Pressure-Induced Metallization in Iron-Based Ladder Compounds Ba$_{1-x}$Cs$_x$Fe$_2$Se$_3$

TL;DR

This study investigates how applying high pressure induces metallic behavior in iron-based ladder compounds Ba$_{1-x}$Cs$_x$Fe$_2$Se$_3$, revealing different insulating mechanisms in parent and doped samples.

Contribution

It provides the first high-pressure resistivity data showing pressure-induced metallization in Ba$_{1-x}$Cs$_x$Fe$_2$Se$_3$ and distinguishes the different origins of insulating states.

Findings

Metallic behavior confirmed in x=0.25 and 0.65 samples above 11.3 and 14.4 GPa.

No metallic conductivity observed in parent compounds up to 30 GPa.

Insulating states are due to Mott and Anderson mechanisms, respectively.

Abstract

Electrical resistivity measurements have been performed on the iron-based ladder compounds Ba$_{1-x}$Cs$_x$Fe$_2$Se$_3$ ($x$ = 0, 0.25, 0.65, and 1) under high pressure. A cubic anvil press was used up to 8.0 GPa, whereas further higher pressure was applied using a diamond anvil cell up to 30.0 GPa. Metallic behavior of the electrical conductivity was confirmed in the $x$ = 0.25 and 0.65 samples for pressures greater than 11.3 and 14.4 GPa, respectively, with the low-temperature $\log T$ upturn being consistent with weak localization of 2D electrons due to random potential. At pressures higher than 23.8 GPa, three-dimensional Fermi-liquid-like behavior was observed in the latter sample. No metallic conductivity was observed in the parent compounds BaFe$_2$Se$_3$ ($x $ = 0) up to 30.0 GPa and CsFe$_2$Se$_3$ ($x$ = 1) up to 17.0 GPa. The present results indicate that the origins of the insulating ground states in the parent and intermediate compounds are intrinsically different; the former is a Mott insulator, whereas the latter is an Anderson insulator owing to the random substitution of Cs for Ba.