[Paper Review] Proximity-Induced Superconductivity with Subgap Anomaly in Type II Weyl Semi-Metal WTe2

Qiao Li, He, Chaocheng+17 more|arXiv (Cornell University)|Nov 15, 2018

2D Materials and ApplicationsMaterials Science3 citations

TL;DR

This study demonstrates proximity-induced superconductivity in thin flakes of type-II Weyl semimetal WTe2 via a van der Waals heterostructure with NbSe2, revealing a long coherence length along the c-axis and an anomalous subgap resistance oscillation during the superconducting-to-normal transition. Theoretical modeling confirms this subgap anomaly as an intrinsic feature of WTe2's superconducting state, advancing its potential for topological quantum computing applications.

ABSTRACT

Due to the non-trivial topological band structure in type-II Weyl semimetal Tungsten ditelluride (WTe2), unconventional properties may emerge in its superconducting phase. While realizing intrinsic superconductivity has been challenging in the type-II Weyl semimetal WTe2, proximity effect may open an avenue for the realization of superconductivity. Here, we report the observation of proximity-induced superconductivity with a long coherence length along c axis in WTe2 thin flakes based on a WTe2/NbSe2 van der Waals heterostructure. Interestingly, we also observe anomalous oscillations of the differential resistance during the transition from superconducting to normal state. Theoretical calculations show excellent agreement with experimental results, revealing that such a sub-gap anomaly is the intrinsic property of WTe2 in superconducting state induced by the proximity effect. Our findings enrich the understanding of superconducting phase of type-II Weyl semimetals, and pave the way for their future applications in topological quantum computing.

Motivation & Objective

• To explore superconducting properties in type-II Weyl semimetal WTe2, which exhibits non-trivial topological band structure.
• To overcome the challenge of realizing intrinsic superconductivity in WTe2 by employing proximity effect via van der Waas heterostructures.
• To investigate the emergence of unconventional superconducting behavior, particularly subgap anomalies, in WTe2 under proximity coupling.
• To establish a link between the observed subgap oscillations and the intrinsic electronic structure of WTe2 in the superconducting state.
• To provide a foundation for future applications of WTe2 in topological quantum computing.

Proposed method

• Fabrication of WTe2/NbSe2 van der Waals heterostructures using mechanical exfoliation and transfer techniques.
• Measurement of differential resistance in the WTe2 flake to probe the superconducting transition and detect subgap anomalies.
• Use of angle-resolved photoemission spectroscopy (ARPES) and theoretical modeling to analyze the band structure and proximity-induced superconductivity.
• Application of BCS-based theoretical calculations to simulate the proximity effect and reproduce the observed subgap oscillations.
• Analysis of the coherence length along the c-axis using transport measurements and comparison with theoretical predictions.
• Correlation of experimental resistance oscillations with the topological nature of WTe2's electronic structure.

Experimental results

Research questions

• RQ1 Can proximity-induced superconductivity be realized in WTe2 thin flakes through a van der Waals heterostructure with NbSe2?
• RQ2 What is the nature and origin of the anomalous subgap resistance oscillations observed during the superconducting-to-normal transition in WTe2?
• RQ3 How does the coherence length in WTe2 compare along the c-axis, and what does it imply about the superconducting pairing symmetry?
• RQ4 Is the subgap anomaly a consequence of the WTe2's topological band structure or an artifact of the heterostructure interface?
• RQ5 Can the observed phenomena be explained by theoretical models of proximity-induced superconductivity in topological semimetals?

Key findings

• Proximity-induced superconductivity is successfully achieved in WTe2 thin flakes via coupling to NbSe2 in a van der Waals heterostructure.
• A long coherence length along the c-axis is observed, indicating strong superconducting pairing and potential for topological superconductivity.
• Anomalous oscillations in differential resistance are detected in the subgap region during the superconducting-to-normal transition, which are not typical of conventional superconductors.
• Theoretical calculations show excellent agreement with experimental data, confirming that the subgap anomaly is an intrinsic property of WTe2 in the superconducting state due to the proximity effect.
• The observed phenomena are attributed to the interplay between the non-trivial topological band structure of WTe2 and proximity-induced superconductivity.
• The findings suggest that WTe2 is a promising platform for hosting Majorana zero modes and advancing topological quantum computing.