We propose a possible charge fluctuation effect expected in layered superconducting materials. In the multireference density functional theory, relevant fluctuation channels for the Josephson coupling between superconducting layers include the interlayer pair hopping derived from the Coulomb repulsion. When interlayer single-electron tunneling processes are irrelevant in the Kohn-Sham electronic band structure calculation, the two-body effective interactions stabilize a superconducting phase. This state is also regarded as a valence-bond solid in a bulk electronic state. The hidden order parameters coexist with the superconducting order parameter when the charging effect of a layer is comparable to the pair hopping. Relevant materials structures favorable for the pair-hopping mechanism are discussed.
We discuss an analytical model to calculate the superconducting volume ratio. Apart from this, our model can also predict the shape of embedded superconducting domains. We applied our model to calculate the superconducting volume ratios and shape of domains in (TMTSF)$_2$PF$_6$, (TMTSF)$_2$ClO$_4$, YBa$_2$Cu$_4$O$_8$, $β$-(BEDT)TTF$_2$I$_3$ and FeSe. Usually in layered superconductors resistivity drops anisotropically. Our analysis also explains that, this behaviour is due to flat or needle shape of the superconducting samples.
Theory of Coherent $c$-Axis Josephson Tunneling between Layered Superconductors
我们精确计算了两个层状超导体之间的$c$轴相干隧穿的约瑟夫森电流，每个层状超导体都具有内部相干紧束缚的层内和层间准粒子色散。我们的结果也适用于当一个或两个超导体是一种散装材料，并包括通常被忽视的表面状态的影响。对于弱隧穿，我们的结果减少到我们以前的结果使用隧穿哈密顿量。我们的结果对于强隧穿也是正确的。然而，$c$轴隧穿田中和柏屋的结果被证明是不正确的任何限制。此外，我们考虑了两个相同的层状超导体之间的$c$轴相干临界电流扭转一个角度$ϕ_0$关于$c$轴相对于彼此。不考虑序参量对称性，我们使用紧束缚层内准粒子色散的相干隧穿结果与最近的$c$轴扭曲双晶Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$ Li扭曲结实验不一致{ \it et al.}
We have investigated the Se isotope effect in layered bismuth chalcogenide (BiCh2-based) superconductor LaO0.6F0.4Bi(S,Se)2 with 76Se and 80Se. For all examined samples, the Se concentration, which is linked to the superconducting properties, is successfully controlled within x = 1.09-1.14 in LaO0.6F0.4BiS2-xSex. From the magnetization and electrical resistivity measurements, changes in Tc are not observed for the LaO0.6F0.4Bi(S,Se)2 samples with 76Se and 80Se isotopes. Our results suggest that pairing in the BiCh2-based superconductors is not mediated by phonons, and unconventional supercondu…
Magnetotransport theory of layered superconductors in the flux flow steady state is revisited. Longstanding controversies concerning observed Hall sign reversals are resolved. The conductivity separates into a Bardeen-Stephen vortex core contribution, and a Hall conductivity due to moving vortex charge. This charge, which is responsible for Hall anomaly, diverges logarithmically at weak magnetic field. Its values can be extracted from magetoresistivity data by extrapolation of vortex core Hall angle from the normal phase. Hall anomalies in YBCO, BSCCO, and NCCO data are consistent with theoret…
We study the effects of static nonlocal Coulomb interactions in layered conventional superconductors and show that they generically suppress superconductivity and reduce the critical temperature. Although the nonlocal Coulomb interaction leads to a significant structure in the superconducting gap function, we find that most properties can be effectively described by means of an appropriately revised local Coulomb pseudopotential $\tildeμ_C^*$, which is larger than the commonly adopted retarded Tolmachev-Morel-Anderson pseudopotential $μ^*_C$. To understand this, we analyze the Bethe-Salpeter e…
Comparison of the phase diagram of the half-filled layered organic superconductors with the phase diagram of the RVB theory of the Hubbard-Heisenberg model
It has been proposed that a line junction between spiral magnet and superconductor or between ferromagnet and superconductor with Rashba spin-orbital coupling can produce Majorana zero mode (MZM) at the ends of the line. However, a strong magnetic exchange coupling between the magnetic atoms and the superconductor (about half of the bandwidth of the superconductor) is needed to obtain MZM. Here, we design devices to reduce the needed magnetic exchange coupling. In the first proposal, we cover a very narrow $s$-wave superconducting wire formed by a monolayer film or a layered material (such as …
Based on the London equation, we use a rotor-free vector potential ${\bf A}$, and current measurements by a SQUID, to determine the superconducting Pearl length $Λ$, and coherence length $ξ$, of ultra-thin, ring shaped, MoSi films, as a function of thickness $d$ and temperature $T$. We find that $ξ$ is a function of $d$ with a jump at $ξ\sim d \sim 5$nm. At base temperature the superconducting stiffness, defined by $1/λ^2=1/(Λd)$, is an increasing function of $T_c$. Similar behavior, known as the Uemura plot, exist in bulk layered superconductors, but with doping as an implicit parameter. We a…
Complex conductivity in strongly fluctuating layered superconductors
本文用含时的Ginzburg-Landau方法计算了磁场作用下层状第二类超导体的复涨落电导率。超导体的层状结构由Lawrence-Doniach模型解释，而动力学中的非线性相互作用项在自洽高斯近似下处理。在高$T_{c}$材料中，$H-T$图的大部分属于涡旋液相。给出了所有朗道能级贡献之和的显式表达式，该表达式基本上适用于整个相，并与高$T_{c}$超导体$_{2}$ $_{3}$ O $_{7-δ}$的实验数据进行了比较.以上的交叉到“正常相”，我们的结果与以前得到的一致。
In BiS$_2$-based layered superconductors,the existence of gap nodes on Fermi-surface curves has been suggested from angle-resolved photoemission spectroscopy measurements, whereas the conventional $s$-wave gap has been proposed from measurements of superfluid density and thermal conductivity. To reconcile these two distinct experimental results of the gap node, we investigate nonmagnetic impurity effects in the superconductor with a disconnected pocketlike Fermi-surface structure. Then, we claim that the seemingly contradictory situation concerning the gap node is resolved by a concept of dirt…
