Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Q9: Electronic Properties of Low Dimensional Systems |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Sergio Ulloa, Ohio University Room: A105 |
Wednesday, March 17, 2010 11:15AM - 11:27AM |
Q9.00001: The optical and electrical properties of Non-tapered InN nanorods grown by plasma-assisted MOCVD Hye-Won Seo, Dever Norman, Li-Wei Tu, Shu-Yu Chiang, In-Gann Chen, Kuo-Hao Lee, Jung-Hwan Kim, New-Jin Ho We report the non-tapered InN nanorods grown by plasma assisted metal-organic vapour deposition (MOCVD) methods. By carefully using RF plasma techniques, we were able to grow InN nanorods without NH3 at below decomposition temperature. The optical and structural qualities were evaluated by temperature dependent photoluminescence (PL) and current-voltage measurement. The PL revealed the low intrinsic carrier concentration and high structural quality of the InN nanorods. The conductance measurement, via nanoprobe system, agreed with the observed PL behaviors. The detail experimental results and their analysis will be discussed in the presentation. [Preview Abstract] |
Wednesday, March 17, 2010 11:27AM - 11:39AM |
Q9.00002: Band gap engineering in ZnO nanowire based alloys Jeverson Arantes, Caetano Miranda, Gustavo Dalpian ZnO nanowires can be manufactured through different ways, including wet chemical routes, chemical vapor deposition and other ones. A broad range of potential applications for these nanostructures have been proposed. Here, we explore the effects of alloying on ZnO based nanostructures, through First Principles Calculations within Density Functional Theory, to better understand the quantum confinement effect. A detailed it ab-initio study of the energetic, electronic and structural properties of ZnO nanowires alloyed with Be, Cd, Mg and Al has been performed. The effects of isovalent impurities such as Be, Cd, Mg is mainly to tune the band gap of the wire. For small impurity concentrations, smaller than 40 \%, we observe an almost linear behavior of the band gap. These impurities tend to be randomly distributed through the wire, what indicates that it should not be very difficult to grow these structures. We have also tested the effect of alloying the wire with Al donors. For this case, we observe a strong tendency for the impurities to be localized at the surface of the wire. [Preview Abstract] |
Wednesday, March 17, 2010 11:39AM - 11:51AM |
Q9.00003: Ballistic Quantum Hole Wires Joseph Sulpizio, Charis Quay, Rafi de Picciotto, David Goldhaber-Gordon, K.W. West, L.N. Pfeiffer We present measurements of hole transport in ballistic quantum wires fabricated by GaAs/AlGaAs cleaved-edge overgrowth. We have developed a new, broadly applicable approach to analyzing the transport measurements of a ballistic one-dimensional system. Applying this analysis to our nonlinear conductance data, we find evidence for the importance of charge interactions for transport in the wires. Additionally, we extract the g-factor from measurements in magnetic field, and find strong g-factor anisotropy, which we associate with spin-orbit coupling. [Preview Abstract] |
Wednesday, March 17, 2010 11:51AM - 12:03PM |
Q9.00004: Why a magnetized quantum wire can act as an active laser medium Manvir Kushwaha The fundamental magnetoplasmon excitations are investigated in a quantum wire characterized by a confining harmonic potential and subjected to a perpendicular magnetic field. The problem involves two length scales: ${\it l}_0=\sqrt{\hbar/m^*\omega_0}$ and ${\it l}_c=\sqrt{\hbar/m^*\omega_c}$, which characterize the relative strengths in the interplay of confinement and the magnetic field. We embark on the charge-density excitations within a two-subband model in the framework of Bohm-Pines' random-phase approximation. The main focus of our study is the intersubband (magnetoroton) excitation which changes the sign of its group velocity twice before merging with the respective single-particle continuum. We analyze the terms and conditions within which the magnetoroton excitation persists in the quantum wires. It is suggested that the electronic device based on such magnetoroton modes can act as an {\it active} laser medium. [Preview Abstract] |
Wednesday, March 17, 2010 12:03PM - 12:15PM |
Q9.00005: Atomic Co Wires: Room and Low Temperature STM/STS Measurements Nader Zaki, Danda Acharya, Denis Potapenko, Peter Johnson, Percy Zahl, Peter Sutter, Richard Osgood We recently reported [1] on a new surface phase of the Co-vicinal-Cu(111) system which exhibits self-assembled uniform Co quantum wires that are stable at 300K.STM images show that the wires form along the leading edge of the step rise, differentiating it from previously theoretically predicted atomic-wire phases as well as experimentally observed step-island formation. Our observations allow us to comment on the formation kinetics of the atomic-wire phase and on the fit of our data to a recently developed lattice-gas model. LT-STS measurements, taken on self-assembled Co chains, reveal a resonance at the Fermi energy. While it has been shown that single Co atoms and Co clusters [2] exhibit a Kondo effect, a Co chain at a Cu step may exhibit a different many-body effect that is the cause for our Fermi-energy resonance observation. \\[4pt] [1] N. Zaki et al, Phys. Rev. B 80, 155419 (2009) \\[0pt] [2] N. N\'{e}el et al, Phys. Rev. Lett. 101, 266803 (2008) [Preview Abstract] |
Wednesday, March 17, 2010 12:15PM - 12:27PM |
Q9.00006: Sintering of Silver Nanoparticle Films Liwei Huang, Yayong Liu, Kaikun Yang, Tom Xu, Howard Wang The sintering process of silver nanoparticle (Ag-NP) films has been studies using time-resolved in situ electrical resistance measurements at various temperatures. Ag-NPs having an average diameter of 4.6 nm were spun-cast on Si wafers to form ca. 100 nm films. Upon heating on a hot stage, organic molecules at the surfaces of Ag-NPs evaporate; Ag-NPs fuse to form a conductive film. Two conduction mechanisms upon crossing the percolation threshold have been revealed. Electrons initially hop among growing particles and later transport through continuous networks. The transition from the former to the latter is associated with activation energy of ca. 600 meV. [Preview Abstract] |
Wednesday, March 17, 2010 12:27PM - 12:39PM |
Q9.00007: Coherent Electronic Grating Cavity Modes in Corrugated Ultrathin Metal Films Yang Liu, Tom Miller, Tai-Chang Chiang Crystal surfaces oriented at a small angle relative to a close packed atomic plane may exhibit a periodic array of atomic steps; such stepped surfaces can serve as a template for growing metal films with a corrugated structure at the nanoscale. The corrugation modulates the electron motion within the film and thus modifies the electronic properties of the system. This work is a study of corrugated films of Ag and Pb using angle-resolved photoemission. A central issue is the degree of electron coherence: are the electrons free to propagate across the steps, thus forming Bloch waves? Or, are the electrons confined by the steps to form localized states? How are the photoemission patterns affected by the corrugation? Our results show that the electronic states in these films are coherent across the steps and can be understood in terms of cavity modes confined by atomic scale diffraction gratings. The photoemission patterns are governed by the blazing condition associated with the diffraction gratings and by quantum interference. [Preview Abstract] |
Wednesday, March 17, 2010 12:39PM - 12:51PM |
Q9.00008: Magnetotransport measurements in mesoscopic thin-film bismuth rings M. Rudolph, J.J. Heremans, A.J. Sigillito Elemental bismuth has been found to exhibit interesting quantum phenomena in high magnetic fields. The phenomena are believed to originate in strongly spin-orbit coupled states at the bismuth surface. We studied magnetotransport oscillations in bismuth thin films patterned into Aharonov-Bohm rings to access the electronic interference patterns of the surface states. Using thin films helps isolate the surface contributions and allows the fabrication of mesoscopic structures. Polycrystalline bismuth thin films (thickness $<$ 50 nm) were grown by thermal evaporation under UHV conditions. Mesoscopic rings (diameter $<$ 1 micron) were patterned by electron beam lithography and standard lift-off techniques. At low applied magnetic fields, low-temperature magnetoresistance measurements over the rings show quantum oscillations with several frequencies, some of which can be geometrically attributed to the Aharanov-Bohm effect. Lower frequency oscillations are also observed and will be discussed. (DOE DE-FG02-08ER46532) [Preview Abstract] |
Wednesday, March 17, 2010 12:51PM - 1:03PM |
Q9.00009: First-principles calculation of novel group-IV nanostructures Ed Sandberg, Lok Lew Yan Voon, Rachel Aga, Amir Farajian The structure, stability and electronic properties of nanosheets of group-IV elements were studied using density-functional theory. The nature of bonding with hydrogen was investigated by analyzing the electron density distribution and by calculating the binding energy. [Preview Abstract] |
Wednesday, March 17, 2010 1:03PM - 1:15PM |
Q9.00010: Semiclassical theory of non-local statistical measures: residual Coulomb interactions Steven Tomsovic, Denis Ullmo, Arnd Baecker Within the context of quantized chaotic billiards, random plane wave and semiclassical theoretical approaches were applied to an example of a relatively new class of statistical measures, i.e.~measures involving both complete spatial integration and energy summation as essential ingredients. A quintessential example comes from the desire to understand residual Coulomb interactions contributions to the ground state energy of ballistic quantum dots. Billiards, fully chaotic or otherwise, provide an ideal class of systems on which to focus as they have proven to be successful in modeling the single particle properties of a Landau-Fermi liquid in typical mesoscopic systems, i.e.~closed or nearly closed quantum dots. It happens that both theoretical approaches give fully consistent results for measure averages, but that surprisingly for fully chaotic systems the semiclassical theory gives a much improved approximation for the fluctuations. Comparison of the theories elucidates two shortcomings of the oft-relied-upon random plane wave approach. Non-fully chaotic systems are treated as well. [Preview Abstract] |
Wednesday, March 17, 2010 1:15PM - 1:27PM |
Q9.00011: Impurity induced bound states and proximity effect in a bilayer exciton condensate Yonatan Dubi, Alexander V. Balatsky The effect of impurities which induce local interlayer tunneling in bilayer exciton condensates is discussed. We show that a localized single fermion bound state emerges inside the gap regardless of the strength of impurity scattering. We calculate the dependence of the impurity state energy and wave function. We show that such an impurity induced single fermion state enhances the interlayer coherence around it, and is similar to the superconducting proximity effect. As a direct consequence, we predict that a finite concentration of such impurities will increase the critical temperature for exciton condensation. [Preview Abstract] |
Wednesday, March 17, 2010 1:27PM - 1:39PM |
Q9.00012: Bulk and surface magnetoinductive breathers in binary metamaterials George Tsironis, Nikos Lazarides, Mario Molina We study theoretically the existence of bulk and surface discrete breathers in a one-dimensional magnetic metamaterial comprised of a periodic binary array of split-ring resonators [1,2]. The two types of resonators differ in slit sizes leading to different SRR resonant frequencies. We construct several types of breather excitations for both the energy-conserved and the dissipative-driven systems using both the rotating wave approximation as well as the method of continuation from the anticontinuous limit to finite couplings. We demonstrate that discrete breathers can appear spontaneously in the dissipative-driven system as a result of a fundamental instability. We connect the appearence of breathers to the properties of wave propagation in the finite medium.\\[4pt] [1] M. Molina, et al. Phys. Rev. E, {\bf 80 }, 046605 (2009)\\[0pt] [2] M. Elefteriou et al., Phys. Rev. E {\bf 80}, 017601 (2009) [Preview Abstract] |
Wednesday, March 17, 2010 1:39PM - 1:51PM |
Q9.00013: Electronic transport through a quantum dot with metallic contacts Surjyo Behera, Shyamalendu Bose, Didier Ndengeyintwali We present a microscopic Green's function theory of electrical transport through a quantum dot with metallic contacts. The quantum dot has a single degenerate level where the energy level is split by a structural distortion (Jahn-Teller distortion). The calculation includes the effect of Coulomb blockade as well as the effect of presence of a magnetic impurity. The two metallic leads are represented by the free electron gas model and their interaction with the dot levels provides their width. The J-T distortion order parameter and the occupancy of the dot levels by up and down spin electrons are calculated self consistently as a function of temperature. These results are used to calculate the electrical conductivity as a function of the temperature. It is found that the J-T distortion order parameter depends strongly on the location of the dot energy level with respect to the Fermi level. While this order parameter shows a first order transition (discontinuous drop to zero) in the absence of the width of the dot level, it shows a second order transition and a reentrant behavior (for low dot energy levels) in its presence. The electrical conductivity has strong dependence on temperature, dot energy, its width, J-T distortion parameter, and magnetization due to the magnetic impurity. [Preview Abstract] |
Wednesday, March 17, 2010 1:51PM - 2:03PM |
Q9.00014: Magnetotransport in curved 2DEGs using a real-space numerical technique Bozidar Novakovic, Kevin Messer, Irena Knezevic 2D nanostructures with curvature have been a subject of intensive fabrication efforts over the recent years, resulting in structures such as group IV and III-V nanotubes, as well as various flexible electronic and nanoelectromechanical systems. Calculating electronic and transport properties of these curved systems is an important prerequisite for their successful application. In this work, we present the calculation of ballistic magnetoconductance and charge density in curved 2DEGs. A real space basis is adopted by solving the Schr\"{o}dinger equation on a grid that follows the natural parameters of the curved surface. This allows for solving the systems with the most general electronic potentials and curvatures. The magnetic field is included through the Peierls substitution in the translation operators on the surface. Several interesting examples of curved systems with flat contacts, such as a curved quantum cavity and a helix-shaped quantum wire, will be presented. [Preview Abstract] |
Wednesday, March 17, 2010 2:03PM - 2:15PM |
Q9.00015: Spatial correlations in chaotic nanoscale systems with spin-orbit coupling Anh Ngo, Eugene Kim, Sergio Ulloa We investigate the statistical properties of wave functions in two-dimensional chaotic nanostructures with spin-orbit interactions.~ We are especially interested in the role that spin-orbit coupling plays on the spatial correlations of eigenfunctions.~ Numerical~results obtained from a scattering formalism [1] for a chaotic stadium billiard are compared with analytic results~from random matrix theory.~ We present results for the evolution of the wave function statistics as the spin-orbit interaction is varied.~ We also discuss consequences of these results on~spin-polarized tunneling experiments.\\[4pt] [1] M. G. E. da Luz, A. S. Lupu-Sax, and E. J. Heller. Phys. Rev. E 56, 2496 - 2507 (1997). [Preview Abstract] |
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