Strain-induced bound states in transition-metal dichalcogenide bubbles

Abstract

We theoretically study the formation of single-particle bound states confined by strain at the center of bubbles in monolayers of transition-metal dichalcogenides (TMDs). Bubbles ubiquitously form in two-dimensional crystals on top of a substrate by the competition between van der Waals forces and the hydrostatic pressure exerted by trapped fluid. This leads to strong strain at the center of the bubble that reduces the bangap locally, creating potential wells for the electrons that confine states inside. We simulate the spectrum versus the bubble radius for the four semiconducting group VI TMDs, MoS2, WSe2, WS2 and MoSe2, and find an overall Fock-Darwin spectrum of bubble bound states, characterised by small deviations compatible with Berry curvature effects. We analyse the density of states, the state degeneracies, orbital structure and optical transition rules. Our results show that elastic bubbles in these materials are remarkably efficient at confining photocarriers. arXiv:1811.01890v2 [cond-mat.mes-hall]

Topological structures of transition metal dichalcogenides: A review on fabrication, effects, applications, and potential

“…Recently, Single‐photon emitters were observed on TMDs monolayers at cryogenic temperatures 146‐151 and on hexagonal boron nitride at room temperature 149 . Single‐photon emitters originate from either defects in the crystalline structure or bandgap modulation by local bending 152,153 . They are observed on bubbles or wrinkles 154 as these topological structures impose localized strain on TMD materials, break original crystal structures, generate defects, and modify intrinsic bandgaps.…”

Imaging strain-localized excitons in nanoscale bubbles of monolayer WSe2 at room temperature

“…However, multiple emitters per nanobubble are typically observed, which is at odds with a single localization site and suggests a possible role of crystallographic defect states or some other sub-nanobubble inhomogeneity 11,18,[22][23][24][25] . Recently, improved microscopic theoretical models predict that quantumdot-like electronic states in TMDs can form within nanobubbles in the absence of defects 26,27 . In particular, a first-principles approach that carefully considers the strain-induced atomic structure 27 (and which we employ here) predicts that strain maxima and multiple low-energy states form in a doughnut-like distribution near the nanobubble periphery.…”

Spin-valley qubits in gated quantum dots in a single layer of transition metal dichalcogenides

“…Using a 3-band tight-binding model limited to metal orbitals, Peeters, and co-workers analyzed the effect of quantum dot shape and external magnetic field on the singleparticle energy spectrum [57,58]. Using an atomistic tight-binding approach, spin-valley qubits have been described in small quantum dots by Bednarek and coworkers [59,60], Szafran and co-workers [61][62][63] and Guinea and co-workers [64]. Using such an approach, two valley-qubit operations have also been recently proposed by some of us [65].…”

“…In order to realize a spin-valley qubit, a way to control spin and valley properties of electrons in these QDs is needed. Several means of manipulating the valley index in quantum dots have been already studied: strain [64], magnetic field [66,68,69], and coupling to impurity [69].…”