# Pressure effect and Superconductivity in $\beta$-Bi$_4$I$_4$ Topological Insulator

## TL;DR

This study investigates how pressure influences the electronic properties and induces superconductivity in the topological insulator $eta$-Bi$_4$I$_4$, revealing a pressure-induced transition from charge density wave order to superconductivity.

## Contribution

It provides the first detailed analysis of pressure effects on $eta$-Bi$_4$I$_4$, demonstrating superconductivity emergence above 10 GPa and characterizing its transport properties under varying pressures.

## Key findings

- Charge density wave order shifts to higher temperatures under pressure.
- Superconductivity appears above 10 GPa with a transition temperature of 4.0 K.
- Pressure causes amorphization of $eta$-Bi$_4$I$_4$ without decomposition.

## Abstract

We report a detailed study of the transport coefficients of $\beta$-Bi$_4$I$_4$ quasi-one dimensional topological insulator. Electrical resistivity, thermoelectric power, thermal conductivity and Hall coefficient measurements are consistent with the possible appearance of a charge density wave order at low temperatures. Both electrons and holes contribute to the conduction in $\beta$-Bi$_4$I$_4$ and the dominant type of charge carrier changes with temperature as a consequence of temperature-dependent carrier densities and mobilities. Measurements of resistivity and Seebeck coefficient under hydrostatic pressure up to 2 GPa show a shift of the charge density wave order to higher temperatures suggesting a strongly one-dimensional character at ambient pressure. Surprisingly, superconductivity is induced in $\beta$-Bi$_4$I$_4$ above 10 GPa with of 4.0 K which is slightly decreasing upon increasing the pressure up to 20 GPa. Chemical characterisation of the pressure-treated samples shows amorphization of $\beta$-Bi$_4$I$_4$ under pressure and rules out decomposition into Bi and BiI$_3$ at room-temperature conditions.

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Source: https://tomesphere.com/paper/1702.04794