Anisotropy in Electronic and Magneto-transport of 2D superconductor NbSe$_2$

Abstract

This article reports the successful synthesis of single crystalline two-dimensional thin flakes of NbSe$_2$. The XRD pattern of the grown crystal ensured its crystallization in a single phase with a hexagonal structure. The EDAX endorsed the stoichiometry of the as grown sample. To study the vibrational modes, the Raman spectra were recorded, which exhibited the expected four Raman active modes. The resistance vs temperature measurement showed a well-established superconducting transition (Tc) at 7.3 K. The ZFC (Zero-Field Cooled) & FC (Field Cooled) magnetization curves, as well as the isothermal MH (Magnetization vs. field) measurements, have been performed for both in plane and out-of-plane H directions. Distinct anisotropy is observed in both magnetization and magneto-transport measurements with field direction, leading to different critical fields (Hc). Out-of-plane magneto-transport data hints towards the existence of a filamentary state. The density functional theory (DFT) has been used to study the band structure of NbSe$_2$. Although the bulk band structure confirmed metallic behavior, the same for mono-layers of NbSe$_2$ within the GGA+U framework showed a band gap of 1.17eV. The article addresses the anisotropy in the electronic and magneto-transport of 2D superconductor NbSe$_2$.