An unexplored MBE growth mode reveals new properties of superconducting NbN

TL;DR

This study explores a novel high-temperature MBE growth mode for NbN, revealing unprecedented surface smoothness, superconducting properties, and vortex imaging, which could impact superconductor fabrication and understanding.

Contribution

It introduces a new MBE growth regime for NbN at temperatures above 1000°C, uncovering unique physical properties and phenomena not observed in previous methods.

Findings

Persistent RHEED oscillations during growth

Atomically smooth NbN surfaces

Superconducting T_c exceeding 15 K and low resistivity

Abstract

Accessing unexplored conditions in crystal growth often reveals remarkable surprises and new regimes of physical behavior. In this work, performing molecular beam epitaxy of the technologically important superconductor NbN at temperatures greater than 1000$^\circ$C, higher than in the past, is found to reveal persistent RHEED oscillations throughout the growth, atomically smooth surfaces, normal metal resistivities as low as 37$\mu\Omega$-cm and superconducting critical temperatures in excess of 15 K. Most remarkably, a reversal of the sign of the Hall coefficient is observed as the NbN films are cooled, and the high material quality allows the first imaging of Abrikosov vortex lattices in this superconductor.