Hastatic Order in URu2Si2 : Hybridization with a Twist

TL;DR

This paper introduces 'hastatic order', a novel spinor hybridization mechanism explaining the hidden order phase in URu2Si2 through symmetry-breaking hybridization between conduction electrons and uranium f-states.

Contribution

It develops the theoretical framework of hastatic order, revealing how spinor hybridization accounts for experimental observations in URu2Si2.

Findings

Predicts a tiny transverse magnetic moment.

Explains large Ising anisotropy in susceptibility.

Accounts for entropy and magnetic anomalies.

Abstract

The broken symmetry that develops below 17.5K in the heavy fermion compound URu2Si2 has long eluded identification. Here we argue that the recent observation of Ising quasiparticles in URu2Si2 results from a spinor hybridization order parameter that breaks double time-reversal symmetry by mixing states of integer and half-integer spin. Such "hastatic order" (hasta:[Latin]spear) hybridizes Kramers conduction electrons with Ising, non-Kramers 5f2 states of the uranium atoms to produce Ising quasiparticles. The development of a spinorial hybridization at 17.5K accounts for both the large entropy of condensation and the magnetic anomaly observed in torque magnetometry. This paper develops the theory of hastatic order in detail, providing the mathematical development of its key concepts. Hastatic order predicts a tiny transverse moment in the conduction sea, a collosal Ising anisotropy in the nonlinear susceptibility anomaly and a resonant energy-dependent nematicity in the tunneling density of states.