Spinon Magnetic Resonance of Quantum Spin Liquids

We describe electron spin resonance in a quantum spin liquid with significant spin-orbit coupling. We find that the resonance directly probes spinon continuum, which makes it an efficient and informative probe of exotic excitations of the spin liquid. Specifically, we consider spinon resonance of three different spinon mean-field Hamiltonians, obtained with the help of projective symmetry group analysis, which model a putative quantum spin liquid state of the triangular rare-earth antiferromagnet ${\mathrm{YbMgGaO}}_4$. The band of absorption is found to be very broad and exhibit strong van Hove singularities of single spinon spectrum as well as pronounced polarization dependence.

Figure 1

Plot of $2I(\omega )/|h{|}^2$ vs $\omega /t_1$ for different polarizations $\theta =0$ (blue dots), $\pi /4$ (orange squares), and $\pi /2$ (green rhombi) for U1A11 state. The inset shows spinon band structure along the high-symmetry path $\mathrm{\Gamma }\text{−}K\text{−}M\text{−}K\text{−}\mathrm{\Gamma }$ in the Brillouin zone. The vertical red line illustrates optical transitions between spinon bands.

Figure 2

Plot of $2I(\omega )/|h{|}^2$ vs $\omega /t_1^{\prime }$ for different polarizations $\theta =0$ (blue dots), $\pi /4$ (orange squares), and $\pi /2$ (green rhombi) for U1A01 state. The inset shows spinon dispersion along the path in Fig. 1.

Figure 3

Plot of $2I(\omega )/|h{|}^2$ vs $\omega /(2t_1)$ for polarizations $\theta =0$ (blue dots), $\pi /4$ (orange squares), and $\pi /2$ (green rhombi) for U1A11 state in the presence of magnetic field $B_z=1$. Note the appearance of strong van Hove singularity at $\omega \approx 4.2t_1$. The thin red line shows Zeeman response of U1A00 state.