Uncovering the hidden order in URu2Si2: Identification of Fermi surface instability and gapping

TL;DR

This paper uses advanced density-functional theory to explain the hidden order in URu2Si2 by identifying Fermi surface instabilities and proposing a symmetry-breaking mechanism involving antiferromagnetic excitations.

Contribution

It provides a microscopic explanation for the hidden order in URu2Si2, linking Fermi surface instabilities to symmetry breaking and gapping.

Findings

Identification of Fermi surface hot spots causing instability

Quantification of Fermi surface gapping due to symmetry breaking

Proposal of antiferromagnetic excitations as the hidden order mechanism

Abstract

Spontaneous, collective ordering of electronic degrees of freedom leads to second-order phase transitions that are characterized by an order parameter. The notion "hidden order" (HO) has recently been used for a variety of materials where a clear phase transition occurs to a phase without a known order parameter. The prototype example is the heavy-fermion compound URu2Si2 where a mysterious HO transition occurs at 17.5K. For more than twenty years this system has been studied theoretically and experimentally without a firm grasp of the underlying physics. Using state-of-the-art density-functional theory calculations, we provide here a microscopic explanation for the HO. We identify the Fermi surface "hot spots" where degeneracy induces a Fermi surface instability and quantify how symmetry breaking lifts the degeneracy, causing a surprisingly large Fermi surface gapping. As mechanism for the HO we propose spontaneous symmetry breaking through collective antiferromagnetic moment excitations.