Signatures of spinorial order in URu$_2$Si$_2$: Landau-Ginzburg theory of hastatic order

TL;DR

This paper develops a Landau-Ginzburg theoretical framework for hastatic order in URu$_2$Si$_2$, revealing new gauge-invariant orders and explaining experimental observations related to symmetry breaking and hidden order.

Contribution

It introduces a Landau-Ginzburg model showing two gauge-invariant orders in hastatic order, highlighting the spinorial nature's effects and predicting a new transition under transverse field.

Findings

Identifies two gauge-invariant orders related to hastatic order.

Explains the absence of in-plane moments in URu$_2$Si$_2$.

Predicts a new phase transition in transverse magnetic fields.

Abstract

The hidden order in URu$_2$Si$_2$ remains a compelling mystery after more than thirty years, with the order parameter still unidentified. One intriguing proposal for the phase has been hastatic order: a symmetry breaking heavy Fermi liquid with a spinorial hybridization that breaks both single and double time-reversal symmetry. Hastatic order is the first spinorial, rather than vectorial order in materials, but previous work has not yet found direct consequences of the spinorial nature. In this paper, we revisit the hastatic proposal within Landau-Ginzburg theory. Rather than a single spinorial order parameter breaking double-time-reversal symmetry, we find two gauge invariant vectorial orders: the expected composite order with on-site moments, and a new quantity capturing symmetries broken solely by the spinorial nature. We address the effect of fluctuations and disorder on the tetragonal symmetry breaking, explaining the absence of in-plane moments in URu$_2$Si$_2$ and predicting a new transition in transverse field.