Review of phonons in moiré superlattices

Abstract

Moiré patterns in physics are interference fringes produced when a periodic template is stacked on another similar one with different displacement and twist angles. The phonon in two-dimensional (2D) material affected by moiré patterns in the lattice shows various novel physical phenomena, such as frequency shift, different linewidth, and mediation to the superconductivity. This review gives a brief overview of phonons in 2D moiré superlattice. First, we introduce the theory of the moiré phonon modes based on a continuum approach using the elastic theory and discuss the effect of the moiré pattern on phonons in 2D materials such as graphene and MoS2. Then, we discuss the electron–phonon coupling (EPC) modulated by moiré patterns, which can be detected by the spectroscopy methods. Furthermore, the phonon-mediated unconventional superconductivity in 2D moiré superlattice is introduced. The theory of phonon-mediated superconductivity in moiré superlattice sets up a general framework, which promises to predict the response of superconductivity to various perturbations, such as disorder, magnetic field, and electric displacement field.

Modulation of Phonons and Excitons Due to Moiré Potentials in Twisted Bilayer of WSe2/MoSe2

“…This suggests that they are zone-folded phonons due to the moiré superlattice. In homo-TBLs composed of MoS 2 or WSe 2 , ,, the evolution of the zone-folded phonon peaks has been carefully analyzed. However, in hetero-TBLs, such analysis is lacking except for the observation of a few zone-folded moiré phonons for a few twist angles .…”

New Nanophotonics Approaches for Enhancing the Efficiency and Stability of Perovskite Solar Cells

“…The new nanophotonics methods provide a lot of new opportunities for high‐efficiency, durable, low‐risk and sustainable PSCs. However, more efforts should be invested toward the large‐scale processes to solve the commercialization challenges of PSCs, e.g., 1) higher efficiency and stability against moisture, air, heat and light with the assistance of novel nanophotonics designs; 2) optimization of plasmonic nanostructures as the key roles in ETL, HTL, perovskite layer as well as grating electrode for hot‐carrier generation, local heating and photon cycling to further enhance the efficiency and stability; [ 206 ] reasonable nanophotonics design, such as Si/perovskite tandem SCs, [ 207 ] to harvest more photons and reduce thermalization loss to boost the efficiency; 4) developing high‐performance radiative cooler with high transmission in solar spectrum range and high emission in atmospheric window to cool the temperature, and thus to extend the long‐term operational lifetime; and 5) integrating the both advantages of semi‐transparent PSCs and the thermochromic glass to realize smart windows for energy‐saving buildings.…”

Pressure-Induced Dynamic Tuning of Interlayer Coupling in Twisted WSe2/WSe2 Homobilayers

“…The twisting of vdW materials has led to the emergence of moiré superlattices with a periodic potential that is modulated by the twist angle. − The periodic potential created by the moiré pattern induces a flat band , that can give rise to intriguing strongly correlated states such as a Mott insulator, superconductivity, and a topological insulator . The moiré superlattice can also be effectively modulated by external fields, such as strain, magnetic field, and electric field, which can alter the behavior of excitons and provide a platform for controlling and exploring quantum phenomena. − In addition, the moiré potential can affect the properties of phonons. − For instance, low-frequency Raman modes in twisted MoS 2 have been observed to be renormalized at small twist angles, leading to the disappearance of shear (S) modes and high-wavenumber breathing (LB) modes and the emergence of low-wavenumber LB modes. Since the non-zone-center phonon modes can be folded into zone center Γ in a moiré superlattice ruled by a phonon folding effect, the twist-angle-dependent folding phonons were observed in the large-twist-angle MoS 2 homostructures .…”