TY - JOUR
T1 - Odd and even Kondo effects from emergent localization in quantum point contacts
AU - Iqbal, M. J.
AU - Levy, Roi
AU - Koop, E. J.
AU - Dekker, J. B.
AU - De Jong, J. P.
AU - Van Der Velde, J. H.M.
AU - Reuter, D.
AU - Wieck, A. D.
AU - Aguado, Ramón
AU - Meir, Yigal
AU - Van Der Wal, C. H.
N1 - Funding Information: Acknowledgements We thank B. J. van Wees, A. Aqeel, S. Ludwig, J. von Delft and Y. Komijani for discussions and B. Wolfs, J. Holstein and M. de Roosz for technical assistance. We acknowledge financial support from the German programmes DFG-SPP 1285, Research School Ruhr-Universität Bochum and BMBF QuaHL-Rep 16BQ1035, and grants FIS2009-08744 and FIS2012-33521 from the Spanish Ministry ofEconomy and Innovation. M.J.I. acknowledgesa scholarship from the Higher Education Commission of Pakistan. Y.M. and R.L. acknowledge support from the ISF.
PY - 2013/9/3
Y1 - 2013/9/3
N2 - A quantum point contact (QPC) is a basic nanometre-scale electronic device: a short and narrow transport channel between two electron reservoirs. In clean channels, electron transport is ballistic and the conductance is then quantized as a function of channel width with plateaux at integer multiples of 2e 2/h (where e is the electron charge and h is Planck's constant). This can be understood in a picture where the electron states are propagating waves, without the need to account for electron-electron interactions. Quantized conductance could thus be the signature of ultimate control over nanoscale electron transport. However, even studies with the cleanest QPCs generically show significant anomalies in the quantized conductance traces, and there is consensus that these result from electron many-body effects. Despite extensive experimental and theoretical studies, understanding these anomalies is an open problem. Here we report that the many-body effects have their origin in one or more spontaneously localized states that emerge from Friedel oscillations in the electron charge density within the QPC channel. These localized states will have electron spins associated with them, and the Kondo effect-related to electron transport through such localized electron spins-contributes to the formation of the many-body state. We present evidence for such localization, with Kondo effects of odd or even character, directly reflecting the parity of the number of localized states; the evidence is obtained from experiments with length-tunable QPCs that show a periodic modulation of the many-body properties with Kondo signatures that alternate between odd and even Kondo effects. Our results are of importance for assessing the role of QPCs in more complex hybrid devices and for proposals for spintronic and quantum information applications. In addition, our results show that tunable QPCs offer a versatile platform for investigating many-body effects in nanoscale systems, with the ability to probe such physics at the level of a single site.
AB - A quantum point contact (QPC) is a basic nanometre-scale electronic device: a short and narrow transport channel between two electron reservoirs. In clean channels, electron transport is ballistic and the conductance is then quantized as a function of channel width with plateaux at integer multiples of 2e 2/h (where e is the electron charge and h is Planck's constant). This can be understood in a picture where the electron states are propagating waves, without the need to account for electron-electron interactions. Quantized conductance could thus be the signature of ultimate control over nanoscale electron transport. However, even studies with the cleanest QPCs generically show significant anomalies in the quantized conductance traces, and there is consensus that these result from electron many-body effects. Despite extensive experimental and theoretical studies, understanding these anomalies is an open problem. Here we report that the many-body effects have their origin in one or more spontaneously localized states that emerge from Friedel oscillations in the electron charge density within the QPC channel. These localized states will have electron spins associated with them, and the Kondo effect-related to electron transport through such localized electron spins-contributes to the formation of the many-body state. We present evidence for such localization, with Kondo effects of odd or even character, directly reflecting the parity of the number of localized states; the evidence is obtained from experiments with length-tunable QPCs that show a periodic modulation of the many-body properties with Kondo signatures that alternate between odd and even Kondo effects. Our results are of importance for assessing the role of QPCs in more complex hybrid devices and for proposals for spintronic and quantum information applications. In addition, our results show that tunable QPCs offer a versatile platform for investigating many-body effects in nanoscale systems, with the ability to probe such physics at the level of a single site.
UR - http://www.scopus.com/inward/record.url?scp=84883743930&partnerID=8YFLogxK
U2 - https://doi.org/10.1038/nature12491
DO - https://doi.org/10.1038/nature12491
M3 - Article
C2 - 23995683
SN - 0028-0836
VL - 501
SP - 79
EP - 83
JO - Nature
JF - Nature
IS - 7465
ER -