Coexisting charge density waves in twisted bilayer NbSe2

TL;DR

This study uses first-principles calculations to reveal coexisting charge density wave states in twisted bilayer NbSe2, showing complex patterns that could influence superconductivity and be verified experimentally.

Contribution

It demonstrates the coexistence of multiple charge density wave states in twisted bilayer NbSe2, a novel finding in twisted 2D materials with ordered monolayers.

Findings

Coexistence of monolayer-like 3x3 charge density waves in low-energy regions

Stripe charge density waves observed in domain walls

Predictions can be tested by scanning tunneling microscopy

Abstract

Twisted bilayers of two-dimensional materials have emerged as a highly tunable platform for studying broken symmetry phases. While most interest has been focused on emergent states in systems whose constituent monolayers do not feature broken symmetry states, assembling monolayers that exhibit ordered states into twisted bilayers can also give rise to interesting phenomena. Here, we use large-scale first-principles density-functional theory calculations to study the atomic structure of twisted bilayer $\mathrm{{N}b{S}e_2}$ whose constituent monolayers feature a charge density wave. We find that different charge density wave states coexist in the ground state of the twisted bilayer: monolayer-like $3\times 3$ triangular and hexagonal charge density waves are observed in low-energy stacking regions, while stripe charge density waves are found in the domain walls surrounding the low-energy stacking regions. These predictions, which can be tested by scanning tunneling microscopy experiments, highlight the potential to create complex charge density wave ground states in twisted bilayer systems and can serve as a starting point for understanding superconductivity occurring at low temperatures.