Browsing by Author "Cheng, SJ"

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Magnetic response of magnetic ion-doped nanocrystals: Effects of single Mn(2+) impurity
(2005-12-01)
Cheng, SJ
;
電子物理學系
;
Department of Electrophysics
We theoretically study the effects of single spin-5/2 magnetic impurity (Mn(2+)) on the magnetic response of nanocrystals containing interacting electrons. The energy spectrum and magnetic susceptibility of II-VI spherical nanocrystals as a function of the electron number (N(e)=1-8) and the location of Mn(2+) ion are calculated by using the configuration interaction method. It is found that the sp-d coupling between the carriers and Mn(2+) ion significantly affects the low-field paramagnetism, depending on electron number and the location of the ion. The competition between electron-electron interaction and the sp-d coupling leads to the pronounced anisotropy of magnetic properties, ground state transitions in magnetic field, and the violation of Hund's second rule.
Magnetic response of magnetic ion-doped nanocrystals: Effects of single Mn2+ impurity
(2005-12-01)
Cheng, SJ
;
電子物理學系
;
Department of Electrophysics
We theoretically study the effects of single spin-5/2 magnetic impurity (Mn2+) on the magnetic response of nanocrystals containing interacting electrons. The energy spectrum and magnetic susceptibility of II-VI spherical nanocrystals as a function of the electron number (N-e=1-8) and the location of Mn2+ ion are calculated by using the configuration interaction method. It is found that the sp-d coupling between the carriers and Mn2+ ion significantly affects the low-field paramagnetism, depending on electron number and the location of the ion. The competition between electron-electron interaction and the sp-d coupling leads to the pronounced anisotropy of magnetic properties, ground state transitions in magnetic field, and the violation of Hund's second rule.
Quantum Hall droplet at excitonic filling factor nu=2 in a self-assembled quantum dot
(2006-01-01)
Cheng, SJ
;
Hawrylak, P
;
電子物理學系
;
Department of Electrophysics
We present a theory of excitonic quantum Hall droplet (EXQHD) at filling factor nu=2 in a self-assembled quantum dot (SAD) subject to strong perpendicular magnetic field B. Using exact diagonalization technique we determine the ground and excited states, the stability against spin flips, and the optical emission spectrum of the nu=2 EXQHDs. In contrast with one-component electronic droplets, the singlet-singlet nu=2 EXQHD is found to be intrinsically correlated, and stable even in high magnetic fields due to the neutrality of exciton. The characteristic spin related emission spectrum and its magnetic field evolution from the EXQHD are predicted.
Shot noise of quantum ring excitons in a planar microcavity
(2005-12-01)
Chen, YN
;
Chuu, DS
;
Cheng, SJ
;
電子物理學系
;
Department of Electrophysics
Shot noise of quantum ring (QR) excitons in a p-i-n junction surrounded by a microcavity is investigated theoretically. Some radiative decay properties of a QR exciton in a microcavity can be obtained from the observation of the current noise, which also gives extra information about one of the tunnel barriers. A different noise feature between the quantum dot (QD) and QR is pointed out, and may be observed in a suitably designed experiment.
Theory of excitonic artificial atoms: InGaAs/GaAs quantum dots in strong magnetic fields
(2003-12-01)
Cheng, SJ
;
Sheng, WD
;
Hawrylak, P
;
電子物理學系
;
Department of Electrophysics
We develop a theory of excitonic artificial atoms in strong magnetic fields. The excitonic atoms are formed by N electrons and holes confined in a quantum dot. The single-particle levels are described by the Fock-Darwin spectrum in a magnetic field. The magnetic field induces crossing of energy levels and allows us to engineer degenerate shells. We apply exact diagonalization techniques to calculate the magnetic-field evolution of the ground state of the N-electron-hole complex and its emission spectra. We focus on degenerate shells and show that excitons condense into correlated states due to hidden symmetry. We relate the Fock-Darwin spectrum, hidden symmetries, and direct and exchange interaction among particles to the emission spectra as a function of number of electron-hole pairs (excitation power) and magnetic field.