Quantum Capacitance of a Topological Insulator-Ferromagnet Interface

TL;DR

This paper investigates how hexagonal warping and in-plane magnetization affect the quantum capacitance of a topological insulator thin film under magnetic fields, revealing monotonic and oscillatory behaviors with energy.

Contribution

It provides a detailed analysis of quantum capacitance modifications due to hexagonal warping and in-plane magnetization, identifying conditions where magnetization effects vanish.

Findings

Hexagonal warping decreases quantum capacitance monotonically with energy.

In-plane magnetization causes oscillations in quantum capacitance.

A specific parameter relation nullifies magnetization effects on capacitance.

Abstract

We study the quantum capacitance in a topological insulator thin film system magnetized in the in-plane direction in the presence of an out-of-plane magnetic field and hexagonal warping. To first order, the modification in quantum capacitance due to hexagonal warping compared to the clean case, where both the in-plane magnetization and hexagonal warping are absent, is always negative, and increases in magnitude monotonically with the energy difference from the charge neutrality point. In contrast, the change in the quantum capacitance due to in-plane magnetization oscillates with the energy in general, except when a certain relation between the inter-surface coupling, out of plane Zeeman energy splitting and magnetic field strength is satisfied. In this special case, the quantum capacitance remains unchanged by the in-plane magnetization for all energies.