Non-Fermi-Liquid Behavior of Superconducting SnH$_4$
Ivan A. Troyan, Dmitrii V. Semenok, Anna G. Ivanova, Andrey V. Sadakov, Di Zhou, Alexander G. Kvashnin, Ivan A. Kruglov, Oleg A. Sobolevskiy, Marianna V. Lyubut… 展开作者
Ivan A. Troyan, Dmitrii V. Semenok, Anna G. Ivanova, Andrey V. Sadakov, Di Zhou, Alexander G. Kvashnin, Ivan A. Kruglov, Oleg A. Sobolevskiy, Marianna V. Lyubutina, Dmitry S. Perekalin, Toni Helm, Stanley W. Tozer, Maxim Bykov, Alexander F. Goncharov, Vladimir M. Pudalov, Igor S. Lyubutin
备注：
Additional acknowledgments are made, one more co-author has been added, equations of the Talantsev-Tallon model have been added and clarified. They were used to obtain the superconducting gap from the V-I characteristics. We also added cif files of tin hydrides to SI
We studied chemical interaction of Sn with H$_2$ by X-ray diffraction methods at pressures of 180-210 GPa. A previously unknown tetrahydride SnH$_4$ with a cubic structure (${fcc}$) exhibiting superconducting properties below ${T}$$_C$ = 72 K was obtained; the formation of a high molecular ${C2/m}$-SnH$_{14}$ superhydride and several lower hydrides, ${fcc}$ SnH$_2$ and ${C2}$-Sn$_{12}$H$_{18}$, was also detected. The temperature dependence of critical current density ${J}$$_C$(T) in SnH$_4$ yields the superconducting gap 2$Δ$(0) = 23 meV at 180 GPa. SnH$_4$ has unusual behavior in strong magnetic fields: ${B,T}$-linear dependences of magnetoresistance and the upper critical magnetic field ${B}$$_{C2}$(T) $\propto$ (${T}$$_C$ - ${T}$). The latter contradicts the Wertheimer-Helfand-Hohenberg model developed for conventional superconductors. Along with this, the temperature dependence of electrical resistance of ${fcc}$ SnH$_4$ in non-superconducting state exhibits a deviation from what is expected for phonon-mediated scattering described by the Bloch-Grüneisen model, and is beyond the framework of the Fermi liquid theory. Such anomalies occur for many superhydrides, making them much closer to cuprates than previously believed.
Satterthwaite and Toepke (1970 Phys. Rev. Lett. 25 741) predicted high-temperature superconductivity in hydrogen-rich metallic alloys, based on an idea that these compounds should exhibit high Debye frequency of the proton lattice, which boosts the superconducting transition temperature, Tc. The idea has got full confirmation more than four decades later when Drozdov et al (2015 Nature 525 73) experimentally discovered near-room-temperature superconductivity in highly-compressed sulphur superhydride, H3S. To date, more than a dozen of high-temperature hydrogen-rich superconducting phases in Ba…
With the motivation of discovering high-temperature superconductors, evolutionary algorithm is employed to search for all stable compounds in the Sn-H system. In addition to the traditional SnH$_4$, new hydrides SnH$_8$, SnH$_{12}$ and SnH$_{14}$ are found to be thermodynamically stable at high pressure. Dynamical stability and superconductivity of tin-hydrides are systematically investigated. I$\bar{4}$m2-SnH$_8$, C2/m-SnH$_{12}$ and C2/m-SnH$_{14}$ exhibit higher superconducting transition temperatures of 81, 93 and 97 K compared to the traditional compound SnH$_4$ with T$_c$ of 52 K at 200 …
Topological superconductors are an intriguing and elusive quantum phase, characterized by topologically protected gapless surface/edge states residing in a bulk superconducting gap, which hosts Majorana fermions. Unfortunately, all currently known topological superconductors have a very low transition temperature, limiting experimental measurements of Majorana fermions. Here we discover the existence of a topological Dirac-nodal-line state in a well-known conventional high-temperature superconductor, MgB2. First-principles calculations show that the Dirac-nodal-line structure exhibits a unique…
Effect of Fermi surface evolution on superconducting gap in superconducting topological insulator
超导拓扑绝缘体是一种很有希望的拓扑超导体。最近的实验表明，三维费米面演化为二维费米面。我们发现费米面上的超导能隙结构随着这种演化而系统地变化。阐明了自旋晶格弛豫速率和比热等体电子性质与费米面的形状和能隙函数的类型有关。这些结果可作为确定Cu $_x$ Bi $_2$ Se $_3$的配对对称性的指导。
Fermi surface effect on spontaneous breaking of time-reversal symmetry in unconventional superconducting films
我们提出了一种有助于稳定具有破缺时间反转对称性的超导态的机制，该机制被预测在d波超导膜中实现[A。B. Vorontsov，Phys. Rev. Lett. 102，177001（2009）]。在此超导相，时间反演对称性破缺伴随着沿膜表面的平移对称性的自发破缺。我们研究如何正常超导相边界的厚度-温度相图中的薄膜被修改取决于费米面形状。特别地，当费米面满足嵌套条件时，发现非均匀超导相基本上延伸到相图中的较小厚度区域。我们证明了这种费米表面效应使用正方形晶格紧束缚模型。
Iron selenide (FeSe) is an iron-based superconductor which shows unique properties, including strongly anisotropic superconducting gap, paramagnetism in undoped compound and extremely small Fermi pocket size. In this work, we demonstrate that the sizes of electron and hole pockets in FeSe monolayer become much smaller than those in bulk. The Fermi energy is in the order of a few meV and can be fine-tuned by the thickness of graphene layers underneath. Despite the low carrier density, the FeSe monolayers grown on trilayer or multi-layer graphene are superconducting. The superconducting gap size…
High resolution laser-based angle-resolved photoemission measurements were carried out on an overdoped $Bi_2Sr_2CaCu_2O_{8+δ}$ superconductor with a Tc of 75 K. Two Fermi surface sheets caused by bilayer splitting are clearly identified with rather different doping levels: the bonding sheet corresponds to a doping level of 0.14 which is slightly underdoped while the antibonding sheet has a doping of 0.27 that is heavily overdoped, giving an overall doping level of 0.20 for the sample. Different superconducting gap sizes on the two Fermi surface sheets are revealed for the first time. The super…
Cooper's formalism for fermionic pairing has been revisited considering upto 3rd neighbour hopping terms, firstly with a Fermi liquid like background on a square lattice keeping in mind the overdopped cuprates. Then the whole scheme is repeated with a Marginal Fermi liquid- like background, taking into account the self energy correction of the mobile electrons to include a more realitic density of states in the calculation. Detailed comparison of our theoretical results with those from experiments strongly supports the Marginal Fermi liquid- like character of the normal phase with exciton medi…
We propose a mechanism for the generation of pure superconducting spin-current carried by equal-spin triplet Cooper pairs in a superconductor (S) sandwiched between a ferromagnet (F) and a normal metal (N$_{\rm so}$) with intrinsic spin-orbit coupling. We show that in the presence of Landau Fermi-liquid interactions the superconducting proximity effect can induce non-locally a ferromagnetic exchange field in the normal layer, which disappears above the superconducting transition temperature of the structure. The internal Landau Fermi-liquid exchange field leads to the onset of a spin supercurr…
We report on the Fermi surfaces and superconducting parameters of CaSb$_2$ single crystals (superconducting below $T_{\text{c}}\sim 1.8~\text{K}$) grown by the self-flux method. The frequency of de-Haas-van-Alphen and Shubnikov-de-Haas oscillations evidences a quasi-two-dimensional (quasi-2D) Fermi surface, consistent with one of the Fermi surfaces forming Dirac lines predicted by first-principles calculations. Measurements in the superconducting state reveal that CaSb$_2$ is close to a type-I superconductor with the Ginzburg-Landau (GL) parameter of around unity. The temperature dependence of…
The van-der-Waals gap of iron chalcogenide superconductors can be intercalated with a variety of inorganic and organic compounds that modify the electron doping level of the iron layers. In Lix(C3N2H10)0.37FeSe, a dome in the superconducting transition temperature Tc has been reported to occur in the doping range of x=0.06 to x=0.68. We use a combination of density functional theory and spin fluctuation theory to capture the evolution of superconducting transition temperatures theoretically. We clearly demonstrate how the changing electronic structure supports an increasing superconducting Tc.…
We consider a non-Hermitian superconducting system by coupling a conventional superconductor to a ferromagnet lead and demonstrate the emergence of exceptional points when an external Zeeman field is applied. We discover that, depending on the non-Hermiticity and the Zeeman field, the exceptional points mark the ends of lines with zero real energy, thus giving rise to topologically protected and highly tunable bulk Fermi arcs, which we coin bulk Bogoliubov Fermi arcs due to their superconducting nature. We show that these bulk Bogoliubov Fermi arcs are the non-Hermitian counterparts of the Her…
Unconventional Pairing in Doped Band Insulators on a Honeycomb Lattice : the Role of the Disconnected Fermi Surface and a Possible Application to Superconducting $β$-MNCl (M=Hf,Zr)
High-temperature superconductivity occurs near antiferromagnetic instabilities and nematic state. Debate remains on the origin of nematic order in FeSe and its relation with superconductivity. Here, we use transport, neutron scatter- ing and Fermi surface measurements to demonstrate that hydro-thermo grown superconducting FeS, an isostructure of FeSe, is a tetragonal paramagnet without nematic order and with a quasiparticle mass significantly reduced from that of FeSe. Only stripe-type spin excitation is observed up to 100 meV. No direct coupling between spin excitation and superconductivity i…
Effects of Fermi surface and superconducting gap structure in the field-rotational experiments: A possible explanation of the cusp-like singularity in YNi$_2$B$_2$C
Fermi surfaces and orbital polarization in superconducting CeO$_{0.5}$F$_{0.5}$BiS$_{2}$ revealed by angle-resolved photoemission spectroscopy
利用偏振相关角分辨光电子能谱（ARPES）研究了BiSPDMATHABMM基CeO $_{0.5}$ F $_{0.5}$ BiS $_2$超导体的电子结构，并成功地阐明了费米面上的轨道特征.在X点周围的矩形费米口袋中，平行于$k_y$方向的直线部分由Bi $6p_x$特征主导。轨道极化表明BiS $_2$系统的准一维电子结构。此外，四边形排列的Bi上的扭曲可以引起带Jahn-Teller效应。
Unconventional superconductivity frequently emerges as the transition temperature of a magnetic phase, typically antiferromagnetic, is suppressed continuously toward zero temperature. Here, we report contrary behavior in pressurized CeRhGe3, a non-centrosymmetric heavy fermion compound. We find that its pressure-tuned antiferromagnetic transition temperature (TN) appears to avoid a continuous decrease to zero temperature by terminating abruptly above a dome of pressure-induced superconductivity. Near 21.5 GPa, evidence for TN suddenly vanishes, the electrical resistance becomes linear in tempe…
Fermion systems with flat bands can boost superconductivity by enhancing the density of states at the Fermi level. We use quasiexact numerical methods to show that repulsive interactions between spinless fermions in a one-dimensional (1D) flat-band system, the Creutz ladder, give a finite pairing energy that increases with repulsion, though charge quasi-order (QO) remains dominant. Adding an attractive component shifts the balance in favor of superconductivity and the interplay of two flat bands further yields a remarkable enhancement of superconductivity, well outside of known paradigms for 1…
A spin-imbalanced Fermi gas with an attractive contact interaction forms a superconducting state whose underlying components are superpositions of Cooper pairs that share minority-spin fermions. This superconducting state includes correlations between all available fermions, making it energetically favorable to the Fulde--Ferrell--Larkin--Ovchinnikov superconducting state. The ratio of the number of up- and down-spin fermions in the instability is set by the ratio of the up- and down-spin density of states in momentum at the Fermi surfaces, to fully utilize the accessible fermions. We present …
In this work we investigate the description of superconducting systems with multiple Fermi surfaces. For the case of one Fermi surface we re-obtain the result that the superconductor is more precisely described as a topological state of matter. Studying the case of more than one Fermi surface, we obtain the effective theory describing a time reversal symmetric topological superconductor. These results are obtained by employing a general procedure to construct effective low energy actions describing states of electromagnetic systems interacting with charges and defects. The procedure consists i…
