Van Hove singularity and spontaneous Fermi surface symmetry breaking in Sr3Ru2O7

TL;DR

This paper models the Fermi surface symmetry breaking in Sr3Ru2O7 under magnetic fields, explaining metamagnetic transitions and associated thermodynamic anomalies without requiring a quantum critical point.

Contribution

It introduces a simple model capturing Fermi surface symmetry breaking and metamagnetic transitions in Sr3Ru2O7, emphasizing the role of van Hove singularities and magnetic field tuning.

Findings

Fermi surface symmetry breaking occurs in both spin bands with different order parameters.

The transition changes from second order at high T to first order at low T, linked to metamagnetism.

Strong temperature dependence of susceptibility and specific heat, including a log T divergence at van Hove filling.

Abstract

The most salient features observed around a metamagnetic transition in Sr3Ru2O7 are well captured in a simple model for spontaneous Fermi surface symmetry breaking under a magnetic field, without invoking a putative quantum critical point. The Fermi surface symmetry breaking happens in both a majority and a minority spin band but with a different magnitude of the order parameter, when either band is tuned close to van Hove filling by the magnetic field. The transition is second order for high temperature T and changes into first order for low T. The first order transition is accompanied by a metamagnetic transition. The uniform magnetic susceptibility and the specific heat coefficient show strong T dependence, especially a log T divergence at van Hove filling. The Fermi surface instability then cuts off such non-Fermi liquid behavior and gives rise to a cusp in the susceptibility and a specific heat jump at the transition temperature.