Valley polarized conductance quantization in bilayer graphene narrow quantum point contact

Sakanashi, Kohei; Wada, Naoto; Murase, K.; Oto, K.; Kim, Gil‐Ho; Watanabe, Kenji; Taniguchi, Takashi; Bird, J. P.; Ferry, D. K.; Aoki, Nobuyuki

doi:10.1063/5.0052845

Cited by 10 publications

(8 citation statements)

References 33 publications

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“…This is in contrast to Ref. [13], where the valley splitting was observed in a similar setup with changing the FIG. 7.…”

Section: A Conductance Plateauscontrasting

confidence: 81%

“…We start by summarizing the most common one for a normal two-dimensional Schrödinger equation, and proceed with an alternative method for BLG. The obtained energy spectrum would extend dispersion (13) in the main text and thus also the density (15).…”

Section: Appendix C: Effective Low-energy Theorymentioning

confidence: 54%

“…where a is a constant. This form of the effectivemodified by interactions-form of single-particle energies in BLG QPC is based on the fourth-order expansion of dispersion relation (13) for N = 0, namely…”

Section: Application To Blgmentioning

confidence: 99%

“…Recently, we have reported [5] on an electrostaticallyinduced quantum point contact (QPC) in bilayer graphene (BLG) [6][7][8][9][10][11][12][13][14], i. e., a system with four-fold spin and valley degeneracy, where the constriction is realized by local band gap engineering with a displacement field perpendicular to the BLG plane. We observed confinement with well-resolved conductance quantization in steps of 4 e 2 h down to the lowest one-dimensional (1D) subband, as well as a peculiar valley subband splitting and merging of K and K ′ valleys from two non-adjacent subbands in an out-of-plane magnetic field (see also Ref.…”

Section: Introductionmentioning

confidence: 99%

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Spin and valley degrees of freedom in a bilayer graphene quantum point contact: Zeeman splitting and interaction effects

Gall¹,

Kraft²,

Gornyi³

et al. 2021

Preprint

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We present a study on the lifting of degeneracy of the size-quantized energy levels in an electrostatically defined quantum point contact in bilayer graphene by the application of in-plane magnetic fields. We observe a Zeeman spin splitting of the first three subbands, characterized by effective Landé g-factors that are enhanced by confinement and interactions. In the gate-voltage dependence of the conductance, a shoulder-like feature below the lowest subband appears, which we identify as a 0.7 anomaly stemming from the interaction-induced lifting of the band degeneracy. We employ a phenomenological model of the 0.7 anomaly to the gate-defined channel in bilayer graphene subject to in-plane magnetic field. Based on the qualitative theoretical predictions for the conductance evolution with increasing magnetic field, we conclude that the assumption of an effective spontaneous spin splitting is capable of describing our observations, while the valley degree of freedom remains degenerate.

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“…This is in contrast to Ref. [13], where the valley splitting was observed in a similar setup with changing the FIG. 7.…”

Section: A Conductance Plateauscontrasting

confidence: 81%

Section: Appendix C: Effective Low-energy Theorymentioning

confidence: 54%

Section: Application To Blgmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Spin and valley degrees of freedom in a bilayer graphene quantum point contact: Zeeman splitting and interaction effects

Gall¹,

Kraft²,

Gornyi³

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…Having l = 0.4 Å would require an electrical field (E z ) of 5V /nm to achieve ∆ z = 0.2eV , which is practically quite achievable [32,49]. Based on this discussion, we choose the parameters involved in our model to be the following: t = 1.3eV , l = 0.4Å and a = 4Å.…”

Section: A Choice Of the Materialsmentioning

confidence: 99%

Robust all-electrical topological valley filtering using monolayer 2D-Xenes

Jana,

Muralidharan

2021

Preprint

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We propose a realizable device design for an all-electrical robust valley filter that utilizes spin protected topological interface states hosted on monolayer 2D-Xene materials with large intrinsic spin-orbit coupling. In contrast with conventional quantum spin-Hall edge states localized around the X-points, the interface states appearing at the domain wall between topologically distinct phases are either from the K or K points, making them suitable prospects for serving as valley-polarized channels. We show that the presence of a large band-gap quantum spin Hall effect enables the spatial separation of the spin-valley locked helical interface states with the valley states being protected by spin conservation, leading to a robustness against short-range non-magnetic disorder. By adopting the scattering matrix formalism on a suitably designed device structure, valley-resolved transport in the presence of non-magnetic short-range disorder for different 2D-Xene materials is also analyzed in detail. Our numerical simulations confirm the role of spin-orbit coupling in achieving an improved valley filter performance with a perfect quantum of conductance attributed to the topologically protected interface states. Our analysis further elaborates clearly the right choice of material, device geometry and other factors that need to be considered while designing an optimized valleytronic filter device.

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Exploring Conductance Quantization Effects in Electroformed Filaments for Their Potential Application to a Resistance Standard

et al. 2023

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The ballistic conduction through narrow constrictions connecting charge reservoirs exhibits conductance quantization effects. Since the quantum of conductance G 0 = 2e 2 ∕h is only related to fundamental constants of nature, these effects might allow the implementation of a standard of resistance, fulfilling the requirements of the 2019 revised International System of Units. Moreover, this standard would be able to work at room temperature and without a magnetic field, thus allowing its on-chip implementation. In this work, the authors propose that breakdown filaments in thin oxide layers might be useful to this purpose. In particular, conductance quantization effects in nanolaminate Al 2 O 3 /HfO 2 dielectrics are reported and the role of intrinsic values of conductance and extrinsic parasitic elements are analyzed. The fact that breakdown filaments are irreversible is an advantage due to their expected stability and to the lack of cycle-to-cycle variations (as compared to resistive switching devices). Although the reported sample-to-sample variations are still too large for a real application, there is room for improving the controlover breakdown filaments through material design and electroforming conditions. Provided that this control is achieved, an on-chip implementation of a resistance standard for the realization of self-calibrating electrical systems and equipment with zero-chain traceability would be possible.

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Valley polarized conductance quantization in bilayer graphene narrow quantum point contact

Cited by 10 publications

References 33 publications

Spin and valley degrees of freedom in a bilayer graphene quantum point contact: Zeeman splitting and interaction effects

Spin and valley degrees of freedom in a bilayer graphene quantum point contact: Zeeman splitting and interaction effects

Robust all-electrical topological valley filtering using monolayer 2D-Xenes

Exploring Conductance Quantization Effects in Electroformed Filaments for Their Potential Application to a Resistance Standard

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