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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-2195
DTSTART:20110712T150000Z
DURATION:PT1H0M0S
DTSTAMP:20240329T083242Z
LAST-MODIFIED:20110706T131200Z
LOCATION:5310 Chamberlin
SUMMARY:Impurity effects in few-electron quantum dots\, Condensed Matt
er Theory Group Seminar\, Nga Nguyen\, University of Maryland - Colleg
e Park
DESCRIPTION:Doping semiconductor nanostructures\, e.g. quantum dots (Q
Ds)\, with magnetic impurities (Mn2+) offers a means to stu
dy spin manipulation through the strong spin exchange interaction betw
een electrons (holes) and magnetic impurities. The magnetic properties
of group II-VI semiconductor QDs doped with magnetic impurities have
recently attracted considerable attention. Studies on those systems ha
ve led to fundamental insights in magnetism and resulted in e.g. diffe
rent effective spin states. In the first part of my talk\, I discuss t
he fundamental many-body effects in strongly interacting few-electron
QDs doped with few magnetic impurities. We investigate ferromagneti
c and antiferromagnetic phases as a consequence of dominant
spin-spin electron-Mn2+ exchange interaction in the Cd(Mn)
Te QDs. A non-trivial phase diagram\, which exhibits substantial diffe
rences for systems with different number of electrons\, is fully calcu
lated. We found frustrated (spin-glass-like) regions\, which on
ly appear when the Mn-ions antiferromagnetically couple with each othe
r and ferromagnetically couple with the electrons. We argue that Kohn'
s theorem no longer holds in Mn2+-doped parabolic few-elect
ron QDs. The magneto-optical absorption (FIR) spectrum now depe
nds strongly on the electron-electron interaction and varies with chan
ging the number of electrons. Spin exchange interaction between electr
on and the Mn-ion results in different cyclotron resonance absorption
lines quantitatively and qualitatively.
\n
\nThe second part o
f my talk is to discuss the effects of having unintentional charged im
purities in laterally coupled two-dimensional double (GaAs\, Si) QDs\,
where each dot contains one or two electrons and a single charged imp
urity. Using molecular orbital and configuration interaction methods\,
we calculate the effect of the impurity on the two-electron energy sp
ectrum of each individual dot as well as on the spectrum of the couple
d-double-dot two-electron system. We find that the singlet-triplet exc
hange splitting between the two lowest-energy states\, both for the in
dividual dots and the coupled-dot system\, depends sensitively on the
location of the impurity and its coupling strength (i.e. the effective
charge). A strong electron-impurity coupling breaks down the equality
of the two doubly occupied singlets in the left and the right dots\,
leading to a mixing between different spin singlets. As a result\, the
maximally entangled qubit states are no longer fully obtained in the
zero-magnetic-field case.
\n
URL:https://www.physics.wisc.edu/events/?id=2195
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