Upper critical magnetic field and multiband superconductivity in artificial superlattices of nano quantum wells
Phys. Rev. Materials 9, 074204 – Published 22 July, 2025
DOI: https://doi.org/10.1103/k2yd-vpbn
Abstract
Artificial superlattices (AHTS) composed of quantum building blocks with tunable superconducting critical temperature have been synthesized by engineering their nanoscale geometry using the Bianconi-Perali-Valletta (BPV) two-gap superconductivity theory. These quantum heterostructures consist of quantum wells made of superconducting, modulation-doped Mott insulators (S), confined by a metallic (N) potential barrier. The lattice geometry has been carefully engineered to induce the predicted Fano-Feshbach shape resonance between the gaps, near a topological Lifshitz transition. Here, we validate the BPV theory by providing compelling experimental evidence that AHTS samples, at the peak of the superconducting dome, exhibit resonant two-band, two-gap superconductivity. This is demonstrated by measuring the temperature dependence of the upper critical magnetic field, , in samples with superlattice periods nm and L/d ratios close to the magic value 2/3 (where L is the thickness of the superconducting layer and is the superlattice period). The data reveal the predicted upward concavity in and a characteristic kink in the coherence length as a function of temperature, confirming the predicted two-band superconductivity with Fermi velocity ratio and significant pair-exchange term among the two condensates.
