# Coexistent spin-triplet superconducting and ferromagnetic phases induced by the Hund's rule coupling and electronic correlations II: Effect of applied magnetic field

## TL;DR

This paper extends a local-correlation-driven pairing model to include an applied magnetic field, explaining phase diagrams and transitions in ferromagnetic and spin-triplet superconducting states, especially for UGe2.

## Contribution

It introduces the effect of Zeeman field into the model, revealing stable spin-triplet superconducting phases and field-driven phase transitions, advancing understanding of coexisting ferromagnetism and superconductivity.

## Key findings

- Identification of stable spin-triplet SC phases under magnetic field
- Field-driven metamagnetic transition between FM1 and FM2 phases
- Respective metasuperconducting phase transformations

## Abstract

Recently proposed local-correlation-driven pairing mechanism, describing ferromagnetic phases (FM1 and FM2) coexisting with spin-triplet superconductivity (SC) within a single orbitally degenerate Anderson lattice model, is extended to the situation with applied Zeeman field. The model provides and rationalizes in a semiquantitative manner the principal features of the phase diagram observed for $\mathrm{UGe_2}$ in the field absence [cf. Phys. Rev. B $\mathbf{97}$, 224519 (2018)]. As spin-dependent effects play a crucial role for both the ferromagnetic and SC states, the role of the Zeeman field is to single out different stable spin-triplet SC phases. This analysis should thus be helpful in testing the proposed real-space pairing mechanism, which may be regarded as complementary to spin-fluctuation theory suitable for $\mathrm{^3He}$. Specifically, we demonstrate that the presence of the two distinct phases, FM1 and FM2, and associated field-driven metamagnetic transition between them, induce respective metasuperconducting phase transformation. At the end, we discuss briefly how the spin fluctuations might be incorporated as a next step into the considered here renormalized quasiparticle picture.