Temperature dependence of structural and electronic properties of the spin-liquid candidateκ-(BEDT-TTF)2Cu2(CN)

Harald O. Jeschke

¹

,

M. de Souza

²

,

Roser Valentí

³

et al.

Abstract

We investigate the effect that the temperature dependence of the crystal structure of a two dimensional organic charge-transfer salt has on the low-energy Hamiltonian representation of the electronic structure. For that, we determine the crystal structure of κ-(BEDT-TTF)2Cu2(CN)3 for a series of temperatures between T = 5 K and 300 K by single crystal X-ray diffraction and analyze the evolution of the electronic structure with temperature by using density functional theory and tight binding methods. We find a considerable temperature dependence of the corresponding triangular lattice Hubbard Hamiltonian parameters. We conclude that even in the absence of change of symmetry, the temperature dependence of quantities like frustration and interaction strength can be significant and should be taken into account.

Power-law dependence of the optical conductivity observed in the quantum spin-liquid compoundκ-(BEDT-TTF)2Cu2(CN)Elsässer1, Wu2, Dressel3 et al. 2012Phys. Rev. BSelf Cite

“…The transition between the Hubbard bands peaks around 2100 cm −1 while the intra-dimer excitations center around 3000 cm −1 (more pronounced for E b); this is marginally lower in energy than for κ-Cl. 26 Calculations by density functional theory and tight binding methods yield an intra-dimer transfer integral t d ≈ 170 meV with a slight increase upon cooling, 21 in accord with our observations. The Hubbard band, on the other hand, shifts to lower energies as the temperature is reduced.…”

“…The inter-dimer transfer integrals are labeled by t and t ′ and can be calculated by tight-binding studies of molecular orbitals or ab-initio calculations. 12,13,21 With the intra-dimer transfer integral t d ≈ 0.2 eV 16,22 and the onsite Coulomb repulsion U ≈ 2t d , 23 one obtains at ambient conditions U/t = 5.5 with the ratio of the two inter-dimer transfer integrals t ′ /t ≈ 0.44 in the case of the Mott insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl. For the spin-liquid compound κ-(BEDT-TTF)2Cu2(CN)3, the effective Hubbard U is larger (U/t = 7.3) and most important the transfer integrals t ′ /t = 0.83 are very close to equality.…”

Anisotropic charge dynamics in the quantum spin-liquid candidateκ−(BEDT-TTF)2Cu2(CN)3

“…From density functional theory calculations we know that at room temperature the ratio of interdimer transfer integrals t ′ /t = 0.83 are very close to unity. 11,14,15 Hence, the system is described as a halffilled band with strong spin frustration that prohibits magnetic ordering and suggests a quantum spin-liquid state. In spite of a great deal of experimental and theoretical studies, no consistent picture of the spin-liquid state can be drawn and no definite understanding has been reached yet on the ground state in κ-CN.…”

“…Accordingly, the structural analysis based on the high P 2 1 /c symmetry assumes a 50% carbon and 50% nitrogen distribution on these two atomic positions. 13,14 While the average structure with P 2 1 /c symmetry can be retained, locally the symmetry is broken.…”

Electronic properties of Fabre charge-transfer salts under various temperature and pressure conditions

“…[5][6][7] The primary avenue of the present work is to understand the microscopic origin of the close competition between the different phases in these compounds as a function of chemical and external pressure as well as temperature. For that, we performed ab initio density functional theory (DFT) 8,9 and model Hamiltonian calculations for several Fabre CT salts whose crystal structures were determined at different temperatures and pressures and investigated variations of their electronic properties with temperature and pressure. 10 By computing the real-space overlaps of Wannier orbitals for the bands near the Fermi level, we parameterize a two-band tight-binding Hamiltonian model for the various systems and examine the differences in their electronic hopping parameters.…”