Dia- and paramagnetic Meissner effect from odd-frequency pairing in multi-orbital superconductors

TL;DR

This paper investigates how odd-frequency pairing influences the Meissner effect in multi-orbital superconductors, revealing that it can produce both diamagnetic and paramagnetic responses depending on the band structure, and does not necessarily cause instability.

Contribution

It demonstrates that odd-frequency pairing contributes to both diamagnetic and paramagnetic Meissner effects, depending on the band structure, challenging previous notions of its destabilizing role.

Findings

Odd-frequency pairing generates both dia- and paramagnetic responses.

In materials with electron- or hole-like bands, odd-frequency effects nearly cancel out.

In topological materials, odd-frequency pairing predominantly produces a diamagnetic response.

Abstract

The Meissner effect is one of the defining properties of superconductivity, with a conventional superconductor completely repelling an external magnetic field. In contrast to this diamagnetic behavior, odd-frequency superconducting pairing has often been seen to produce a paramagnetic Meissner effect, which instead makes the superconductor unstable due to the attraction of magnetic field. In this work we study how both even- and odd-frequency superconducting pairing contributes to the Meissner effect in a generic two-orbital superconductor with a tunable odd-frequency pairing component. By dividing the contributions to the Meissner effect into intra- and inter-band processes, we find that the odd-frequency pairing actually generates both dia- and paramagnetic Meissner responses, determined by the normal-state band structure. More specifically, for materials with two electron-like (hole-like) low-energy bands we find that the odd-frequency inter-band contribution is paramagnetic but nearly canceled by a diamagnetic odd-frequency intra-band contribution. Combined with a diamagnetic even-frequency contribution, such superconductors thus always display a large diamagnetic Meissner response to an external magnetic field, even in the presence of large odd-frequency pairing. For materials with an inverted, or topological, band structure, we find the odd-frequency inter-band contribution to instead be diamagnetic and even the dominating contribution to the Meissner effect in the near-metallic regime. Taken together, our results show that odd-frequency pairing in multi-orbital superconductors does not generate a destabilizing paramagnetic Meissner effect and can even generate a diamagnetic response in topological materials.