Magnetically Hidden Order of Kramers Doublets in $d^1$ Systems: Sr$_2$VO$_4$

TL;DR

This paper proposes a theoretical model for a hidden magnetic order in Sr$_2$VO$_4$, characterized by a composite spin-orbital order parameter that breaks time-reversal symmetry without local magnetic moments.

Contribution

It introduces an effective Hamiltonian for $d^1$ Kramers doublets and predicts a novel hidden order with a composite order parameter in layered perovskite Sr$_2$VO$_4$.

Findings

Hidden order with vanishing local moments.

Order parameter is a spin-orbital analog of a magnetic octupole.

Predicted realization in Sr$_2$VO$_4$.

Abstract

We formulate and study an effective Hamiltonian for low-energy Kramers doublets of $d^1$-ions on a square lattice. We find that the system exhibits a magnetically hidden order in which the expectation values of the local spin and orbital moments both vanish. The order parameter responsible for a time-reversal symmetry breaking has a composite nature and is a spin-orbital analog of a magnetic octupole. We argue that such a hidden order is realized in the layered perovskite Sr$_2$VO$_4$.