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Browsing by Department "Karlsruhe Institute of Technology"

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Advances in nanocarbon composite materials
(2018-01-03) Malik, Sharali; Krasheninnikov, Arkady V.; Marchesan, Silvia; Karlsruhe Institute of Technology; Department of Applied Physics; University of Trieste
Andreev levels as a quantum dissipative environment
(2017-10-10) Galaktionov, Artem V.; Golubev, Dmitry S.; Zaikin, Andrei D.; Russian Academy of Sciences; Department of Applied Physics; Karlsruhe Institute of Technology
We argue that at subgap energies quantum behavior of superconducting weak links can be exactly accounted for by an effective Hamiltonian for a Josephson particle in a quantum dissipative environment formed by Andreev levels. This environment can constitute an important source for intrinsic inelastic relaxation and dephasing in highly transparent weak links. We investigate the problem of macroscopic quantum tunneling in such weak links demonstrating that-depending on the barrier transmission-the supercurrent decay can be described by three different regimes: (i) weak intrinsic dissipation, (ii) strong intrinsic dissipation, and (iii) strong capacitance renormalization. Crossover between quantum and thermally assisted supercurrent decay regimes can also be strongly affected by the Andreev level environment.
Big bang as a topological quantum phase transition
(American Physical Society, 2022-04-15) Klinkhamer, F. R.; Volovik, G. E.; Karlsruhe Institute of Technology; Topological Quantum Fluids; Department of Applied Physics
It has been argued that a particular type of quantum-vacuum variable q can provide a solution to the main cosmological constant problem and possibly also give a cold-dark-matter component. We now show that the same q field may suggest a new interpretation of the big bang, namely as a quantum phase transition between topologically inequivalent vacua. These two vacua are characterized by the equilibrium values q=±q0, and there is a kink-type solution q(t) interpolating between q=-q0 for t→-∞ and q=+q0 for t→∞, with conformal symmetry for q=0 at t=0.
Broadband anti-reflective coating based on plasmonic nanocomposite
(2016-07-28) Hedayati, Mehdi Keshavarz; Abdelaziz, Moheb; Etrich, Christoph; Homaeigohar, Shahin; Rockstuhl, Carsten; Elbahri, Mady; Kiel University; Friedrich Schiller University Jena; Department of Chemistry; Karlsruhe Institute of Technology
We report on the fabrication, the characterization, and the optical simulation of a gold-silica nanocomposite and present its integration into a broadband anti-reflective coating (ARC) for a silicon substrate. The two-layer ARC consists of a nanocomposite (randomly distributed gold cluster in a silica matrix) and a pure silica film. We capitalize on the large refractive index of the composite to impose an abrupt phase change at the interface of the coating to diminish the light reflection from the substrate through the ultrathin nanocoating. The average reflectivity of the silicon can be reduced by such a coating to less than 0.1% in the entire visible spectrum. We experimentally and numerically prove that percolated nanocomposites with an overall thickness of 20 nm can provide anti-reflectivity up to near infrared (NIR). The ARC bandwidth can be shifted more than 500 nm and broadened to cover even the NIR wavelength by changing the volume filling fraction of the gold clusters. The angular sensitivity of thinultrathin antireflective coating is negligible up to 60°. The present ARC could find applications in thermo-photovoltaics and bolometers.
Critical current fluctuations in graphene Josephson junctions
(Nature Publishing Group, 2021-10-06) Haque, Mohammad T.; Will, Marco; Tomi, Matti; Pandey, Preeti; Kumar, Manohar; Schmidt, Felix; Watanabe, Kenji; Taniguchi, Takashi; Danneau, Romain; Steele, Gary; Hakonen, Pertti; Centre of Excellence in Quantum Technology, QTF; Quantum Circuits and Correlations; Kavli Institute of Nanoscience Delft; National Institute for Materials Science; Karlsruhe Institute of Technology; Department of Applied Physics
We have studied 1/f noise in critical current Ic in h-BN encapsulated monolayer graphene contacted by NbTiN electrodes. The sample is close to diffusive limit and the switching supercurrent with hysteresis at Dirac point amounts to ≃ 5 nA. The low frequency noise in the superconducting state is measured by tracking the variation in magnitude and phase of a reflection carrier signal vrf at 600–650 MHz. We find 1/f critical current fluctuations on the order of δIc/ Ic≃ 10 - 3 per unit band at 1 Hz. The noise power spectrum of critical current fluctuations SIc measured near the Dirac point at large, sub-critical rf-carrier amplitudes obeys the law SIc/Ic2=a/fβ where a≃ 4 × 10 - 6 and β≃ 1 at f> 0.1 Hz. Our results point towards significant fluctuations in Ic originating from variation of the proximity induced gap in the graphene junction.
Cross-correlated shot noise in three-terminal superconducting hybrid nanostructures
(American Physical Society, 2019-04-04) Golubev, Dmitry S.; Zaikin, Andrei D.; Centre of Excellence in Quantum Technology, QTF; Karlsruhe Institute of Technology; Department of Applied Physics
We work out a unified theory describing both nonlocal electron transport and cross-correlated shot noise in a three-terminal normal-superconducting-normal (NSN) hybrid nanostructure. We describe noise cross correlations both for subgap and overgap bias voltages and for arbitrary distribution of channel transmissions in NS contacts. We specifically address a physically important situation of diffusive contacts and demonstrate nontrivial behavior of nonlocal shot noise exhibiting both positive and negative cross correlations depending on the bias voltages. For this case, we derive a relatively simple analytical expression for cross-correlated noise power which contains only experimentally accessible parameters.
Determination of physical emulsion stabilization mechanisms of wood hemicelluloses
(2016) Mikkonen, K. S.; Merger, D.; Kilpeläinen, P.; Murtomäki, L.; Schmidt, U. S.; Wilhelm, M.; University of Helsinki; Karlsruhe Institute of Technology; Luke Natural Resources Institute Finland; Department of Chemistry
Materials manufacturing industries seek efficient, economic, and sustainable compounds for stabilizing dispersed systems such as emulsions. In this study, novel, abundant biobased hydrocolloids spruce galactoglucomannans (GGM) and birch glucuronoxylans (GX) were obtained from a forestry biorefining process and characterized as versatile stabilizers of rapeseed oil-in-water emulsions. For the first time, GGM and GX isolated by pressurized hot water extraction (PHWE) of spruce and birch saw meal, respectively, were studied in emulsions. The PHWE wood hemicelluloses - polysaccharides with relatively low molar mass - facilitated the formation of emulsions with small average droplet size and efficiently prevented droplet coalescence. GGM and GX lowered the surface tension of emulsions' oil-water interface and increased the viscosity of the continuous phase. However, viscosity of the wood hemicellulose-based systems was low compared to that of commercial polymeric stabilizers. GGM-stabilized emulsions with varying oil volume fractions were characterized in terms of their rheological properties, including large amplitude oscillation shear (Laos) measurements, and compared to emulsions prepared with a classical small-molecular surfactant, Tween20. The physical emulsion stabilization mechanisms of GGM and GX are suggested as steric repulsion assisted by Pickering-type stabilization. Wood hemicelluloses have potential as highly promising future bioproducts for versatile industrial applications involving colloidal systems and soft materials.
The Future of Enterprise Information Systems
(Springer, 2023-12) Sunyaev, Ali; Dehling, Tobias; Strahringer, Susanne; Da Xu, Li; Heinig, Martin; Perscheid, Michael; Alt, Rainer; Rossi, Matti; Karlsruhe Institute of Technology; Technische Universität Dresden; Old Dominion University; SAP Research; University of Potsdam; Leipzig University; Department of Information and Service Management
Mesoscopic electron transport and atomic gases, a review of Frank W.J. Hekking's scientific work
(SCIPOST FOUNDATION, 2018-07) Amico, Luigi; Basko, Denis M.; Bergeret, Sebastian; Buisson, Olivier; Courtois, Herve; Fazio, Rosario; Guichard, Wiebke; Minguzzi, Anna; Pekola, Jukka; Schon, Gerd; University of Catania; Université Grenoble Alpes; Donostia International Physics Center; Consiglio Nazionale delle Ricerche (CNR); Department of Applied Physics; Karlsruhe Institute of Technology
In this article, we provide an overview of the scientific contributions of Frank W.J. Hekking to the fields of mesoscopic electron transport and superconductivity as well as atomic gases. Frank Hekking passed away in May 2017. We hope that the present review gives a faithful testimony of his scientific legacy.
Mie Resonances and Kerker Effects in Parametric Time-Modulated Spheres
(2022) Asadchy, V.; Lamprianidis, A. G.; Ptitcyn, G.; Albooyeh, M.; Rituraj; Karamanos, T.; Alaee, R.; Tretyakov, S. A.; Rockstuhl, C.; Fan, S.; Department of Electronics and Nanoengineering; Karlsruhe Institute of Technology; Mobix Labs Inc.; Indian Institute of Technology Kanpur; Stanford University
We provide a theoretical description of light scattering by a spherical particle whose permittivity is modulated with twice the frequency of the incident light. Such a sphere acts as a finite-size photonic time crystal and permits optical parametric amplification. We show that the control of the temporal modulation strength provides a qualitatively new route to spectrally overlap different parametric Mie resonances in the sphere for controlling its far-field pattern and satisfying the Kerker scattering conditions.
Overview of ASDEX Upgrade results
(2017-10) Aguiam, D.; Aho-Mantila, L.; Angioni, C.; Arden, N.; Parra, R. Arredondo; Asunta, O.; de Baar, M.; Balden, M.; Behler, K.; Bergmann, A.; Bernardo, J.; Bernert, M.; Beurskens, M.; Biancalani, A.; Bilato, R.; Birkenmeier, G.; Bobkov, V.; Bock, A.; Bogomolov, A.; Bolzonella, T.; Boeswirth, B.; Bottereau, C.; Bottino, A.; van den Brand, H.; Brezinsek, S.; Brida, D.; Brochard, F.; Bruhn, C.; Buchanan, J.; Buhler, A.; Burckhart, A.; Cambon-Silva, D.; Camenen, Y.; Carvalho, P.; Carrasco, G.; Cazzaniga, C.; Carr, M.; Carralero, D.; Casali, L.; Castaldo, C.; Cavedon, M.; Challis, C.; Chankin, A.; Chapman, I.; Clairet, F.; Classen, I.; Coda, S.; Coelho, R.; Coenen, J. W.; Colas, L.; Conway, G.; Costea, S.; Coster, D. P.; Croci, G.; Cseh, G.; Czarnecka, A.; D'Arcangelo, O.; Day, C.; Delogu, R.; de Marne, P.; Denk, S.; Denner, P.; Dibon, M.; D'Inca, R.; Di Siena, A.; Douai, D.; Drenik, A.; Drube, R.; Dunne, M.; Duval, B. P.; Dux, R.; Eich, T.; Elgeti, S.; Engelhardt, K.; Erdos, B.; Erofeev, I.; Esposito, B.; Fable, E.; Faitsch, M.; Fantz, U.; Faugel, H.; Felici, F.; Fietz, S.; Figueredo, A.; Fischer, R.; Ford, O.; Frassinetti, L.; Freethy, S.; Froeschle, M.; Fuchert, G.; Fuchs, J. C.; Fuenfgelder, H.; Galazka, K.; Galdon-Quiroga, J.; Gallo, A.; Gao, Y.; Garavaglia, S.; Garcia-Munoz, M.; Geiger, B.; Cianfarani, C.; Giannone, L.; Giovannozzi, E.; Gleason-Gonzalez, C.; Gloeggler, S.; Gobbin, M.; Goerler, T.; Goodman, T.; Gorini, G.; Gradic, D.; Graeter, A.; Granucci, G.; Greuner, H.; Griener, M.; Groth, M.; Gude, A.; Guenter, S.; Guimarais, L.; Haas, G.; Hakola, A. H.; Ham, C.; Happel, T.; Harrison, J.; Hatch, D.; Hauer, V.; Hayward, T.; Heinemann, B.; Heinzel, S.; Hellsten, T.; Henderson, S.; Hennequin, P.; Herrmann, A.; Heyn, E.; Hitzler, F.; Hobirk, J.; Hoelzl, M.; Hoeschen, T.; Holm, J. H.; Hopf, C.; Hoppe, F.; Horvath, L.; Houben, A.; Huber, A.; Igochine, V.; Ilkei, T.; Ivanova-Stanik, I.; Jacob, W.; Jacobsen, A. S.; Jacquot, J.; Janky, F.; Jardin, A.; Jaulmes, F.; Jenko, F.; Jensen, T.; Joffrin, E.; Kaesemann, C.; Kallenbach, A.; Kalvin, S.; Kantor, M.; Kappatou, A.; Kardaun, O.; Karhunen, J.; Kasilov, S.; Kernbichler, W.; Kim, D.; Kimmig, S.; Kirk, A.; Klingshirn, H. -J.; Koch, F.; Kocsis, G.; Koehn, A.; Kraus, M.; Krieger, K.; Krivska, A.; Kraemr-Flecken, A.; Kurki-Suonio, T.; Kurzan, B.; Lackner, K.; Laggner, F.; Lang, P. T.; Lauber, P.; Lazanyi, N.; Lazaros, A.; Lebschy, A.; Li, L.; Li, M.; Liang, Y.; Lipschultz, B.; Liu, Y.; Lohs, A.; Luhmann, N. C.; Lunt, T.; Lyssoivan, A.; Madsen, J.; Maier, H.; Maj, O.; Mailloux, J.; Maljaars, E.; Manas, P.; Mancini, A.; Manhard, A.; Manso, M. -E.; Mantica, P.; Mantsinen, M.; Manz, P.; Maraschek, M.; Martens, C.; Martin, P.; Marrelli, L.; Martitsch, A.; Mastrostefano, S.; Mayer, A.; Mayer, M.; Mazon, D.; McCarthy, P. J.; McDermott, R.; Meisl, G.; Meister, H.; Medvedeva, A.; Merkel, P.; Merkel, R.; Merle, A.; Mertens, V.; Meshcheriakov, D.; Meyer, H.; Meyer, O.; Miettunen, J.; Milanesio, D.; Mink, F.; Mlynek, A.; Monaco, F.; Moon, C.; Nazikian, R.; Nemes-Czopf, A.; Neu, G.; Neu, R.; Nielsen, A. H.; Nielsen, S. K.; Nikolaeva, V.; Nocente, M.; Noterdaeme, J. -M.; Nowak, S.; Oberkofler, M.; Oberparleiter, M.; Ochoukov, R.; Odstrcil, T.; Olsen, J.; Orain, F.; Palermo, F.; Papp, G.; Perez, I. Paradela; Pautasso, G.; Enzel, F.; Petersson, P.; Pinzon, J.; Piovesan, P.; Piron, C.; Plaum, B.; Ploeckl, B.; Plyusnin, V.; Pokol, G.; Poli, E.; Porte, L.; Potzel, S.; Prisiazhniuk, D.; Puetterich, T.; Ramisch, M.; Rapson, C.; Rasmussen, J.; Raupp, G.; Refy, D.; Reich, M.; Reimold, F.; Ribeiro, T.; Riedl, R.; Rittich, D.; Rocchi, G.; Rodriguez-Ramos, M.; Rohde, V.; Ross, A.; Rott, M.; Rubel, M.; Ryan, D.; Ryter, F.; Saarelma, S.; Salewski, M.; Salmi, A.; Sanchis-Sanchez, L.; Santos, G.; Santos, J.; Sauter, O.; Scarabosio, A.; Schall, G.; Schmid, K.; Schmitz, O.; Schneider, P. A.; Schneller, M.; Schrittwieser, R.; Schubert, M.; Schwarz-Selinger, T.; Schweinzer, J.; Scott, B.; Sehmer, T.; Sertoli, M.; Shabbir, A.; Shalpegin, A.; Shao, L.; Sharapov, S.; Siccinio, M.; Sieglin, B.; Sigalov, A.; Silva, A.; Silva, C.; Simon, P.; Simpson, J.; Snicker, A.; Sommariva, C.; Sozzi, C.; Spolaore, M.; Stejner, M.; Stober, J.; Stobbe, F.; Stroth, U.; Strumberger, E.; Suarez, G.; Sugiyama, K.; Sun, H. -J.; Suttrop, W.; Szepesi, T.; Tal, B.; Tala, T.; Tardini, G.; Tardocchi, M.; Terranova, D.; Tierens, W.; Told, D.; Tudisco, O.; Trevisan, G.; Treutterer, W.; Trier, E.; Tripsky, M.; Valisa, M.; Valovic, M.; Vanovac, B.; Varela, P.; Varoutis, S.; Verdoolaege, G.; Vezinet, D.; Vianello, N.; Vicente, J.; Vierle, T.; Viezzer, E.; von Toussaint, U.; Wagner, D.; Wang, N.; Wang, X.; Weidl, M.; Weiland, M.; White, A. E.; Willensdorfer, M.; Wiringer, B.; Wischmeier, M.; Wolf, R.; Wolfrum, E.; Xiang, L.; Yang, Q.; Yang, Z.; Yu, Q.; Zagorski, R.; Zammuto, I.; Zarzoso, D.; Zhang, W.; van Zeeland, M.; Zehetbauer, T.; Zilker, M.; Zoletnik, S.; Zohm, H.; IST; VTT Technical Research Centre of Finland; Max Planck Inst Astrophys, Max Planck Society; Department of Applied Physics; TEC; JET EFDA, Culham Sci Ctr; Technische Universität München; Consorzio RFX; IRFM; Assoc EURATOM FZJ, Euratom, Julich Research Center, Forschungszentrum Julich, Inst Energy & Climate Res; University of Lorraine; ENEA; Istituto Fisica del Plasma "Piero Caldirola" (IFP-CNR); Swiss Federal Institute of Technology Lausanne; Innsbruck Medical University; Hungarian Academy of Sciences; Institute of Plasma Physics & Laser Microfusion (IFPiLM); Karlsruhe Institute of Technology; Eindhoven University of Technology; Swedish Research Council (VR); General Atomics & Affiliated Companies; University of Sevilla; University of Texas at Austin; Max Planck Comp & Data Facil; Ecole Polytechnique; Hochschule der Medien; Technical University of Denmark; Budapest University of Technology and Economics; University of California at Santa Barbara; School services, SCI; LPP-ERM/KMS EURATOM Association; Vienna University of Technology; Assoc EURATOM Hellen Republ, NCSR Demokritos; IPP; York University; CCFE Fusion Assoc; BSC; Univ Coll Cork UCC; Princeton University; Ghent University; Chinese Acad Sci, Chinese Academy of Sciences, Natl Astron Observ; Department of Radio Science and Engineering; Massachusetts Institute of Technology; Chinese Academy of Sciences; Univ Aix Marseille 1, Centre National de la Recherche Scientifique (CNRS), University of Aix-Marseille, Universite de Provence - Aix-Marseille I, UMR 6098, CNRS
The ASDEX Upgrade (AUG) programme is directed towards physics input to critical elements of the ITER design and the preparation of ITER operation, as well as addressing physics issues for a future DEMO design. Since 2015, AUG is equipped with a new pair of 3-strap ICRF antennas, which were designed for a reduction of tungsten release during ICRF operation. As predicted, a factor two reduction on the ICRF-induced W plasma content could be achieved by the reduction of the sheath voltage at the antenna limiters via the compensation of the image currents of the central and side straps in the antenna frame. There are two main operational scenario lines in AUG. Experiments with low collisionality, which comprise current drive, ELM mitigation/suppression and fast ion physics, are mainly done with freshly boronized walls to reduce the tungsten influx at these high edge temperature conditions. Full ELM suppression and non-inductive operation up to a plasma current of I-p = 0.8 MA could be obtained at low plasma density. Plasma exhaust is studied under conditions of high neutral divertor pressure and separatrix electron density, where a fresh boronization is not required. Substantial progress could be achieved for the understanding of the confinement degradation by strong D puffing and the improvement with nitrogen or carbon seeding. Inward/outward shifts of the electron density profile relative to the temperature profile effect the edge stability via the pressure profile changes and lead to improved/decreased pedestal performance. Seeding and D gas puffing are found to effect the core fueling via changes in a region of high density on the high field side (HFSHD). The integration of all above mentioned operational scenarios will be feasible and naturally obtained in a large device where the edge is more opaque for neutrals and higher plasma temperatures provide a lower collisionality. The combination of exhaust control with pellet fueling has been successfully demonstrated. High divertor enrichment values of nitrogen E-N >= 10 have been obtained during pellet injection, which is a prerequisite for the simultaneous achievement of good core plasma purity and high divertor radiation levels. Impurity accumulation observed in the all-metal AUG device caused by the strong neoclassical inward transport of tungsten in the pedestal is expected to be relieved by the higher neoclassical temperature screening in larger devices.
Propagating q-field and q-ball solution
(2017) Klinkhamer, F.R.; Volovik, G. E.; Karlsruhe Institute of Technology; Department of Applied Physics
One possible solution of the cosmological constant problem involves a so-called q-field, which self-adjusts so as to give a vanishing gravitating vacuum energy density (cosmological constant) in equilibrium. We show that this q-field can manifest itself in other ways. Specifically, we establish a propagating mode (q-wave) in the nontrivial vacuum and find a particular soliton-type solution in flat spacetime, which we call a q-ball by analogy with the well-known Q-ball solution. Both q-waves and q-balls are expected to play a role for the equilibration of the q-field in the very early universe.
Relaxation of vacuum energy in q-theory
(2017-08-01) Klinkhamer, F. R.; Savelainen, M.; Volovik, G. E.; Karlsruhe Institute of Technology; Department of Applied Physics
The q-theory formalism aims to describe the thermodynamics and dynamics of the deep quantum vacuum. The thermodynamics leads to an exact cancellation of the quantum-field zero-point-energies in equilibrium, which partly solves the main cosmological constant problem. But, with reversible dynamics, the spatially flat Friedmann–Robertson–Walker universe asymptotically approaches the Minkowski vacuum only if the Big Bang already started out in an initial equilibrium state. Here, we extend q-theory by introducing dissipation from irreversible processes. Neglecting the possible instability of a de-Sitter vacuum, we obtain different scenarios with either a de-Sitter asymptote or collapse to a final singularity. The Minkowski asymptote still requires fine-tuning of the initial conditions. This suggests that, within the q-theory approach, the decay of the de-Sitter vacuum is a necessary condition for the dynamical solution of the cosmological constant problem.
Role of tip apices in scanning force spectroscopy on alkali halides at room temperature-chemical nature of the tip apex and atomic-scale deformations
(IOP Publishing Ltd., 2021-01-15) Wagner, Philipp; Foster, Adam; Yi, Insook; Abe, Masayuki; Sugimoto, Yoshiaki; Hoffmann-Vogel, Regina; Karlsruhe Institute of Technology; Surfaces and Interfaces at the Nanoscale; Osaka University; University of Potsdam; Department of Applied Physics
We have revealed processes of the tip apex distortion in the measurements of non-contact scanning force microscopy. High-spatial-resolution two-dimensional force mapping on KCl(100) surfaces for a large number of tips, seven tips, enabled us to see the complex behavior of the tip apex distortion. The tips are from Si without additional coating, but are altered by the tip-sample interaction and show the behavior of different atomic species. On the KCl(001) surfaces, the tip apex, consisting of K and Cl atoms or of Si, distorted several times while changing the distance even in a weak attractive region. There are variations in rigidity of the tip apex, but all tips distorted in the small attractive region. This complex behavior was categorized in patterns by our analyses. We compare the experimental force-distance data to atomistic simulations using rigid KCl-terminated tips and KCl-terminated tips with an additional KCl-pair designed to perform atomic jumps. We also compare the experimental force-distance datato first principles simulations using Si tips. We mainly find K-terminated tips and Si-terminated tips. We find that Si tips show only one force minimum whereas KCl-terminated tips show two force minima in line with the stronger rigidity of Si compared to KCl. At room temperature, the tip apex atoms can perform atomic jumps that change the atomic configuration of the tip apex.
The room-temperature chemiresistive properties of potassium titanate whiskers versus organic vapors
(2017-12-19) Varezhnikov, Alexey S.; Fedorov, Fedor S.; Burmistrov, Igor N.; Plugin, Ilya A.; Sommer, Martin; Lashkov, Andrey V.; Gorokhovsky, Alexander V.; Nasibulin, Albert G.; Kuznetsov, Denis V.; Gorshenkov, Michail V.; Sysoev, Victor V.; Saratov State Technical University; Skolkovo Institute of Science and Technology; Karlsruhe Institute of Technology; Department of Applied Physics; National University of Science and Technology
The development of portable gas-sensing units implies a special care of their power efficiency, which is often approached by operation at room temperature. This issue primarily appeals to a choice of suitable materials whose functional properties are sensitive toward gas vapors at these conditions. While the gas sensitivity is nowadays advanced by employing the materials at nano-dimensional domain, the room temperature operation might be targeted via the application of layered solid-state electrolytes, like titanates. Here, we report gas-sensitive properties of potassium titanate whiskers, which are placed over a multielectrode chip by drop casting from suspension to yield a matrix mono-layer of varied density. The material synthesis conditions are straightforward both to get stable single-crystalline quasi-one-dimensional whiskers with a great extent of potassium replacement and to favor the increase of specific surface area of the structures. The whisker layer is found to be sensitive towards volatile organic compounds (ethanol, isopropanol, acetone) in the mixture with air at room temperature. The vapor identification is obtained via processing the vector signal generated by sensor array of the multielectrode chip with the help of pattern recognition algorithms.
Scattering of light by spheres made from a time-modulated and dispersive material
(2021-09-20) Ptitcyn, G.; Lamprianidis, A.; Karamanos, T.; Muller, M.; Alaee, R.; Asadchy, V. S.; Mirmoosa, M. S.; Albooyeh, M.; Fan, S.; Rockstuhl, C.; Tretyakov, S. A.; Department of Electronics and Nanoengineering; Karlsruhe Institute of Technology; Stanford University; Panasonic Aviation Corporation
We derive the dispersion relation of eigenmodes propagating in a time-varying and dispersive medium. We use these eigenmodes to analytically study the scattering of light by a sphere made from a time-varying and dispersive medium. These results are compared to full-wave optical simulations and excellent agreement is observed. With that, we provide tools and outline a path towards further explorations of light scattering by time-varying finite particles.
Temporal Parity-Time-Symmetric Metasurfaces
(2023) Wang, Xuchen; Song, A. Y.; Mirmoosa, M. S.; Asadchy, V.; Rockstuhl, C.; Karlsruhe Institute of Technology; University of Sydney; Department of Electronics and Nanoengineering
In this talk, we present the concept of temporal parity-time-symmetric metasurfaces. In contrast to spatial parity-time symmetric structure, here, the metasurface exhibits gain and loss in the temporal domain, and the gain and loss are virtually created by time-varying lossless reactive components. It is found that the alternation of gain and loss in the temporal domain results in the closing of the momentum bandgap. At the exceptional point where the size of the momentum bandgap becomes zero, the metasurface exhibits an exotic response for pulse illuminations, expressed in the localization and linear growing of the pulse energy.
Tetrads and q-theory
(MAIK NAUKA/INTERPERIODICA/SPRINGER, 2019-03) Klinkhamer, F. R.; Volovik, G. E.; Karlsruhe Institute of Technology; Department of Applied Physics
As the microscopic structure of the deep relativistic quantum vacuum is unknown, a phenomenological approach (q-theory) has been proposed to describe the vacuum degrees of freedom and the dynamics of the vacuum energy after the Big Bang. The original q-theory was based on a four-form field strength from a three-form gauge potential. However, this realization of q-theory, just as others suggested so far, is rather artificial and does not take into account the fermionic nature of the vacuum. We now propose a more physical realization of the q-variable. In this approach, we assume that the vacuum has the properties of a plastic (malleable) fermionic crystalline medium. The new approach unites general relativity and fermionic microscopic (trans-Planckian) degrees of freedom, as the approach involves both the tetrad of standard gravity and the elasticity tetrad of the hypothetical vacuum crystal. This approach also allows for the description of possible topological phases of the quantum vacuum.
Thermal and quantum decay of supercurrent in highly transparent weak links
(Springer Verlag, 2019-03-01) Galaktionov, Artem V.; Golubev, Dmitry S.; Zaikin, Andrei D.; RAS - P.N. Lebedev Physics Institute; Centre of Excellence in Quantum Technology, QTF; Karlsruhe Institute of Technology; Department of Applied Physics
We analyze a trade-off between thermal activation (TA) and quantum tunneling in the problem of supercurrent decay in superconducting junctions with highly transparent barriers. In such systems – unlike in conventional tunnel junctions – the supercurrent decay is essentially influenced by low energy Andreev levels forming an intrinsic quantum dissipative environment for the Josephson particle. We evaluate the temperature dependent supercurrent decay rate Γ(T) and elucidate a variety of different regimes for such a decay. We demonstrate that no classical-to-quantum crossover exists in the limit of fully transparent barriers, in which case quantum tunneling always prevails over TA.
Unleashing Infinitely Wide Momentum Bandgaps in Photonic Time Crystals
(2023) Wang, Xuchen; Garg, P.; Lamprianidis, A. G.; Mirmoosa, M. S.; Asadchy, V.; Rockstuhl, C.; Karlsruhe Institute of Technology; Department of Electronics and Nanoengineering
The emergence of photonic time crystals has engendered considerable scientific curiosity, owing to their unique features, including the momentum bandgaps. However, the generation of experimentally detectable momentum bandgaps poses a formidable challenge, particularly at high frequencies, necessitating the use of high-power pumping that may lead to deleterious material overheating. To tackle this problem, we propose two routes toward theoretically unlimited enhancement of the momentum bandgap size.

Browsing by Department "Karlsruhe Institute of Technology"

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