Correlation between the Extraordinary Hall Effect and Resistivity

We study the contribution of different types of scattering sources to the extraordinary Hall effect. Scattering by magnetic nano-particles embedded in normal-metal matrix, insulating impurities in magnetic matrix, surface scattering and temperature dependent scattering are experimentally tested. Our new data, as well as previously published results on a variety of materials, are fairly interpreted by a simple modification of the skew scattering model

G-Quadruplex Dynamics Contribute To Regulation Of Mitochondrial Gene Expression

Single-stranded DNA or RNA sequences rich in guanine (G) can adopt non-canonical structures known as G-quadruplexes (G4). Mitochondrial DNA (mtDNA) sequences that are predicted to form G4 are enriched on the heavy-strand and have been associated with formation of deletion breakpoints. Increasing evidence supports the ability of mtDNA to form G4 in cancer cells; however, the functional roles of G4 structures in regulating mitochondrial nucleic acid homeostasis in non-cancerous cells remain unclear. Here, we demonstrate by live cell imaging that the G4-ligand RHPS4 localizes primarily to mitochondria at low doses. We find that low doses of RHPS4 do not induce a nuclear DNA damage response but do cause an acute inhibition of mitochondrial transcript elongation, leading to respiratory complex depletion. We also observe that RHPS4 interferes with mtDNA levels or synthesis both in cells and isolated mitochondria. Importantly, a mtDNA variant that increases G4 stability and anti-parallel G4-forming character shows a stronger respiratory defect in response to RHPS4, supporting the conclusion that mitochondrial sensitivity to RHPS4 is G4-mediated. Taken together, our results indicate a direct role for G4 perturbation in mitochondrial genome replication, transcription processivity, and respiratory function in normal cells

Heat kernel of integrable billiards in a magnetic field

We present analytical methods to calculate the magnetic response of non-interacting electrons constrained to a domain with boundaries and submitted to a uniform magnetic field. Two different methods of calculation are considered - one involving the large energy asymptotic expansion of the resolvent (Stewartson-Waechter method) is applicable to the case of separable systems, and another based on the small time asymptotic behaviour of the heat kernel (Balian-Bloch method). Both methods are in agreement with each other but differ from the result obtained previously by Robnik. Finally, the Balian-Bloch multiple scattering expansion is studied and the extension of our results to other geometries is discussed.Comment: 13 pages, Revte

Correlations in a confined magnetized free-electron gas

Equilibrium quantum statistical methods are used to study the pair correlation function for a magnetized free-electron gas in the presence of a hard wall that is parallel to the field. With the help of a path-integral technique and a Green function representation the modifications in the correlation function caused by the wall are determined both for a non-degenerate and for a completely degenerate gas. In the latter case the asymptotic behaviour of the correlation function for large position differences in the direction parallel to the wall and perpendicular to the field, is found to change from Gaussian in the bulk to algebraic near the wall.Comment: 24 pages, 10 figures, submitted to J. Phys. A: Math. Ge

Quantum kinetic approach to the calculation of the Nernst effect

We show that the strong Nernst effect observed recently in amorphous superconducting films far above the critical temperature is caused by the fluctuations of the superconducting order parameter. We employ the quantum kinetic approach for the derivation of the Nernst coefficient. We present here the main steps of the calculation and discuss some subtle issues that we encountered while calculating the Nernst coefficient. In particular, we demonstrate that in the limit T=0 the contribution of the magnetization ensures the vanishing of the Nernst signal in accordance with the third law of thermodynamics. We obtained a striking agreement between our theoretical calculations and the experimental data in a broad region of temperatures and magnetic fields.Comment: 24 pages, 13 figure

Exact first-order density matrix for a d-dimensional harmonically confined Fermi gas at finite temperature

We present an exact closed form expression for the {\em finite temperature} first-order density matrix of a harmonically trapped ideal Fermi gas in any dimension. This constitutes a much sought after generalization of the recent results in the literature, where exact expressions have been limited to quantities derived from the {\em diagonal} first-order density matrix. We compare our exact results with the Thomas-Fermi approximation (TFA) and demonstrate numerically that the TFA provides an excellent description of the first-order density matrix in the large-N limit. As an interesting application, we derive a closed form expression for the finite temperature Hartree-Fock exchange energy of a two-dimensional parabolically confined quantum dot. We numerically test this exact result against the 2D TF exchange functional, and comment on the applicability of the local-density approximation (LDA) to the exchange energy of an inhomogeneous 2D Fermi gas.Comment: 12 pages, 3 figures included in the text, RevTeX4. Text before Eq.(25) corrected. Additional equation following Eq.(25) has been adde

The onset of the vortex-like Nernst signal above Tc in La_{2-x}Sr_xCuO_4 and Bi_2Sr_{2-y}La_yCuO_6

The diffusion of vortices down a thermal gradient produces a Josephson signal which is detected as the vortex Nernst effect. In a recent report, Xu et al., Nature 406, 486 (2000), an enhanced Nernst signal identified with vortex-like excitations was observed in a series of La_{2-x}Sr_xCuO_4 (LSCO) crystals at temperatures 50-100 K above T_c. To pin down the onset temperature T_{\nu} of the vortex-like signal in the lightly doped regime (0.03 < x < 0.07), we have re-analyzed in detail the carrier contribution to the Nernst signal. By supplementing new Nernst measurements with thermopower and Hall-angle data, we isolate the off-diagonal Peltier conductivity \alpha_{xy} and show that its profile provides an objective determination of T_{\nu}. With the new results, we revise the phase diagram for the fluctuation regime in LSCO to accomodate the lightly doped regime. In the cuprate Bi_2Sr_{2-y}La_yCuO_6, we find that the carrier contribution is virtually negligible for y in the range 0.4-0.6. The evidence for an extended temperature interval with vortex-like excitations is even stronger in this system. Finally, we discuss how T_{\nu} relates to the pseudogap temperature T* and the implications of strong fluctuations between the pseudogap state and the d-wave superconducting state.Comment: 10 pages, 10 figure

Some exact results for a trapped quantum gas at finite temperature

We present closed analytical expressions for the particle and kinetic energy spatial densities at finite temperatures for a system of noninteracting fermions (bosons) trapped in a d-dimensional harmonic oscillator potential. For d=2 and 3, exact expressions for the N-particle densities are used to calculate perturbatively the temperature dependence of the splittings of the energy levels in a given shell due to a very weak interparticle interaction in a dilute Fermi gas. In two dimensions, we obtain analytically the surprising result that the |l|-degeneracy in a harmonic oscillator shell is not lifted in the lowest order even when the exact, rather than the Thomas-Fermi expression for the particle density is used. We also demonstrate rigorously (in two dimensions) the reduction of the exact zero-temperature fermionic expressions to the Thomas-Fermi form in the large-N limit.Comment: 14 pages, 4 figures include

A Variational Procedure for Time-Dependent Processes

A simple variational Lagrangian is proposed for the time development of an arbitrary density matrix, employing the "factorization" of the density. Only the "kinetic energy" appears in the Lagrangian. The formalism applies to pure and mixed state cases, the Navier-Stokes equations of hydrodynamics, transport theory, etc. It recaptures the Least Dissipation Function condition of Rayleigh-Onsager {\bf and in practical applications is flexible}. The variational proposal is tested on a two level system interacting that is subject, in one instance, to an interaction with a single oscillator and, in another, that evolves in a dissipative mode.Comment: 25 pages, 4 figure

Quantum transport through mesoscopic disordered interfaces, junctions, and multilayers

The study explores perpendicular transport through macroscopically inhomogeneous three-dimensional disordered conductors using mesoscopic methods (real-space Green function technique in a two-probe measuring geometry). The nanoscale samples (containing $\sim1000$ atoms) are modeled by a tight-binding Hamiltonian on a simple cubic lattice where disorder is introduced in the on-site potential energy. I compute the transport properties of: disordered metallic junctions formed by concatenating two homogenous samples with different kinds of microscopic disorder, a single strongly disordered interface, and multilayers composed of such interfaces and homogeneous layers characterized by different strength of the same type of microscopic disorder. This allows us to: contrast resistor model (semiclassical) approach with fully quantum description of dirty mesoscopic multilayers; study the transmission properties of dirty interfaces (where Schep-Bauer distribution of transmission eigenvalues is confirmed for single interface, as well as for the stack of such interfaces that is thinner than the localization length); and elucidate the effect of coupling to ideal leads (``measuring apparatus'') on the conductance of both bulk conductors and dirty interfaces When multilayer contains a ballistic layer in between two interfaces, its disorder-averaged conductance oscillates as a function of Fermi energy. I also address some fundamental issues in quantum transport theory--the relationship between Kubo formula in exact state representation and ``mesoscopic Kubo formula'' (which gives the zero-temperature conductance of a finite-size sample attached to two semi-infinite ideal leads) is thoroughly reexamined by comparing their answers for both the junctions and homogeneous samples.Comment: 18 pages, 17 embedded EPS figure