Anomalous Lattice Response at the Mott Transition in a Quasi-2D Organic Conductor

Abstract

Discontinuous changes of the lattice parameters at the Mott metal-insulator transition are detected by high-resolution dilatometry on deuterated crystals of the layered organic conductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br. The uniaxial expansivities uncover a striking and unexpected anisotropy, notably a zero effect along the in-plane c axis along which the electronic interactions are relatively strong. A huge thermal expansion anomaly is observed near the end point of the first-order transition line enabling us to explore the critical behavior with very high sensitivity. The analysis yields critical fluctuations with an exponent alpha approximately 0.8+/-0.15 at odds with the novel criticality recently proposed for these materials [Kagawa et al., Nature (London) 436, 534 (2005)]. Our data suggest an intricate role of the lattice degrees of freedom in the Mott transition for the present materials.

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. B

“…Pressure dependent investigations on κ-Cl showed that the bandwidth-controlled Mott criticality involves critical fluctuations in charge, 58 spin, 59 and lattice. 60,61 Nothing like that is known for the spin-liquid compound κ-CN for the intermediate temperature range. While this issue can be clarified by further experimental studies, considerable theoretical work is required in order to describe the power-law behavior the dimer Mott insulator with a quantum spin-liquid state, in the low-frequency limit as well as in the far-infrared range.…”

Photoinduced Phase Transitions in α-, θ-, and κ-type ET Salts: Ultrafast Melting of the Electronic Ordering

“…Such ferroelectricity induced by the electronic origin (electronic ferroelectricity [27][28][29]) is advantageous for high speed switching or modulation of dielectric properties. Figure 5c are Dimer-Mott (DM) insulators [30][31][32][33][34][35]. In κ-type ET salts, the ET layer has a unit comprising a pair of ET molecules (ET dimer).…”

Magnetic field induced lattice effects in a quasi-two-dimensional organic conductor close to the Mott metal-insulator transition

“…The first-order character of the transition was confirmed by the observation of hysteresis in both R(T ) and relative length changes ( l/l) around T MI for another crystal. 7 The drop of the resistance at T c = 11.6 K, accompanied by a tiny kink (indicated by the arrow) in α b (T ), are signatures of a percolative SC in minor portions of the sample volume coexisting with the AFI state (see, e.g., Refs. 27 and 28).…”

“…24,26 Upon further cooling, a second anomaly around T P = 30 K is observed. This feature has been assigned to critical fluctuations associated with the second-order critical end point of the first-order line, 7,18 indicated by the solid triangle in Fig. 1.…”

“…16 Furthermore, from 12 C NMR studies evidence for phase separation into metallic/superconducting and magnetic phases in κ-D8-Br was reported in the literature. 17 From temperature-dependent measurements of the coefficient of thermal expansion, the role of the lattice degrees of freedom for the Mott transition 7 and the Mott criticality 18 were studied. The latter results were found to be at odds with the Mott criticality derived from conductivity 19 and NMR 20 studies on pressurized κ-Cl.…”