Browsing by Author "Dinu, I. V."

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    Analysis of the phase lapse problem in closed interferometers
    (Elsevier B.V., 2012) Tolea, M.; Moldoveanu, V.; Dinu, I. V.; Tanatar, Bilal
    We investigate the connection between the asymmetry of the Fano resonances in a mesoscopic interferometer with an embedded quantum dot and the π lapses in the phase of the bare dot transmittance. Consecutive Fano resonances with the same (opposite) sign of the Fano parameter imply the presence (absence) of a phase lapse with π between the corresponding resonances of the dot. Our results suggest that the famous phase lapse problem, first reported by Schuster et al. [R. Schuster, E. Buks, M. Heiblum, D. Mahalu, V. Umansky, H. Shtrikman, Nature 385 (1997) 417], can therefore be experimentally addressed in closed interferometers. It is also proposed that the Fano effect can be used to extract the phase distributions of the eigenfunctions for a mesoscopic 2D shape, via the parity of the resonances. In the presence of electron-electron interaction, one can calculate the phases of the T-matrix elements. The numerical results lead to the same conclusions as for the non-interacting case.
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    Fano effect in a double T-shaped interferometer
    (Springer, 2009) Moldoveanu, V.; Dinu, I. V.; Tanatar, Bilal
    We study the coherent transport in a one-dimensional lead with two side-coupled quantum dots using the Keldysh's Green function formalism.The effect of the interdot Coulomb interaction is taken into account by computing the firstand second order contributions to the self-energy.We show that the Fano interference due to the resonance of one dotis strongly affected by the fixed parameters that characterize the second dot. If the second dot is tuned close to resonance an additionalpeak develops between the peak and dip of the Fano line shape of the current. In contrast, when the second dotis off-resonance and its occupation number is close to unity the interdot Coulomb interaction merely shifts the Fano line and no other maxima appear.The system we consider is more general than the single-dot interferometer studied experimentally by Kobayashi et al. [Phys. Rev. B 70, 035319 (2004)] and may be used for controlling quantum interference and studying decoherence effects in mesoscopic transport.
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    Light-hole exciton mixing and dynamics in Mn-doped quantum dots
    (American Physical Society, 2016) Moldoveanu, V.; Dinu, I. V.; Dragomir, R.; Tanatar, Bilal
    We investigate theoretically the spectral and dynamical effects of the short-range exchange interaction between a single manganese (Mn) atom hosted by cylindrical CdTe quantum dots and its light-hole excitons or biexcitons. Our approach is based on the Kohn-Luttinger k·p theory and configuration interaction method, the dynamics of the system in the presence of intraband relaxation being derived from the von Neumann-Lindblad equation. The complex structure of the light-hole exciton absorption spectrum reveals the exchange-induced exciton mixing and depends strongly on the Mn position. In particular, if the Mn atom is closer to the edges of the cylinder, the bright and dark light-hole excitons are mixed by the hole-Mn exchange alone. Consequently, their populations exhibit exchange-induced Rabi oscillations which can be viewed as optical signatures of light-hole spin reversal. Similar results are obtained for mixed biexcitons, in this case the exchange-induced Rabi oscillations being damped by the intraband hole relaxation processes. The effect of light-hole heavy-hole mixing is also discussed.
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    Non-equilibrium transport and spin dynamics insingle-molecule magnets.
    (Academic Press, 2015) Moldoveanu, V.; Dinu, I. V.; Tanatar, Bilal
    The time-dependent transport through single-molecule magnets (SMM) coupled to mag-netic or non-magnetic electrodes is studied in the framework of the generalized Masterequation (GME) method. We calculate the transient currents which develop when themolecule is smoothly coupled to the source and drain electrodes. The signature of theelectrically induced magnetic switching on these transient currents is investigated. Oursimulations show that the magnetic switching of the molecular spin can be read indirectlyfrom the transient currents if one lead is magnetic and it is much faster if the leads haveopposite spin polarizations. We identify effects of the transverse anisotropy on thedynamics of molecular states.
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    Quantum turnstile operation of single-molecule magnets
    (Institute of Physics Publishing, 2015) Moldoveanu, V.; Dinu, I. V.; Tanatar, Bilal; Moca, C. P.
    The time-dependent transport through single-molecule magnets coupled to magnetic or non-magnetic electrodes is studied in the framework of the generalized master equation method. We investigate the transient regime induced by the periodic switching of the source and drain contacts. If the electrodes have opposite magnetizations the quantum turnstile operation allows the stepwise writing of intermediate excited states. In turn, the transient currents provide a way to read these states. Within our approach we take into account both the uniaxial and transverse anisotropy. The latter may induce additional quantum tunneling processes which affect the efficiency of the proposed read-and-write scheme. An equally weighted mixture of molecular spin states can be prepared if one of the electrodes is ferromagnetic. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
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    Unpinning of heavy hole spin in magnetic quantum dots
    (Wiley-VCH Verlag, 2017) Dinu, I. V.; Moldoveanu, V.; Dragomir, R.; Tanatar, Bilal
    Using the k · p theory and configuration interaction method, we analyze the effect of heavy hole–light hole (HH–LH) mixing in CdTe quantum dots (QDs) with a single manganese (Mn) ion. We find that the hole-Mn exchange switches the coupling between two excitons whose Luttinger spinors have both HH and LH components. If the magnetic dopant is off-centered and the QD is subjected to a single π pulse the system periodically bounces between bright and dark mostly HH excitons with opposite HH spins. A pump-and-probe setup allows to estimate the efficiency of this HH spin unpinning from the biexciton response. The biexciton absorption spectrum is also discussed.