# Monolayer FeSe on SrTiO$_3$

## TL;DR

This review discusses the dramatic increase in superconducting transition temperature of monolayer FeSe on SrTiO$_3$, exploring experimental findings and potential microscopic mechanisms behind this enhancement.

## Contribution

It provides a comprehensive survey of experimental results and examines possible microscopic mechanisms for high-temperature superconductivity in monolayer FeSe on SrTiO$_3$.

## Key findings

- Significant $T_c$ enhancement in monolayer FeSe on SrTiO$_3$
- Contrasting evidence for phononic and magnetic/orbital pairing mechanisms
- Open questions about cooperative effects in electron pairing

## Abstract

Epitaxial engineering of solid-state heterointerfaces is a leading avenue to realizing enhanced or novel electronic states of matter. As a recent example, bulk FeSe is an unconventional superconductor with a modest transition temperature ($T_c$) of 9 K. When a single atomic layer of FeSe is grown on SrTiO$_3$, however, its $T_c$ can skyrocket by an order of magnitude to 65 K or 109 K. Since this discovery in 2012, efforts to reproduce, understand, and extend these findings continue to draw both excitement and scrutiny. In this review, we first present a critical survey of experimental measurements performed using a wide range of techniques. We then turn to the open question of microscopic mechanisms of superconductivity. We examine contrasting indications for both phononic (conventional) and magnetic/orbital (unconventional) means of electron pairing, and speculations about whether they could work cooperatively to boost $T_c$ in a monolayer of FeSe.