Hybrid magnet-superconductor heterostructures attract significant interest for their potential to host unconventional superconductivity, topological superconductivity, and Majorana physics. Transition-metal dihalides ($\mathrm{M}{X}_2, \mathrm{M}=\mathrm{transition}$ metal, $X=\mathrm{Cl}$, Br, I) are compelling magnetic candidates due to their novel magnetic structures and possible ferroelectricity. Here, we employ low-temperature scanning tunneling microscopy/spectroscopy to investigate the interfaces fabricated by growing helimagnet candidate ${\mathrm{CrBr}}_2$ on $s$-wave superconductor ${\mathrm{NbSe}}_2$. Our results reveal that the monolayer ${\mathrm{CrBr}}_2$ is insulating; the measured low-energy electronic states on it derive entirely from the ${\mathrm{NbSe}}_2$ substrate. The superconducting properties of $\mathrm{CrB}{\mathrm{r}}_2/\mathrm{NbS}{\mathrm{e}}_2$ are nearly identical to the bare ${\mathrm{NbSe}}_2$, manifested by the superconducting gap spectra and their temperature and magnetic-field dependence, as well as the spatial distribution and bound states of magnetic vortices. Furthermore, in-gap excitations appear only at the dirty edges of ${\mathrm{CrBr}}_2$ islands and are absent from clean edges, suggesting the lack of intrinsic edge states. Taken together, these findings establish the topologically trivial nature of the helimagnetic insulator/$s$-wave superconductor system $\mathrm{CrB}{\mathrm{r}}_2/\mathrm{NbS}{\mathrm{e}}_2$, attributable to the absence of interfacial superconducting proximity and weak magnetic coupling.

Close

PrevNext

View figure in article

• Superconductivity
• Topological superconductors
• Helimagnets
• Interfaces
• Superconductors
• Scanning tunneling microscopy