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Mikulics M.,Julich Research Center | Kordos P.,JARA Fundamentals of Future Information Technology | Kordos P.,Slovak University of Technology in Bratislava | Kordos P.,Slovak Academy of Sciences | And 8 more authors.
IEEE Photonics Technology Letters | Year: 2011

We have fabricated and characterized ultrafast metal-semiconductor-metal (MSM) photodetectors integrated with metal-semiconductor-field-effect- transistors (MESFETs) integrated in coplanar strip lines in the GaN/AlN/SiC material system. We recorded electrical transients of the single photodetector as short as 0.9 ps wide by optoelectric pump-probe measurements using 360-nm-wavelength and 100-fs-duration laser pulses. Electric photoresponse transients of the photodetector with 6-mV peak amplitude were amplified by the MESFET, resulting in 4-ps-wide and 35-mV peak amplitude signals. This monolithically integrated optoelectronic circuit is presented as a potential candidate for high-speed ultraviolet optoelectronics. © 2011 IEEE.

Schulenborg J.,Chalmers University of Technology | Saptsov R.B.,RWTH Aachen | Haupt F.,JARA Fundamentals of Future Information Technology | Haupt F.,RWTH Aachen | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

We study the transient heat current out of a confined electron system into a weakly coupled electrode in response to a voltage switch. We show that the decay of the Coulomb interaction energy for this repulsive system exhibits signatures of electron-electron attraction, and is governed by an interaction-independent rate. This can only be understood from a general duality that relates the nonunitary evolution of a quantum system to that of a dual model with inverted energies. Deriving from the fermion-parity superselection postulate, this duality applies to a large class of open systems. © 2016 American Physical Society.

Kuhlen S.,RWTH Aachen | Schmalbuch K.,RWTH Aachen | Hagedorn M.,RWTH Aachen | Schlammes P.,RWTH Aachen | And 5 more authors.
Physical Review Letters | Year: 2012

Full electric-field control of spin orientations is one of the key tasks in semiconductor spintronics. We demonstrate that electric-field pulses can be utilized for phase-coherent ±π spin rotation of optically generated electron spin packets in InGaAs epilayers detected by time-resolved Faraday rotation. Through spin-orbit interaction, the electric-field pulses act as local magnetic field pulses. By the temporal control of the local magnetic field pulses, we can turn on and off electron spin precession and thereby rotate the spin direction into arbitrary orientations in a two-dimensional plane. Furthermore, we demonstrate a spin-echo-type spin drift experiment and find an unexpected partial spin rephasing, which is evident by a doubling of the spin dephasing time. © 2012 American Physical Society.

Bruggemann D.,Julich Research Center | Bruggemann D.,Trinity College Dublin | Michael K.E.,JARA Fundamentals of Future Information Technology | Wolfrum B.,Julich Research Center | Offenhausser A.,Julich Research Center
International Journal of Nano and Biomaterials | Year: 2012

Cell-electrode interfaces play a critical role in extracellular recording. Enlarging the electrode surface area with nanostructures yields higher signal-to-noise-ratios due to lower interface impedance. Adhesion and viability of various cell types on large-scale gold nanopillar electrodes to improve cell-electrode coupling were investigated. Cardiac muscle and human embryonic kidney cells survived and adhered well on gold nanopillars. The muscle cells even protruded into inter-pillar cavities with diameters below 100 nm. However, an unexpectedly low viability and adhesion of primary rat neurons was observed on nanopillars. A cross-sectional analysis of the cell-nanopillar interface showed large distances between neuronal cell bodies and nanopillars, whereas the neurites adhered tightly. Furthermore, actin assembly within the neuronal growth cones was modified on nanopillars. In summary, the adhesion response of the investigated cell lines will be beneficial for improved extracellular signalling, whereas a better understanding of neuronal responses to nanotopographies is required to enhance the neuronal viability. Copyright © 2012 Inderscience Enterprises Ltd.

Spilla S.,RWTH Aachen | Spilla S.,University of Palermo | Hassler F.,JARA Fundamentals of Future Information Technology | Hassler F.,RWTH Aachen | Splettstoesser J.,RWTH Aachen
New Journal of Physics | Year: 2014

We study a flux qubit made of a superconducting loop interrupted by three Josephson junctions, which is subject to a temperature gradient. We show that the heat current induced by the temperature gradient, being sensitive to the superconducting phase differences at the junctions, depends significantly on the state of the qubit. We furthermore investigate the impact of the heat current on the coherence properties of the qubit state. We have found that even small temperature gradients can lead to dephasing times of the order of microseconds for the Delft-qubit design. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

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