2,863 Works

Giant anisotropy of zeeman splitting of quantum confined acceptors in Si/Ge

K.-M. Haendel, R. Winkler, U. Denker, O.G. Schmidt & Rolf J. Haug
Shallow acceptor levels in Si/Ge/Si quantum well heterostructures are characterized by resonant-tunneling spectroscopy in the presence of high magnetic fields. In a perpendicular magnetic field we observe a linear Zeeman splitting of the acceptor levels. In an in-plane field, on the other hand, the Zeeman splitting is strongly suppressed. This anisotropic Zeeman splitting is shown to be a consequence of the huge light-hole-heavy-hole splitting caused by a large biaxial strain and a strong quantum confinement...

Probing a Kondo-correlated quantum dot with spin spectroscopy

D. Kupidura, M.C. Rogge, M. Reinwald, W. Wegscheider & Rolf J. Haug
We investigate the Kondo effect and spin blockade observed in a many-electron quantum dot and study the magnetic field dependence. At lower fields, a pronounced Kondo effect is found, which is replaced by the spin blockade at higher fields. In an intermediate regime, both effects are visible. We make use of this combined effect to gain information about the internal spin configuration of our quantum dot. We find that the data cannot be explained assuming...

Enhanced shot noise in tunneling through a stack of coupled quantum dots

P. Barthold, Frank Hohls, Niels Maire, Klaus Pierz & Rolf J. Haug
We have investigated the noise properties of the tunneling current through vertically coupled self-assembled InAs quantum dots. We observe super-Poissonian shot noise at low temperatures. For increased temperature this effect is suppressed. The super-Poissonian noise is explained by capacitive coupling between different stacks of quantum dots. © 2006 The American Physical Society.

Spin-orbit coupling and anisotropy of spin splitting in quantum dots

J. Könemann, Rolf J. Haug, D.K. Maude, V.I. Fal'Ko & B.L. Altshuler
In lateral quantum dots, the combined effect of both Dresselhaus and Bychkov-Rashba spin-orbit coupling is equivalent to an effective magnetic field ±BSO which has the opposite sign for sz=±1/2 spin electrons. When the external magnetic field is perpendicular to the planar structure, the field BSO generates an additional splitting for electron states as compared to the spin splitting in the in-plane field orientation. The anisotropy of spin splitting has been measured and then analyzed in...

Phonon excitations of composite-fermion Landau levels

F. Schulze-Wischeler, Frank Hohls, U. Zeitler, D. Reuter, A.D. Wieck & Rolf J. Haug
The phonon excitations of fractional quantum Hall (FQH) states at filling factors ν =1÷3,2÷5, 4÷7, 3÷5, 4÷3, and 5÷3 were investigated. The excitations were found to be based on Landau-level transitions of composite fermions (CF). It was observed that at filling factor ν = 2÷3, a linear field dependence of the excitation energy in the high field regime showed a spin transition, which was excited by the phonons. All the transport gaps, except the one...

Observation of an interedge magnetoplasmon mode in a degenerate two-dimensional electron gas

G. Sukhodub, Frank Hohls & Rolf J. Haug
The propagation of edge magnetoplasmons (EMP) in a degenerated two-dimensional electron gas was analyzed. Investigations show that an interedge EMP mode attributed to the excitations of boundary between two regions with constant but different charge densities. The splitting of an incident voltage pulse into several EMP modes propagating with different velocities was also observed. The results show that the internal spatial parameters of the edge structure were derived from the analysis of the propagation velocities...

Direct measurement of the g factor of composite fermions

F. Schulze-Wischeler, E. Mariani, Frank Hohls & Rolf J. Haug
The activation gap δ of the fractional quantum Hall states was measured as a function of the perpendicular magnetic field. A linear dependence of δ on magnetic field was observed while approaching the spin-polarization transition. Composite fermions (CF) were introduced via the Chern-Simons gauge transformation on the many-electron wave function. The sharp linear magnetic field scaling of δ while approaching the spin-polarization transition yields a direct measurement of the CF 'g' factor alone.

Noise enhancement due to quantum coherence in coupled quantum dots

G. Kießlich, E. Schöll, T. Brandes, Frank Hohls & Rolf J. Haug
We show that the intriguing observation of noise enhancement in the charge transport through two vertically coupled quantum dots can be explained by the interplay of quantum coherence and strong Coulomb blockade. We demonstrate that this novel mechanism for super-Poissonian charge transfer is very sensitive to decoherence caused by electron-phonon scattering as inferred from the measured temperature dependence. © 2007 The American Physical Society.

Interaction-induced spin polarization in quantum dots

M.C. Rogge, E. Räsänen & Rolf J. Haug
The electronic states of lateral many-electron quantum dots in high magnetic fields are analyzed in terms of energy and spin. In a regime with two Landau levels in the dot, several Coulomb-blockade peaks are measured. A zigzag pattern is found as it is known from the Fock-Darwin spectrum. However, only data from Landau level 0 show the typical spin-induced bimodality, whereas features from Landau level 1 cannot be explained with the Fock-Darwin picture. Instead, by...

Channel blockade in a two-path triple-quantum-dot system

M. Kotzian, F. Gallego-Marcos, G. Platero & Rolf J. Haug
Electronic transport through a two-path triple-quantum-dot system with two source leads and one drain is studied and the interaction between the two paths is analyzed. We observe a channel blockade as a result of interchannel Coulombic interaction. The experimental results are understood with the help of a theoretical model which allows one to obtain the parameters of the system, the stability regions of each state, and the full dynamical transport in the triple-dot resonances. ©...

Charge reconfiguration in arrays of quantum dots

Johannes C. Bayer, Timo Wagner, Eddy P. Rugeramigabo & Rolf J. Haug
Semiconductor quantum dots are potential building blocks for scalable qubit architectures. Efficient control over the exchange interaction and the possibility of coherently manipulating electron states are essential ingredients towards this goal. We studied experimentally the shuttling of electrons trapped in serial quantum dot arrays isolated from the reservoirs. The isolation hereby enables a high degree of control over the tunnel couplings between the quantum dots, while electrons can be transferred through the array by gate...

Nonequilibrium mesoscopic conductance fluctuations as the origin of 1/f noise in epitaxial graphene

C.-C. Kalmbach, F.J. Ahlers, J. Schurr, A. Müller, J. Feilhauer, M. Kruskopf, Klaus Pierz, Frank Hohls & Rolf J. Haug
We investigate the 1/f noise properties of epitaxial graphene devices at low temperatures as a function of temperature, current, and magnetic flux density. At low currents, an exponential decay of the 1/f noise power spectral density with increasing temperature is observed that indicates mesoscopic conductance fluctuations as the origin of 1/f noise at temperatures below 50 K. At higher currents, deviations from the typical quadratic current dependence and the exponential temperature dependence occur as a...

Linear magnetoresistance in compensated graphene bilayer

G.Y. Vasileva, D. Smirnov, Y.L. Ivanov, Y.B. Vasilyev, P.S. Alekseev, A.P. Dmitriev, I.V. Gornyi, V.Y. Kachorovskii, M. Titov, B.N. Narozhny & Rolf J. Haug
We report a nonsaturating linear magnetoresistance in charge-compensated bilayer graphene in a temperature range from 1.5 to 150 K. The observed linear magnetoresistance disappears away from charge neutrality, ruling out the traditional explanation of the effect in terms of the classical random resistor network model. We show that experimental results qualitatively agree with a phenomenological two-fluid model taking into account electron-hole recombination and finite-size sample geometry. © 2016 American Physical Society.

Magnetoresistance induced by rare strong scatterers in a high-mobility two-dimensional electron gas

L. Bockhorn, I.V. Gornyi, D. Schuh, C. Reichl, W. Wegscheider & Rolf J. Haug
We observe a strong negative magnetoresistance at nonquantizing magnetic fields in a high-mobility two-dimensional electron gas. This strong negative magnetoresistance consists of a narrow peak around zero magnetic field and a huge magnetoresistance at larger fields. The peak shows parabolic magnetic field dependence and is attributed to the interplay of smooth disorder and rare strong scatterers. We identify the rare strong scatterers as macroscopic defects in the material and determine their density from the peak...

Kondo effect in a few-electron quantum ring

U.F. Keyser, C. Fühner, S. Borck, Rolf J. Haug, M. Bichler, G. Abstreiter & W. Wegscheider
A small tuneable quantum ring with less than ten electrons was shown to exhibit Aharonov-Bohm oscillations as well as Coulomb blockade. At strong coupling to the leads, evidence of a Kondo effect induced by a single spin on the ring was obtained. Analysis of the phase evolution of the Aharonov-Bohm effect in the Kondo regime yielded phase jumps by π at the Coulomb-blockade resonances and a smooth shift of the Aharonov-Bohm maxima in between.

Spin-dependent shot noise enhancement in a quantum dot

Niels Ubbelohde, Christian Fricke, Frank Hohls & Rolf J. Haug
The spin-dependent dynamical blockade was investigated in a lateral quantum dot in a magnetic field. Spin-polarized edge channels in the two-dimensional leads and the spatial distribution of Landau orbitals in the dot modulate the tunnel coupling of the quantum dot level spectrum. In a measurement of the electron shot noise we observe a pattern of super-Poissonian noise which is correlated to the spin-dependent competition between different transport channels. © 2013 American Physical Society.

Dynamical scaling of the quantum Hall plateau transition

Frank Hohls, U. Zeitler, Rolf J. Haug, R. Meisels, K. Dybko & F. Kuchar
The dynamical scaling of the quantum Hall plateau phase transition in the frequency range 0.1-55 GHz was examined. A universal scaling function was observed, yielding a dynamical exponent 0.9 ± 0.2. The universal behavior was independent of material, density, mobility, experimental technique, temperature and filling factor.

Hopping conductivity in the quantum Hall effect: Revival of universal scaling

Frank Hohls, U. Zeitler & Rolf J. Haug
The temperature and electric field dependence of the conductivity in the quantum Hall effect (QHE) plateau transition for samples where no universal behavior is found in the conventional temperature dependent peak-width scaling experiments was examined. A revival of universality in the variable-range hopping (VRH) regime was found. Furthermore, it was possible to rescale all the data on the Landau gap side of the transition on a single parameter function over more than 5 orders of...

Magnetoresistance anisotropy in Si/SiGe in tilted magnetic fields: Experimental evidence for a stripe-phase formation

U. Zeitler, Hans W. Schumacher, A.G.M. Jansen & Rolf J. Haug
The anisotropies induced by an in-plane field in the magnetotransport properties of coinciding Landau levels in the two dimensional electron system of a silicon/silicon germanium (Si/SiGe) heterostructure were investigated. The anisotropies were caused by the formation of a unidirectional stripe phase from two Landau levels with opposite spin of electrons.

Multiple transitions of the spin configuration in quantum dots

M.C. Rogge, C. Fühner & Rolf J. Haug
Single electron tunneling is studied in a many electron quantum dot in high magnetic fields. For such a system multiple transitions of the spin configuration are theoretically predicted. With a combination of spin blockade and Kondo effect we are able to detect five regions with different spin configurations. Transitions are induced with changing electron numbers. © 2006 The American Physical Society.

High frequency conductivity in the quantum Hall regime

Frank. Hohls, U. Zeitler & Rolf J. Haug
The frequency dependence of the longitudinal conductivity σxx for frequencies up to 6 GHz was measured. It was possible to access both the real part and the imaginary part of σxx which allowed to perform a new test of scaling behavior. Using the theory of Polyakov and Shklovskii on variable-range hopping in the QHE, the localization length was deduced.

Energy dependence of quasiparticle relaxation in a disordered Fermi liquid

T. Schmidt, P. König, E. McCann, V.I. Fal'Ko & Rolf J. Haug
Direct measurement of the energy dependence of the inelastic decay rate τ(E) of a quasiparticle state in a disordered conductor was performed using resonant tunneling spectroscopy. Decay rate was obtained from the analysis of the magnitude of disorder-induced fluctuations in the local density of states. Quantitative comparison with the standard theory was achieved.

Magnetic control of electric-field domains in semiconductor superlattices

T. Schmidt, A.G.M. Jansen, Rolf J. Haug, K.V. Klitzing & K. Eberl
Applying magnetic fields up to B = 29 T, we investigate the formation of electric-field domains in Landau-quantized semiconductor superlattices. Surprisingly, the electric-field distribution remains determined by the subband spacing rather than by the cyclotron energy. At the domain boundary, however, strong inter-Landau-level tunneling occurs, which leads to a magnetically tunable number of extra resonances in the current-voltage curve. In addition, we discuss a novel magnetic-field assisted high-field domain also stabilized by inter-Landau-level tunneling.

Spectroscopy of the single-particle states of a quantum-dot molecule

T. Schmidt, Rolf J. Haug, K. V. Klitzing, A. Förster & H. Lüth
We investigate low-temperature transport through two identical vertically coupled quantum dots in a triple-barrier heterostructure. The current-voltage curve exhibits two series of current steps of different magnitude. On the basis of magnetotunneling measurements, we relate the current steps to the single-particle levels of a quantum-dot molecule. From the absence of many-particle phenomena, an upper limit of 1 ns is determined for the energy-relaxation time in the double-dot system.

Observation of the local structure of landau bands in a disordered conductor

T. Schmidt, Rolf J. Haug, V.I. Fal'Ko, K. V. Klitzing, A. Förster & H. Lüth
The local density of states of heavily doped GaAs is explored at high magnetic fields, where only a single or few Landau bands are occupied. Our experiment is based on resonant tunneling through impurity states and images the local density of states both below and above the Fermi level. Fan-type mesoscopic fluctuations are observed in the energy-magnetic-field plane, which we attribute to the interplay of Landau quantization and quantum interference of scattered electron waves in...

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