Theory of rare-earth Kramers magnets on a Shastry-Sutherland lattice: dimer phases in presence of strong spin-orbit coupling

TL;DR

This paper develops a theoretical model for rare-earth Shastry-Sutherland magnets incorporating strong spin-orbit coupling, revealing novel triplet dimer phases that respond to magnetic fields and relate to recent experimental findings.

Contribution

It introduces a generic effective-spin model with extended XYZ interactions accounting for strong spin-orbit coupling on a Shastry-Sutherland lattice, predicting new triplet dimer phases.

Findings

Identification of triplet dimer phases stabilized by spin-orbit coupling

Prediction that these phases respond to magnetic fields and evolve into polarized states

Application of the model to Yb2Be2GeO7, linking theory to experiment

Abstract

Shastry-Sutherland magnet is a typical frustrated spin system hosting rich phases. While the Heisenberg limit has been extensively studied, the role of spin-orbit coupling is not well explored. Motivated by newly discovered rare-earth Shastry-Sutherland magnets, we construct a generic effective-spin model that describes the interactions between Kramers doublet local moments on a Shastry-Sutherland lattice. Due to the strong spin-orbit coupling, the model takes the form of extended XYZ interactions on both intra- and inter-dimer bonds. We show that, in addition to the conventional "singlet" dimer phase, strong spin-orbit coupling can stabilize peculiar "triplet" dimer phases. These "triplet" dimer phases, though fully gapped, respond immediately to magnetic fields and evolve smoothly into the fully polarized phase. We present that the recently discovered Shastry-Sutherland magnet Yb$_2$Be$_2$GeO$_7$ belongs to the "triplet" dimer phase, and discuss the implication of our results to a broad class of quantum magnets in general.