[NCTS Lecture Series] Lattice relaxation, soliton networks, and domain-wall modes in bilayer moirés
Title: [NCTS Lecture Series] Lattice relaxation, soliton networks, and domain-wall modes in bilayer moirés
Speaker: Dr. Christophe De Beule (University of Antwerp)
Time: 2025/6/23 (Mon.) 13:30-14:30
Place: Seminar Room 307, 3F, Cosmology Hall, NTU
Abstract
In this talk, we present analytical results for atomic relaxation in twisted homobilayers with D6 and D3 symmetry, e.g. twisted bilayer graphene and twisted bilayer transition metal dichalcogenides.We first consider "large" twist angles for which relaxation is weak. In this case, one can treat the problem perturbatively within continuum elasticity. Our results compare well with ab-initio calculations and allow us to obtain expressions for the moiré potentials and magic angle in twisted bilayer graphene in the presence of atomic relaxation [1].
On the other hand, for "small" twist angles, the moiré forms a network of constant layer stacking domains that are separated by dislocation solitons. We obtain accurate expressions for the atomic displacement field by matching the exact solution of an isolated soliton near a domain wall. Our results show remarkable agreement with molecular-dynamics and density-functional theory simulations [2].
Finally, we present new results on electronic domain-wall modes in twisted K valley insulators such as twisted hexagonal boron nitride or twisted tungsten diselenide. Using a local stacking Hamiltonian, we show that the domain wall acts as a potential well giving rise to electronic modes above the bulk bands localized at the domain walls that emerge for smaller twist angles. In the twisted bilayer these modes form a scattering network that gives rise to the topmost moiré bands relevant to experiments. We speculate on the consequences such a Chern number sequences and strongly-correlated phenomena.
[1] Mohammed M. Al Ezzi, Gayani N. Pallewela, Christophe De Beule, E. J. Mele, and Shaffique Adam. Phys. Rev. Lett. 133, 266201 (2024).
[2] Christophe De Beule, Gayani N. Pallewela, Mohammed M. Al Ezzi, Liangtao Peng, E. J. Mele, and Shaffique Adam. arXiv:2503.19162.
