# Two-dimensional hole transport in ion-gated diamond surfaces: A brief review

## TL;DR

This review discusses advances in controlling two-dimensional hole gases on diamond surfaces via ionic gating, highlighting tunable transport, orientation-dependent properties, and potential superconductivity for future electronic applications.

## Contribution

It summarizes recent progress in ionic gating of diamond surfaces, emphasizing the control of transport properties and the theoretical prediction of field-induced superconductivity.

## Key findings

- Ionic gating effectively tunes conductivity, carrier density, and mobility.
- Surface orientation influences magnetotransport and spin-orbit coupling.
- Superconductivity may be induced in certain diamond surfaces by electric fields.

## Abstract

Electrically-conducting diamond is a promising candidate for next-generation electronic, thermal and electrochemical applications. One of the major obstacles towards its exploitation is the strong degradation that some of its key physical properties - such as the carrier mobility and the superconducting transition temperature - undergo upon the introduction of disorder. This makes the two-dimensional hole gas induced at its surface by electric field-effect doping particularly interesting from both a fundamental and an applied perspective, since it strongly reduces the amount of extrinsic disorder with respect to the standard boron substitution. In this short review, we summarize the main results achieved so far in controlling the electric transport properties of different field-effect doped diamond surfaces via the ionic gating technique. We analyze how ionic gating can tune their conductivity, carrier density and mobility, and drive the different surfaces across the insulator-to-metal transition. We review their strongly orientation-dependent magnetotransport properties, with a particular focus on the gate-tunable spin-orbit coupling shown by the (100) surface. Finally, we discuss the possibility of field-induced superconductivity in the (110) and (111) surfaces as predicted by density functional theory calculations.