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arXiv · 1503.08887

Theory of excitations and dielectric response at a spin-orbital quantum critical point

Daniel Ish·Leon Balents
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Abstract

Despite possessing a local spin $2$ moment on the iron site and a Curie-Weiss temperature of $45K$, the A site spinel FeSc$_2$S$_4$ does not magnetically order down to 50mK. Previous theoretical work by Chen and Balents advanced an explanation for this observation in the form of the "$J_2$-$λ$" model which places FeSc$_2$S$_4$ close to a quantum critical point on the disordered side of a quantum phase transition between a Néel ordered phase and a "Spin-Orbital Liquid" in which spins and orbitals are entangled, quenching the magnetization. We present new theoretical studies of the optical properties of the $J_2$-$λ$ model, including a computation of the dispersion relation for the quasiparticle excitations and the form of the collective response to electric field. We argue that the latter directly probes a low energy excitation continuum characteristic of quantum criticality, and that our results reinforce the consistency of this model with experiment.

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Daniel Ish, Leon Balents. 2015-07-21. Theory of excitations and dielectric response at a spin-orbital quantum critical point. https://doi.org/10.1103/physrevb.92.094413

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