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Articles 1 - 30 of 50
Full-Text Articles in Physical Sciences and Mathematics
Extreme Sensitivity Of Differential Momentum Transfer Cross Sections To Target Atom Initial Conditions, Ronald E. Olson, J. Fiol
Extreme Sensitivity Of Differential Momentum Transfer Cross Sections To Target Atom Initial Conditions, Ronald E. Olson, J. Fiol
Physics Faculty Research & Creative Works
Heavy-particle cross sections differential in the momentum transferred to the target are investigated using the classical trajectory Monte Carlo method. with the 3.6 MeV/u Au53++He system as a test case, it is shown that these cross sections are extremely sensitive to the initial target temperature. In particular, when thermal motion is varied for one of the target's initial momentum components between 0 and 25 K the absolute cross sections vary by orders of magnitude and, in addition, their relative shapes undergo major changes. We find that by setting one of the target's transverse momenta to a temperature of 16 K, …
Nonrelativistic Qed Approach To The Lamb Shift, Ulrich D. Jentschura, Andrzej Czarnecki, Krzysztof Pachucki
Nonrelativistic Qed Approach To The Lamb Shift, Ulrich D. Jentschura, Andrzej Czarnecki, Krzysztof Pachucki
Physics Faculty Research & Creative Works
We calculate the one- and two-loop corrections of order α(Zα)6 and α2(Zα)6, respectively, to the Lamb shift in hydrogenlike systems using the formalism of nonrelativistic quantum electrodynamics. We obtain general results valid for all hydrogenic states with nonvanishing orbital angular momentum and for the normalized difference of S states. These results involve the expectation value of local effective operators and relativistic corrections to Bethe logarithms. The one-loop correction is in agreement with previous calculations for the particular cases of S, P, and D states. The two-loop correction in the order α2(Zα)6 includes …
Mutual Ionization In 200-Kev H⁻+ He Collisions, T. Ferger, Daniel Fischer, Michael Schulz, R. Moshammer, A. B. Voitkiv, B. Najjari, J. Ullrich
Mutual Ionization In 200-Kev H⁻+ He Collisions, T. Ferger, Daniel Fischer, Michael Schulz, R. Moshammer, A. B. Voitkiv, B. Najjari, J. Ullrich
Physics Faculty Research & Creative Works
We studied mutual ionization in 200-keV H-+He collisions in a kinematically complete experiment by measuring the fully momentum-analyzed recoil ions and both active electrons in coincidence. Comparison of the data to our calculations, based on various theoretical models, show that mutual ionization proceeds predominantly through the interaction between both electrons. The post-collision interaction between the outgoing ejected electrons as well as higher order processes involving the interaction between the core of both collision partners are also important.
Percolation Quantum Phase Transitions In Diluted Magnets, Thomas Vojta, Jörg Schmalian
Percolation Quantum Phase Transitions In Diluted Magnets, Thomas Vojta, Jörg Schmalian
Physics Faculty Research & Creative Works
We show that the interplay of geometric criticality and quantum fluctuations leads to a novel universality class for the percolation quantum phase transition in diluted magnets. All critical exponents involving dynamical correlations are different from the classical percolation values, but in two dimensions they can nonetheless be determined exactly. We develop a complete scaling theory of this transition, and we relate it to recent experiments in La2Cu1-p(Zn,Mg)pO4. Our results are also relevant for disordered interacting boson systems.
Erratum: Publisher's Note: Calculation Of The One- And Two-Loop Lamb Shift For Arbitrary Excited Hydrogenic States (Physical Review Letters (2005) 95 (180404)), Andrzej Czarnecki, Ulrich D. Jentschura, Krzysztof Pachucki
Erratum: Publisher's Note: Calculation Of The One- And Two-Loop Lamb Shift For Arbitrary Excited Hydrogenic States (Physical Review Letters (2005) 95 (180404)), Andrzej Czarnecki, Ulrich D. Jentschura, Krzysztof Pachucki
Physics Faculty Research & Creative Works
No abstract provided.
Laser-Dressed Vacuum Polarization In A Coulomb Field, A. I. Milstein, Ivan S. Terekhov, Ulrich D. Jentschura, Christoph H. Keitel
Laser-Dressed Vacuum Polarization In A Coulomb Field, A. I. Milstein, Ivan S. Terekhov, Ulrich D. Jentschura, Christoph H. Keitel
Physics Faculty Research & Creative Works
We investigate quantum electrodynamic effects under the influence of an external, time-dependent electromagnetic field, which mediates dynamic modifications of the radiative corrections. Specifically, we consider the quantum electrodynamic vacuum-polarization tensor under the influence of two external background fields: a strong laser field and a nuclear Coulomb field. We calculate the charge and current densities induced by a nuclear Coulomb field in the presence of a laser field. We find the corresponding induced scalar and vector potentials. The induced potential, in first-order perturbation theory, leads to a correction to atomic energy levels. The external laser field breaks the rotational symmetry of …
Precise Calculation Of Transition Frequencies Of Hydrogen And Deuterium Based On A Least-Squares Analysis, Ulrich D. Jentschura, Svetlana A. Kotochigova, Eric Olivier Le Bigot, Peter J. Mohr, Barry N. Taylor
Precise Calculation Of Transition Frequencies Of Hydrogen And Deuterium Based On A Least-Squares Analysis, Ulrich D. Jentschura, Svetlana A. Kotochigova, Eric Olivier Le Bigot, Peter J. Mohr, Barry N. Taylor
Physics Faculty Research & Creative Works
We combine a limited number of accurately measured transition frequencies in hydrogen and deuterium, recent quantum electrodynamics (QED) calculations, and, as an essential additional ingredient, a generalized least-squares analysis, to obtain precise and optimal predictions for hydrogen and deuterium transition frequencies. Some of the predicted transition frequencies have relative uncertainties more than an order of magnitude smaller than that of the g factor of the electron, which was previously the most accurate prediction of QED.
Sub-Femtosecond Correlated Dynamics Explored With Antiprotons, J. Ullrich, A. Dorn, Daniel Fischer, R. Moshammer, B. Najjari, Michael Schulz, A. B. Voitkiv, C. P. Welsch
Sub-Femtosecond Correlated Dynamics Explored With Antiprotons, J. Ullrich, A. Dorn, Daniel Fischer, R. Moshammer, B. Najjari, Michael Schulz, A. B. Voitkiv, C. P. Welsch
Physics Faculty Research & Creative Works
Ionizing collisions of antiprotons with atoms or molecules at energies between a few keV up to about one MeV provide a unique tool to explore correlated dynamics of electrons at large perturbations on a time scale between several femtoseconds (1 fs = 10-15 s) down to some tens of attoseconds (1 as = 10-18 s). Exploiting and developing many-particle imaging methods - Reaction-Microscopes - integrated into a novel ultra-low energy storage ring (USR) for slow antiprotons will enable to access for the first time fully differential cross sections for single and multiple ionization in such collisions. Moreover, the …
Calculation Of The One- And Two-Loop Lamb Shift For Arbitrary Excited Hydrogenic States, Andrzej Czarnecki, Ulrich D. Jentschura, Krzysztof Pachucki
Calculation Of The One- And Two-Loop Lamb Shift For Arbitrary Excited Hydrogenic States, Andrzej Czarnecki, Ulrich D. Jentschura, Krzysztof Pachucki
Physics Faculty Research & Creative Works
General expressions for quantum electrodynamic corrections to the one-loop self-energy [of order α(Zα)6] and for the two-loop Lamb shift [of order α2(Zα)6] are derived. The latter includes all diagrams with closed fermion loops. The general results are valid for arbitrary excited non-S hydrogenic states and for the normalized Lamb shift difference of S states, defined as Δn=n3ΔE(nS)-ΔE(1S). We present numerical results for one-loop and two-loop corrections for excited S, P, and D states. In particular, the normalized Lamb shift difference of S states is calculated with an uncertainty of order …
Relativistic Electron Correlation, Quantum Electrodynamics, And The Lifetime Of The 1s²2s²2p²PO3/2 Level In Boronlike Argon, Alain Lapierre, Ulrich D. Jentschura, Jose R. Crespo Lopez-Urrutia, Jean Pierre Braun, Gunter Brenner, Hjalmar Bruhns, Daniel A. Fischer, Antonio J. Gonzalez, Zoltan Harman, Walter Johnson, Christoph H. Keitel, Vladimir Sergeyevich Mironov, C. J. Osborne, Guenther Sikler, R. Soria Orts, Vladimir M. Shabaev, Hiroyuki Tawara, I. I. Tupitsyn, Joachim Hermann Ullrich, Andrey V. Volotka
Relativistic Electron Correlation, Quantum Electrodynamics, And The Lifetime Of The 1s²2s²2p²PO3/2 Level In Boronlike Argon, Alain Lapierre, Ulrich D. Jentschura, Jose R. Crespo Lopez-Urrutia, Jean Pierre Braun, Gunter Brenner, Hjalmar Bruhns, Daniel A. Fischer, Antonio J. Gonzalez, Zoltan Harman, Walter Johnson, Christoph H. Keitel, Vladimir Sergeyevich Mironov, C. J. Osborne, Guenther Sikler, R. Soria Orts, Vladimir M. Shabaev, Hiroyuki Tawara, I. I. Tupitsyn, Joachim Hermann Ullrich, Andrey V. Volotka
Physics Faculty Research & Creative Works
The lifetime of the Ar13+ 1s22s22p2Po3/2 metastable level was determined at the Heidelberg Electron Beam Ion Trap to be 9.573(4)(5)ms(stat)(syst). The accuracy level of one per thousand makes this measurement sensitive to quantum electrodynamic effects like the electron anomalous magnetic moment (EAMM) and to relativistic electron-electron correlation effects like the frequency-dependent Breit interaction. Theoretical predictions, adjusted for the EAMM, cluster about a lifetime that is approximately 3σ shorter than our experimental result.
Renormalization-Group Analysis Of Layered Sine-Gordon Type Models, I. Nandori, Sandor Alex Nagy, Kornel Sailer, Ulrich D. Jentschura
Renormalization-Group Analysis Of Layered Sine-Gordon Type Models, I. Nandori, Sandor Alex Nagy, Kornel Sailer, Ulrich D. Jentschura
Physics Faculty Research & Creative Works
We analyze the phase structure and the renormalization group (RG) flow of the generalized sine-Gordon models with nonvanishing mass terms, using the Wegner-Houghton RG method in the local potential approximation. Particular emphasis is laid upon the layered sine-Gordon (LSG) model, which is the bosonized version of the multi-flavour Schwinger model and approaches the sum of two "normal", massless sine-Gordon (SG) models in the limit of a vanishing interlayer coupling J. Another model of interest is the massive sine-Gordon (MSG) model. The leading-order approximation to the UV (ultraviolet) RG flow predicts two phases for the LSG as well as for the …
Channel Electron Multiplier And Channelplate Efficiencies For Detecting Positive Ions, M. Krems, J. Zirbel, Mark Allan Thomason, Robert D. Dubois
Channel Electron Multiplier And Channelplate Efficiencies For Detecting Positive Ions, M. Krems, J. Zirbel, Mark Allan Thomason, Robert D. Dubois
Physics Faculty Research & Creative Works
Absolute detection efficiencies for singly and multiply charged positive ions have been measured for a channelplate and for two different channel electron multipliers (CEM). The efficiencies were measured for impact energies between approximately 0.25 and 25 keV and for ion masses ranging from 14 to 132. The maximum efficiencies were found to be the same for all ions investigated and were approximately 58% for a channelplate and 89% for the CEMs. For a channelplate it is shown that the detection efficiencies for heavier ions scale to a single curve if plotted versus the impact energy divided by the square root …
Signature Of Chaos In High-Lying Doubly Excited States Of The Helium Atom, Anh-Thu Le, Toru Morishita, X.-M. Tong, C. D. Lin
Signature Of Chaos In High-Lying Doubly Excited States Of The Helium Atom, Anh-Thu Le, Toru Morishita, X.-M. Tong, C. D. Lin
Physics Faculty Research & Creative Works
We examined nearest-neighbor spacing (NNS) statistics in doubly excited states of helium near the double ionization threshold. Using the Brody parameter q to measure the NNS distribution between the regular Poisson distribution (q=0) and the chaotic Wigner distribution (q=1), we showed that for levels near the N=20 threshold of He⁺, or at about 0.13eV below the double ionization threshold, the NNS distribution has q=0.66. The result shows the slow approach of the NNS of helium energy levels towards the Wigner distribution vs the excitation energy. Using an s-wave model where the angular momentum of each electron is restricted to zero, …
Exchange Distortion And Postcollision Interaction For Intermediate-Energy Electron-Impact Ionization Of Argon, A. Prideaux, Don H. Madison, K. Bartschat
Exchange Distortion And Postcollision Interaction For Intermediate-Energy Electron-Impact Ionization Of Argon, A. Prideaux, Don H. Madison, K. Bartschat
Physics Faculty Research & Creative Works
Measurements of fully differential cross sections for electron impact ionization of atoms have been performed for over 30 years. However, only within the last ten years has agreement between experiment and theory been achieved for ionization of hydrogen and helium. For the heavier inert gases, reasonably good agreement between experiment and theory has only been achieved for high incident energies while serious discrepancies are common for intermediate and low incident energies. It is believed that a major source of the problem stems from an improper/inadequate treatment of exchange distortion (ED) and the effects of post-collision interactions (PCIs). In this paper, …
Charge-Exchange-Produced K -Shell X-Ray Emission From Ar¹⁶⁺ In A Tokamak Plasma With Neutral-Beam Injection, P. Beiersdorfer, M. Bitter, M. Marion, Ronald E. Olson
Charge-Exchange-Produced K -Shell X-Ray Emission From Ar¹⁶⁺ In A Tokamak Plasma With Neutral-Beam Injection, P. Beiersdorfer, M. Bitter, M. Marion, Ronald E. Olson
Physics Faculty Research & Creative Works
High-resolution spectroscopy of a hot tokamak plasma seeded with argon ions and interacting with an energetic, short-pulse neutral hydrogen beam was used to obtain a high-resolution K -shell x-ray spectrum formed solely by charge exchange. The observed K -shell emission of Ar16+ is dominated by the intercombination and forbidden lines, providing clear signatures of charge exchange. Results from an ab initio atomic cascade model provide excellent agreement, validating a semiclassical approach for calculating charge-exchange cross sections.
Pm Emission From A Commercial Jet Engine -- Project Apex, Donald E. Hagen, Philip D. Whitefield, Prem Lobo, Max B. Trueblood
Pm Emission From A Commercial Jet Engine -- Project Apex, Donald E. Hagen, Philip D. Whitefield, Prem Lobo, Max B. Trueblood
Physics Faculty Research & Creative Works
Project APEX (Aircraft Particle Emissions eXperiment) was a multi-agency commercial aircraft emission characterization and technology demonstration experiment. Its objective was to characterize particle and trace gas precursor species in the emissions from a NASA DC-8 aircraft with General Electric CFM56-2C1 engines at the engine exit plane as well as selected down stream locations. This was to advance the understanding of particle emissions and their evolution in the atmosphere from a current in-service turbofan engine. The test was conducted at the NASA Dryden Flight Research Center at Edwards Air Force Base California during April 15-30, 2004. Participants included the National Aeronautics …
Complete Two-Loop Correction To The Bound-Electron Factor, Krzysztof Pachucki, Andrzej Czarnecki, Ulrich D. Jentschura, Vladimir A. Yerokhin
Complete Two-Loop Correction To The Bound-Electron Factor, Krzysztof Pachucki, Andrzej Czarnecki, Ulrich D. Jentschura, Vladimir A. Yerokhin
Physics Faculty Research & Creative Works
Within a systematic approach based on dimensionally regularized nonrelativistic quantum electrodynamics, we derive a complete result for the two-loop correction to order ( α/ π )2 ( Zα )4 for the g factor of an electron bound in an nS state of a hydrogenlike ion. The results obtained significantly improve the accuracy of the theoretical predictions for the hydrogenlike carbon and oxygen ions and influence the value of the electron mass inferred from g-factor measurements. D
Autoionization Of He Atoms By Partially Stripped Ion Impact, Sebastian Otranto, Ronald E. Olson
Autoionization Of He Atoms By Partially Stripped Ion Impact, Sebastian Otranto, Ronald E. Olson
Physics Faculty Research & Creative Works
A study of the autoionization process induced by partially stripped ion impact is performed. Electron spectra in momentum space are predicted within a classical model for partially stripped ions. The results are compared with those obtained for pure Coulomb-like projectiles. A quantum-mechanical extension of the Barrachina-Macek model is proposed for partially stripped projectiles. Structure on the electron angular distribution arising in quantum and classical treatments is identified and compared. The presence of rainbow scattering interference is observed in the binary ring profile of the outgoing autoionized electrons for positive-ion impact.
Three-Coulomb-Wave Pluvinage Model For Compton Double Ionization Of Helium In The Region Of The Cross-Section Maximum, S. Jones, Joseph H. Macek, Don H. Madison
Three-Coulomb-Wave Pluvinage Model For Compton Double Ionization Of Helium In The Region Of The Cross-Section Maximum, S. Jones, Joseph H. Macek, Don H. Madison
Physics Faculty Research & Creative Works
Double ionization of ground-state helium by the Compton scattering of a photon is calculated using the well-known product of three Coulomb waves (3C) wave function for the final double-continuum state of the atom and the Pluvinage wave function for the initial ground state (also a product of three Coulomb waves). The theoretical model fails to predict both the shape and the overall magnitude of the observed integrated cross section vs. Incident-photon energy. However, when the monopole part of the electron-photon interaction is removed by an ad hoc procedure, qualitative agreement is obtained, although the absolute size of the cross section …
Self-Energy Values For P States In Hydrogen And Low-Z Hydrogenlike Ions, Ulrich D. Jentschura, Peter J. Mohr
Self-Energy Values For P States In Hydrogen And Low-Z Hydrogenlike Ions, Ulrich D. Jentschura, Peter J. Mohr
Physics Faculty Research & Creative Works
We describe a nonperturbative (in Z α ) numerical evaluation of the one-photon electron self-energy for 3P1/2 , 3P3/2 , 4P1/2, and 4P3/2 states in hydrogenlike atomic systems with charge numbers Z = 1 to 5. The numerical results are found to be in agreement with known terms in the expansion of the self-energy in powers of Z α and lead to improved theoretical predictions for the self-energy shift of these states.
Charge Transfer In Slow Collisions Of C⁶⁺ With H Below 1 Kev / Amu, Chen-Nan Liu, Shu-Chun Cheng, Anh-Thu Le, C. D. Lin
Charge Transfer In Slow Collisions Of C⁶⁺ With H Below 1 Kev / Amu, Chen-Nan Liu, Shu-Chun Cheng, Anh-Thu Le, C. D. Lin
Physics Faculty Research & Creative Works
We reexamine the charge transfer cross sections for C⁶⁺ + H collisions for energies below 1 keV / amu using a fully quantum mechanical approach, based on the hyperspherical close-coupling method. Whereas most previous theoretical and experimental data agree well for the dominant charge transfer to the C⁵⁺(n=4) states, there is significant disagreement among the theories for the transition to the weaker n=5 states. Using the present quantum mechanical calculations we analyze the origin of the discrepancy among these previous calculations. We further extend the calculations to collision energies down to about 1 eV and show that electron capture to …
Calculation Of Hydrogenic Bethe Logarithms For Rydberg States, Ulrich D. Jentschura, Peter J. Mohr
Calculation Of Hydrogenic Bethe Logarithms For Rydberg States, Ulrich D. Jentschura, Peter J. Mohr
Physics Faculty Research & Creative Works
We describe the calculation of hydrogenic (one-loop) Bethe logarithms for all states with principal quantum numbers 200. While, in principle, the calculation of the Bethe logarithm is a rather easy computational problem involving only the nonrelativistic (Schrdinger) theory of the hydrogen atom, certain calculational difficulties affect highly excited states, and in particular states for which the principal quantum number is much larger than the orbital angular momentum quantum number. Two evaluation methods are contrasted. One of these is based on the calculation of the principal value of a specific integral over a virtual photon energy. The other method relies directly …
Erratum: Nonrelativistic Qed Approach To The Bound-Electron G Factor (Phys. Rev. Lett. (2004) 93 (150401)), Krzysztof Pachucki, Ulrich D. Jentschura, Vladimir A. Yerokhin
Erratum: Nonrelativistic Qed Approach To The Bound-Electron G Factor (Phys. Rev. Lett. (2004) 93 (150401)), Krzysztof Pachucki, Ulrich D. Jentschura, Vladimir A. Yerokhin
Physics Faculty Research & Creative Works
No abstract provided.
Temperature Dependence Of Homogeneous Nucleation Rates For Water: Near Equivalence Of The Empirical Fit Of Wölk And Strey, And The Scaled Nucleation Model, Barbara N. Hale
Physics Faculty Research & Creative Works
It is pointed out that the temperature fitting function of Wölk and Strey [J. Phys. Chem. 105, 11683 (2001)], recently shown to convert the Becker-Döring [Ann. Phys. (Leipzig) 24, 719 (1935)] nucleation rate into an expression in agreement with much of the experimental water nucleation rate data, also converts the Becker-Döring rate into a form nearly equivalent with the scaled nucleation rate model, Jscaled=Joc exp[-16πΩ3(Tc/T-1)3/3(ln S)2]. In the latter expression Joc is the inverse thermal wavelength cubed/sec, evaluated at Tc.
Relic Gravitons On Kasner-Like Branes, Marco Cavaglia, G. De Risi, M. Gasperini
Relic Gravitons On Kasner-Like Branes, Marco Cavaglia, G. De Risi, M. Gasperini
Physics Faculty Research & Creative Works
We discuss the cosmological amplification of tensor perturbations in a simple example of brane-world scenario, in which massless gravitons are localized on a higher-dimensional Kasner-like brane embedded in a bulk AdS background. Particular attention is paid to the canonical normalization of the quadratic action describing the massless and massive vacuum quantum fluctuations, and to the exact mass-dependence of the amplitude of massive fluctuations on the brane. The perturbation equations can be separated. In contrast to de Sitter models of brane inflation, we find no mass gap in the spectrum and no enhancement for massless modes at high curvature. The massive …
Positronium Formation In Positron-Li And Positron-Na Collisions At Low Energies, Anh-Thu Le, M. W. J. Bromley, C. D. Lin
Positronium Formation In Positron-Li And Positron-Na Collisions At Low Energies, Anh-Thu Le, M. W. J. Bromley, C. D. Lin
Physics Faculty Research & Creative Works
We present the positronium formation cross sections for a positron colliding with lithium and sodium for the collision energies from 0.01 eV up to 20 eV by the hyperspherical close-coupling method. For Li, our results agree with the experimental data and with other calculations. Our results for Na remain in agreement with previous close-coupling calculations, but do not support the latest experimental data for Na below 1 eV. To validate our model potentials and method in the low-energy regime, the binding energies of positronic lithium and positronic sodium as well as the s-wave scattering lengths for positronium scattering from Li⁺ …
Doubly Differential Cross Sections For Single And Multiple Ionization Of Ne By Electron Impact, Antonio C. Santos, Ahmad Hasan, Robert D. Dubois
Doubly Differential Cross Sections For Single And Multiple Ionization Of Ne By Electron Impact, Antonio C. Santos, Ahmad Hasan, Robert D. Dubois
Physics Faculty Research & Creative Works
We present doubly differential cross sections for single and multiple ionization of the outer shell of neon by 750 eV electron impact. The distinction between single and multiple ionization was achieved by performing a charge state analysis of the recoil ions in coincidence with forward scattered, energy analyzed electrons. By a comparison to photon impact data, the contribution of the second-order double ionization mechanism is estimated and found to be neglible at this impact energy. Following a similar procedure adopted by J. A. R. Samson [Phys. Rev. Lett. 65, 2861 (1990)], the importance of the first-order TS-1 double ionization mechanism …
Muon Transfer From Muonic Hydrogen To Atomic Oxygen And Nitrogen, Anh-Thu Le, C. D. Lin
Muon Transfer From Muonic Hydrogen To Atomic Oxygen And Nitrogen, Anh-Thu Le, C. D. Lin
Physics Faculty Research & Creative Works
The results of diabatic hyperspherical close-coupling calculations are presented for the charge exchange of a negative muon from muonic hydrogen to oxygen and nitrogen for collision energies from 10-3 to 103 eV. It is shown that converged results can be obtained using a much smaller number of channels than in the traditional adiabatic approach. For the energy range below 10 eV our results for nitrogen are in good agreements with the available experimental data and the recent calculations within hyperspherical elliptic coordinates. However, discrepancies were found in the case of oxygen, where a p -wave shape resonance is …
Quantum Griffiths Effects In Itinerant Heisenberg Magnets, Thomas Vojta, Jörg Schmalian
Quantum Griffiths Effects In Itinerant Heisenberg Magnets, Thomas Vojta, Jörg Schmalian
Physics Faculty Research & Creative Works
We study the influence of quenched disorder on quantum phase transitions in itinerant magnets with Heisenberg spin symmetry, paying particular attention to rare disorder fluctuations. In contrast to the Ising case where the Landau damping of the spin fluctuations suppresses the tunneling of the rare regions, the Heisenberg system displays strong power-law quantum Griffiths singularities in the vicinity of the quantum critical point. We discuss these phenomena based on general scaling arguments, and we illustrate them by an explicit calculation for O(N) spin symmetry in the large-N limit. We also discuss broad implications for the classification of quantum phase transitions …
Spin-System Radio-Frequency Superradiation: A Phenomenological Study And Comparison With Numeric Simulations, Carrie L. Davis, Victor K. Henner, Aleksandr V. Chernatynskiy, Ilia V. Kaganov
Spin-System Radio-Frequency Superradiation: A Phenomenological Study And Comparison With Numeric Simulations, Carrie L. Davis, Victor K. Henner, Aleksandr V. Chernatynskiy, Ilia V. Kaganov
Physics Faculty Research & Creative Works
We discuss the coherent behavior of a polarized, nuclear or electron, spin system for which the magnetic dipole radiation emitted in the radio-frequency region, has approximately quadratic dependence on the number of spins. An effective method of describing these phenomena is provided by computer simulation of a microscopic model of the spin system. Important aspects of this numeric simulation are described, together with a comparison with the theoretical predictions. The behavior of the transverse component of the magnetic moment, M+ (t), in super-radiant conditions is studied. In addition, the role of dipole-dipole interactions in super-radiation phenomena is investigated in …