Band-selective Plasmonic Polaron in Thermoelectric Semimetal Ta$_2$PdSe$_6$ with ultra-high power factor

TL;DR

This study uncovers the electronic structure of Ta$_2$PdSe$_6$, revealing unique plasmonic polaron features and chain-dependent scattering effects that contribute to its high thermoelectric power factor, opening new avenues in semimetal-based thermoelectrics.

Contribution

It provides the first detailed ARPES analysis of Ta$_2$PdSe$_6$, highlighting plasmonic polaron effects and chain-specific electron interactions in a thermoelectric semimetal.

Findings

Observation of plasmonic polaron replica structures.

Identification of asymmetric scattering effects in atomic chains.

High thermoelectric power factor in a semimetal.

Abstract

We report the electronic structure of the thermoelectric semimetal Ta$_2$PdSe$_6$ with a large thermoelectric power factor and giant Peltier conductivity by means of angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra reveal the coexistence of a sharp hole band with a light electron mass and a broad electron band with a relatively heavy electron mass, which originate from different quasi-one-dimensional (Q1D) chains in Ta$_2$PdSe$_6$. Moreover, the electron band around the Brillouin-zone (BZ) boundary shows a replica structure with respect to the energy originating from plasmonic polarons due to electron-plasmon interactions. The different scattering effects and interactions in each atomic chain lead to asymmetric transport lifetimes of carriers: a large Seebeck coefficient can be realized even in a semimetal. Our findings pave the way for exploring the thermoelectric materials in previously overlooked semimetals and provide a new platform for low-temperature thermoelectric physics, which has been challenging with semiconductors.