Moiré confinement of strain-induced topological phase transitions in 2D Van der Waals Heterostructures

Understanding how to grow new materials with functional properties that are relevant for quantum information science is critical for new applications. Of specific importance to realizing new material paradigms such as topological superconductivity since they are predicted to host massless Majorana fermions which are predicted to robust against quantum decoherence. In this work, we demonstrate a route to stabilize possible topological superconductors using molecular beam epitaxy and interface engineering. Specifically, we target generating long-range moiré [MB1] reconstruction through lattice mismatch among two van der Waal materials, which we show can effectively be used to generate a strain-protected topological phase transition. First-principles density functional theory (DFT) calculations indicate both uniform and non-uniform strain change the topology of the Fermi surface of PdTe2. When substrate-induced strain is modulated by the moiré superlattice, the transition between regions of changing topology leads to a protected boundary mode, periodic with the moiré itself. Experimentally the strain-induced topological phase transition can be achieve by varying the lattice parameter of the X₂Y₃ substrate (X=Bi,Sb; Y=Se,Te). Here, the long-range moiré parameter appears prominently in the scanning tunneling microscopy (STM) data and strongly depends on lattice parameter of the topological substrate layer. In-situ STM, scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy enables the extraction of the macroscale electronic structure as well as the local strain and electronic properties, which allows for direct comparison with the DFT predicted local density of states and effects of the emergent long-range moiré pattern for various strain conditions.