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Physics Faculty Publications

Condensed Matter Physics

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Full-Text Articles in Physical Sciences and Mathematics

Multi-Metallic Conduction Cooled Superconducting Radio-Frequency Cavity With High Thermal Stability, Gianluigi Ciovati, Gary Cheng, Uttar Pudasaini, Robert A. Rimmer Jul 2020

Multi-Metallic Conduction Cooled Superconducting Radio-Frequency Cavity With High Thermal Stability, Gianluigi Ciovati, Gary Cheng, Uttar Pudasaini, Robert A. Rimmer

Physics Faculty Publications

Superconducting radio-frequency cavities are commonly used in modern particle accelerators for applied and fundamental research. Such cavities are typically made of high-purity, bulk Nb and with cooling by a liquid helium bath at a temperature of ∼2 K. The size, cost and complexity of operating a particle accelerator with a liquid helium refrigerator make the current cavity technology not favorable for use in industrial-type accelerators. We have developed a multi-metallic 1.495 GHz elliptical cavity conductively cooled by a cryocooler. The cavity has a ∼2 μm thick layer of Nb3Sn on the inner surface, exposed to the rf field, …

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Transient Transmission Oscillations In Doped And Undoped Lithium Niobate Induced By Near-Infrared Femtosecond Pulses, Bryan J. Crossman, Gregory J. Taft Dec 2018

Transient Transmission Oscillations In Doped And Undoped Lithium Niobate Induced By Near-Infrared Femtosecond Pulses, Bryan J. Crossman, Gregory J. Taft

Physics Faculty Publications

Transient transmission oscillations in X-cut and Z-cut congruent, iron-doped, and magnesium-doped lithium niobate samples were measured using 50 fs, 800 nm, 0.5 nJ pulses from a self-mode-locked Ti:sapphire laser in an optical pump–probe system. Several Raman-active oscillation modes excited by these pulses were observed as changes in the transmitted probe intensity versus time delay between the pump and probe pulses. The samples were rotated to determine how the incident polarization of the pump pulses affects the mode excitations. The observed Raman-active oscillations correspond to previously reported symmetry modes measured with traditional, continuous-wave, Raman spectroscopy using the same scattering …

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Current-Driven Production Of Vortex-Antivortex Pairs In Planar Josephson Junction Arrays And Phase Cracks In Long-Range Order, Francisco Estellés-Duart, Miguel Ortuño, Andrés M. Somoza, Valerii M. Vinokur, Alex Gurevich Oct 2018

Current-Driven Production Of Vortex-Antivortex Pairs In Planar Josephson Junction Arrays And Phase Cracks In Long-Range Order, Francisco Estellés-Duart, Miguel Ortuño, Andrés M. Somoza, Valerii M. Vinokur, Alex Gurevich

Physics Faculty Publications

Proliferation of topological defects like vortices and dislocations plays a key role in the physics of systems with long-range order, particularly, superconductivity and superfluidity in thin films, plasticity of solids, and melting of atomic monolayers. Topological defects are characterized by their topological charge reflecting fundamental symmetries and conservation laws of the system. Conservation of topological charge manifests itself in extreme stability of static topological defects because destruction of a single defect requires overcoming a huge energy barrier proportional to the system size. However, the stability of driven topological defects remains largely unexplored. Here we address this issue and investigate numerically …

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Tuning Vortex Fluctuations And The Resistive Transition In Superconducting Films With A Thin Overlayer, Alex Gurevich Jan 2018

Tuning Vortex Fluctuations And The Resistive Transition In Superconducting Films With A Thin Overlayer, Alex Gurevich

Physics Faculty Publications

It is shown that the temperature of the resistive transition Tr of a superconducting film can be increased by a thin superconducting or normal overlayer. For instance, deposition of a highly conductive thin overlayer onto a dirty superconducting film can give rise to an “antiproximity effect,” which manifests itself in an initial increase of Tr (d2) with the overlayer thickness d2 followed by a decrease of Tr (d2)at larger d2. Such a nonmonotonic thickness dependence of Tr (d2) results from the interplay of the …

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Surface Impedance And Optimum Surface Resistance Of A Superconductor With An Imperfect Surface, Alex Gurevich, Takayuki Kubo Nov 2017

Surface Impedance And Optimum Surface Resistance Of A Superconductor With An Imperfect Surface, Alex Gurevich, Takayuki Kubo

Physics Faculty Publications

We calculate a low-frequency surface impedance of a dirty, s-wave superconductor with an imperfect surface incorporating either a thin layer with a reduced pairing constant or a thin, proximity-coupled normal layer. Such structures model realistic surfaces of superconducting materials which can contain oxide layers, absorbed impurities, or nonstoichiometric composition. We solved the Usadel equations self-consistently and obtained spatial distributions of the order parameter and the quasiparticle density of states which then were used to calculate a low-frequency surface resistance Rs (T) and the magnetic penetration depth λ(T) as functions of temperature in the limit of local London electrodynamics. It …

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Temperature Tuning From Direct To Inverted Bistable Electroluminescence In Resonant Tunneling Diodes, F. Hartmann, A. Pfenning, Mariama Rebello Sousa Dias, F. Langer, S. Höfling, M. Kamp, L. Worschech, L. K. Castelano, G. E. Marques, V. Lopez-Richard Jan 2017

Temperature Tuning From Direct To Inverted Bistable Electroluminescence In Resonant Tunneling Diodes, F. Hartmann, A. Pfenning, Mariama Rebello Sousa Dias, F. Langer, S. Höfling, M. Kamp, L. Worschech, L. K. Castelano, G. E. Marques, V. Lopez-Richard

Physics Faculty Publications

We study the electroluminescence (EL) emission of purely n-doped resonant tunneling diodes in a wide temperature range. The paper demonstrates that the EL originates from impact ionization and radiative recombination in the extended collector region of the tunneling device. Bistable currentvoltage response and EL are detected and their respective high and low states are tuned under varying temperature. The bistability of the EL intensity can be switched from direct to inverted with respect to the tunneling current and the optical on/off ratio can be enhanced with increasing temperature. One order of magnitude amplification of the optical on/off ratio can be …

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Mimicking Of Pulse Shape-Dependent Learning Rules With A Quantum Dot Memristor, P. Maier, F. Hartmann, Mariama Rebello Sousa Dias, M. Emmerling, C. Schneider, L. K. Castelano, M. Kamp, G. E. Marques, V. Lopez-Richard, S. Höfling Jan 2016

Mimicking Of Pulse Shape-Dependent Learning Rules With A Quantum Dot Memristor, P. Maier, F. Hartmann, Mariama Rebello Sousa Dias, M. Emmerling, C. Schneider, L. K. Castelano, M. Kamp, G. E. Marques, V. Lopez-Richard, S. Höfling

Physics Faculty Publications

We present the realization of four different learning rules with a quantum dot memristor by tuning the shape, the magnitude, the polarity and the timing of voltage pulses. The memristor displays a large maximum to minimum conductance ratio of about 57 000 at zero bias voltage. The high and low conductances correspond to different amounts of electrons localized in quantum dots, which can be successively raised or lowered by the timing and shapes of incoming voltage pulses. Modifications of the pulse shapes allow altering the conductance change in dependence on the time difference. Hence, we are able to mimic different …

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Light Sensitive Memristor With Bi-Directional And Wavelength-Dependent Conductance Control, P. Maier, F. Hartmann, Mariama Rebello Sousa Dias, M. Emmerling, C. Schneider, L. K. Castelano, M. Kamp, G. E. Marques, V. Lopez-Richard, L. Worschech, S. Höfling Jan 2016

Light Sensitive Memristor With Bi-Directional And Wavelength-Dependent Conductance Control, P. Maier, F. Hartmann, Mariama Rebello Sousa Dias, M. Emmerling, C. Schneider, L. K. Castelano, M. Kamp, G. E. Marques, V. Lopez-Richard, L. Worschech, S. Höfling

Physics Faculty Publications

We report the optical control of localized charge on positioned quantum dots in an electro-photosensitive memristor. Interband absorption processes in the quantum dot barrier matrix lead to photogenerated electron-hole-pairs that, depending on the applied bias voltage, charge or discharge the quantum dots and hence decrease or increase the conductance. Wavelength-dependent conductance control is observed by illumination with red and infrared light, which leads to charging via interband and discharging via intraband absorption. The presented memristor enables optical conductance control and may thus be considered for sensory applications in artificial neural networks as light-sensitive synapses or optically tunable memories.

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First Results Of Magnetic Field Penetration Measurements Of Multilayer Sis Structures, O. B. Malyshev, L. Gurran, R. Valizadeh, S. Pattalwar, N. Pattalwar, K. D. Dumbell, A. Gurevich Jan 2016

First Results Of Magnetic Field Penetration Measurements Of Multilayer Sis Structures, O. B. Malyshev, L. Gurran, R. Valizadeh, S. Pattalwar, N. Pattalwar, K. D. Dumbell, A. Gurevich

Physics Faculty Publications

The performance of superconducting RF cavities made of bulk Nb is limited by a breakdown field of Bp ≈200 mT, close to the superheating field for Nb. A potentially promising solution to enhance the breakdown field of the SRF cavities beyond the intrinsic limits of Nb is a multilayer coating suggested in [1]. In the simplest case, such a multilayer may be a superconductor-insulator-superconductor (S-I-S) coating, for example, bulk niobium (S) coated with a thin film of insulator (I) followed by a thin layer of another superconductor (S) which could be e.g. dirty niobium [2]. Here we report the …

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Universal Far-From-Equilibrium Dynamics Of A Holographic Superconductor, Julian Sonner, Adolfo Del Campo, Wojciech H. Zurek Jun 2015

Universal Far-From-Equilibrium Dynamics Of A Holographic Superconductor, Julian Sonner, Adolfo Del Campo, Wojciech H. Zurek

Physics Faculty Publications

Symmetry-breaking phase transitions are an example of non-equilibrium processes that require real-time treatment, a major challenge in strongly coupled systems without long-lived quasiparticles. Holographic duality provides such an approach by mapping strongly coupled field theories in D dimensions into weakly coupled quantum gravity in Dþ1 anti-de Sitter spacetime. Here we use holographic duality to study the formation of topological defects—winding numbers—in the course of a superconducting transition in a strongly coupled theory in a 1D ring. When the system undergoes the transition on a given quench time, the condensate builds up with a delay that can be deduced using the …

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Photocurrent-Voltage Relation Of Resonant Tunneling Diode Photodetectors, Andreas Pfenning, Favbian Hartmann, Mariama Rebello Sousa Dias, Fabian Langer, Martin Kamp, Leonardo Kleber Castelano, Victor Lopez-Richard, Gilmar Eugenio Marques, Sven Höfling, Lukas Worschech Jan 2015

Photocurrent-Voltage Relation Of Resonant Tunneling Diode Photodetectors, Andreas Pfenning, Favbian Hartmann, Mariama Rebello Sousa Dias, Fabian Langer, Martin Kamp, Leonardo Kleber Castelano, Victor Lopez-Richard, Gilmar Eugenio Marques, Sven Höfling, Lukas Worschech

Physics Faculty Publications

We have investigated photodetectors based on an AlGaAs/GaAs double barrier structure with a nearby lattice-matched GaInNAs absorption layer. Photons with the telecommunication wavelength λ = 1.3 µm lead to hole accumulation close to the double barrier inducing a voltage shift ΔV(V) of the current-voltage curve, which depends strongly on the bias voltage V. A model is proposed describing ΔV(V) and the photocurrent response in excellent agreement with the experimental observations. According to the model, an interplay of the resonant tunneling diode (RTD) quantum efficiency ƞ(V), the lifetime of photogenerated …

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Electron Transport In Quantum Dot Chains: Dimensionality Effects And Hopping Conductance, V. P. Kunets, Mariama Rebello Sousa Dias, T. Rembert, M. E. Ware, Y. I. Mazur, V. Lopez-Richard, H. A. Mantooth, G. E. Marques, G. J. Salamo May 2013

Electron Transport In Quantum Dot Chains: Dimensionality Effects And Hopping Conductance, V. P. Kunets, Mariama Rebello Sousa Dias, T. Rembert, M. E. Ware, Y. I. Mazur, V. Lopez-Richard, H. A. Mantooth, G. E. Marques, G. J. Salamo

Physics Faculty Publications

Detailed experimental and theoretical studies of lateral electron transport in a system of quantum dot chains demonstrate the complicated character of the conductance within the chain structure due to the interaction of conduction channels with different dimensionalities. The one-dimensional character of states in the wetting layer results in an anisotropic mobility, while the presence of the zero-dimensional states of the quantum dots leads to enhanced hopping conductance, which affects the low-temperature mobility and demonstrates an anisotropy in the conductance. These phenomena were probed by considering a one-dimensional model of hopping along with band filling effects. Differences between the model and …

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Proton Transfer In Surface-Stabilized Chiral Motifs Of Croconic Acid, Donna A. Kunkel, James Hooper, Scott Simpson, Geoffrey A. Rojas, Stephen Ducharme, Timothy Usher, Eva Zurek, Axel Enders Jan 2013

Proton Transfer In Surface-Stabilized Chiral Motifs Of Croconic Acid, Donna A. Kunkel, James Hooper, Scott Simpson, Geoffrey A. Rojas, Stephen Ducharme, Timothy Usher, Eva Zurek, Axel Enders

Physics Faculty Publications

The structure and cooperative proton ordering of two-dimensional sheets of croconic acid were studied with scanning tunneling microscopy and first-principles calculations. Unlike in the crystalline form, which exhibits a pleated, densely packed polar sheet structure, the confinement of the molecules to the surface results in hydrogen-bonded chiral clusters and networks. First-principles calculations suggest that the surface stabilizes networks of configurational isomers, which arise from direct hydrogen transfer between their constituent croconic acid monomers. Some of these configurations have a net polarization. It is demonstrated through constrained molecular dynamics simulations that simultaneous proton transfer between any two molecules can occur spontaneously. …

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Comment On "On The Theory Of Nuclear Resonant Forward Scattering Of Synchrotron Radiation", Gilbert R. Hoy, Jos Odeurs Jan 2009

Comment On "On The Theory Of Nuclear Resonant Forward Scattering Of Synchrotron Radiation", Gilbert R. Hoy, Jos Odeurs

Physics Faculty Publications

Recently, in a paper by Kohn and Smirnov, a formula previously derived by Kagan et al. was developed to explain the forward scattering of gamma radiation by a nuclear-resonant sample excited by pulsed synchrotron radiation. Their derivation followed, directly, a procedure developed by Heitler, Harris, and Hoy. Previously, a completely different formula was developed by Hoy et al. to explain the same process. As a result, Kohn and Smirnov discuss the correctness and validity of the two models. In this Comment a detailed numerical comparison of the two theories has also been made. It is shown that their comparison is …

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Suppression Of Switchable Polarization In Kdp By Ionizing Radiation, Timothy D. Usher Jan 1998

Suppression Of Switchable Polarization In Kdp By Ionizing Radiation, Timothy D. Usher

Physics Faculty Publications

Switching curves were obtained from KH2PO4 single crystals exposed to x-ray radiation for various time intervals, up to 8 h. The applied electric field was varied between 370 and 740 V/cm, as well. The temperature was held constant at 99 K. The switching curves were fit to a three-parameter nucleation and growth model based on the original works by Johnson and Mehl, and independently by Avrami. The two dynamic parameters, characteristic time tc, and effective domain wall dimensionality n, produced values consistent with unirradiated studies, however, they did not show any clear dependancy on …

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