Power-law dependence of the optical conductivity observed in the quantum spin-liquid compoundκ-(BEDT-TTF)2Cu2(CN)

S. Elsässer

¹

,

Dan Wu

²

,

Martin Dressel

³

et al.

Magneto-optical Faraday effect in spin-liquid candidates

“…We calculate the Hall conductivity of one layer σ xy ∼ 4 × 10 (1), we find an estimate of the Faraday rotation to be about 0.2 mrad for a 30 μm sample using a dielectric constant of ∼ 4 [18]. Extrapolating from IR data, we estimate that there should be reasonable transmission through this thickness at 1 THz [2]. Recent experiments have resolutions of down to 30 μrad, so this effect should be within experimental limitations [19].…”

“…After making this substitution into the spin Hamiltonian and introducing an integration over an auxiliary scalar field to enforce the constraint [13], we apply a mean field treatment of the resulting four-Fermi term to get the mean field Hamiltonian (2) with χ ij = f † i f j and λ enforcing the constraint of one fermion per site on average. We can interpret f † as the creation operator of fermionic spinons.…”

“…Recent experiments in the spin-liquid candidates herbertsmithite and κ-(ET) 2 Cu 2 (CN) 3 have observed a power law in the conductivity below the Mott gap [1,2]. One of the potential explanations of this conductivity is optical excitations of spinons in a spin-liquid state [3,4].…”

“…The quasi-two-dimensional materials κ-(ET) 2 Cu 2 (CN) 3 and herbertsmithite are both well described by half-filled Hubbard models. In the organic κ-(ET) 2 Cu 2 (CN) 3 the spins form a nearly isotropic triangle lattice and it is just on the insulating side of the Mott transition [5].…”

“…In the organic κ-(ET) 2 Cu 2 (CN) 3 the spins form a nearly isotropic triangle lattice and it is just on the insulating side of the Mott transition [5]. It is believed to have a spin-liquid phase with spinon excitations forming a Fermi surface [6,7].…”