Possible Field–Temperature Phase Diagrams of Two-Band Superconductors with Paramagnetic Pair-Breaking

Abstract

Possible field-temperature superconducting (SC) phase diagrams in two-band quasi-twodimensional materials with a strong paramagnetic pair-breaking (PPB) are considered theoretically. Attention is paid to the case under a magnetic field perpendicular to the SC layers and to essential differences from the counterpart in the ordinary single-band material. It is found by examining the H c2 (T ) curve and the vortex lattices to be realized close to H c2 that a PPB-induced SC phase with a spatial modulation parallel to the field tends to occur more easily than in the single-band case, and that a crisscrossing vortex lattice proposed previously can occur in place of the conventional Fulde-Ferrell-Larkin-Ovchinnikov state within a parameter range. The relevance of the obtained results to FeSe and other iron-based superconductors is discussed.

Fluctuation Conductivity and Vortex State in Superconductor with Strong Paramagnetic Pair Breaking

“…1, the possibility that the mean field transition on the H c2line defined in the n = 0 LL becomes discontinuous [9] has not been taken into account, because it is believed based on the available experiments [10][11][12] that the mean field transition on the H c2 -line in FeSe should be continuous. In fact, it has been pointed out in a previous work [31] that, in the case of two-band systems characteristic of the Iron-based superconductors, there are situations in which the H c2 -transition within the n = 0 LL remains continuous even under strong PPB. Further, in such a sit-uation, the H c2 -transition in the n = 1 LL is usually kept continuous under strong PPB [9].…”

“…( 27). Then, the sign of the correction (31) to the normal conductivity is negative and leads to a negative magnetoresistive behavior. It should be noted that this negative contribution to the conductivity is due to the n = 1 LL fluctuation and is different in nature from that seen in 2D dirty limit [23? ] in the quantum regime, because the latter is a feature of the n = 0 LL fluctuation.…”

Quantum FFLO State in Clean Layered Superconductors

“…As a consequence, the FFLO instability persists for arbitrarily small interlayer hopping, and the instability temperature for the case cos ð4πγ z Þ < 0 can be still estimated from Eq. (20). The nature of the FFLO state developing at low In contrast to the quasiclassical case, the FFLO states emerge at finite T FFLO even when the γ z is very small.…”

“…In addition, these compounds have high transition temperatures and very high upper critical fields H C2 , up to 70 T, likely limited by the paramagnetic effect. These properties make iron-based superconductors plausible candidates for the realization of the FFLO state, which motivated the generalization of the theory of this state for multiple-band materials [19][20][21].…”

Imbalanced Fermi systems and exotic superconducting phases

“…The authors claimed their results to be in agreement with the experimental observations on CeCoIn 5 . A Ginzburg Landau theory based study was carried out by Adachi and Ikeda on two-band Pauli limited superconductors, which is expected to provide useful insights to the behavior of Pauli limited iron superconductors such as KFe 2 As 2 [156].…”