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In the high-pressure phases of Sr, the Sr-V phase is considered an incommensurate host–guest structure. However, just as a low-temperature phase Ba-VI exists in the pressure region of the Ba-IV phase of high-pressure Ba, Sr also has a Sr-VI phase on the low-temperature region of the Sr-V phase according to experiments. We investigated the pressure range from 40 to 2400 GPa using first-principles calculations and found a group of promising candidate structures for the Sr-VI phase. At higher pressures, the lowest-enthalpy structure became hexagonal close-packed (hcp) around 160 GPa and is consistent with experiments for the Sr-VII phase, and the hcp structure transformed to a double hcp (dhcp) structure around 1000 GPa, and then, the dhcp structure changed to a face-centered cubic structure around 2200 GPa. The superconducting state remained intact through these structural phase transitions, although with a decreasing Tc with increasing pressure. [ABSTRACT FROM AUTHOR]

The manipulation of low-energy matter properties such as superconductivity, ferromagnetism, and ferroelectricity via cavity quantum electrodynamics engineering has been suggested as a way to enhance these many-body collective phenomena. In this work, we investigate the effective interactions between low-energy matter excitations induced by the off-resonant coupling with cavity electromagnetic modes. We extend a previous work by going beyond the dipole approximation accounting for the full polarization and magnetization densities of matter. We further include the often neglected diamagnetic interaction and, for the cavity, we consider general linear absorbing media with possibly non-local and non-reciprocal response. We demonstrate that, even in this general scenario, the effective cavity-induced interactions between the matter degrees of freedom are of electrostatic and magnetostatic nature. This confirms the necessity of a multimode description for cavity engineering of matter systems where the low-energy assumption holds. Our findings provide a theoretical framework for studying the influence of general optical environments on extended low-energy matter excitations. [ABSTRACT FROM AUTHOR]

Noncentrosymmetric superconductors (NCSs) are emerging as potential materials for the investigation of nontraditional phenomena, including both the presence of a spin-singlet pairing configuration and the occurrence of a spin-triplet pairing configuration, as well as the manifestation of topological superconductivity. In this work, we constructed a high-throughput theoretical design and performed a computational screening of Th-based NCSs with ZrNiAl-like structures based on the first principles method. Through systematic stability evaluations, we expanded the range of Th-based ZrNiAl-like compounds with superior stability to 45 materials. In this group of substances, we have pinpointed 17 prospective entities exhibiting notable band separation in the vicinity of the Fermi level. Electron–phonon coupling calculations indicated that 14 of these compounds are superconducting. By performing an analysis of electronic properties, we proposed that ThAlRu and ThAlOs are two promising NCSs in this family. This work may aid in the exploration of the design and synthesis of Th-based ZrNiAl-like materials, leading to the discovery of more NCSs with unique superconducting properties. [ABSTRACT FROM AUTHOR]

Motivated by searching room-temperature superconductors that could be realized near ambient conditions, palladium hydrides were chosen as the research subject considering that they can stably exist under ambient conditions, and Li as an electron donor for its outstanding performance in chemically tuning stability. A novel cubic phase structure of Li2PdH6 with a remarkably high estimated Tc of ∼165 K at 90 GPa was found using particle swarm optimization algorithm calculations. The superconducting behavior persists down to 10 GPa with a high Tc of 106.382 K. Even though the parent binary Pd–H system is not a good superconductor, the introduction of extra electrons breaks up the H2 molecules, inducing the increase of atomic hydrogen compared with parent hydride, which is necessary for outstanding superconducting behavior. The existence of relatively soft phonons associated with the H atoms in phonon dispersion curves is responsible for its high-Tc. Our results indicated that the doping of Li to binary hydrides, especially to binary hydrides with low-Tc that exist under ambient pressure, can produce robust phonon-mediated superconductivity. This may be a strategy to design and optimize room-temperature superconductors that can be synthesized under modest pressure. The findings may pave the way for realizing new high-Tc superconductors in experiments under lower pressure than recently documented superconducting hydrides. [ABSTRACT FROM AUTHOR]

The phenomenon of Berezinskii–Kosterlitz–Thouless (BKT) phase fluctuations and the superconducting fluctuations is investigated in a 40 nm thick granular aluminum film using magneto-transport measurements. The transport measurements suggest the possibility of strong electron–phonon (el–ph) interactions in contrast to a Bardeen–Cooper–Schrieffer superconductor. It shows a BKT transition of 2.304 K and a superconducting mean-field transition at 2.32 K. The presence of the resistive tail even before the BKT transition reflects the abundance of thermally activated free vortices. By analyzing the excess conductivity, Gaussian–Ginzburg–Landau superconducting fluctuations are observed above the superconducting transition, which causes rounding of the transition region even before the superconducting transition. The temperature dependence of the fluctuation conductivity in zero magnetic field exhibits distinct signatures of the two-dimensional direct Aslamazov–Larkin theory, with a significant contribution from the Maki–Thompson (MT) model. Furthermore, the anomalous behavior of the fluctuation conductivity at higher temperatures and perpendicular magnetic fields (up to 700 mT) is explained in terms of the total-energy cutoff (=0.72) in the low-wavelength region of the superconducting fluctuations and a pair-breaking parameter (∼0.031). Further studies on the pair-breaking parameter indicate the presence of the el–ph scattering, which diminishes the MT contribution. Our study carries important bearings on how the BKT phase fluctuations and superconducting amplitude fluctuations control the conductivity of granular superconductor near and above the transition region as non-equilibrium properties of weakly disordered granular superconductors. This research is of significance, offering insights into the fundamental properties of granular superconductivity and aiding in the comprehension of nano-structured thin film devices. [ABSTRACT FROM AUTHOR]

The recent discovery of MoB2 with a superconducting transition temperature (Tc) of up to 32 K at 100 GPa provides new insights into the metallization and subsequently high-Tc superconductivity of diborides, highlighting the potential of transition metals in these compounds. We herein re-evaluated the structure, mechanical, and superconducting properties of IrB4 under pressure up to 300 GPa using first-principles. Our calculations reveal that a new P21/c phase exhibiting a hardness of 15.75 GPa surpasses the stability of the C2/m structure identified through the particle swarm optimization at ambient pressure. Upon compressing, the P21/c phase transforms into an MgB2-type structure with a space group of P63/mmc at 62.5 GPa and then into the orthorhombic Cmca phase above 109 GPa. Unlike semiconductor behavior of the atmospheric pressure phase, the two high-pressure structures are metallic and superconducting, with Tc values of 29.90 for P63/mmc at 62.5 GPa and 13.45 K for Cmca at 125 GPa. Analysis of the electronic structure and electron–phonon coupling (EPC) reveals that the high Tc, similar to MgB2-type MoB2, stems from the Van Hove Singularities (VHS) near the Fermi level donated by transition metal Ir. The effect further enhances the EPC based on the boron contribution. More interestingly, pressure has little impacts on the position of the VHS. These findings provide a new platform for designing advanced high-Tc superconductors. [ABSTRACT FROM AUTHOR]

The recent discovery of MoB2 with a superconducting transition temperature (Tc) of up to 32 K at 100 GPa provides new insights into the metallization and subsequently high-Tc superconductivity of diborides, highlighting the potential of transition metals in these compounds. We herein re-evaluated the structure, mechanical, and superconducting properties of IrB4 under pressure up to 300 GPa using first-principles. Our calculations reveal that a new P21/c phase exhibiting a hardness of 15.75 GPa surpasses the stability of the C2/m structure identified through the particle swarm optimization at ambient pressure. Upon compressing, the P21/c phase transforms into an MgB2-type structure with a space group of P63/mmc at 62.5 GPa and then into the orthorhombic Cmca phase above 109 GPa. Unlike semiconductor behavior of the atmospheric pressure phase, the two high-pressure structures are metallic and superconducting, with Tc values of 29.90 for P63/mmc at 62.5 GPa and 13.45 K for Cmca at 125 GPa. Analysis of the electronic structure and electron–phonon coupling (EPC) reveals that the high Tc, similar to MgB2-type MoB2, stems from the Van Hove Singularities (VHS) near the Fermi level donated by transition metal Ir. The effect further enhances the EPC based on the boron contribution. More interestingly, pressure has little impacts on the position of the VHS. These findings provide a new platform for designing advanced high-Tc superconductors. [ABSTRACT FROM AUTHOR]

Recent experiments on α-MoB2 with MgB2-type structure achieved superconductivity at ∼32 K under 90 GPa, the highest among transition-metal diborides, rekindling interest in their superconducting properties. Our study systematically investigates the band structures of AlB2-type transition metal diborides. We found that the superior superconductivity of MoB2, WB2, and TcB2 correlates with their von Hove singularities near the Fermi level (EF), potentially linked to electron–phonon coupling. These three diborides exhibit similar critical temperature (Tc) trends under pressure: rising initially, peaking around 60 GPa, and then declining. While unstable at ambient pressure, their thermodynamic and dynamical stability limits vary significantly, possibly explaining experimental discrepancies. To stabilize MoB2 at ambient pressure, we designed MoXB4 compounds (X = other transition metals) by substituting every other Mo layer in MoB2 with an X layer. This modification aims to stabilize the structure and enhance superconductivity by reducing d-electron concentration at EF. This principle extends to other potential superconducting diborides, such as WB2 and TcB2. Using Nb as an example, we found that Nb atoms in AlB2-type MoNbB4 may exhibit random occupancy, potentially explaining disparities between theoretical predictions and experimental results. Our study offers valuable insights into superconductivity in transition metal diborides, paving the way for future research and applications. [ABSTRACT FROM AUTHOR]

Electronic properties of twisted bilayer graphene-like materials can be modified substantially by manipulating twist angles, allowing for many exotic correlated phenomena. However, typical moiré flatbands holding these phenomena only appear with specific small twist angles. Here, we report a class of pressure-tuned superflat bands and localized electronic states over a wide range of twist angles, beyond the physics of twisted bilayer graphene near the Fermi energy. Under the slowly varying lattice distortion approximation, localized electronic states deterministically emerge in isolation at the edge of bulk spectra and are spatially centered around the AA stacked region, governed by macroscopic effective potential wells of moiré superlattices. Moreover, as macroscopic effects, pressure-tuned superflat bands and localized electronic states exhibit excellent stability against small perturbations. Our results suggest that applying pressure in generic twisted bilayer graphene-like materials may evoke widespread electronic correlations, providing opportunities for exploring electronic interactions and superconductivity. [ABSTRACT FROM AUTHOR]

We successfully synthesized tetragonal FeS with various Fe:S molar ratios using a hydrothermal method, and the EDS and XRF results confirmed that FeS exhibits superconductivity within the Fe and S element ratio range of 1.155–1.274, rather than a strict stoichiometric ratio. The reaction temperature can not only play a crucial role in determining the purity of the obtained FeS phase but also significantly alter its micromorphology. Significantly, by analyzing the relationship between the Fe:S actual molar ratio and Tc as well as the Fe:S actual molar ratio and unit cell volume, FeS exhibits dome-shaped superconductivity and shows a negative correlation with Tc and chemical pressure. Furthermore, considering the correlation between anion height (hanion) and Tc, Tc reaches the maximum value of 4.53 K for hanion ≈ 1.28 Å, a behavior distinct from that of observed in Fe-pnictide superconductors. In short, our experimental results provide a unique perspective to deepen our understanding of FeS superconductors. [ABSTRACT FROM AUTHOR]

The report on near-ambient superconductivity in nitrogen-doped lutetium hydride is still under controversy. Here, guided by x-ray diffraction data of nitrogen-doped lutetium hydride, we choose a possible cubic superconducting phase named rocksalt-type LuH (RS-LuH) and study the superconductivity of pristine RS-LuH, nitrogen-doped RS-LuH named Lu 4 NH 3 , and lanthanide elements substitution of RS-LuH at pressures 0, 1, and 10 GPa by performing density functional theory and isotropic Eliashberg equation. As pressure increases from 0 to 10 GPa, all phonon spectra notably harden, resulting in the suppression of electron–phonon coupling. Moreover, the decrease in superconducting critical temperature (T c) of Lu 4 NH 3 is due to the reduction of electron–phonon coupling and the density of states at the Fermi level compared with pristine RS-LuH. Finally, our investigation reveals a monotonic increase in T c with ascending atomic numbers via lanthanide element substitution. Notably, RS-LuH exhibits the highest T c (T c = 19.7 K) among all compounds we studied. Therefore, our theoretical exploration enriches the understanding of the superconductivity in nitrogen-doped lutetium hydride under varying pressures. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) Janus transition metal dichalcogenides MXY manifest novel physical properties owing to the breaking of out-of-plane mirror symmetry. Recently, the 2H phase of MoSH has been demonstrated to possess intrinsic superconductivity, whereas the 1T phase exhibits a charge density waves state. In this paper, we have systematically studied the stability and electron–phonon interaction characteristics of MoSLi. Our results have shown that both the 2H and 1T phases of MoSLi are stable, as indicated by the phonon spectrum and the ab initio molecular dynamics. However, the 1T phase exhibits an electron–phonon coupling constant that is twice as large as that of the 2H phase. In contrast to MoSH, the 1T phase of MoSLi exhibits intrinsic superconductivity. By employing the ab initio anisotropic Migdal-Eliashberg formalism, we have revealed the two-gap superconducting nature of 1T-MoSLi, with a transition temperature (Tc) of 14.8 K. The detailed analysis indicates that the superconductivity in 1T-MoSLi primarily originates from the interplay between the vibration of the phonon modes in the low-frequency region and the dz2 orbital. These findings provide a fresh perspective on superconductivity within Janus structures. [ABSTRACT FROM AUTHOR]

Thorium nitrides have been the topic of intense studies due to their prospective applications as advanced nuclear fuels. The phase diagram of the Th–N scheme, however, continues unknown at low temperatures and extremely high pressures. In this article, we examine the Th–N system's phase diagram up to 300 GPa from the first-principle approach using universal structure predictor: evolutionary Xtallography (USPEX) method. Apart from the experimentally observed phase (ThN, Th2N3, and Th3N4), there are several unique chemical stoichiometries, i.e., ThN3, ThN4, ThN6, ThN8, ThN10, and ThN12 are found to have stability fields on the Th–N phase diagram at pressure of 3.0, 32, 100, 42, 28, and 236 GPa along with previously predicted composition ThN2 at 3.5 GPa. The structural stability of the predicted compositions is further assessed by evaluating the elastic and dynamic stability. Out of all above mentioned compositions, ThN3 is possibly a metastable one at 0 GPa. Electronic structure calculations predict that all newly discovered compositions are metallic except ThN10, which is semi-metallic at high pressures. Further, we predict that ThN4 and ThN6 have high electron–phonon coupling constant of 1.874 and 0.894 with Tc around 21.22 and 25.02 K, respectively, at 100 GPa. [ABSTRACT FROM AUTHOR]

The effect of the YBCO superconducting (SC) state on the magnetic properties of as-grown YBCO/Co/IrMn heterostructures has been systematically studied using magnetometry and ferromagnetic resonance. The obtained data showed that the superconductivity of the YBCO substrate strongly affects the ferromagnetic properties of the deposited Co layer deeper (up to 50 nm) than the coherence length of the YBCO (≃ 4 nm) by an exchange interaction between the Co magnetic moments and the superconducting pairs at the YBCO/Co interface. The interfacial exchange interaction, switched on while the YBCO enters the SC state, pins Co spins and yields an enhancement of the Co magnetic properties. [ABSTRACT FROM AUTHOR]

The theory-led prediction of LaBeH8, which has a high superconducting critical temperature (Tc) above liquid nitrogen under a pressure level below 1 Mbar, has been experimentally confirmed. YBeH8, which has a structural configuration similar to that of LaBeH8, has also been predicted to be a high-temperature superconductor at high pressure. In this study, we focus on the structural phase transition and superconductivity of YBeH8 under pressure by using first-principles calculations. Except for the known face-centered cubic phase of Fm 3 ̄ m, we found a monoclinic phase with P 1 ̄ symmetry. Moreover, the P 1 ̄ phase transforms to the Fm 3 ̄ m phase at ∼200 GPa with zero-point energy corrections. Interestingly, the P 1 ̄ phase undergoes a complex electronic phase transition from semiconductor to metal and then to superconducting states with a low Tc of 40 K at 200 GPa. The Fm 3 ̄ m phase exhibits a high Tc of 201 K at 200 GPa, and its Tc does not change significantly with pressure. When we combine the method using two coupling constants, λopt and λac, with first-principles calculations, λopt is mainly supplied by the Be–H alloy backbone, which accounts for about 85% of total λ and makes the greatest contribution to the high Tc. These insights not only contribute to a deeper understanding of the superconducting behavior of this ternary hydride but may also guide the experimental synthesis of hydrogen-rich compounds. [ABSTRACT FROM AUTHOR]

The theory-led prediction of LaBeH8, which has a high superconducting critical temperature (Tc) above liquid nitrogen under a pressure level below 1 Mbar, has been experimentally confirmed. YBeH8, which has a structural configuration similar to that of LaBeH8, has also been predicted to be a high-temperature superconductor at high pressure. In this study, we focus on the structural phase transition and superconductivity of YBeH8 under pressure by using first-principles calculations. Except for the known face-centered cubic phase of Fm 3 ̄ m, we found a monoclinic phase with P 1 ̄ symmetry. Moreover, the P 1 ̄ phase transforms to the Fm 3 ̄ m phase at ∼200 GPa with zero-point energy corrections. Interestingly, the P 1 ̄ phase undergoes a complex electronic phase transition from semiconductor to metal and then to superconducting states with a low Tc of 40 K at 200 GPa. The Fm 3 ̄ m phase exhibits a high Tc of 201 K at 200 GPa, and its Tc does not change significantly with pressure. When we combine the method using two coupling constants, λopt and λac, with first-principles calculations, λopt is mainly supplied by the Be–H alloy backbone, which accounts for about 85% of total λ and makes the greatest contribution to the high Tc. These insights not only contribute to a deeper understanding of the superconducting behavior of this ternary hydride but may also guide the experimental synthesis of hydrogen-rich compounds. [ABSTRACT FROM AUTHOR]

The enigmatic mechanism underlying unconventional high-temperature superconductivity, especially the role of lattice dynamics, has remained a subject of debate. Theoretical insights have long been hindered due to the lack of an accurate first-principles description of the lattice dynamics of cuprates. Recently, using the r2SCAN meta-generalized gradient approximation (meta-GGA) functional, we have been able to achieve accurate phonon spectra of an insulating cuprate YBa2Cu3O6 and discover significant magnetoelastic coupling in experimentally interesting Cu–O bond stretching optical modes [Ning et al., Phys. Rev. B 107, 045126 (2023)]. We extend this work by comparing Perdew–Burke–Ernzerhof and r2SCAN performances with corrections from the on-site Hubbard U and the D4 van der Waals (vdW) methods, aiming at further understanding on both the materials science side and the density functional side. We demonstrate the importance of vdW and self-interaction corrections for accurate first-principles YBa2Cu3O6 lattice dynamics. Since r2SCAN by itself partially accounts for these effects, the good performance of r2SCAN is now more fully explained. In addition, the performances of the Tao–Mo series of meta-GGAs, which are constructed in a different way from the strongly constrained and appropriately normed (SCAN) meta-GGA and its revised version r2SCAN, are also compared and discussed. [ABSTRACT FROM AUTHOR]

The enigmatic mechanism underlying unconventional high-temperature superconductivity, especially the role of lattice dynamics, has remained a subject of debate. Theoretical insights have long been hindered due to the lack of an accurate first-principles description of the lattice dynamics of cuprates. Recently, using the r2SCAN meta-generalized gradient approximation (meta-GGA) functional, we have been able to achieve accurate phonon spectra of an insulating cuprate YBa2Cu3O6 and discover significant magnetoelastic coupling in experimentally interesting Cu–O bond stretching optical modes [Ning et al., Phys. Rev. B 107, 045126 (2023)]. We extend this work by comparing Perdew–Burke–Ernzerhof and r2SCAN performances with corrections from the on-site Hubbard U and the D4 van der Waals (vdW) methods, aiming at further understanding on both the materials science side and the density functional side. We demonstrate the importance of vdW and self-interaction corrections for accurate first-principles YBa2Cu3O6 lattice dynamics. Since r2SCAN by itself partially accounts for these effects, the good performance of r2SCAN is now more fully explained. In addition, the performances of the Tao–Mo series of meta-GGAs, which are constructed in a different way from the strongly constrained and appropriately normed (SCAN) meta-GGA and its revised version r2SCAN, are also compared and discussed. [ABSTRACT FROM AUTHOR]

Though YB6 and LaB6 share the same crystal structure, atomic valence electron configuration, and phonon modes, they exhibit drastically different phonon-mediated superconductivity. YB6 superconducts below 8.4 K, giving it the second-highest critical temperature of known borides, second only to MgB2. LaB6 does not superconduct until near-absolute zero temperatures (below 0.45 K), however. Though previous studies have quantified the canonical superconductivity descriptors of YB6's greater Fermi-level (Ef) density of states and higher electron-phonon coupling (EPC), the root of this difference has not been assessed with full detail of the electronic structure. Through chemical bonding, we determine low-lying, unoccupied 4f atomic orbitals in lanthanum to be the key difference between these superconductors. These orbitals, which are not accessible in YB6, hybridize with π B-B bonds and bring this π-system lower in energy than the σ B-B bonds otherwise at Ef. This inversion of bands is crucial: the optical phonon modes we show responsible for superconductivity cause the σ-orbitals of YB6 to change drastically in overlap, but couple weakly to the π-orbitals of LaB6. These phonons in YB6 even access a crossing of electronic states, indicating strong EPC. No such crossing in LaB6 is observed. Finally, a supercell (the M k-point) is shown to undergo Peierls-like effects in YB6, introducing additional EPC from both softened acoustic phonons and the same electron-coupled optical modes as in the unit cell. Overall, we find that LaB6 and YB6 have fundamentally different mechanisms of superconductivity, despite their otherwise near-identity.

Boron-based compounds have triggered substantial attention due to their multifunctional properties, incorporating excellent hardness and superconductivity. While tetragonal metal borides LiB4 and NaB4 with BaAl4-type structure and striking clathrate boron motif have been induced under compression, there is still a lack of deep understanding of their potential properties at ambient pressure. We herein conduct a comprehensive study on I4/mmm-structured LiB4 and NaB4 under ambient pressure via first-principles calculations. Remarkably, both LiB4 and NaB4 are found to possess high Vickers hardness of 39 GPa, which is ascribed to the robust boron framework with strong covalency. Furthermore, their high hardness values together with distinguished stability make them highly potential superhard materials. Meanwhile, electron–phonon coupling analysis reveals that both LiB4 and NaB4 are conventional phonon-mediated superconductors, with critical temperatures of 6 and 8 K at 1 atmosphere pressure (atm), respectively, mainly arising from the coupling of B 2p electronic states and the low-frequency phonon modes associated with Li-, Na-, and B-derived vibrations. This work provides valuable insights into the mechanical and superconducting behaviors of metal borides and will boost further studies of emergent borides with multiple functionalities. [ABSTRACT FROM AUTHOR]

Transition metal oxides provide opportunities to induce and modulate the superconducting state, due to the delicate interplay between charge, spin, orbital, and lattice order. In this work, 5d transition metal oxide SrTaO3 films were deposited by pulsed laser deposition, and an anomalous negative resistance was observed. The negative resistance can be ascribed to the nonuniform conductivity, associated with nonuniform electronic states in the SrTaO3 thin films, as confirmed by conductive atomic force microscopy and x-ray photoelectron spectroscopy. Moreover, a sharp drop in the resistance together with a decrease in magnetization was observed at around 40 K. This might imply a possible superconducting state. The negative resistance can be well explained based on an equivalent circuit comprising normal and superconductive states, also supporting the possible superconducting state in SrTaO3 thin films. This work promotes the exploring and revealing of the mechanism in tantalates superconductivity. [ABSTRACT FROM AUTHOR]

Boron-based compounds have triggered substantial attention due to their multifunctional properties, incorporating excellent hardness and superconductivity. While tetragonal metal borides LiB4 and NaB4 with BaAl4-type structure and striking clathrate boron motif have been induced under compression, there is still a lack of deep understanding of their potential properties at ambient pressure. We herein conduct a comprehensive study on I4/mmm-structured LiB4 and NaB4 under ambient pressure via first-principles calculations. Remarkably, both LiB4 and NaB4 are found to possess high Vickers hardness of 39 GPa, which is ascribed to the robust boron framework with strong covalency. Furthermore, their high hardness values together with distinguished stability make them highly potential superhard materials. Meanwhile, electron–phonon coupling analysis reveals that both LiB4 and NaB4 are conventional phonon-mediated superconductors, with critical temperatures of 6 and 8 K at 1 atmosphere pressure (atm), respectively, mainly arising from the coupling of B 2p electronic states and the low-frequency phonon modes associated with Li-, Na-, and B-derived vibrations. This work provides valuable insights into the mechanical and superconducting behaviors of metal borides and will boost further studies of emergent borides with multiple functionalities. [ABSTRACT FROM AUTHOR]

A real-space method using generating integers is used to determine possible commensurate lattice Moiré patterns for a bilayer of two equal hexagonal lattices, which can in principle be extended to lattice mismatched bilayers. These Moiré patterns can be classified by a pair of relatively prime integers (n , m) , wherein a rotation θ (n , m) of the top hexagonal lattice maps its lattice vector (n , m) to (m , n) of the bottom lattice. Within this formulation, the area of the commensurate supercell is proportional to (n 2 + m 2 + n m) and the number of coincident lattice sites per supercell is given by (n − m) 2. Taking bilayer boron nitride (BN) as an example, we present how to systematically generate Moiré patterns and explore the differences in local chemistry in the interstitial region by impurity intercalation. Systematic calculations of the properties of intercalated 3d transition metals were performed in an h-BN (4 , 3) bilayer, corresponding to a rotation of 9.43 degrees. These calculations reveal that local symmetry in the intercalated region significantly affect the energetics and magnetization of the intercalated species. These results highlight that Moiré pattern physics is not limited to optoelectronic/electronic phenomena, such as interfacial exciton formation or magic angle superconductivity, but it also produces chemical and magnetic atomic site selectivity, which may play important roles in adsorption, catalysis, or quantum information. [ABSTRACT FROM AUTHOR]

Elucidating the phase diagram of solid hydrogen is a key objective in condensed matter physics. Several decades ago, it was proposed that at low temperatures and high pressures, solid hydrogen would be a metal with a high superconducting transition temperature. This transition to a metallic state can happen through the closing of the energy gap in the molecular solid or through a transition to an atomic solid. Recent experiments have managed to reach pressures in the range of 400-500 GPa, providing valuable insights. There is strong evidence suggesting that metallization via either of these mechanisms occurs within this pressure range. Computational and experimental studies have identified multiple promising crystal phases, but the limited accuracy of calculations and the limited capabilities of experiments prevent us from determining unequivocally the observed phase or phases. Therefore, it is crucial to investigate the superconducting properties of all the candidate phases. Recently, we reported the superconducting properties of theC2/c-24,Cmca-12,Cmca-4 andI41/amd-2 phases, including anharmonic effects. Here, we report the effects of anisotropy on superconducting properties using Eliashberg theory. Then, we investigate the superconducting properties of deuterium and estimate the size of the isotope effect for each phase. We find that the isotope effect on superconductivity is diminished by anharmonicity in theC2/c-24 andCmca-12 phases and enlarged in theCmca-4 andI41/amd-2 phases. Our anharmonic calculations of theC2/c-24 phase of deuterium agree closely with the most recent experiment by Loubeyreet al(2022Phys. Rev. Lett.29035501), indicating that theC2/c-24 phase remains the leading candidate in this pressure range, and has a strong anharmonic character. These characteristics can serve to distinguish among crystal phases in experiment. Furthermore, expanding our understanding of superconductivity in pure hydrogen holds significance in the study of high-Tchydrides.

Iron chalcogenide superconductors of iron‐based superconductor (IBS) family, have attracted much attention recently. For the study of unconventional superconductors, uniaxial strain effect plays an important role with the actuator method as the main approach with quite limited strain. This is unfavorable for uncovering the full behavior and the understanding of strain effect. Here, FeSe0.5Te0.5 thin films are grown on mica to induce strains via different bending states with strain reaching 2%, roughly an order of magnitude larger than that of the actuator method. Both the lattice parameters and transport properties show changes with strain. The variation of superconducting transition temperature (Tc) with compressive strain shows a nonmonotonic change with a maximum. Theoretical calculations suggest that superconductivity is influenced by the spin fluctuation in different bending states. The nonmonotonic change of Tc with compressive strain can be understood by considering the strain‐dependent competition between the spin fluctuation and nematic order. This work provides valuable insights for understanding the superconducting mechanism of IBS and also paves the way for exploring unconventional superconductivity via bending strains. [ABSTRACT FROM AUTHOR]

I summarize recent progress on obtaining rigorous upper bounds on superconducting transition temperature T c in two dimensions independent of pairing mechanism or interaction strength. These results are derived by finding a general upper bound for the superfluid stiffness for a multi-band system with arbitrary interactions, with the only assumption that the external vector potential couples to the kinetic energy and not to the interactions. This bound is then combined with the universal relation between the superfluid stiffness and the Berezinskii–Kosterlitz–Thouless T c in 2D. For parabolic dispersion, one obtains the simple result that k B T c ≤ E F ∕ 8 , which has been tested in recent experiments. More generally, the bounds are expressed in terms of the optical spectral weight and lead to stringent constraints for the T c of low-density, strongly correlated superconductors. Results for T c bounds for models of flat-band superconductors, where the kinetic energy vanishes and the vector potential must couple to interactions, are briefly summarized. Upper bounds on T c in 3D remains an open problem, and I describe how questions of universality underlie the challenges in 3D. [ABSTRACT FROM AUTHOR]

Niobium nitrides have garnered significant research interest since their discovery due to their exceptional properties and broad applications. In this study, NbNx thin films are successfully grown on 4H(6H)‐SiC(001) substrates using nitrogen‐assisted molecular beam epitaxy. Through scanning transmission electron microscopy and X‐ray diffraction, it is confirmed that the crystal structure of the thin films corresponds to the β‐Nb2N. Different from the previously reported structure of the βA phase (P63/mmc) of β‐Nb2N, the results clearly match with the βB phase (P3¯m1${\mathrm{P}}\bar{3}{\mathrm{m}}1$). Resistivity measurements reveal that β‐Nb2N exhibits superconductivity at ≈10 K with an upper critical field of ≈5 T. Its 3D electronic structure is further elucidated using angle‐resolved photoemission spectroscopy combined with theoretical calculations. The observed superconductivity in β‐Nb2N is attributed to its relatively high electron–phonon coupling strength and density of states at Fermi level. Interestingly, it is found that the sample is close to a Lifshitz transition, suggesting potential for tunable physical properties. The results provide a comprehensive understanding of the crystal and electronic structures of β‐Nb2N, facilitating its future applications. [ABSTRACT FROM AUTHOR]

To explore the possibility of improving the critical current density (J c) of polycrystalline La 1.84 Sr 0.16 CuO 4 (LSCO) superconductor ceramics, high density La 1.84 Sr 0.16 CuO 4 samples have been prepared by means of spark plasma sintering (SPS). Structural and superconducting properties of samples made by different variations of the process have been measured for systematic comparison. The density of the SPS samples can reach up to 98 % of the theoretical density of LSCO, but the critical temperature (T c) and critical current density (J c) are suppressed by the process. Subsequent annealing has been applied to improve the properties of the SPS samples. After treatment at 1050 °C, in spite of partial decomposition that was observed on the surface of the samples, the J c of LSCO was significantly improved. Detailed data as well as assumptions for explaining these results are provided. The SPS technique, coupled with a suitable post-annealing treatment is thereby appearing as a possible methodology to improve the critical current density of polycrystalline high temperature cuprate superconductors. [ABSTRACT FROM AUTHOR]

During the synthetic exploration targeting the polycrystalline compound LK‐99, an unexpected phase, Pb5(PO4)3OHδ, was identified as a byproduct. We elucidated the composition of this compound through single‐crystal X‐ray diffraction analysis. Subsequent synthesis of the target compounds was achieved via high‐temperature solid‐state pellet reactions. The newly identified Pb5(PO4)3OHδ has an orthorhombic crystal structure with space group Pnma, representing a unique structure differing from the hexagonal apatite phases of Pb10(PO4)6O and Pb5(PO4)3OH. Comprehensive temperature‐ and magnetic‐field‐dependent magnetization studies unveiled a temperature‐independent magnetic characteristic of Pb5(PO4)3OHδ. Solid‐state nuclear magnetic resonance spectroscopy was employed to decipher the origins of the phase stability and confirm the presence of hydrogen atoms in Pb5(PO4)3OHδ. These investigations revealed the presence of protonated oxygen sites, in addition to the interstitial water molecules within the structure, which may play critical roles in stabilizing the orthorhombic phase. [ABSTRACT FROM AUTHOR]

The rapid development of quantum magnonics can be attributed to its potential applications in quantum computing, information processing and the creation of hybrid quantum systems. Quantum quasiparticles, known as magnons, undergo Bose condensation at high densities, a phenomenon observed during radiofrequency excitation. This phenomenon was initially discovered in the antiferromagnetic superfluid 3 He. Magnonic superfluidity effects, Josephson effect and magnon tunnelling were also observed in this system. Similar effects have been identified in yttrium iron garnet at room temperature, suggesting the possibility of utilising these effects in a manner akin to superconductivity. In this article, we conduct simulations of magnon tunnelling processes across the energy gap, aiming to compare these simulations with experimental findings. [ABSTRACT FROM AUTHOR]

Nb x Re 1 − x is a non-centrosymmetric superconductor recently realized in thin film form. The access to the basic physics that governs this material is hindered by the polycrystalline structure of the films which consist of grains of small dimensions. In these conditions, films are not decisive in revealing the nature of the superconducting order parameter, and, in particular, the possible presence of a spin-triplet component. In this work, post-deposition annealing procedures were performed to improve the crystalline quality of the as-grown films. As determined by x-ray diffraction measurements, by tuning the annealing process, it was possible to increase the crystalline size from 1–2 nm up to several nanometers, beyond the values of the superconducting coherence length. Pair distribution function analyses revealed the non-centrosymmetric crystal structure of the treated NbRe films. Finally, electrical transport measurements, performed to study the relationship between structural and transport properties of the samples, showed an improved metallicity and a reduction of the superconducting critical temperature after the thermal treatment. This last result can be reasonably ascribed, for instance, to oxygen contamination, modification of the electronic density of states at the Fermi level, or change in the electron–phonon coupling. The results of this work are useful to realize films for future experiments meant to access nature of the superconducting order parameter. [ABSTRACT FROM AUTHOR]

The recently discovered kagome superconductors A V3Sb5 (A = K, Rb, Cs) provide a new platform to explore intertwined symmetry-breaking orders. However, great controversies exist to date, including the origin of charge density wave (CDW), the unconventional or conventional nature of superconductivity, and the presence or absence of time-reversal symmetry breaking. A thorough understanding of the fundamental electronic structure is crucial for addressing these disputes. In this review, we provide an extensive summary of the key structural and electronic properties of A V3Sb5 compounds and evaluate the current research on their unconventional electronic order, especially the superconductivity and CDW, with a particular focus on insights from angle-resolved photoemission spectroscopy studies. We expect this review to be timely due to the convergence of various experimentally observed phenomena related to the CDW and superconducting order parameters in A V3Sb5 compounds. Our goal is to guide future investigations aimed at uncovering the microscopic origins of these unconventional electronic properties in kagome superconductors. [ABSTRACT FROM AUTHOR]

Platinum‐group transition‐metal dichalcogenides have emerged as a subject of considerable interest in condensed matter physics because of their remarkable topological properties and unconventional superconducting behavior. In this study, the synthesis and superconducting characteristics of a layered chalcogenide RhSeTe crystallized in the 1T$T$‐structure, known for hosting materials with nontrivial topology characteristics are reported. RhSeTe exhibits type‐II superconductivity, with a superconducting transition temperature of 4.72 K and a high upper critical field 4.06(7) T. [ABSTRACT FROM AUTHOR]

We report a new family of chiral intermetallic superconductors TaAl x Ge2− x . The mother compound TaGe2 has a C40-type chiral hexagonal crystal structure with a pair of enantiomorphic space groups of P 6222 and P 6422. By substituting Ge with Al, TaAl x Ge2− x polycrystals with the C40 structure were synthesized with Al substitution x from 0 to 0.8. Magnetic susceptibility, magnetization curves and electrical resistivity revealed that TaAl x Ge2− x with x of 0.2–0.4 was a type-II superconductor with a superconducting transition temperature T c of 2.0–2.2 K. The superconductivity disappeared or was largely suppressed at x less than 0.2 and more than 0.4, although all the measurements were performed at temperatures above 1.8 K. An emergence of superconductivity is discussed in terms of the lattice constants changes with the Al substitution. [ABSTRACT FROM AUTHOR]

A novel material is obtained by modifying pristine YBCO superconductor via simultaneous partial substitution of Sr for Ba and Se for O. The intended stoichiometry was YBa2−xSrxCu3O7−xSex with x=0.5, 0.75 and 1; and x≈1 yielded the most interesting results considered in detail. We confirmed that Se atoms indeed enter the superconductor lattice cell. The obtained polycrystalline material contains five phases, with the major phase (>44wt.%) being YBa1.4Sr0.6Cu3O6Se0.5. The synthesized superconductor demonstrates unique properties, including (i) two superconducting transitions with Tc1≈36K and Tc2≈13K yielding the Wohlleben effect; (ii) strong-coupling d-wave superconductivity (with 2Δ∕(kBTc)≈ 5); (iii) Schottky anomaly in the heat capacity; and, most importantly, (iv) a very unusual anomaly in the heat capacity which can be associated with the quantum criticality typically observable at much higher fields. The fact that the quantum criticality is visible in weaker fields (∼7T) may open opportunities for exploration of the interplay between superconductivity and pair density waves by wide research community particularly when its pure phase is available. To facilitate this, the stability of single-phase YBa1.4Sr0.6Cu3O6Se0.5 is analyzed using machine learning methods. [ABSTRACT FROM AUTHOR]

Understanding surface collective dynamics in quantum materials is crucial for advancing quantum technologies. For example, surface phonon modes in quantum paraelectrics are thought to be essential in facilitating interfacial superconductivity. However, detecting these modes, especially below 1 terahertz, is challenging because of limited sampling volumes and the need for high spectroscopic resolution. Here, we report surface soft transverse optical (TO1) phonon dynamics in KTaO3 and SrTiO3 by surface-sensitive spintronic terahertz spectroscopy that can sense the collective modes only a few nanometers deep from the surface. In KTaO3, the TO1 mode softens and sharpens with decreasing temperature, leveling off at 0.7 terahertz. In contrast, this mode in SrTiO3 broadens substantially below the quantum paraelectric crossover and coincides with the hardening of a sub-milli-electron volt phonon mode related to the antiferrodistortive transition. These observations that deviate from their bulk properties may have implications for interfacial superconductivity and ferroelectricity. The developed technique opens opportunities for sensing low-energy surface collective excitations. [ABSTRACT FROM AUTHOR]

We introduce the notion of nonreciprocal superconductors where inversion and time-reversal symmetries are broken, giving rise to an asymmetric energy dispersion. We demonstrate that nonreciprocal superconductivity can be detected by Andreev reflection. In particular, a transparent junction between a normal metal and a nonreciprocal superconductor generally exhibits an asymmetric current-voltage characteristic, which serves as a defining feature of nonreciprocal superconductivity. Unlike the superconducting diode effects, our detection scheme has the advantage of avoiding large critical currents that turn the superconducting state to normal. Last, we discuss candidates for nonreciprocal superconductivity, including graphene, UTe2, as well as engineered platforms. [ABSTRACT FROM AUTHOR]

We uncover a superconducting state with partial spin polarization induced by a magnetic field. This state, which we call "magnonic superconductor," lacks a conventional pairing order parameter but is characterized instead by a composite order parameter that represents the binding of electron pairs and magnons. We rigorously demonstrate the existence of magnonic superconductivity with high transition temperature in one-dimensional and two-dimensional Hubbard models with repulsive interaction. We further show that magnonic Cooper pairs can attract to form higher-charge bound states, which can give rise to charge-6e superconductivity. [ABSTRACT FROM AUTHOR]

Quantum Griffiths phase (QGP), marked by a quantum Griffiths singularity with a divergent effective critical exponent, has garnered considerable attention in the realm of superconductivity. However, the ability to control QGP remains elusive. Here, we demonstrate that QGP at the LaAlO3/KTaO3(110) interface can be efficiently modulated by the orientation of applied magnetic field: With a perpendicular field, an anomalous QGP emerges in the low-temperature regime, characterized by a decreasing critical field as temperature lowers; conversely, with a parallel field, a normal QGP arises, where the critical field increases with decreasing temperature. Such opposite characteristics stem from the controllable quantum fluctuations and conductivity corrections under distinct magnetic field orientations. Furthermore, we show the effective tuning of the phase boundary by electrostatic gating, attributed to the gate-controlled quantum fluctuations. These findings not only demonstrate how to experimentally manipulate QGP but also provide a comprehensive understanding of how quantum fluctuations can effectively modulate QGP. [ABSTRACT FROM AUTHOR]

High-entropy materials (HEMs) exhibit significant potential for diverse applications owing to their tunable properties, which can be precisely engineered through the selection of specific elements and the modification of stoichiometric ratios. The discovery of superconductivity in HEMs has garnered considerable interest, leading to accelerated advancements in this field in recent years. This review provides an overview of various high-entropy superconductors, highlighting their distinct features, such as disordered crystal structure, factors affecting the critical temperature (Tc), unconventional superconductivity, and topological bands. A perspective on this field is subsequently proposed, drawing upon insights from recently published academic literature. The objective is to provide researchers with a comprehensive and clear understanding of the newly developed high-entropy superconductivity, thereby catalyzing further advancements in this domain. The discovery of superconductivity in high-entropy materials has garnered considerable interest, leading to accelerated advancements in this field in recent years. Some interesting phenomena have been found in high-entropy superconductors, such as the robustness of superconductivity to pressure, large upper critical field, strong coupling behavior, and topological band structure. Accordingly, the present review article is dedicated to summarizing the recently reported works on the structural type and physical properties of high-entropy superconductors, as well as their potential applications. Finally, we provide our perspective on the future challenges of high-entropy superconductors. [ABSTRACT FROM AUTHOR]

Recent observations of superconductivity in infinite-layer nickelates offer insights into high-temperature superconductivity mechanisms. However, defects and dislocations in doped films complicate the realization of superconductivity, limiting current research to superconducting nickelate heterostructures. The lack of research on superconductivity in superlattices composed of ultrathin nickelates severely impedes not only the exploration of the interface effect on superconductivity, but also the utilization of heterostructure engineering for exploring higher superconducting temperature Tc. Here, we demonstrated superconducting infinite-layer nickelate superlattices [(Nd0.8Sr0.2NiO2)8/(SrTiO3)2]10 via topotactic reduction. Our study uncovered that only above a critical thickness can high-quality superlattices be achieved, with structural formation dependent on nickelate layer thickness. The superconducting superlattice showed a Tc of 12.5 K and a 2D superconducting feature, indirectly indicate the intrinsic superconductivity of infinite-layer nickelates. Our study offers promising avenues for delving into the superconducting mechanism and for exploring multilevel interface engineering of infinite-layer nickelates, thus opening new horizons for the study of infinite-layer nickelates. So far infinite-layer nickelates have only been observed to superconduct in single-thin-film form. Here, the authors demonstrate superconductivity in [(Nd0.8Sr0.2NiO2)8/(SrTiO3)2]10 superlattices. [ABSTRACT FROM AUTHOR]

Charge order has been a central focus in the study of cuprate high-temperature superconductors due to its intriguing yet not fully understood connection to superconductivity. Recent advances in resonant inelastic x-ray scattering (RIXS) in the soft x-ray regime have enabled the first momentum-resolved studies of dynamic charge order correlations in the cuprates. This progress has opened a window for a more nuanced investigation into the mechanisms behind the formation of charge order (CO) correlations. This review provides an overview of RIXS-based measurements of dynamic CO correlations in various cuprate materials. It specifically focuses on electron-doped cuprates and Bi-based hole-doped cuprates, where the CO-related RIXS signals may reveal signatures of the effective Coulomb interactions. This aims to explore a connection between two central phenomena in the cuprates: strong Coulomb correlations and CO-forming tendencies. Finally, we discuss current open questions and potential directions for future RIXS studies as the technique continues to improve and mature, along with other probes of dynamic correlations that would provide a more comprehensive picture. [ABSTRACT FROM AUTHOR]

Hydrogen, the first element in the periodic table, is predicted to become metallic at extremely high‐pressure conditions. Solid metallic hydrogen is believed to possess extraordinary physical properties, such as room‐temperature superconductivity and superfluidity, earning it the title of the "holy grail" in high‐pressure research. The pursuit of solid metallic hydrogen has spanned nine decades. Despite numerous fascinating discoveries related to dense hydrogen, metallic hydrogen has yet to be experimentally realized. This article aims to provide an overview of the major progress made in this field and offers an outlook on future developments. [ABSTRACT FROM AUTHOR]

Ferroelectricity, band topology, and superconductivity are respectively local, global, and macroscopic properties of quantum materials, and understanding their mutual couplings offers unique opportunities for exploring rich physics and enhanced functionalities. In this mini‐review, the attempt is to highlight some of the latest advances in this vibrant area, focusing in particular on ferroelectricity‐tuned superconductivity and band topology in 2D materials and related heterostructures. First, results from predictive studies of the delicate couplings between ferroelectricity and topology or superconductivity based on first‐principles calculations and phenomenological modeling are presented, with ferroelectricity‐enabled topological superconductivity as an appealing objective. Next, the latest advances on experimental studies of ferroelectricity‐tuned superconductivity based on different 2D materials or van der Waals heterostructures are covered. Finally, as perspectives, schemes are outlined that may allow to materialize new types of 2D systems that simultaneously harbor ferroelectricity and superconductivity, or that may lead to enhanced ferroelectric superconductivity, ferroelectric topological superconductivity, and new types of superconducting devices such as superconducting diodes. [ABSTRACT FROM AUTHOR]

The hybrid ferromagnet-superconductor heterostructures have attracted extensive attention as they potentially host topological superconductivity. Relevant experimental signatures have recently been reported in CrBr3/NbSe2 ferromagnet-superconductor heterostructure, but controversies remain. Here, we reinvestigate CrBr3/NbSe2 by an ultralow temperature scanning tunneling microscope with higher spatial and energy resolutions. We find that the single-layer CrBr3 film is insulating and acts likely as a vacuum barrier, the measured superconducting gap and vortex state on it are nearly the same as those of NbSe2 substrate. Meanwhile, in-gap features are observed at the edges of CrBr3 island, which display either a zero-energy conductance peak or a pair of particle-hole symmetric bound states. They are discretely distributed at the edges of CrBr3 film, and their appearance is found closely related to the atomic lattice reconstruction near the edges. By increasing tunneling transmissivity, the zero-energy conductance peak quickly splits, while the pair of nonzero in-gap bound states first approach each other, merge, and then split again. These behaviors are unexpected for Majorana edge modes, but in consistent with the conventional Yu-Shiba-Rusinov states. Our results provide critical information for further understanding the interfacial coupling in CrBr3/NbSe2 heterostructure. There has been substantial interest in realizing topological superconductivity, with various systems being considered as potential hosts. Heterostructures such as CrBr3/NbSe2 are one example. Here, Li and coauthors show, via scanning tunnelling microscope measurements, that signatures hitherto associated with topological superconductivity in CrBr3/NbSe2 are consistent with a topologically trivial superconductor. [ABSTRACT FROM AUTHOR]

The current pressing challenge in the field of superconducting hydride research is to lower the stable pressure of such materials for practical applications. Molecular hydrides are usually stable under moderate pressure, but the underlying metallization mechanism remains elusive. Here, the important role of chemical interactions in governing the structures and properties of molecular hydrides is demonstrated. A new mechanism is proposed for obtaining high‐temperature and even room‐temperature superconductivity in molecular hydrides and report that the ternary hydride NaKH12 hosts Tc values up to 245 K at moderate pressure of 60 GPa. Both the excellent stability and superconductivity of NaKH12 originate from the fact that the localized electrons in the interstitial region of the metal lattice occupying the crystal orbitals well matched with the hydrogen lattice and forming chemical templates to assist the assembly of H2 units. These localized electrons weaken the H─H covalent bonds and improve the charge connectivity between the H2 units, ensuring the strong coupling between electrons and hydrogen‐dominated optical phonons. The theory provides a key perspective for understanding the superconductivity of molecular hydrides with various structural motifs, opening the door to obtaining high‐temperature superconductors from molecular hydrides at moderate pressures. [ABSTRACT FROM AUTHOR]

The impact of the interface phenomena on the properties of nanostructured materials is the focus of modern physics. We studied the magnetic properties of the nanostructured In–Ag alloy confined within a porous glass. The alloy composition was close to the eutectic point in the indium-rich range of the phase diagram. Temperature dependences of DC magnetization evidenced two superconducting transitions at 4.05 and 3.38 K. The magnetization isotherms demonstrated the superposition of two hysteresis loops with low and high critical fields below the second transition, a single hysteresis between the transitions and ferromagnetism with weak remanence in the normal state of the alloy. The shape of the loop seen below the second transition, which closes at a low magnetic field, corresponded to the intermediate state of the type-I superconductor. It was ascribed to strongly linked indium segregates. The loop observed below the first transition is referred to as type-II superconductivity. The secondary and tertiary magnetization branches measured at decreasing and increasing fields were shifted relative to each other, revealing the proximity of superconducting and ferromagnetic phases at the nanometer scale. This phenomenon was observed for the first time in the alloy, whose components were not magnetic in bulk. The sign of the shift shows the dominant role of the stray fields of ferromagnetic regions. Ferromagnetism was suggested to emerge at the interface between the In and AgIn2 segregates. [ABSTRACT FROM AUTHOR]

Understanding the physical and chemical processes at the interfaces of metals and topological insulators is crucial for the development of the next generation of topological quantum devices. Here, we report the discovery of robust superconductivity in Pd/Bi2Se3 bilayers fabricated by sputtering Pd on the surface of Bi2Se3. Through transmission electron microscopy measurements, we identify that the observed interfacial superconductivity originates from the diffusion of Pd into Bi2Se3. In the diffusion region, Pd chemically reacts with Bi2Se3 and forms a layer of PdBiSe, a known superconductor with a bulk transition temperature of 1.5 K. Our work provides a method for the introduction of superconductivity into Bi2Se3, laying the foundation for the development of sophisticated Bi2Se3-based topological devices. [ABSTRACT FROM AUTHOR]

Finding high‐temperature superconductivity in light‐weight element containing compounds at atmosphere pressure is currently a research hotspot but has not been reached yet. Here it is proposed that hard or superhard materials can be promising candidates to possess the desirable high‐temperature superconductivity. By studying the electronic structures and superconducting properties of H and Li doped c‐BN within the framework of the first‐principles, it is demonstrated that the doped c‐BN are indeed good superconductors at ambient pressure after undergoing the phase transition from the insulating to metallic behavior, though holding different nature of metallization. Li doped c‐BN is predicted to exhibit the superconducting transition temperature of ≈58 K, while H doped c‐BN has stronger electron–phonon interaction and possesses a higher transition temperature of 122 K. These results and findings thus point out a new direction for exploring the ambient‐pressure higher‐temperature superconductivity in hard or superhard materials. [ABSTRACT FROM AUTHOR]