Griffiths-like phase close to the Mott transition

Abstract

We explore the coexistence region in the vicinity of the Mott critical end point employing a compressible cell spin-$1/2$ Ising-like model. We analyze the case for the spin-liquid candidate $\kappa$-(BEDT-TTF)${}_2$Cu${}_2$(CN)${}_3$, where close to the Mott critical end point metallic puddles coexist with an insulating ferroelectric phase. Our results are fourfold: $i$) a universal divergent-like behavior of the Grüneisen parameter upon crossing the first-order transition line; $ii$) based on scaling arguments, we show that within the coexistence region, for $any$ system close to the critical point, the relaxation time is entropy-dependent; $iii$) we propose the electric Grüneisen parameter ${\Gamma }_E$, which quantifies the electrocaloric effect; $iv$) we identify the metallic/insulating coexistence region as an electronic Griffiths-like phase. Our findings suggest that ${\Gamma }_E$ governs the dielectric response close to the critical point and that an electronic Griffiths-like phase emerges in the coexistence region.

7 pages, 3 figures (suppl. material upon request). To appear in Journal of Applied Physics