Fulde-Ferrell-Larkin-Ovchinnikov state in disordereds-wave superconductors

Abstract

The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is a superconducting state stabilized by a large Zeeman splitting between up-and down-spin electrons in a singlet superconductor. In the absence of disorder, the superconducting order parameter has a periodic spatial structure, with periodicity determined by the Zeeman splitting. Using the Bogoliubov-de Gennes (BdG) approach, we investigate the spatial profiles of the order parameters of FFLO states in a two-dimensional s-wave superconductors with nonmagnetic impurities. The FFLO state is found to survive under moderate disorder strength, and the order parameter structure remains approximately periodic. The actual structure of the order parameter depends on not only the Zeeman field, but also the disorder strength and in particular the specific disorder configuration.

Phase diagram and local tunneling spectroscopy of the Fulde-Ferrell-Larkin-Ovchinnikov states of a two-dimensional square-latticed-wave superconductor

“…In addition, our numerical study indicates that for a 2D s-wave superconductor, the FFLO state is always 1D like and no 2D pattern could be obtained, this conclusion is consistent with that of Ref. [15,16] and the result will not be presented here.We start from a phenomenological BCS-type model with the Zeeman splitting effect caused by an exchange field or in-plane magnetic field. On a two-dimensional square lattice with a pairing interaction V between the nearest-neighbor sites, the mean-field Hamiltonian leading to the d wave superconductivity can be written as,…”

“…In addition, our numerical study indicates that for a 2D s-wave superconductor, the FFLO state is always 1D like and no 2D pattern could be obtained, this conclusion is consistent with that of Ref. [15,16] and the result will not be presented here.…”

“…In fact, in the past, the FFLO state has been studied intensively based on the above two techniques [12,13,14,15,16,17,18]. For a 2D system, it is somewhat established [14,15]that the order parameter has a 2D checkerboard pattern for a superconductor with d-wave pairing symmetry, and a 1D stripe-like pattern for s-wave pairing symmetry [15,16]. On the other hand, it has been shown that in the presence of dilute impurities, the pattern of the FFLO state becomes 1D stripe-like in a 2D d-wave superconductor [17,18].…”

“…Another effective method is the Bogoliubovde-Gennes (BdG) technique and it has been proven to be a powerful tool to study the inhomogeneous state and the local density of states (LDOS) self-consistently in the lowdimensional system. In fact, in the past, the FFLO state has been studied intensively based on the above two techniques [12,13,14,15,16,17,18]. For a 2D system, it is somewhat established [14,15]that the order parameter has a 2D checkerboard pattern for a superconductor with d-wave pairing symmetry, and a 1D stripe-like pattern for s-wave pairing symmetry [15,16].…”

Spectroscopic signatures of the Larkin-Ovchinnikov state in the conductance characteristics of a normal-metal/superconductor junction

“…Such pairing states are now collectively known as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. This novel inhomogeneous superconducting state has attracted broad theoretical interest [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] due to the experiments suggestive of its existence in various superconductors such as heavy-fermion, [19][20][21] organic and other superconductors, 22,23 and its possible realization in cold atom systems, 24,25 high-density quark matter, and nuclear matter. 26 Though it is long believed that the FFLO state can only exist in unconventional superconductors, experimental indication of disordered FFLO phase was reported in a conventional superconductor recently.…”