Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session S26: Nanowires I: Theory and Modeling |
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Sponsoring Units: DCOMP DMP Chair: Daniel Stein, University of Arizona Room: LACC 501B |
Wednesday, March 23, 2005 2:30PM - 2:42PM |
S26.00001: Multi-channel impurity scattering effects on the carrier mobility in semiconductor nanowires Kunal Das, Ari Mizel We consider the mobility of charged carriers in a semiconducting nanowire. The suppression of scattering phase space in small radius wires can enhance mobility. This can compete with an increased density of impurities and defects in the interior and surface of small radius wires that can decrease mobility. We study the dependence of these effects on wire radius, providing insight into the transition from bulk transport to effective one dimensional transport. [Preview Abstract] |
Wednesday, March 23, 2005 2:42PM - 2:54PM |
S26.00002: Nonlinear dynamics of the thinning process of metallic nanocylinders J\'er\^ome B\"urki, Charles A. Stafford A nonlinear partial differential equation for the shape evolution of metallic nanowires is presented and applied to the description of the thinning process of nanocylinders. Using concepts from fluid dynamics, the PDE is derived from a semiclassical energy functional that includes electron-shell effects. The thinning is found to occur through nucleation of kink-like solitons at the boundary of the nanowire, which subsequently move along the wire. We discuss a rich dynamics involving interactions between kinks that substantially alters their motion along the wire, and compare our results with experiments on gold nanowires. [Preview Abstract] |
Wednesday, March 23, 2005 2:54PM - 3:06PM |
S26.00003: Universal activation barriers for metastable metal nanowires Charles Stafford, J\'er\^ome B\"urki, Daniel Stein We introduce a continuum approach to study the lifetimes of monovalent metal nanowires, which includes the competing effects of surface tension and electron-shell structure on an equal footing. Thermal fluctuations of cylindrical nanowires are modeled through the use of stochastic Ginzburg-Landau field theories. The fluctuation-induced thinning of metal nanowires is predicted to occur via the nucleation of surface kinks at the ends of the wire, consistent with recent electron microscopy studies. The activation barriers of the most stable structures are predicted to be ``universal,'' i.e., independent of the radius of the wire, and proportional to the square root of the surface tension. The reduction of the activation barrier under strain is also determined. [Preview Abstract] |
Wednesday, March 23, 2005 3:06PM - 3:18PM |
S26.00004: Transport and Magnetic Properties of Metal Nanowire under Finite Voltages Chang-hua Zhang The electronic transport and magnetic properties of metallic nanocylinders have been studied under the finite bias in a generalized mean-field electron model. The electron-electron interaction is treated in the self-consistent Hartree approximation so that the calculated physical quantities are ``gauge invariant.'' The modulation of the cohesion force is a few nano-Newtons for a few Volts and is correlated to the jumps of the differential conductance. The screening of electron-electron interactions is also found to be very sensitive to the magnetic field, which leads to a high sensitivity of the magnetotension and magnetoconductance coefficients on a longitudinal magnetic field. [Preview Abstract] |
Wednesday, March 23, 2005 3:18PM - 3:30PM |
S26.00005: The charge density wave transition in metallic nanowires Daniel F. Urban, Charles A. Stafford, Hermann Grabert A quantum mechanical stability analysis of metallic nanowires reveals an instability of the Peierls type in the regime where the Rayleigh instability is suppressed by electron shell effects. Therefore the length of stable wires with magic radii is limited. Near the Peierls transition, the singular part of the energy shows finite-size scaling consistent with the hyperscaling ansatz for a quantum phase transition. Based on this critical behavior, we study the dynamics of surface fluctuations and discuss the crossover to the CDW phase as a function of the length of the wire. [Preview Abstract] |
Wednesday, March 23, 2005 3:30PM - 3:42PM |
S26.00006: Structured Energy Distribution and Coherent AC Transport in Mesoscopic Wires Andrey Shytov Electron energy distribution in a mesoscopic AC-driven diffusive wire generally is not characterized by an effective temperature. At low temperatures, the distribution has a form of a multi-step staircase, with the step width equal to the field energy quantum. Analytic results for the field frequency high and low compared to Thouless energy are presented, while the intermediate frequency regime is analyzed numerically. Manifestations in the tunneling spectroscopy and noise measurements are discussed. [Preview Abstract] |
Wednesday, March 23, 2005 3:42PM - 3:54PM |
S26.00007: Wigner Crystallization in inhomogeneous one dimensional wires Erich Mueller I present a theory of the crossover between weak and strong interactions in a one dimensional electron gas confined by a power law potential [cond-mat/0410773]. Upon increasing the interaction strength, Friedel oscillations in the density of the noninteracting gas smoothly increase in amplitude, eventually resulting in well-separated electrons. I extract the momentum space wavefunction of the electron at the Fermi surface, which can be measured in experiments on tunneling between parallel wires. The onset of localization leads to a dramatic broadening of the momentum space wavefunction together with pronounced sharpening (in energy) of the tunneling spectrum. [Preview Abstract] |
Wednesday, March 23, 2005 3:54PM - 4:06PM |
S26.00008: Midgap States and Generalized Supersymmetry in Semi-infinite Nanowires Chung-Yu Mou, Bor-Luen Huang, Shin-Tza Wu Edge states of semi-infinite nanowires in tight binding limit are examined. We argue that understanding these edge states provides a pathway to generic comprehension of surface states in many semi-infinite physical systems. It is shown that the edge states occur within the gaps of the corresponding bulk spectrum (thus also called the midgap states). More importantly, we show that the presence of these midgap states reflects an underlying generalized supersymmetry. This supersymmetric structure is a generalized rotational symmetry among sublattices and results in a universal tendency: all midgap states tend to vanish with periods commensurate with the underlying lattice. Based on our formulation, we propose a structure with superlattice in hopping to control the number of localized electronic states occurring at the ends of the nanowires. Other implications are also discussed. In particular, it is shown that the ordinarily recognized impurity states can be viewed as disguised midgap states. [Preview Abstract] |
Wednesday, March 23, 2005 4:06PM - 4:18PM |
S26.00009: Nanotube in a Wigner crystal regime Dmitry Novikov A narrow--gap nanotube is studied close to half--filling, focussing on the effects of the curvature of the electronic dispersion controlled by the gap. Curvature couples charge and spin--valley SU(4) "flavor" sectors, resulting, in particular, in the effects of commensuration. In the charge sector, the latter are manifest when the tube is subjected to a periodic external potential, in which case the Wigner crystal of electrons becomes locked into incompressible configurations. Commensuration in the flavor sector can be manifest in the presence of external magnetic field. In this case, commensurability between the densities of electrons with opposing spin polarizations results in the flavor ordering that could be revealed in magnetization measurements, when the Zeeman energy is larger than the renormalized gap at half--filling. Work supported by NSF MRSEC grant DMR 02-13706. [Preview Abstract] |
Wednesday, March 23, 2005 4:18PM - 4:30PM |
S26.00010: Curved Nanowire Structures Jens Gravesen, Morten Willatzen Schroedinger eigenstates and associated eigenvalues are found and discussed in terms of symmetry properties for a quantum- mechanical particle confined to a curved nanowire having arbitrary cross-sectional geometry. The three-dimensional Schroedinger problem is simplified mathematically using differential-geometry arguments so as to obtain three ordinary differential equations which can be solved computationally fast even for complex-curved nanowire structures. This simplification is possible as long as the nanowire radius of curvature is considerably larger than the nanowire cross- sectional dimensions. We consider in details the computational problems of a straight nanowire with two subsequent 90 degree bendings, the sinusoidal-shaped nanowire, the elliptical-shaped nanowire based on the analytical fact that the model presented gives exact (excellent) agreement with the corresponding three- dimensional treatment in the cases of a nanowire with a straight-line shaped (circular-shaped) axis. [Preview Abstract] |
Wednesday, March 23, 2005 4:30PM - 4:42PM |
S26.00011: Theory of momentum resolved tunneling into a short quantum wire Jiang Qian, Gregory Fiete, Yaroslav Tserkovnyak , Bertrand Halperin Motivated by recent tunneling experiments in the parallel wire geometry[1], we calculate results for momentum resolved tunneling into a short one-dimensional wire containing a small number of electrons. We derive some general theorems about the momentum dependence, and we carry out exact calculations for up to N=4 electrons in the final state, for a system with screened Coulomb interactions that models the situation of the experiments. Both the case of electrons with spin and the case of completely polarized electrons are considered. The electron density and momentum-dependent tunneling matrix elements at various inter-particle spacings are analyzed. At large interactions the spin dynamics of the system can be approximated with a Heisenberg model, and we derive an effective Heisenberg coupling constant J from the gap between ground state and first excited state. We shall discuss implications of the calculations for the experiments on parallel wires. [1] O. Auslaender et. al, unpublished. [Preview Abstract] |
Wednesday, March 23, 2005 4:42PM - 4:54PM |
S26.00012: Novel Gapped Quantum Wire Trinanjan Datta, Erica W. Carlson High quality state of the art quantum wires (QWRs) can be fabricated by the novel cleaved edge overgrowth technique, proposed by (Pfeiffer {\em et al.}, 1990). Transverse quantization in these QWRs leads to a succession of nested energy bands. With the lowest two successive energy levels occupied, gapped phases are possible including, e.g, an intersubband charge density wave (ICDW) and a Cooper phase with strong superconducting fluctuations (Starykh {\em et al.}, 2000). Due to the possibility of density reorganization, in which it becomes favorable for the two lowest subbands to match their densities, the ICDW is usually the most likely state. Recently, by exploiting the valley degeneracy in AlAs, a single QWR has been fabricated with two degenerate nonoverlapping bands separated in k space by half an Umklapp vector (Moser {\em et al.} 2004). For low densities this structure is able to access a multiple subband regime that is not subject to the density reorganizing ICDW, leaving the Cooper phase to flourish. Using Abelian bosonization, we explore the relevant interaction terms for this system, including Umklapp assisted Cooper scattering, and discuss the phase diagram. [Preview Abstract] |
Wednesday, March 23, 2005 4:54PM - 5:06PM |
S26.00013: Coulomb correlations in ultrathin wires Michael Fogler We compute the ground-state energy and the density-density correlation function of electron liquid in a thin one- dimensional wire. The calculation is based on an approximate mapping of the problem with a realistic Coulomb interaction law onto exactly solvable models of mathematical physics. This approach becomes asymptotically exact in the limit of small wire radius but remains numerically accurate even for modestly thin wires. Possible experimental realizations of the model include semiconducting carbon nanotubes on high-kappa dielectric substrates and quantum wires near metallic gates. [Preview Abstract] |
Wednesday, March 23, 2005 5:06PM - 5:18PM |
S26.00014: Quantum thermal conductance of quasi-one-dimensional insulating rods Padraig Murphy, Joel Moore At low temperatures the thermal conductance of mesoscopic quasi-one-dimensional systems is determined by the transmission probability of various propagating modes. We study the effect of disorder on the quantum thermal conductance of thin insulating rods by a dynamical transfer-matrix method valid in the harmonic approximation. In particular we examine the dependence of heat transmission and localization on the width of the system, the degree of disorder, and the temperature. Increasing the wire width changes not only the number of propagating modes, but also the behavior of each mode, in a fashion quite different from electronic localization in one dimension. [Preview Abstract] |
Wednesday, March 23, 2005 5:18PM - 5:30PM |
S26.00015: Ab initio calculations for the electronic properties of III-V semiconductor nanowires Manuel Alemany, Xiangyang Huang, James Chelikowsky The electronics industry is pushing the size of traditional semiconductor-based devices towards their physical limits, i.e., the miniaturization of devices, which is needed for increasing the efficiency, is restricted by the fundamental limitations of current lithography techniques. In contrast, the use of nanoscale structures as basic units for constructing electronic devices can potentially overcome such limitation. As building blocks for devices, semiconductor nanowires have created great interest in recent years. Here we will present results of an \textit{ab initio} study of the electronic properties of semiconductor nanowires of III-V materials. We have performed calculations using a real-space pseudopotential approach for these systems. We will discuss the role of quantum confinement on the electronic properties of such materials by comparisons to quantum dots and experiment [Preview Abstract] |
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S26.00016: Electronic and Structural Properties of Chains of Metals Michael Springborg, Yi Dong, Abu Assaduzzaman We report results of parameter-free calculations of the structural and electronic properties of isolated metal chains. The calculations have been performed using our own density-functional methods that has been developed for isolated, infinite, periodic, helical chains with a straight chain axis. We study linear, zigzag, double-zigzag, and tetragonal chains of Au, Ag, Al, Pt, Bi, Pb, and Tl, and discuss the relative stability of the different forms, distortion modes, effects of spin-orbit couplings, and band structures. [Preview Abstract] |
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