Dana Alan Browne

Louisiana State University | LSU · Department of Physics & Astronomy

An investigation of the structural, magnetic, thermodynamic, and charge transport properties of noncentrosymmetric hexagonal ScFeGe reveals it to be an anisotropic metal with a transition to a weak itinerant incommensurate helimagnetic state below TN=36 K. Neutron diffraction measurements discovered a temperature and field independent helical wave...

We report the high-field superconducting properties of thin, disordered Re films via magnetotransport and tunneling density of states measurements. Films with thicknesses in the range of 9 to 3 nm had normal-state sheet resistances of ∼0.2kΩ to ∼1kΩ and corresponding transition temperatures in the range of 6 to 3 K. Tunneling spectra were consisten...

We report the high-field superconducting properties of thin, disordered Re films via magneto-transport and tunneling density of states measurements. Films with thicknesses in the range of 9 nm to 3 nm had normal state sheet resistances of $\sim$0.2 k$\Omega$ to $\sim$1 k$\Omega$ and corresponding transition temperatures in the range of 6 K to 3 K....

An investigation of the structural, magnetic, thermodynamic, and charge transport properties of non-centrosymmetric hexagonal ScFeGe reveals it to be an anisotropic metal with a transition to a weak itinerant incommensurate helimagnetic state below $T_N = 36$ K. Neutron diffraction measurements discovered a temperature and field independent helical...

The layered transition-metal dichalcogenide PdTe2 has been discovered to possess bulk Dirac points as well as topological surface states. By measuring the magnetization (up to 7 T) and magnetic torque (up to 35 T) in single crystalline PdTe2, we observe distinct de Haas-van Alphen (dHvA) oscillations. Eight frequencies are identified with H||c, wit...

The noncentrosymmetric superconductor (NCS) AuBe is investigated using a variety of thermodynamic and resistive probes in magnetic fields of up to 65 T and temperatures down to 0.3 K. Despite the polycrystalline nature of the samples, the observation of a complex series of de Haas–van Alphen (dHvA) oscillations has allowed the calculated band struc...

We report the measurements of de Haas-van Alphen (dHvA) oscillations in the noncentrosymmetric superconductor BiPd. Several pieces of a complex multisheet Fermi surface are identified, including a small pocket (α∼40 T) which is three dimensional and anisotropic. From the temperature dependence of the amplitude of the oscillations, the cyclotron eff...

The noncentrosymmetric superconductor (NCS) AuBe is investigated using a variety of thermodynamic and resistive probes in magnetic fields of up to 65~T and temperatures down to 0.3~K. Despite the polycrystalline nature of the samples, the observation of a complex series of de Haas-van Alphen (dHvA) oscillations has allowed the calculated bandstruct...

RuGe, a diamagnetic small-band gap semiconductor, and CoGe, a nonmagnetic semimetal, are both isostructural to the Kondo insulator FeSi and the skyrmion lattice host MnSi. Here, we have explored the magnetic and transport properties of Co-doped RuGe: Ru$_{1-x}$Co$_x$Ge. For small values of $x$, a magnetic ground state emerges with $T_{c}\approx$ 5...

We investigate the connection between crystal symmetry and temporal and spectral properties of high-order harmonics in solids. We calculate the orientation-dependent harmonic spectrum driven by an intense, linearly polarized infrared laser field, using a momentum-space description of the generation process in terms of strong-field-driven electron d...

We report the measurements of the de Haas-van Alphen (dHvA) oscillations in the noncentrosymmetric superconductor BiPd. Several pieces of a complex multi-sheet Fermi surface have been identified. Among those, a 40 T pocket was found to be three dimensional and anisotropic in nature. From the temperature dependence of the amplitude of the oscillatio...

Solid-state high-harmonic sources offer the possibility of compact, high-repetition-rate attosecond light emitters. However, the time structure of high harmonics must be characterized at the sub-cycle level. We use strong two-cycle laser pulses to directly control the time-dependent nonlinear current in single-crystal MgO, leading to the generation...

We report the electronic structure, synthesis, and measurements of the magnetic, transport, and thermal properties of the polycrystalline noncentrosymmetric compound Re6Zr. We observed a bulk superconducting transition at temperature Tc∼6.7 K, and measured the resistivity, heat capacity, thermal conductivity, and the London penetration depth below...

Strong-field laser excitation of solids can produce extremely nonlinear electronic and optical behaviour. As recently demonstrated, this includes the generation of high harmonics extending into the vacuum-ultraviolet and extreme-ultraviolet regions of the electromagnetic spectrum. High harmonic generation is shown to occur fundamentally differently...

We report the electronic structure, synthesis, and measurements of the magnetic, transport, and thermal properties of polycrystalline Re$_{6}$Zr. A bulk superconducting transition temperature was observed at $T_{c}$ $\sim$ 6.7 K. The density of states at the Fermi surface was found to be dominated by Re \emph{d}-bands. X-ray diffraction confirmed t...

We examine the Nagel-Schreckenberg traffic model for a variety of maximum speeds. We show that the low density limit can be described as a dilute gas of vehicles with a repulsive core. At the transition to jamming, we observe finite-size effects in a variety of quantities describing the flow and the density correlations, but only if the maximum spe...

We present magnetization, specific heat, resistivity, and Hall effect measurements on the cubic B20 phase of MnGe and CoGe and compare to measurements of isostructural FeGe and electronic structure calculations. In MnGe, we observe a transition to a magnetic state at $T_c=275$ K as identified by a sharp peak in the ac magnetic susceptibility, as we...

We report the electrical transport, magnetic, and thermodynamic properties of polycrystalline PdTe which exhibits superconductivity below 4.5 K. Using the measured values for the lower (H(c1)) and upper (H(c2)) critical fields, and the specific heat C(p), we estimate the thermodynamic critical field H(c)(0), coherence length ξ(0), penetration depth...

PdTe is a long-known superconductor but its physical properties are almost unknown. We have recently studied its basic physical properties in both normal and superconducting states. While FeTe forms different crystallographic structure and is known to form spin density wave below TN = 70 K, we have successfully synthesized Pd1-xFexTe with x from 0...

Transport measurements on the cuprates suggest the presence of a quantum critical point (QCP) hiding underneath the superconducting dome near optimal hole doping. We provide numerical evidence in support of this scenario via a dynamical cluster quantum Monte Carlo study of the extended two-dimensional Hubbard model. Single-particle quantities, such...

For the past five years, L.S.U. has been engaged in revamping its secondary education science teaching program for its science majors. Our new program, Geaux Teach, (www.lsu.edu/secondaryed/) is modeled after the GoTeach program at U.T. Austin. This status report will discuss our prior program, how we got started, where we are now, what is left to...

The growth mechanism of β-amyloid (Aβ) peptide fibrils was studied by a physics-based coarse-grained united-residue model and molecular dynamics (MD) simulations. To identify the mechanism of monomer addition to an Aβ(1-40) fibril, we placed an unstructured monomer at a distance of 20 Å from a fibril template and allowed it to interact freely with...

The magneto-optical properties of the ferromagnetic semiconductor Ga$_{1-x}$Mn$_{x}$As are studied within the dynamical mean-field approximation (DMFA). A material-specific multiband $sp^{3}$ tight-binding Hamiltonian is employed for the dispersion of the GaAs host. The calculated density of states shows an impurity band and a distorted valence ban...

We have synthesized polycrystalline samples of the noncentrosymmetric superconductor Mo3Al2C by arc and RF melting, measured its transport, magnetic and thermodynamic properties, and computed its band structure. Experimental results indicate a bulk superconducting transition at Tc∼9.2 K while the density of states at the Fermi surface is found to b...

The Hall effect and resistivity of the carrier-doped magnetic semiconductor Fe1−xCoxS2 were measured for 0≤x≤0.16, temperatures between 0.05 and 300 K, and fields of up to 9 T. Our Hall data indicate electron charge carriers with a density of only 10–30 % of the Co density of our crystals. The charge-carrier transport is dominated by a Kondo-like a...

MnSi is a metallic helimagnet below 29 K. Above 1.46 GPa, the moment is completely suppressed resulting in an unusual magnetic state. Density functional theory (DFT) predicts that MnSi has a moment of 1.0 muB/Mn, which is much larger than the measured value of ˜0.4 4muB/Mn. Additionally, DFT predicts a smaller magnetovolume coupling than found in e...

We have presented experimental results of resistivity, magnetic susceptibility, penetration depth and specific heat measurements for a polycrystalline sample of the noncentrosymmetric superconductor Mo3Al2C. All measurements confirm a bulk superconducting transition at 9 K in this compound. A high value of the upper critical field Hc2(0) suggests t...

We present the results of a self-consistent dynamical mean field treatment of the ferromagnetic order in GaAs doped with Mn. We use the sp^3 tight binding model as the non-interacting Hamiltonian for the parent material's (GaAs) band structure. The spin-orbit interaction is introduced as lambdaalphas.l where alpha=c and a for cation (Ga) and anion...

Doping of the band insulator FeS$_2$ with Co on the Fe site introduces a small density of itinerant carriers and magnetic moments. The lattice constant, AC and DC magnetic susceptibility, magnetization, and specific heat have been measured over the $0\le x\le 0.085$ range of Co concentration. The variation of the AC susceptibility with hydrostatic...

The Hall effect and resistivity of the carrier doped magnetic semiconductor Fe$_{1-x}$Co$_x$S$_2$ were measured for $0\le x \le 0.16$, temperatures between 0.05 and 300 K, and fields of up to 9 T. Our Hall data indicate electron charge carriers with a density of only 10 to 30% of the Co density of our crystals. Despite the previous identification o...

We explored the anomalously low moment in MnSi found by experiment (~0.4 $\mu_{\text{B}}$/Mn) vs the moment predicted by density functional theory (~1.0 $\mu_{\text{B}}$/Mn). With the addition of a Hubbard-U correction, we found several solutions with lower moments. These lower moment solutions show an unusual magnetic order and a magnetic quadrupo...

We have investigated the origin of the anomalously low measured moment of MnSi (0.4μB/Mn) when compared to DFT calculations (1.0μB/Mn) by adding a Hubbard-U. By treating the Hubbard-U as an adjustable parameter, we have found two ground state solutions. For low values of U, a high-moment solution is energetically favored with μ≈1.0μB/Mn. For , the...

MnSi is a metallic helimagnet below 29 K. Density functional theory predicts that it has a moment of 1.0 muB/Mn, which is much larger than the measured value of 0.4 muB/Mn. By adding a Hubbard-U correction, we have found a ground state with a moment consistent with the experimental value. These solutions posess a novel quadrupolar spin ordering. We...

Critical points that can be suppressed to zero temperature are interesting because quantum fluctuations have been shown to dramatically alter electron gas properties. Here, the metal formed by Co doping the paramagnetic insulator FeS2, Fe1-xCoxS2 is demonstrated to order ferromagnetically at x > xc = 0.01+/-0.005, where we observe unusual transport...

We report the results of magnetotransport and de Haas?van Alphen (dHvA) measurements on high quality single crystals of VB2 grown from a molten aluminum flux. In addition, we compare these results to energy band calculations. At low temperature the magnetoresistance of VB2 is very large (~1100%) and is found to be extremely sensitive to sample qua...

Photoelectron spectroscopy is one of the most important methods for extracting information about the Fermi surface (FS) of materials. An electron photoexcited from the FS is emitted from the crystal conserving the parallel momentum, , while the perpendicular momentum is reduced due to the surface potential barrier. A simple interpretation of the pr...

We have performed magnetotransport and dHvA measurements on high quality single crystals of VB2 grown from a molten aluminum flux. At low temperature the magnetoresistance (MR) of VB2 is very large (˜1100%) and is found to be extremely sensitive to sample quality. The field dependence of the MR is proportional to the applied field squared, as is ex...

We consider an electron in a small 1-dimensional conducting ring subject to a large electric field induced by a linearly ramped magnetic flux. In the absence of inelastic scattering this constitutes a Hamiltonian system. The adiabatic eigenstates form a complete set of mini-bands which are separated by gaps determined by the static scattering poten...

Irreversible many particle dynamical systems are relevant to a broad scope of phenomena in physics, chemistry and biology. We present a study of an irreversible kinetic reaction model for a one component autocatalytic reaction A + A → A2. The system is updated as follows: if an atom adsorbed on a lattice has any neighbors it reacts with one of them...

Carrier doping of ``fool's gold'', the paramagnetic insulator FeS2 by partial substitution of Co for Fe, results in an insulator-to-metal transition at x

We present a general method of analyzing the influence of finite size and boundary effects on the dynamics of localized solutions of non-linear spatially extended systems. The dynamics of localized structures in infinite systems involve solvability conditions that require projection onto a Goldstone mode. Our method works by extending the solvabili...

We study the Ising-Bloch bifurcation in two systems, the complex Ginzburg Landau equation (CGLE) and a FitzHugh Nagumo (FN) model in the presence of spatial inhomogeneity introduced by Dirichlet boundary conditions. It is seen that the interaction of fronts with boundaries is similar in both systems, establishing the generality of the Ising-Bloch b...

We report the results of de Haas–van Alphen measurements in high magnetic fields on the anisotropic compound LaSb2. Our measurements reveal three extremal orbits of the Fermi surface. One is very small and ellipsoidal, while the remaining two are larger and have a nearly cylindrical shape indicating a quasi-two-dimensional Fermi surface. We compare...

Nonlinear reaction-diffusion models with multiple steady states can show nonequilibrium Ising/Bloch wall bifurcations. We study the behavior of the Bloch wall dynamics in the presence of a boundary where Dirichlet (fixed) boundary conditions are imposed. In both a parametrically forced complex Ginzburg-Landau model and a Fitzhugh-Nagumo model we fi...

LaSb2 is a nonmagnetic material that exhibits a large linear magnetoresistance. We have calculated its electronic structure using a full potential LAPW GGA density functional method including the spin-orbit interaction. We find that the Fermi surface consists of both two dimensional sheets and three dimensional bands. Our results are consistent wit...

In this work we present valence band studies of LaSb2 using angle-resolved photoelectron spectroscopy with synchrotron radiation and compare these data with band structure calculations. Valence band spectra reveal that Sb 5p states are dominant near the Fermi level and are hybridized with the La 5d states just below. The calculations show a fair ag...

The conductivity and magnetization of Fe1-xCoxS2 were measured to investigate quantum critical behavior in disordered itinerant magnets. Small x (<0.001) is required to convert insulating iron pyrite into a metal, followed by a paramagnetic-to-ferromagnetic metal transition at x = 0.032+/-0.004. Singular contributions are discovered that are distin...

These two compounds have been identified^1 as superconducting compounds^2 that form instead of the Be analogue of MgB_2. We present calculations of the electronic structure and optical properties of Be_29B_81 and Be_31B_81, using both full potential LAPW and LCAO methods. The Be_29 compound has three bands at the Fermi level, with a gap of 0.8eV se...

The compounds CeMIn5 (M=Co, Rh, Ir) have been shown to exhibit heavy fermion behavior. In order to better understand this effect and the nature of the observed superconductivity, we have synthesized and characterized the non-magnetic analogs, LaMIn5 (M=Co, Rh, Ir). The structures of LaCoIn5, LaRhIn5, and LaIrIn5 were determined by single-crystal X-...

Few-body problems involving Coulomb or gravitational interactions between pairs of particles, whether in classical or quantum physics, are generally handled through a standard multipole expansion of the two-body potentials. We develop an alternative based on an old, but hitherto forgotten, expression for the inverse distance between two points that...

We report measurements of temperature and magnetic field dependent magnetic susceptibility and electron paramagnetic resonance in the paramagnetic phase of CeB{sub 6}. From calculations of the possible ground state level structure of the interacting 4f electrons it is found that the fourfold degenerate {Gamma}{sub 8} is split into two doublets with...

An oscillatory medium subject to external forcing at a frequency equal twice its natural frequency is studied in a regime where the nonvariational coefficients cannot be treated as small perturbations. We reveal numerically that domain walls can be stabilized to produce a moving stable domain and examine its stability against wavenumber instability...

The author calculates the transverse phonon spectrum of a three-dimensional Wigner crystal in a large magnetic field where the electrons occupy the lowest spin-polarized Landau level. The calculation differs from that for a conventional phonon spectrum because the lattice is stable only in the presence of the magnetic field. They give specific resu...

We present a lattice dynamics study of CdTe-HgTe superlattices grown along the (001) and (111) directions within the framework of the adiabatic bond charge model. We find that the long-range Coulomb interaction between particles situated on the opposite sides of the interface needs to be handled carefully to get sensible frequencies and eigenvector...

The development of high intensity VUV sources opens the possibility of exploring the regime of high frequency stabilization (intensities of alpha >1) for photon energies greater than the field free ground state ionization potential. Detecting high frequency stabilization effects is complicated, however, by the fact that in a focused, Gaussian laser...

We study the one dimensional three species monomer-monomer reaction model in the reaction controlled limit using mean-field theory and dynamic Monte Carlo simulations. The phase diagram consists of a reactive steady state bordered by three equivalent adsorbing phases where the surface is saturated with one monomer species. The transitions from the...

We study the phase diagram and critical behavior of an interacting one-dimensional two-species monomer-monomer catalytic surface reaction model with a reactive phase as well as two equivalent adsorbing phases where one of the species saturates the system. The model depends on two parameters: the relative adsorption rates of the two species and a re...

We study the multicritical behavior of multispecies monomer-monomer catalytic reaction models. These far-from-equilibrium models have continuous adsorbing phase transitions from a reactive steady state to a passivated state completely filled with a single monomer species. At multicritical points, the adsorbing transitions are from a reactive steady...

We study a three species monomer-monomer catalytic surface reaction model with a reactive steady state bordered by three equivalent unreactive phases where the surface is saturated with one species. The transition from the reactive to a saturated phase shows directed percolation critical behavior. Each pair of these reactive-saturated phase boundar...

We study the phase diagram and critical behavior of a one dimensional three species monomer-monomer surface reaction model. Static Monte Carlo simulations show a phase diagram consisting of a reactive steady state bordered by three equivalent unreactive phases where the surface is saturated with one monomer species. The transitions from the reactiv...

We study how the interaction with an external incoherent environment induces a crossover from quantum to classical behavior for a particle whose classical motion is chaotic. Posing the problem in the semiclassical regime, we find that noise produced by the bath coupling rather than dissipation is primarily responsible for the dephasing that results...

We extend the adiabatic bond charge model, originally developed for group IV semiconductors and III-V compounds, to study phonons in more ionic II-VI compounds with a zincblende structure. Phonon spectra, density of states and specific heats are calculated for six II-VI compounds and compared with both experimental data and the results of other mod...

We report a first principles, self-consistent, all electron, linear combination of Gaussian orbitals (LCGO) calculation of a comprehensive collection of magneto-optical properties of nickel and iron based on density functional theory. Among the many magneto-optical effects, we have studied the equatorial Kerr effect for absorption in the optical as...

We extend the adiabatic bond charge model, originally developed for group IV semiconductors and III-V compounds, to study phonons in more ionic II-VI compounds with a zincblende structure. Phonon spectra, density of states and specific heats are calculated for six II-VI compounds and compared with both experimental data and the results of other mod...

We have used the real-axis Eliashberg equations for an anisotropic superconductor to study the quasiparticle density of states of superconducting YBa2Cu3O7 in a temperature range from 0 up to 120 K. A first-principles electronic structure and a nonorthogonal tight-binding method was used to calculate the electron-phonon interaction. The large varia...

We consider an initially bound quantum particle subject to an external time-dependent field. When the external field is large, the particle shows a tendency to repeatedly return to its initial state, irrespective of whether the frequency of the field is sufficient for escape from the well. These recurrences, which are absent in a classical calculat...

We study the quantum chaotic dynamics of an initially well-localized wave packet in a cosine potential perturbed by an external time-dependent force. For our choice of initial condition and with $\hbar$ small but finite, we find that the wave packet behaves classically (meaning that the quantum behavior is indistinguishable from that of the analogo...

Kinetic models for nonequilibrium phase transitions have been extensively studied via mean-field theory, series expansions, and Monte Carlo simulation. In this paper we present a different approach based on studying the normal-mode solutions of the master equation for the system to extract information on the static and dynamic behavior of the syste...

We compare the quantum and classical dynamics of a particle moving in a cosine potential while subject to a time-dependent force. We concentrate here on the behavior of an initially well-localized wave packet at times before the classically chaotic motion is fully developed. We find that the quantum and classical dynamics are indistinguishable well...

The occurrence of kinetic oscillations in the catalytic oxidation of CO on Pd(110) has been attributed to the periodic formation and depletion of subsurface oxygen. Using a Langmuir–Hinshelwood mechanism and the individual reaction steps, Bassett and Imbihl proposed a simple reaction model for the oscillations. In this article, we apply their model...

We present results from simulations on two aspects of quark confinement in the pure gauge sector. First is the calculation of the profile of the flux tube connecting a static $q \bar{q}$ pair in $SU(2)$. By using the Michael sum rules as a constraint we give evidence that the energy density at the center of the flux tube goes to a constant as a fun...

We calculate the electric field and the curl of the magnetic monopole current for U(1) and for SU(2) in the maximal Abelian gauge in the mid-plane between a quark antiquark pair. The results can be understood as a dual Abrikosov vortex in the Ginzburg-Landau theory.

We calculate the electric flux and magnetic monopole current distribution in the presence of a static quark-antiquark pair of SU(2) lattice gauge theory in the maximal Abelian gauge. The current distribution confines the flux in a dual Abrikosov vortex whose core size is comparable to the flux penetration depth. The observed structure is described...

We explore the analogy between quark confinement and the Meissner effect in superconductors. We measure the response of color-magnetic "supercurrents" from Dirac magnetic monopoles to the presence of a static quark-antiquark pair in four dimensional U(1) lattice gauge theory. Our results indicate that in the confined phase these currents screen the...

Analysis of data from several experimental groups on electron mobility in dense neutral gases from 3 to 300 K reveals the existence of a correction to the mobility arising from incoherent multiple scattering that is proportional to 1/klo. This correction overwhelms the traditionally used 1/(klo)2 term arising from coherent backscattering and domina...

It is well established that anisotropy does not affect the critical behavior of a system in thermodynamic equilibrium that undergoes a second-order phase transition. We study here an anisotropic kinetic model for heterogeneous catalysis that mimics the oxidation of CO on the (110) surface of a transition metal like Pd. We have mapped out the phase...

We discuss a number of models associated with phase transitions in purely kinetic models where detailed balance does not hold as in thermal equilibrium systems. These models include some of the features of heterogeneous catalysis on a surface, and are used to examine the effect of local correlations on the reaction process. We argue that many model...

Irreversible many-particle dynamical systems are relevant to a variety of phenomena in physics, chemistry, and biology. We present a study of an irreversible kinetic reaction model for a one-component autocatalytic reaction A+A-->A2. In this model, if an atom adsorbing on a lattice site has any neighbors, it reacts with one of them with a probabili...

We report measurements of the specific heat of GdBa2-xSrxCu3O7 for x=0, 0.25, and 0.5 in the temperature range 0.6–5 K. In addition, measurements in magnetic fields from 0 to 3 T for the x=0 sample are reported. In each case a peak in the specific heat at the antiferromagnetic ordering temperature is recorded and analyzed. Strontium doping does not...

A simple irreversible kinetic model recently introduced by Ziff, Gulari, and Barshad [Phys. Rev. Lett. 56, 2553 (1986)] to describe the catalysis of chemical reactions on regular surfaces has been shown to have a second-order phase transition from an absorbing state, wherein the surface is passivated (rendered catalytically inactive or ‘‘poisoned’’...