The rise and fall of the superconducting transition temperature $T_c$ upon tuning carrier density or external parameters, such as pressure or magnetic field, is ubiquitously observed in a wide range of quantum materials. In order to investigate such domes of $T_c$, we go beyond the prototypical attractive Hubbard model, and consider a lattice model of electrons coupled via instantaneous, spatially extended, attractive interactions. By numerically solving the mean-field equations, as well as going beyond mean field theory using a functional renormalization group approach, we find that for a characteristic interaction range $\ell$, there exists a dome in $T_c$ around $k_F \ell \! \sim \! {\mathcal{O}}(1)$. For multiband systems, our mean field theory shows the presence of additional domes in the vicinity of Lifshitz transitions. Our results hold in both two and three dimensions and can be intuitively understood from the geometric relation between the Fermi surface and the interaction range. Our model may be relevant for domes of $T_c$ in dilute weakly coupled superconductors or in engineered cold atom systems.
An indispensable ingredient for pair density wave (PDW) superconductivity is the presence of an attractive pairing interaction at finite momentum. Here, we show how this condition can be met with straightforward electron-density interactions in multiband systems. The electron-density interaction, when projected to the band basis, acquires form factors with nontrivial momentum dependence and thereby exhibits a potential tendency to a finite-momentum pairing instability. By applying a mean-field analysis to two simple multiband models, the checkerboard lattice and three-band Hubbard model, we fi…
This paper addresses the transition from the normal to the superfluid state in strongly correlated two dimensional fermionic superconductors and Fermi gases. We arrive at the Berezinskii-Kosterlitz-Thouless (BKT) temperature $T_{\text{BKT}}$ as a function of \emph{attractive} pairing strength by associating it with the onset of "quasi-condensation" in the normal phase. Our approach builds on a criterion for determining the BKT transition temperature for atomic gases which is based on a well established Quantum Monte Carlo analysis of the phase space density. This latter quantity, when derived …
In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors, in which superconductivity may coexist with magnetism, and only a few examples are known, when superconductivity itself induces spontaneous magnetism. The most known compounds are Sr$_2$RuO$_4$ and some noncentrosymmetric superconductors. Here, we report the finding of a narrow dome of a novel $s+is'$ superconducting (SC) phase with broken time-reversal symmetry (BTRS) inside the broad $s$-wave SC region of the centrosymmetric multiband superconductor Ba$_{\rm 1-x…
p-wave superconductivity near a transverse saturation field
本文研究了在横向磁场h_x作用下伊辛铁磁超导体URhGe的重入超导电性。本文计算了p波序参量T_{sc}的超导转变温度，并给出了两个随h_x变化的半球。我们发现强增强的T_{sc}在高场圆顶附近的饱和场h_s的自旋排列在横向方向。软磁振子在那里产生强吸引相互作用。电子对的自旋分量在h_x h_s之间有明显的变化<h_s and h_x>。我们还讨论了由于外场和交换场的相互抵消而导致的零自旋对超导现象的出现。
We consider the two-body problem in a periodic potential, and study the bound-state dispersion of a spin-$\uparrow$ fermion that is interacting with a spin-$\downarrow$ fermion through a short-range attractive interaction. Based on a variational approach, we obtain the exact solution of the dispersion in the form of a set of self-consistency equations, and apply it to tight-binding Hamiltonians with onsite interactions. We pay special attention to the bipartite lattices with a two-point basis that exhibit time-reversal symmetry, and show that the lowest-energy bound states disperse quadratical…
Upper critical magnetic field and multiband superconductivity in artificial high-Tc superlattices of nano quantum wells
Institute of Crystallography, National Research Council, CNR（意大利国家研究委员会晶体学研究所）；Rome International Center for Materials Science Superstripes RICMASS（罗马超带材料科学国际中心）；Department of Industrial, Electronic and Mechanical Engineering, Roma Tre University（罗马第三大学工业、电子与机械工程系）；Istituto Nazionale di Fisica Nucleare INFN, Sezione Roma Tre（意大利国家核物理研究所罗马三分部）；Max Planck Institute for Solid State Research（马克斯·普朗克固体研究所）；National High Magnetic Field Laboratory, (NHMFL) Los Alamos National Laboratory (LANL)（洛斯阿拉莫斯国家实验室国家高磁场实验室）；National High Magnetic Field Laboratory (NHMFL), Florida State University (FSU)（佛罗里达州立大学国家高磁场实验室）；Istituto di Ingegneria e Fisica dei Materiali, Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino（都灵理工学院应用科学与技术学院材料与物理工程研究所）；School of Science and Technology, Physics Division, University of Camerino（卡梅里诺大学理学院物理系）；Istituto Nazionale di Fisica Nucleare, Sezione di Perugia（意大利国家核物理研究所佩鲁加分部）；School of Pharmacy, Physics Unit, University of Camerino（卡梅里诺大学药学院物理组）；Institute for Microelectronics and Microsystems, National Reesearch Council CNR（意大利国家研究委员会微电子与微系统研究所）
We study superconductivity of twisted bilayer graphene with local and non-local attractive interactions. We obtain the superfluid weight and Berezinskii-Kosterlitz-Thouless (BKT) transition temperature for microscopic tight-binding and low-energy continuum models. We predict qualitative differences between local and non-local interaction schemes which could be distinguished experimentally. In the flat band limit where the pair potential exceeds the band width we show that the superfluid weight and BKT temperature are determined by multiband processes and quantum geometry of the band.
A critical result in superconductivity is that flat bands, though dispersionless, can still host nonzero superfluid weight due to quantum geometry. We show that the derivation of the mean field superfluid weight in previous literature is incomplete, which can lead to severe quantitative and even qualitative errors. We derive the complete equations and demonstrate that the minimal quantum metric -- the metric with minimum trace -- is related to the superfluid weight in isolated flat bands. We complement this result with an exact calculation of the Cooper pair mass in attractive Hubbard models w…
Slope of the upper critical field at $T_{c}$ in two-band superconductors with non-magnetic disorder: $s_{++}$ superconductivity in $\textrm{Ba}_{1-x}\textrm{K}_{x}\textrm{Fe}_{2}\textrm{As}_{2}$
Emergent Fano-Feshbach resonance in two-band superconductors with an incipient quasi-flat band: Enhanced critical temperature evading particle-hole fluctuations
该研究针对两带超导中粒子-空穴涨落抑制配对的问题，通过GMB形式体系研究准平带体系，发现涌现的Fano-Feshbach共振可规避涨落抑制、提升$T_{\ m c}$，揭示多带超导的普适特征。
