Events at Physics |
Events on Thursday, October 1st, 2009
- R. G. Herb Condensed Matter Seminar
- Dephasing and disorder effects in quantum spin Hall effect
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Xincheng Xie, Oklahoma State University
- Abstract: The influence of dephasing on the quantum spin Hall effect (QSHE) is studied. In the absence of dephasing, the longitudinal resistance in a QSHE system exhibits the quantum plateaus. We find that these quantum plateaus are robust against the normal dephasing but fragile with the spin dephasing. Thus, these quantum plateaus only survive in mesoscopic samples. Moreover, the longitudinal resistance increases linearly with the sample length but is insensitive to the sample width. These characters are in excellent agreement with the recent experimental results [Science 318, 766 (2007)]. In addition, we define a new spin Hall resistance that also exhibits quantum plateaus. In particular, these plateaus are robust against any type of dephasing and therefore, survive in macroscopic samples and better reflect the topological nature of QSHE.
In addition, we also study the disorder effect on the transport properties in QSHE. We confirm that at a moderate disorder strength, the initially un-quantized two terminal conductance becomes quantized, and the system makes a transition to the novel topological Anderson insulator (TAI). Conductances calculated for the stripe and cylinder samples reveal the topological feature of TAI and supports the idea that the helical edge states may cause the anomalous quantized plateaus. The influence of disorder is studied by calculating the distributions of local currents. Base on the above-mentioned picture, the phenomena induced by disorder in the quantum spin Hall region and TAI region are directly explained. - Host: Robert Joynt
- Introductory Graduate Seminar
- Biophysics
- Time: 5:30 pm
- Place: 2223 Chamberlin Hall
- Speaker: Coppersmith, Gilbert, University of Wisconsin Department of Physics