# Bi-2212/1T-TaS$_2$ Van der Waals junctions: Interplay of proximity induced high-$T_c$ superconductivity and CDW order

## TL;DR

This study investigates the interaction between high-temperature superconductivity and charge density waves at a Van der Waals interface, revealing proximity-induced superconductivity and its relation to CDW phases in layered materials.

## Contribution

It demonstrates proximity-induced high-$T_c$ superconductivity in 1T-TaS$_2$ via Van der Waals junctions with Bi-2212, highlighting the interplay with CDW order and identifying boson modes.

## Key findings

- Proximity-induced superconductivity with a 20 meV gap in 1T-TaS$_2$
- Presence of two boson modes linked to dip-hump features
- Superconductivity driven by coupling to a metastable metallic phase

## Abstract

Understanding the coexistence, competition and/or cooperation between superconductivity and charge density waves (CDWs) in the transition metal dichalcogenides (TMDs) is an elusive goal which, when realized, promises to reveal fundamental information on this important class of materials. Here, we use four-terminal current-voltage measurements to study the Van der Waals interface between freshly exfoliated flakes of the high-$T_{c}$ superconductor, Bi-2212, and the CDW-dominated TMD layered material, 1T-TaS$_{2}$. For highly transparent barriers, there is a pronounced Andreev reflection feature providing evidence for proximity-induced high-$T_{c}$ superconductivity in 1T-TaS$_{2}$ with a surprisingly large energy gap ($\sim 20\thinspace $meV) equal to half that of intrinsic Bi-2212 ($\sim 40\thinspace $meV). Our systematic study using conductance spectroscopy of junctions with different transparencies also reveals the presence of two separate boson modes, each associated with a "dip-hump" structure. We infer that the proximity-induced high-$T_c$ superconductivity in the 1T-TaS$_2$ is driven by coupling to the metastable metallic phase coexisting within the Mott commensurate CDW (CCDW) phase and associated with a concomitant change of the CCDW order parameter in the interfacial region.