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
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
We investigate the energy bands,magnetism,and superconductivity of bilayer octagraphene with A-A stackingunder a perpendicular electric field.A tight-binding model is used to analyze the band structure of the system.T...We investigate the energy bands,magnetism,and superconductivity of bilayer octagraphene with A-A stackingunder a perpendicular electric field.A tight-binding model is used to analyze the band structure of the system.The doubling of the unit cell results in each band of the single layer splitting into two.We find that applyinga perpendicular electric field increases the band splitting.As the electric field strength increases,the nestingof the Fermi surface(FS)weakens,eventually disrupting the antiferromagnetic order,and bilayer octagrapheneexhibits superconductivity.Spin fluctuations can induce unconventional superconductivity with s±-wave pairing.Applying a perpendicular electric field to bilayer octagraphene parent weakens the nesting of the FS,ultimatelykilling the spin-density-wave(SDW)ordered state and transitioning it into the superconducting state,whichworks as a doping effect.We use the random-phase approximation approach to obtain the pairing eigenvaluesand pairing symmetries of the perpendicular electric field-tuned bilayer octagraphene in the weak coupling limit.By tuning the strength of the perpendicular electric field,the critical interaction strength for SDW order can bemodified,which in turn may promote the emergence of unconventional superconductivity.展开更多
The recently discovered titanium-based kagome metal ATi_(3)Bi_(5)(A=Cs,Rb)provides a new platform to explore novel quantum phenomena.In this work,the transport properties of ATi_(3)Bi_(5)(A=Cs,Rb)are systematically in...The recently discovered titanium-based kagome metal ATi_(3)Bi_(5)(A=Cs,Rb)provides a new platform to explore novel quantum phenomena.In this work,the transport properties of ATi_(3)Bi_(5)(A=Cs,Rb)are systematically investigated under high pressure.Although ATi_(3)Bi_(5)(A=Cs,Rb)shows no evidence of superconductivity at ambient pressure,the pressure-induced double-dome superconductivity is observed in both compounds,resembling the superconducting phase diagram of AV_(3)Sb_(5)(A=Cs,Rb,and K)under pressure.High-pressure X-ray difraction measurements exclude the pressure-induced structural phase transition.A slope change in the c/a ratio was found between 12.4 and 14.9 GPa,indicating the occurrence of lattice distortion.The distinct changes in the electronic band structure revealed by frst-principles calculations further explain the emergence of superconductivity in the two domes.These fndings suggest that pressure can efectively tune the electronic properties of ATi_(3)Bi_(5),providing new insights into the rich physics of kagome metals.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
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
The recent discovery of type-Ⅶboron-carbon clathrates with calculated superconducting transition temperatures approaching~100 K has sparked interest in exploring new conventional superconductors that may be stabilize...The recent discovery of type-Ⅶboron-carbon clathrates with calculated superconducting transition temperatures approaching~100 K has sparked interest in exploring new conventional superconductors that may be stabilized at ambient pressure.The electronic structure of the clathrate is highly tunable based on the ability to substitute different metal atoms within the cages,which may also be large enough to host small molecules.Here we introduce molecular hydrogen(H_(2))within the clathrate cages and investigate its impact on electron-phonon coupling interactions and the superconducting transition temperature(T_(c)).Our approach involves combining molecular hydrogen with the new diamond-like covalent framework,resulting in a hydrogen-encapsulated clathrate,(H_(2))B_(3)C_(3).A notable characteristic of(H_(2))B_(3)C_(3)is the dynamic behavior of the H_(2)molecules,which exhibit nearly free rotations within the B-C cages,resulting in a dynamic structure that remains cubic on average.The static structure of(H_(2))B_(3)C_(3)(a snapshot in its dynamic trajectory)is calculated to be dynamically stable at ambient and low pressures.Topological analysis of the electron density reveals weak van der Waals interactions between molecular hydrogen and the B-C cages,marginally influencing the electronic structure of the material.The electron count and electronic structure calculations indicate that(H_(2))B_(3)C_(3)is a hole conductor,in which H_(2)molecules donate a portion of their valence electron density to the metallic cage framework.Electron-phonon coupling calculation using the Migdal-Eliashberg theory predicts that(H_(2))B_(3)C_(3)possesses a T_(c) of 46 K under ambient pressure.These results indicate potential for additional light-element substitutions within the type-Ⅶclathrate framework and suggest the possibility of molecular hydrogen as a new approach to optimizing the electronic structures of this new class of superconducting materials.展开更多
The interplay between electronic topological phase transitions and superconductivity in the field of condensed matter physics has consistently captivated researchers.Here we have succeeded in modulating the Lifshitz t...The interplay between electronic topological phase transitions and superconductivity in the field of condensed matter physics has consistently captivated researchers.Here we have succeeded in modulating the Lifshitz transition by pressure and realized superconductivity.At 25.7 GPa,superconductivity with a transition temperature of 1.9 K has been observed in 3R-NbS_(2).The Hall coefficient changes from negative to positive at 14 GPa,indicating a Lifshitz transition in 3R-NbS_(2),and the carrier concentration continues to increase with increasing pressure.X-ray diffraction results indicate that the appearance of superconductivity cannot be attributable to structural transitions.Based on theoretical calculations,the emergence of a new band is attributed to the Lifshitz transition and the new band coincides with the Fermi surface at the pressure of 30 GPa.These findings provide new insights into the relationship between the Lifshitz transition and superconductivity.展开更多
Two-dimensional double-layer honeycomb(DLHC)materials are known for their diverse physical properties,but superconductivity has been a notably absent characteristic in this structure.We address this gap by investigati...Two-dimensional double-layer honeycomb(DLHC)materials are known for their diverse physical properties,but superconductivity has been a notably absent characteristic in this structure.We address this gap by investigating M_(2)N_(2)(M=Nb,Ta)with DLHC structure using first-principles calculations.Our results show that M_(2)N_(2)are stable and metallic,exhibiting superconducting behavior.Specifically,Nb_(2)N_(2)and Ta_(2)N_(2)display superconducting transition temperatures of 6.8 K and 8.8 K,respectively.Their electron-phonon coupling is predominantly driven by the coupling between metal d-orbitals and low-frequency metal-dominated vibration modes.Interestingly,two compounds also exhibit non-trivial band topology.Thus,M_(2)N_(2)are promising platforms for studying the interplay between topology and superconductivity and fill the gap in superconductivity research for DLHC materials.展开更多
We investigate the hole-doped Hubbard model on a honeycomb lattice using a fermionic projected entangled pair states(f PEPS)method.Our study reveals the presence of quasi-long-range order of Cooper pairs,characterized...We investigate the hole-doped Hubbard model on a honeycomb lattice using a fermionic projected entangled pair states(f PEPS)method.Our study reveals the presence of quasi-long-range order of Cooper pairs,characterized by powerlaw decay of correlation functions with exponents K>1.We further analyze the competing phases of superconductivity,specifically the antiferromagnetic(AFM)order and the charge density wave(CDW)order.Our results show that there are domain wall structures when the hole dopingδis small and the Coulomb parameter U is large.However,these structures disappear as we increase the hole dopingδor decrease U.Furthermore,for small hole doping,the system exhibits AFM order,which diminishes forδ>0.05.Conversely,as the doping level increases,the CDW order gradually decreases.Notably,a considerable CDW order persists even at higher doping levels.These findings suggest a progressive suppression of the AFM order and a growing prominence of the CDW order with increasingδ.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
This study systematically investigates the transport and point-contact Andreev reflection spectroscopy(PCARS) properties of Bi-doped BaFe_(2)(As_(1-x)Bi_(x))_(2) crystals under high pressures up to 8.7 GPa. The superc...This study systematically investigates the transport and point-contact Andreev reflection spectroscopy(PCARS) properties of Bi-doped BaFe_(2)(As_(1-x)Bi_(x))_(2) crystals under high pressures up to 8.7 GPa. The superconducting critical temperature(T_(c)) and upper critical field(H_(c2)) initially decrease with pressure but exhibit a local maximum around 2.9 GPa before further suppression, which can be related to the superconducting transition in the parent compound. The conductance spectrum is consistent with a two-band s-wave model, confirming multi-band superconductivity. The superconducting energy gaps and coupling strengths decrease monotonically with pressure, with the larger gap transitioning from strong to weak coupling. These results provide insight into the interplay between structural, electronic, and superconducting properties in isovalent-doped 122 Fe-based superconductors.展开更多
Ising superconductivity, induced by the strong spin–orbit coupling(SOC) and inversion symmetry breaking, can lead to the in-plane upper critical field exceeding the Pauli limit and hold significant potential for adva...Ising superconductivity, induced by the strong spin–orbit coupling(SOC) and inversion symmetry breaking, can lead to the in-plane upper critical field exceeding the Pauli limit and hold significant potential for advancing the study of topological superconductivity. However, the enhancement of Ising superconductivity is still a challenging problem, important for engineering Majorana fermions and exploring topological quantum computing. In this study, we investigated the superconducting properties of a series of van der Waals NbSe_(2-x)Te_(x) nanosheets. The Ising superconductivity in NbSe_(2-x)Te_(x) nanosheets can be significantly enhanced by the substitution of Te, an element with strong SOC. The fitted in-plane upper critical field of Nb Se_(1.5)Te_(0.5) nanosheets at absolute zero temperature reaches up to 3.2 times the Pauli limit. Angular dependence of magnetoresistance measurements reveals a distinct two-fold rotational symmetry in the superconducting transition region, highlighting the role of strong SOC. In addition, the fitting results of the Berezinskii–Kosterlitz–Thouless(BKT) transition and the two-dimensional(2D) Tinkham formula provide strong evidence for 2D superconductivity. These findings offer new perspectives for the design and modulation of the Ising superconducting state and pave the way for their potential applications in topological superconductivity and quantum technologies.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
Transition metal dichalcogenides(TMDs), exhibit a range of crystal structures and topological quantum states. The1T phase, in particular, shows promise for superconductivity driven by electron–phonon coupling(EPC), s...Transition metal dichalcogenides(TMDs), exhibit a range of crystal structures and topological quantum states. The1T phase, in particular, shows promise for superconductivity driven by electron–phonon coupling(EPC), strain, pressure,and chemical doping. In this theoretical investigation, we explore 1T-Rh Se Te as a novel type of TMD superconductor with topological electronic states. The optimal doping structure and atomic arrangement of 1T-Rh Se Te are constructed.Phonon spectrum calculations validate the integrity of the constructed doping structure. The analysis of the electron–phonon coupling using the electron–phonon Wannier(EPW) method has confirmed the existence of a robust electron–phonon interaction in 1T-Rh Se Te, resulting in total EPC constant λ = 2.02, the logarithmic average frequency ω_(log)= 3.15 me V and T_c = 4.61 K, consistent with experimental measurements and indicative of its classification as a BCS superconductor.The band structure analysis revealed the presence of Dirac-like band crossing points. The topological non-trivial electronic structures of the 1T-Rh Se Te are confirmed via the evolution of Wannier charge centers(WCCs) and time-reversal symmetryprotected topological surface states(TSSs). These distinctive properties underscore 1T-Rh Se Te as a possible candidate for a topological superconductor, warranting further investigation into its potential implications and applications.展开更多
The unique three-dimensional orthorhombic NbS(o-NbS)compound synthesized in 1969 has recently been experimentally confirmed to be a superconductor[Phys.Rev.B 108174517(2023)].However,there is currently no theoretical ...The unique three-dimensional orthorhombic NbS(o-NbS)compound synthesized in 1969 has recently been experimentally confirmed to be a superconductor[Phys.Rev.B 108174517(2023)].However,there is currently no theoretical research on its superconducting mechanism.In this work,we investigate the superconducting properties of o-Nb S from first-principles calculations.Based on the Eliashberg equation,it is found that the superconductivity mainly originates from the coupling between the electrons of Nb-4d orbitals and the vibrations of Nb atoms in the low-frequency region and those of S atoms in the high-frequency region.A superconducting transition temperature(T_c)of 10.7 K is obtained,which is close to the experimental value and higher than most transition metal chalcogenides(TMCs).The calculated thermodynamic properties in the superconducting state,such as specific heat,energy gap,isotope coefficient,etc.,also indicate that o-NbS is a conventional phonon-mediated superconductor.These results are consistent with recent experimental reports and provide a good understanding of the superconducting mechanism of o-Nb S.Furthermore,the TMCs of o-TaS and o-WS are also investigated;these belong to the same and neighboring groups of Nb,and we find that o-TaS and o-WS are also phonon-mediated superconductors with T_c of 8.9 K and 7.2 K,respectively.展开更多
We present a comprehensive investigation into the superconducting properties of L_(a3)Al,a La-based metal with a kagome structure.L_(a3)Al crystallizes in a Ni_(3)Sn-type crystal structure(space group P63/mmc),where t...We present a comprehensive investigation into the superconducting properties of L_(a3)Al,a La-based metal with a kagome structure.L_(a3)Al crystallizes in a Ni_(3)Sn-type crystal structure(space group P63/mmc),where the La atoms form a kagome lattice.Resistivity measurements reveal superconducting transition with T_(c)^(onset)=6.37 K and Tczero=6.18 K.In magnetic susceptibility measurements,the superconducting transition is observed at 6.16 K.The lower and upper critical fields are determined to be 22.17 mT and 6.69 T,respectively.Heat capacity measurements confirm the bulk superconductivity,showing a normalized specific heat change of△Ce/(_(γ)T_(c))=2.16 and an electron-phonon coupling strength ofλ_(ep)=0.92.DFT calculations reveal the intricate band structure of La_(3)Al.The notable specific heat jump,coupled with the electron-phonon coupling strengthλ_(ep),indicates that La_(3)Al exhibits characteristics of an intermediately coupled type-Ⅱsuperconductor.展开更多
The regulation of superconductivity in thin films can provide important information on low-dimensional superconducting properties,and also has important reference values for the application in superconducting devices....The regulation of superconductivity in thin films can provide important information on low-dimensional superconducting properties,and also has important reference values for the application in superconducting devices.Herein,we report the successful regulation of both the superconductivity and normal-state properties of Nb films in a wide range by the controllable introduction of interstitial oxygen atoms.The lattice parameter is enhanced for an extent as large as 4.4%,and the normal-state resistivityρ_(n)is tuned for more than 15 times.The slope of upper critical field near T_(c)shows a close correlation withρ_(n)in a wide range.Importantly,it is found that the suppression of T_(c)by disorder reveals a linear dependence withρ_(n)in the region with an unchanged crystalline quality,which can be understood based on the picture of three-dimensional ballistic motion.展开更多
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 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 R&D Program of China(Grant No.2022YFA1402802)the National Natural Science Foundation of China(Grant Nos.12494591 and 92165204)+4 种基金the Leading Talent Program of Guangdong Special Projects(Grant No.201626003)the Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices(Grant No.2022B1212010008)the Research Center for Magnetoelectric Physics of Guangdong Province(Grant No.2024B0303390001)the Guangdong Provincial Quantum Science Strategic Initiative(Grant No.GDZX2401010)supported by the National Natural Science Foundation of China(Grant Nos.12234016 and 12074031)。
文摘We investigate the energy bands,magnetism,and superconductivity of bilayer octagraphene with A-A stackingunder a perpendicular electric field.A tight-binding model is used to analyze the band structure of the system.The doubling of the unit cell results in each band of the single layer splitting into two.We find that applyinga perpendicular electric field increases the band splitting.As the electric field strength increases,the nestingof the Fermi surface(FS)weakens,eventually disrupting the antiferromagnetic order,and bilayer octagrapheneexhibits superconductivity.Spin fluctuations can induce unconventional superconductivity with s±-wave pairing.Applying a perpendicular electric field to bilayer octagraphene parent weakens the nesting of the FS,ultimatelykilling the spin-density-wave(SDW)ordered state and transitioning it into the superconducting state,whichworks as a doping effect.We use the random-phase approximation approach to obtain the pairing eigenvaluesand pairing symmetries of the perpendicular electric field-tuned bilayer octagraphene in the weak coupling limit.By tuning the strength of the perpendicular electric field,the critical interaction strength for SDW order can bemodified,which in turn may promote the emergence of unconventional superconductivity.
基金supported by the Natural Science Foundation of China(Grant No.12174064)the Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01)+5 种基金the Innovation Program for Quantum Science and Technology(Grant No.2024ZD0300104)the support by the Natural Science Foundation of China(Grant No.12204383)the Young Elite Scientists Sponsorship Program by CAST(Grant No.2023QNRC001)the Young Talent Fund of the Association for Science and Technology in Shaanxi(Grant No.CLGC202201)supported by the open project of Beijing National Laboratory for Condensed Matter Physics(Grant No.ZBJ2106110017)the Double First-Class Initiative Fund of Shanghai Tech University。
文摘The recently discovered titanium-based kagome metal ATi_(3)Bi_(5)(A=Cs,Rb)provides a new platform to explore novel quantum phenomena.In this work,the transport properties of ATi_(3)Bi_(5)(A=Cs,Rb)are systematically investigated under high pressure.Although ATi_(3)Bi_(5)(A=Cs,Rb)shows no evidence of superconductivity at ambient pressure,the pressure-induced double-dome superconductivity is observed in both compounds,resembling the superconducting phase diagram of AV_(3)Sb_(5)(A=Cs,Rb,and K)under pressure.High-pressure X-ray difraction measurements exclude the pressure-induced structural phase transition.A slope change in the c/a ratio was found between 12.4 and 14.9 GPa,indicating the occurrence of lattice distortion.The distinct changes in the electronic band structure revealed by frst-principles calculations further explain the emergence of superconductivity in the two domes.These fndings suggest that pressure can efectively tune the electronic properties of ATi_(3)Bi_(5),providing new insights into the rich physics of kagome metals.
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 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.
基金supported by Carnegie Canada and Natural Sciences and Engineering Research Council of Canada(NSERC)support from the U.S.Department of Energy(DOE),Office of Science,Basic Energy Sciences,under Award No.DESC0020683。
文摘The recent discovery of type-Ⅶboron-carbon clathrates with calculated superconducting transition temperatures approaching~100 K has sparked interest in exploring new conventional superconductors that may be stabilized at ambient pressure.The electronic structure of the clathrate is highly tunable based on the ability to substitute different metal atoms within the cages,which may also be large enough to host small molecules.Here we introduce molecular hydrogen(H_(2))within the clathrate cages and investigate its impact on electron-phonon coupling interactions and the superconducting transition temperature(T_(c)).Our approach involves combining molecular hydrogen with the new diamond-like covalent framework,resulting in a hydrogen-encapsulated clathrate,(H_(2))B_(3)C_(3).A notable characteristic of(H_(2))B_(3)C_(3)is the dynamic behavior of the H_(2)molecules,which exhibit nearly free rotations within the B-C cages,resulting in a dynamic structure that remains cubic on average.The static structure of(H_(2))B_(3)C_(3)(a snapshot in its dynamic trajectory)is calculated to be dynamically stable at ambient and low pressures.Topological analysis of the electron density reveals weak van der Waals interactions between molecular hydrogen and the B-C cages,marginally influencing the electronic structure of the material.The electron count and electronic structure calculations indicate that(H_(2))B_(3)C_(3)is a hole conductor,in which H_(2)molecules donate a portion of their valence electron density to the metallic cage framework.Electron-phonon coupling calculation using the Migdal-Eliashberg theory predicts that(H_(2))B_(3)C_(3)possesses a T_(c) of 46 K under ambient pressure.These results indicate potential for additional light-element substitutions within the type-Ⅶclathrate framework and suggest the possibility of molecular hydrogen as a new approach to optimizing the electronic structures of this new class of superconducting materials.
基金Project supported by the National Key R&D Program of China(Grant No.2022YFA1405500)the National Natural Science Foundation of China(Grant Nos.52072188 and 12304072)+1 种基金Program for Science and Technology Innovation Team in Zhejiang(Grant No.2021R01004)the Natural Science Foundation of Ningbo(Grant No.2021J121)。
文摘The interplay between electronic topological phase transitions and superconductivity in the field of condensed matter physics has consistently captivated researchers.Here we have succeeded in modulating the Lifshitz transition by pressure and realized superconductivity.At 25.7 GPa,superconductivity with a transition temperature of 1.9 K has been observed in 3R-NbS_(2).The Hall coefficient changes from negative to positive at 14 GPa,indicating a Lifshitz transition in 3R-NbS_(2),and the carrier concentration continues to increase with increasing pressure.X-ray diffraction results indicate that the appearance of superconductivity cannot be attributable to structural transitions.Based on theoretical calculations,the emergence of a new band is attributed to the Lifshitz transition and the new band coincides with the Fermi surface at the pressure of 30 GPa.These findings provide new insights into the relationship between the Lifshitz transition and superconductivity.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074213 and 11574108)the National Key R&D Program of China(Grant No.2022YFA1403103)+2 种基金the Major Basic Program of Natural Science Foundation of Shandong Province(Grant No.ZR2021ZD01)the Natural Science Foundation of Shandong Province(Grant No.ZR2023MA082)the Project of Introduction and Cultivation for Young Innovative Talents in Colleges and Universities of Shandong Province。
文摘Two-dimensional double-layer honeycomb(DLHC)materials are known for their diverse physical properties,but superconductivity has been a notably absent characteristic in this structure.We address this gap by investigating M_(2)N_(2)(M=Nb,Ta)with DLHC structure using first-principles calculations.Our results show that M_(2)N_(2)are stable and metallic,exhibiting superconducting behavior.Specifically,Nb_(2)N_(2)and Ta_(2)N_(2)display superconducting transition temperatures of 6.8 K and 8.8 K,respectively.Their electron-phonon coupling is predominantly driven by the coupling between metal d-orbitals and low-frequency metal-dominated vibration modes.Interestingly,two compounds also exhibit non-trivial band topology.Thus,M_(2)N_(2)are promising platforms for studying the interplay between topology and superconductivity and fill the gap in superconductivity research for DLHC materials.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12134012 and 12104433)。
文摘We investigate the hole-doped Hubbard model on a honeycomb lattice using a fermionic projected entangled pair states(f PEPS)method.Our study reveals the presence of quasi-long-range order of Cooper pairs,characterized by powerlaw decay of correlation functions with exponents K>1.We further analyze the competing phases of superconductivity,specifically the antiferromagnetic(AFM)order and the charge density wave(CDW)order.Our results show that there are domain wall structures when the hole dopingδis small and the Coulomb parameter U is large.However,these structures disappear as we increase the hole dopingδor decrease U.Furthermore,for small hole doping,the system exhibits AFM order,which diminishes forδ>0.05.Conversely,as the doping level increases,the CDW order gradually decreases.Notably,a considerable CDW order persists even at higher doping levels.These findings suggest a progressive suppression of the AFM order and a growing prominence of the CDW order with increasingδ.
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Project supported by the National Natural Science Foundation of China (Grant Nos. 12461160274 and 12004104)Shenzhen Fundamental Research Program (Grant No. JCYJ20230807093301003)+1 种基金the Major Science and Technology Infrastructure Project of Material Genome Big-science Facilities Platform supported by Municipal Development and Reform Commission of Shenzhensupported by Guangdong Provincial Quantum Science Strategic Initiative (Grant No. GDZX2201001)。
文摘This study systematically investigates the transport and point-contact Andreev reflection spectroscopy(PCARS) properties of Bi-doped BaFe_(2)(As_(1-x)Bi_(x))_(2) crystals under high pressures up to 8.7 GPa. The superconducting critical temperature(T_(c)) and upper critical field(H_(c2)) initially decrease with pressure but exhibit a local maximum around 2.9 GPa before further suppression, which can be related to the superconducting transition in the parent compound. The conductance spectrum is consistent with a two-band s-wave model, confirming multi-band superconductivity. The superconducting energy gaps and coupling strengths decrease monotonically with pressure, with the larger gap transitioning from strong to weak coupling. These results provide insight into the interplay between structural, electronic, and superconducting properties in isovalent-doped 122 Fe-based superconductors.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 62488201 and 1240041502)the China Postdoctoral Science Foundation (Grant No. 2024T170990)+2 种基金the National Key R&D Program of China (Grant No. 2022YFA1204100)the Chinese Academy of Sciences (Grant No. XDB33030100)the Innovation Program of Quantum Science and Technology (Grant No. 2021ZD0302700)。
文摘Ising superconductivity, induced by the strong spin–orbit coupling(SOC) and inversion symmetry breaking, can lead to the in-plane upper critical field exceeding the Pauli limit and hold significant potential for advancing the study of topological superconductivity. However, the enhancement of Ising superconductivity is still a challenging problem, important for engineering Majorana fermions and exploring topological quantum computing. In this study, we investigated the superconducting properties of a series of van der Waals NbSe_(2-x)Te_(x) nanosheets. The Ising superconductivity in NbSe_(2-x)Te_(x) nanosheets can be significantly enhanced by the substitution of Te, an element with strong SOC. The fitted in-plane upper critical field of Nb Se_(1.5)Te_(0.5) nanosheets at absolute zero temperature reaches up to 3.2 times the Pauli limit. Angular dependence of magnetoresistance measurements reveals a distinct two-fold rotational symmetry in the superconducting transition region, highlighting the role of strong SOC. In addition, the fitting results of the Berezinskii–Kosterlitz–Thouless(BKT) transition and the two-dimensional(2D) Tinkham formula provide strong evidence for 2D superconductivity. These findings offer new perspectives for the design and modulation of the Ising superconducting state and pave the way for their potential applications in topological superconductivity and quantum technologies.
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Project supported by the National Natural Science Foundation of China (Grant No. 12204400)Science Research Project of Hebei Education Department (Grant No. QN2022169)+1 种基金the Natural Science Foundation of Hebei Province (Grant Nos. A2022203010 and A2024203011)Innovation Capability Improvement Project of Hebei Province (Grant No. 22567605H)。
文摘Transition metal dichalcogenides(TMDs), exhibit a range of crystal structures and topological quantum states. The1T phase, in particular, shows promise for superconductivity driven by electron–phonon coupling(EPC), strain, pressure,and chemical doping. In this theoretical investigation, we explore 1T-Rh Se Te as a novel type of TMD superconductor with topological electronic states. The optimal doping structure and atomic arrangement of 1T-Rh Se Te are constructed.Phonon spectrum calculations validate the integrity of the constructed doping structure. The analysis of the electron–phonon coupling using the electron–phonon Wannier(EPW) method has confirmed the existence of a robust electron–phonon interaction in 1T-Rh Se Te, resulting in total EPC constant λ = 2.02, the logarithmic average frequency ω_(log)= 3.15 me V and T_c = 4.61 K, consistent with experimental measurements and indicative of its classification as a BCS superconductor.The band structure analysis revealed the presence of Dirac-like band crossing points. The topological non-trivial electronic structures of the 1T-Rh Se Te are confirmed via the evolution of Wannier charge centers(WCCs) and time-reversal symmetryprotected topological surface states(TSSs). These distinctive properties underscore 1T-Rh Se Te as a possible candidate for a topological superconductor, warranting further investigation into its potential implications and applications.
基金Project 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)+1 种基金the Natural Science Foundation of Shandong Province(Grant No.ZR2023MA082)the Project of Introduction and Cultivation for Young Innovative Talentsin Colleges and Universities of Shandong Province。
文摘The unique three-dimensional orthorhombic NbS(o-NbS)compound synthesized in 1969 has recently been experimentally confirmed to be a superconductor[Phys.Rev.B 108174517(2023)].However,there is currently no theoretical research on its superconducting mechanism.In this work,we investigate the superconducting properties of o-Nb S from first-principles calculations.Based on the Eliashberg equation,it is found that the superconductivity mainly originates from the coupling between the electrons of Nb-4d orbitals and the vibrations of Nb atoms in the low-frequency region and those of S atoms in the high-frequency region.A superconducting transition temperature(T_c)of 10.7 K is obtained,which is close to the experimental value and higher than most transition metal chalcogenides(TMCs).The calculated thermodynamic properties in the superconducting state,such as specific heat,energy gap,isotope coefficient,etc.,also indicate that o-NbS is a conventional phonon-mediated superconductor.These results are consistent with recent experimental reports and provide a good understanding of the superconducting mechanism of o-Nb S.Furthermore,the TMCs of o-TaS and o-WS are also investigated;these belong to the same and neighboring groups of Nb,and we find that o-TaS and o-WS are also phonon-mediated superconductors with T_c of 8.9 K and 7.2 K,respectively.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52272268 and 52250308)the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant No.XDB33010100)+1 种基金the Informatization Plan of Chinese Academy of Sciences(Grant No.CAS-WX2021SF0102)the Synergetic Extreme Condition User Facility(SECUF)。
文摘We present a comprehensive investigation into the superconducting properties of L_(a3)Al,a La-based metal with a kagome structure.L_(a3)Al crystallizes in a Ni_(3)Sn-type crystal structure(space group P63/mmc),where the La atoms form a kagome lattice.Resistivity measurements reveal superconducting transition with T_(c)^(onset)=6.37 K and Tczero=6.18 K.In magnetic susceptibility measurements,the superconducting transition is observed at 6.16 K.The lower and upper critical fields are determined to be 22.17 mT and 6.69 T,respectively.Heat capacity measurements confirm the bulk superconductivity,showing a normalized specific heat change of△Ce/(_(γ)T_(c))=2.16 and an electron-phonon coupling strength ofλ_(ep)=0.92.DFT calculations reveal the intricate band structure of La_(3)Al.The notable specific heat jump,coupled with the electron-phonon coupling strengthλ_(ep),indicates that La_(3)Al exhibits characteristics of an intermediately coupled type-Ⅱsuperconductor.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0670000)the National Key Research and Development Program of China(Grant No.2023YFB4404904)+1 种基金the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2020B0303030002)the Autonomous Deployment Project of State Key Laboratory of Materials for Integrated Circuits(Grant No.SKLJC-Z2024-B04).
文摘The regulation of superconductivity in thin films can provide important information on low-dimensional superconducting properties,and also has important reference values for the application in superconducting devices.Herein,we report the successful regulation of both the superconductivity and normal-state properties of Nb films in a wide range by the controllable introduction of interstitial oxygen atoms.The lattice parameter is enhanced for an extent as large as 4.4%,and the normal-state resistivityρ_(n)is tuned for more than 15 times.The slope of upper critical field near T_(c)shows a close correlation withρ_(n)in a wide range.Importantly,it is found that the suppression of T_(c)by disorder reveals a linear dependence withρ_(n)in the region with an unchanged crystalline quality,which can be understood based on the picture of three-dimensional ballistic motion.
