Physics Commons^™

Path Integral Study Of The Correlated Electronic States Of Na4–Na6, Randall W. Hall

Collected Faculty Scholarship

Feynman’s path integral formulation of quantum mechanics is used to study the correlated electronic states of Na4–Na6. Two types of simulations are performed: in the first, the nuclei are allowed to move at finite temperature in order to find the most stable geometries. In agreement with previous calculations, we find that planar structures are the most stable and that there is significant vibrational amplitude at finite temperatures, indicating that the Born–Oppenheimer surface is relatively flat. In the second type of simulation, the nuclei are held fixed at symmetric and asymmetric geometries and the correlated electron density is found. Our results …

The Exchange Potential In Path Integral Studies: Analytical Justification, Randall W. Hall

Collected Faculty Scholarship

We present analytical justification for our previously described exchange pseudopotential. We show how the fermi quantum partition function can be constructed from the Boltzmann (distinguishable particle) wave functions if the states that correspond to like‐spin electrons occupying the same quantum state are excluded. A class of weighting functions that satisfy this constraint approximately is discussed. Our previous pseudopotential falls under this class. Essentially, our pseudopotential forces the unwanted states to have high energy and, hence, to make negligible contribution to the partition function. Exchange potentials of the form discussed in this article should be useful for studying systems where the …

The Energy-Dependence Of Polarization Observables In The ²H(D,Γ)⁴He Reaction, H. R. Weller, R. M. Whitton, J. Langenbrunner, Evans Hayward, W. R. Dodge, S. Kuhn, D. R. Tilley

Physics Faculty Publications

Measurements of the tensor and vector analyzing powers, A_yy(130°) and A_y(130°), have been obtained for the ²H(d,γ )⁴He reaction for energies ranging from E_d(lab) = 0.3 MeV to E_d(lab) = _{50 MeV}. The A_yy(130°) data are sensitive to the D-state present in the ground state of ⁴He and are observed to have their maximum value near E_d = 30 MeV. The vector analyzing power data show a maximum near E_d = 3 MeV. The data are compared to the results of a microscopic …

Quantum Electrodynamics Based On Self-Fields, Without Second Quantization: A Nonrelativisitc Calculation Of G – 2, A. O. Barut, Jonathan P. Dowling, Jean F. Van Huele

Faculty Publications

Using a formulation of quantum electrodynamics that is not second quantized, but rather based on self-fields, we compute the anomalous magnetic moment of the electron to first order in the fine structure constant α. In the nonrelativistic (NR) case and in the dipole approximation, our result is a_e≡(g—2)/2=(4Λ/3m)(α/2π), where Λ is a positive photon energy cutoff and m the electron mass. A reasonable choice of cutoff, Λ/m=¾, yields the correct sign and magnitude for g—2 namely, a_e=+α/2π. . In our formulation the sign of a₃ is correctly positive, …

Paramagnetic Resonance Of Cu2+ Ions In The Superconductor Y0.2Ba0.8CuoX, F. Mehran, S. E. Barnes, T. R. Mcguire, W. J. Gallagher, R. L. Sandstrom, T. R. Dinger, D. A. Chance

Physics Articles and Papers

A strong paramagnetic resonance signal characteristic of Cu²⁺ ions in ‖x²-y²〉 states is observed in the high-T_c≊90 K superconductor Y_0.2Ba_0.8CuO_x. The line intensity of the ioniclike signal shows a deviation from Curie behavior at T≳T_c. It is speculated that the phase that is responsible for the signal is an example of an Anderson lattice with an unusually high Kondo temperature.

Laser Pump And Probe Excited State Absorption Measurements, Shawpin Jong

Electrical & Computer Engineering Theses & Dissertations

A pump and probe technique was used to investigate triplet-triplet excited state absorption in solutions of the scintillators 2,5 diphenyloxazole (PPO) and 2,1 naphthyl,5 phenylzole (a-NPO) in several solvents.

KrF excimer radiation (248 nm) was used to pump the samples under investigation as well as a tunable dye laser which was used as the probe. Time-resolution was obtained by changing the optical path difference between the pump and probe beams.

Transient excited state absorption was measured in a wide spectral region between 330 nm and 600 nm, showing a peak at 400 nm for PPO solutions, and two …

Renormalization Group Equations In Broken Supersymmetric Theories Using Superspace Methods, Asim Gangopadhyaya, Darwin Chang

Physics: Faculty Publications and Other Works

We apply the superfield method with the spurion technique to derive the renormalization-group equations in broken supersymmetric theories. We point out some possible ambiguities in this procedure and show that it is in general necessary to express the supersymmetry-breaking terms in explicit D-type form. We also found that it is possible to construct broken supersymmetric theories where some of the symmetry-breaking parameters do not receive any infinite renormalization.

Theory Of In Situ Measurement Of Wave-Vector-Dependent Dynamic Susceptibility And Esr Spectroscopy Using The Ac Josephson Effect, S. E. Barnes, F. Mehran

Physics Articles and Papers

The elementary theory of in situ measurements of the wave-vector-dependent dynamic susceptibility χ(q,ω) in superconductor-insulator-superconductor (SIS) and superconductor–normal-metal–superconductor (SNS) Josephson junctions is presented in some detail. The theory for more complicated SISN and SINS junctions is also described. In addition, the theory of point-contact and superconducting quantum interference device geometries, relevant to the recent experiments of Baberschke, Bures, and Barnes is developed. Involved is a detailed application of the Maxwell and London equations along with the distributed Josephson effect. In a measurement of χ(q,ω), the frequency ω is determined by the relation 2eV₀=ħω where V₀ is the …

Derivation Of Exact Results For The Single-Ion Kondo Problem With The Use Of Diagrammatic Methods, S. E. Barnes

Physics Articles and Papers

It is shown that exact results for the single-impurity Kondo problem can be obtained by diagrammatic methods. The results for the susceptibility and specific heat agree with those obtained by Wilson’s numerical methods. In particular, the crossover W’=(π/e)^1/2 and Wilson R=2 ratios are reproduced exactly. Conduction-electron scattering from the impurity reaches the unitarity limit corresponding to a phase shift δ=π/2. Both this and the compensation of the impurity spin are also exact results. The methods described are relatively easily extended to the Anderson model and the corresponding lattice problems.

Kl−Ks Mass Difference And Supersymmetric Left-Right-Symmetric Theories, Asim Gangopadhyaya

Physics: Faculty Publications and Other Works

The supersymmetric contributions to the K_L−K_S mass difference makes the previously obtained bounds on the right-handed scale (M_R>1.6 TeV) much weaker. This raises the interesting possibility that the left-right model could be tested as an alternative to SU_L(2)⊗U(1) at low energies. Also we find that to demand that the supersymmetric contribution to the K_L−K_S mass difference be less than 3.5×10⁻¹⁵ GeV requires that scalar-quark masses be more than 400 GeV.

Solution Of The Kondo Problem By Diagrammatic Methods, S. E. Barnes

Physics Articles and Papers

A self-consistent parquet approximation is shown to give exact results for the Kondo problem in the scaling limit.

Quantum Electrodynamics Based On Self-Energy: Lamb Shift And Spontaneous Emission Without Field Quantization, A. O. Barut, Jean F. Van Huele

Faculty Publications

The theory of radiative processes in quantum theory is formulated on the basis of self-energy, in analogy to classical radiation theory, and is explicitly carried out for the calculation of the Lamb shift and spontaneous emission.

Superspace Ward Identities In Supersymmetric Gauge Theories, Asim Gangopadhyaya, Darwin Chang

Physics: Faculty Publications and Other Works

In superspace formulation of supersymmetric gauge theories, gauge invariance requires an infinite set of identities between the infinite set of renormalization constants. Using Ward identities in superspace, the same is derived. These identities at one loop level are also demonstrated.

Esr And Magnetization Of The Spin-Glass Cumn At Low Concentrations, F. R. Hoekstra, G. J. Nieuwenhuys, K. Baberschke, S. E. Barnes

Physics Articles and Papers

We have determined the resonance frequency ω versus resonant field H diagram for CuMn with Mn concentrations 2, 3.5, and 5 at.%, both when H⃗ is parallel and antiparallel to the cooling field H⃗_c. From the parallel measurements we find anisotropy energy density constants K that are in agreement with K values determined from transverse susceptibility and torque measurements. However, the K values determined from the remanence reversal of dc magnetization are smaller by a factor of approximately 2. We suggest that this is caused by a breakdown of rigid-body spin rotations. By combining the parallel data with …

Esr In Situ With A Josephson Tunnel Junction, K. Baberschke, K. D. Bures, S. E. Barnes

Physics Articles and Papers

The in situ electron-spin resonance of a voltage-biased NbAuNb Josephson junction is reported. The Au barrier is doped with Gd or ¹⁶⁷Er ions. Sharp resonances appear in the I-V curves at frequencies equivalent to the crystal-field splitting of AuGd (1.0 and 1.7 GHz) and to the hyperfine splitting of Au¹⁶⁷Er (2.87 GHz). The principle of this new type of ESR-Josephson-junction spectrometer, as well as its application, is discussed.

Esr Relaxation In Spin Glasses, S. E. Barnes

Physics Articles and Papers

The Bloch-Hasegawa theory for the ESR of magnetic alloys is adapted and extended to spin glasses in the paramagnetic regime, that is, for temperatures T>T_G, the cusp temperature. Negative residual widths, reduced thermal broadening, and a possible critical divergence of the residual width are all explained in terms of minor extensions of the standard theory.

Scaling Approach To Spin-Glass Phenomena, S. E. Barnes, A. P. Malozemoff, B. Barbara

Physics Articles and Papers

The scaling model of spin-glass phenomena is extended to consider both longitudinal and transverse order parameters q₁ and q_t. The lowest-order coupling in the free energy goes as q_l²q_t². The field (h) dependence of the reduced temperature t for transverse freezing is found to be t∼h^4/δ where δ is the conventional nonlinear susceptibility field exponent (χ∼h^2/δ). While the transverse correlation length diverges at t=0, the longitudinal correlation length remains finite.

Radiation Damage To Gaas Solar Cells Including Isotropic Effects, Larry Victor Stock

Physics Theses & Dissertations

A model is developed for the short circuit current of a GaAs solar cell due to radiation (proton or electron) induced defects in the crystal structure. This model is verified by a comparison with proton and electron irradiation results. For electron radiation and energetic protons (energy> 10 MeV), it is found that the damage in the crystal is independent of the angle of incidence. On the other hand, for lower energy proton radiation, the damage as a function of cell thickness is highly dependent on incident angle and energy. The cell's response to low energy protons is strongly dependent on …

Theory Of Josephson-Type Oscillations In A Moving Charge-Density Wave - Errata, S. E. Barnes, A. Zawadowski

Physics Articles and Papers

Errata to Original Article: S. E. Barnes and A. Zawadowski, Theory of Josephson-Type Oscillations in a Moving Charge-Density Wave, Physical Review Letters, 51, 1499 (1983).

Theory Of Josephson-Type Oscillations In A Moving Charge-Density Wave, S. E. Barnes, A. Zawadowski

Physics Articles and Papers

A theory of Josephson-type phenomena is presented, in which the two macroscopic quantum states are the two components of an incommensurate charge-density wave with opposite wave vectors. The Fermi levels of these two states are split for a moving charge-density wave and impurity scattering induces quantum oscillations. Such oscillations may be responsible for the observed narrow-band noise in materials such as NbSe₃ and TaS₃.

Non-Mean-Field Interpretation Of The Irreversibility Line In Spin-Glasses, A. P. Malozemoff, S. E. Barnes, B. Barbara

Physics Articles and Papers

Susceptibility data on an amorphous GdAl spin-glass show an irreversibility onset line t=-A_-H^2/φ_- and a susceptibility crossover line t=+A₊H^2/φ₊ (t is reduced temperature; H is field). The exponents φ are both close to 3, and the amplitudes A differ only by a factor of 2. In contrast to earlier explanations of the irreversibility in terms of a de Almeida-Thouless mean-field instability, here both crossovers are explained in terms of a non-mean-field scaling theory.

Magnetic Resonance In The Spin-Glass (Lagd)Al2, M. Zomack, K. Baberschke, S. E. Barnes

Physics Articles and Papers

ESR has been measured in the spin-glass (La_1-xGd_x)Al₂, 1≤x≤15 at.% for 1, 3, 9, and 35 GHz, corresponding to different applied magnetic fields and in the temperature range of 100 mK to 30 K. The comparison of data for different frequencies shows that the linewidth depends very much on the frequency and/or field and therefore the temperature T_min of the linewidth minimum is not an intrinsic parameter and the shift of the resonance position is almost independent of frequency. The former effect is analyzed and theoretically explained in terms of the temperature dependence …

Γ8(3) Resonance In Esr Of (Ery)Al2 Single Crystals, U. Döbler, K. Baberschke, S. E. Barnes

Physics Articles and Papers

Angle-dependent ESR results are given for 500-, 2500-, and 5000-ppm Er-doped YAl₂ single crystals. An almost perfect analysis of the X- and Q-band data is achieved if the admixture of the first excited state Γ₈⁽²⁾ into the ground state Γ₈⁽³⁾ via the Zeeman interaction is taken into consideration. This enables us to determine the crystal electric field (CEF) parameter x=-0.322(20) and W=-0.29(2) K. The g-value shift yields N(E_F)J^Δg=+0.09(5) and the thermal broadening of the linewidth |N(E_F)J^ΔH|=0.059(5). The precision of the experimental data allows, in principle, the determination …

Modeling Charge Diffusion From Proton-Induced Ionization Tracks In Silicon Photodiode Arrays, Lee Cole Smith

Physics Theses & Dissertations

We are modeling the combined problem of generation and collection of charge carriers created during passage of energetic protons through a silicon photodiode array. We have also experimentally obtained pulse-height distributions of noise charge collected during exposure of a Digicon-type diode array to 21 and 75 MeV protons. It is shown that the magnitude of charge collected by a diode from each proton event is determined not only by diffusion, but by statistical considerations involving the ionization process itself. Utilizing analytical solutions to the diffusion equation for transport of minority carriers, together with the Vavilov-Landau theory of energy-loss fluctuations in …

Electron-Spin-Resonance Modes And The Edwards-Anderson Theory Of The Spin-Glass State, S. E. Barnes

Physics Articles and Papers

It is shown that the ESR modes observed in Cu: Mn alloys can be explained in terms of an Edwards-Anderson-type theory for a spin-glass when an anisotropy energy is included. Unlike other theories, the present one involves the conventional form for this anisotropy, U_K=Ksin²θ, where θ is the angle the local microscopic magnetization makes with the symmetry rather than equilibrium direction. The present theory is distinguished by a predicted, but as yet unobserved, angular dependence of single-crystal samples with axial symmetry.

Franck Condon Factors And R-Centeroids For Six Diatomic Molecules, Patricia M. Fazio

Physics Theses & Dissertations

The Franck Condon factor is defined as the square of the overlap integral and is so named because of its ties with the Franck Condon Principle. The r-centroid is the internuclear separation associated with the electronic transition of the diatomic molecule. The physical meaning of these integrals is discussed. Two methods for construction of the wavefunctions are presented. Both methods employ the Morse Potential Energy function. The first method calculates the integrals using the analytic wavefunction of Morse and the second method has numerically constructed wavefunct!ons. The twelve transitions and six diatomic molecules studied include; B ²Σ+ to X …

Design And Construction Of An Inexpensive Anechoic Chamber, Charles E. Hughes Jr.

Journal of the Arkansas Academy of Science

No abstract provided.

The Effects Of Electron Irradiation On Mosfets, Mark D. Skeldon

Physics Theses & Dissertations

The characteristics of n and p-channel MOSFETs have been investigated while irradiated with electron radiation from Strontium 9Ø. The drain current vs. gate voltage of the p-channel MOSFET and the threshold voltage changes in n and p-channel MOSFETs have been studied with and without aluminum shielding. The switching characteristics and threshold voltage changes of COS/MOS dual input NAND gates have been investigated while exposed to electron radiation. Various methods of annealing the radiation damage to these devices is discussed.

Compton's 'Crucial Test' - Theoretical Preconceptions And Experimental Interpretation, Roger H. Stuewer

Journal of the Minnesota Academy of Science

Arthur Holly Compton, as a result of his own research and confidence in the validity of classical electrodynamics, was convinced in 1921 that homogeneous x-rays and gamma rays could be affected in only two possible ways when passing through matter: either they gave rise to "truly scattered" radiation of the same wavelength as that of the incident rays, or they excited "fluorescent" radiation of a longer wavelength. When Compton was led to carry out experiments using homogeneous x-rays and actually found secondary radiation of longer wavelength, he regarded his result as a crucial test between the "truly scattered" and the …

The Intentionality Structure Of Complementarity, Patrick A. Heelan

Research Resources

In this article Heelan argues that the return to the concrete and empirical implied in Heisenberg's insight on the importance of observables in physics was not, however, in Heisenberg's case, accompanied by a thorough re-thinking of the rationalist presuppositions of classical physics. The effect on Bohr, however, was to lead him to a complete rejection of rationalism and to the adoption of the contrary extreme, empiricism. The profound – though largely implicit – cause of the disagreement between Bohr and Heisenberg as to the correct interpretation of quantum mechanics, was resolved in the sumnler of 1927, by the common acceptance …