# Enhanced Seebeck coefficient by a filling-induced Lifshitz transition in KxRhO2

## TL;DR

This study reveals that in K$_{x}$RhO$_{2}$, a filling-induced Lifshitz transition at a critical composition enhances the Seebeck coefficient, indicating a topological change in the Fermi surface that affects thermoelectric properties.

## Contribution

It provides experimental evidence of a Lifshitz transition in K$_{x}$RhO$_{2}$ and links it to anomalous thermoelectric behavior, a novel insight in layered rhodium oxides.

## Key findings

- Seebeck coefficient is anomalously enhanced below x=0.64
- A critical composition x* ≈ 0.65 marks a change in transport behavior
- Filling-induced Lifshitz transition causes topological change in Fermi surface

## Abstract

We have systematically measured the transport properties in the layered rhodium oxide K$_{x}$RhO$_{2}$ single crystals ($0.5\lesssim x \lesssim 0.67$), which is isostructural to the thermoelectric oxide Na$_{x}$CoO$_{2}$. We find that below $x = 0.64$ the Seebeck coefficient is anomalously enhanced at low temperatures with increasing $x$, while it is proportional to the temperature like a conventional metal above $x=0.65$, suggesting an existence of a critical content $x^{*} \simeq 0.65$. For the origin of this anomalous behavior, we discuss a filling-induced Lifshitz transition, which is characterized by a sudden topological change in the cylindrical hole Fermi surfaces at the critical content $x^*$.