Giant hysteretic magnetoresistance accompanying the Mott transition and spin-glass state in organic metal

TL;DR

This work investigates giant hysteretic magnetoresistance near the Mott metal–insulator transition in the organic metal $\\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br, where spin-glass frustration on a triangular lattice and spin–charge entanglement play central roles. The authors combine detailed low-temperature, high-pressure magnetotransport experiments with a qualitative theory and a simple toy model showing that Zeeman-field–driven reconfiguration of spin bonds can cause strong, isotropic magnetoresistance and slow relaxation near the MIT, beyond standard DMFT expectations. They find that metallic–insulating phase coexistence persists over a broad pressure range, with the giant effect strongest near $p_c\\approx 3$ kbar and at $T\\lesssim 10$ K, and that magnetic prehistory crucially affects resistance. As a result, they propose a new class of extreme magnetoresistance mechanisms in strongly correlated, frustrated systems, tied to spin–charge entanglement and glassy spin dynamics, with potential relevance to other Mott systems.

Abstract

The giant magnetoresistance with a huge hysteresis is observed in the organic metal k-(BEDTTTF)2Hg(SCN)2Br at low temperature in a pressure interval around 3 kbar of a width ~1 kbar. The hysteretic magnetoresistance is isotropic with respect to the direction of magnetic field, which excludes the orbital effect of magnetic field as its origin. The observed temperature and magnetic-field dependence of this hysteresis and of its relaxation time indicates the strong influence of spin-glass state on magnetoresistance. Although a quantitative theory of this effect, originating from strong electronic correlations, requires complex numerical calculations, we suggest its explanation and a simple model which qualitatively describes the observed magnetoresistance behavior and shows a strong charge-spin entanglement. The proposed effect suggests a new class of extreme magnetoresistance mechanisms.

Figures (10)

• Figure 1: Temperature dependences of the reduced interlayer resistance $R/R_{min}$ of the sample $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br at different pressures. $R_{min}$ - the resistance value at minimum on the $R(T)$ dependence in the region of structural phase transition.
• Figure 2: Sample magnetoresistance $(R(6T)-R(0))/R(0)$ at $T$=10$\,$K as function of pressure.
• Figure 3: $R(B)$ dependence at various temperatures and pressure $p=3.4\,$kbar.
• Figure 4: $R(B)$ dependences at various pressures. $T$=1.4$\,$K.
• Figure 5: $R(B)$ dependence at $p=3$ kbar and $T=0.5\,$K.