Coexisting Charge Density Waves in Twisted Bilayer\nNbSe₂

Abstract

Twisted bilayers\nof 2D materials have emerged as a tunable platform\nfor studying broken symmetry phases. While most interest has been\nfocused toward emergent states in systems whose constituent monolayers\ndo not feature broken symmetry states, assembling monolayers that\nexhibit ordered states into twisted bilayers can also give rise to\ninteresting phenomena. Here, we use first-principles density-functional\ntheory calculations to study the atomic structure of twisted bilayer\nNbSe₂ whose constituent monolayers feature a charge density\nwave. We find that different charge density wave states coexist in\nthe ground state of the twisted bilayer: monolayer-like 3 × 3\ntriangular and hexagonal charge density waves are observed in low-energy\nstacking regions, while stripe charge density waves are found in the\ndomain walls surrounding the low-energy stacking regions. These predictions,\nwhich can be tested by scanning tunneling microscopy experiments,\nhighlight the potential to create complex charge density wave ground\nstates in twisted bilayer systems.