van der Waals heterostructures based on atomically-thin superconductors

TL;DR

This paper demonstrates the fabrication and electrical characterization of van der Waals heterostructures using atomically-thin superconductors, revealing phase transitions and Andreev reflections, and discusses potential for exploring new emergent properties in 2D material combinations.

Contribution

It introduces a method to integrate 2D materials with superconductors in vdWHs and characterizes their electrical properties, including phase transitions and conductance behavior.

Findings

Detection of phase transitions like charge density wave and superconductivity.

Observation of resistance enhancement due to Andreev reflections.

Conductance behavior consistent with BCS theory.

Abstract

Van der Waals heterostructures (vdWHs) allow the assembly of high-crystalline two-dimensional (2D) materials in order to explore dimensionality effects in strongly correlated systems and the emergence of potential new physical scenarios. In this work, it is illustrated the feasibility to integrate 2D materials in-between 2D superconductors. Particularly, it is presented the fabrication and electrical characterization of vertical vdWHs based on air-unstable atomically-thin transition metal dichalcogenides formed by NbSe2/TaS2/NbSe2 stacks, with TaS2 being the insulator 1T-TaS2 or the metal 2H-TaS2. Phase transitions as 1T-TaS2 charge density wave and NbSe2 superconductivity are detected. An enhancement of the vdWH resistance due to Andreev reflections is observed below the superconducting transition temperature of the NbSe2 flakes. Moreover, in the NbSe2 superconducting state, the field and temperature dependence of the normalized conductance is analyzed within the Dynes' model and the overall behavior is consistent with the Bardeen-Cooper-Schrieffer theory. This vdWH approach can be extended to other 2D materials, such as 2D magnets or topological insulators, with the aim of exploring the new emergent properties that may arise from such combinations.