SU(2)-invariant Majorana spin liquid with stable parton Fermi surfaces in an exactly solvable model

TL;DR

This paper presents an exactly solvable SU(2)-invariant Majorana spin liquid model with stable parton Fermi surfaces, exhibiting power-law correlations, robustness under magnetic fields, and unique magnetization plateaus, advancing understanding of quantum spin liquids.

Contribution

The authors construct a new exactly solvable spin-orbital model on a decorated square lattice that realizes a Majorana spin liquid with stable Fermi surfaces, including novel magnetic field responses.

Findings

Power-law spin and spin-nematic correlations with $1/|{f r}|^3$ decay.

Model remains solvable under Zeeman magnetic field, with Fermi surface evolution.

Identification of a half-magnetization plateau with gapful spin excitations and gapless spinless excitations.

Abstract

We construct an exactly solvable spin-orbital model on a decorated square lattice that realizes an SU(2)-invariant Majorana spin liquid with parton Fermi surfaces, of the kind discussed recently by Biswas et al. [ Phys. Rev. B. {\bf 83}, 245131(2011)]. We find power-law spin correlations as well as power-law spin-nematic correlations with the same dominant $1/|{\bf r}|^3$ envelope. The model is solvable also in the presence of Zeeman magnetic field. One fermion species carries $S^z=0$ quantum number and its Fermi surface is not altered in the field, while the Fermi surfaces of the other species evolve and can disappear. In particular, we find an interesting half-magnetization plateau phase in which spin excitations are gapful while there remain spinless gapless excitations that still produce metal-like thermal properties. In the fully-magnetized phase, the model reduces to the one proposed by Baskaran et al., [arXiv:0908.1614v3] in terms of the orbital degrees of freedom.