Quantum coherence in a single quantum ring
Kwangseuk Kyhm1*
1Department of Opto-mechtronics, Department of Physics Education, Pusan National University, Busan 609-735, Korea
* Presenter:Kwangseuk Kyhm
As long as quantum coherence is preserved around a ring structure, the rotating charge was known to give rise to novel physics, the so-called Aharonov-Bohm (AB) effect, which can be manifested in terms of persistent current in a metal ring or conductance oscillation for increasing an external magnetic field in a mesoscopic device based on a quantum point contact. While these electric measurements require extreme low temperature of a few mK, optical version of the AB effect in a semiconductor quantum ring (QR) can be observable near 10 K. Type-II hetero-structure is often used for the optical AB effect as either electron or hole is rotating in the shell with respect to the other in the core structure. However, optical AB effect of a neutral exciton in a single QR still is in debate and analysis is limited to an idealized ring ignoring the asymmetry and anisotropy.
As a consequence of the quantum coherence in a quantum ring[1,2,3,4], we have observed optical Aharonov-Bohm oscillations in a single GaAs/GaAlAs quantum ring, where the quantization of ring orbital angular momentum states can also be revealed in terms of quantum beats. We also found those oscillations can be ccontrolled by excitation intensity. With a weak excitation intensity, the optical Aharonov-Bohm oscillation period of biexcitons was observed to be half that of excitons in accordance with the period expected for a two-exciton Wigner molecule. When the excitation intensity is increased by an order of magnitude, a gradual deviation of the Wigner molecule condition occurs with decreased oscillation periods and diamagnetic coefficients for both excitons and biexcitons along with a spectral shift. These results suggest that the effective orbit radii and rim widths of electrons and holes in a single quantum ring can be modified by light intensity via photo-excited carriers, which are possibly trapped at interface defects resulting in a local electric field.

[1] Heedae Kim, Seongho Park, Rin Okuyama, Kwangseuk Kyhm(*), Mikio Eto, Robert A. Taylor, Gilles Nogues, Le Si Dang, Marek Potemski, Koochul Je, Jongsu Kim, Jihoon Kyhm, and Jindong Song, Nano Letters, 18(10), 6188 (2018)
[2] H. D. Kim, R. Okuyama, K. Kyhm(*), M. Eto, R. A. Taylor, A. A. L. Nicholet, M. Potemski, G. Nogues, L. S. Dang, K. C. Je, J. S. Kim, J. H. Kyhm, K. H. Yeon, E. H. Lee, J. Y. Kim, I. K. Han, W. J. Choi, and J. D. Song, Nano Letters, 16(1) 27-33 (2016)
[3] Koochul Je, Kwangseuk Kyhm(*), Phys. Stat. Solidi-Rapid Research Letter (on-line Oct 2018)
[4] Heedae Kim, Woojin Lee, Seongho park, Kwangseuk Kyhm, Koochul Je, Robert A. Taylor, Gilles Nogues, Le Si Dang
& Jin Dong Song, Scientific Reports, Rep 7, 40026 (2017)

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