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

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 "$J_2$-$\lambda$" 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 $J_2$-$\lambda$ 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.

9 pages, 5 figures

References in corpus (3)

• A Spin-Orbital Singlet and Quantum Critical Point on the Diamond Lattice: FeSc2S4
• Spin-orbiton and quantum criticality in FeSc2S4
• Comparative study of FeCr2S4 and FeSc2S4: Spinels with orbitally active A site

Cited by in corpus (5)

• Antiferromagnetic and Orbital Ordering on a Diamond Lattice Near Quantum Criticality
• Terahertz Spin-Orbital Excitations in the paramagnetic state of multiferroic Sr${}_2$FeSi${}_2$O${}_7$
• Magnetic field dependence of excitations near spin-orbital quantum criticality
• Quantum Loop States in Spin-Orbital Models on the Honeycomb Lattice
• Absence of nematic ordering transition in a diamond lattice: Application to $FeS{c}_2{S}_4$