Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session G14: Focus Session: Mesoscopic Materials and Devices |
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Sponsoring Units: DMP Chair: Nina Markovic, Johns Hopkins University Room: 008A |
Tuesday, March 3, 2015 11:15AM - 11:51AM |
G14.00001: Nano Josephson Superconducting Tunnel Junctions Direct-patterned in Y-Ba-Cu-O with a Focused Helium Ion Beam Invited Speaker: Shane Cybart Functional oxide materials are very sensitive to disorder and many transition from metal to insulator as disorder increases. This phenomenon has been used for many years to fabricate Josephson junctions in cuprate high-transition-temperature ($T_{\mathrm{C}})$ superconductors like YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7-\delta }}$ (YBCO). In this approach, ion irradiation is used to selectively disorder a nanoscale region of material between two superconducting electrodes, that serves as a Josephson barrier. Historically, the barriers created in this manner have been tens of nanometers in length which only allowed for the creation of superconductor-reduced-$T_{\mathrm{C}}$-superconductor-superconductor junctions. We have reduced the length of the Josephson barriers to just a few nm by using a 500 pm diameter focused beam of helium ions. The smaller length of these barriers allows us to change the properties continuously from reduced $T_{\mathrm{C}}$ superconductor to normal metal, to insulator as a function of irradiation dose. We present data for several Josephson junctions fabricated in this manner using controlled doses. Our results are well-described by the Blonder, Tinkham, Klapwijk model (BTK) for microscopic electrical transport at an interface between a superconductor and a normal material. This model uses a single parameter related to barrier strength (irradiation dose in our experiments) and can describe current-voltage characteristics for barriers ranging from a strong barrier, such as an insulator in a tunnel junction, to a weak barrier like a normal metal. In the case of a strong barrier (a tunnel barrier) the only transport mechanism for Cooper pairs is direct Josephson tunneling whereas in the case of weaker barriers both tunneling and Andreev reflection occur. This technique could provide a reliable method for the realization of reproducible high-$T_{\mathrm{C}}$ Josephson junctions. I will present details of the technique and analysis of the results. [Preview Abstract] |
Tuesday, March 3, 2015 11:51AM - 12:03PM |
G14.00002: Controlled fabrication of sub-15nm nanostructures of an arbitrary conductive material Hannah Hughes, Tyler Morgan-Wall, Nikolaus Hartman, Nina Markovic Traditional lithographic techniques that are used to produce low-dimensional nanostructures are often limited in both the minimum achievable size and the control over the final resistance of the device. To achieve such control, we had developed a wet etching method with in-situ monitoring of resistance, but this method relies on an oxide layer to electrically isolate the monitoring circuit from the etching solution. We will present a more general method for fabricating sub-15 nm nanostructures out of various conductive materials without a need for an oxide layer. [Preview Abstract] |
Tuesday, March 3, 2015 12:03PM - 12:15PM |
G14.00003: Black Silicon Formation in Cryogenic Reactive Ion Etching David Abi Saab, Philippe Basset, Matthew J. Pierotti, Matthew L. Trawick, Dan E. Angelescu We present both experimental data and computational modeling that explain some aspects of the formation of black silicon during cryogenic reactive ion etching (RIE) processes. We generate a phase diagram that predicts combinations of RIE parameters that lead to different black silicon geometries. We also show that the combination of needle- and hole-like features of various heights and depths in black silicon creates a uniquely smooth transition in refractive index that is responsible for the material's low optical reflectivity. These details are captured by our model and confirmed by focused ion beam (FIB) nanotomography and scanning electron microscopy of black silicon surfaces during various stages of development. The model also correctly describes dynamical characteristics such as the dependence of aspect ratio on process time, and the prediction of new etching fronts appearing at topographical saddle points. [Preview Abstract] |
Tuesday, March 3, 2015 12:15PM - 12:27PM |
G14.00004: Spin-filtering in nickel-oxide atomic junctions Ran Vardimon, Marina Klionsky, Oren Tal Generating a highly spin-polarized current governed by electrons of a single spin type is of central importance for realization of nanoscale spintronics. We report on the detection of up to 100{\%} spin-polarized currents across nickel-oxide atomic junctions formed between two nickel electrodes under cryogenic vacuum conditions. The degree of spin polarization is probed by analyzing the quantum shot noise resulting from the discrete statistics of electron transport. In sharp contrast to the insulating character of bulk nickel-oxide, our results can be explained by the emergence of a local half-metallic electronic structure, stemming from the distinct orbital hybridization of the low-coordinated junction atoms. These findings illuminate new directions for spin transport manipulations by atomic-scale material design. [Preview Abstract] |
Tuesday, March 3, 2015 12:27PM - 12:39PM |
G14.00005: Evolution of Ni nanofilaments and electromagnetic coupling in the resistive switching of NiO Yuxiang Luo Resistive switching effect in conductor/insulator/conductor thin-film stacks is promising for resistance random access memory with high-density, fast speed, low power dissipation and high endurance, as well as novel computer logic architectures. NiO is a model system for the resistive switching effect and the formation/rupture of Ni nanofilaments is considered to be essential. However, it is not clear how the nanofilaments evolve in the switching process. Moreover, since Ni nanofilaments should be ferromagnetic, it provides an opportunity to explore the electromagnetic coupling in this system. Here, we report a direct observation of Ni nanofilaments and their specific evolution process for the first time by a combination of various measurements and theoretical calculation. We found that multi-nanofilaments are involved in the low resistance state and the nanofilaments become thin and rupture separately in the RESET process with subsequent increase of the rupture gaps. Theoretical calculations reveal the role of oxygen vacancy amount in the evolution of Ni nanofilaments. We also demonstrate electromagnetic coupling in this system, which opens a new avenue for multifunctional devices. [Preview Abstract] |
Tuesday, March 3, 2015 12:39PM - 12:51PM |
G14.00006: Electronic Transport properties of SET and REST states of interfacial phase-change memory Hisao Nakamura, Junji Tominaga, Yoshihiro Asai, Ivan Rungger, Awadhesh Narayan, Stefano Sanvito The phase change memory (PCM) is one of most promising nonvolatile information storage technologies. Recently, the superlattice structure of GeTe/Sb2Te3 is proposed as PCM to reduce the restive switching energy. This PCM is called interfacial PCM (iPCM) and it is considered that SET and RESET states are realized only by the flip-flop transition of Ge atoms in crystal phase because of small loss of entropy. Furthermore, the GeTe is sandwiched by Sb2Te3 topological insulator. In this study, we performed the first principles electric transport calculations including spin-orbit interactions. We presents the mechanism of resistive switch by the transition of Ge atoms as well as the volume change effect and the role of spin-orbit interaction to resistance ration of SET and RESE states. [Preview Abstract] |
Tuesday, March 3, 2015 12:51PM - 1:03PM |
G14.00007: A mesoscopic magnetron as an open quantum system Tadeusz Pudlik, Antonio Castro Neto, David Campbell The emergence of materials with room temperature electron mean free paths of a micron or more opens up new possibilities in the design of solid state devices. One such potential new paradigm are solid state quasi-free electron devices, which promise to combine the wide frequency tunability of classical vacuum tube devices with the small size and low costs of semiconductor technology. As a step towards realistic models of these devices, we develop a quantum mechanical description of a mesoscopic magnetron, in which the vacuum chamber of traditional magnetron is replaced with a semiconductor. We show that the problem can be mapped to a Bose-Hubbard dimer coupled to a dissipative bath and study the effect of the band structure of the medium on device performance. [Preview Abstract] |
Tuesday, March 3, 2015 1:03PM - 1:15PM |
G14.00008: Interplay between magnetic anisotropy and vibron-assisted tunneling in a single-molecule magnet transistor Kyungwha Park, Alexander McCaskey, Yoh Yamamoto, Michael Warnock, Enrique Burzuri, Herre van der Zant Molecules trapped in single-molecule devices vibrate with discrete frequencies characteristic to the molecules, and the molecular vibrations can couple to electronic charge and/or spin degrees of freedom. For a significant electron-vibron coupling, electrons may tunnel via the vibrational excitations unique to the molecules. Recently, electron transport via individual anisotropic magnetic molecules (referred to as single-molecule magnets) has been observed in single-molecule transistors. A single-molecule magnet has a large spin moment and a large magnetic anisotropy barrier. So far, studies of electron-vibron coupling effects in single-molecule devices, are mainly for isotropic molecules. Here we investigate how the electron-vibron coupling influences electron transport via a single-molecule magnet Fe$_4$, by using a model Hamiltonian with parameter values obtained from density-functional theory (arXiv:1411.2677). We show that the magnetic anisotropy of the Fe$_4$ induces new features in vibrational conductance peaks and creates vibrational satellite peaks. The main and satellite peak heights have a strong, unusual dependence on the direction and magnitude of applied magnetic field, because the magnetic anisotropy barrier is comparable to vibrational energies. [Preview Abstract] |
Tuesday, March 3, 2015 1:15PM - 1:27PM |
G14.00009: Single Molecule Magnetic Force Detection with a Carbon Nanotube Resonator Kyle Willick, Sean Walker, Jonathan Baugh Single molecule magnets (SMMs) sit at the boundary between macroscopic magnetic behaviour and quantum phenomena. Detecting the magnetic moment of an individual SMM would allow exploration of this boundary, and could enable technological applications based on SMMs such as quantum information processing. Detection of these magnetic moments remains an experimental challenge, particularly at the time scales of relaxation and decoherence. We present a technique for sensitive magnetic force detection that should permit such measurements. A suspended carbon nanotube (CNT) mechanical resonator is combined with a magnetic field gradient generated by a ferromagnetic gate electrode, which couples the magnetic moment of a nanomagnet to the resonant motion of the CNT. Numerical calculations of the mechanical resonance show that resonant frequency shifts on the order of a few kHz arise due to single Bohr magneton changes in magnetic moment. A signal-to-noise analysis based on thermomechanical noise shows that magnetic switching at the level of a Bohr magneton can be measured in a single shot on timescales as short as 10$\mu$s. This sensitivity should enable studies of the spin dynamics of an isolated SMM, within the spin relaxation timescales for many available SMMs. [Preview Abstract] |
Tuesday, March 3, 2015 1:27PM - 1:39PM |
G14.00010: Leakage radiation microscope for observation of non-transparent samples Juan M. Merlo, Fan Ye, Michael J. Burns, Michael J. Naughton Surface plasmon interactions are confined to be proximate to the surface on which they are excited, such that common optical microscopic imaging is precluded. In order to overcome this limitation, the leakage radiation microscopy technique can be employed to obtain images of interactions at a metallic surface where the surface plasmon propagates [1]. A disadvantage of this configuration is that the metallic layer must be optically thin, resulting in the (additional) direct observation of the excitation source. Here, we describe a leakage radiation microscope that can be used to observe plasmonic interactions in optically $non-transparent$ samples [2]. We show that theoretically-calculated values of the surface plasmon wavelength and propagation length agree with the measured values. This configuration opens the possibility to study important effects where samples are optically non-transparent, as in plasmonic cavities, without the use of time-consuming near-field scanning optical microscopy. \\ $[1]$ A. Hohenau, J. R. Krenn, A. Drezet, O. Mollet, S. Huant, C. Genet, B. Stein, and T. W. Ebbesen, Opt. Express $\bf{19}$, 25749 (2011). \\ $[2]$ J. M. Merlo, F. Ye, M. J. Naughton, Opt. Express $\bf{22}$, 22895 (2014). [Preview Abstract] |
Tuesday, March 3, 2015 1:39PM - 1:51PM |
G14.00011: Random Telegraph Signal in a Metallic Double-Dot System Yuval Vardi, Avraham Guttman, Israel Bar-Joseph Double quantum dot systems offer a unique opportunity for studying the world of quantum transport. This stems from the ability to localize an electron in a limited region in space on the dot, and monitor its presence and properties. Another system, in which electrons can be stored and measured, is an electronic trap in solid. The electrons in such a trap are better isolated from the environment. However, their measurement and control are more difficult. Here we demonstrate how these two systems, metallic double-dots and electronic traps, are combined to yield a hybrid structure in which an electron can be stored for long durations and can be easily detected and measured. We investigate the dynamics of a single electron surface trap, embedded in a self-assembly metallic double-dot system. The charging and discharging of the trap by a single electron is manifested as a random telegraph signal of the current through the double-dot device. We find that we can control the duration that an electron resides in the trap through the current, varying it between fractions of a second to more than an hour, at the Coulomb blockade region. We suggest that the observed switching is the electrical manifestation of the optical blinking phenomenon, commonly observed in semiconductor quantum dots. [Preview Abstract] |
Tuesday, March 3, 2015 1:51PM - 2:03PM |
G14.00012: Negative Differential Transconductance in Silicon Quantum Well MOSFET/Bipolar Hybrid Transistors Clint Naquin, Mark Lee, Hal Edwards, Tathagata Chatterjee, Guru Mathur, Ken Maggio Introducing explicit quantum transport into Si transistors in a manner amenable to industrial fabrication has proven challenging. Hybrid field-effect / bipolar Si transistors fabricated on an industrial 45 nm process line are shown to demonstrate explicit quantum transport signatures. These transistors incorporate a lateral ion implantation-defined quantum well (QW) whose potential depth is controlled by a gate voltage (VG). Quantum transport in the form of negative differential transconductance (NDTC) is observed to temperatures \textgreater 200 K. The NDTC is tied to a non-monotonic dependence of bipolar current gain on VG that reduces drain-source current through the QW. These devices establish the feasibility of exploiting quantum transport to transform the performance horizons of Si devices fabricated in an industrially scalable manner. [Preview Abstract] |
Tuesday, March 3, 2015 2:03PM - 2:15PM |
G14.00013: Single-Molecule Diodes with High On/Off Ratios Through Environmental Control Brian Capozzi, Jianlong Xia, Emma Dell, Olgun Adak, Zhen-Fei Liu, Jeffrey Neaton, Luis Campos, Latha Venkataraman Single-Molecule diodes were first proposed with an asymmetric molecule comprising a donor-bridge-acceptor architecture to mimic a semiconductor p-n junction. Progress in molecular electronics has led to the realization of several single-molecule diodes; these have relied on asymmetric molecular backbones, asymmetric molecule-electrode linkers, or asymmetric electrode materials. Despite these advances, molecular diodes have had limited potential for functional applications due to several pitfalls, including low rectification ratios (``on''/``off'' current ratios \textless 10). Here, we introduce a powerful approach for inducing rectification in conventionally symmetric single-molecule junctions, taking advantage of environmental factors about the junction. By utilizing an asymmetric environment instead of an asymmetric molecule, we reproducibly achieve high rectification ratios at low operating voltages for molecular junctions based on a family of symmetric small-gap molecules. This technique serves as an unconventional approach for developing functional molecular-scale devices and probing their charge transport characteristics. Furthermore, this technique should be applicable to other nanoscale devices, providing a general route for tuning device properties. [Preview Abstract] |
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