Miftah Hadi Syahputra Anfa

arXiv2025

Light induced transitions of valley Chern numbers and flat bands in a non-twisted moire graphene-hexagonal boron nitride superlattice

Motivated by the rich topology and interesting quasi-band structure of twisted moire materials subjected to light, we study a non-twisted moire material under the influence of light. Our work is in part motivated by a desire to find an easier-to-synthesize platform that can help experimentally elucidate the interesting physics of moiré materials coupled to light. Similar to twisted moire materials, we uncover rich topology and interesting band flattening effects, which we summarize in relevant plots such as a topological phase diagram. Our work demonstrates that much of the interesting phenomenology of twisted moire materials under the influence of electromagnetic waves seems to be generically present even in more experimentally accessible untwisted moire platforms, which remain highly tunable by light.

cond-mat.mes-hall↗

arXiv2025

Effective K valley Hamiltonian for TMD bilayers under pressure and application to twisted bilayers with pressure-induced topological phase transitions

Motivated by recent studies on topologically non-trivial moiré bands in twisted bilayer transition metal dichalcogenides (TMDs), we study MoTe$_2$ bilayer systems subject to pressure, which is applied perpendicular to the material surface. We start our investigation by first considering an untwisted bilayer system with an arbitrary relative shift between layers; a symmetry analysis for this case permits us to obtain a simplified effective low-energy Hamiltonian valid near the important $\mathbf{K}$ valley region of the Brillouin zone. Ab initio density functional theory (DFT) was then employed to obtain relaxed geometric structures for pressures within the range of 0.0 - 3.5 GPa and corresponding band structures. The DFT data were then fitted to the low-energy Hamiltonian to obtain a pressure-dependent Hamiltonian. We then apply our model to a twisted system by treating the twist as a position-dependent shift between layers - here, we assume rigid layers, which is a crucial simplification. In summary, this approach allowed us to obtain the explicit analytical expressions for a Hamiltonian that describes a twisted MoTe\textsubscript{2} bilayer under pressure. Our Hamiltonian then permitted us to study the impact of pressure on the band topology of the twisted system. As a result, we identified many pressure-induced topological phase transitions as indicated by changes in valley Chern numbers. Moreover, we found that pressure could be employed to flatten bands in some of the cases we considered.

cond-mat.mes-hall↗