Doping-induced topological transition and enhancement of thermopower in the Dirac-semimetal system Cd$_{3-x}$Zn$_x$As$_2$

TL;DR

This study demonstrates how alloying Cd$_3$As$_2$ with Zn induces a topological phase transition and significantly enhances thermopower, leading to improved thermoelectric performance at room temperature.

Contribution

It reveals the doping-induced topological transition and its impact on thermoelectric properties in Cd$_{3-x}$Zn$_x$As$_2$, combining experimental and spectroscopic analyses.

Findings

Topological phase transition occurs around x~1.

Thermopower is strongly enhanced at higher x.

Thermoelectric figure of merit exceeds 0.3 at room temperature.

Abstract

Cd$_3$As$_2$ is one of the prototypical topological Dirac semimetals. Here, we manipulate the band inversion responsible for the emergence of Dirac nodes by alloying Cd$_3$As$_2$ with topologically trivial Zn$_3$As$_2$. We observe the expected topological phase transition around a Zn concentration of $x\sim 1$ while the carrier density monotonically decreases as $x$ is increased. For larger $x$, the thermoelectric figure of merit exhibits comparably large values exceeding 0.3 at room temperature, due to the combined effects of a strong enhancement of the thermopower, an only moderate increase of the resistivity, and a suppression of the thermal conductivity. Complementary quantum-oscillation data and optical-conductivity measurements allow to infer that the enhanced thermoelectric performance is due to a flattening of the band structure in the higher-$x$ region in Cd$_{3-x}$Zn$_x$As$_2$.