Insulator-metal-superconductor transition in medium-entropy van der Waals compound MEPSe3 (ME=Fe, Mn, Cd, and In) under high pressures

TL;DR

This study demonstrates that entropy-enhancement can induce insulator-metal-superconductor transitions in medium-entropy MPX3 compounds under high pressure, revealing new pathways to tune electronic properties in van der Waals materials.

Contribution

It introduces an entropy-enhancement strategy to synthesize medium-entropy MPX3 compounds and explores their pressure-induced electronic phase transitions, including superconductivity.

Findings

Pressure causes a giant collapse in c-axis, affecting electronic structure.

P-P dimer dissociation increases band gap and alters magnetic properties.

Transition from insulator to superconductor observed under high pressure.

Abstract

MPX3 (M=metals, X=S or Se) represents a large family of van der Waals (vdW) materials featuring with P-P dimers of ~2.3 {\AA} separation. Its electrical transport property and structure can hardly be tuned by the intentional chemical doping and ionic intercalation. Here, we employ an entropy-enhancement strategy to successfully obtain a series of medium-entropy compounds MEPSe3 (ME=Fe, Mn, Cd and In), in which the electrical and magnetic properties changed simultaneously. Lone-pair electrons of P emerge due to the dissociation of the dimers as evidenced by a 35% elongation in the P-P interatomic distance. The band gap widens from 0.1 eV to 0.7 eV by this dissociation. Under external physical pressure up to ~50 GPa, a giant collapse of up to 15% in the c-axis happens, which is in contrast to the in-plane shrinkage of their counterparts Fe/MnPSe3. It leads to the recombination of P3- with lone pair electrons into a P-P dimer and the smallest bulk modulus of 28 GPa in MPX3. The MEPSe3 transits from a spin-glass insulator to metal, and to superconductor, which is rarely observed in the MPX3. Our findings highlight the P-P dimer as an indicator to probe diverse electronic structure and the effectiveness of entropy-enhancement in materials science.