Temperature Controlled Fulde-Ferrell-Larkin-Ovchinnikov Instability in Superconductor-Ferromagnet Hybrids

Abstract

We show that a wide class of layered superconductor-ferromagnet (S/F) hybrids demonstrates the emergence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase well below the superconducting transition temperature. By decreasing the temperature, one can switch the system from uniform to the FFLO state which is accompanied by the damping of the diamagnetic Meissner response down to zero and also by the sign change in the curvature of the current-velocity dependence. Our estimates show that an additional layer of the normal metal (N) covering the ferromagnet substantially softens the conditions required for the predicted FFLO instability, and for existing S/F/N systems, the temperature of the transition into the FFLO phase can reach several kelvins.

Tuning the in-plane Fulde-Ferrell-Larkin-Ovchinnikov state in a superconductor/ferromagnet/normal-metal hybrid structure by current or magnetic field

“…Consequently, the increase of Λ −1 with magnetic field can serve as a precursor of the FFLO state as the increase of Λ −1 with increasing of temperature. 8 At larger d F , i.e. with getting further from the FFLO domain, Λ −1 (H = 0) increases and starting from some value of d F (≈ 2 D F /h) the inverse penetration depth Λ −1 decreases in a weak magnetic field (see Fig.…”

Quasiclassical free energy of superconductors: Disorder-driven first-order phase transition in superconductor/ferromagnetic-insulator bilayers

“…Superconductor/ferromagnet systems are studied quite intensively in view of spintronic applications [46,47]. With the help of free-energy expressions found in this paper it is possible to analyze complicated behavior of competing superconducting phases, such as 0-π Josephson junctions [8], cryptoferromagnetism [48][49][50][51][52], FFLO states [53,54] modified by different geometrical factors [27,55], and configurations with different vorticities [56,57] in such systems using rigorous microscopic calculations.…”

“…The expression which has been used [26][27][28][29] for the dirty superconductors with spin-singlet s-wave pairing described by the pairing constant…”

Reply to "Comment on Yerin et al., Phys. Rev. Lett. 121, 077002 (2018), and Mironov et al., Phys. Rev. Lett. 109, 237002 (2012)" by A. F. Volkov, F. S. Bergeret, and K. B. Efetov

“…In our paper, we do not pretend to introduce this idea, which by the way was mentioned in the works [4,5] published before that of the authors of the comment [2,3]. Therefore, the first part of the comment [1] seems to be irrelevant to our works [6,7].…”

“…Finally they cite from our paper [7]: "It is exactly this FFLO instability which makes impossible to observe the global paramagnetism predicted in [34][35][36]. The latter paramagnetic state just does not correspond to the free energy minimum [37]".…”