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Articles 1 - 24 of 24
Full-Text Articles in Condensed Matter Physics
Multi-Metallic Conduction Cooled Superconducting Radio-Frequency Cavity With High Thermal Stability, Gianluigi Ciovati, Gary Cheng, Uttar Pudasaini, Robert A. Rimmer
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, …
Transient Transmission Oscillations In Doped And Undoped Lithium Niobate Induced By Near-Infrared Femtosecond Pulses, Bryan J. Crossman, Gregory J. Taft
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 …
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
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 …
Tuning Vortex Fluctuations And The Resistive Transition In Superconducting Films With A Thin Overlayer, Alex Gurevich
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 …
Surface Impedance And Optimum Surface Resistance Of A Superconductor With An Imperfect Surface, Alex Gurevich, Takayuki Kubo
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 …
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
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 …
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
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 …
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
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.
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
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 …
Universal Far-From-Equilibrium Dynamics Of A Holographic Superconductor, Julian Sonner, Adolfo Del Campo, Wojciech H. Zurek
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 …
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
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 …
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
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 …
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
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. …
Comment On "On The Theory Of Nuclear Resonant Forward Scattering Of Synchrotron Radiation", Gilbert R. Hoy, Jos Odeurs
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 …
An Evaluation Of Supercritical Drying And Peg/Freeze Drying Of Waterlogged Archaeological Wood, Eric Schindelholz, Robert Blanchette, Desmond C. Cook, Michael Drews, Steve Hand, Benjamin Held, Joel Jurgens, Betty Seifert
An Evaluation Of Supercritical Drying And Peg/Freeze Drying Of Waterlogged Archaeological Wood, Eric Schindelholz, Robert Blanchette, Desmond C. Cook, Michael Drews, Steve Hand, Benjamin Held, Joel Jurgens, Betty Seifert
Physics Faculty Publications
This study was undertaken to evaluate the physical effects of drying waterlogged archaeological wood using supercritical carbon dioxide as compared to air drying and the popular polyethylene glycol (PEG)/freeze drying method. Previous studies have shown supercritical drying to be a potentially advantageous alternative to current methods of drying waterlogged wood through reduced processing time, minimal shrinkage, and increased success for reversibility. Samples in the form of blocks and planks of a few centimeters in size were prepared from two archaeological waterlogged wood sources and grouped into three treatment sets: one for air drying, one for PEG/freeze drying, and the other …
Effect Of Cr3+ And So42- On The Structure Of Rust Layer Formed On Steels By Atmospheric Corrosion, Masato Yamashita, Hitoshi Uchida,, Desmond C. Cook .
Effect Of Cr3+ And So42- On The Structure Of Rust Layer Formed On Steels By Atmospheric Corrosion, Masato Yamashita, Hitoshi Uchida,, Desmond C. Cook .
Physics Faculty Publications
The effect of chromium ion (Cr3+) and sulfate ion (SO42-) on the structure of the rust layer formed by thin electrolyte-film corrosion of low-alloy steels has been examined. By using X-ray diffraction spectroscopy, it was found that coexistence of Cr3+ and SO42- in the electrolyte film covering the steel surface quickly forms the Cr-goethite (α-(Fe 1-X, CrX)OOH) layer which has been known as the final protective rust layer. Scanning vibrating electrode measurements showed that the rust layer formed under the electrolyte film containing Cr3+ and SO42- …
Mössbauer Effect Determination Of Relative Recoilless Fractions For Iron Oxides, Sei J. Oh, Desmond C. Cook
Mössbauer Effect Determination Of Relative Recoilless Fractions For Iron Oxides, Sei J. Oh, Desmond C. Cook
Physics Faculty Publications
The relative recoilless fraction (F-value) of each of six iron oxides, defined as the ratio of the recoil-free fractions of two different materials, was experimentally determined relative to hematite at 300 K and 77 K by Mössbauer spectroscopy. Using the relative recoil-free fractions compared to that of hematite, the relative recoilless fractions between all pairs of the seven iron oxides were determined. The F-values can allow conversion of Mössbauer subspectral areas to the relative atomic, molecular, or weight fractions of each iron oxide present in a mixed oxide phase sample.
Suppression Of Switchable Polarization In Kdp By Ionizing Radiation, Timothy D. Usher
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 …
Mechanical Alloying Of Nitrogen Into Iron Powders, J. Rawers, D. Govier, D. C. Cook
Mechanical Alloying Of Nitrogen Into Iron Powders, J. Rawers, D. Govier, D. C. Cook
Physics Faculty Publications
Mechanical alloying of nitrogen into bcc-fe powder is a very effective and efficient means of obtaining very high concentration of nitrogen in micron-size iron particles. Mechanical alloying increases the concentration of nitrogen in the iron powder far in excess of the bcc-Fe lattice low nitrogen solubility, however most of the infused nitrogen resides on the nano-size grain boundaries and in nano-size bct-fe that forms during mechanical alloying.
Measurement Of Nuclear Quadrupole Interactions Using Mössbauer Spectroscopy, Desmond C. Cook
Measurement Of Nuclear Quadrupole Interactions Using Mössbauer Spectroscopy, Desmond C. Cook
Physics Faculty Publications
Mössbauer spectroscopy is a useful probe for investigating nuclear quadrupole interactions. It enables the magnitude, sign and asymmetry of the electric quadrupole coupling constant to be determined. It is especially important for its ability to measure these parameters for excited nuclear states. The Mössbauer effect is used to measure excited state quadrupole moments in materials whose electric field gradient (EFG) is known. More commonly however, it is used to determine the EFG from which atomic bonding and electronic structure are determined. The technique also allows temperature dependent orientation of sublattice magnetization to be measured using the direction of the electric …
Magnetic-Field Distributions In Zinc-Nickel Ferrite, T. A. Dooling, Desmond C. Cook
Magnetic-Field Distributions In Zinc-Nickel Ferrite, T. A. Dooling, Desmond C. Cook
Physics Faculty Publications
The Mössbauer effect has been used to study the microscopic magnetic properties of the cubic microwave ferrite (Zn0.41Ni0.59)Fe2O4 at 300 K. The magnetically split spectrum is broad and unresolved due to the overlap of the hyperfine magnetic fields at the tetrahedral and octahedral sites. This is caused by a distribution of magnetic fields at each site. The distribution is especially large and asymmetric at the octahedral site and is due to the fact that the iron atoms at this site are influenced by the presence of both iron and zinc at the tetrahedral …
Phase Changes In Plasma‐Sprayed Zinc‐Nickel Ferrite, T. A. Dooling, Desmond C. Cook
Phase Changes In Plasma‐Sprayed Zinc‐Nickel Ferrite, T. A. Dooling, Desmond C. Cook
Physics Faculty Publications
The magnetic and crystalline properties of a plasma‐sprayed coating of the microwave absorbing zinc‐nickel ferrite, (Zn0.41Ni0.59 )Fe2O4 have been studied at 300 K using the Mössbauer effect and x‐ray diffraction (XRD). Both techniques indicate that the plasma‐sprayed material separated into two phases. The first is a nickel‐rich phase with magnetic fields of 47.5 and 44.5 T at the tetrahedral and octahedral sites, respectively. The second is a zinc‐rich phase, zinc meta‐ferrite, having a small magnetic field of 4.2 T. The quadrupole splitting of this second phase is ΔE=0.34 mm s−1, …
Mössbauer Spectroscopic Studies Of Hemoglobin And Its Isolated Subunits, G. R. Hoy, D. C. Cook, R. L. Berger, F. K. Friedman
Mössbauer Spectroscopic Studies Of Hemoglobin And Its Isolated Subunits, G. R. Hoy, D. C. Cook, R. L. Berger, F. K. Friedman
Physics Faculty Publications
Samples of 90% enriched 57Fe hemoglobin and its isolated subunits have been prepared. Mössbauer spectroscopic measurements have been made on three such samples. Sample one contained contributions of oxyhemoglobin, deoxyhemoglobin, and carbonmonoxyhemoglobin. This sample was studied from a temperature of 90 K down to 230 mK. Measurements were also made at 4.2 K using a small applied magnetic field of 1.0 T. In general, the measured quadrupole splittings and isomer shifts for each component agreed with previous measurements on single component samples in the literature, and thus demonstrated that chemically enriched hemoglobin has not been altered. The second and …
Feasibility Studies Of Conversion Electron Mössbauer Spectroscopy (Cems) Of Iron-Doped Inp, Gilbert R. Hoy, Desmond C. Cook, Edward Agyekum
Feasibility Studies Of Conversion Electron Mössbauer Spectroscopy (Cems) Of Iron-Doped Inp, Gilbert R. Hoy, Desmond C. Cook, Edward Agyekum
Physics Faculty Publications
An electron detector for conversion electron Moessbauer spectroscopy CEMS has been designed and built. Tests have been performed to study the effects on the detector resolution with respect to high voltage, gas flow rate, and counting rate. These parameters have been optimized to detect the 7.3keV conversion electrons emitted following resonant absorption of the 14.4keV source gamma rays associated with the Moessbauer effect using Fe57. CEMS spectra have been obtained using standard Fe57 enriched and natural iron samples. CEMS spectra have also been obtained for InPFe samples supplied by the Naval Research Laboratory. So far we have only been successful …