Pressure-induced 0-πtransitions and supercurrent crossover in antiferromagnetic weak links

Abstract

We compute self-consistently the Josephson current in a superconductor-antiferromagnet-superconductor junction using a lattice model, focusing on 0 − π transitions occurring when the width of the antiferromagnetic region changes from an even to an odd number of lattice sites. Previous studies predicted 0 − π transitions when alternating between an even and an odd number of sites for sufficiently strong antiferromagnetic order. We study numerically the magnitude of the threshold value for this to occur, and also explain the physics behind its existence in terms of the phase-shifts picked up by the quasiparticles constituting the supercurrent in the antiferromagnet. Moreover, we show that this threshold value allows for pressure-induced 0 − π transitions by destroying the antiferromagnetic nesting properties of the Fermi surface, a phenomenon which has no counterpart in ferromagnetic Josephson junctions, offering a new way to tune the quantum ground state of a Josephson junction without the need of multiple samples. Introduction. The study of the interplay between superconductivity and magnetism has been of considerable interest in condensed matter physics over the last decades. Phenomena such as the 0 − π-transition 1 in ferromagnetic Josephson junctions has received much attention both from a fundamental quantum physics point of view in addition to being suggested as a potential basis for qubits. 2 . While most of the focus in the above context has been on ferromagnetic (F) order, antiferromagnetic (AF) Josephson junctions are also of fundamental interest, due to the close relationship between the superconducting (S) phase and the antiferromagnetic phase in for instance high-temperature cuprate and iron-pnictide superconductors. Superconductivity and antiferromagnetism spindensity wave states may even coexist in the superconducting pnictides. 3 Similar to SFS junctions, antiferromagnetic Josephson junctions (SAFS) have been predicted to display 0 − π-transitions 4 . However, for SAFS these transitions display a high sensitivity to the exact number of atomic layers (even vs. odd number) in the antiferromagnet. Ref. 5 reported that an antiferromagnetic Josephson junction is in a π-state for an odd number of layers, while it is in the 0-state for an even number of layers provided that the antiferromagnetic order is much stronger than the superconducting order. An evenodd effect has also been observed in Josephson junctions with magnetic impurities in the middle layer. 6 In this Rapid Communication, we report on a novel aspect of antiferromagnetic Josephson junctions which allows for control over 0 − π transitions within a single sample in a way which has no counterpart in SFS structures. We first compute numerically the threshold value for the antiferromagnetic order parameter at which the even-odd effect occurs. Below this threshold, even and odd junctions behave qualitatively similar, both displaying a monotonic decay of the supercurrent with superimposed small-scale oscillations, but without any sign-change of t...

Giant anisotropy in the Josephson effect and switching of staggered order in antiferromagnets

“…For an odd number of chains in the antiferromagnet, there will be a net magnetization proportional to the number of sites on each chain. Such an uncompensated interface with a net magnetization allows for interesting properties not found in compensated interfaces [11,12,14]. Assuming translational invariance in the 𝑧direction, the Fourier-transformed Hamiltonian may be written in compact matrix form…”

Electrically controlled crossed Andreev reflection in two-dimensional antiferromagnets

“…Recently, the potential of using antiferromagnets in superconducting spintronics has been recognized. For instance, at the interface between an antiferromagnet and a superconductor, normal reflection and AR have been demonstrated to be both specular and retroreflective [49][50][51][52][53][54][55][56][57][58][59][60][61][62]. In heterostructures, these anomalous processes fundamentally change the behaviour of the electrical and thermal conductance [49].…”

“…In heterostructures, these anomalous processes fundamentally change the behaviour of the electrical and thermal conductance [49]. In Josephson junctions, atomic-scale 0 − π transitions [51][52][53][54][55][56] are predicted to occur. The existence of Josephson effects has been experimentally verified [57][58][59][60][61][62], but the remaining theoretical predictions have yet to be explored.…”

Electrical and Thermal Transport in Antiferromagnet-Superconductor Junctions

“…It has been theoretically shown that AF-S junctions exhibit additional scattering processes different from those in N(F)-S junctions [56]. In Josephson junctions, these new scattering processes create low-energy bound states [57] that lead to anomalous phase shifts [58] and atomic-scale 0−π transitions [59][60][61][62]. On the other hand, although the existence of Josephson supercurrents in S-AF-S junctions has been experimentally reported [63][64][65][66][67][68], other theoretical predictions have yet to be explored.…”