@incollection{SteffensSuhrkeRoessler, author = {Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Ground state and collective excitations of quantum dots: Correlation effects and Hund's rule in magnetic field}, series = {Advances in Solid State Physics}, volume = {39}, booktitle = {Advances in Solid State Physics}, editor = {Kramer, Bernhard}, publisher = {Friedr. Vieweg \& Sohn}, address = {Braunschweig}, isbn = {978-3-540-44553-1}, doi = {10.1007/BFb0107469}, pages = {111 -- 120}, abstract = {We review ground-state properties and collective excitations of semiconductor quantum dots in a magnetic field obtained from current-spin density-functional theory. Due to exchange-correlation, a generalized Hund's rule in magnetic field can be established which leads to spin alignment in partially occupied energy shells at the Fermi energy. This results, in distinct spin structures in single-electron addition spectra. Current-dependent exchange-correlation modifies the magnetic-field dependence of the ground state configuration and leads to deviations from plain spin-density calculations. Moreover it gives rise to spontaneous current textures at zero magnetic field. Collective excitation spectra, explicitly calculated for inelastic light scattering, exhibit novel features in their magnetic field dependence due to a finite ground-state spin density.}, language = {en} } @article{SteffensSchloesserRotteretal., author = {Steffens, Oliver and Schl{\"o}sser, Tilman and Rotter, Peter and Ensslin, Klaus and Suhrke, Michael and Kotthaus, J{\"o}rg and R{\"o}ssler, Ulrich and Holland, M.}, title = {From the two-dimensional electron gas to antidot superlattices: Magnetoresistance effects in the transition regime}, series = {Journal of Physics: Condensed Matter}, volume = {10}, journal = {Journal of Physics: Condensed Matter}, number = {17}, issn = {0953-8984}, doi = {10.1088/0953-8984/10/17/016}, pages = {3859 -- 3872}, abstract = {Magnetoresistance measurements and theoretical calculations for two-dimensional electron systems under a perpendicular magnetic field are presented which illuminate transport effects due to a periodic electrostatic potential modulation. We focus on features arising from the resolution of the magnetic miniband structure which are beyond the perturbative regime governed by the dispersion of Landau bands. Our non-perturbative quantum-mechanical calculations reveal that the dispersion of individual minibands is responsible for the complicated behaviour of the magnetoresistance in the regime of intermediate modulation strength. In particular, the interplay between miniband and scattering contributions to the conductivity leads to an almost structureless magnetoresistance in this regime followed by the formation of antidot peaks due to the miniband conductivity.}, language = {en} } @article{SteffensSuhrkeRoessler, author = {Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Shell structure and exchange-related spin effects for quantum dots in a magnetic field}, series = {Physica B}, volume = {256-258}, journal = {Physica B}, doi = {10.1016/S0921-4526(98)00557-2}, pages = {147 -- 151}, abstract = {Ground-state calculations based on current spin density-functional theory for circular parabolic quantum dots are presented which reveal interesting spin effects in dependence on an external magnetic field: Hund's first rule (well-known from atomic physics for zero magnetic field) is related to the level occupancy near the Fermi energy and determines the spin configuration of the ground state in finite magnetic field. Consequently, the addition spectrum of the quantum dot exhibits a specific non-monotonous dependence on magnetic field, which is visible in recent quantum transport experiments.}, language = {en} } @article{SteffensRoesslerSuhrke, author = {Steffens, Oliver and R{\"o}ssler, Ulrich and Suhrke, Michael}, title = {Generalized Hund's rule in the addition spectrum of a quantum dot}, series = {EPL (Europhysics Letters)}, volume = {42}, journal = {EPL (Europhysics Letters)}, number = {5}, doi = {10.1209/epl/i1998-00276-4}, pages = {529 -- 534}, abstract = {We report on ground-state calculations based on current-spin density-functional theory for circular parabolic quantum dots. Hund's first rule, well-known from atomic physics, applies not only at zero magnetic field; analogous rules, related to the level occupancy near the Fermi energy, determine the spin configuration of the ground state in finite magnetic field. Consequently, the addition spectrum of the quantum dot exhibits a specific non-monotonous dependence on magnetic field. We discuss our results with focus on recent experiments which may already contain indications of this new feature.}, language = {en} } @article{SteffensSuhrkeRoessler, author = {Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Spontaneously-broken time-reversal symmetry in quantum dots}, series = {EPL (Europhysics Letters)}, volume = {44}, journal = {EPL (Europhysics Letters)}, issn = {1286-4854}, doi = {10.1209/EPL/I1998-00460-0}, pages = {222 -- 228}, abstract = {We present current-spin density-functional calculations for circular parabolic quantum dots in zero magnetic field. We find the possibility for broken time-reversal symmetry via exchange correlation with spontaneously induced orbital currents. For certain electron numbers, this results in new current textures which give rise to a finite magnetization even for ground states with vanishing total angular momentum.}, language = {en} } @article{WensauerSteffensSuhrkeetal., author = {Wensauer, Andreas and Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Laterally coupled few-electron quantum dots}, series = {Physical Review B}, volume = {62}, journal = {Physical Review B}, number = {4}, doi = {10.1103/PhysRevB.62.2605}, pages = {2605}, abstract = {We present ground-state calculations for laterally coupled quantum dots containing 2, 4, and 8 electrons. As our emphasis is on spin effects our results are obtained by applying spin-density functional theory (SDFT). By varying the distance between the centers of the coupled quantum dots, the transition from weak to strong coupling situation is realized. For the 2-electron system we also apply the Heitler-London approximation and analytical concepts to check the reliability of SDFT calculations in this case. In addition we discuss the features of the Coulomb staircase of laterally coupled quantum dots in the weak and strong coupling regimes in comparison to that of a circular parabolic quantum dot.}, language = {en} } @inproceedings{SteffensSuhrkeRoessler, author = {Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Correlation in few-electron quantum dots: Spin effects and spontaneous currents}, series = {24rd International Conference on the Physics of Semiconductors (ICPS 24), Jerusalem, Israel, August 2-7, 1998}, booktitle = {24rd International Conference on the Physics of Semiconductors (ICPS 24), Jerusalem, Israel, August 2-7, 1998}, editor = {Gershoni, David}, publisher = {World Scientific}, address = {Singapore}, isbn = {978-981-02-3613-7}, language = {en} } @article{MayrockMikhailovSteffensetal., author = {Mayrock, Oliver and Mikhailov, Sergej A. and Steffens, Oliver and R{\"o}ssler, Ulrich}, title = {Observability of the acoustic plasma mode in double-layered quantum dots}, series = {Physica E: Low-dimensional Systems and Nanostructures}, volume = {1}, journal = {Physica E: Low-dimensional Systems and Nanostructures}, number = {1-4}, doi = {10.1016/S1386-9477(97)00048-9}, pages = {232 -- 234}, abstract = {Double-layered quantum dots represent a novel realization of a multi-component plasma system. By modelling the system and applying classical concepts we investigate the oscillator strength of the acoustic plasma mode and its dependence on the system parameters. In view of recent experimental results, we discuss the observability of this collective excitation.}, language = {en} } @article{SteffensSuhrkeRotteretal., author = {Steffens, Oliver and Suhrke, Michael and Rotter, Peter and R{\"o}ssler, Ulrich}, title = {From Landau levels to universal fluctuations: Level statistics for lateral superlattices}, series = {Physical Review B}, volume = {55}, journal = {Physical Review B}, number = {7}, doi = {10.1103/PhysRevB.55.4486}, pages = {4486 -- 4493}, abstract = {We study the energy-level statistics for electrons in a lateral two-dimensional superlattice in dependence on the strength of the modulation potential at a given perpendicular magnetic field. The interminiband statistics at some selected point in the magnetic Brillouin zone shows a transition from degenerate Landau levels to universal spectral correlations while the corresponding classical dynamics displays a crossover from regular cyclotron orbits to chaotic motion. In terms of the nearest-neighbor spacing distribution, we observe the occurrence of level repulsion for all nonzero modulation amplitudes, which indicates a discontinuous transition to universal fluctuations for the smallest level spacings when the rotational invariance of the system is broken by a finite superlattice potential. In order to test the universality of the transition on larger scales, we propose a random matrix model with one transition parameter for comparison. Confirmed by two different types of potential shapes, we detect an explicit influence of the potential shape on the level spacing distributions, which hence cannot be described by the one-parameter model. Using the spectral rigidity, however, universal long-range fluctuations in the regime of negligible Landau-level mixing are found, in agreement with our random matrix model.}, language = {en} } @article{SuhrkeSteffensRotteretal., author = {Suhrke, Michael and Steffens, Oliver and Rotter, Peter and R{\"o}ssler, Ulrich}, title = {Quantum chaos and magnetotransport in lateral superlattices: The transition from weak to strong modulation potential}, series = {Physica E: Low-dimensional Systems and Nanostructures}, volume = {1}, journal = {Physica E: Low-dimensional Systems and Nanostructures}, number = {1-4}, issn = {1386-9477}, doi = {10.1016/S1386-9477(97)00060-X}, pages = {281 -- 287}, abstract = {Magnetotransport in lateral superlattices covers a variety of apparently different physics dependent on the amplitude of the modulation potential relative to the Fermi energy ranging from the weakly modulated 2DEG to the antidot lattice. Here we investigate the transition between weak modulation and antidots within the quantum-mechanical theory by studying (i) the single-particle spectrum with respect to quantum signatures of classical chaos and (ii) the change of characteristic features in the magnetoresistance starting from the Kubo formula.}, language = {en} } @techreport{SteffensRoesslerSuhrke, author = {Steffens, Oliver and R{\"o}ssler, Ulrich and Suhrke, Michael}, title = {Comment on "Shell Filling and Spin Effects in a Few Electron Quantum Dot"}, series = {Physical Review Letters}, volume = {77}, journal = {Physical Review Letters}, pages = {3613}, abstract = {We briefly report on calculated addition spectra for electrons in a circular quantum dot with perpendicular magnetic field. We compare our current density functional theory calculations with recent experiments by Tarucha et al. [PRL 77, 3613 (1996)]. We find a very good qualitative agreement of the structures and find an additional effect caused by Hund's first rule in magnetic field, which gives rise to new substructures not discussed in the paper by Tarucha.}, language = {en} }