Nature of electron states and symmetry breaking in quantum point contacts according to the local spin density approximation

Berggren, Karl‐Fredrik; Yakimenko, I. I.

doi:10.1088/0953-8984/20/16/164203

Cited by 22 publications

(36 citation statements)

References 39 publications

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“…When the potential barrier of the QPC is above the Fermi level, there are two regions of low density, one on each side of the barrier, where charges could spontaneously localize. Numerical simulations of this peculiar situation encountered near pinch off supports the presence of bound states [61,62] detected in coupled QPCs experiments [54,63]. This scenario has also been proposed in Ref.…”

Section: Discussionsupporting

confidence: 76%

Thermoelectric Scanning-Gate Interferometry on a Quantum Point Contact

et al. 2019

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We introduce a new scanning probe technique derived from scanning gate microscopy (SGM) in order to investigate thermoelectric transport in two-dimensional semiconductor devices. The thermoelectric scanning gate microscopy (TSGM) consists in measuring the thermoelectric voltage induced by a temperature difference across a device, while scanning a polarized tip that locally changes the potential landscape. We apply this technique to perform interferometry of the thermoelectric transport in a quantum point contact (QPC). We observe an interference pattern both in SGM and TSGM images, and evidence large differences between the two signals in the low density regime of the QPC. In particular, a large phase jump appears in the interference fringes recorded by TSGM, which is not visible in SGM. We discuss this difference of sensitivity using a microscopic model of the experiment, based on the contribution from a resonant level inside or close to the QPC. This work demonstrates that combining scanning gate microscopy with thermoelectric measurements offers new information as compared to SGM, and provides a direct access to the derivative of the device transmission with respect to energy, both in amplitude and in phase.

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Section: Discussionsupporting

confidence: 76%

Thermoelectric Scanning-Gate Interferometry on a Quantum Point Contact

et al. 2019

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“…Conductance for this case is G = 0.005G 0 (G 0 = 2e 2 /h). In this regime localized states reside near the two openings of a QPC (as argued in [12] and [15]). For V sg = −1.4 eV (Fig.…”

Section: Results Of Numerical Simulationsmentioning

confidence: 89%

“…The electric current characteristics is measured experimentally if a small source-drain bias is applied at the two edges of this structure. To find them theoretically we will start (as in our previous papers [12] and [27]) from the two-dimensional Kohn-Sham equations:…”

Section: Model Of Heterostructure With Randomly Distributed Donorsmentioning

confidence: 99%

Probing dopants in wide semiconductor quantum point contacts

Yakimenko¹,

Berggren²

2016

J. Phys.: Condens. Matter

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Effects of randomly distributed impurities on conductance, spin polarization and electron localization in realistic gated semiconductor quantum point contacts (QPCs) have been simulated numerically. To this end density functional theory in the local spin-density approximation has been used. In the case when the donor layer is embedded far from the two-dimensional electron gas (2DEG) the electrostatic confinement potential exhibits the conventional parabolic form, and thus the usual ballistic transport phenomena take place both in the devices with split gates alone and with an additional metallic gate on the top. In the opposite case, i.e. when the randomly distributed donors are placed not far away from the 2DEG layer, there are drastic changes like the localization of electrons in the vicinity of confinement potential minima which give rise to fluctuations in conductance and resonances. The conductance as a function of the voltage applied to the top gate for asymmetrically charged split gates has been calculated. In this case resonances in conductance caused by randomly distributed donors are shifted and decrease in amplitude while the anomalies caused by interaction effects remain unmodified. It has been also shown that for a wide QPC the polarization can appear in the form of stripes. The importance of partial ionization of the random donors and the possibility of short range order among the ionized donors are emphasized. The motivation for this work is to critically evaluate the nature of impurities and how to guide the design of high-mobility devices.

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“…A scenario proposed in several of these studies is that such modifications can lead to the formation of a quantum-dot-like bound state (BS), capable of localizing a single electron, at the QPC center [29][30][31][32][33][34]. The microscopic structure of this BS remains the subject of debate [35,36], however, so that further experiments are called for to confirm its existence. Utilizing the FR as a key signature of the presence of a discrete state, we have implemented a mesoscopic version of the FR experiment, in which the mutual interaction between a pair of coupled QPCs reveals the signature of the BS [22][23][24][25][26].…”

Section: Bound-state Formation In Quantum Point Contactsmentioning

confidence: 99%

Coupling Quantum States through a Continuum: A Mesoscopic Multistate Fano Resonance

et al. 2012

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We demonstrate a fully tunable realization of a multistate Fano resonance, in which a pair of remote quantum states experience an effective coupling due to their mutual overlap with a continuum. Our mesoscopic implementation of this system exploits the ability of the semiconductor nanostructures known as quantum point contacts (QPCs) to serve, in the low-density limit close to pinch-off, as an on-demand localized state. By coupling the states formed on two separate QPCs, through a two-dimensional electron gas that serves as a continuum, we observe a robust effective interaction between the QPCs. To explain this result, we develop a theoretical formulation, based on the ideas of the Schrieffer-Wolff transformation, which is able to reproduce our key experimental findings. According to this model, the robust character of the interaction between the two remote states arises from the fact that the interaction is essentially mediated by a large number of degenerate continuum states. While the continuum is often viewed as a source of decoherence, our experiment therefore instead suggests the possibility of using this medium to support the interaction of quantum states, a result that may allow new approaches to coherently couple nanostructures in extended geometries.

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Nature of electron states and symmetry breaking in quantum point contacts according to the local spin density approximation

Cited by 22 publications

References 39 publications

Thermoelectric Scanning-Gate Interferometry on a Quantum Point Contact

Thermoelectric Scanning-Gate Interferometry on a Quantum Point Contact

Probing dopants in wide semiconductor quantum point contacts

Coupling Quantum States through a Continuum: A Mesoscopic Multistate Fano Resonance

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