High-Field Superconductivity at an Electronic Topological Transition in URhGe

TL;DR

This study reveals that in URhGe, superconductivity at high magnetic fields is linked to a topological Fermi surface transition, where the Fermi surface collapses without a divergence in quasiparticle mass, challenging previous theories.

Contribution

It demonstrates that magnetic field-tuning of the Fermi surface, not just quantum criticality, can govern superconductivity in URhGe, with direct evidence from quantum oscillations.

Findings

Fermi surface undergoes a topological transition near the metamagnetic field.

Quasiparticle mass decreases but remains finite at the transition.

Superconductivity re-emerges at high magnetic fields due to Fermi surface collapse.

Abstract

The emergence of superconductivity at high magnetic fields in URhGe is regarded as a paradigm for new state formation approaching a quantum critical point. Until now, a divergence of the quasiparticle mass at the metamagnetic transition was considered essential for superconductivity to survive at magnetic fields above 30 tesla. Here we report the observation of quantum oscillations in URhGe revealing a tiny pocket of heavy quasiparticles that shrinks continuously with increasing magnetic field, and finally disappears at a topological Fermi surface transition close to or at the metamagnetic field. The quasiparticle mass decreases and remains finite, implying that the Fermi velocity vanishes due to the collapse of the Fermi wavevector. This offers a novel explanation for the re-emergence of superconductivity at extreme magnetic fields and makes URhGe the first proven example of a material where magnetic field-tuning of the Fermi surface, rather than quantum criticality alone, governs quantum phase formation.