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Condensed Matter Seminars
Condensed Matter
Thursday, April 11, 2002
4:00 PM
Physics Building, Room 204
Note special time.
Note special room.

Xiaoya Qi
[Host: D. Louca]
University of Virginia
"Quantum fluctuations of charge and phase transitions of alarge Coulombblockaded quantum dot"

ABSTRACT:
We analyze groundstate properties of a large gated quantum dot coupled via
a quantum point contact to a reservoir of onedimensional interacting
spinless electrons. We find that the classical steplike dependence of the
dot population on the gate voltage is preserved under certain conditions. We
point out that the problem is related to the classical onedimensional Ising
model with inversesquare interactions. This Ising universality class
further subdivides into (i) the Kondo/Ising class and (ii) the tricritical
class. For systems of the Kondo/Ising class, and repulsive electrons, the
gate voltage dependence of the dot population is continuous for sufficiently
open dots, while taking the form of a modified staircase for dots
sufficiently isolated from the reservoir. At the phase transition between
the two regimes the magnitude of the dot population jump is universal. For
systems in the tricritical class we find in addition an intermediate regime
where the dot population jumps from near integer value to a region of stable
population centered about a halfinteger value. In particular, this
tricritical behaviour (together with the two dependencies already seen in
the Kondo/Ising class) is realized for noninteracting electrons. 



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