Dr. Tomosuke Aono (Ben-Gurion University, Physics Department, Condensed Matter Theory Group)
"Shot Noise in the quantum point contact"
The conductance of quantum point contact (QPC) is quantized at integer
multiples of 2 e2/h. In addition to these conductance steps, an extra
conductance plateau around 0.7 (2 e2/h) has been experimentally
observed. Experimental evidences indicate the phenomenon is associated
with the spin degrees of freedom near the QPC; especially, Kondo
physics has been observed at low temperature and voltage bias.
Density-functional calculations reveal the formation of a quasi-bound
state at the QPC. Motivated by the results, a generalized
single-impurity Anderson model has been invoked to describe transport
through QPCs . According to this model, the tunneling of a second
electron through that state is suppressed by Coulomb interactions, and
is enhanced at low temperatures by the Kondo effect. Thus, at
temperatures larger than the Kondo temperature, the conductance will
be dominated by transport through the singly occupied level e2/h,
growing at lower temperature towards the unitary limit, 2 e2/h.
In recent experiments, the current shot noise and dephasing rate have
been investigated. The shot noise is measured from high magnetic
fields to zero field. The current shot noise in the QPCs show a
reduction of the noise near the 0.7 structure. The dephasing rate
shows a double peak structure. We explain the results using the
Anderson model. Suppression of Shot Noise in Quantum Point Contacts
in the ''0.7 Regime.
A. Golub, T. Aono, Y. Meir, Phy. Rev. Lett. 97, 186801 (2006).