arXiv subjects

M. Bichler

Publications and source records attributed to M. Bichler.

80 records · Page 5Linked to original sources

arXiv2000

Signatures of spin pairing in a quantum dot in the Coulomb blockade regime

Coulomb blockade resonances are measured in a GaAs quantum dot in which both shape deformations and interactions are small. The parametric evolution of the Coulomb blockade peaks shows a pronounced pair correlation in both position and amplitude, which is interpreted as spin pairing. As a consequence, the nearest-neighbor distribution of peak spacings can be well approximated by a smeared bimodal Wigner surmise, provided that interactions which go beyond the constant interaction model are taken into account.

cond-mat.mes-hall↗

arXiv1999

Shifting a Quantum Wire through a Disordered Crystal: Observation of Conductance Fluctuations in Real Space

A quantum wire is spatially displaced by suitable electric fields with respect to the scatterers inside a semiconductor crystal. As a function of the wire position, the low-temperature resistance shows reproducible fluctuations. Their characteristic temperature scale is a few hundred millikelvin, indicating a phase-coherent effect. Each fluctuation corresponds to a single scatterer entering or leaving the wire. This way, scattering centers can be counted one by one.

cond-mat.mes-hall↗

arXiv1999

Lateral tunneling through the controlled barrier between edge channels in a two-dimentional electron system

We study the lateral tunneling through the gate-voltage-controlled barrier, which arises as a result of partial elimination of the donor layer of a heterostructure along a fine strip using an atomic force microscope, between edge channels at the depletion-induced edges of a gated two-dimensional electron system. For a sufficiently high barrier a typical current-voltage characteristic is found to be strongly asymmetric and include, apart from a positive tunneling branch, the negative branch that corresponds to the current overflowing the barrier. We establish the barrier height depends linearly on both gate voltage and magnetic field and we describe the data in terms of electron tunneling between the outermost edge channels.

cond-mat.mes-hall↗

arXiv1999

Anomalous Kondo-effect in Quantum Dot at non-zero bias

We present measurements on the Kondo-effect in a small quantum dot connected strongly to one lead and weakly to the other. The conductance of the dot reveals an offset of the Kondo resonance at zero magnetic field. While the resonance persists in the negative bias regime, it is suppressed in the opposite direction. This demonstrates the pinning of the Kondo resonance to the Fermi levels of the left and right lead. As an outlook we exploit the spin blockade effect to gain information about the spin state of the quantum dot in the Kondo regime.

cond-mat.mes-hall↗

arXiv1998

Nano-ploughed Josephson Junctions as on-chip Radiation Sources

A new technique is presented which enables the fabrication of highly transparent Josephson junctions in combination with mesoscopic devices. We utilize a modified AFM tip to plough grooves into superconducting material, thus defining a weak link. This weak link is made within the superconducting split-gates, which are used to electrostatically form a conventional quantum dot and serves as a source of millimeter wave radiation around 100 GHz. We show the characteristics of typical junctions built and discuss their high-frequency properties. We find that the millimeter wave emission of the weak link leads to a bolometric effect in the case of quantum point contact spectroscopy.

cond-mat.mes-hall↗

arXiv1998

A New Type of Electron Nuclear-Spin Interaction from Resistively Detected NMR in the Fractional Quantum Hall Effect Regime

Two dimensional electron gases in narrow GaAs quantum wells show huge longitudinal resistance (HLR) values at certain fractional filling factors. Applying an RF field with frequencies corresponding to the nuclear spin splittings of {69}Ga, {71}Ga and {75}As leads to a substantial decreases of the HLR establishing a novel type of resistively detected NMR. These resonances are split into four sub lines each. Neither the number of sub lines nor the size of the splitting can be explained by established interaction mechanisms.

cond-mat.mes-hall↗

arXiv1998

Huge Longitudinal Resistance in the Fractional Quantum Hall Effect Regime

The magneto resistance of a narrow single quantum well is spectacularly different from the usual behavior. At filling factors 2/3 and 3/5 we observe large and sharp maxima in the longitudinal resistance instead of the expected minima. The peak value of the resistance exceeds those of the surrounding magnetic field regions by a factor of up to three. The formation of the maxima takes place on very large time scales which suggests a close relation with nuclear spins. We discuss the properties of the observed maxima due to a formation of domains of different electronic states.

cond-mat.mes-hall↗

arXiv1997

Lateral superlattices as voltage-controlled traps for excitons

We demonstrate the localisation of quantum well excitons in a periodic array of linear traps using photoluminescence experiments. The excitonic traps are induced by applying spatially alternating external voltages via interdigitated metal gates. The localisation originates from the periodical modulation of the strength of the quantum-confined Stark effect in the plane of the quantum well. In our experiments, the trap depth is easily tuned by the voltages applied to the interdigitated gates. Furthermore, we find that a perpendicular magnetic field reduces the exciton diffusion length. In short-period lateral superlattices, we observe a magnetic-field-induced stabilisation of excitons in the presence of strong in-plane electric fields.

cond-mat.mes-hall↗