bilayer nickelate La_(3)Ni_(2)O_(7)with superconducting critical temperature(T_(c))of 80 K at pressure above 14 GPa.Recent efforts have been devoted to the study of La_(2)PrNi_(2)O_(7),while the detailed structure remains unclear.In this work,we explore the stability and physical properties of such an interesting system by using density functional theory and the U parameter simulation method implemented in VASP.The results show that the enthalpy of La_(2)PrNi_(2)O_(7)is slightly larger than its parent material bilayer R-P nickelate La_(3)Ni_(2)O_(7).The electronic structure analysis indicates that near the Fermi level,the eg orbit of Ni dominates and strongly hybridizes with the 2p orbit of O,thereby forming a significant van Hove singularity that is conducive to superconductivity.The Amam phase to the I4/mmm phase occurs,accompanied by an increase in the bandwidth of Ni 3d_(z)_(2) and an enhancement of the bonding-antibonding splitting(from about 0.5 eV to 1.5 eV),which leads to an increase in the density of states at the Fermi level.Our findings provide insights into the preparation and superconductivity of R-P bilayer nickelate.
基金supported by the National Natural Science Foundation of China(Grant Nos.12204280 and 12147135)the Natural Science Foundation of Shandong Province(Grant No.ZR202103010004)+1 种基金the China Postdoctoral Science Foun-dation(Certificate Nos.2023T160396 and 2021M691980)the Youth Innovation Team Plan of Colleges and Universities in Shandong Province(Grant No.2023KJ350).
文摘Obtaining room-temperature superconductors has long been a research hotspot in the field of condensed matter physics.Previous studies have shown that doping strategies can effectively enhance the superconducting properties of materials.In this work,we employed first-principles calculations combined with the particle swarm optimization method to explore the structural possibilities of the Ca-doped As-H ternary system and to calculate the electronic and superconducting properties of the newly identified structures.Two thermodynamically stable hydrides were found under high pressure.The P4/nmm-Ca_(2)AsH_(4)phase remains thermodynamically stable within the pressure range of 90-200 GPa,while the Cc-Ca_(2)AsH_(6)phase exhibits stability over a broader range of 79-200 GPa.Electron-phonon coupling analysis indicates that the superconducting critical temperatures(Tc)of P4/nmm-Ca_(2)AsH_(4)and Cc-Ca_(2)AsH_(6)are 11 K and 16 K at 100 GPa,respectively.The incorporation of Ca significantly reduces the thermodynamic stability pressure of As-H compounds with higher hydrogen content,thereby improving their synthetic accessibility.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12274169,12122405,and 52072188)the National Key Research and Development Program of China(Grant No.2022YFA1402304)+1 种基金the Program for Science and Technology Innovation Team in Zhejiang Province,China(Grant No.2021R01004)the Fundamental Research Funds for the Central Universities.
文摘Two-dimensional(2D)superconductors have attracted significant research interest due to their promising potential applications in optoelectronic and microelectronic devices.Herein,we employ first-principles calculations to predicted a new 2D conventional superconductor,Tc_(2)B_(2),demonstrating its stable structural configuration.Remarkably,under biaxial strain,the superconducting transition temperature(T_(c))of Tc_(2)B_(2)demonstrates a significant enhancement,achieving 19.5 K under 3%compressive strain and 9.2 K under 11%tensile strain.Our study reveals that strain-induced modifications in Fermi surface topology significantly enhance the Fermi surface nesting effect,which amplifies electron–phonon coupling interactions and consequently elevates Tc.Additionally,the presence of the Lifshitz transition results in a more pronounced rise in Tc under compressive strain compared to tensile strain.These insights offer important theoretical guidance for designing 2D superconductors with high-Tc through strain modulation.
基金work was supported by the National Key Research and Development Program of China(Grant Nos.2023YFA1406200 and 2022YFA1405500)the National Natural Science Foundation of China(Grant Nos.12304021 and 52072188)+4 种基金Zhejiang Provincial Natural Science Foundation of China(Grant No.LQ23A040004)Program for Science and Technology Innovation Team in Zhejiang(Grant No.2021R01004)the Natural Science Foundation of Ningbo(Grant No.2022J091)the Program for Changjiang Scholars and Innovative Research Team in University(Grant No.IRT 15R23)Parts of calculations were performed at the Supercomputer Center of Ningbo University.
文摘The emergence of high-temperature superconductivity in hydrogen-rich compounds has opened up promising avenues for investigating unique hydrogen motifs that exhibit exceptional superconducting properties.Nevertheless,the requirement for extremely high synthesis pressures poses significant barriers to experimentally probing potential physical properties.Here,we have designed a structure wherein NH_(3)tetrahedra are intercalated into the body-centered cubic lattice of Yb,resulting in the formation of Yb(NH_(3))_(4).Our first-principles calculations reveal that metallic behavior emerges from the ionization of sp^(3)-hybridized s-bonds in NH_(3),which is enabled by electron transfer from ytterbium orbitals to NH_(3)anti-bonding s-orbitals.A distinctive feature of this structure is the Fermi surface nesting,which leads to optical phonon softening and consequently enhances electron-phonon coupling.The subsequent density-functional theory(DFT)calculations demonstrate that this I-43m phase of Yb(NH_(3))4 exhibits a superconducting critical temperature(T_(c))of 17.32 K under a modest pressure of 10 GPa.Our investigation presents perspectives on achieving phonon-mediated superconductivity at relatively low pressures,thereby opening up extensive possibilities for the attainment of high-temperature superconductivity in hydrogen-based superconducting systems with specific ionized molecular groups.
基金supported by the Jilin Provincial Natural Science Foundation(Grant No.20230101183JC)the Center for Computational Research at Jilin Province.
文摘The particle swarm optimization algorithm has predicted a series of binary cadmium hydrides that could be dynamically stable at pressures between 100 GPa and 300 GPa.These low-energy phases are composed of both Cd atoms and H_(2)molecules.Here,we propose a hitherto unknown metastable Cmcm-CdH_(6)phase,consisting of one-dimensional zigzag graphite-like hydrogenic H_(6)chains,quasimolecular H_(2)units and Cd atoms,which is metallic above 290 GPa.Due to H_(2)s→Cd d donation and Cd d→H_(2)σ^(*)back-donation,the electrons occupy antibonding orbitals for both types of hydrogen atoms.This results in weakened chemical bonds in the Cmcm-CdH_(6)phase via a Kubas-like mechanism,promoting the emergence of high superconductivity,which is estimated to be up to~60 K at 290 GPa.This work will inspire the search for superconductivity in materials based on group IIB hydrides under pressure.
基金supported by the National Natural Science Foundation of China(Grant Nos.12374050,12004014,U1930401,and 12375304)the National Key R&D Program of China(Grant Nos.2021YFA1400300 and 2023YFA1608900)the Major Program of the National Natural Science Foundation of China(Grant No.22090041).
文摘Lead chalcogenides represent a significant class of materials that exhibit intriguing physical phenomena,including remarkable thermoelectric properties and superconductivity.In this study,we present a comprehensive investigation on the superconductivity of PbSe single crystal under high pressure.The signature of superconducting(SC)transition starts to appear at 7.2 K under 16.5 GPa.Upon further compression,the SC temperature(T_(c))decreases,and it is reduced to 3.5 K at 45.0 GPa.The negative pressure dependent behavior of T_(c)is consistent with the trend of T_(c)-P relations observed in other lead chalcogenides.The highest T_(c)is 8.0 K observed at 20.5 GPa during decompression process,which is also the highest record among all other PbSe derivatives,such as doped samples,superlattices,and so on.The phase boundaries of the structural and electronic transitions are well defined by Raman spectroscopy,and then phase diagrams are plotted for both compression and decompression processes.This work corrects the previous claim of positive pressure dependence of T_(c)in PbSe and provides clear phase diagrams for intrinsic superconductivity in PbSe under pressure.
