Interplay of dipoles and spins in κ−(BEDT−TTF)2X , where X=Hg(

Abstract

We combine first-principles density functional calculations with empirical relationships for the Coulomb interactions in the monomer model of κ-(BEDT-TTF) 2 X. This enables us to calculate the parameters for the model of coupled dipolar and spin degrees of freedom proposed by Hotta [Phys. Rev. B 82, 241104 (2010)], and Naka and Ishihara [J. Phys. Soc. Jpn. 79, 063707 (2010)]. In all materials studied, retaining only the largest interactions leads to a transverse-field Ising model of the dipoles. This quantifies, justifies, and confirms recent claims that the dipoles are of crucial importance for understanding these materials. We show that the competition between two effects are responsible for a range of behaviors found in the dipoles in different κ-(BEDT-TTF) 2 X salts. (i) The intradimer hopping, t b1 , which gives rise to the transverse field in the Ising model for the dipoles (H T = 2t b1), is between a third and a tenth smaller in the mercuric materials than for the mercury-free salts. (ii) The Ising model of dipoles is in the quasi-one-dimensional limit for the mercuric salts, but quasi-two-dimensional (between the square and isotropic triangular limits) for the mercury-free materials. Thus, the dimensionless critical fields will be quite different in the two sets of materials. Effect (ii) is much larger than effect (i). Simple explanations of both effects based on the band structures of the different salts are given. We show that dipolar order and even short-range dipolar correlations have a profound impact on the nature of the interdimer magnetic (superexchange) interactions. For example, dipole crystallization drives the materials toward quasi-one-dimensional magnetic interactions, which could be important for understanding the spin liquids found in some of these materials.

Anomalously field-susceptible spin soft-matter emerging in an electric-dipole liquid candidate

“…At the same time, the local moments grow as characterized by a Curie-Weiss (C-W) temperature, ∼25 K [the inset of Fig. 3(c)], which is consistent with the first-principles calculations that project an exchange interaction of ∼ 10 2 K between spins on ET molecules [31] or ET dimers [35]. Thus, in the temperature range of 20-50 K, the spin clusters gradually take shape with middle-scale staggered spin configurations developed.…”

Selective observation of spin and charge dynamics in an organic superconductor λ−(BETS)2GaCl4 using Ga

“…In fact, we succeeded in detecting the charge anomaly in κ-(ET) 2 Cu 2 (CN) 3 by 63,65 Cu-NQR experiments [10]. This technique will greatly contribute to elucidating the physical properties of systems in which the charge degree of freedom is important, e.g., β -(ET) 4 [(H 3 O)Ga(C 2 O 4 ) 3 ] • C 6 H 5 NO 2 [47,48] and κ-(ET) 2 Hg(SCN) 2 Y (Y = Cl, Br) [5][6][7][8], where 69,71 Ga, 35,37 Cl, and 79,81 Br NMR experiments will be appropriate probes.…”

“…Accordingly, electronic spin plays a major role in the dimer-Mott system; however, physical properties originating from the charge degree of freedom have also been recently observed. For example, dielectric anomalies in many types of κ-type organic insulators [2][3][4], charge ordering and a quantum dipole liquid in κ-(ET) 2 Hg(SCN) 2 Y (Y = Cl, Br) [5][6][7][8], and a mysterious physical property called the 6 K anomaly in the quantum-spin-liquid candidate κ-(ET) 2 Cu 2 (CN) 3 [9,10], have been reported. These phenomena have attracted considerable attention from the perspective of multiferroicity.…”

Spin Vortex Crystal Order in Organic Triangular Lattice Compound

“…With increasing J , the spins completely tilt towards a common plane, leading to the coplanar spin-vortex crystal (SVC) [7,11]. κ-Mn differs from other organics primarily in terms of J /J ≈ (t /t) 2 , which can been estimated as ∼ 0.2−0.35 for κ-Cl [48,[52][53][54], ∼ 0.8 − 1.2 for κ-Cu [48,52,53,55], and ∼ 2 for κ-Mn. Recent DMRG studies [17,19] of the Hubbard model have found a similar phase diagram, enriched by QSL states.…”