Insulator-metal-superconductor transition in the medium-entropy van der Waals compound <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>M</mml:mi><mml:mi mathvariant="normal">P</mml:mi><mml:msub><mml:mi>Se</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow><mml:mo> </mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mi>M</mml:mi><mml:mo>=</mml:mo><mml:mi>Fe</mml:mi><mml:mo>,</mml:mo><mml:mi>Mn</mml:mi><mml:mo>,</mml:mo><mml:mi>Cd</mml:mi><mml:mo>,</mml:mo><mml:mspace width="0.28em"/><mml:mtext>and</mml:mtext><mml:mspace width="0.28em"/><mml:mi>In</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:math> under high pressure
Chen Xu, Junjie Wang, Tianping Ying, Dajian Huang, Huiyang Gou, Qinghua Zhang, Yanchun Li, Hideo Hosono, Jiangang Guo, Xiaolong Chen
Abstract
$M\mathrm{P}{X}_{3}$ ($M=\mathrm{metals}$; $X=\mathrm{S}\phantom{\rule{0.28em}{0ex}}\mathrm{or}\phantom{\rule{0.28em}{0ex}}\mathrm{Se}$) represents a large family of van der Waals (vdW) materials featuring P-P dimers of $\ensuremath{\sim}2.3\phantom{\rule{0.16em}{0ex}}\AA{}$ separation. A dramatic alteration of its electrical transport properties, such as metal-insulator transition, has not been realized by intentional chemical doping and ionic intercalation. Here, we employ an entropy-enhancement strategy to successfully obtain a series of medium-entropy $M\mathrm{P}{\mathrm{Se}}_{3}$ $(M=\mathrm{Fe},\mathrm{Mn},\mathrm{Cd},\phantom{\rule{0.28em}{0ex}}\mathrm{and}\phantom{\rule{0.28em}{0ex}}\mathrm{In})$, in which the electrical and magnetic properties change 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 to 0.7 eV by this dissociation. Under external physical pressure up to $\ensuremath{\sim}50$ 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 $\mathrm{Fe}/\mathrm{MnP}{\mathrm{Se}}_{3}$. It leads to the recombination of ${\mathrm{P}}^{3\ensuremath{-}}$ with lone-pair electrons into a P-P dimer and the smallest bulk modulus of 28 GPa in $M\mathrm{P}{X}_{3}$. The medium-entropy $M\mathrm{P}{\mathrm{Se}}_{3}$ transitions from a spin-glass insulator to metal, and to superconductor, which is rarely observed in $M\mathrm{P}{X}_{3}$. Our findings highlight the P-P dimer as an indicator to probe diverse electronic structure and the effectiveness of entropy enhancement in materials science.