Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S53: Focus Session: Electron, Ion, and Exciton Transport in Nanostructures I |
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Sponsoring Units: DMP Chair: Matthew Gilbert, University of Illinois Room: Mile High Ballroom 2C |
Thursday, March 6, 2014 8:00AM - 8:12AM |
S53.00001: Screening in Non-Equilibrium Dissipative System Jiajun Li, Jong Han Effect of screening is one crucial property of interacting electrons. However, it is still not completely understood in non-equilibrium dissipative system, partly due to a lack of convenient theoretical tool. It is recently shown that a DC-driven lattice attached to fermionic reservoirs [1,2] reproduces major physical properties of real system, and is accessible by comprehensive theoretical study even in strong field and correlated electron region. In this presentation, we will show a study of electronic screening within this model. First of all, current distribution out of impurities will be shown in steady-state non-equilibrium. With parameters changing in the regimes of linear and high-field, DC current shows distinctly different patterns, reflecting the underlying interplay between quantum dissipation and non-equilibrium physics. In addition, the density-density correlation function is calculated and RPA is used to study dielectric screening. The electron-hole excitation spectrum will be presented, which indicates interesting physics while fermionic dissipation, Coulomb interaction and external field compete with each other. \\[4pt] [1] J. E. Han, Phys. Rev. B \textbf{87}, 085119 (2013)\\[0pt] [2] J. E. Han, J. Li, Phys. Rev. B \textbf{88}, 075113 (2013) [Preview Abstract] |
Thursday, March 6, 2014 8:12AM - 8:24AM |
S53.00002: Strong correlation and multi-phase solution in nonequilibrium lattice systems coupled to dissipation medium Jong Han, Jiajun Li, Camille Aron, Gabriel Kotliar How does a strongly correlated electronic solid evolve continuously out of equilibrium when an electric field is applied? While this question may seem deceptively simple, it requires rigorous understanding of dissipation. We formulate the nonequilibrium steady-state lattice coupled to fermion baths in the Coulomb gauge. We demonstrate that the Hubbard model solved using the iterative perturbation theory within the dynamical mean-field approximation recovers the DC conductivity independent of the Coulomb interaction in a very narrow linear response regime. Due to the singular dependence of the effective temperature on the damping in the steady-state~\footnote{J. E. Han and Jiajun Li, Phys. Rev. B {\bf 88}, 075113 (2013)}, systems with damping have dramatic field-dependent effect, very different from dissipationless systems. We conclude that the dominant physics in lattice nonequilibrium is not the field vs quasi-particle energy, but rather the Joule heat vs the quasi-particle energy. Furthermore, we show that, in the vicinity of the Mott-insulator transition, the solution supports mixed-phase state scenario which indicates that the electron transport in solids under high-field can be spatially inhomogeneous leading to filamentary conducting paths, as suggested by experiments. [Preview Abstract] |
Thursday, March 6, 2014 8:24AM - 8:36AM |
S53.00003: Metastable Dynamics of Topological Superfluids Moon Jip Park, Matthew Gilbert Superfluid states resulting from the condensation of indirectly bound excitons arising from the attractive Coulomb coupling of electrons in one layer and holes in another spatially segregated layer have attracted a great deal of interest from both a fundamental and applied perspective due to their remarkable interlayer transport properties. Within these systems, one of the most important quantities is the critical current, the maximum interlayer current that can flow before coherence is lost. While a great deal is known about the superfluid state prior to reaching critical current, very little is known about the fate of the system after critical current. In this talk, we study non-equilibrium response of a dipolar intersurface superfluid in a 3D time-reversal invariant topological insulator using a fully time-dependent formulation of the Kadanoff-Baym equations. We find that past critical current there exist different metastable regions of intersurface voltage characterized by distinct time-dependent responses. While we will discuss the resultant physics of the metastable states present beyond the critical current within topological insulators, the physics is broadly applicable to both graphene and quantum Hall systems. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 8:48AM |
S53.00004: Crossover between the Hikami and spin-resolved band limits of weak anti-localization in two-dimensional electron gases Yasufumi Araki, Guru Khalsa, Allan H. MacDonald We investigate the quantum interference corrections to transport which lead to weak localization (WL) or weak anti-localization (WAL) for the case of spin-independent disorder scattering in two-dimensional electron gases with spin-orbit interactions of arbitrary strength. We formulate our theory in terms of microscopic linear response including multiple scattering by the disorder potential to derive the current-current response function when Rashba (or Dresselhaus) spin-orbit coupling is included in the electronic band structure. We analyze the crossover from the weak spin-orbit coupling limit in which spin-splitting of the bands is not resolved, to the strong spin-orbit coupling limit of clearly spin-split bands. In the weak and strong spin-orbit coupling limits we generally recover the well-known WL and WAL behavior first predicted by Hikami, Larkin and Nagaoka, although the degeneracy of spin triplet channels is lifted leading to a more complex crossover between the traditional WL and WAL limits. Our results can be summarized by a phase diagram in spin-orbit coupling strength and temperature (or the coherence length from inelastic scattering), with several regions separated by different crossover lines. [Preview Abstract] |
Thursday, March 6, 2014 8:48AM - 9:00AM |
S53.00005: ABSTRACT WITHDRAWN |
Thursday, March 6, 2014 9:00AM - 9:12AM |
S53.00006: Hanbury Brown --Twiss type exchange effects in a four terminal diffusive conductor Jayanta Sarkar, Antti Puska, Akira Hida, Maciej Weisner, Pertti Hakonen We have investigated current-current correlations in a mesoscopic four-terminal diffusive conductor, and performed an electronic equivalent of Hanbury Brown -Twiss (HBT) type of experiment. In the experiment, cross -spectrum noise between two terminals of a cross is measured in three different bias configurations and exchange correction factor $\Delta $S $=$ \textbar SC\textbar - \textbar SA\textbar - \textbar SB\textbar [1] is calculated from these measurements. In the non-interacting regime, we find an increase in $\Delta $S with bias from the thermal limit and with further increase in bias the $\Delta $S becomes bias independent [2]. In contrast to the diffusive cross, our measurements on metallic islands yielded strong HBT-type of correlations that agree with the expected intrinsic correlations in a four-terminal cavity coupled to reservoirs by weak tunneling contacts. Moreover, we find non-classical HBT contributions for the case of interacting electrons (hot electrons), where $\Delta $S is found to be negative.\\[4pt] [1] Ya. M. Blanter, M. B\"{u}ttiker, Phys. Rev. B \textbf{56}, 2127 (1997).\\[0pt] [2] E. V. Shukhorukov, D. Loss, Phys. Rev. B \textbf{59}, 13054 (1999). [Preview Abstract] |
Thursday, March 6, 2014 9:12AM - 9:24AM |
S53.00007: Magnetotransport across the artificially designed tilted grain boundaries Aiping Chen, Zhenxing Bi, Chen-Fong Tsai, Li Chen, Qing Su, Xinghang Zhang, Haiyan Wang Single-phase epitaxial La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) thin films with significantly enhanced low-field magnetoresistance (LFMR) properties are demonstrated in this work. The LSMO films on SrTiO$_{3}$ (001) substrates exhibit tilted and well-aligned nanocolumn structure achieved by pulsed laser oblique-angle deposition (PLOAD) followed by subsequent postannealing. The tilted aligned nanocolumnar (TAN) arrays have been achieved at relative high deposition angles ($\ge $30$^{\circ})$ and low deposition temperatures ($\le $450 $^{\circ}$C). More attractively, the tilted grain boundaries (GBs) can be systematically manipulated by the postannealing process and so can the LFMR values of the LSMO TAN films. These results demonstrate that the tilted nanocolumnar films achieved by PLOAD and the GB tailoring by postannealing may provide a new approach to control and manipulate the magnetotransport properties of single-phase manganite perovskite films for device applications that require large LFMR effects, high epitaxial quality, and low resistivity. [Preview Abstract] |
Thursday, March 6, 2014 9:24AM - 9:36AM |
S53.00008: Dragon Segments in Electron Transport through Nanostructures Mark Novotny In transport through nanostructures connected to two semi-infinite leads, the transmission probability ${\cal T}(E)$ as a function of the energy $E$ of the incoming electron enters the Landauer calculation of the electrical conductance. Ballistic propagation occurs in pure materials due to the lack of scattering, and consequently ${\cal T}(E)=1$. It is shown that there is a large class of strongly disordered quasi-1D segments that also have ${\cal T}(E)=1$. Such segments are called quantum dragon segments. Quantum dragon segments have a serpentine quasi-1D structure, and if present cannot be observed by electron transport since ${\cal T}(E)=1$. Dragon segments are only possible when there is correlated disorder, thereby overcoming the Anderson localization that is present in 1D systems with random disorder. Dragon segments are found by using an exact mapping for ${\cal T}(E)$ at the level of the single-band tight-binding model. The mapping is from the quasi-1D model of the nanostructure onto a 1D model. Presented examples of dragon segments will include: select single-walled carbon nanotubes, Bethe lattices, conjoined Bethe lattices with random hopping within each ring, and quasi-1D systems formed from rectangular or orthorhombic lattice slices. [Preview Abstract] |
Thursday, March 6, 2014 9:36AM - 9:48AM |
S53.00009: Theory of Plasmonic Waves on a Chain of Metallic Nanoparticles in a Liquid Crystalline Host David Stroud, Nicholas Pike Linearly polarized plasmonic waves can propagate along a chain of metallic particles, of sufficiently small diameter and spacing. We have calculated the dispersion relations for these plasmonic waves when the host is either a nematic or a cholesteric liquid crystal (NLC or CLC). An NLC is found to alter the dispersion relations of both transverse ($T$) and or longitudinal ($L$) waves significantly from those for an isotropic host. If the NLC director is perpendicular to the metallic chain, the doubly degenerate $T$ branch is split into two linearly polarized branches. Similar results are obtained for a CLC with twist axis parallel to the chain, except that the $T$ branches are elliptically polarized. When a magnetic field is applied parallel to the chain, the dispersion relations for the $T$ branches are no longer symmetric about $k=0$ and the chain may act as a one-way waveguide at certain frequencies. We present numerical examples assuming spherical metal particle with a Drude dielectric function. [Preview Abstract] |
Thursday, March 6, 2014 9:48AM - 10:24AM |
S53.00010: Electrical Contacts in Carbon Nanotube Transistors Invited Speaker: Vasili Perebeinos Electrical properties of low-dimensional devices are dominated by the contact resistance. For carbon nanotube field effect transistors (CNT-FETs), as for graphene and MoS$_{\mathrm{2}}$ transistors, the electrical contacts are a key factor limiting device performance. Contact resistance reflects a complex interplay of many factors. With advances in scaling, the contact resistance and transfer length are becoming even more critical. We have developed a general purpose CNT device simulator which is unique in including quantum-mechanical tunneling, both acoustic and optical-phonon scattering, as well as the crucial transfer of carriers between the CNT and metal contact. To illustrate the unique capabilities relative to existing approaches such as non-equilibrium Green's function (NEGF) formalism, we predict the scaling of on-state current with contact length. The behavior is surprising. The transfer length is roughly a factor of two shorter at a typical drain voltage than at low bias. This reflects the onset of optical-phonon scattering underneath the metal contact for a ballistic channel. As we change the nanotube diameter (i.e. bandgap) and metal workfunction a Schottky to ohmic crossover in device characteristics takes place. Although the on-state current varies continuously, the transfer characteristics reveal a relatively abrupt crossover from Schottky to ohmic contacts [1]. The typical high-performance devices fall surprisingly close to the crossover. Therefore, tunneling plays an important role even in this regime, so that current fails to saturate with gate voltage as was expected due to ``source exhaustion''.\\[4pt] [1] V. Perebeinos, J. Tersoff, W. Haensch, Phys. Rev. Lett. (in press). [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 10:36AM |
S53.00011: Exciton and electron transport in metal oxide and metal-insulator nanostructures Wayne Hess, Alan Joly, Matthew Halliday, Alexander Shluger, Peter Sushko Understanding the dynamics of electronic excited states in solids is essential to forming mechanistic models relevant to electron and energy transport in materials. Irradiation of materials by ultraviolet (UV) photons, produces energetic species such as holes and free electrons, that relax to form electron-hole pairs and excitons capable of driving surface and bulk reactions such as atomic desorption. Photostimulated desorption experiments, when combined with ab-initio calculations, can be used to develop models for exciton transport and subsequent excited state dynamics. We use pulsed UV lasers to excite specific surface and bulk states of nano-structured metal oxides and measure velocities of desorbed atoms under controlled conditions. By measuring O-atom kinetic energy distributions, as a function of laser frequency, we demonstrate exciton transport on the surface and in the bulk of metal-oxides. We further interrogate electron and exciton dynamics at the metal-insulator interface of thin CsBr films grown on Cu(100). Photoexcitation at 6.4 eV specifically excites the CsBr surface exciton which leads to desorption of neutral Br-atoms with hyperthermal kinetic energies. In dramatic contrast, we observe thermal energy Br atoms from CsBr grown on Cu. The hyperthermal desorption channel is entirely quenched for UV laser desorption of Br atoms even for thick (\textgreater 60 nm) CsBr films on Cu. Possible models for electron transport and exciton relaxation will be discussed. [Preview Abstract] |
Thursday, March 6, 2014 10:36AM - 10:48AM |
S53.00012: Observation of an insulating to conducting transition in an artificial quantum dot lattice Neal Staley, Nirat Ray, Marc Kastner, Micah Hanson, Arthur Gossard In a single quantum dot, where the electron occupation is controlled by the interplay between the geometry, and thus charging energy of the dot, and the externally applied gate voltage it is possible to observe a mesoscopic analog to a neutral atom. If one were to create a lattice of these ``artificial atoms'' with sufficiently low disorder it would be possible to create an artificial solid with tunable properties. Electrical transport measurements on quantum dot lattices have thus far been dominated by disorder. We fabricated quantum dot lattices on GaAs using electron beam lithography and reactive ion etching to define the boundary of each dot, with the electron density controlled by a global top gate. For single quantum dots fabricated using this technique we observe ``Coulomb diamond'' features characteristic of single electron charging into the dot when the device is depleted into the few electron regime. For lattices however we observe a striking transition from a high resistance (low current) state to low resistance (high current) as a function of increasing source drain bias. This transition occurs over a large range in gate voltage, and temperature and could be an indication of collective phenomena occurring within these artificial quantum dot lattices. [Preview Abstract] |
Thursday, March 6, 2014 10:48AM - 11:00AM |
S53.00013: ABSTRACT WITHDRAWN |
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