Three-dimensional networks of superconducting NbSe2 flakes with nearly isotropic large upper critical field

Chisato Ando,Yusuke Nakanishi,Taishi Takenobu,Jiang Pu,Yasumitsu Miyata,Mitsufumi Saito,Togo Takahashi

doi:10.1038/s41699-021-00210-7

Chisato Ando, Yusuke Nakanishi + Show 5 more

Open Access

https://doi.org/10.1038/s41699-021-00210-7

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Abstract

Increasing the upper critical field Hc2 in superconductors is one of the most significant requirements for superconducting applications. Two-dimensional (2D) noncentrosymmetric NbSe2 is a promising candidate because its pair breaking is protected by the spin-momentum locking effect, resulting in a giant in-plane Hc2 (~50 T). However, the strong anisotropy of 2D NbSe2 suppresses the robustness of out-of-plane Hc2 (<5 T). To overcome this issue, we propose a synthetic approach to produce superconducting NbSe2 films with a nearly isotropic large Hc2. Scalable selenization methods are tailored to create 3D superconducting networks in which 2D NbSe2 flakes are vertically aligned to the substrates. The angle-resolved magneto-transports reveal enhanced Hc2 values that exceed 20 T for arbitrary directions under externally applied magnetic fields. The isotropic nature of Hc2 is attributed to the averaging intrinsic anisotropy of NbSe2 through 3D structured films, which was determined by X-ray diffraction measurements. The proposed synthetic approach will provide a new method for creating practical superconductors that are robust against magnetic fields.

Highlights

The upper critical field, Hc2, which is a magnetic field that completely destroys superconductivity, is a key physical parameter when designing robust superconducting device applications[1,2]
Gao et al recently reported a similar approach to preparing superconducting NbSe2 films with atomic-level thickness and smoothness[25]. Their thicknesses are tunable by the growth conditions, 1Department of Applied Physics, Nagoya University, Nagoya, Japan. 2Department of Physics, Tokyo Metropolitan University, Tokyo, Japan. 3Department of Electrical Engineering, Tokyo Metropolitan University, Tokyo, Japan. 4These authors contributed : Togo Takahashi, Chisato Ando. ✉email: naka24ysk@gmail.com ; jiang.pu@nagoya-u.jp ; takenobu@nagoya-u.jp
The top schematics illustrate the film morphology based on its corresponding scanning electron microscopy (SEM) image

Summary

Introduction

The upper critical field, Hc2, which is a magnetic field that completely destroys superconductivity, is a key physical parameter when designing robust superconducting device applications[1,2]. Materials for which noncentrosymmetricity and spin–orbit interactions coexist, such as 2D superconducting NbSe2, may offer a higher-limit upper critical field strength and ameliorate the design constraints[3,4]. NbSe2 offers a possible robust superconductor against external magnetic fields, its significant anisotropy restricts its potential utility for future practical device designs. The versatility of superconducting NbSe2 can be expanded by realizing NbSe2 films with isotropic, large Hc2. These films would overcome the disparity issue between H||c2 and H⊥c2. One possible approach is to fabricate properly tailored 3D structures using nanoscale elements as building blocks[16,17,18]

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