Probing the Microscopic Structure of Bound States in Quantum Point Contacts

Yoon, Young-Soo; Mourokh, Lev G.; Morimoto, Takahiro; Aoki, Nobuyuki; Ochiai, Y.; Reno, John L.; Bird, J. P.

doi:10.1103/physrevlett.99.136805

Cited by 55 publications

(120 citation statements)

References 23 publications

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“…Confirming that this feature is associated uniquely with physics that arises near pinch-off, no other resonances are observed as higher subbands of the swept QPC are subsequently populated. The resonance is reproduced, however, in devices with different gate configurations [22,24], in various QPCs fabricated on the same chip [24][25][26], and in multiple cooling cycles performed over a period of several years. From these collective observations, we are able to infer that the resonance does indeed result from the intrinsic properties of the QPC and is not a random-impurity effect.…”

Section: Bound-state Formation In Quantum Point Contactsmentioning

confidence: 98%

“…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]. In these experiments, one QPC (the detector) is configured with fixed gate bias, while the gate voltage applied to the second (swept) QPC is varied continuously, driving it to pinch-off where BS formation is expected.…”

Section: Bound-state Formation In Quantum Point Contactsmentioning

confidence: 99%

“…Since our experimental demonstration of the continuummediated coupling is based on exploiting the specific properties of quantum point contacts (QPCs) near pinch-off, in Sec. II we first briefly review our recent work [22][23][24][25][26] in which we have shown how these structures may be used as an on-demand source of a localized quantum state. In Sec.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Bound-state Formation In Quantum Point Contactsmentioning

confidence: 98%

Section: Bound-state Formation In Quantum Point Contactsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2012

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“…This difference indicates that the observed phase shift does not result from scattering on a localized state. The spontaneously localized states are indeed expected at larger energy and to survive up to much higher temperatures 49 . Here, we are dealing with a low-energy phenomenon, that we attribute to the screening of the localized states by the Kondo effect at very low temperature 5,8,9 .…”

Section: Quantum Point Contactsmentioning

confidence: 99%

Electron Phase Shift at the Zero-Bias Anomaly of Quantum Point Contacts

et al. 2016

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The Kondo effect is the many-body screening of a local spin by a cloud of electrons at very low temperature. It has been proposed as an explanation of the zero-bias anomaly in quantum point contacts where interactions drive a spontaneous charge localization. However, the Kondo origin of this anomaly remains under debate, and additional experimental evidence is necessary. Here we report on the first phase-sensitive measurement of the zero-bias anomaly in quantum point contacts using a scanning gate microscope to create an electronic interferometer. We observe an abrupt shift of the interference fringes by half a period in the bias range of the zero-bias anomaly, a behavior which cannot be reproduced by single-particle models. We instead relate it to the phase shift experienced by electrons scattering off a Kondo system. Our experiment therefore provides new evidence of this many-body effect in quantum point contacts. Quantum point contacts1,2 (QPCs) are small constrictions in high-mobility two-dimensional electron gases (2DEGs) controlled by a metallic split gate at the surface of a semiconductor heterostructure. Despite their apparent simplicity, they reveal complex many-body phenomena which defy our understanding. When these quasione-dimensional ballistic channels are sufficiently open, electrons are perfectly transmitted via each available transverse mode 3 , and the conductance is quantized in units of the conductance quantum 2e 2 /h. Below the first conductance plateau however, this single-particle picture fails due to the increasing importance of many-body effects. An additional shoulder shows up in the linear conductance curve around 0.7 × 2e 2 /h, called the 0.7 anomaly 4 , and a narrow peak of enhanced conductance appears around zero bias in the non-linear conductance curves at low enough temperature, called the zero-bias anomaly 7 (ZBA). The peak behavior versus temperature and magnetic field was shown to share strong similarities with the Kondo effect in quantum dots 6,7 (QDs), i.e. the many-body screening of a local spin by conduction electrons below a characteristic temperature 5,8,9 . However, deviations of the ZBA from the established Kondo effect have been reported [6][7][8]11 , and the occurrence of this effect in QPCs remains a debated issue [14][15][16]

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“…At one extreme, this may be a near perfect quantum wire with a very shallow confining potential which, for example, might occur within a point contact constriction in a 2DES in a semiconductor. As we have suggested before [14,15,16], the origin of the confining potential may be some fluctuation due to remote defects or gates or, in very clean systems, may be due to the single electron itself, a possibility that has received some recent support both theoretically [17,18] and experimentally [19]. The potential well may also be created (or enhanced) with a narrow strip-gate perpendicular to a quantum wire such as in a carbon nanotube [20].…”

Section: Two-electron Problem and Entanglementmentioning

confidence: 99%

Entanglement and transport anomalies in nanowires

Jefferson¹,

Ramšak²,

Rejec³

2008

J. Phys.: Condens. Matter

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Abstract. A shallow potential well in a near-perfect quantum wire will bind a single-electron and behave like a quantum dot, giving rise to spin-dependent resonances of propagating electrons due to Coulomb repulsion and Pauli blocking. It is shown how this may be used to generate full entanglement between static and flying spin-qubits near resonance in a two-electron system via singlet or triplet spin-filtering. In a quantum wire with many electrons, the same pairwise scattering may be used to explain conductance, thermopower and shot-noise anomalies, provided the temperature/energy scale is sufficiently high for Kondolike many-body effects to be negligible.

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Probing the Microscopic Structure of Bound States in Quantum Point Contacts

Cited by 55 publications

References 23 publications

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

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

Electron Phase Shift at the Zero-Bias Anomaly of Quantum Point Contacts

Entanglement and transport anomalies in nanowires

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