Possible Phase Transition Deep Inside the Hidden Order Phase of Ultraclean URu2Si2

TL;DR

This study reveals a possible internal phase transition within the hidden order phase of URu2Si2, characterized by a Fermi surface reconstruction and quantum oscillations, suggesting an itinerant electron mechanism.

Contribution

The paper provides evidence of an internal phase transition inside the hidden order phase of URu2Si2 using high-purity crystals and high-field measurements, highlighting a Fermi surface change.

Findings

An anomaly in Hall resistivity at 22.5 T indicating Fermi surface reconstruction.

Appearance of a novel quantum oscillation above a specific magnetic field.

Evidence supporting an itinerant electron model for the hidden order transition.

Abstract

To elucidate the underlying nature of the hidden order (HO) state in heavy-fermion compound URu2Si2, we measure electrical transport properties of ultraclean crystals in a high field/low temperature regime. Unlike previous studies, the present system with much less impurity scattering resolves a distinct anomaly of the Hall resistivity at H*=22.5 T well below the destruction field of the HO phase ~36 T. In addition, a novel quantum oscillation appears above a magnetic field slightly below H*. These results indicate an abrupt reconstruction of the Fermi surface, which implies a possible phase transition well within the HO phase caused by a band-dependent destruction of the HO parameter. The present results definitely indicate that the HO transition should be described by an itinerant electron picture.