Chiral spin-orbital liquids with nodal lines

TL;DR

This paper proposes a stable chiral spin-orbital liquid phase in heavy-element double perovskites, featuring Majorana fermions with nodal lines, topological defects, and dispersing surface states, with potential experimental signatures.

Contribution

It introduces a realistic model for heavy-element double perovskites that hosts a novel chiral spin-orbital liquid with topologically protected nodal lines and Majorana excitations.

Findings

Nodal lines are topological defects of a non-Abelian Berry connection.

The spin liquid exhibits dispersing surface states.

Potential experimental signatures are discussed and compared with Ba2YMoO6.

Abstract

Strongly correlated materials with strong spin-orbit coupling hold promise for realizing topological phases with fractionalized excitations. Here we propose a chiral spin-orbital liquid as a stable phase of a realistic model for heavy-element double perovskites. This spin liquid state has Majorana fermion excitations with a gapless spectrum characterized by nodal lines along the edges of the Brillouin zone. We show that the nodal lines are topological defects of a non-Abelian Berry connection and that the system exhibits dispersing surface states. We discuss some experimental signatures of this state and compare them with properties of the spin liquid candidate Ba_2YMoO_6.