We propose that an excitonic gap can be generated along nodal directions by Coulomb interaction in the mixed state of d-wave cuprate superconductors. In a superconductor, the Coulomb interaction usually can not generate any fermion gap since its strength is weakened by superfluidity. It becomes stronger as superfluid density is suppressed by external magnetic field, and is able to generate a gap for initially gapless nodal quasiparticles beyond some critical field $H_{c}$. By solving the gap equation, it is found that the nodal gap increases with growing field $H$, which leads to a suppression of thermal conductivity at zero temperature. This mechanism naturally produces the field-induced thermal metal-insulator transition observed in transport experiments.
Vortex Charging Effect in a Chiral $p_x\pm i p_y$-Wave Superconductor
在Bogoliubov-de Gennes（BdG）理论的基础上，考虑了电荷屏蔽和电流屏蔽，研究了$p_x\pm i p_y$波超导体中单个涡旋周围的准粒子态.由于时间反演对称性的破坏，有两种类型的涡是由它们的缠绕方向相对于手征库珀对的角动量区分。BdG解表明两种涡旋的电荷有很大的不同，反映了$p_x\pm i p_y$ -波配对态的转动库珀对。
By solving the Bogoliubov-de Gennes equations for a $d$-wave superconductor, we explore how the interplay between disorder and the orbital depairing of an external magnetic field influences the superconductor-metal transition of the hole-overdoped cuprates. For highly disordered systems, we find granular Cooper paring to persist above the critical field where the superfluid stiffness goes to zero. We also show that because the vortices are attracted to regions where the superconducting pairing is already weak, the Caroli-de Gennes-Matricon zero-bias peak in the local density of states at the v…
We study the thermal transport in a two-dimensional system with coexisting superconducting (SC) and nematic orders. We analyze the nature of the coexistence phase in a tight-binding square lattice where the nematic state is modelled as a $d$-wave Pomeranchuk type instability and the feedback of the symmetry breaking nematic state on the SC order is accounted for by mixing of the $s$, $d$ paring interaction. The electronic thermal conductivity is computed within the framework of Boltzmann kinetic theory where the impurity scattering collision is treated in the both the Born and Unitary limits. …
We propose that cuprate superconductors are in the vicinity of a spontaneous d-wave type Fermi surface symmetry breaking, often called a d-wave Pomeranchuk instability. This idea is explored by means of a comprehensive study of magnetic excitations within the slave-boson mean-field theory of the t-J model. We can naturally understand the pronounced xy anisotropy of magnetic excitations in untwinned YBa_{2}Cu_{3}O_{y} and the sizable change of incommensurability of magnetic excitations at the transition temperature to the low-temperature tetragonal lattice structure in La_{2-x}Ba_{x}CuO_{4}. In…
Recently discovered Z2 topological kagome metals AV3Sb5 (A = K, Rb, and Cs) exhibit charge density wave (CDW) phases and novel superconducting paring states, providing a versatile platform for studying the interplay between electron correlation and quantum orders. Here we directly visualize CDW-induced bands renormalization and energy gaps in RbV3Sb5 using angle-resolved photoemission spectroscopy, pointing to the key role of tuning van Hove singularities to the Fermi energy in mechanisms of ordering phases. Near the CDW transition temperature, the bands around the Brillouin zone (BZ) boundary…
Unconventional superconductivity in the BiS$_2$-based layered superconductor NdO$_{0.71}$F$_{0.29}$BiS$_2$
我们研究了最近发现的BiS $_2$基超导体之一，NdO $_{0.71}$ F $_{0.29}$ BiS $_2$（$T_c$ $\sim$ 5 K）的超导带隙各向异性，使用基于激光的角分辨光电子能谱。先前发现的高$T_c$超导体如铜氧化物和铁基超导体（其被认为具有非常规超导机制）在其导带中具有$3d$电子，而BiS $_2$基超导体的导带主要由Bi 6 $p$电子组成，因此可以预期常规超导机制。与此相反，我们观察到一个强各向异性的超导带隙。这一结果强烈地表明NdO $_{0.71}$ F $_{0.29}$ BiS $_2$的配对机制是非常规的，我们将观察到的各向异性归因于竞争或合作的多重配对相互作用。
High temperature superconducting materials have been known since the pioneering work of Bednorz and Mueller in 1986. While the microscopic mechanism responsible for high Tc superconductivity is still debated, most materials showing high Tc contain highly electronic polarizable ions, suggesting that the mechanism driving high Tc superconductivity can be related to the ion electronic polarizability in high Tc materials. Here we show that a free charge carrier polarizes the ions surrounding it and the total electrical potential generated by the charge carrier itself and the polarized ions becomes…
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…
We perform a two-loop renormalization group (RG) analysis of a 2D effective multiband model, which is relevant for describing the low-energy properties of some iron-chalcogenide superconducting materials. Crucial ingredients in this analysis are the calculation of higher-order contributions in the RG scheme that go beyond the widely-used parquet approximation and the consequent inclusion of nontrivial self-energy effects of the model that yield an anisotropic renormalization of the quasiparticle weight in the system. The motivation of our work is the experimental discovery by Sprau et al. (201…
We explore superconducting instability for a clean two-band layered superconductor with deep and shallow bands in the magnetic field applied perpendicular to the layers. In the shallow band, the quasiclassical approximation is not applicable, and Landau quantization has to be accounted for exactly. The electronic spectrum of this band in the magnetic field is composed of the one-dimensional Landau-level minibands. With increasing magnetic field the system experiences series of Lifshitz transitions when the chemical potential enters and exits the minibands. These transitions profoundly influenc…
The advances in the field of unconventional superconductivity are largely driven by the discovery of novel superconducting systems. Here we report on the discovery of superconductivity on the border of antiferromagnetic order in a quasi-one-dimensional RbMn6Bi5 via measurements of resistivity and magnetic susceptibility under high pressures. With increasing pressure, its antiferromagnetic transition with TN = 83 K at ambient pressure is first enhanced moderately and then suppressed completely at a critical pressure of Pc = 13 GPa, around which bulk superconductivity emerges and exhibits a dome…
We investigate the influence of Landau quantization on the superconducting instability for a pure layered superconductor in the magnetic field directed perpendicular to the layers. We demonstrate that the quantization corrections to the Cooper-pairing kernel with finite Zeeman spin splitting promote the formation of the nonuniform state in which the order parameter is periodically modulated along the magnetic field, i.e., between the layers (Fulde-Ferrell-Larkin-Ovchinnikov [FFLO] state). The conventional uniform state experiences such a quantization-induced FFLO instability at low temperature…
Paramagnetic instability at normal-metal - superconductor interfaces
研究了介观正常金属薄膜（N）与超导体（S）接触时的邻近相干性。考虑到正常金属中电子之间的排斥相互作用，我们发现靠近NS界面的局域态密度增强。密度的尖峰被钉扎到费米能，并导致自发顺磁界面电流。诱导轨道磁矩表现出在正常金属涂覆的超导圆柱体中观察到的顺磁重入的特征[Phys. Rev. Lett. 65，1514（1990）]。
