Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A49: Nanostructures: Interaction Effects |
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Sponsoring Units: DCMP Chair: Michael Scheibner, University of California, Merced Room: Mile High Ballroom 1C |
Monday, March 3, 2014 8:00AM - 8:12AM |
A49.00001: Elementary Electronic Excitations of quantum wells probed by resonant Raman scattering Virgilio Anjos, Alison Arantes, Maria Jose Bell Electron-electron interactions and quantization may be investigated by means of Raman scattering. Its selection rules on the incoming and outgoing light polarizations allows one to study the intersubband charge- and spin-density excitations. The first gives information about the collective charge-density excitations raised by Coulombian interactions. The latter only collective spin-density excitations due to exchange-correlation effects are present. When the incoming laser light matches an optical gap of the host semiconductor, the electron gas presents also excitations whose energies turn out to be close to the bare electronic transitions of the conduction subbands of the semiconductor. By this reason such excitations are called single-particle excitations. In this work, we study the intersubband excitations of modulation-doped GaAs-AlGaAs quantum-wells where the incoming laser light is resonant with the split-off gap of the GaAs. From the theoretical point of view, we show that the intersubband single-particles excitations are actually \textit{coherent} collective excitations and that physically, a direct correspondence between the resonant Raman scattering and the formation of superconducting state in the BCS theory of normal metals exists. [Preview Abstract] |
Monday, March 3, 2014 8:12AM - 8:24AM |
A49.00002: Collective modes in coupled electronic systems of different dimensionalities Ben Yu-Kuang Hu, E.H. Hwang We consider electronic collective modes in coupled systems in which the individual components have different dimensionalities. Many-body diagramnatic techniques are used to derive formal results for the screened intra- and inter-system Coulomb interaction. We evaluate the screened intra- and inter-system Coulomb interaction within the random phase approximation. We investigate the spatial dependence of the coupled 1-d + 2-d collective modes within the two-dimensional electron gas, and show that the coupled modes within that layer vary from being purely two-dimensional in character far away from the quantum wire to being strongly hybridized close to the wire. We existence of modes which have hybrid properties characteristic of both one- and two-dimensional systems. We also find that in certain circumstances, the coupling between the one- and two-dimensional plasmons causes the one-dimensional plasmons modes experience significant damping and essentially disappear. [Preview Abstract] |
Monday, March 3, 2014 8:24AM - 8:36AM |
A49.00003: The edge-state mediated collective transport in a network of quantum dot array W.Y. Wei, K.T. Lin, D.C. Ling, C.C. Chi, J.C. Chen We report the edge-state mediated transport property of a one-dimensional quantum dot array, consisting of six quantum dots defined by the surface gating technique in the two-dimensional electron gas formed at the interface of the GaAs/AlGaAs heterostructure. The conductance G in high magnetic field (B) exhibits a series of dip structures on the last quantized plateau, and a series of Coulomb blockade peaks before the conductance channel is closed by biasing the gate voltage to a sufficiently negative value. The dips in conductance evolve with B and reveal a pronounced charging effect, which are gradually smeared with increasing temperature. The Coulomb blockade diamonds in the differential conductance spectrum show nested features distinctly different from what are observed in conventional quantum dot systems. After careful data analysis and theoretical modeling, our results suggest that our sample, which although meant to be a serial quantum dot array by design, actually behaves like a parallel dot array under certain specific B and gate voltage. A novel collective quantum transport in the network of quantum dot array mediated by the edge states is responsible for the observed phenomena. [Preview Abstract] |
Monday, March 3, 2014 8:36AM - 8:48AM |
A49.00004: Synthetic helical liquid in a quantum wire Mariana Malard, George Japaridze, Henrik Johannesson We show that the combination of a Dresselhaus interaction and a spatially periodic Rashba interaction leads to the formation of a helical liquid in a quantum wire when the electron-electron interaction is weakly screened. The effect is sustained by a helicity-dependent effective band gap which depends on the size of the Dresselhaus and Rashba spin-orbit couplings. We propose a design for a semiconductor device in which the helical liquid can be realized and probed experimentally. [Preview Abstract] |
Monday, March 3, 2014 8:48AM - 9:00AM |
A49.00005: Correlation between Tc and roughness in Nb/Mo superlattices Juan Pereiro, Thomas Saerbeck, Ivan K. Schuller We have studied the superconducting properties of Nb/Mo superlattices grown by RF sputtering at different temperatures. Both Mo and Nb are elemental superconductors, with opposite behavior of the critical temperature as a function of disorder. The critical temperature of Nb decreases as it disorders, while the critical temperature of Molybdenum increases as it becomes amorphous. In superlattices the disorder is imposed by the growth process within each layer and by the period of the structure. We varied the superlattice period between 2 nm and 45 nm and control the intrinsic disorder by the substrate temperature. The samples were characterized by X-Ray reflectivity, X-Ray diffraction, electrical transport, and magnetization measurements. The behavior of the critical temperature as a function of the period shows two different regimes, depending on whether the crystallite size is imposed by the structure or by the growth temperature, $i.e.$ if the grains are larger or smaller than the period of the structure. Furthermore, we will show a correlation between the critical temperature and the interface roughness. [Preview Abstract] |
Monday, March 3, 2014 9:00AM - 9:12AM |
A49.00006: Non-linear Conductance Study of Electron Correlation Effects in Asymmetric Quantum Point Contacts Hao Zhang, Phillip Wu, Albert Chang Both the linear and non-linear(dI/dV) conductance of highly asymmetric quantum point contacts (QPCs) show evidence of quasi-bound states formation \footnote{P. Wu, P. Li, H. Zhang, A. M. Chang, Phy. Rev. B, 85, 085305(2012)} and Kondo-related physics.\footnote{H. Zhang, P. Wu , A. M. Chang, Phy. Rev. B, 88, 075311(2013)} . The non-linear conductance of highly asymmetric QPCs shows additional peaks near zero bias below the first quantized conductance level ($2e^2/h$) at low temperature (down to 25 mK). We have studied the evolution of these extra peaks by tuning the gate voltages at different temperature and different in plane magnetic field. By investigating the evolution of these extra peaks, which can not be fully understood by conventional theory, we explore the possible connections with electron correlation and spin correlated physics. [Preview Abstract] |
Monday, March 3, 2014 9:12AM - 9:24AM |
A49.00007: Interplay between the Kondo, Rashba, and Zeeman effects Arturo Wong, Kevin Ingersent, Nancy Sandler, Sergio Ulloa Motivated by proposed optical experiments on semiconductor nanostructures, we investigate the properties of a magnetic impurity in a two-dimensional electron gas with strong Rashba spin-orbit interactions when the system is subjected to an effective magnetic field $B$ that couples only to the host spins. Even in the absence of spin-orbit coupling, this problem departs from the well-studied Kondo physics in a field that couples to the impurity and possibly also to the conduction band. Through a combination of perturbative and numerical renormalization-group analysis, we show that the effect of the magnetic field can be subsumed into a spin-splitting of the impurity level. The impurity magnetization is found to be a universal function of $\Gamma B / F T_K$, where $\Gamma$ is the hybridization width of the impurity level, $T_K$ is the Kondo temperature in the absence of the field, and $F$ is a function of $E_R$ and of energy scales associated with the impurity. This behavior contrasts with the standard Kondo effect where $T_K$ alone sets the scale for the magnetic-field-induced destruction of the Kondo effect. [Preview Abstract] |
Monday, March 3, 2014 9:24AM - 9:36AM |
A49.00008: Multichannel Numerical Renormalization Group study of the Anderson Hamiltonian with multiple impurities James Stokes, Robert Konik Using the Numerical Renormalization Group (NRG), the low energy sector of the Anderson Hamiltonian with two impurities in parallel has been previously argued to be consistent with an underscreened spin-1 Kondo effect (R. Zitko and J. Bonca, Phys. Rev. B 76, 241305 (2007); Logan et al., Phys. Rev. B 80, 125117 (2009)). Bethe Ansatz and slave boson calculations have given the ground state as a singlet (M. Kulkarni and R. M. Konik, Phys. Rev. B 83, 245121 (2011)). As an attempt to understand these differences, we have developed a modified NRG routine that takes into account the multiple channels arising from the logarithmic discretization of the Fermi sea. This could conceivably allow for more complicated screening processes suggested by the Bethe ansatz computations. Results of studies using this code for various numbers of impurities and channels will be presented and discussed in relationship to these conflicting views. [Preview Abstract] |
Monday, March 3, 2014 9:36AM - 9:48AM |
A49.00009: Decoherence of an entangled states of a strongly-correlated double quantum dot structure through tunneling processes C.A. B\"usser, F. Heidrich-Meisner The entanglement of the spin state of two quantum dots is investigated out of equilibrium. First, we prepare a two-dot system in a perfect singlet state at time $t=0$. For $t>0$, one of the dots is tunnel-coupled to leads, including a finite voltage. Using the time-dependent density matrix renormalization group method, we study the time evolution of the spin correlations and the concurrence as a function of time since electrons hopping on and off the tunnel-coupled dot lead to decoherence. We observe that the spin correlation between the dots decays exponentially determining a decoherence rate. A similar rate can be defined for the concurrence. We study the dependence of these rates on voltage, tunnel coupling, and Coulomb repulsion and compare our numerical results to a master-equation approach derived for the weak-coupling limit. [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A49.00010: Discovery of supercoupling between heavy-hole and light-hole in self-assembled quantum dots Jun-Wei Luo, Gabriel Bester, Alex Zunger The mixing of quantum states is a fundamental principle of quantum mechanics. In the case of a diatomic molecule, the eigenstates of atom A mix with the ones of atom B to form molecular orbitals with a mixing inversely proportional to the energy separation between the respective eigenvalues. This fundamental result of quantum mechanics leads to the expectation that states that are well separated in energy will tend to retain their own character and avoid mixing. By studying self-assembled quantum dots, often denoted as ``artificial atoms", we show that heavy-hole (HH) states can significantly mix with light-hole (LH) states, despite the fact that they are energetically well separated, through supercoupling --- a coupling meditated by intermediate states (as in superexchange). This new interband coupling mechanism explains light-hole mixing, which is the key quantity for the use of quantum dots in quantum information and quantum optical schemes, such as for the generation of entangled photon pairs, the decoherence of hole states, the optical polarization anisotropy and the preparation of qubits. [Preview Abstract] |
Monday, March 3, 2014 10:00AM - 10:12AM |
A49.00011: Resolution effects on the current measurement in a resonant level model Yasuhiro Yamada, Masatoshi Imada Current measurements have attracted much attention in studies on understanding the intrinsic information of nanoscale systems. Here, we theoretically study the influence of the smallest detectable change in the measurement, i.e. resolution, on the outcomes of the measurements, using an extension of the full counting statistics for a resonant level model. It is shown that the limited resolution of current measurement gives rise to a positive excess noise, which leads to a violation of the Johnson-Nyquist relation naively expected between the measured conductance and the measured current noise. The deviation from the Johnson-Nyquist relation exhibits universal single-parameter scaling with the nondimensional scaling variable $S_0/S_M$ where $S_0$ is the intrinsic noise and $S_M$ represents the characteristic noise determined from the measurement process. In addition, our findings offer an explanation for anomalous enhancement of noise temperature observed in Johnson noise thermometry. [1] Y. Yamada and M. Imada, arXiv:1307.7535. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A49.00012: Visualization of Percolation Path in a Two-Dimensional Array of Nanoparticle Exhibiting Room Temperature Single Electron Effect Jason Kee Yang Ong, Jennifer Kane, Ravi Saraf The conductance of a two-dimensional (2D) metal nanoparticle array is sensitive to local charging of nanoparticles at a single electron level, which leads to a threshold bias, VT caused by Coulomb blockade along the percolation path. As a result, the current flowing through the array of nanoparticles does not obey Ohm's-law. Generally, cryogenic temperatures are required to observe a robust VT. It is theorized that the charge centers posing the Coulomb blockade on the percolation path are fixed and independent of external bias. With the self-assembly of 1D nanoparticle necklaces into 2D array, it was possible to observe VT at room temperature due to the high topological constraint on the percolation path. Along with the success of nanofabrication of nanoparticle necklace array on a substrate using a combined technique of soft-lithography and electron beam writing, a single electron device with a single percolation pathway was tailored where the ``opening'' of the conduction path was directly visualized using field-emission Scanning Electron Microscopy (FESEM) as the Coulomb blockade due to the quenched charge distribution was progressively overcome. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A49.00013: Effect of Substrate Annealing and Seeding on ZnO Nanowires Synthesized Using a Hydrothermal Method Orlando Lopez, Ashley Tucker, Kimberly Singh, Spencer Mamer, Huizhong Xu ZnO nanowires have been extensively studied due to their remarkable mechanical, thermodynamic, electrical and optical properties. Amongst the various ZnO nanowire synthesis methods, the hydrothermal growth method is quite attractive due to its simplicity and tolerable growth conditions. In this work, we apply the hydrothermal method to grow ZnO nanowires on gold-coated glass substrates and study how different pre-growth treatment of the substrates affects the morphology, distribution, and dimensions of the ZnO nanowires. We have found that pre-growth annealing of the substrate at temperatures above 250 $^{\circ}$C is required to have vertically aligned nanowires. Our results have also revealed that the nanowire density and dimension are dramatically different for substrates pre-seeded with ZnO nanoparticles and unseeded substrates. The ZnO nanoparticle seeds play an important role in providing nucleation sites that are much smaller than the critical size of precipitation out of the solution, resulting in nanowires of smaller dimensions for pre-seeded substrates. The dependence of the nanowire dimensions on the precursor concentration for both pre-seed and unseeded samples is also studied and discussed. [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A49.00014: Eshelby Twist and Magic Helical Zinc Oxide Nanowires and Nanotubes Traian Dumitrica, Evgeniya Akatyeva Twisted zinc oxide nanowires and nanotubes were recently synthesized by screw-dislocation growth. We show theoretically that once their diameter increases above a critical size of the order of a few atomic spacings, the existence of these structures can be rationalized in terms of the energetics of surfaces and veritable Eshelby's twist linear elasticity mechanics supplemented by a nonlinear core term. For Burgers vector larger than the minimum allowed one, a twisted nanotube with well-defined thickness, rather than a nanowire, is the most stable nanostructure. Results are assistive for designing ultrathin nanostructures made out of nonlayered materials [1]. \\[4pt] [1] E. Akatyeva and T. Dumitrica, Phys. Rev. Lett. 109, 035501 (2012). [Preview Abstract] |
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