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A Fuhrer

Publications and source records attributed to A Fuhrer.

8 recordsLinked to original sources
PubMed2004

Spatially resolved manipulation of single electrons in quantum dots using a scanned probe.

The scanning metallic tip of a scanning force microscope was coupled capacitively to electrons confined in a lithographically defined gate-tunable quantum dot at a temperature of 300 mK. Single electrons were made to hop on or off the dot by moving the tip or by changing the tip bias voltage owing to the Coulomb-blockade effect. Spatial images of conductance resonances map the interaction potential between the tip and individual electronic quantum dot states. Under certain conditions this interaction is found to contain a tip-voltage induced and a tip-voltage-independent contribution.

Journal Article↗
PubMed2004

Kondo effect in a many-electron quantum ring.

The Kondo effect is investigated in a many-electron quantum ring as a function of the magnetic field. For fields applied perpendicular to the plane of the ring a modulation of the Kondo effect with the Aharonov-Bohm period is observed. This effect is discussed in terms of the energy spectrum of the ring and the parametrically changing tunnel coupling. In addition, we use gate voltages to modify the ground-state spin of the ring. The observed splitting of the Kondo-related zero-bias anomaly in this configuration is tuned with an in-plane magnetic field.

Journal Article↗
PubMed2004

Magnetic-field-dependent transmission phase of a double-dot system in a quantum ring.

The Aharonov-Bohm effect is measured in a four-terminal open ring geometry. Two quantum dots are embedded in the structure, one in each of the two interfering paths. The number of electrons in the two dots can be controlled independently. The transmission phase is measured as electrons are added to or taken away from the individual quantum dots. Although the measured phase shifts are in qualitative agreement with theoretical predictions, the phase evolution exhibits unexpected dependence on the magnetic field. Phase lapses are found only in certain ranges of the magnetic field.

Journal Article↗
PubMed2003

Singlet-triplet transition tuned by asymmetric gate voltages in a quantum ring.

Wave-function and interaction effects in the addition spectrum of a Coulomb-blockaded many-electron quantum ring are investigated as a function of asymmetrically applied gate voltages and magnetic field. Hartree and exchange contributions to the interaction are quantitatively evaluated at a crossing between states extended around the ring and states which are more localized in one arm of the ring. A gate tunable singlet-triplet transition of the two uppermost levels of this many-electron ring is identified at zero magnetic field.

Journal Article↗
PubMed2001

Energy spectra of quantum rings.

Quantum mechanical experiments in ring geometries have long fascinated physicists. Open rings connected to leads, for example, allow the observation of the Aharonov-Bohm effect, one of the best examples of quantum mechanical phase coherence. The phase coherence of electrons travelling through a quantum dot embedded in one arm of an open ring has also been demonstrated. The energy spectra of closed rings have only recently been studied by optical spectroscopy. The prediction that they allow persistent current has been explored in various experiments. Here we report magnetotransport experiments on closed rings in the Coulomb blockade regime. Our experiments show that a microscopic understanding of energy levels, so far limited to few-electron quantum dots, can be extended to a many-electron system. A semiclassical interpretation of our results indicates that electron motion in the rings is governed by regular rather than chaotic motion, an unexplored regime in many-electron quantum dots. This opens a way to experiments where even more complex structures can be investigated at a quantum mechanical level.

Journal Article↗
PubMed1997

[New treatment possibilities for skin changes with the CO2 laser in head and neck surgery].

Laser treatment of various skin changes has become common clinical practice in recent years. Due to its physical properties, the CO2 laser is particularly well suited for cutting and ablating tissue. The high absorption of its wavelength in water (lambda = 10600 nm) is responsible for its low penetration depth in biological tissue. Shortening the exposure time minimizes thermal side effects, such as carbonization and coagulation. This effect can be lessened with the Silk Touch scanner, since the focussed laser beam is moved over a defined area by rapidly rotating mirrors. This enables a controlled and reliable removal of various dermal lesions. Particularly well-suited for treatment hypertrophic scars, post-acne scarring, perioral and periorbital wrinkles, rhinophymas and benign neoplasms including verruca vulgaris. Cosmetically favorable reepithelialization of the treated skin surfaces occurs within a very short time after treatment. Periorbital resurfacing and correction of a rhinophyma are used as examples of dermal treatment with the CO2 laser and the Silk Touch scanner.

Adult↗
PubMed1994

[Current status of laser surgery in the area of the soft palate and adjoining regions].

The amount of different clinically available lasers is increasing. The ENT surgeon can therefore use the best laser for the planned operation. As the resources of the hospital do not increase with the laser technology, a decision has to be made whether in addition to the universal CO2-laser other types must be acquired and which type is best. This paper presents the characteristics and typical tissue interactions of several lasers for the area of the soft palate. Typical operative examples are shown, e.g. partial resection of the soft palate in patients with bronchopathy and sleep apnoea syndrome, tonsillectomy, tonsillotomy and adenotomy in adults.

Adenoidectomy↗