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PRODID:UW-Madison-Physics-Events
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UID:UW-Physics-Event-2195
DTSTART:20110712T150000Z
DURATION:PT1H0M0S
DTSTAMP:20260309T062126Z
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 (Mn<sup>2+</sup>) 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 <i>ferromagneti
 c</i> and <i>antiferromagnetic</i> phases as a consequence of dominant
  spin-spin electron-Mn<sup>2+</sup> 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 <i>frustrated</i> (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 Mn<sup>2+</sup>-doped parabolic few-elect
 ron QDs. The <i>magneto-optical absorption</i> (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.<br>
\n<br>
\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.<br>
\n
URL:https://www.physics.wisc.edu/events/?id=2195
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