Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B36: Electronic and Transport Phenomena of Nanostructures I |
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Sponsoring Units: DMP DCMP Chair: David Strubbe, University of California, Merced Room: 299 |
Monday, March 13, 2017 11:15AM - 11:27AM |
B36.00001: Electron-Phonon interactions in Isotopic Diamond Superlattice Yuki Bando, Masayuki Toyoda, Susumu Saito In isotopic diamond superlattices where $^{12}$C and $^{13}$C diamond layers are alternately stacked, the confinement of carriers to $^{12}$C diamond layers has been demonstrated experimentally. It is expected that the confinement of carriers is caused by the difference of strong electron-phonon interactions between two isotopic diamond layers. However, the details of the phenomena have not been revealed theoretically nor experimentally. The objective of our study is to reveal the electronic structure including electron-phonon interactions and isotope effects in isotopic diamond superlattices. We compute the dependence of lattice vibrations on the thickness of each isotopic diamond layer based on density functional perturbation theory to estimate the effect of electron-phonon interactions. We also compute the electron-phonon interactions based on Allen-Heine-Cardona theory. As a result, it is found that the characteristic electron pockets in diamond are anisotropically modified in thin isotopic diamond superlattices where each isotopic diamond layers are stacked along [001] direction. [Preview Abstract] |
Monday, March 13, 2017 11:27AM - 11:39AM |
B36.00002: Dynamics of Exciton and Polaron Formation in Structurally Tunable Low Dimensional Materials Jason Leicht, Susan Dexheimer We present measurements of the coupled electronic and vibrational dynamics of exciton and polaron formation using femtosecond wavepacket techniques. The experiments are carried out on mixed-valence halide-bridged transition metal linear chain complexes in which the electronic excitations are confined to the one-dimensional geometry defined by the chain. The strength of the electron-phonon coupling that drives the localization dynamics can be systematically controlled via the chemical composition, and we compare the dynamics in PtCl and PtBr, which have strong and intermediate coupling strengths, respectively. In these materials, excitation well above the optical gap energy can result in the formation of charged polarons in addition to the self-trapped excitons that form following excitation near the band edge. Our measurements reveal formation of both types of excitations on femtosecond time scales, accompanied by coherent oscillations at distinct frequencies for each excitation. The rapid polaron formation time, together with the observation of the accompanying vibrational coherence, indicates that the polarons form directly from the initial photoexcitation, rather than by delayed dissociation of primary excitons. [Preview Abstract] |
Monday, March 13, 2017 11:39AM - 11:51AM |
B36.00003: Transport of Indirect Excitons in High Magnetic Fields C. J. Dorow, Y. Y. Kuznetsova, E. V. Calman, L. V. Butov, J. Wilkes, K. L. Campman, A. C. Gossard Spatially- and spectrally-resolved photoluminescence measurements of indirect excitons in high magnetic fields are presented [1]. The high magnetic field regime for excitons is realized when the cyclotron splitting compares to the exciton binding energy. Due to small mass and binding energy, the high magnetic field regime for excitons is achievable in lab, requiring a few Tesla. Long indirect exciton lifetimes allow large exciton transport distances before recombination, giving an opportunity to study transport and relaxation kinetics of indirect magnetoexcitons via optical imaging. Indirect excitons in several Landau level states are realized. $0_{\rm e} - 0_{\rm h}$ indirect magnetoexcitons (formed from electrons and holes at zeroth Landau levels) travel over large distances and form an emission ring around the excitation spot. In contrast, the $1_{\rm e} - 1_{\rm h}$ and $2_{\rm e} - 2_{\rm h}$ states do not exhibit long transport distances, and the spatial profiles of the emission closely follow the laser excitation. The $0_{\rm e} - 0_{\rm h}$ indirect magnetoexciton transport distance reduces with increasing magnetic field. Accompanying theoretical work explains these effects in terms of magnetoexciton energy relaxation and effective mass enhancement. [1] arXiv:1610.03116. [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B36.00004: Spatially and time resolved kinetics of indirect magnetoexcitons Matthew Hasling, Chelsey Dorow, Erica Calman, Leonid Butov, Joe Wilkes, Kenneth Campman, Arthur Gossard The small exciton mass and binding energy give the opportunity to realize the high magnetic field regime for excitons in magnetic fields of few Tesla achievable in lab~ Long lifetimes of indirect exciton give the opportunity to study kinetics of magnetoexciton transport by time-resolved optical imaging of exciton emission. We present spatially and time resolved measurements showing the effect of increased magnetic field on transport of magnetoexcitons. We observe that increased magnetic field leads to slowing down of magnetoexciton transport. [Preview Abstract] |
Monday, March 13, 2017 12:03PM - 12:15PM |
B36.00005: Strongly anisotropic magnetoresistance due to snake states in open tubular nanostructures Ching Hao Chang, Carmine Ortix When a charge carrier moves along an interface switching the chirality of trajectory, it curves back and forth to form snake orbits moving along the interface. Snake orbits have first been realized in semiconducting two-dimensional electron gases (2DEGs) with an interface inverting the magnetic field direction, and have been recently manufactured in graphene using a p-n junction. Snake orbits, however, can also form in tubular nanostructures subject to weak homogeneous magnetic fields. In this talk, I will discuss how in open tubes both the location and the number of snake orbits can be controlled by rotating the field direction, which eventually leads to a large anisotropic magnetoresistance (AMR) up to 80 {\%} in the diffusive transport regime. These results offer a promising route for engineering AMR effects in the absence of both magnetism and spin-orbit coupling effect. [Preview Abstract] |
Monday, March 13, 2017 12:15PM - 12:27PM |
B36.00006: Electron Conduction Mechanism And Inelastic Electron Tunneling Spectroscopy Of Porphyrin In A Nanoscale Molecular Junction Teresa Esposito, Peter H. Dinolfo, Vincent Meunier, Kim Michelle Lewis In order to determine the mechanism for electron conduction through a porphyrin molecular junction, temperature dependent current-voltage (I/V) studies have been performed and compared to existing models of electron transport. Porphyrin molecular junctions are being studied for their potential application as an interconnect in molecular electronics due to their low attenuation factor ($\beta<$0.01 nm$^{-1}$). Based on previous studies of porphyrin molecules the mechanism of conduction is expected to be direct tunneling. Three types of porphyrins are being investigated: a free base porphyrin, and porphyrins with either a zinc or an iron atom ligated to the porphyrin ring. Molecular junctions are formed by depositing porphyrins into a 3-5 nm gap created using a zig-zag electromigration technique from a 30x50 nm gold nanowire. I/V, dI/dV, and d$^2$I/dV$^2$ are measured simultaneously at temperatures from 4.2 to 300 K. d$^2$I/dV$^2$ is the inelastic electron tunneling spectrum (IETS) of the molecular junction, which is used to verify the presence of a molecule in the gap. Peaks in the spectra indicate the excitation of a vibrational mode which are compared to Fourier transform infrared spectroscopy and theoretical density functional theory calculations. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B36.00007: Artificial lattices in nano-patterned GaAs Heterostructure Lingjie Du, Sheng Wang, Diego Scarabelli, Shalom J. Wind, Loren N. Pfeiffer, Ken West, Michael J. Manfra, Vittorio Pellegrini, Aron Pinczuk Artificial lattices in semiconductors have been realized with honeycomb lattices superimposed on 2D electron systems in GaAs quantum well to serve as advanced quantum simulators for probing novel electron behavior in low dimensional systems. Here, we report on recent experimental progresses in artificial lattice studies using the cutting-edge fabrication technology and exploration of created electron states by optical spectroscopy experiments using photoluminescence and resonant inelastic light scattering at low temperature. Very short period (as small as 40 nm) honeycomb lattices realize massless Dirac-fermions in a highly tunable GaAs quantum well system. We also explore the triangular antidot lattice, where Dirac fermions occur at larger period. Control over carrier density and Fermi level to tune massless Dirac fermions, and the realization of topological insulator states in artificial lattices will be discussed. [Preview Abstract] |
Monday, March 13, 2017 12:39PM - 12:51PM |
B36.00008: Conductance oscillations in a non-proportionally-coupled dot-cavity system in the Kondo regime. Luis Dias da Silva, Caio Lewenkopf, Edson Vernek, Gerson Ferreira, Sergio Ulloa The well-known Meir and Wingreen conductance formula [1] for interacting systems is limited in application to "proportionally coupled" terminals. We extend this formalism to consider non-proportionally-coupled structures, such as the quantum dot (QD)-quantum cavity (QC) geometry recently realized in Ref.[2]. We study an interacting QD connected coherently to tunable electronic cavity modes. The QD and the QC are coupled to the right lead but only the QD is coupled to the left lead. This non-proportionally coupled geometry is shown to exhibit a well defined Kondo effect over a wide range of the QD-QC coupling strength. Owing to quantum interference, changes in the cavity geometry dramatically modify the conductance and the spin configuration of the QD. Our numerical renormalization group calculations show that the cavity modes modulate the effective density of metallic states coupled to the QD, inducing unexpected splittings in the Kondo resonances. Moreover, the calculated conductance through the device exhibits oscillatory Fano-like features at large QD-QC couplings, while maintaining strong spin correlations with the electronic reservoir, in agreement with recent experimental results[2]. [1] Meir and Wingreen, PRL 68 2512 (1992) [2] C. Rossler et al., PRL 115 166603 (2015) [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:03PM |
B36.00009: `Kondo Blockade' due to quantum interference in single-molecule transistors Andrew Mitchell, Kim Pedersen, Per Hedegaard, Jens Paaske \\ Molecular electronics offers unique scientific and technological possibilities resulting from both the nanometer scale of the devices and their reproducible chemical complexity. Two fundamental yet different effects, with no classical analogue, have been demonstrated experimentally in single-molecule transistors: quantum interference due to competing electron transport pathways, and the Kondo effect due to entanglement from strong electronic interactions. In this talk I discuss recent progress in unifying these phenomena within an exact theoretical framework, showing how quantum interference leads to new types of Kondo-mediated transport beyond the standard single-orbital paradigm. Conductance can be strongly enhanced by the Kondo effect, but can take a different universal form from that of magnetic impurities or quantum dots. By contrast, we prove that a quantum interference node in exchange cotunneling leads to a novel `Kondo Blockade' mechanism, resulting in an exact node in the total conductance at low temperatures. Analytic results are supported by full numerical renormalization group calculations for simple molecular junctions where efficient transistor function is predicted, exploiting gate-controllable tuning between Kondo resonance and Kondo blockade. [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:15PM |
B36.00010: Fourier-domain Mobility Spectrum Analysis (FMSA) for Characterizing Semiconductors with Multi-Electron/Hole Species Boya Cui, Edward Kielb, Jiajun Luo, Yang Tang, Matthew Grayson Superlattices and narrow gap semiconductors often host multiple conducting species, such as electrons and holes, requiring a mobility spectral analysis (MSA) method to separate contributions to the conductivity. Here, a least-squares MSA method is introduced: the QR-algorithm Fourier-domain MSA (FMSA). Like other MSA methods, the FMSA sorts the conductivity contributions of different carrier species from magnetotransport measurements, arriving at a best fit to the experimentally measured longitudinal and Hall conductivities $\sigma_{xx}$ and $\sigma_{xy}$, respectively. This method distinguishes itself from other methods by using the so-called QR-algorithm of linear algebra to achieve rapid convergence of the mobility spectrum as the solution to an eigenvalue problem, and by alternately solving this problem in both the mobility domain and its Fourier reciprocal-space. The result accurately fits a mobility range spanning nearly four orders of magnitude ($\mu =$ 300 to 1,000,000 cm$^{2}$/V$\cdot $s). This method resolves the mobility spectra as well as, or better than, competing MSA methods while also achieving high computational efficiency, requiring less than 30 second on average to converge to a solution on a standard desktop computer. [Preview Abstract] |
Monday, March 13, 2017 1:15PM - 1:27PM |
B36.00011: Magneto-transport Characterization of Thin Film In-plane and Cross-plane Conductivity Yang Tang, Matthew Grayson Thin films with highly anisotropic in-plane and cross-plane conductivities are widely used in devices, such as infrared emitters and detectors, and the proper magneto-transport characterization in both directions can reveal information about the doping density, impurities, carrier life times and band structure. This work introduces a novel method for deducing the complete anisotropic electrical conductivity tensor of such an anisotropic resistive layer atop a highly conducting bottom contact, which is a standard part of the device structure. Three strip-line contacts separated by a length scale comparable to the film thickness are applied atop the resistive thin film layer of interest, with the highly conducting back-plane as a back-contact. The potential distribution in the device is modeled, using both scaling and conformal transformation to minimize the calculated volume. As a proof of concept, triple strip-line devices for GaAs and GaAs/AlGaAs superlattice thin films are fabricated. To achieve narrow strip-line contacts with sub-micron scale widths, non-annealed Ni/Au contacts form ohmic contacts to a patterned $n^+$-GaAs cap layer atop the anisotropic thin films. Preliminary experimental data will be presented as a validation of this method. [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B36.00012: Transport through an AC-driven impurity: Fano interference and bound states in the continuum Sebastian Reyes, Daniel Thuberg, Enrique Mu\~noz, Daniel Perez, Sebastian Eggert Using the Floquet formalism we study transport through an ac-driven impurity in a tight binding chain. The results obtained are exact and valid for all frequencies and barrier amplitudes. At frequencies comparable to the bulk bandwidth we observe a breakdown of the transmission $T=0$ which is related to the phenomenon of Fano resonances associated to AC-driven bound states in the continuum. We also demonstrate that the location and width of these resonances can be modified by tuning the frequency and amplitude of the driving field. It is shown that at high frequencies there is a close relation between the resonances and the phenomenon of coherent destruction of tunneling. We also discuss a generalization of these results including two spin channels, a local Zeeman splitting and interparticle interactions at the impurity site. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B36.00013: Tunneling into a quantum confinement created by a single-step nano-lithography of conducting oxide interfaces Eran Maniv, Alon Ron, Moshe Goldstein, Alexander Palevski, Yoram Dagan A new nano-lithography technique compatible with conducting oxide interfaces, which requires a single lithographic step with no additional amorphous layer deposition or etching, is presented. It is demonstrated on SrTiO3/LaAlO3 interface where a constriction is patterned in the electron liquid. We find that an additional back-gating can further confine the electron liquid into an isolated island. Conductance and differential conductance measurements show resonant tunneling through the island. The data at various temperatures and magnetic fields are analyzed and the effective island size is found to be of the order of 10nm. The magnetic field dependence suggests absence of spin degeneracy in the island. Our method is suitable for creating superconducting and oxide interface based electronic devices. [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B36.00014: Nuclear demagnetisation cooling of a nanoelectronic device Alex Jones, Ian Bradley, Tony Gu\'{e}nault, David Gunnarsson, Richard Haley, Stephen Holt, Yuri Pashkin, Jari Penttil\"{a}, Jonathan Prance, Mika Prunnila, Leif Roschier We present a new technique for on-chip cooling of electrons in a nanostructure: nuclear demagnetisation of on-chip, thin-film copper refrigerant. We are motivated by the potential improvement in the operation of nanoelectronic devices below $10~\mathrm{mK}$. At these temperatures, weak electron-phonon coupling hinders traditional cooling, yet here gives the advantage of thermal isolation between the environment and the on-chip electrons, enabling cooling significantly below the base temperature of the host lattice. To demonstrate this we electroplate copper onto the metallic islands of a Coulomb blockade thermometer (CBT), and hence provide a direct thermal link between the cooled copper nuclei and the device electrons. The CBT provides primary thermometry of its internal electron temperature, and we use this to monitor the cooling. Using an optimised demagnetisation profile we observe the electrons being cooled from $9~\mathrm{mK}$ to $4.5~\mathrm{mK}$, and remaining below $5~\mathrm{mK}$ for an experimentally useful time of 1200 seconds. We also suggest how this technique can be used to achieve sub-$1~\mathrm{mK}$ electron temperatures without the use of elaborate bulk demagnetisation stages. [1] Bradley et al., arXiv:1611.02483 (2016) [Preview Abstract] |
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