Physics Commons^™

Enhanced Mixing Of Intrinsic States In Deformed Hf Nuclei, E. A. Mccutchan, R. F. Casten, V. Werner, E. Williams, R. Winkler, A. Wolf, Z. Berant, G. Gurdal, J. Qian, H. Ai, L. Amon, C. W. Beausang, D. S. Brenner, R. Cakirli, R. J. Casperson, C. R. Fitzpatrick, D Franks, A. B. Garnsworthy, A. Heinz, R. Luttke, A. F. Mertz, Y. Oktem, N. Pietralla, P. H. Regan, B. Shoraka, J. R. Terry, N. J. Thompson

Physics Faculty Publications

Excited low-spin, nonyrast states in ^170,172,174Hf were populated in β + /∈decay and studied through off-beam γ-ray spectroscopy. New coincidence data allowed for a substantial revision of the level schemes of Hf^170,172 and a confirmation of the level scheme of ¹⁷⁴Hf. The Hf isotopes represent a unique situation in which a crossing of collective intrinsic excitations occurs, enhancing significantly the effects of mixing. Using branching ratios from excited 2⁺ states, this mixing is followed and studied. The resulting mixing matrix elements are found to be ∼30 keV—an …

Spectral Time Moment Analysis Of Microgel Structure And Dynamics, Kiril A. Streletzky, John T. Mckenna, Rami Mohieddine

Physics Faculty Publications

The structure and dynamics of crosslinked nanoparticles (microgels) made out of hydroxypropylcellulose (HPC) polymer chains were studied using dynamic light scattering spectroscopy. The microgel light scattering spectra were found to be highly nonexponential requiring a spectral time moment analysis in which the spectra were fit to a sum of stretched exponentials. Each term offers three parameters for analysis and represents a single spectral mode. At room temperature microgel spectra reveal three modes. Two faster modes are almost diffusive and correspond to apparent sizes of 25 and 450–650 nm. The slowest mode is independent of scattering angle and is reminiscent of …

Effects Of Annealing In N(2) Ambient On Traps And Persistent Conduction In Hydrothermally Grown Zno, Z-Q. Fang, B. Claflin, David C. Look

Physics Faculty Publications

Thermally stimulated current (TSC) spectroscopy and temperature–dependent dark current (DC) measurements have been applied to study traps and photoinduced persistent surface conduction in two hydrothermally grown bulk ZnO samples, as-grown, and annealed at 600 °C in N₂ ambient for 30 min, respectively. The as-grown sample had a room-temperature (RT) resistivity of 1.6×10³ Ω cm, mobility of 2.1×10² cm²/V s, and carrier concentration of 1.8×10¹³ cm⁻³, while the annealed sample was highly resistive, with RT resistivity of 3.6×10⁶ Ω cm, mobility of 4.4 cm²/V s, and carrier concentration of 3.9×10 …

Investigation Of Magnetic Interactions In Large Arrays Of Magnetic Nanowires, Petru S. Fodor, G. M. Tsoi, L. W. Wenger

Physics Faculty Publications

The magnetic interactions in large arrays of ordered magnetic nanowires with 12-48 nm diameter and 55-95 nm spacing were investigated using modified Henkel plots. The measurements for nanowire arrays ac demagnetized with the field applied parallel to the nanowire axis (the easy magnetization axis) indicate that the dominant interaction during the switching process is the magnetostatic coupling between the nanowires. Nevertheless, while the strength of the magnetostatic interactions increases with the magnetic moment associated with the nanowires, the increase is not linear with respect to the volume of the nanowires. Moreover, the dependence of the remanence curves on the field …

A Refined View Of Vertical Mass Transport By Cumulus Convection, Harmen J.J. Jonker, Thijs Heus, Peter P. Sullivan

Physics Faculty Publications

The purpose of this letter is to show that the traditional view of transport by shallow cumulus clouds needs important refinement. On the basis of a straightforward geometrical analysis of Large Eddy Simulation results of shallow cumulus clouds, we conclude (1) that the upward mass transport by clouds is strongly dominated by regions close to the edge of clouds rather than by the core region of clouds and (2) that the downward mass transport is dominated by processes just outside the cloud. The latter finding contradicts the accepted view of a uniformly descending dry environment. We therefore advocate a refined …

Investigation Of Loading Of Pulsed And Continuous-Wave Optical Dipole Force Traps, M. Shiddiq, E. M. Ahmed, M. D. Havey, C. I. Sukenik

Physics Faculty Publications

We have investigated the behavior of an optical dipole force trap realized using a mode-locked Nd:YAG laser and have compared performance to a continuous-wave (cw) trap built using the same laser but running in a cw mode. The traps are used to confine ultracold 85Rb atoms which are loaded from a magneto-optical trap (MOT). In most respects, the two traps behave similarly over a wide range of laser parameters provided that the average potential well depth is the same; however, there is a notable difference in the dipole trap loading efficiency dependence on the detuning of the MOT trap laser …

The Surface Stability Of Cos2(100), Ning Wu, Renat F. Sabirianov, Chun-Gang Duan, Wai-Ning Mei, David Wisbey, Ya B. Losovyj, M. Manno, Christopher Leighton, En Cai, Jiandi Zhang, Peter Dowben

Physics Faculty Publications

The stability of various possible terminations of the CoS2 (1 × 1) surface have been explored and theoretical expectations are found to agree with experiment. With extensive annealing, there is a phase separation at the (100) surface of CoS2. Sulfur segregation to the surface leads to a significant change in the largely sulfur bands due to changes in the hybridized bands, with cobalt. Resonant photoemission spectra indicate clearly that the hybridized cobalt and sulfur bands, characteristic of the CoS2 bulk, lie at higher binding energies than those of segregated sulfur layers. This is discussed in terms of the stability of …

Extended Tuning Of An Injection-Locked Diode Laser, M. K. Shaffer, G. Ranjit, C. I. Sukenik

Physics Faculty Publications

We have investigated the application of an electronic feedback technique recently reported by Repasky, et.al. [Appl. Opt. 45, 9013 (2006)] to an injection-locked semiconductor diode laser. We find that without electronic feedback, the injection-locked slave laser will only follow the master for less than 1 GHz, but once the electronic feedback is applied, the slave laser is capable of following for more than 20 GHz, corresponding to the full scan range of the master laser.

Terahertz Imaging System Performance Model For Concealed-Weapon Identification, Steven R. Murrill, Eddie L. Jacobs, Steven K. Moyer, Carl E. Halford, Steven T. Griffin, Frank C. De Lucia, Douglas T. Petkie, Charmaine C. Franck

Physics Faculty Publications

The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory have developed a terahertz (THz) -band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination. The model is based on recent U.S. Army NVESD sensor performance modeling technology that couples system design parameters to observer–sensor field performance by using the acquire methodology for weapon identification performance predictions. This THz model has been developed in support …

Elastically Induced Coexistence Of Surface Reconstructions, Jessica E. Bickel, Normand A. Modine, Chris Pearson, Joanna Mirecki Millunchick

Physics Faculty Publications

Scanning tunneling microscopy of Sb-capped GaAs shows the coexistence of different surface reconstructions. The majority of the surface consists of an α2(2×4) reconstruction typically observed for GaAs(001) surfaces. At step edges, an α(4×3) reconstruction, common for GaSb(001), is observed. We argue that strain couples the surface reconstruction to the film morphology. Density functional theory calculations show that the (2×4) reconstruction is stabilized in GaSb films when the lattice parameter is constrained to that of GaAs, as happens in the middle of a terrace, while the (4×3) reconstruction is stabilized when the lattice parameter is allowed to relax toward that of …

Rabi Oscillations Between Ground And Rydberg States With Dipole-Dipole Atomic Interactions, Todd A. Johnson, E. Urban, T. Henage, L. Isenhower, D. D. Yavuz, T. G. Walker, M Saffman

Physics Faculty Publications

We demonstrate Rabi oscillations of small numbers of ⁸⁷Rb atoms between ground and Rydberg states with n≤43. Coherent population oscillations are observed for single atoms, while the presence of two or more atoms decoheres the oscillations. We show that these observations are consistent with van der Waals interactions of Rydberg atoms.

Dipole In A Magnetic Field, Work, And Quantum Spin, Robert J. Deissler

Physics Faculty Publications

The behavior of an atom in a nonuniform magnetic field is analyzed, as well as the motion of a classical magnetic dipole (a spinning charged ball) and a rotating charged ring. For the atom it is shown that, while the magnetic field does no work on the electron-orbital contribution to the magnetic moment (the source of translational kinetic energy being the internal energy of the atom), whether or not it does work on the electron- spin contribution to the magnetic moment depends on whether the electron has an intrinsic rotational kinetic energy associated with its spin. A rotational kinetic energy …

Subsiding Shells Around Shallow Cumulus Clouds, Thijs Heus, Harmen J.J. Jonker

Physics Faculty Publications

In this study large-eddy simulations (LES) are used to gain more knowledge on the shell of subsiding air that is frequently observed around cumulus clouds. First, a detailed comparison between observational and numerical results is presented to better validate LES as a tool for studies of microscale phenomena. It is found that horizontal cloud profiles of vertical velocity, humidity, and temperature are in good agreement with observations. They show features similar to the observations, including the presence of the shell of descending air around the cloud. Second, the availability of the complete 3D dataset in LES has been exploited to …

Measurement Of Conversion Coefficients In Normal And Triaxial Strongly Deformed Bands In 167Lu, G. Gurdal, C. W. Beausang, D. S. Brenner, H. Ai, R. F. Casten, B. Crider, A. Heinz, E. Williams, D. J. Hartley, M. P. Carpenter, A. A. Hecht, R.V. F. Janssens, T.` Lauritsen, C. J. Lister, R. Raabe, D. Seweryniak, S. Zhu, J. X. Saladin

Physics Faculty Publications

Internal conversion coefficients have been measured for transitions in both normal deformed and triaxial strongly deformed bands in ¹⁶⁷Lu using the Gammasphere and ICE Ball spectrometers. The results for all in-band transitions are consistent with E2 multipolarity. Upper limits are determined for the internal conversion coefficients for linking transitions between TSD Band 2 and TSD Band 1, the n_w = 1 and n_w = 0 wobbling bands, respectively.

Electronic And Magnetic Properties Of Endohedrally Doped Fullerene Mn@C60: A Total Energy Study, Guangping Li, Renat F. Sabirianov, Jing Lu, Xiao Cheng Zeng, Wai-Ning Mei

Physics Faculty Publications

We perform total energy calculations on a manganese atom encapsulated inside a C₆₀ cage using density functional theory with the generalized gradient approximation through three optimization schemes and along four paths inside the cage. We find that when Mn is located in the central region, its electronic and magnetic properties are not exactly the same as those of a free Mn atom due to weak coupling between Mn and the cage. As Mn is shifted toward to the edge, the total energy and spin start to change significantly when Mn is situated about one-third of the way between the …

Atomic Size Mismatch Strain Induced Surface Reconstructions, Jessica E. Bickel, Normand A. Modine, Anton Van Der Ven, Joanna Mirecki Millunchick

Physics Faculty Publications

The effects of lattice mismatch strain and atomic size mismatch strain on surface reconstructions are analyzed using density functional theory. These calculations demonstrate the importance of an explicit treatment of alloying when calculating the energies of alloyed surface reconstructions. Lattice mismatch strain has little impact on surface dimer ordering for the α2(2×4) reconstruction of GaAs alloyed with In. However, atomic size mismatch strain induces the surface In atoms to preferentially alternate position, which, in turn, induces an alternating configuration of the surface anion dimers. These results agree well with experimental data for α2(2×4) domains in InGaAs∕GaAs surfaces.

Dynamic And Temperature Effects In Spin-Transfer Switching, Dorin Cimpoesu, Huy Pham, Leonard Spinu, Alexandru Stancu

Physics Faculty Publications

We have studied the dynamic switching triggered by spin angular momentum transfer in a pulsed current of a spin-valve-type trilayer structure, and its dependence on thermal effects. In order to determine the current pulse parameters, where fast and stable switching can be achieved, we have studied the magnetization’s dynamics properties as a function of applied current pulse amplitude and shape, waiting time, and initial orientation, and also as a function of the Gilbert damping constant. The magnetic layer is assumed to be single domain, ellipsoid shaped. In this paper also we present the thermal fluctuation effects on the switching behavior. …

Measurement Of The Critical Curve Of A Synthetic Antiferromagnet, Cosmin Radu, Dorin Cimpoesu, Alexandru Stancu, Leonard Spinu

Physics Faculty Publications

In this paper, we propose a method for a synthetic antiferromagnet structure’s critical curve determination. The method is based on reversible susceptibility’s singularities detection, as the magnetic field is swept along easy axis, in both positive and negative direction, while a hard axis bias field is also applied. By performing susceptibility measurements with different values of the bias field, the critical curve can be determined. Knowing the critical curve of a synthetic antiferromagnetic structure is essential for devices such as magnetic random access memories.

The Temperature Dependence Of Hysteretic Processes In Co Nanowires Arrays, I Astefanoaei, I Dumitru, A Diaconu, L Spinu, A Stancu

Physics Faculty Publications

In this paper, the temperature dependence of the hysteretic processes of Co nanowires, squarelly ordered in an array prepared by electrodeposition in nanopores of alumina membranes was analyzed. Both the magnetostatic interactions induced in the nanowires arrays and the thermal stresses (radial, azimuthal and axial stresses), which appear during the cooling of the system (nanowire and alumina template) from room temperature to 3 K was evaluated. The analysis of thermal induced stresses provides useful informations concerning the magnetic anisotropy in the Co nanowires. The temperature dependence of the remanent magnetization and coercitive field as an effect of the induced thermal …

Superconductivity Close To Magnetic Instability In Fe(Se1−Xtex)0.82, M H. Fang, H M. Pham, B Qian, T J. Liu, E K. Vehstedt, Y Liu, L Spinu, Z Q. Mao

Physics Faculty Publications

We report our study of the evolution of superconductivity and the phase diagram of the ternary Fe(Se_1−xTe_x)_0.82 (0≤x≤1.0) system. We discovered a superconducting phase with T_c,max=14 K in the 0.30.82, which exhibits an incommensurate antiferromagnetic order. We discuss the relationship between the superconductivity and magnetism of this material system in terms of recent results from neutron-scattering measurements. Our results and analyses suggest that superconductivity in this class of Fe-based compounds is associated with magnetic fluctuations and therefore may be unconventional in nature.

High-Frequency Characterization Of Permalloy Nanosized Strips Using Network Analyzer Ferromagnetic Resonance, Bijoy K. Kuanr, Radek Lopusnik, Leszek M. Malkinski, Matt Wenger, Minghui Yu, Donald Scherer Ii, Z Celinski, R E. Camley

Physics Faculty Publications

We report on the dynamic properties of Permalloy nanostrips at gagahertz frequencies. The thickness of the strips is 100 nm, strip width is 300 nm, strip spacing is 1 μm, and length is 0.3–100 μm; aspect ratios are 1:1, 1:2, 1:3, 1:5, 1:10, and 1:333. The dynamic behavior was studied by network analyzer ferromagnetic resonance (FMR) using Permalloy strips on a coplanar waveguide in flip-chip geometry. The FMR mode frequencies (f_r) can be controlled by the aspect ratio as well as by the applied magnetic field (H). In longer strips (1:10 and 1:333), …

Unusual Heavy-Mass Nearly Ferromagnetic State With A Surprisingly Large Wilson Ratio In The Double Layered Ruthenates (Sr1−Xcax)3ru2o7, Zhe Qu, Leonard Spinu, Huiqiu Yuan, Vladimir Dobrosavljevic, Wei Bao, Jeffrey W. Lynn, M. Nicklas, Jin Peng, Tijang Liu, David Fobes, Etienne Flesch, Z. Q. Mao

Physics Faculty Publications

We report an unusual nearly ferromagnetic heavy-mass state with a surprisingly large Wilson ratio R_w (e.g., R_w∼700 for x=0.2) in double layered ruthenates (Sr_1−xCa_x)₃Ru₂O₇ with 0.08

Switching Behavior Of A Stoner–Wohlfarth Particle Subjected To Spin-Torque Effect, Dorin Cimpoesu, Alexandru Stancu, Leonard Spinu, Huy Pham

Physics Faculty Publications

Recently, the current-induced spin-transfer torque has been proposed as a convenient writing process in high density magnetic random access memory. A spin-polarized current can switch the magnetization of a ferromagnetic layer more efficiently than a current induced magnetic field. Our paper discusses the switching properties of a Stoner–Wohlfarth magnetic particle for the case when spin torques and external field pulses are simultaneously present. The theoretical investigation of precessional motion is described by using Landau–Lifschitz–Gilbert equation with a spin-transfer torque term included. The main goal is to determine the parameters of field pulse for that the fast and stable switching can …

Poisson Equation For Weak Gravitational Lensing, Thomas P. Kling, B. Campbell

Physics Faculty Publications

Using the Newman and Penrose [ E. T. Newman and R. Penrose J. Math. Phys. (N.Y.) 3 566 (1962)] spin-coefficient formalism, we examine the full Bianchi identities of general relativity in the context of gravitational lensing, where the matter and space-time curvature are projected into a lens plane perpendicular to the line of sight. From one component of the Bianchi identity, we provide a rigorous, new derivation of a Poisson equation for the projected matter density where the source term involves second derivatives of the observed weak gravitational lensing shear. We also show that the other components of the Bianchi …

Crystal Structure Of The Catalytic Trimer Of Methanococcus Jannaschii Aspartate Transcarbamoylase, Jacqueline Vitali, Michael Colaneri Colaneri, Evan Kantrowitz

Physics Faculty Publications

The catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylase is extremely heat stable, maintaining 75% of its activity after heat treatment for 60 min at 75 degrees C. We undertook its structural analysis in order to understand the molecular basis of its thermostability and gain insight on how its catalytic function adapts to high temperature. Several structural elements potentially contributing to thermostability were identified. These include: (i) changes in the amino acid composition such as a decrease in the thermolabile residues Gln and Asn, an increase in the charged residues Lys and Glu, an increase in Tyr and a decrease in …

Theory Of The Piezomagnetic Effect In Mn-Based Antiperovskites, Pavel Lukashev, Renat F. Sabirianov, Kirill Belashchenko

Physics Faculty Publications

Recent experimental and theoretical studies of the magnetoelectric ME effect in the nanocomposite structures and in laminates show an enhanced ME coefficient. These materials combine piezoelectric properties of the paramagnetic phase and piezomagnetic properties of the magnetic phase. We propose to fabricate heterostructures formed by piezoelectric materials and magnetic antiperovskites as magnetoelectric materials. We show that the magnetic structure of antiperovskite, such as Mn3GaN, can be controlled by a small applied biaxial strain. The lowering of symmetry with the strain causes the local magnetic moments of Mn atoms to rotate from the trigonal 5g structure with symmetric curl of spin …

Local Structures Surrounding Zr In Nanostructurally Stabilized Cubic Zirconia: Structural Origin Of Phase Stability, Y. L. Soo, P. J. Chen, S. H. Huang, T. J. Shiu, T Y. Tsai, Y. H. Chow, Y. C. Lin, S. C, Weng, S. L. Chang, G. Wang, Chin Li Cheung, Renat F. Sabirianov, Wai-Ning Mei, Fereydoon Namavar, Hani Haider, Kevin L. Garvin, J. F. Lee, H. Y. Lee, P. P. Chu

Physics Faculty Publications

Local environment surrounding Zr atoms in the thin films of nanocrystalline zirconia (ZrO₂) has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. These films prepared by the ion beam assisted deposition exhibit long-range structural order of cubic phase and high hardness at room temperature without chemical stabilizers. The local structure around Zr probed by EXAFS indicates a cubic Zr sublattice with O atoms located on the nearest tetragonal sites with respect to the Zr central atoms, as well as highly disordered locations. Similar Zr local structure was also found in a ZrO₂ nanocrystal …

Tailoring Magnetic Anisotropy At The Ferromagnetic/Ferroelectric Interface, Chun-Gang Duan, Julian P. Velev, R. F. Sabirianov, W. N. Mei, S. S. Jaswal, E. Y. Tsymbal

Physics Faculty Publications

It is predicted that magnetic anisotropy of a thin magnetic film may be affected by the polarization of a ferroelectric material. Using a Fe∕BaTiO3 bilayer as a representative model and performing first-principles calculations, we demonstrate that a reversal of the electric polarization of BaTiO3 produces a sizable change in magnetic anisotropy energy of Fe films. Tailoring the magnetic anisotropy of a nanomagnet by an adjacent ferroelectric material may yield entirely new device concepts, such as electric-field controlled magnetic data storage.

We thank Ruqian Wu for fruitful discussions. This work was supported by the NSF and the Nanoelectronics Research Initiative through …

Ratios Of 15N/12C And 4He/12C Inclusive Electroproduction Cross Sections In The Nucleon Resonance Region, P. E. Bosted, R. Fersch, G. Adams, M. Amaryan, S. Anefalos, M. Anghinolfi, G. Asryan, H. Avakian, H. Badasaryan, N. Baillie, M. Bektasoglu, S. Bültmann, S. L. Careccia, G. E. Dodge, K. V. Dharmawardane, T. A. Forest, G. Gavalian, N. Guler, C. E. Hyde-Wright, N. Kalantarians, A. Klein, S. E. Kuhn, J. Lachniet, R. A. Niyazov, L. M. Qin, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Zhang, Clas Collaboration

Physics Faculty Publications

The (W,Q²) dependence of the ratio of inclusive electron scattering cross sections for ¹⁵N/¹²C was determined in the kinematic ranges 0.8 < W < 2 GeV and 0.2 < Q² < 1 GeV² using 2.285 GeV electrons and the CLAS detector at Jefferson Lab. The ratios exhibit only slight resonance structure, in agreement with a simple phenomenological model and an extrapolation of deep-inelastic scattering ratios to low Q². Ratios of ⁴He/¹²C using 1.6 to 2.5 GeV electrons were measured with very high statistical precision and were used to correct for He in the N and C targets. …

Next-To-Leading Order Evolution Of Color Dipoles, Ian Balitsky, Giovanni A. Chirilli

Physics Faculty Publications

The small-x deep inelastic scattering in the saturation region is governed by the nonlinear evolution of Wilson-line operators. In the leading logarithmic approximation it is given by the Balitsky-Kovchegov equation for the evolution of color dipoles. In the next-to-leading order the Balitsky-Kovchegov equation gets contributions from quark and gluon loops as well as from the tree gluon diagrams with quadratic and cubic nonlinearities. We calculate the gluon contribution to the small-x evolution of Wilson lines (the quark part was obtained earlier).