A quantum dot in topological insulator nanofilm

Herath, Thakshila M.; Hewageegana, Prabath; Apalkov, Vadym

doi:10.1088/0953-8984/26/11/115302

Cited by 7 publications

(11 citation statements)

References 30 publications

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“…1. This surprising result contrasts with the usual bulk-edge correspondence in TIs, as the non-topological dots here exhibit edge states with spin-angular-momentum locking similar to topological dots [14][15][16][17][18][19][20][21][22][23][24][25]. Interestingly, our quantum transport calculation shows that circulating currents [28,29] (Fig.…”

contrasting

confidence: 68%

“…Following these pioneering works, a few other TI proposals [5][6][7][8][9][10][11] have been put forward with some experimental support [12,13]. More recently, topological QDs with cylindrical confinement have been investigated [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Their spectra feature discrete helical edge states protected against non-magnetic scattering and showing spinangular-momentum locking.…”

mentioning

confidence: 99%

“…We define our QDs by adding to Eq. (1) the in-plane cylindrical confinement [14][15][16][17][18][19][20][21][22][23][24][25][26]…”

mentioning

confidence: 99%

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Blurring the Boundaries Between Topological and Nontopological Phenomena in Dots

2018

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We investigate the electronic and transport properties of topological and non-topological InAs0.85Bi0.15 quantum dots (QDs) described by a ∼ 30 meV gapped Bernevig-Hughes-Zhang (BHZ) model with cylindrical confinement, i.e., "BHZ dots". Via modified Bessel functions, we analytically show that non-topological dots quite unexpectedly have discrete helical edge states, i.e., Kramers pairs with spin-angular-momentum locking similar to topological dots. These unusual non-topological edge states are geometrically protected due to confinement in a wide range of parameters thus remarkably contrasting the bulk-edge correspondence in TIs. Moreover, for a conduction window with four edge states, we find that the two-terminal conductance G vs. the QD radius R and the gate Vg controlling its levels shows a double peak at 2e 2 /h for both topological and trivial BHZ QDs. Our results blur the boundaries between topological and non-topological phenomena for conductance measurements in small systems such as QDs. This is in stark contrast to conductance measurements in 2D quantum spin Hall and trivial insulators. All of these results were also found in HgTe QDs. Bi-based BHZ dots should also prove important as hosts to room-temperature edge spin qubits.

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confidence: 68%

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confidence: 99%

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Blurring the Boundaries Between Topological and Nontopological Phenomena in Dots

2018

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“…Thus our approach serves as a useful tool for modeling the effect of quantum confinement in TI nanoparticles, especially as long as atomistic band-structure calculations [70] can be performed only for very small systems [5,40]. Results presented here also provide an interesting reference point for understanding size-quantization effects in other TI nanostructures such as cylindrical quantum dots [71] or nanowires with finite [72] and infinite length [73][74][75].…”

Section: Discussionmentioning

confidence: 88%

Spherical topological insulator nanoparticles: Quantum size effects and optical transitions

et al. 2019

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We have investigated the interplay between band inversion and size quantization in spherically shaped nanoparticles made from topological-insulator (TI) materials. A general theoretical framework is developed based on a versatile continuum-model description of the TI bulk band structure and the assumption of a hard-wall mass confinement. Analytical results are obtained for the wave functions of single-electron energy eigenstates and the matrix elements for optical transitions between them. As expected from spherical symmetry, quantized levels in TI nanoparticles can be labeled by quantum numbers j and m = −j, −j + 1, . . . , j for total angular momentum and its projection on an arbitrary axis. The fact that TIs are narrow-gap materials, where the charge-carrier dynamics is described by a type of two-flavor Dirac model, requires j to assume half-integer values and also causes a doubling of energy-level degeneracy where two different classes of states are distinguished by being parity eigenstates with eigenvalues (−1) j∓1/2 . The existence of energy eigenstates having the same j but opposite parity enables optical transitions where j is conserved, in addition to those adhering to the familiar selection rule where j changes by ±1. All optical transitions satisfy the usual selection rule ∆m = 0, ±1. We treat intra-and inter-band optical transitions on the same footing and establish ways for observing unusual quantum-size effects in TI nanoparticles, including oscillatory dependences of the band gap and of transition amplitudes on the nanoparticle radius. Our theory also provides a unified perspective on multi-band models for charge carriers in semiconductors and Dirac fermions from elementary-particle physics.

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“…In the case of 3D topological insulator nanofilm, the magnitude of the gap depends on the film thickness. Thus the trapping potential in this case can be realized through modulation of the film thickness [6], which results in modulation of the band gap.…”

Section: Introductionmentioning

confidence: 99%

Energy spectra and optical transitions in germanene quantum dots

Herath

Apalkov

2016

J. Phys.: Condens. Matter

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The band gap of buckled graphene-like materials, such as silicene and germanene, depends on external perpendicular electric field. Then specially design profile of electric field can produce trapping potential for electrons. We study theoretically the energy spectrum and optical transitions for such designed quantum dots in graphene-like materials. The energy spectra depend on the size of the quantum dot and applied electric field in the region of the quantum dot. The number of the states in the quantum dot increases with increasing the size of the dot and the energies of the states have almost linear dependence on the applied electric field with the slope which increases with increasing the dot size. The optical properties of the quantum dots are characterized by two type of absorption spectra: interband (optical transitions between the states of the valence and conduction bands) and intraband (transitions between the states of conduction/valence band). The interband absorption spectra have triple-peak structure with peak separation around 10 meV, while intraband absorption spectra, which depend on the number of electrons in the dot, have double-peak structure.

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A quantum dot in topological insulator nanofilm

Cited by 7 publications

References 30 publications

Blurring the Boundaries Between Topological and Nontopological Phenomena in Dots

Blurring the Boundaries Between Topological and Nontopological Phenomena in Dots

Spherical topological insulator nanoparticles: Quantum size effects and optical transitions

Energy spectra and optical transitions in germanene quantum dots

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