Fermi surface instability at the hidden-order transition of URu2Si2

TL;DR

This study uses angle-resolved photoemission spectroscopy to directly observe a significant reorganization of the Fermi surface in URu2Si2 during its mysterious hidden-order transition, revealing a new type of Fermi-surface instability.

Contribution

First direct spectroscopic evidence of Fermi surface reorganization at the hidden-order transition in URu2Si2, advancing understanding of correlated electron systems.

Findings

Heavy quasi-particle band drops below Fermi level at transition

Large electronic structure reorganization occurs during hidden order

Reveals a new Fermi-surface instability mechanism

Abstract

Solids with strong electron correlations generally develop exotic phases of electron matter at low temperatures. Among such systems, the heavy-fermion semi-metal URu2Si2 presents an enigmatic transition at To = 17.5 K to a `hidden order' state whose order parameter remains unknown after 23 years of intense research. Various experiments point to the reconstruction and partial gapping of the Fermi surface when the hidden-order establishes. However, up to now, the question of how this transition affects the electronic spectrum at the Fermi surface has not been directly addressed by a spectroscopic probe. Here we show, using angle-resolved photoemission spectroscopy, that a band of heavy quasi-particles drops below the Fermi level upon the transition to the hidden-order state. Our data provide the first direct evidence of a large reorganization of the electronic structure across the Fermi surface of URu2Si2 occurring during this transition, and unveil a new kind of Fermi-surface instability in correlated electron systems