Dana A. Browne

Solid-state harmonics beyond the atomic limit

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 in solids and in dilute atomic gases. How the microscopic mechanisms in the solid and the gas differ remains a topic of intense debate. Here we report a direct comparison of high harmonic generation in the solid and gas phases of argon and krypton. Owing to the weak van der Waals interaction, rare (noble)-gas solids are a near-ideal medium in which to study the role of high density and periodicity in the generation process. We find that the high harmonic generation spectra from the rare-gas solids exhibit multiple plateaus extending well beyond the atomic limit of the corresponding gas-phase harmonics measured under similar conditions. The appearance of multiple plateaus indicates strong interband couplings involving multiple single-particle bands. We also compare the dependence of the solid and gas harmonic yield on laser ellipticity and find that they are similar, suggesting the importance of electron–hole recollision in these solids. This implies that gas-phase methods such as polarization gating for attosecond pulse generation and orbital tomography could be realized in solids.

Lattice dynamics of II-VI materials using the adiabatic bond-charge model

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 models. We show that the 6-parameter bond charge model gives a good description of the lattice dynamics of these materials. We also discuss trends in the parameters with respect to the ionicity and metallicity of these compounds.

Structure of Abrikosov vortices in SU(2) lattice gauge theory

Abstract 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 by a dual Ginzburg-Landau model.

Useful alternative to the multipole expansion of 1 / r potentials

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 discuss an alternative based on a compact, cylindrical Green’s function expansion that should have wide applicability throughout physics. Two-electron “direct” and “exchange” integrals in many-electron quantum systems are evaluated to illustrate the procedure which is more compact than the standard one using Wigner coefficients and Slater integrals.

Discovery of the Griffiths phase in the itinerant magnetic semiconductor Fe1-xCoxS2.

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, magnetic, and thermodynamic properties. We show that this magnetic semiconductor undergoes a percolative magnetic transition with distinct similarities to the Griffiths phase, including singular behavior at xc and zero temperature.

FIRST-PRINCIPLES LCGO CALCULATION OF THE MAGNETO-OPTICAL PROPERTIES OF NICKEL AND IRON

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 well as soft X-ray region, where it is called X-ray magnetic linear dichroism (X-MLD). In the optical region the effect is of the order of 2\% while in the X-ray region it is of the order of 1\% for the incident angles considered. In addition, the polar Kerr effect, X-ray magnetic circular dichroism (X-MCD) and total X-ray absorption at the L

Multilevel perspective on high-order harmonic generation in solids

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London relation and fluxoid quantization for monopole currents in U(1) lattice gauge theory

edges, soft X-ray Faraday effect at the L

Structure and physical properties of the noncentrosymmetric superconductor Mo 3 Al 2 C

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Nonequilibrium Critical Dynamics of a Three Species Monomer-Monomer Model

edges have also been calculated. Our results are in good agreement with experiments and other first principles methods that have been used to calculate some of these properties.