Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDeep moire potentials in twisted transition metal dichalcogenide bilayers
93
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In twisted bilayers of semiconducting transition metal dichalcogenides (TMDs), a combination of structural rippling and electronic coupling gives rise to periodic moire potentials that can confine charged and neutral excitations. Here, we report experimental measurements of the structure and spectroscopic properties of twisted bilayers of WSe2 and MoSe2 in the H-stacking configuration using scanning tunneling microscopy (STM). Our experiments reveal that the moire potential in these bilayers at small angles is unexpectedly large, reaching values of above 300 meV for the valence band and 150 meV for the conduction band - an order of magnitude larger than theoretical estimates based on interlayer coupling alone. We further demonstrate that the moire potential is a non-monotonic function of moire wavelength, reaching a maximum at around a 13nm moire period. This non-monotonicity coincides with a drastic change in the structure of the moire pattern from a continuous variation of stacking order at small moire wavelengths to a one-dimensional soliton dominated structure at large moire wavelengths. We show that the in-plane structure of the moire pattern is captured well by a continuous mechanical relaxation model, and find that the moire structure and internal strain rather than the interlayer coupling is the dominant factor in determining the moire potential. Our results demonstrate the potential of using precision moire structures to create deeply trapped carriers or excitations for quantum electronics and optoelectronics.
rate research
Read More
Fabricating van der Waals (vdW) bilayer heterostructures (BL-HS) by stacking the same or different two-dimensional (2D) layers, offers a unique physical system with rich electronic and optical properties. Twist-angle between component layers has emerged as a remarkable parameter that can control the period of lateral confinement, and nature of the exciton (Coulomb bound electron-hole pair) in reciprocal space thus creating exotic physical states including moire excitons. In this review article, we focus on opto-electronic properties of excitons in transition metal dichalcogenide (TMD) semiconductor twisted BL-HS. We look at existing evidence of moire excitons in localized and strongly correlated states, and at nanoscale mapping of moire superlattice and lattice-reconstruction. This review will be helpful in guiding the community as well as motivating work in areas such as near-field optical measurements and controlling the creation of novel physical states.
The long wavelength moire superlattices in twisted 2D structures have emerged as a highly tunable platform for strongly correlated electron physics. We study the moire bands in twisted transition metal dichalcogenide homobilayers, focusing on WSe$_2$, at small twist angles using a combination of first principles density functional theory, continuum modeling, and Hartree-Fock approximation. We reveal the rich physics at small twist angles $theta<4^circ$, and identify a particular magic angle at which the top valence moire band achieves almost perfect flatness. In the vicinity of this magic angle, we predict the realization of a generalized Kane-Mele model with a topological flat band, interaction-driven Haldane insulator, and Mott insulators at the filling of one hole per moire unit cell. The combination of flat dispersion and uniformity of Berry curvature near the magic angle holds promise for realizing fractional quantum anomalous Hall effect at fractional filling. We also identify twist angles favorable for quantum spin Hall insulators and interaction-induced quantum anomalous Hall insulators at other integer fillings.
We develop a minimal theory for the recently observed metal-insulator transition (MIT) in two-dimensional (2D) moire multilayer transition metal dichalcogenides (mTMD) using Coulomb disorder in the environment as the underlying mechanism. In particular, carrier scattering by random charged impurities leads to an effective 2D MIT approximately controlled by the Ioffe-Regel criterion, which is qualitatively consistent with the experiments. We find the necessary disorder to be around $5$-$10times10^{10}$cm$^{-2}$ random charged impurities in order to quantitatively explain much, but not all, of the observed MIT phenomenology as reported by two different experimental groups. Our estimate is consistent with the known disorder content in TMDs.
Flexible long period moir e superlattices form in two-dimensional van der Waals crystals containing layers that differ slightly in lattice constant or orientation. In this Letter we show theoretically that isolated flat moir e bands described by generalized triangular lattice Hubbard models are present in twisted transition metal dichalcogenide heterobilayers. The hopping and interaction strength parameters of the Hubbard model can be tuned by varying the twist angle and the three-dimensional dielectric environment. When the flat moire bands are partially filled, candidate many-body ground states at some special filling factors include spin-liquid states, quantum anomalous Hall insulators and chiral $d$-wave superconductors.
An important step in understanding the exotic electronic, vibrational, and optical properties of the moir{e} lattices is the inclusion of the effects of structural relaxation of the un-relaxed moir{e} lattices. Here, we propose novel structures for twisted bilayer of transition metal dichalcogenides (TMDs). For $thetagtrsim 58.4^{circ}$, we show a dramatic reconstruction of the moir{e} lattices, leading to a trimerization of the unfavorable stackings. We show that the development of curved domain walls due to the three-fold symmetry of the stacking energy landscape is responsible for such lattice reconstruction. Furthermore, we show that the lattice reconstruction notably changes the electronic band-structure. This includes the occurrence of flat bands near the edges of the conduction as well as valence bands, with the valence band maximum, in particular, corresponding to localized states enclosed by the trimer. We also find possibilities for other complicated, entropy stabilized, lattice reconstructed structures.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
