Browsing by Author "Hsiao, J. H."

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0.7 anomaly due to the Rashba interaction in a nonuniform electric field
(2009-01-01)
Hsiao, J. H.
;
Liu, K. M.
;
Hsu, S. Y.
;
Hong, T. M.
;
電子物理學系
We demonstrate that three conductance features, 0.5 and 0.7G(0) plateaus and a dip at 0.5G(0), observed in quantum point contacts (QPCs) can be consistently explained by the Rashba interaction in the nonuniform electric field created by the side gates along the transport direction. A quantity gamma is defined which depends on the extent of this nonuniformity and the electron density. A short QPC tends to have a small gamma. Only when gamma is large will the Rashba interaction produce a potential well deep enough to localize the electron. This provides the bound state that forms the Kondo resonance with the tunneling electrons. We propose to compare the medium/long QPC to small/large quantum dots, which are governed by the Kondo physics and the Coulomb blockade, respectively. The relation between 0.7 anomaly and the side-gate voltage, length of QPC, and temperature can all be determined to agree qualitatively with the experiments.
The formation of bound states and the conductance modulation on 0.7 anomaly in a quantum wire
(2009)
Liu, K. M.
;
Hsiao, J. H.
;
Hong, T. M.
;
Umansky, V.
;
Hsu, S. Y.
The electron transport in a short quasi-1D quantum wire is studied. In addition to the conductance quantization, several resonances are observed. Two of the resonances appear as extra plateaus below 2e(2)/h. A gate voltage offset is used to tune the local potential of the quantum wire. A robust resonance is seen and the resonances evolve continuously with respect to the offset. The conductance has opposite responses to temperature in successive regions of gate voltage V(g). In the source-drain bias spectroscopy, two more conductance peaks are observed in addition to the Zero-Bias-Anomaly. The locations of the extra peaks evolve with respect to V(g) showing a pattern similar to that in a quantum dot. We suggest that a bound state forms in the quantum wire. The prominent 0.7 anomally in our quantum wire is recognized as the residue of conductance resonance.