Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F18: Quantum Wires and 1-Dimensional Nanostructures: Transport and Electronic Properties |
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Sponsoring Units: DCMP DMP Chair: Joseph Hagmann, NIST -Natl Inst of Stds & Tech Room: LACC 306B |
Tuesday, March 6, 2018 11:15AM - 11:27AM |
F18.00001: The Observability of the Quantum Pinch Effect in Magnetized Semiconducting Quantum Wires Manvir Kushwaha We investigate a two-component, cylindrical, quasi-one-dimensional quantum plasma subjected to |
Tuesday, March 6, 2018 11:27AM - 11:39AM |
F18.00002: Manipulating Quantum Interference Effect and Magnetotransport of ZnO Nanowires through Interfacial Doping Nan Pan, Siwen Zhao, Huaiyi Ding, Xiaoping Wang ZnO possesses outstanding excitonic properties but suffers from moderate electron transport properties, to construct a high-performance electron and exciton system on the same unit of a ZnO nanostructure is still a challenge. Gifting ZnO nanowires (NWs) with unique interfacial doping profiles holds the key to build a freeway of carriers, by introducing a tubular, high-mobility conductive channel built in and shielded by the surrounding ZnO. For this purpose, we prepared interfacial Al-doped (IAD) and interfacial natively-doped (IND) ZnO NWs by introducing atomic-layer interfacial-doping between the two steps of CVD growth. Electron transport and magnetotransport behaviors of the NWs were systematically studied. By virtue of the unique architecture, a series of quantum interference effects are clearly observed in the IAD ZnO NWs, including weak localization, universal conductance fluctuation and Altshuler-Aronov-Spivak oscillations. The phase-coherence length (L_{φ}) of electrons exceeds 100 nm, much longer than those in the IND NWs and most conventionally-doped ZnO. The ability to efficiently manipulate a variety of quantum interference effects in ZnO NWs is very desirable for the applications in nano-optoelectronics, nano-&quantum-electronics and solid-state quantum computing. |
Tuesday, March 6, 2018 11:39AM - 11:51AM |
F18.00003: Quantum transport of nanoscale Hall crosses ADITI NETHWEWALA, Anthony Tylan-Tyler, Yuhe Tang, Jianan Li, Hyungwoo Lee, Jungwoo Lee, Chang-Beom Eom, Patrick Irvin, Jeremy Levy Quantized Hall resistance in 2D electron systems arises due to edge modes. However, quantum transport in the extreme 1D limit is not as well understood, because quasi-1D semiconductor devices are highly susceptible to localization from disorder. Highly ballistic electron waveguides can now be routinely created at the LaAlO3/SrTiO3 (LAO/STO) interface using conductive atomic force microscopy lithography. These channels exhibit quantized ballistic conduction which is associated with lateral and vertical confinement within the waveguide. In this work, we investigate the transport characteristics of nanoscale Hall crosses. By creating transverse voltage probing leads inside the gated region of the waveguide, we can explore the interplay between confinement potential and magnetic field, and potentially investigate the transition between 1D waveguide modes and 2D edge states. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F18.00004: Orbital contributions to the electron g-factor in semiconductor nanowires Georg Winkler, Daniel Varjas, Rafal Skolasinski, Alexey Soluyanov, Matthias Troyer, Michael Wimmer Recent experiments on Majorana fermions in semiconductor nanowires [Albrecht et al., Nat. 531, 206 (2016)] revealed a surprisingly large electronic Land\'e g-factor, several times larger than the bulk value - contrary to the expectation that confinement reduces the g-factor. Here we assess the role of orbital contributions to the electron g-factor in nanowires and quantum dots. We show that an LS coupling in higher subbands leads to an enhancement of the g-factor of an order of magnitude or more for small effective mass semiconductors. We validate our theoretical finding with simulations of InAs and InSb, showing that the effect persists even if cylindrical symmetry is broken. A huge anisotropy of the enhanced g-factors under magnetic field rotation allows for a straightforward experimental test of this theory. |
Tuesday, March 6, 2018 12:03PM - 12:15PM |
F18.00005: Hole Spins in Ge/Si Nanowires Florian Froning, Mirko Rehmann, Joost Ridderbos, Matthias Brauns, Erik Bakkers, Floris Zwanenburg, Dominik Zumbuhl, Floris Braakman Ge/Si core/shell nanowires form a promising platform to implement a unique kind of spin qubit that is highly controllable and highly coherent. Both silicon and germanium can be isotopically purified to contain virtually no non-zero nuclear spins. Moreover, hole spins have due to their p-wave character zero contact-hyperfine interaction with any nuclear spins. These factors promise high coherence times of qubits defined by single holes in Ge/Si nanowires. |
Tuesday, March 6, 2018 12:15PM - 12:27PM |
F18.00006: Parity Symmetry Protected Spin Entanglement in the Two Impurity Model Benedikt Lechtenberg, Frithjof Anders We consider the Two Impurity Kondo Model where two spin ½ impurity spins, separated by a distance R, are coupled via a Heisenberg interaction to the electron spin densities of a conduction band. |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F18.00007: Spin Manipulation in One Dimensional Structures Michael Pepper, Chengyu Yan, Sanjeev Kumar, Kalarikad Thomas, David Ritchie, Patrick See, Jonathan Griffiths, Ian Farrer, Geraint Jones We have investigated electron injection, in GaAs, from a quasi one-dimensional region into a two-dimensional electron gas. The spin texture of the injected electron is obtained by measuring focussing and we find that a spin separation is observed which is dependent on the length of the one-dimensional injector, the role of spin-orbit coupling in the 2D region is found to be dependent on the degree of polarisation of the injected electrons. The magnitude of the 0.7 anomaly follows the degree of spin polarisation which can be manipulated by injector geometry. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F18.00008: Edge state spectroscopy in GaAs quantum wires Taras Patlatiuk, C. Scheller, D. Hill, Yaroslav Tserkovnyak, Amir Yacoby, Loren Pfeiffer, K West, Dominik Zumbuhl We probe the integer quantum Hall edge states in a GaAs/AlGaAs 2D electron gas at low electron temperature T_{e }≈ 10mK using an adjacent, tunnel coupled quantum wire. The tunnelling current peaks when energy and momentum conservation are fulfilled. A vector magnetic field provides a momentum kick to the tunnelling electrons and allows for spectroscopic imaging of more than the first ten Landau level edge states with nanometer real space resolution and down to magnetic fields around 10 mT where n_{bulk} ≈ 500. Upon increasing the field, these states are compressed towards the sample edge, until eventually they become magnetically depopulated and move back into the bulk. In addition the spectroscopy experiment reveals spin splitting, fermi-level pinning, demonstrates the chiral nature of the current carrying edge states, and allows us to extract the exchange interaction in the quantum Hall regime. Theoretical predictions using both, an analytical model and numerical solutions from a single particle Schrödinger solver for hard wall confined Landau levels show excellent agreement with the experiment over the entire range of magnetic field. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F18.00009: Superconducting Tunneling Spectroscopy of InSb Nanowires John Jeffrey Damasco, Stephen Gill, Sasa Gazibegovic, Erik Bakkers, Nadya Mason Semiconducting InSb nanowires that are proximity-coupled to s-wave superconductors are strong candidates to host Majorana zero modes, which are non-abelian anyonic quasiparticles that may be "braided" in a two-dimensional system to serve as quantum logic gates. This motivates an in-depth study of the quasiparticle transport inside the nanowire. First, we present a technique to construct minimally invasive superconducting tunnel probes on the 1.2 micron-long nanowire devices, which show Fabry-Perot signatures, implying coherent electron transport. We then discuss the gate- and bias-dependence of tunneling measurements, which demonstrate the functionality of the tunnel probes on the nanowires. Finally, we demonstrate non-equilibrium tunneling spectroscopy measurements, which suggest that strong electron-electron interactions characterize the quasiparticle transport within the nanowires. |
Tuesday, March 6, 2018 1:03PM - 1:15PM |
F18.00010: Width Dependent Transport Properties of Manganite Nanostrips Yang Yu, Qian Shi, Hanxuan Lin, Wenbin Wang, Lifeng Yin, Jian Shen Manganites are known to have pronounced electronic phase separation (EPS) phenomena that dominate their physical properties. Under spatial confinement, the role of EPS may become different. In this work, we fabricate series of nanostrips with different widths from a single La_{5/12}Pr_{5/24}Ca_{3/8}MnO_{3} thin film grown on LaAlO_{3} (001) substrate. The widths of the nanostrips range from 1.5um to 50nm. We measured the transport properties of the nanostrips at different temperatures and external magnetic fields. Interestingly, the resistivity of the strips decreases with decreasing width. The phase competition was observed to occur most dramatically at 700 nm wide nanostrip, which has the highest critical magnetic fields for metal-insulator-transition. The interplay between EPS and the edge effect of the nanostrips plays a critical role for the observed width dependence of the transport behavior. |
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F18.00011: Carrier Transport in Axial Silicon-Germanium Nanowire Heterojunctions Leonid Tsybeskov, Xaolu Wang, David Lockwood, Xiaohua Wu, Theodore Kamins Recent advances in forming semiconductor heterojunctions within nanowires (NWs) show that the known limitations in the lattice-mismatched hetero-growth should be reconsidered. In this work, we produced axial Si-Ge heterojunction NWs and analyzed their structural and electrical properties. The observed non-linear and rectifying current-voltage characteristics, strong flicker noise and damped current oscillations with frequencies of 20-30 MHz are explained using the proposed SiGe heterojunction NW energy band diagram including energy states associated with the NW near-surface structural imperfections revealed by transmission electron microscopy. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F18.00012: Designing Nanomagnet Arrays for an Engineered Spin-Orbit Gap in Si Leon Maurer, John Gamble, Lisa Tracy, Tzu-Ming Lu Materials with strong spin-orbit coupling (SOC) are required for a variety of proposed quantum computing and spintronic devices. While bulk Si does not have a usable SOC, nanomagnet arrays (NMAs) can create an effective SOC-induced gap in Si/SiGe nanowires by producing a spatially rotating magnetic field. We consider in detail how realistic magnet geometry, strength, and polarization affect the spin-orbit gap. After carefully modeling magnetic fields from the NMAs, band structure calculations indicate which designs are feasible. We find that some previously proposed designs do not result in a meaningful spin-orbit gap. By optimizing device geometry, we propose experimentally realizable designs. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F18.00013: Non-Coulombic frictional drag currents in coupled LaAlO_{3}/SrTiO_{3} nanowires Yuhe Tang, Anthony Tylan-Tyler, Hyungwoo Lee, Jungwoo Lee, Michelle Tomczyk, Mengchen Huang, Chang-Beom Eom, Patrick Irvin, Jeremy Levy Frictional drag phenomena are investigated in coupled nanowires formed at LaAlO_{3}/SrTiO_{3} heterointerfaces. The weak decay of drag resistance with increasing wire separation rules out Coulomb interactions as the dominant coupling mechanism. The observed unidirectional current drag is explained using a simple model that invokes slight asymmetries within nanowires. These results provide new insights into non-Coulombic electron-electron interaction effects that must be accounted for in any full description of electron transport at oxide interfaces. |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F18.00014: Towards room-temperature superconductivity in low-dimensional carbon nanostructures David Tomanek, Dan Liu, Savas Berber, Dogan Erbahar We propose to raise the critical temperature T_{c} for superconductivity in doped C_{60} molecular crystals by increasing the electronic density of states at the Fermi level N(E_{F}) and thus the electron-phonon coupling constant in low-dimensional C_{60} nanoarrays. We consider both electron and hole doping and present numerical results for N(E_{F}), which increases with decreasing bandwidth of the partly filled h_{u} and t_{1u} derived frontier bands with decreasing coordination number of C_{60}. Whereas a significant increase of N(E_{F}) occurs in 2D arrays of doped C_{60} intercalated in-between graphene layers, we propose that the highest T_{c} values approaching room temperature may occur in bundles of nanotubes filled by 1D arrays of externally doped C_{60} or La@C_{60}, or in diluted 3D crystals, where quasi-1D arrangements of C_{60} form percolation paths. |
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