C. Ellenberger

Excitation Spectrum of Two Correlated Electrons in a Lateral Quantum Dot with Negligible Zeeman Splitting

The excitation spectrum of a two-electron quantum dot is investigated by tunneling spectroscopy in conjunction with theoretical calculations. The dot made from a material with negligible Zeeman splitting has a moderate spatial anisotropy leading to a splitting of the two lowest triplet states at zero magnetic field. In addition to the well-known triplet excitation at zero magnetic field, two additional excited states are found at finite magnetic field. The lower one is identified as the second excited singlet state on the basis of an avoided crossing with the first excited singlet state at finite fields. The measured spectra are in remarkable agreement with exact-diagonalization calculations. The results prove the significance of electron correlations and suggest the formation of a state with Wigner-molecular properties at low magnetic fields.

Stray-field-induced modification of coherent spin dynamics

Electron spins in an InGaAs semiconductor quantum well are used as a magnetometer of magnetic stray fields from patterned Fe stripes. Using time-resolved Faraday rotation, the coherent precession of quantum-well spins in the inhomogeneous field below the Fe stripes is measured for varying magnetic fields. Comparing with reference stripes made of Au, we find an enhancement of the spin precession frequency proportional to the Fe magnetization, in line with a decrease of the spin decay time, which is attributed to the inhomogeneous magnetic stray field in the quantum-well layer.

Magnetotransport in C-doped AlGaAs heterostructures

High-quality C-doped p-type AlGaAs heterostructures with mobilities exceeding 150000cm2∕Vs are investigated by low-temperature magnetotransport experiments. We find features of the fractional quantum Hall effect as well as a highly resolved Shubnikov–de Haas oscillations at low magnetic fields. This allows us to determine the densities, effective masses, and mobilities of the holes populating the spin-split subbands arising from the lack of inversion symmetry in these structures.

Gate tunability of stray-field-induced electron spin precession in a GaAs/InxGa1 xAs quantum well below an interdigitated magnetized Fe grating

Time-resolved Faraday rotation is used to measure the coherent electron spin precession in a

Two-subband quantum Hall effect in parabolic quantum wells

\mathrm{Ga}\mathrm{As}∕{\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}

QUANTUM DOTS BASED ON PARABOLIC QUANTUM WELLS: IMPORTANCE OF ELECTRONIC CORRELATIONS

quantum well below an interdigitated magnetized Fe grating. We show that the electron spin precession frequency can be modified by applying a gate voltage of opposite polarity to neighboring bars. A tunability of the precession frequency of

Excitation spectra of two correlated electrons in a quantum dot

0.5\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}∕\mathrm{V}

Stray‐field‐induced modification of coherent spin dynamics

has been observed. Modulating the gate potential with a gigahertz frequency allows the electron spin precession to be controlled on a nanosecond timescale.

Optimized stray-field-induced enhancement of the electron spin precession by buried Fe gates

We report on pronounced minima between integer filling factors in low‐temperature magnetoresistance of parabolic quantum wells due to the occupation of the second subband. With a single‐particle model including Gaussian broadened Landau levels and an effective g‐factor for both subbands, the experimental data can be explained qualitatively.

Electronic properties of C‐doped (100) AlGaAs heterostructures

We present measurements and theoretical interpretation of the magnetic field dependent excitation spectra of a two-electron quantum dot. The quantum dot is based on an AlxGa1-xAs parabolic quantum well with effective g⋆-factor close to zero. Results of tunneling spectroscopy of the four lowest states are compared to exact diagonalization calculations and a generalized Heitler–London approximation and good agreement is found. Electronic correlations, associated with the formation of an H2-type Wigner molecule, turn out to be very important in this system.