Hastatic Order in URu2Si2

TL;DR

This paper proposes hastatic order, a novel spinor order parameter breaking double time-reversal symmetry, explaining the hidden order phase in URu2Si2 through hybridization of conduction electrons with uranium 5f^{2} states.

Contribution

It introduces the concept of hastatic order as a new form of symmetry breaking to explain the hidden order in URu2Si2, linking it to Ising quasiparticles and specific experimental anomalies.

Findings

Hastatic order accounts for the hidden order phase in URu2Si2.

Predicts a tiny transverse magnetic moment and strong Ising anisotropy.

Explains observed entropy and magnetic anomalies.

Abstract

The development of collective long-range order via phase transitions occurs by the spontaneous breaking of fundamental symmetries. Magnetism is a consequence of broken time-reversal symmetry while superfluidity results from broken gauge invariance. The broken symmetry that develops below 17.5K in the heavy fermion compound URu2Si2 has long eluded such identification. Here we show that the recent observation of Ising quasiparticles in URu2Si2 results from a spinor order parameter that breaks double time-reversal symmetry, mixing states of integer and half-integer spin. Such "hastatic order" hybridizes conduction electrons with Ising 5f^{2} states of the uranium atoms to produce Ising quasiparticles; it accounts for the large entropy of condensation and the magnetic anomaly observed in torque magnetometry. 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.