Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C36: Electronic and Transport Phenomena of Nanostructures II |
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Sponsoring Units: DMP DCMP Chair: Paul Simmonds, Boise State University Room: 299 |
Monday, March 13, 2017 2:30PM - 2:42PM |
C36.00001: Magnetically tunable 1D Coulomb drag: Theory Anthony Tylan-Tyler, Yuhe Tang, Jeremy Levy In this work, we examine the Coulomb drag effect in 1D nanowires in close proximity, focusing on experimental parameters relevant to complex-oxide nanostructures. Previous work on this problem examined Coulomb drag through quantum point contacts, where effective capacitive coupling between the 2D leads of the system generates the drag voltage. In our case, the entire system is composed of 1D components and thus a more careful treatment of the Coulomb interactions is required. This more complex environment then leads to the ability to switch the drag voltage by an applied magnetic field without altering the current supplied to the drive system. [Preview Abstract] |
Monday, March 13, 2017 2:42PM - 2:54PM |
C36.00002: Magnetically tunable 1D Coulomb drag: Experiment Yuhe Tang, Anthony Tylan-Tyler, Michelle Tomczyk, Mengchen Huang, Jianan Li, Jung-Woo Lee, Sangwoo Ryu, Chang-Beom Eom, Patrick Irvin, Jeremy Levy In an electronic system with two closely spaced but isolated conductors, current that is sourced in one conductor can induce a current or voltage in the second conductor. This phenomenon, known as “Coulomb drag”, represents a powerful approach to probe Coulomb interactions and electron correlations. Here we examine Coulomb drag in a pair of nanowires created with conductive-AFM lithography at the $LaAlO_3/SrTiO_3$ interface. Coulomb drag measurements are performed by sourcing current in one wire and measuring the induced voltage or current in the other wire. Experimental features depend strongly on magnetic field. At low magnetic fields, the wires can be superconducting, leading to large drag resistance when the wire is driven past the critical current. At high magnetic field, distinct oscillations are observed that are associated with the electron subband structure in the wires. [Preview Abstract] |
Monday, March 13, 2017 2:54PM - 3:06PM |
C36.00003: Electronic homogeneity of nanowire heterostructure Light Emitting Diodes (LEDs) Camelia Selcu, Brelon J. May, A. T. M. Golam Sarwar, Roberto C. Myers In addition to low defect densities and great tunability bandgap within a single heterostructure, the possibility of growing (Al, In,\textunderscore ) GaN nanowire heterostructure LEDs on different substrates while maintaining their high electronic and optical properties makes them very attractive. We investigated the electronic homogeneity of the (Al, In,\textunderscore ) GaN nanowire ensemble by acquiring current maps at certain applied biases using conductive AFM. By taken IVs on individual nanowires, we found that different wires have different turn on voltages and that some of the nanowires degrade due to the applied bias. [Preview Abstract] |
Monday, March 13, 2017 3:06PM - 3:18PM |
C36.00004: Bound state in the continuum in a quantum wire Luiz H. Guessi, Antonio C. Seridonio, Luiz N. Oliveira Bound States in the Continuum (BICs) are states with localized wave-functions even though lying in the continuum. Such states occur because two or more wave-functions or resonances interfere destructively. Here, we theoretically study the emergence of BICs in a quantum wire with two side-coupled adatoms. The adatoms are decoupled from each other, but both are coupled to (i) the same adsorption site and (ii) the two neighboring sites. We employ the spin-degenerate Anderson Hamiltonian to model the system. In the Hubbard I approximation, we have analytically found two BICs associated to the singly- and doubly-occupied impurity levels. To more accurately describe the Coulomb interaction, we have also computed the spectral density with the Numerical Renormalization Group method. The numerical results confirm the presence of the two BICs and, in addition, show the expected Kondo peak at the Fermi level. We have checked that (a) in the absence of Coulomb interactions and (b) for two impurities coupled to the adsorption site only, the BICs leak into the continuum. [Preview Abstract] |
Monday, March 13, 2017 3:18PM - 3:30PM |
C36.00005: Spin-orbit coupling in quasi-one-dimensional Wigner crystals Viktoriia Kornich, Christopher Pedder, Thomas Schmidt We study the effect of Rashba spin-orbit coupling (SOC) on the charge and spin degrees of freedom of a quasi-one-dimensional (quasi-1D) Wigner crystal. As electrons in a quasi-1D Wigner crystal can move in the transverse direction, SOC cannot be gauged away in contrast to the pure 1D case. We show that for weak SOC, a partial gap in the spectrum opens at certain ratios between density of electrons and the inverse Rashba length. We present how the low-energy branch of charge degrees of freedom deviates due to SOC from its usual linear dependence at small wave vectors. In the case of strong SOC, we show that spin sector of a Wigner crystal cannot be described by an isotropic antiferromagnetic Heisenberg Hamiltonian any more, and that instead the ground state of neighboring electrons is mostly a triplet state. We present a new spin sector Hamiltonian and discuss the spectrum of Wigner crystal in this limit. [Preview Abstract] |
Monday, March 13, 2017 3:30PM - 3:42PM |
C36.00006: Conductance of long Aharonov-Bohm-Kondo rings Zheng Shi, Yashar Komijani We calculate the finite temperature linear DC conductance of closed and open long Aharonov-Bohm-Kondo (ABK) rings. We show that, as with the short ABK ring, there is a contribution to the conductance from the connected 4-point Green's function of the conduction electrons. At sufficiently low temperatures this contribution can be eliminated, and the conductance can be expressed as a linear function of the T-matrix of the screening channel. For closed rings we show that at temperatures high compared to the Kondo temperature, the conductance behaves differently for temperatures above and below $v_{F}/L$ where $v_{F}$ is the Fermi velocity and $L$ is the circumference of the ring. For open rings, when the ring arms have both a small transmission and a small reflection, we show from the microscopic model that the ring behaves like a two-path interferometer, and that the Kondo temperature is unaffected by details of the ring. Our findings confirm that ABK rings are potentially useful in the detection of the size of the Kondo screening cloud, the $\pi/2$ scattering phase shift from the Kondo singlet, and the suppression of Aharonov-Bohm oscillations due to inelastic scattering. [Preview Abstract] |
Monday, March 13, 2017 3:42PM - 3:54PM |
C36.00007: Apparent pairing and subperiods in integer quantum Hall interferometers Bernd Rosenow, Giovanni A. Frigeri, Daniel D. Scherer We theoretically investigate the flux and gate voltage dependence of the conductance in an integer quantum Hall Fabry-P\'{e}rot interferometer, taking into account the interactions between the interfering edge mode, a second non-interfering edge mode, and the bulk. We obtain a halving of the flux periodicity, compared to the periodicity found in an interferometer without second edge mode, for weak bulk-edge coupling and sufficiently strong inter-edge interaction. Interestingly, the periodicity reduction occurs when the interferometer operates in the Aharonov-Bohm regime. Even in the regime of strong bulk-edge coupling, this behavior can be observed as a subperiodicity of the interference signal in the Coulomb dominated regime. We do not find evidence for a connection between a reduced flux period and electron pairing, though. Our results are relevant for the interpretation of recent experimental findings and can reproduce the observed features in the conductance. [Preview Abstract] |
Monday, March 13, 2017 3:54PM - 4:06PM |
C36.00008: Photo-conductance of a single Quantum Dot Alexandre Zimmers, Hongyue Wang, Emmanuel Lhuillier, Qian Yu, Benoit Dubertret, Herve Aubin, Christian Ulysse One promising strategy for the development of nanoscale resonant spin sensors is to measure the spin-dependent photo-current in Quantum Dots (QDots) containing spin-dependent recombination centers. To reach single spin sensitivity will require measurements of the photo-conductance of single QDots. We present here an experimental study of the conductance and photo-conductance of single HgSe QDots as function of drain and gate voltage. The evolution of the differential conductance dI/dV spectrum with the gate voltage demonstrates that single HgSe QDots are forming the junction. The amplitude of the gap measured in the differential conductance spectrum changes with the occupation level. A large inter-band gap, 0,85eV, is observed for the empty QDot, a smaller intra-band gap 0,25eV is observed for the doubly occupied QDot. These gap energies are consistent with the values extracted from the optical absorption spectrum. Upon illuminating the QDot junction, we show that the photo-conductive signal produced by this single QDot can be measured with a simple demodulation method. [Preview Abstract] |
Monday, March 13, 2017 4:06PM - 4:18PM |
C36.00009: Single electron capacitance spectroscopy of ultra clean quantum dots in high magnetic field Neal Staley, Raymond Ashoori, Ken West, Kirk Baldwin, Loren Pfeiffer Single quantum dots are mesoscopic semiconducting islands with a tunable occupation number. Interestingly, at low density and magnetic field, they are best described as artificial atoms with weakly interacting electrons, while at high density and field they should show the mesoscopic analog of bulk collective behavior such as the fractional quantum Hall effect. However observing collective behavior in quantum dots has been non trivial due to the extreme difficulty fabricating sufficiently high quality devices. We study the electron addition spectroscopy of ultra clean quantum dots using a capacitance technique. We measure the magnetic field dependence of the ground state energy from a completely depopulated dot, up to large electron number. We find both the expected non-interacting Fock-Darwin like behavior, as well as deviations suggestive of more novel physics. [Preview Abstract] |
Monday, March 13, 2017 4:18PM - 4:30PM |
C36.00010: Impedance measurement of Cobalt doped ZnO Quantum dots. Ram Tiwari, Amrit Kaphle, Parameswar Hari We investigated structural, thermal and electrical properties of ZnO Quantum dots grown by precipitation method. QDs were spin coated on ITO and annealed at various temperatures ranging from 100$^{\mathrm{0}}$C to 300 $^{\mathrm{0}}$C. ZnO QDs were doped with cobalt for concentration ranging from 0-15{\%}. XRD measurement showed increase in bond length, strain, dislocation density and Cell volume as the doping level varied from 0{\%} to 15{\%}. Impedance Spectroscopy measurements represented by Cole-Cole plot showed reduction in resistance as the cobalt doping concentration increased from 0-15{\%}. Thermal activation energy was obtained by plotting resistivity Vs temperature for doped samples at temperatures from 100$^{\mathrm{0}}$C to 300$^{\mathrm{0}}$C. The thermal activation energy decreased from 85.13meV to 58.21meV as doping increased from 0-15{\%}. Relaxation time was extracted by fitting data to RC model. Relaxation time varied from 61.57 ns to 3.76 ns as the cobalt concentration increased from 0{\%} to 15{\%}. We will also discuss applications of cobalt doped ZnO QDs on improving conversion efficiency of solar cells. [Preview Abstract] |
Monday, March 13, 2017 4:30PM - 4:42PM |
C36.00011: Defect states and charge transport in quantum dot solids Nicholas Brawand, Matthew Goldey, Marton Voros, Giulia Galli Defects at the surface of semiconducting quantum dots (QD) give rise to electronic states within the gap, which are detrimental to charge transport properties of QD devices. We investigated charge transport in silicon quantum dots with deep and shallow defect levels, using ab initio calculations and constrained density functional theory.[1] We found that shallow defects may be more detrimental to charge transport than deep ones, with associated transfer rates differing by up to 5 orders of magnitude for the small dots (1-2 nm) considered here. Hence our results indicate that the common assumption that the ability of defects to trap charges is determined by their position in the energy gap of the QD, is too simplistic, and our findings call for a reassessment of the role played by shallow defects in QD devices. Overall, our results highlight the key importance of taking into account the atomistic structural properties of QD surfaces when investigating transport properties. [1] N. P. Brawand, Matthew B. Goldey, Marton Voros, and Giulia Galli, submitted [Preview Abstract] |
Monday, March 13, 2017 4:42PM - 4:54PM |
C36.00012: Tailoring the electronic properties of semiconducting nanocrystal-solids: InAs embedded in SnS$_x$ matrices Emilio Scalise, Stefan Wippermann, Giulia Galli, Dmitri V. Talapin Recent advances in wet chemical techniques enable the facile synthesis of nanocrystals (NCs) and their assembly into complex solid structures (NC-solids), offering exciting prospects for solar energy conversion, light emission and electronic applications. The properties of these composites are strongly determined by structural details at the NC/matrix interface and the composition of the embedding matrix. We carried out a systematic study of the interaction between InAs NCs and SnS$_x$ matrices using a grand canonical \emph{ab initio} thermodynamics approach to identify general trends for the stability of structural motifs possibly occurring at the NC/matrix interface. The resulting models have been used as a basis for \emph{ab initio} molecular dynamics calculations to investigate the impact of different mass densities and stoichiometries on the internal matrix structure and the NC-solids' electronic properties. We demonstrate that both the NC-matrix interface and the internal regions of the matrix show complex structural features, depending on specific synthesis conditions. Thus to obtain a detailed understanding of experimental data it is necessary to take into account such complex interfacial and matrix-internal structures beyond simplified NC-solid models. [Preview Abstract] |
Monday, March 13, 2017 4:54PM - 5:06PM |
C36.00013: Band transport of PbS quantum dot superlattices Yun Liu, Nolan Peard, Jeffrey Grossman The efficiency of PbS based quantum dot (QD) photovoltaics (PV) has risen to the current record of 11.3$\%$. However, continued increase in QDPV efficiency requires substantial improvements in the electronic transport within QD films. Recent reports of bandlike transport in QD superlattices have been shown to enhance carrier mobility due to increased coupling and reduced energetic disorder. In this work, we systematically investigated the effects of ligands and packing geometry on the transport properties of PbS QD superlattices. Treating each QD as a pseudo-atom, conductivities were calculated using density functional theory and Boltzmann transport theory as a function of their various lattice arrangements. Our results show that shorter atomic ligands enhance transport properties compared to longer organic ligands. We also find that higher packing density does not always increase the conductivity; rather the specific coupling facet is also important. Coupling through $\{100\}$ facet in the simple cubic lattice enhances the conductivity by around 50$\%$ compared to coupling through $\{111\}$ facet in body centered cubic configuration. The improved understanding allows us to design superlattice based devices that further enhance the carrier mobilities and improve the PV efficiency [Preview Abstract] |
Monday, March 13, 2017 5:06PM - 5:18PM |
C36.00014: Seeing the strongly-correlated zero-bias anomaly in double quantum dot measurements Rachel Wortis, Joshua Folk, Silvia Luescher, Sylvia Luyben The combination of disorder and interactions generally leads to a suppression in the single-particle density of states in bulk electronic systems. Numerical studies of the Anderson-Hubbard model point to a unique zero-bias anomaly in strongly correlated materials with a width proportional to the inter-site hopping amplitude $t$. A zero-bias anomaly with the same parameter dependence also appears in ensembles of two-site systems. We describe how this zero-bias anomaly in two-site systems is reflected in existing data from double quantum dots, and we propose a method to see the zero bias anomaly explicitly, emphasizing that it is a unique signature of the presence of strong correlations. [Preview Abstract] |
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