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Full-Text Articles in Physics
Electronic Structure Of Nuclear-Spin-Polarization-Induced Quantum Dots, Yuriy V. Pershin Dr
Electronic Structure Of Nuclear-Spin-Polarization-Induced Quantum Dots, Yuriy V. Pershin Dr
Faculty Publications
We study a system in which electrons in a two-dimensional electron gas are confined by a nonhomogeneous nuclear-spin polarization. The system consists of a heterostructure that has nonzero nuclei spins. We show that in this system electrons can be confined into a dot region through a local nuclear-spin polarization. The nuclear-spin-polarization-induced quantum dot has interesting properties indicating that electron energy levels are time dependent because of the nuclear-spin relaxation and diffusion processes. Electron confining potential is a solution of diffusion equation with relaxation. Experimental investigations of the time dependence of electron energy levels will result in more information about nuclear-spin …
Slow Spin Relaxation In Two-Dimensional Electron Systems With Antidots, Yuriy V. Pershin Dr, Vladimir Privman
Slow Spin Relaxation In Two-Dimensional Electron Systems With Antidots, Yuriy V. Pershin Dr, Vladimir Privman
Faculty Publications
We report a Monte Carlo investigation of the effect of a lattice of antidots on spin relaxation in twodimensional electron systems. The spin relaxation time is calculated as a function of geometrical parameters describing the antidot lattice, namely the antidot radius and the distance between their centers. It is shown that spin polarization relaxation can be efficiently suppressed by the chaotic spatial motion due to the antidot lattice. This phenomenon offers a new approach to spin coherence manipulation in spintronics devices.
Solar Neutrinos, Sno And Neutrino-Deuteron Reactions, Vladimir Gudkov, Kuniharu Kubodera
Solar Neutrinos, Sno And Neutrino-Deuteron Reactions, Vladimir Gudkov, Kuniharu Kubodera
Faculty Publications
The standard nuclear physics approach and effective field theory approach for calculations of neutrino–deuteron cross sections for the solar neutrino energies are considered. Their main features, the level of accuracy and problems to be addressed for further developments are discussed.
High-Field Measurements Of Electron Decoherence Time In Metallic Nanowires: Switching Off Magnetic Impurity Spins, P. Mohanty, Richard A. Webb
High-Field Measurements Of Electron Decoherence Time In Metallic Nanowires: Switching Off Magnetic Impurity Spins, P. Mohanty, Richard A. Webb
Faculty Publications
We report low-temperature measurements of electron decoherence time in a series of pure gold wires, 18 nm thick and 30 nm wide. At fields up to 15 T, large enough to polarize any concentration of magnetic impurity spins, conductance fluctuation measurements show almost no temperature dependence of the decoherence time below 300 mK, both in the correlation field for interference and the root-mean-square value of the fluctuations. Combined with previous low-field weak localization measurements on samples from similar material, our experiment suggests that the ubiquitous saturation of decoherence time in these samples is not due to any mechanism based on …
Focusing Of Spin Polarization In Semiconductors By Inhomogeneous Doping, Yuriy V. Pershin Dr, Vladimir Privman
Focusing Of Spin Polarization In Semiconductors By Inhomogeneous Doping, Yuriy V. Pershin Dr, Vladimir Privman
Faculty Publications
We study the evolution and distribution of nonequilibrium electron spin polarization in n-type semiconductors within the two-component drift-diffusion model in an applied electric field. Propagation of spin-polarized electrons through a boundary between two semiconductor regions with different doping levels is considered.We assume that inhomogeneous spin polarization is created locally and driven through the boundary by the electric field.We show that an initially created narrow region of spin polarization can be further compressed and amplified near the boundary. Since the boundary involves variation of doping but no real interface between two semiconductor materials, no significant spin polarization loss is expected. …
Electronic Transport Through A Nuclear-Spin-Polarization-Induced Quantum Wire, Yuriy V. Pershin Dr, S. N. Shevchenko, I. D. Vagner, P. Wyder
Electronic Transport Through A Nuclear-Spin-Polarization-Induced Quantum Wire, Yuriy V. Pershin Dr, S. N. Shevchenko, I. D. Vagner, P. Wyder
Faculty Publications
Electron transport in a low-dimensional structure—the nuclear-spin-polarization-induced quantum wire is theoretically studied. In the proposed system the local nuclear-spin polarization creates the effective hyperfine field that confines the electrons with the spins opposite to the hyperfine field to the regions of maximal nuclear-spin polarization. The influence of the nuclear-spin relaxation and diffusion on the electron energy spectrum and on the conductance of the quantum wire is calculated and the experimental feasibility is discussed.
De Haas-Van Alphen Oscillations In The Quasi-Two-Dimensional Organic Conductor Κ-(Et)2cu(Ncs)2: The Magnetic Breakdown Approach, V. M. Gvozdikov, Yuriy V. Pershin Dr, E. Steep, A. G. M. Jansen, P. Wyder
De Haas-Van Alphen Oscillations In The Quasi-Two-Dimensional Organic Conductor Κ-(Et)2cu(Ncs)2: The Magnetic Breakdown Approach, V. M. Gvozdikov, Yuriy V. Pershin Dr, E. Steep, A. G. M. Jansen, P. Wyder
Faculty Publications
We present both experimental data and an analytic theory for the de Haas–van Alphen ~dHvA! effect in the two-dimensional organic single-crystal conductor k -(ET)2Cu(NCS)2. We show that the magnetization oscillation pattern and the fast Fourier transform (FFT) spectrum of our measurements are well described theoretically within the coherent magnetic breakdown (MB) model for a two-dimensional Fermi surface consisting of two open sheets and closed pockets connected by magnetic breakdown centers. The spectrum of Landau quantized energy levels changes substantially due to the MB. Landau bands develop whose bandwidth and relative distance between them oscillate in inverse magnetic field. These oscillations …
Anomalous Conductance Distribution In Quasi-One-Dimensional Gold Wires: Possible Violation Of The One-Parameter Scaling Hypothesis, Pritiraj Mohanty, Richard A. Webb
Anomalous Conductance Distribution In Quasi-One-Dimensional Gold Wires: Possible Violation Of The One-Parameter Scaling Hypothesis, Pritiraj Mohanty, Richard A. Webb
Faculty Publications
We report measurements of conductance distribution in a set of quasi-one-dimensional gold wires. The distribution includes the second cumulant or the variance which describes the universal conductance fluctuations, and the third cumulant which denotes the leading deviation. We have observed an asymmetric contribution—or, a nonvanishing third cumulant—contrary to the expectation for quasi-one-dimensional systems in the noninteracting theories in the one-parameter scaling framework, which include the perturbative diagrammatic calculations and the random matrix theory.
Neutrino Reactions On The Deuteron, S. Nakamura, T. Sato, Vladimir Gudkov, K. Kubodera
Neutrino Reactions On The Deuteron, S. Nakamura, T. Sato, Vladimir Gudkov, K. Kubodera
Faculty Publications
The cross sections for the ν-d and ν̅ -d reactions are calculated for incident energy up to Eν=170 MeV with the use of a phenomenological Lagrangian approach. We assess and improve the reliability of the employed calculational method by examining the dependence of the results on various input and approximations that go into the calculation. The main points of improvement over the existing work are (1) use of the “modern” NN potentials, (2) use of the more accurate nucleon weak-interaction form factors, and (3) monitoring the strength of a vertex that governs the exchange-current contribution, with the use …
Diamagnetic Persistent Current In Diffusive Normal-Metal Rings, E. M.Q. Jariwala, P. Mohanty, M. B. Ketchen, Richard A. Webb
Diamagnetic Persistent Current In Diffusive Normal-Metal Rings, E. M.Q. Jariwala, P. Mohanty, M. B. Ketchen, Richard A. Webb
Faculty Publications
We have measured a diamagnetic persistent current with flux periodicities of both h/e and h/2e in an array of thirty diffusive mesoscopic gold rings. At the lowest temperatures, the magnitudes of the currents per ring corresponding to the h/e- and h/2e-periodic responses are both comparable to the Thouless energy Ec≡ħ/τD, where τD is the diffusion time. Taken in conjunction with earlier experiments, our results strongly challenge the conventional theories of persistent current. We consider a new approach associated with the saturation of …
Low Temperature Anomaly In Mesoscopic Kondo Wires, P. Mohanty, Richard A. Webb
Low Temperature Anomaly In Mesoscopic Kondo Wires, P. Mohanty, Richard A. Webb
Faculty Publications
We report the observation of an anomalous magnetoresistance in extremely dilute quasi-one-dimensional AuFe wires at low temperatures, along with a hysteretic background at low fields. The Kondo resistivity does not show the unitarity limit down to the lowest temperature, implying uncompensated spin states. We suggest that the anomalous magnetoresistance may be understood as the interference correction from the accumulation of geometric phase in the conduction electron wave function around the localized impurity spin.
Insulator-Metal Crossover Near Optimal Doping In Pr22xcexcuo4: Anomalous Normal-State Low Temperature Resistivity, P. Fournier, P. Mohanty, E. Maiser, S. Darzens, T. Venkatesan, C. J. Lobb, G. Czjzek, Richard A. Webb, R. L. Greene
Insulator-Metal Crossover Near Optimal Doping In Pr22xcexcuo4: Anomalous Normal-State Low Temperature Resistivity, P. Fournier, P. Mohanty, E. Maiser, S. Darzens, T. Venkatesan, C. J. Lobb, G. Czjzek, Richard A. Webb, R. L. Greene
Faculty Publications
Normal-state resistivity measurements at high fields and low temperatures in electron-doped Pr2-xCexCuO4 thin films reveal an insulator-metal crossover near a doping level x≈0.15, similar to a previous report on hole-doped La2-xSrxCuO4. The temperature dependence of the resistivity of insulatinglike samples is sublogarithmic, while for metallic samples (with x = 0.17) the resistivity is linear from 40 mK to 40 K. This surprising latter observation suggests an unusual contribution to the scattering processes at low temperature in these materials. We conclude that the ground state at x = 0.15, corresponding …
Intrinsic Decoherence In Mesoscopic Systems, P. Mohanty, E. M.Q. Jariwala, Richard A. Webb
Intrinsic Decoherence In Mesoscopic Systems, P. Mohanty, E. M.Q. Jariwala, Richard A. Webb
Faculty Publications
We present measurements of the phase coherence time τφ in six quasi-1D Au wires and clearly show that τφ is temperature independent at low temperatures. We suggest that zero-point fluctuations of the phase coherent electrons are responsible for the observed saturation of τφ. We introduce a new functional form for the temperature dependence and present the results of a calculation for the saturation value of τφ. This explains the observed temperature dependence of our samples as well as many 1D and 2D systems reported to date.
Dynamics Of Conversion Of Conduction Electrons Into A Collective Charge-Density-Wave Current, Alexander S. Kovalev, Yuriy V. Pershin Dr, Alexander S. Rozhavsky
Dynamics Of Conversion Of Conduction Electrons Into A Collective Charge-Density-Wave Current, Alexander S. Kovalev, Yuriy V. Pershin Dr, Alexander S. Rozhavsky
Faculty Publications
The exactly solvable model which describes the dynamics of transformation of conduction electrons into nonlinear charge-carrying excitations of charge-density waves in quasi-one-dimensional Peierls-Frohlich conductors is formulated and studied by the inverse scattering transformation method. The pair of self-trapped conduction electrons transform into a charged 2π kink localized in a single conducting chain and surrounded by dipoles in neighboring chains.
Absence Of Size Dependence Of The Kondo Resistivity, V. Chandrasekhar, P. Santhanam, N. A. Penebre, Richard A. Webb, H. Vloeberghs, C. Van Haesendonck, Y. Bruynseraede
Absence Of Size Dependence Of The Kondo Resistivity, V. Chandrasekhar, P. Santhanam, N. A. Penebre, Richard A. Webb, H. Vloeberghs, C. Van Haesendonck, Y. Bruynseraede
Faculty Publications
We have measured the low temperature resistivity of AuFe wires in the dilute magnetic impurity limit as a function of wire width, temperature, and magnetic field. When the width dependence of the electron-electron interaction contribution to the resistivity is taken into account, the temperature dependence of the remaining Kondo contribution to the resistivity of all samples with the same impurity concentration is identical. Similar behavior is observed for the magnetic field dependent resistivity. Thus, the Kondo contribution to the resistivity is independent of width down to 38 nm, much smaller than the Kondo length ξK=ħvF/kB …
Neutron Reflection Interferometry: Physical Principles Of Surface Analysis With Phase Information, Vladimir Gudkov, G. I. Opat, A. G. Klein
Neutron Reflection Interferometry: Physical Principles Of Surface Analysis With Phase Information, Vladimir Gudkov, G. I. Opat, A. G. Klein
Faculty Publications
It is shown that the analysis of surface layers by neutron reflection interferometry is considerably enhanced by performing the reflectometry with phase information. We discuss two methods of providing such information. One method involves physically adding an extra reference layer, whose amplitude and phase are known theoretically. The other uses the Lloyd's mirror configuration, in which a directly propagating ray that interferes with the reflected ray supplies the phase information. The methods have much in common with holography.
Cp-Odd Nucleon Potential, Vladimir Gudkov, Xiao-Gang He, Bruce H.J. Mckellar
Cp-Odd Nucleon Potential, Vladimir Gudkov, Xiao-Gang He, Bruce H.J. Mckellar
Faculty Publications
The P-odd and CP-odd nucleon potential for different models of CP violation in the one-meson exchange approximation is studied. It is shown that the main contribution is due to the π-meson exhcange which leads to a simple one-parameter CP-odd nucleon potential.
In-Medium Behavior Of The Qcd ϴ Term And The Value Of Cp Violation In Nuclei, Vladimir Gudkov
In-Medium Behavior Of The Qcd ϴ Term And The Value Of Cp Violation In Nuclei, Vladimir Gudkov
Faculty Publications
The expectation value of the θ term in QCD for nuclear matter is estimated in the nucleon gas approximation. There is no significant renormalization (to an accuracy ∼10%) of the CP violation in nuclei due to the similar behaviors for the in-medium values of the θ term and quark condensates.
Sign Correlations And The Mechanism For Parity Violation, Vladimir Gudkov
Sign Correlations And The Mechanism For Parity Violation, Vladimir Gudkov
Faculty Publications
The problem of possible sign correlations of P-odd effects due to parity mixing on the compound nuclear stage is discussed. For an unambiguous test of the conventional model of parity violation on the compound nuclear stage, it is not enough only to measure the sign correlation of P-odd effects on some resonances, but it is necessary also to know the neutron decay amplitudes for each resonance.
Recoil Effects And Cp Violation In Neutron Scattering, Vladimir Gudkov
Recoil Effects And Cp Violation In Neutron Scattering, Vladimir Gudkov
Faculty Publications
The problem of the imitation of CP violation in neutron scattering is discussed. The thermal motion of nuclei cannot contribute to symmetry-violating effects. The influence of the nuclear depolarization due to neutron scattering is estimated.
Magnetic Response Of A Single, Isolated Gold Loop, V. Chandrasekhar, Richard A. Webb, M. J. Brady, M. B. Ketchen, W. J. Gallagher, A. Kleinsasser
Magnetic Response Of A Single, Isolated Gold Loop, V. Chandrasekhar, Richard A. Webb, M. J. Brady, M. B. Ketchen, W. J. Gallagher, A. Kleinsasser
Faculty Publications
Measurements have been made of the low-temperature magnetic response of single, isolated, micron-size Au loops. The magnetic response is found to contain a component which oscillates with the applied magnetic flux with a fundamental period of Φ0=h/e. The amplitude of the oscillatory component corresponds to a persistent current of ≃(0.3–2.0)evF/L, 1 to 2 orders of magnitude larger than predicted by current theories.
Single-Electron Charging Effects In Insulating Wires, Venkat Chandrasekhar, Zvi Ovadyahu, Richard A. Webb
Single-Electron Charging Effects In Insulating Wires, Venkat Chandrasekhar, Zvi Ovadyahu, Richard A. Webb
Faculty Publications
We present measurements of the transport properties of 0.75-μm-long, narrow, insulating indium oxide wires and rings. These devices have no apparent tunnel barriers, yet they exhibit effects similar to those found in series arrays of very small-capacitance tunnel junctions: highly nonlinear I-V characteristics and a zero-bias conductance which is periodic in a voltage applied by means of a lateral gate. These effects are due to the influence of single-electron charging on transport through localized states in the insulating regime.
Universal Scaling Of Nonlocal And Local Resistance Fluctuations In Small Wires, H. Haucke, S. Washburn, A. D. Benoit, C. P. Umbach, Richard A. Webb
Universal Scaling Of Nonlocal And Local Resistance Fluctuations In Small Wires, H. Haucke, S. Washburn, A. D. Benoit, C. P. Umbach, Richard A. Webb
Faculty Publications
Resistance fluctuations in small metal samples result from coherent transport of the carriers. The wave functions of the carriers extend into regions which are not accessible classically. We have directly measured the length dependence of the nonlocal magnetoresistance fluctuations in Sb and Au wires by studying regions of our samples separated from the classical current path by a distance L which varied from 3Lcphi down to 0.2Lcphi (where Lcphi is the phase coherence length for the carriers in the metal). These fluctuations decay exponentially with L/Lcphi. Measurements along the classical current paths scale more slowly …
Experimental Study Of Nonlinear Conductance In Small Metallic Samples, Richard A. Webb, S. Washburn, C. P. Umbach
Experimental Study Of Nonlinear Conductance In Small Metallic Samples, Richard A. Webb, S. Washburn, C. P. Umbach
Faculty Publications
We have directly observed current-dependent, nonlinear contributions to the conductance fluctuations of phase-coherent metallic wires and loops. The fluctuations in the current-voltage curves are reproducible, asymmetric about I=0, and in qualitative agreement with theoretical predictions. In ac measurements, the nonlinear terms also generate large harmonic signals of the conductance fluctuations whose dependence on the drive current can be understood qualitatively. The spectra of harmonics from loops and wires have different dependences on the voltage across the sample.
Normal-Metal Aharonov-Bohm Effect In The Presence Of A Transverse Electric Field, S. Washburn, H. Schmid, D. Kern, Richard A. Webb
Normal-Metal Aharonov-Bohm Effect In The Presence Of A Transverse Electric Field, S. Washburn, H. Schmid, D. Kern, Richard A. Webb
Faculty Publications
The effects of transverse electric fields on the conductance fluctuations in an Sb loop have been studied. We show that the electric field can be used to tune the position (or phase) of Aharonov-Bohm oscillations as well as to alter the aperiodic conductance fluctuation patterns. We disucss two mechanisms which might cause the observed dependence of the fluctuation pattern on transverse electric field. The first is the electrostatic Aharonov-Bohm effect, and the second is the spatial shifting of the electron trajectories by the electric field.
Length-Independent Voltage Fluctuations In Small Devices, A. Benoit, C. P. Umbach, R. B. Laibowitz, Richard A. Webb
Length-Independent Voltage Fluctuations In Small Devices, A. Benoit, C. P. Umbach, R. B. Laibowitz, Richard A. Webb
Faculty Publications
Conductance fluctuations in one-dimensional lines of length L shorter than the phase-coherence length Lφ are not universal but diverge as L-2. Using the Onsager relations and voltage additivity, we show that the voltage fluctuations are independent of the distance between voltage probes. The antisymmetric (Hall-type) contribution to the voltage fluctuations is constant for all values of L. Measurements of the voltage fluctuations and correlation function between different regions in Au and Sb lines confirm these results.
Asymmetry In The Magnetoconductance Of Metal Wires And Loops, A. D. Benoit, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb
Asymmetry In The Magnetoconductance Of Metal Wires And Loops, A. D. Benoit, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb
Faculty Publications
Universal conductance fluctuations in wires and Aharonov-Bohm oscillations in loops are not symmetric about H=0. The observation of asymmetry in the periodic oscillations is possible when the phase-coherence length of the wave function is comparable to the separation of the voltage probes. In both cases, four-probe measurements yield resistances which depend on lead configuration. The asymmetries appear like Hall voltages, and are consistent with Onsager's relations.
Observation Of Resonant Tunneling In Silicon Inversion Layers, A. B. Fowler, G. L. Timp, J. J. Wainer, Richard A. Webb
Observation Of Resonant Tunneling In Silicon Inversion Layers, A. B. Fowler, G. L. Timp, J. J. Wainer, Richard A. Webb
Faculty Publications
Measurements of the temperature and carrier-density dependence of the strongly localized conductance of short silicon inversion layers are reported. At the lowest temperatures we observe well-isolated, large conductance peaks whose width and temperature dependence are only consistent with resonant tunneling and are inconsistent with Mott hopping. Several new features are observed which we believe may be the result of Coulomb interactions.
Interaction Effects Among Two-Dimensional Electrons And Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki
Interaction Effects Among Two-Dimensional Electrons And Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki
Faculty Publications
We report large logarithmic corrections to the conductivity of two-dimensional electrons and holes in GaSb-InAs-GaSb double heterostructures. From ∼ 40 mK to 1 K, the conductivity increased with the logarithm of the temperature but with a slope as much as 30 times larger than estimated from the theories of weak localization and carrier interaction. The discrepancy apparently results from electron-hole interactions not included in the theory.
Interaction Effects Among Two-Dimensional Electrons And Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki
Interaction Effects Among Two-Dimensional Electrons And Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki
Faculty Publications
We report large logarithmic corrections to the conductivity of two-dimensional electrons and holes in GaSb-InAs-GaSb double heterostructures. From ∼ 40 mK to 1 K, the conductivity increased with the logarithm of the temperature but with a slope as much as 30 times larger than estimated from the theories of weak localization and carrier interaction. The discrepancy apparently results from electron-hole interactions not included in the theory.