Nanoscale Investigations of High-Temperature Superconductivity in a Single Atomic Layer of Iron Selenide

Abstract

The potential of interface engineering to enhance electronic properties is exemplified in a single atomic layer of FeSe grown on SrTiO$_3$, which exhibits an order-of-magnitude increase in its superconducting transition temperature ($T_c$ up to 110 K) compared to bulk ($T_c$ = 8 K). Since this discovery in 2012, efforts to reproduce, understand, and extend this finding continue to draw both excitement and scrutiny. In this thesis, we report the use of a combined molecular beam epitaxy (MBE) and scanning tunneling microscopy (STM) system to grow and image films of superconducting FeSe/SrTiO$_3$. In particular, we investigate and harness atomic defects in as-grown films to derive microscopic insights in two directions. First, we image quasiparticle interference (QPI) patterns generated around defects in order to reconstruct the electronic structure of the unperturbed system, and uncover pieces of the puzzle of high-$T_c$ superconductivity in a monolayer of FeSe. Second, we characterize the atomic structure of defects using density functional theory (DFT), with possible implications on film quality and nanostructuring.