Electronic and magnetic characterization of epitaxial CrBr$_3$ monolayers

TL;DR

This study demonstrates the synthesis and characterization of a superconductor-magnet heterostructure combining NbSe₂ and CrBr₃ monolayers, revealing preserved ferromagnetism and proximity effects influencing superconductivity.

Contribution

It introduces a direct MBE synthesis method for NbSe₂/CrBr₃ heterostructures and confirms ferromagnetic ordering and proximity effects through experimental and theoretical analysis.

Findings

CrBr₃ monolayer retains ferromagnetic order with out-of-plane anisotropy

Superconducting gap of NbSe₂ is slightly reduced in the heterostructure

Vortex lattice formation observed under magnetic field

Abstract

The ability to imprint a given material property to another through proximity effect in layered two-dimensional materials has opened the way to the creation of designer materials. Here, we use molecular-beam epitaxy (MBE) for a direct synthesis of a superconductor-magnet hybrid heterostructure by combining superconducting niobium diselenide (NbSe$_2$) with the monolayer ferromagnetic chromium tribromide (CrBr$_3$). Using different characterization techniques and density-functional theory (DFT) calculations, we have confirmed that the CrBr$_3$ monolayer retains its ferromagnetic ordering with a magnetocrystalline anisotropy favoring an out-of-plane spin orientation. Low-temperature scanning tunneling microscopy (STM) measurements show a slight reduction of the superconducting gap of NbSe$_2$ and the formation of a vortex lattice on the CrBr$_3$ layer in experiments under an external magnetic field. Our results contribute to the broader framework of exploiting proximity effects to realize novel phenomena in 2D heterostructures.