Investigation of the upper critical field in artificially engineered Nb/V/Ta superlattices

Abstract

Abstract Artificially engineered superlattice offers highly flexible control of the quantized electronic state by manipulating its lattice structure. We fabricated artificially engineered superlattices [Nb/V/Ta] n as a new class of superconducting superlattices and investigated the upper critical field H c2 in terms of the structural difference. It is found that the out-of-plane upper critical field H c 2 ⊥ significantly increases compared with that of a Nb single layer film as the thickness of the constituent Nb, V, and Ta layers becomes thin. In the case of the superlattice [Nb/V/Ta] n , the H c 2 ⊥ is basically governed by the orbital pair-breaking effect rather than Pauli pair-breaking effect and increases only when the crystalline size of the superlattice decreases by the insertion of V layers. Thus, we conclude that the shortening of the coherence length of Cooper pairs due to the crystalline disorder predominantly contributes to the increase of the H c 2 ⊥ in the superlattice [Nb/V/Ta] n .