Magnetothermopower and magnon-assisted transport in ferromagnetic tunnel junctions

We present a model of the thermopower in a mesoscopic tunnel junction between two ferromagnetic metals based upon magnon-assisted tunneling processes. In our model, the thermopower is generated in the course of thermal equilibration between two baths of magnons, mediated by electrons. We predict a particularly large thermopower effect in the case of a junction between two half-metallic ferromagnets with antiparallel polarizations, $S_{AP} \sim - (k_B/e)$, in contrast to $S_{P} \approx 0$ for a parallel configuration.Comment: 3 pages, 1 eps figur

Degeneracy breaking and intervalley scattering due to short-ranged impurities in finite single-wall carbon nanotubes

We present a theoretical study of degeneracy breaking due to short-ranged impurities in finite, single-wall, metallic carbon nanotubes. The effective mass model is used to describe the slowly varying spatial envelope wavefunctions of spinless electrons near the Fermi level at two inequivalent valleys (K-points) in terms of the four component Dirac equation for massless fermions, with the role of spin assumed by pseudospin due to the relative amplitude of the wave function on the sublattice atoms (``A'' and ``B''). Using boundary conditions at the ends of the tube that neither break valley degeneracy nor mix pseudospin eigenvectors, we use degenerate perturbation theory to show that the presence of impurities has two effects. Firstly, the position of the impurity with respect to the spatial variation of the envelope standing waves results in a sinusoidal oscillation of energy level shift as a function of energy. Secondly, the position of the impurity within the hexagonal graphite unit cell produces a particular 4 by 4 matrix structure of the corresponding effective Hamiltonian. The symmetry of this Hamiltonian with respect to pseudospin flip is related to degeneracy breaking and, for an armchair tube, the symmetry with respect to mirror reflection in the nanotube axis is related to pseudospin mixing.Comment: 20 pages, 10 eps figure

Universality in escape from a modulated potential well

We show that the rate of activated escape $W$ from a periodically modulated potential displays scaling behavior versus modulation amplitude $A$. For adiabatic modulation of an optically trapped Brownian particle, measurements yield $\ln W\propto (A_{\rm c} - A)^{\mu}$ with $\mu = 1.5$. The theory gives $\mu=3/2$ in the adiabatic limit and predicts a crossover to $\mu=2$ scaling as $A$ approaches the bifurcation point where the metastable state disappears.Comment: 4 pages, 3 figure

Supporting Social Justice Literacy in Student Affairs and Higher Education Graduate Preparation Programs

This study highlights a promising practice for learning and teaching in social justice or diversity courses in graduate preparation programs (GPPs). In these contexts, pedagogical approaches that both challenge and support students’ understanding of core concepts of social justice curriculum. Novel to the social justice courses in this study was a two-part photo project wherein students from dominant and non-dominant identity groups benefitted from the curriculum. Interpretations are based on qualitative data from students and faculty in a required social justice course in a GPP. Findings are presented through an imperfect narrative among study participants

Master\u27s Students\u27 Experiences in a Graduate Preparation Program: Multicultural Competency and Social Justice Curriculum

This dissertation study focused on master\u27s students experiences with multicultural competency curriculum in graduate preparation programs (GPPs) and contributes to gaps in the extant literature on multicultural issues in higher education. The two overarching research questions for the study considered how, if at all, students\u27 understanding of core concepts of the required course (privilege, oppression, and social justice) changed over time as evidenced by a primary curricular component called the photo elicitation project. Educators\u27 experiences were also addressed, per their impact on the context in which students learned. This study employed a qualitative approach and, in line with the study\u27s epistemology, represented findings through two multi-genre mediations (i.e., two separate chapters). Primary sources of data for this study were 12 master\u27s students\u27 two-part photo elicitation projects and one-on-one semi-structured interviews with the 12 students and three educators. Findings from this study showed that students\u27 understanding of core concepts of the required multicultural competency and social justice course changed over time. Curricular experiences that related privilege, oppression, and social justice in relationship to students\u27 daily lives facilitated the most change in students\u27 understanding of the three core concepts. Educators\u27 experiences in teaching the curriculum overlapped with students\u27 experiences in many ways. Select implications for higher education research and practice include shifting the discourse from multicultural competency to social justice literacy as a way to understand master\u27s students\u27 experiences with required multicultural competency and social justice-related curriculum. Additionally, there is more room to foreground the voices of students from diverse backgrounds and to focus solely on the impact of educators who teach required multicultural and social justice-related curriculum

Ultracold, radiative charge transfer in hybrid Yb ion - Rb atom traps

Ultracold hybrid ion-atom traps offer the possibility of microscopic manipulation of quantum coherences in the gas using the ion as a probe. However, inelastic processes, particularly charge transfer can be a significant process of ion loss and has been measured experimentally for the Yb$^{+}$ ion immersed in a Rb vapour. We use first-principles quantum chemistry codes to obtain the potential energy curves and dipole moments for the lowest-lying energy states of this complex. Calculations for the radiative decay processes cross sections and rate coefficients are presented for the total decay processes. Comparing the semi-classical Langevin approximation with the quantum approach, we find it provides a very good estimate of the background at higher energies. The results demonstrate that radiative decay mechanisms are important over the energy and temperature region considered. In fact, the Langevin process of ion-atom collisions dominates cold ion-atom collisions. For spin dependent processes \cite{kohl13} the anisotropic magnetic dipole-dipole interaction and the second-order spin-orbit coupling can play important roles, inducing couplingbetween the spin and the orbital motion. They measured the spin-relaxing collision rate to be approximately 5 orders of magnitude higher than the charge-exchange collision rate \cite{kohl13}. Regarding the measured radiative charge transfer collision rate, we find that our calculation is in very good agreement with experiment and with previous calculations. Nonetheless, we find no broad resonances features that might underly a strong isotope effect. In conclusion, we find, in agreement with previous theory that the isotope anomaly observed in experiment remains an open question.Comment: 7 figures, 1 table accepted for publication in J. Phys. B: At. Mol. Opt. Phys. arXiv admin note: text overlap with arXiv:1107.114

Minimal conductivity in bilayer graphene

Using the Landauer formula approach, it is proven that minimal conductivity of order of $e^{2}/h$ found experimentally in bilayer graphene is its intrinsic property. For the case of ideal crystals, the conductivity turns our to be equal to $e^{2}/2h$ per valley per spin. A zero-temperature shot noise in bilayer graphene is considered and the Fano factor is calculated. Its value $1-2/\pi$ is close to the value 1/3 found earlier for the single-layer graphene.Comment: 3 pages, 1 figur

Weak localisation magnetoresistance and valley symmetry in graphene.

Due to the chiral nature of electrons in a monolayer of graphite (graphene) one can expect weak antilocalisation and a positive weak-field magnetoresistance in it. However, trigonal warping (which breaks p to −p symmetry of the Fermi line in each valley) suppresses antilocalisation, while inter-valley scattering due to atomically sharp scatterers in a realistic graphene sheet or by edges in a narrow wire tends to restore conventional negative magnetoresistance. We show this by evaluating the dependence of the magnetoresistance of graphene on relaxation rates associated with various possible ways of breaking a ’hidden’ valley symmetry of the system