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arXiv 2012.02403cond-mat.supr-con
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强Pauli限制准二维超导体中垂直磁场中的Fulde-Ferrell-Larkin-Ovchinnikov态

Fulde-Ferrell-Larkin-Ovchinnikov State in Perpendicular Magnetic Fields in Strongly Pauli-Limited Quasi-Two-Dimensional Superconductors

Hiroshi Shimahara

摘要:

我们研究费米表面效应称为嵌套效应的FFLO状态在强保利限制Q2 D超导体,专注于三维因素的影响,如层间电子转移,层间配对,和离面磁场,包括那些垂直于最导电层。我们研究了具有大的Maki参数的系统,使得轨道对断裂效应可以忽略不计,除了FFLO矢量q的方向锁定在场方向上。已知在QLD系统中,通过施加平行于层的磁场来抑制轨道对断裂效应,FFLO状态的嵌套效应可以很强。因此,有时有人建议,嵌套效应可能很难提高垂直场的FFLO状态的稳定性。我们说明,与这种观点相反,嵌套效应可以强烈稳定的FFLO状态的垂直领域以及平行领域时,tz是小的,使费米表面是开放的kz方向,其中tz表示层间转移能量。特别地,垂直场中的嵌套效应在层间态中可能很强。例如,在具有扭曲了tz /= 0的圆柱费米表面的系统中,对于垂直场,具有Dlt_k propsin k_z的层间态表现出mu_e Hc=1.65 Dlt_a0,这比平行场的典型值大得多,例如在tz=0的圆柱系统中,s波态的mu_e Hc=Dlt_s0,d波态的mu_e Hc = 1.28 Delta_d0。目前的结果可以潜在地提供一个物理原因,为什么在相图中的区域所占据的高场相的垂直和平行的领域是相同的顺序在CeCoIn 5和FeSe。

英文摘要:

We examine the Fermi-surface effect called the nesting effect for the FFLO state in strongly Pauli-limited Q2D superconductors, focusing on the effect of 3D factors, such as interlayer electron transfer, interlayer pairing, and off-plane magnetic fields including those perpendicular to the most conductive layers. We examine the systems with a large Maki parameter so that the orbital pair-breaking effect is negligible, except for the locking of the direction of the FFLO vector q in the field direction.It is known that the nesting effect for the FFLO state can be strong in QLD systems in which the orbital pair-breaking effect is suppressed by applying the mag. field parallel to the layers. Hence, it has sometimes been suggested that the nesting effect may hardly enhance the stability of the FFLO state for perpendicular fields. We illustrate that, contrary to this view, the nesting effect can strongly stabilize the FFLO state for perpendicular fields as well as for parallel fields when tz is small so that the Fermi surfaces are open in the kz-direction, where tz denotes the interlayer transfer energy. In particular, the nesting effect in perpendicular fields can be strong in interlayer states. For example, in systems with cylindrical Fermi surfaces warped by tz /= 0, interlayer states with Dlt_k prop sin k_z exhibit mu_e Hc=1.65 Dlt_a0 for perpendicular fields, which is much larger than typical values for parallel fields, such as mu_e Hc=Dlt_s0 of the s-wave state and mu_e Hc = 1.28 Delta_d0 of the d-wave state in cylindrical systems with tz=0. The present result could potentially provide a physical reason why the areas in the phase diagrams occupied by the high-field phases for the perpendicular and parallel fields are of the same order in CeCoIn5 and FeSe.

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