Odd and even Kondo effects from emergent localization in quantum point contacts

Iqbal, Muhammad Javaid; Levy, Roi; Koop, E. J.; Dekker, J. B.; Jong, J.P. de; Velde, van der Jasper; Reuter, D.; Wieck, A. D.; Aguado, Ramón; Meir, Yigal; Wal, van der Caspar

doi:10.1038/nature12491

Cited by 75 publications

(103 citation statements)

References 30 publications

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“…This phenomenon is supported by two recent experiments where localized states with even and odd numbers of charges have been observed 13,21 . The development of a Kondo effect is therefore expected at very low temperature, but its specific properties for a self-consistently localized state have not been calculated yet, due to the complexity of the problem.…”

Section: Quantum Point Contactssupporting

confidence: 71%

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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Section: Quantum Point Contactssupporting

confidence: 71%

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

et al. 2016

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“…A detailed study of this type of periodicity can be found in Ref. 18. This example illustrates the validity and importance of our type of QPCs in studies of length-dependent transport properties.…”

Section: Experimental Realization Of Length-tunable Qpcsmentioning

confidence: 61%

Split-gate quantum point contacts with tunable channel length

Iqbal

Jong

Reuter

et al. 2013

Journal of Applied Physics

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We report on developing split-gate quantum point contacts (QPCs) that have a tunable length for the transport channel. The QPCs were realized in a GaAs/AlGaAs heterostructure with a twodimensional electron gas (2DEG) below its surface. The conventional design uses 2 gate fingers on the wafer surface which deplete the 2DEG underneath when a negative gate voltage is applied, and this allows for tuning the width of the QPC channel. Our design has 6 gate fingers and this provides additional control over the form of the electrostatic potential that defines the channel. Our study is based on electrostatic simulations and experiments and the results show that we developed QPCs where the effective channel length can be tuned from about 200 nm to 600 nm. Length-tunable QPCs are important for studies of electron many-body effects because these phenomena show a nanoscale dependence on the dimensions of the QPC channel.

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“…A number of theoretical investigations focused on the role of quantum interference [4,5], spontaneous spin polarization [1, 6,7], Wigner crystallization [8] and the Kondo effect [9][10][11]. Even very recently, two papers provided evidence for the Kondo scenario, based on the formation of a quasi-bound state at the constriction [12,13]. On the other hand, another recently proposed model involves a "van Hove ridge" in the density of states of the QPC that strongly enhances interaction effects for subopen QPCs without needing spin-polarization or quasi-bound states [14].…”

Section: Introductionmentioning

confidence: 99%

Scanning gate imaging of quantum point contacts and the origin of the 0.7 anomaly

et al. 2014

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The origin of the anomalous transport feature appearing at conductance G ≈ 0.7 x (2e 2 /h) in quasi-1D ballistic devices − the so-called 0.7 anomaly − represents a long standing puzzle. Several mechanisms were proposed to explain it, but a general consensus has not been achieved. Proposed explanations are based on quantum interference, Kondo effect, Wigner crystallization, and more. A key open issue is whether point defects that can occur in these low-dimensional devices are the physical cause behind this conductance anomaly. Here we adopt a scanning gate microscopy technique to map individual impurity positions in several quasi-1D constrictions and correlate these with conductance characteristics. Our data demonstrate that the 0.7 anomaly can be observed irrespective of the presence of localized defects, and we conclude that the 0.7 anomaly is a fundamental property of low-dimensional systems.

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Odd and even Kondo effects from emergent localization in quantum point contacts

Cited by 75 publications

References 30 publications

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

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

Split-gate quantum point contacts with tunable channel length

Scanning gate imaging of quantum point contacts and the origin of the 0.7 anomaly

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