Tunable strain soliton networks confine electrons in van der Waals materials

Edelberg, Drew; Kumar, Hemant; Shenoy, Vivek B.; Ochoa, Héctor; Pasupathy, Abhay

doi:10.1038/s41567-020-0953-2

Cited by 73 publications

(63 citation statements)

References 31 publications

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“…Furthermore, we study the localization of the wave functions corresponding to these flat bands. The wave functions localize at different stackings compared to twisted TMDs, and our results are in excellent agreement with recent spectroscopic experiments [1].…”

supporting

confidence: 92%

“…Most of the studies so far focus on the emergence of flat-electronic bands due to the moiré pattern formation from twisting and from stacking two dissimilar materials. A recent experiment, however, suggests that electrons can be efficiently trapped in strain engineered moiré pattern in TMDs [1]. This hints at the formation of flat-electronic bands in such systems.…”

Section: Introductionmentioning

confidence: 98%

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Atomic reconstruction and flat bands in strain engineered transition metal dichalcogenide bilayer moiré systems

Kundu,

Maity,

Bajaj

et al. 2021

Preprint

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Strain-induced lattice mismatch leads to moiré patterns in homobilayer transition metal dichalcogenides (TMDs). We investigate the structural and electronic properties of such strained moiré patterns in TMD homobilayers. The moiré patterns in strained TMDs consist of several stacking domains which are separated by tensile solitons. Relaxation of these systems distributes the strain unevenly in the moiré superlattice, with the maximum strain energy concentrating at the highest energy stackings. The order parameter distribution shows the formation of aster topological defects at the same sites. In contrast, twisted TMDs host shear solitons at the domain walls, and the order parameter distribution in these systems shows the formation of vortex defects. The strained moiré systems also show the emergence of several well-separated flat bands at both the valence and conduction band edges, and we observe a significant reduction in the band gap. The flat bands in these strained moiré superlattices provide platforms for studying the Hubbard model on a triangular lattice as well as the ionic Hubbard model on a honeycomb lattice. Furthermore, we study the localization of the wave functions corresponding to these flat bands. The wave functions localize at different stackings compared to twisted TMDs, and our results are in excellent agreement with recent spectroscopic experiments [1].

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supporting

confidence: 92%

Section: Introductionmentioning

confidence: 98%

Atomic reconstruction and flat bands in strain engineered transition metal dichalcogenide bilayer moiré systems

Kundu,

Maity,

Bajaj

et al. 2021

Preprint

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“…where local matrix elements are defined as in Eqs. ( 18) and (20). For the full range of twist angles, the valence band edge at K lies more than 50 meV higher than that at the point across a moiré supercell; see Fig.…”

Section: A Valence-band-edge Modulation At the And K Pointsmentioning

confidence: 91%

“…Moiré superlattices induce a plethora of physical effects, such as long-range interlayer hybridization, leading to flat minibands with strongly correlated electronic states [2][3][4][5][6][7][8][9][10] and minibands for excitons in transition metal dichalcogenide (TMD) bilayers [11,12] at twist angles θ 10 • , for which the moiré periodicity exceeds the exciton Bohr radius, thus affecting the system's optoelectronic properties [13][14][15][16][17]. Moreover, piezoelectric effects caused by lattice reconstruction in TMD bilayers [1,18,19] create periodic traps for charge carriers [20,21] and excitons [22], whereas interlayer charge transfer [23,24] induces ferroelectric polarization in these structures [25][26][27].…”

Section: Introductionmentioning

confidence: 99%

Multifaceted moiré superlattice physics in twisted WSe2 bilayers

et al. 2021

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Lattice reconstruction in twisted transition-metal dichalcogenide (TMD) bilayers gives rise to piezo-and ferroelectric moiré potentials for electrons and holes, as well as a modulation of the hybridization across the bilayer. Here, we develop hybrid k • p tight-binding models to describe electrons and holes in the relevant valleys of twisted TMD homobilayers with parallel (P) and antiparallel (AP) orientations of the monolayer unit cells. We apply these models to describe moiré superlattice effects in twisted WSe 2 bilayers, in conjunction with microscopic ab initio calculations, and considering the influence of encapsulation, pressure, and an electric displacement field. Our analysis takes into account mesoscale lattice relaxation, interlayer hybridization, piezopotentials, and a weak ferroelectric charge transfer between the layers, and it describes a multitude of possibilities offered by this system, depending on the choices of P or AP orientation, twist angle magnitude, and electron/hole valley.

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“…Recent work analyzing the transient spectral response of excitons in GaAs to incident solitons (Scherbakov et al, 2007) has shown definitively an electronic-soliton coupling is present in this common device material. Recent investigations in 2D materials (Alden et al, 2013;Edelberg et al, 2020) have shown that static strain solitons form under certain conditions related to twisted van der Waals stacking patterns. These static solitons could be used to confine electronic states and one can consider dynamic soliton trains and the interaction between static and dynamic solitons may be sufficient to manipulate the charge states in novel device schemes.…”

Section: Discussionmentioning

confidence: 99%

Soliton Generation in Negative Thermal Expansion Materials

et al. 2021

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Strain solitons have been observed statically in several 2D materials and dynamically in substrate materials using ultrafast laser pulses. The latter case relies on lattice relaxation in response to ultrafast heating in a light-absorbing transducer material, a process which is sensitive to the thermal expansion coefficient. Here we consider an unusual case where the sign of the thermal expansion coefficient is negative, a scenario which is experimentally feasible in light of rapid and recent advances in the discovery of negative thermal expansion materials. We present numerical solutions to a nonlinear differential equation which has been repeatedly demonstrated to quantitatively model experimental data and discuss the salient results using realistic parameters for material linear and nonlinear elasticity. The solitons that emerge from the initial value problem with negative and positive thermal expansion are qualitatively different in several ways. The new case of negative thermal expansion gives rise to a nearly-periodic soliton train with chirped profile and free of an isolated shock front. We suggest this unanticipated result may be realized experimentally and assess the potential for certain applications of this generic effect.

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Tunable strain soliton networks confine electrons in van der Waals materials

Cited by 73 publications

References 31 publications

Atomic reconstruction and flat bands in strain engineered transition metal dichalcogenide bilayer moiré systems

Atomic reconstruction and flat bands in strain engineered transition metal dichalcogenide bilayer moiré systems

Multifaceted moiré superlattice physics in twisted WSe2 bilayers

Soliton Generation in Negative Thermal Expansion Materials

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