M Korkusinski

Publications of M Korkusinski

• Quantum interference in exciton-Mn spin interactions in a CdTe semiconductor quantum dot

  Authors: A. Trojnar, M Korkusinski, E. Kadantsev, P. Hawrylak, M. Goryca, T. Kazimierczuk, P. Kossacki, P. Wojnar, M. Potemski

  05/2011;

  We show theoretically and experimentally the existence of a new quantum interference(QI) effect between the electron-hole interactions and the scattering by a single Mn impurity. Theoretical model,We show theoretically and experimentally the existence of a new quantum interference(QI) effect between the electron-hole interactions and the scattering by a single Mn impurity. Theoretical model, including electron-valence hole correlations, the short and long range exchange interaction of Mn ion with the heavy hole and with electron and anisotropy of the quantum dot, is compared with photoluminescence spectroscopy of CdTe dots with single magnetic ions. We show how design of the electronic levels of a quantum dot enable the design of an exciton, control of the quantum interference and hence engineering of light-Mn interaction.

• Magnetism and correlations in fractionally filled degenerate shells of graphene quantum dots.

  Authors: A D Güçlü, P Potasz, O Voznyy, M Korkusinski, P Hawrylak

  Physical review letters. 12/2009; 103(24):246805.

  We show that the ground state and magnetization of the macroscopically degenerate shell of electronic states in triangular gated graphene quantum dots depends on the filling fraction of the shell.We show that the ground state and magnetization of the macroscopically degenerate shell of electronic states in triangular gated graphene quantum dots depends on the filling fraction of the shell. The effect of degeneracy, finite size, and electron-electron interactions are treated nonperturbatively using a combination of density functional theory, tight-binding, Hartree-Fock and configuration interaction methods. We show that electronic correlations play a crucial role in determining the nature of the ground state as a function of filling fraction of the degenerate shell at the Fermi level. We find that the half-filled charge neutral shell leads to full spin polarization but this magnetic moment can be completely destroyed by adding a single electron.

• Magnetism and correlations in fractionally filled degenerate shells of graphene quantum dots

  Authors: A. D. Guclu, P. Potasz, O. Voznyy, M Korkusinski, P. Hawrylak

  07/2009;

  When an electron is confined to a triangular atomic thick layer of graphene [1-5] with zig-zag edges, its energy spectrum collapses to a shell of degenerate states at the Fermi level (Dirac point)When an electron is confined to a triangular atomic thick layer of graphene [1-5] with zig-zag edges, its energy spectrum collapses to a shell of degenerate states at the Fermi level (Dirac point) [6-9]. The degeneracy is proportional to the edge size and can be made macroscopic. This opens up the possibility to design a strongly correlated electronic system as a function of fractional filling of the zero-energy shell, in analogy to the fractional quantum Hall effect in a quasi-two-dimensional electron gas[10], but without the need for a high magnetic field. In this work we show that electronic correlations, beyond the Hubbard model[6,7] and mean-field density functional theory (DFT) [7,8] play a crucial role in determining the nature of the ground state and the excitation spectrum of triangular graphene quantum dots as a function of dot size and filling fraction of the shell of zero-energy states. The interactions are treated by a combination of DFT, tight-binding, Hartree-Fock and configuration interaction methods (TB-HF-CI) and include all scattering and exchange terms within second nearest neighbors as well as interaction with metallic gate. We show that a half filled charge neutral shell leads to full spin polarization of the island but this magnetic moment is completely destroyed by the addition of a single electron, in analogy to the effect of skyrmions on the quantum Hall ferromagnet [11-14] and spin depolarization in electrostatically defined semiconductor quantum dots[15-18]. The depolarization of the ground state is predicted to result in blocking of current through a graphene quantum dot due to spin blockade (SB) [18]. Comment: v2: minor corrections, new format

• Multiexciton complexes in InAs self-assembled quantum dots

  Authors: M. Korkusinski, M. Zielinski, P. Hawrylak

  Journal of Applied Physics. 07/2009;

  We review our recent work on multiexciton complexes in InAs self-assembled quantum dots using a combination of effective mass, k∙p , and atomistic sp³s^*d⁵We review our recent work on multiexciton complexes in InAs self-assembled quantum dots using a combination of effective mass, k∙p , and atomistic sp³s^*d⁵ tight-binding approaches. The single-particle levels from effective mass, k∙p , and atomistic tight-binding models are used as input into configuration-interaction calculation of multiexciton spectra. We describe the principles of the atomistic approach and apply all these computational tools to illustrate the concept of hidden symmetry as underlying principle in energy levels of multiexciton complexes, optical detection of electron spin polarization, tunneling of holes in quantum dot molecules, and tuning of multiexciton spectra with lateral electric fields for entangled photon pair generation.

• Antibonding ground states in InAs quantum-dot molecules.

  Authors: M. F. Doty, J. I. Climente, M Korkusinski, M. Scheibner, A. S. Bracker, P. Hawrylak, D. Gammon

  Physical review letters. 02/2009; 102(4):047401.

  Coherent tunneling between two InAs quantum dots forms delocalized molecular states. Using magnetophotoluminescence spectroscopy we show that when holes tunnel through a thin barrier, the lowestCoherent tunneling between two InAs quantum dots forms delocalized molecular states. Using magnetophotoluminescence spectroscopy we show that when holes tunnel through a thin barrier, the lowest energy molecular state has bonding orbital character. However, as the thickness of the barrier increases, the molecular ground state changes character from a bonding orbital to an antibonding orbital, confirming recent theoretical predictions. We explain how the spin-orbit interaction causes this counterintuitive reversal by using a four-band k.p model and atomistic calculations that account for strain.

• Spin-selective aharonov-bohm oscillations in a lateral triple quantum dot.

  Authors: F. Delgado, Y. -P. Shim, M Korkusinski, L. Gaudreau, S. A. Studenikin, A. S. Sachrajda, P. Hawrylak

  Physical review letters. 12/2008; 101(22):226810.

  We present a theory of spin-selective Aharonov-Bohm oscillations in a lateral triple quantum dot. We show that to understand the Aharonov-Bohm (AB) effect in an interacting electron system within aWe present a theory of spin-selective Aharonov-Bohm oscillations in a lateral triple quantum dot. We show that to understand the Aharonov-Bohm (AB) effect in an interacting electron system within a triple quantum dot molecule (TQD) where the dots lie in a ring configuration requires one to not only consider electron charge but also spin. Using a Hubbard model supported by microscopic calculations we show that, by localizing a single electron spin in one of the dots, the current through the TQD molecule depends not only on the flux but also on the relative orientation of the spin of the incoming and localized electrons. AB oscillations are predicted only for the spin singlet electron complex resulting in a magnetic field tunable "spin valve."

• Intershell Exchange and Sequential Electrically Injected Spin Populations of InAs Quantum-Dot Shell States.

  Authors: G. Kioseoglou, M. Yasar, C. H. Li, M Korkusinski, M Diaz-Avila, A. T. Hanbicki, P. Hawrylak, A. Petrou, B. T. Jonker

  Physical review letters. 12/2008; 101(22):227203.

  We report sequential spin population of individual shell states of self-assembled InAs quantum dots controlled by a spin-polarized current from an Fe contact, and determine the s-p and p-d intershellWe report sequential spin population of individual shell states of self-assembled InAs quantum dots controlled by a spin-polarized current from an Fe contact, and determine the s-p and p-d intershell exchange energies. We resolve excitonic features in the electroluminescence (EL) spectra associated with individual quantum levels. In contrast with simple models of shell occupation, the EL circular polarization exhibits maxima shifted with respect to the intensity peaks. Calculations show that this is due to intershell exchange. Exchange energies for the s-p and p-d shells are 7+/-2 and 13.5+/-1 meV, respectively.

• Prepositioned single quantum dot in a lateral electric field

  Authors: M. E. Reimer, M. Korkusinski, D. Dalacu, J. Lefebvre, J. Lapointe, P. J. Poole, G. C. Aers, W. R. McKinnon, P. Hawrylak, R. L. Williams

  Physical Review B (Condensed Matter and Materials Physics). 11/2008; 78:195301--8.

• Antibonding ground states in semiconductor artificial molecules

  Authors: M. F. Doty, J. I. Climente, M Korkusinski, M. Scheibner, A. S. Bracker, P. Hawrylak, D. Gammon

  04/2008;

  The spin-orbit interaction is a crucial element of many semiconductor spintronic technologies. Here we report the first experimental observation, by magneto-optical spectroscopy, of a remarkableThe spin-orbit interaction is a crucial element of many semiconductor spintronic technologies. Here we report the first experimental observation, by magneto-optical spectroscopy, of a remarkable consequence of the spin-orbit interaction for holes confined in the molecular states of coupled quantum dots. As the thickness of the barrier separating two coupled quantum dots is increased, the molecular ground state changes character from a bonding orbital to an antibonding orbital. This result is counterintuitive, and antibonding molecular ground states are never observed in natural diatomic molecules. We explain the origin of the reversal using a four band k.p model that has been validated by numerical calculations that account for strain. The discovery of antibonding molecular ground states provides new opportunities for the design of artificially structured materials with complex molecular properties that cannot be achieved in natural systems. Comment: 10 pages, 4 figures, with additional 5 pages of supplementary material

• Direct observation of polarons in electron populated quantum dots by resonant Raman scattering.

  Authors: B. Aslan, H.C. Liu, M Korkusinski, P. Hawrylak, D J Lockwood

  Journal of nanoscience and nanotechnology. 03/2008; 8(2):789-94.

  The general problem of the pairing of strongly interacting elementary excitations producing new quasiparticles such as polarons arises in many areas of solid state physics. Recent interest in polaronThe general problem of the pairing of strongly interacting elementary excitations producing new quasiparticles such as polarons arises in many areas of solid state physics. Recent interest in polaron formation in semiconductor quantum dots has been motivated by the need to understand the physical nature of the carrier relaxation processes and their role in quantum-dot based devices. We report on the direct observation of polarons in InAs/GaAs self-assembled quantum dots populated by few electrons where the polarons are strongly coupled modes of quantum dot phonons and electron intersublevel transitions. The degree of coupling is varied in a systematic way in a set of samples having electron intersublevel spacing changing from larger to smaller than the longitudinal optical phonon energy. The signature of polarons is evidenced clearly by the observation of a large (12-20 meV) anticrossing for both InAs and GaAs-like quantum dot phonons using resonant Raman spectroscopy.

• Antibonding hole ground state in artificial molecules

  Authors: J. I. Climente, M Korkusinski, M. F. Doty, M. Scheibner, A. S. Bracker, G. Goldoni, D. Gammon, and P. Hawrylak

  OAtube Nanotechnology. 01/2008;

  Resonant tunneling of carriers between vertically coupled quantum dots enables the formation of hybridized, molecular-like orbitals which are important in many quantum dot-based devices, includingResonant tunneling of carriers between vertically coupled quantum dots enables the formation of hybridized, molecular-like orbitals which are important in many quantum dot-based devices, including those aiming at optically-controlled quantum information storage.[1] The differences in size and composition of quantum dots is overcome by the application of the vertical electric field, which brings the two quantum dot levels into resonance and induces either electron or hole tunneling.[2] The tunneling of electrons is now well understood[1-4], it leads to the formation of bonding molecular ground states in analogy to natural diatomic molecules. However, tunneling of holes does not have a counterpart in diatomic molecules and is less understood. In fact, previous atomistic calculations suggested a reversal of bonding and antibonding hole molecular ground states as the interdot barrier distance increases.[5-7]In this work, we present theory and experimental observation of the formation of the antibonding hole molecular ground state. Using a 4-band k·p approximation, the hole states are described as Luttinger spinors[8], which contain all the relevant symmetries. It is shown that the strong spin-orbit interaction in the valence band breaks the parity in the growth direction, mixing bonding and antibonding heavy- and light-hole components of the spinor. This mixing destabilizes (stabilizes) the otherwise pure bonding (antibonding) states, leading to the state reversal. Molecular ground states are then found to have up to ~95% antibonding character. These conclusions are reproduced by numerical, atomistic multi-million-atom calculations using a sp^3d^5s* tight-binding model applied to the realistic self-assembled InGaAs/GaAs double quantum dot structures, including strain, structural asymmetries and vertical electric fields. The results are in qualitative agreement with the k·p theory and predict a bonding-to-antibonding ground state reversal at interdot distances of d»2 nm. Clear experimental evidence of this peculiar hole behavior is found in magneto-photoluminescence experiments of double dots. The character of the hole molecular orbitals is identified from the electric field dependence of the Zeeman splitting of the neutral exciton when resonant hole tunneling is induced[9]. Comparison of samples with different inter-dot separation shows the bonding-to-antibonding ground state reversal in agreement with theory [10].

• Theory of spin, electronic and transport properties of the lateral triple quantum dot molecule in a magnetic field

  Authors: F. Delgado, Y. -P. Shim, M Korkusinski, P. Hawrylak

  07/2007;

  We present a theory of spin, electronic and transport properties of a few-electron lateral triangular triple quantum dot molecule in a magnetic field. Our theory is based on a generalization of aWe present a theory of spin, electronic and transport properties of a few-electron lateral triangular triple quantum dot molecule in a magnetic field. Our theory is based on a generalization of a Hubbard model and the Linear Combination of Harmonic Orbitals combined with Configuration Interaction method (LCHO-CI) for arbitrary magnetic fields. The few-particle spectra obtained as a function of the magnetic field exhibit Aharonov-Bohm oscillations. As a result, by changing the magnetic field it is possible to engineer the degeneracies of single-particle levels, and thus control the total spin of the many-electron system. For the triple dot with two and four electrons we find oscillations of total spin due to the singlet-triplet transitions occurring periodically in the magnetic field. In the three-electron system we find a transition from a magnetically frustrated to the spin-polarized state. We discuss the impact of these phase transitions on the addition spectrum and the spin blockade of the lateral triple quantum dot molecule. Comment: 30 pages (one column), 9 figures

• Optical readout of charge and spin in a self-assembled quantum dot in a strong magnetic field

  Authors: M Korkusinski, P. Hawrylak, A. Babinski, M. Potemski, S. Raymond, Z. Wasilewski

  06/2007;

  We present a theory and experiment demonstrating optical readout of charge and spin in a single InAs/GaAs self-assembled quantum dot. By applying a magnetic field we create the filling factor 2We present a theory and experiment demonstrating optical readout of charge and spin in a single InAs/GaAs self-assembled quantum dot. By applying a magnetic field we create the filling factor 2 quantum Hall singlet phase of the charged exciton. Increasing or decreasing the magnetic field leads to electronic spin-flip transitions and increasing spin polarization. The increasing total spin of electrons appears as a manifold of closely spaced emission lines, while spin flips appear as discontinuities of emission lines. The number of multiplets and discontinuities measures the number of carriers and their spin. We present a complete analysis of the emission spectrum of a single quantum dot with N=4 electrons and a single hole, calculated and measured in magnetic fields up to 23 Tesla. Comment: 9 pages, 3 figures, submitted to Europhysics Letters

• Stability diagram of a few-electron triple dot.

  Authors: L. Gaudreau, S. A. Studenikin, A. S. Sachrajda, P. Zawadzki, A. Kam, J. Lapointe, M Korkusinski, P. Hawrylak

  Physical review letters. 08/2006; 97(3):036807.

  Individual and coupled quantum dots containing one or two electrons have been realized and are regarded as components for future quantum information circuits. In this Letter we map out experimentallyIndividual and coupled quantum dots containing one or two electrons have been realized and are regarded as components for future quantum information circuits. In this Letter we map out experimentally the stability diagram of the few-electron triple dot system, the electron configuration map as a function of the external tuning parameters, and reveal experimentally for the first time the existence of quadruple points, a signature of the three dots being in resonance. In the vicinity of these quadruple points we observe a duplication of charge transfer transitions related to charge and spin reconfigurations triggered by changes in the total electron occupation number. The experimental results are largely reproduced by equivalent circuit analysis and Hubbard models. Our results are relevant for future quantum mechanical engineering applications within both quantum information and quantum cellular automata architectures.

• Charging characteristics of a few electron triple lateral quantum dot system in GaAs/AlGaAs

  Authors: S. Studenikin, L. Gaudreau, A. Sachrajda, P. Zawadzki, A. Kam, J. Lapointe, M. Korkusinski, P. Hawrylak

  Nanotechnology, 2006. IEEE-NANO 2006. Sixth IEEE Conference on; 07/2006

  We report the first experimental realization of a semiconductor triple quantum dot system in a few electrons regime. Charging properties of this "artificial tri-atom" are studied using non-invasiveWe report the first experimental realization of a semiconductor triple quantum dot system in a few electrons regime. Charging properties of this "artificial tri-atom" are studied using non-invasive charge detection technique. The most fundamental configuration was initialized in which a single electron is shared resonantly between the three dots and also equivalent arrangements involving two or three electrons. Using gates we are able to tune through the quadruple points, a unique feature of triple dot systems. At a quadruple point the quantum states in all three dots resonantly coincide with each other and with the chemical potential of the leads. Unexpectedly, novel charge re-arrangement lines were observed in vicinity of quadruple points. The observed charge re-arrangement can be viewed as a basic realization of quantum cellular automata in the few electron regime. Such phenomenon may be expected for all multiple quantum dot systems greater than two, in which a change in the state of one dot may instantaneously trigger a charge rearrangement of the system. The results may lead to new opportunities for fundamental physics research and for other applications, e.g. quantum computing.

• Quantum Dots: Building Blocks of Quantum Devices?

  Authors: Manfred Bayer, G. Ortner, A. Larionov, D.R. Yakovlev, M. Schwab, P. Borri, W. Langbein, U. Woggon, I. Yugova, G. Baldassarri Höger von Högersthal, Y.B. Lyanda-Geller, T.L. Reinecke, S. Fafard, Z. Wasilewski, M. Korkusinski, P. Hawrylak, A. Forchel, J.P. Reithmaier

  01/2004: pages 1224--1225;

• Optical detection of the Aharonov-Bohm effect on a charged particle in a nanoscale quantum ring.

  Authors: M. Bayer, M Korkusinski, P. Hawrylak, T. Gutbrod, M. Michel, A. Forchel

  Physical review letters. 06/2003; 90(18):186801.

  We study spectroscopically the current produced by a charged particle moving in a nanosize semiconductor quantum ring subject to a perpendicular magnetic field. Several Aharonov-Bohm oscillations areWe study spectroscopically the current produced by a charged particle moving in a nanosize semiconductor quantum ring subject to a perpendicular magnetic field. Several Aharonov-Bohm oscillations are observed in the emission of a charged exciton confined in a single ring structure. The magnetic field period of the oscillations correlates well with the size of the rings.

• Collapse of the spin-singlet phase in quantum dots.

  Authors: M. Ciorga, A. Wensauer, M. Pioro-Ladriere, M Korkusinski, J. Kyriakidis, A. S. Sachrajda, P. Hawrylak

  Physical review letters. 07/2002; 88(25 Pt 1):256804.

  We present experimental and theoretical results on a new regime in quantum dots in which the filling factor two-singlet state is replaced by new spin polarized phases. We make use of spin blockadeWe present experimental and theoretical results on a new regime in quantum dots in which the filling factor two-singlet state is replaced by new spin polarized phases. We make use of spin blockade spectroscopy to identify the transition to this new regime as a function of the number of electrons. The key experimental observation is a reversal of the phase in the systematic oscillation of the amplitude of Coulomb blockade peaks as the number of electrons is increased above a critical number. It is found theoretically that correlations are crucial to the existence of the new phases.

• Coupling and entangling of quantum states in quantum dot molecules.

  Authors: M. Bayer, P. Hawrylak, K. Hinzer, S. Fafard, M Korkusinski, Z.R. Wasilewski, O. Stern, A. Forchel

  Science (New York, N.Y.). 02/2001; 291(5503):451-3.

  We demonstrate coupling and entangling of quantum states in a pair of vertically aligned, self-assembled quantum dots by studying the emission of an interacting electron-hole pair (exciton) in aWe demonstrate coupling and entangling of quantum states in a pair of vertically aligned, self-assembled quantum dots by studying the emission of an interacting electron-hole pair (exciton) in a single dot molecule as a function of the separation between the dots. An interaction-induced energy splitting of the exciton is observed that exceeds 30 millielectron volts for a dot layer separation of 4 nanometers. The results are interpreted by mapping the tunneling of a particle in a double dot to the problem of a single spin. The electron-hole complex is shown to be equivalent to entangled states of two interacting spins.

• Building semiconductor nanostructures atom by atom

  Authors: M Korkusinski, P. Hawrylak, M Zielinski, W. Sheng, Gerhard Klimeck

  Birck and NCN Publications.

  We present an atomistic tight-binding approach to calculating the electronic structure of semiconductor nanostructures. We start by deriving the strain distribution in the structure using the valenceWe present an atomistic tight-binding approach to calculating the electronic structure of semiconductor nanostructures. We start by deriving the strain distribution in the structure using the valence force field model. The strain field is incorporated into the tight-binding electronic structure calculation carried out in the frame of the effective bond orbital model and the fully atomistic Sp(3)d(5)s* approach. We apply the method to a vertically coupled self-assembled double-dot molecule. Using the effective mass approach, we establish the existence of electronic bonding and antibonding molecular orbitals for electrons and holes, whose probability density is shared equally between the dots. In the atomistic calculation we recover the molecular character of electron orbitals, but find that structural and atomistic details of the sample modify the hole orbitals, leading to a strongly asymmetric distribution of the probability density between the dots.