Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session W50: Focus Session: Mesoscopic Materials and Devices III |
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Sponsoring Units: DMP Chair: Ivan Schuller, University of California, San Diego Room: Mile High Ballroom 1D |
Thursday, March 6, 2014 2:30PM - 3:06PM |
W50.00001: Low Frequency Noise in Mesoscopic Magnetic Dots Invited Speaker: E. Dan Dahlberg Measurements of random telegraph noise (RTN) in individual mesoscopic sized NiFe alloy dots will be presented; the dots dimensions are as small as 200nm x 200nm x 10nm. The temperature and magnetic field dependence of the RTN are explained by the energy landscape in the dots; the energy landscape RTN was independently measured [Appl. Phys. Lett. 103, 042409 (2013)]. The research was motivated by questions raised in understanding magnetic noise in magnetic tunnel junctions and giant magnetoresistance devices [Appl. Phys. Lett. 95, 062512 (2009) and Phys. Rev. B 88, 014409 (2013)]. This work was supported primarily by ONR Grant N00014-11-1-0850 and the MRSEC Program of the NSF under Grant No. DMR-0819885. Additional support for work done using the University of Minnesota Nanofabrication Center and Characterization Facility was provided by the NSF NNIN network. [Preview Abstract] |
Thursday, March 6, 2014 3:06PM - 3:18PM |
W50.00002: Tuning the gate efficiency in epitaxially grown InGaAs-InAs heterostructures C.J. Palmstr{\O}m, J. Shabani Fabrication of gate-defined devices on epitaxially grown heterostructures containing InAs layers is highly desirable as it offers the possibility of tuning the confinement potential, carrier density and spin orbit coupling. However, reliable gating has proven difficult in these materials due to gate leakage and hysteretic behavior. In addition, charge traps and Fermi level pinning could screen the applied electric field and significantly reduce the gate efficiency. In this work, we have studied the effect of surface gating on epitaxially grown In$_{0.75}$Ga$_{0.25}$As-InAs-In$_{0.75}$Ga$_{0.25}$As quantum wells. We find that the application of the gate bias barely changes the carrier density and the efficiency of the gate to be poor. However when a positive voltage is applied to the gate during cool down, the gate efficiency is improved. Furthermore, the change in density as a function of gate bias becomes linear and the slope matches closely to the simple capacitance model. We have also fabricated a quantum point contact using a split gate design on a similar structure and achieved full depletion under the gates. The conductance plot as a function of side gate voltages shows quantized plateaus reminiscent of ballistic one-dimensional transport. [Preview Abstract] |
Thursday, March 6, 2014 3:18PM - 3:30PM |
W50.00003: Quantum transport in a single quantum wire fabricated on epitaxially grown InGaAs-InAs heterostructures J. Shabani, Y. Kim, R.M. Lutchyn, C. Nayak, C.J. Palmstr{\O}m One-dimensional semiconducting quantum wires with strong spin orbit interaction represent a unique platform for realization of exotic topological states of matter such as Majorana fermions and novel spintronic devices. Self-assembled nanowires have shown great promise in providing a testbed for one-dimensional experiments. However, controlled assembly of nanowires for scaling and building complex architectures will be challenging. Molecular beam epitaxy (MBE) growth of large area two-dimensional systems combined with semiconductor processing could provide a venue to overcome these issues. In this work, we have studied quantum transport in a single quantum wire fabricated on MBE grown InGaAs-InAs two dimensional electron systems. The magneto-conductance measurements show a clear weak anti localization (WAL) peak and conductance fluctuation at low magnetic field. Further we show that the spin orbit interaction in this quantum wire can be controlled by changing the confinement potential using an external top gate. Quantitative analysis of measured WAL peaks using one-dimensional theoretical model shows an excellent agreement between theory and experiment. [Preview Abstract] |
Thursday, March 6, 2014 3:30PM - 3:42PM |
W50.00004: Proximity effect in a Nb-InAs-Nb nanowire junction Jonathan Baugh, Kaveh Gharavi, Greg Holloway, Chris Haapamaki, Ray R. LaPierre Proximity effect superconductivity in semiconductor-superconductor hybrid devices contains rich physics and could be key to the realization of topological quantum information processing. We have performed a series of low temperature electronic transport measurements on an InAs nanowire contacted with Niobium leads. The channel length ($\sim4$ times the nanowire diameter) is shorter than the electronic phase coherence length, but longer than the elastic mean free path, leading to behaviour that can be modelled by a superconductor-normal-superconductor junction in the diffusive transport regime. A supercurrent is observed below a critical current $I_c$ of up to $\sim$50 nA. The critical current varies with local gate voltages and correlates with the normal state conductance, producing modulation of $I_c$ related to universal conductance fluctuations. An applied magnetic field produces a Gaussian decay of $I_c$, consistent with known theory. Analysis of multiple Andreev reflection corrections to conductance indicates a contact transparency $\approx$0.6. The full results help to shed light on the nature of proximity effect superconductivity in a quasi-one-dimensional semiconductor in the quasi-diffusive regime. [Preview Abstract] |
Thursday, March 6, 2014 3:42PM - 3:54PM |
W50.00005: Thouless dephasing and amplitude modulation of Aharonov-Bohm oscillations in mesoscopic InGaAs/InAlAs interferometers J. J. Heremans, S.L. Ren, Yao Zhang, C.K. Gaspe, S. Vijeyaragunathan, T.D. Mishima, M.B. Santos Aharonov-Bohm oscillations in the low-temperature magnetoresistance of mesoscopic interferometric rings are investigated for their dependence on bias current and temperature, and to explore origins of the observed amplitude modulation in magnetic field. Single-ring interferometers of radius 650 nm and lithographic arm width 300 nm were fabricated on a high-mobility high-density InGaAs/InAlAs heterostructure. The rings show interference oscillations over a wide range of magnetic fields, with amplitudes subject to modulation with applied magnetic field. The quantum phase coherence length is extracted by analysis of the fundamental and higher Fourier components of the oscillations, and by comparative study of the amplitude. The variation of the amplitude with bias current and temperature shows the existence of a critical excitation energy consistent with the Thouless energy for quantum phase smearing. Autocorrelation and Fourier analysis are used to determine the quasi-period of the amplitude modulation, which is found to be consistent with an origin in the magnetic flux threading the finite width of the interferometer arms, changing the mesoscopic realization of the system. Supported by DOE DE-FG02-08ER46532 (VT) and NSF DMR-0520550 (UoO). [Preview Abstract] |
Thursday, March 6, 2014 3:54PM - 4:06PM |
W50.00006: Decoherence mechanisms of Aharonov-Bohm excitons in type-II quantum dots Bidisha Roy, Haojie Ji, Siddharth Dhomkar, Lev Murokh, Jonathan Ludwig, Dmitry Smirnov, Maria Tamargo, Igor Kuskovsky The Aharonov-Bohm (AB) effect is one of the most important verifications of phase coherence of quantum particles. It has been extensively used to study quantum coherence in mesoscopic systems by transport measurements, where contacts play a significant role. The AB effects can also be observed in magneto-photoluminescence (PL) of polarized excitons in quantum rings and type-II quantum dots (QD), which is a contactless technique. The AB effect reveals itself as oscillation(s) in both energy and intensity of the emission. The magnitude of these oscillations directly relates to the quantum coherence of the AB excitons. To study decoherence mechanisms for such AB excitons, and the AB effect in general, we performed temperature dependent magneto-PL on several samples consisting of stacked type-II ZnTe/ZnSe QDs. The PL as a function of the magnetic field exhibits a strong peak, whose magnitude decreases with increasing temperature, due to loss of coherence. The effect persisted up to 30-35 K depending on the sample. This observed decrease in the AB peak is modeled via one-dimensional electron-phonon and electron-electron scattering of ballistic electrons, assuming strong hole confinement, for temperatures above 3K. The physical meaning of the fitting parameters is discussed. [Preview Abstract] |
Thursday, March 6, 2014 4:06PM - 4:18PM |
W50.00007: Generating electron-hole superfluidity in experimentally realizable graphene and GaAs heterostructures David Neilson, Andrea Perali, Andrew Croxall, Alexander Hamilton Exciton bound states in solids between electrons and holes have been predicted to form a superfluid at high temperatures. We present results of determination of the experimental parameter ranges needed for generating electron-hole superfluidity in three different heterostructures: double bilayer graphene, GaAs double quantum wells, and hybrid hole-bilayer graphene -- GaAs electron-quantum well structures. We find that in the double bilayer graphene [1] and GaAs quantum well systems, the sample parameters necessary to generate equilibrium superfluidity of the electron-hole pairs are close to values already achieved in experiments. Our results indicate that the superfluid transition temperatures should be at or above liquid helium in both cases. For the hybrid bilayer graphene -- GaAs quantum well structure, we obtain chiral superfluid states with phase coherence across the graphene--GaAs interface. Our results are based on a mean field approach with self-consistent screening of the pair Coulomb interaction. This approach has been successfully tested in a quantitative way [2] against recent Diffusion Quantum Monte Carlo results in a related system. \\[4pt] [1] A. Perali, \textit{et al.}, Phys. Rev. Lett. \textbf{110}, 146803 (2013)\\[0pt] [2] D. Neilson, \textit{et al., }arXiv:1308.0280 [Preview Abstract] |
Thursday, March 6, 2014 4:18PM - 4:30PM |
W50.00008: Spontaneously broken time reversal symmetry in strongly interacting two dimensional electron systems in Si and Ge Saquib Shamim, S. Mahapatra, G. Scappucci, W.M. Klesse, M.Y. Simmons, Arindam Ghosh Time reversal invariance is a fundamental and robust symmetry of nonmagnetic quantum systems whose violation often results in nontrivial and exotic phenomena ranging from delocalization of electrons, quantum Hall liquid, the quantum anomalous Hall effect in topological insulators or chiral superconductivity predicted in graphene. An external magnetic field or magnetic impurities is employed in experiments to break the time reversal symmetry. Here we show that strong Coulomb interactions can lift the time reversal symmetry in two dimensional systems formed by atomically confined doping of phosphorus (P) atoms inside bulk crystalline silicon and germanium at zero magnetic field. Weak localization corrections to the conductivity and the universal conductance fluctuations were both found to decrease with decreasing doping in the Si:P and Ge:P $\delta $-layers, suggesting delocalization driven by Coulomb interactions. In-plane magnetotransport measurements indicate the presence of local spin fluctuations at low doping, resulting in spontaneous lifting of the time reversal symmetry. Our experiments suggest the existence of a new delocalized many-body state in two dimensions when strongly interacting electrons are confined to narrow half-filled impurity bands. [Preview Abstract] |
Thursday, March 6, 2014 4:30PM - 4:42PM |
W50.00009: Tailoring topological super\-conductivity using super\-cu\-rrents Panagiotis Kotetes, Andreas Heimes, Daniel Mendler, Alexander Shnirman, Gerd Sch\"{o}n Recent experiments have provided the first promising indications of Majorana fermions (MFs) in heterostructures consisting of semiconducting wires and superconductors in the presence of a Zeeman field. By performing a complete classification of engineered topological superconductors (TSCs) [1] we predict that MFs are accessible in quasi-1d Rashba semiconductors with proximity induced superconductivity, even in the absence of magnetism. The only requirement is the presence of a Josephson current, with a suitable direction of flow. Here, we demonstrate how MFs emerge in our proposed setup when multi-wire or multi-channel semiconductors are involved. The crucial effect of the supercurrent flow is to convert the inter-wire/channel spin-orbit coupling into an effective Zeeman term. Finally, we further extend the particular scheme and discuss how the control of supercurrents can be also used to engineer and manipulate TSC in antiferromagnetically doped conventional superconductors.\\[4pt] [1] P. Kotetes, 2013 \textit{New J. Phys.} \textbf{15} 105027 (Focus issue on MFs). [Preview Abstract] |
Thursday, March 6, 2014 4:42PM - 4:54PM |
W50.00010: Origin of the Au/Ge(001) metallic state Ren\'{e} Heimbuch, Mikhail Kuzmin, Nick de Jong, Mark Golden, Harold J.W. Zandvliet Electronic transport in one-dimensional systems is a highly investigated topic, as electronic devices continue to shrink in size further and further. To understand the exotic behavior of electrons in structures of atomic length scales is crucial for future technological advances in electronics. We studied the spatial variation of the metallic state of the Au-induced nanowires on Ge(001). Spatial maps of the differential conductivity of the metallic state, which has its energy minimum at 0.1-0.15 eV below the Fermi level, are recorded with a low-temperature scanning tunneling microscope. The metallic state is not located on the ridges of the nanowires, but in the troughs between the nanowires. Electronic end effects were investigated and spatial profiling of the density of states, as a function of temperature reveal great inside into Tomonaga-Luttinger liquid in 1D electron systems. [Preview Abstract] |
Thursday, March 6, 2014 4:54PM - 5:06PM |
W50.00011: Quantum Transport in LaAlO$_3$/SrTiO$_3$ Nanowire Cavities Guanglei Cheng, Michelle Tomczyk, Shicheng Lu, Mengchen Huang, Josh Veazey, Patrick Irvin, Sangwoo Ryu, Chang-Beom Eom, Jeremy Levy Hybrid superconductor-nanowire devices have attracted extensive interest for quantum computation based on electron spins, superconducting quantum bits and Majorana fermions. Such devices, which regulate the flow of single Cooper pairs and electron quasiparticles, are conventionally created by aligning normal nanowires in intimate contact with superconductors. New opportunities for creating such devices exist using a new class of complex-oxide interfaces. In particular, the interface of two insulating oxides, LaAlO$_3$ and SrTiO$_3$, exhibits a rich set of gate-tunable phases including intrinsic superconductivity, metal-insulator transition, and spin-orbit interaction. Here we investigate a superconducting nanowire cavity created by reversible ``write'' and ``erase'' processes using a conductive atomic force microscope (c-AFM) tip.\footnote{C. Cen \textit{et al.} Nat. Mater. \textbf{7}, 298 (2008)} Low-temperature magnetotransport experiments show that electrons can be subject to Coulomb blockade, Cooper pair tunneling, Andreev reflection and Fabry-Perot interference in a single device. [Preview Abstract] |
Thursday, March 6, 2014 5:06PM - 5:18PM |
W50.00012: Black Phosphorus Field-effect Transistors Likai Li, Yijun Yu, Guojun Ye, Qingqin Ge, Xuedong Ou, Hua Wu, Donglai Feng, Xianhui Chen, Yuanbo Zhang Black phosphorus is a layered allotropy of phosphorus that closely resembles graphite. But unlike graphene monolayer, black phosphorus is a semiconductor with a predicted band gap of $\sim$2 eV, which reduces to $\sim$0.3 eV in the bulk crystal. We investigate the electric property of black phosphors thin flakes with thickness down to a few nanometers. High conductance modulations up to 10$^{6}$ and field effect mobility up to 1000 cm$^{2}$/Vs at room temperature are achieved in a Metal-Insulator-Silicon (MIS) field effect transistor structure. We further uncover the mechanism that limits the mobility in black phosphorus thin flakes through temperature-dependent electronic transport measurements. Our results provide the first basic understanding of the electronic properties of black phosphorus thin flakes, and will greatly facilitate further exploration of its future applications. [Preview Abstract] |
Thursday, March 6, 2014 5:18PM - 5:30PM |
W50.00013: The Role of Catalytic Substrate Morphology on the Shape and Domain Size of Two-Dimensional Boron Nitride Sheets Mark Griep, Roland Tay, Travis Tumlin, Edwin Teo, Govind Mallick, Shashi Karna Two-dimensional (2D) nanomaterials, including graphene and boron nitride (BN), has been of intense interest in recent years due to their exceptional electronic, thermal, and mechanical properties. Tailoring these novel properties to their maximum potential requires precise control of the atomic layer growth process. In recent years, catalytic growth of 2-D nanomaterials using chemical vapor deposition (CVD) process has emerged as an attractive approach due to their low-cost, scalalibility, and ability totransfer the grown materials on various substrates. In this approach, The the morphology and purity of the catalytic surface plays a critical role on the shape, size, and growth kintectics of the 2D nanomaterial. In this work, we present the results of our systematic studies of the role of catalytic surface morphology on the shape and domain size of CVD grown hexagonal boron nitride (hBN) films. The present work clearly demonstrates that that the presence of surface roghness in the form of ridges leads to a preferential growth of small-domain triangular BN sheets. A 10 to 100-fold reduction in the surfcae roughness leads to increased domain BN triangles, eventually transitioning to large-domain hexagonal shaped hBN sheets. [Preview Abstract] |
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