Electron-beam collimation with a quantum point contact

Molenkamp, L. W.; Staring, A. A. M.; Beenakker, C. W. J.; Eppenga, R.; Timmering, C.E.; Williamson, J.; Harmans, C.J.P.M.; Foxon, C.T.

doi:10.1103/physrevb.41.1274

Cited by 155 publications

(108 citation statements)

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“…(2) and the actual measurement (corrected for the background resistance) we find that G series is enhanced by 12% over G/2, which is somewhat smaller than the enhancement of 20% which one would expect from measurements of the direct transmission probability. 7 Clearly, the series resistance experiment is not an accurate way to determine the direct transmission probability.…”

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confidence: 99%

“…This hörn collimation effect 6 was recently demonstrated experimentally. 7 In strenger magnetic fields, where direct transmission is suppressed, a simple relation between the two-terminal series conductance G series and the number of occupied subbands becomes possible. This regime is the subject of the present paper.…”

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confidence: 99%

“…From measurements of the direct transmission probability, following the method of Ref. 7, we determine this to be the case for \B\ >0. l T. We assume a square-well confining potential in the point contacts (of width W and electron density n), which should be a reasonable approximation at the low (negative) gate voltages considered. The number of occupied hybrid magnetoelectric subbands N is given in this case by (assuming spin degeneracy and ignoring the discreteness of 7V since we are interested in the overall behavior only) 3 …”

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Magnetoconductance of two point contacts in series

et al. 1990

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The magnetic-field dependence of the conductance of two opposite point contacts in series is studied experimentally, for magnetic flelds extending into the quantum Hall effect regime. The magnetoconductance has a nonmonotonic, "camel-back" shape, in quantitative agreement with a recent theory. In addition, Aharonov-Bohm-type periodic magnetoconductance oscillations are observed, which are attributed to circulating edge states in a shallow potential basin between the point contacts.The conductance of a constriction in a high-mobility two-dimensional electron gas (2D EG) measures directly the number of occupied one-dimensional subbands, N, in the constriction. This was demonstrated in the experiments by Van Wees et al.' and Wharam et al., 2 who discovered that the two-terminal conductance G of such a quantum point contact is given approximately byA magnetic field B perpendicular to the 2D EG depopulates the subbands, leading to a monotonic decrease 3 of G with B. The series conductance of two opposite point contacts in general does not have äs simple a relation äs Eq. (1) with the number of occupied subbands. In weak magnetic field the series conductance was found by Wharam et a/. 4 and Beton et al. 5 to be strongly enhanced above the value which would follow from Ohmic addition of the separate point-contact resistances. As pointed out by Beenakker and Van Houten,6 this is due to the direct transmission of ballistic electrons from one point contact to the other, without intervening equilibration. The direct transmission probability is enhanced by the collimation of the electron beam injected into the 2D EG by a horn-shaped point contact. This hörn collimation effect 6 was recently demonstrated experimentally. 7In strenger magnetic fields, where direct transmission is suppressed, a simple relation between the two-terminal series conductance G series and the number of occupied subbands becomes possible. This regime is the subject of the present paper. Theoretically, it was predicted in Ref.6 that G series has a nonmonotonic ("camel-back" shaped) B dependence, provided that the transmission from one point contact to the other occurs with intervening equilibration of the current-carrying edge states. This curious behavior results from the following relation between G^HPQ and the number of subbands:Equation (2) results from the additivity of the fourterminal longitudinal magnetoresistance of the individual point contacts, 6 ' 8 which holds in the case of intervening equilibration. Here, N : and N 2 are the number of occupied subbands in the two point contacts, and N L is the number of Landau levels occupied in the region between the point contacts. At low magnetic fields G series first increases because the depopulation of the hybrid magnetoelectric subbands in the point contacts is delayed compared to the depopulation of Landau levels in the wide 2D EG between the point contacts. When the cyclotron radius becomes much smaller than the point-contact width, the confinement of the electrons in the point contacts is fu...

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Magnetoconductance of two point contacts in series

et al. 1990

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“…When the arch QPC and reflector are operated together, collimated ballistic 1D electrons [31] injected from the QPC are reflected by the potential barrier created by the reflector and cause a voltage drop V 34 between Ohmics 3 and 4, such that…”

Section: Resultsmentioning

confidence: 99%

“…Both the length and width of the QPC embedded in the arch are 200 nm, the width of the reflector is 300 nm [29]. The angle of the inclined reflector is crucial because it allows reflected electrons to propagate ballistically to Ohmic contact 3, while multiple scattering of others set up a continuum of cavity states (considering the normal 30°spread of the collimated 1D electrons [31]). A direct scattering of a beam of electrons from the reflector at or near the entrance of the QPC establishes the bound defined state.…”

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Interference Effects in a Tunable Quantum Point Contact Integrated with an Electronic Cavity

et al. 2017

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We show experimentally how quantum interference can be produced using an integrated quantum system comprising an arch-shaped short quantum wire (or quantum point contact, QPC) of 1D electrons and a reflector forming an electronic cavity. On tuning the coupling between the QPC and the electronic cavity, fine oscillations are observed when the arch QPC is operated in the quasi-1D regime. These oscillations correspond to interference between the 1D states and a state which is similar to the Fabry-Perot state and suppressed by a small transverse magnetic field of AE60 mT. Tuning the reflector, we find a peak in resistance which follows the behavior expected for a Fano resonance. We suggest that this is an interesting example of a Fano resonance in an open system which corresponds to interference at or near the Ohmic contacts due to a directly propagating, reflected discrete path and the continuum states of the cavity corresponding to multiple scattering. Remarkably, the Fano factor shows an oscillatory behavior taking peaks for each fine oscillation, thus, confirming coupling between the discrete and continuum states. The results indicate that such a simple quantum device can be used as building blocks to create more complex integrated quantum circuits for possible applications ranging from quantum-information processing to realizing the fundamentals of complex quantum systems.

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2006

Mesoscopic Electronics in Solid State Nanostructures

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Electron-beam collimation with a quantum point contact

Cited by 155 publications

References 10 publications

Magnetoconductance of two point contacts in series

Magnetoconductance of two point contacts in series

Interference Effects in a Tunable Quantum Point Contact Integrated with an Electronic Cavity

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