Moiré engineering of Cooper-pair density modulation states.

Abstract

Cooper-pair density modulation (CPDM) states are superconducting phases in which the order parameter varies periodically in real space without breaking translational symmetry^1-3. Moiré superlattices in layered materials^4-18 have recently emerged as powerful platforms for engineering charge density with tunable lattice symmetry, offering a new route to creating and controlling CPDM states. Here we demonstrate moiré-induced CPDM states in a bilayer heterostructure formed by epitaxially stacking one quintuple layer (1QL) of topological insulator Sb₂Te₃ on a six-unit-cell (6UC) antiferromagnetic FeTe layer. Scanning tunnelling microscopy and spectroscopy (STM/S) measurements reveal a moiré superlattice formed between the hexagonal tellurium lattice of Sb₂Te₃ and the square tellurium lattice of FeTe, which spatially modulates the two superconducting gaps of the 1QL Sb₂Te₃/6UC FeTe bilayer. Our Josephson STM/S measurements provide direct real-space imaging of the CPDM states with a wavelength corresponding to the periodicity of the moiré superlattice. By substituting Sb₂Te₃ with Bi₂Te₃, we achieve control over both the periodicity and magnitude of the CPDM states. Our work demonstrates an epitaxial strategy for synthesizing moiré superlattices from materials with different crystal symmetries and reveals a new mechanism for engineering CPDM states in designer bilayer heterostructures.