本文报道了Fe（Se_（1-x）Tex）_（0.82）（0<=x<=1.0）三元体系的超导电性演化和相图。在0.3 < x < 1.0范围内，我们发现了一个新的超导相，Tc，max = 14 K。这种超导相被抑制时，样品组合物接近端员FeTe 0.82，表现出不相称的反铁磁秩序。我们讨论的超导性和磁性之间的关系，这种材料系统的最新结果从中子散射测量。我们的研究结果和分析表明，在这类新的铁基化合物的超导性与磁波动，因此可能是非常规的性质。
英文摘要：
We report our study of the evolution of superconductivity and the phase diagram of the ternary Fe(Se1-xTex)0.82 (0<=x<=1.0) system. We discovered a new superconducting phase with Tc,max = 14 K in the 0.3 < x < 1.0 range. This superconducting phase is suppressed when the sample composition approaches the end member FeTe0.82, which exhibits an incommensurate antiferromagnetic order. We discuss the relationship between the superconductivity and magnetism of this material system in terms of recent results from neutron scattering measurements. Our results and analyses suggest that superconductivity in this new class of Fe-based compounds is associated with magnetic fluctuations, and therefore may be unconventional in nature.
Specific-heat study of superconducting and normal states in FeSe1-xTex (0.6<=x<=1) single crystals: Strong-coupling superconductivity, strong electron-correlation, and inhomogeneity
We report a combined experimental and theoretical study of the PdSe2-xTex system. With increasing Te fraction, structural evolutions, first from an orthorhombic phase (space group Pbca) to a monoclinic phase (space group C2/c) and then to a trigonal phase (space group P-3m1), are observed accompanied with clearly distinct electrical transport behavior. The monoclinic phase (C2/c) is a completely new polymorphic phase and is discovered within a narrow range of Te composition (0.3 \leq x \leq 0.8). This phase has a different packing sequence from all known transition metal dichalcogenides to dat…
A possibility of high, room-temperature superconductivity was predicted for metallic hydrogen in the 1960s. However, metallization and superconductivity of hydrogen are yet to be unambiguously demonstrated in the laboratory and may require pressures as high as 5 million atmospheres. Rare earth based "superhydrides" such as LaH10 can be considered a close approximation of metallic hydrogen even though they form at moderately lower pressures. In superhydrides the predominance of H-H metallic bonds and high superconducting transition temperatures bear the hallmarks of metallic hydrogen. Still, ex…
Interplay of Pomeranchuk instability (spontaneous symmetry breaking of the Fermi surface) and d-wave superconductivity is studied for the repulsive Hubbard model on the square lattice with the dynamical mean field theory combined with the fluctuation exchange approximation (FLEX+DMFT). We show that the four-fold symmetric Fermi surface becomes unstable against a spontaneous distortion into two-fold near the van Hove filling, where the symmetry of superconductivity coexisting with the Pomeranchuk distorted Fermi surface is modified from the d-wave pairing to (d+s)-wave. By systematically shifti…
Charge-density-wave (CDW) instability and pressure-induced superconductivity in bulk 1T-NbS2 are predicted theoretically by first-principles calculations. We reveal a CDW instability towards the formation of a stable commensurate CDW order, resulting in a sqart(13)*sqart(13) structural reconstruction featured with star-of-David clusters. The CDW phase exhibits one-dimensional metallic behavior with in-plane flat-band characteristics, and coexists with an orbital-density-wave order predominantly contributed by 4d_(z^2-r^2 ) orbital from the inner Nb atoms of the star-of-David cluster. By doubli…
Local Lattice Instability and Superconductivity in La$_{1.85}$Sr$_{0.15}$Cu$_{1-x}$M$_x$O$_4$ (M=Mn, Ni, and Co)
用极化扩展X射线吸收精细结构（EXAFS）研究了La $_{1.85}$ Sr $_{0.15}$ Cu $_{1-x}$ M $_x$ O $_4$（M=Mn，Ni，Co）单晶的局域晶格结构.低温下的局域晶格不稳定性可用面内Cu-O键分裂来描述。我们发现，Mn替代Cu引起的局部晶格不稳定性的扰动很小，而Ni和Co替代强烈抑制的不稳定性。Cu位取代对超导电性的抑制与晶格不稳定性的扰动有关，表明局域晶格不稳定性（极化子）在超导电性中起着重要作用。
The physical properties and structural evolution of the MX$_2$-type solid solution Au$_{1-x}$Pd$_x$Te$_2$ are reported. The end member AuTe$_2$ is a normal metal with a monoclinic distorted CdI$_2$-type structure with preformed Te-Te dimers. A monoclinic--trigonal structural phase transition at a finite temperature occurs upon Pd substitution and is suppressed to zero temperature near $x$ = 0.55, and a superconducting phase with a maximum $T_{\rm c}$ = 4.65 K emerges. A clear indication of strong coupling superconductivity is observed near the composition of the structural instability. The com…
Superconductivity was recently observed in CrAs as the helimagnetic order is suppressed by applying pressure, suggesting possible unconventional superconductivity. To reveal the nature of the superconducting order parameter of CrAs, here we report the angular dependence of the upper critical field under pressure. Upon rotating the field by 360 degrees in the $bc$-plane, six maxima are observed in the upper critical field, where the oscillations have both six-fold and two-fold symmetric components. Our analysis suggests the presence of an unconventional odd-parity spin triplet state.
Quantum Geometry and Pair Breaking in Intra- and Intervalley Superconductivity of Rhombohedral Graphene
Theoretical Division, Los Alamos National Lab（洛斯阿拉莫斯国家实验室理论部）；Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA（田纳西大学诺克斯维尔分校物理与天文系）；Min H. Kao Department of Electrical Engineering and Computer Science, University of Tennessee, Knoxville, Tennessee 37996, USA（田纳西大学诺克斯维尔分校明浩高电气与计算机科学系）；Theoretical Division, T-4, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA（洛斯阿拉莫斯国家实验室T-4理论部）；Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA（洛斯阿拉莫斯国家实验室集成纳米技术中心）
Motivated by the recent realization of the infinite-layer nickelate superconductivity (SC), we quantitatively investigate a two-orbital $d$-$s$ model by dynamic cluster quantum Monte Carlo calculations. Focusing on the impact of inter-orbital hybridization on the superconducting properties, our simulations indicate that the $d$-$s$ hybridization strength has a decisive role in the suppression of the $d$-wave pairing in the doping regime relevant to infinite-layer nickelates. Although we confirm on the single-orbital description at weak hybridization, at relatively large hybridization, there ex…
The relation between the polar structural instability and superconductivity in a Weyl semimetal candidate MoTe2 has been clarified by finely controlled physical and chemical pressure. The physical pressure as well as the chemical pressure, i.e., the Se substitution for Te, enhances the superconducting transition temperature Tc at around the critical pressure where the polar structure transition disappears. From the heat capacity and thermopower measurements, we ascribe the significant enhancement of Tc at the critical pressure to a subtle modification of the phonon dispersion or the semimetall…
We derive the effective Ginzburg-Landau theory for finite momentum (FFLO/PDW) superconductivity without spin population imbalance from a model with local attraction and repulsive pair-hopping. We find that the GL free energy must include up to sixth order derivatives of the order parameter, providing a unified description of the interdependency of zero and finite momentum superconductivity. For weak pair-hopping the phase diagram contains a line of Lifshitz points where vanishing superfluid stiffness induces a continuous change to a long wavelength Fulde-Ferrell (FF) state. For larger pair-hop…
We study the superconducting instability mediated by spin fluctuations in the Eliashberg theory for a minimal two-band model of iron-based superconductors. While antiferromagnetic spin fluctuations can drive superconductivity (SC) as is well established, we find that spin fluctuations necessarily contain a contribution to suppress SC even though SC can eventually occur at lower temperatures. This self-restraint effect stems from a general feature of the spin-fluctuation mechanism, namely the repulsive pairing interaction, which leads to phase frustration of the pairing gap and consequently the…
We study the pairing instability of a two-dimensional metallic system induced by Ising-nematic quantum fluctuations in the presence of an unavoidable relevant coupling of the nematic order parameter to the elastic modes (acoustic phonons) of the lattice. We find that this nematoelastic coupling $λ_\mathrm{latt}$ leads to a decrease of both the superconducting (SC) critical temperature $T_c$ and the gap function $Δ$, regardless of the gap symmetry. Interestingly, we show that $λ_\mathrm{latt}$ provides a knob that allows us to investigate the emergence of the SC phase at low temperatures, as an…
I describe the issues of the competing orders in normal state of a parent and Ni-doped iron pnictide superconductor, SrF e 2 As 2 , using LMTO band structure calculation plus multi orbital dynamical mean-field theory. Strong, electronic correlations along with minimal antiferromagnetic instability create a partially gapped Fermi surface, in qualitative agreement with earlier experiments. A good semiquantitative similarity in both normal and ordered state with the earlier experimental transport data is observed along with suppression of magnetic ordering and explained within a correlated, mul- …
