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

Abstract Increasing the upper critical field H_c2 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 H_c2 (~50 T). However, the strong anisotropy of 2D NbSe₂ suppresses the robustness of out-of-plane H_c2 (<5 T). To overcome this issue, we propose a synthetic approach to produce superconducting NbSe₂ films with a nearly isotropic large H_c2. 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 H_c2 values that exceed 20 T for arbitrary directions under externally applied magnetic fields. The isotropic nature of H_c2 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.