Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session P9: Electronic Properties of Quantum Dots |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Luis Dias da Silva, University of Tennessee Room: A105 |
Wednesday, March 17, 2010 8:00AM - 8:12AM |
P9.00001: Strong electromechanical coupling of an AFM cantilever to a few-electron quantum dot Steven D. Bennett, Lynda Cockins, Yoichi Miyahara, Peter Grutter, Aashish A. Clerk Mechanical objects provide extremely sensitive probes to measure quantum electronic systems. The damping of an atomic force microscope (AFM) cantilever capacitively coupled to a quantum dot exhibits Coulomb blockade peaks as a function of bias voltage in much the same way that Coulomb blockade peaks occur in the conductance through a quantum dot. It has long been predicted that level degeneracy in the dot results in asymmetric lineshapes in the Coulomb blockade peaks of the conductance, as well as temperature-dependent shifts of the peak positions. We extend this theory to the case of mechanical damping, and find that the effects of degeneracy are enhanced due to an increased sensitivity to the asymmetry between adding or removing an electron from the dot. Furthermore, by driving the cantilever to large oscillation amplitudes we enter a regime of strong coupling where the lineshape asymmetry is enhanced dramatically. The high sensitivity of the AFM damping to level degeneracy has allowed both the shifts and asymmetric lineshapes of Coulomb blockade peaks to be measured in recent experiments for the first time, showing excellent agreement with theory. [Preview Abstract] |
Wednesday, March 17, 2010 8:12AM - 8:24AM |
P9.00002: Transport and correlations in double dots: 1/N expansion and SBMFT Robert Konik, Manas Kulkarni, Alexei Tsvelik Large-N diagrammatic and SBMFT approaches are used to study a double dot system in a parallel geometry. We extract fully the pole structure of its Green's function matrix and also obtain the partition function and dot occupancy via diagrams in 1/N. We show that the Friedel sum rule holds and we use this fact to calculate the conductance. We find that the conductance vanishes at the particle-hole symmetric point. These diagrammatic results agree with our SBMFT analysis for the same system. Through SBMFT, we study how transport properties are affected upon tuning the coupling between the leads and dots. Conductance at finite temperature is also studied. When applicable, we compare our results to a Bethe ansatz analysis of the same system [1]. [1] R.Konik PRL 99, 076602 (2007) [Preview Abstract] |
Wednesday, March 17, 2010 8:24AM - 8:36AM |
P9.00003: Extraordinary Tunneling through a Periodic Array of Quantum Dots L.S. Petrosyan, T.V. Shahbazyan We study theoretically electron tunneling through a periodic system of quantum dots. We show that the coupling of dots via continuum of electronic states in the leads causes a strong enhancement, relative to the single-dot case, of the low-energy tail of resonant tunneling conductance when the Fermi wavelength in the leads is larger than system period. We calculated tunneling conductance for periodic one- and two-dimensional arrays of dots sandwiched between two- and three-dimensional leads and found that the enhancement factor can reach one and two orders of magnitude, respectively. The enhancement is accompanied by conductance oscillations as a function of gate voltage with maxima corresponding to the Fermi momentum in the leads being multiples of the reciprocal lattice constant. The predicted effect can be viewed as transport analogue of the extraordinary light transmission through periodic subwavelength hole array on metal film. [Preview Abstract] |
Wednesday, March 17, 2010 8:36AM - 8:48AM |
P9.00004: Germanium based electrostatic quantum dots: design and characterization. Giovanni Mazzeo, Eli Yablonovitch, Hong-Wen Jiang While the less mature Germanium technology requires an extra effort for the realization of single electron quantum dots, unique properties of Germanium rich heterostructures together with spin coherence times comparable to Silicon, can justify the development of such new technology. We report our progresses on the formation of electrostatic quantum dots in Germanium. We employ an MOS-like structure with no modulation doping already successfully proven in Silicon devices. A two level gate stack is used: the top gate is positively biased to attract electrons while the lowers gates are negatively biased to form the quantum dot and attract holes in a transistor channel, used to detect the electrons in the adjacent quantum dot. Finite Element Method simulations are used to prove the concept of this hybrid holes-transistor/electron-QD device and estimate the sensitivity of the charge detection. Preliminary characterizations of quantum dot devices built with this structure are reported. [Preview Abstract] |
Wednesday, March 17, 2010 8:48AM - 9:00AM |
P9.00005: Formation of directed self-assembled Ge/Si quantum dots Dongyue Yang, Jeremy Levy, Jerrold Floro, Chris Petz Directed self assembly of sub-10-nm Ge islands are candidates for producing laterally coupled quantum dot molecules with geometrically defined spin exchange couplings. We describe low-temperature magnetotransport measurements on small arrays of Ge islands grown on semi-insulating silicon substrates. The islands are created by a technique for precise nucleation of Ge islands using nanoscale SiC templates defined by direct-write electron-beam lithography.\footnote{O. Guise, J. Ahner, J. John T. Yates, V. Vaithyanathan, D. G. Schlom, J. Levy, Appl. Phys. Lett. $\bf{87}$, 1902 (2005).} Ge island arrays are coupled through ohmic contacts to the Si capping layer, and geometries are defined that are suitable for either vertical or lateral transport. [Preview Abstract] |
Wednesday, March 17, 2010 9:00AM - 9:12AM |
P9.00006: Conduction across Silicon Nanoparticle-Metal Interfaces Matthew Stupca, Munir Nayfeh, Adam Smith We deposited a thin film of 1nm diameter silicon nanoparticles between two metallic films. The nanoparticles are created by an electrochemical process and are collected into solution. The particles are then deposited by evaporating the solution through electrospray or spin coating processes. The nanoparticle films of closely packed particles are observed to strongly absorb UV photons and fluoresce in the blue -- a characteristic of individual nanoparticles. We examine the photoconductivity of the films under UV illumination using IV spectroscopy. Our measurements indicate that the photoconductivy exhibits asymmetry and rectification in current flow for two metals which have different work functions. These results suggest that these films of nanoparticles, while retaining their nanoparticle characteristic luminescence, show the Shottky barrier associated with bulk behavior. [Preview Abstract] |
Wednesday, March 17, 2010 9:12AM - 9:24AM |
P9.00007: Effect of Iron(II) Ion Interactions on Silicon Nanoparticle Electronic Structure Kevin Mantey, Munir Nayfeh A better understanding of the interaction of silicon nanoparticles with ions can lead to diverse applications including biomedical sensing, filtering, and optoelectronics. Density functional theory is employed to investigate a simple ion test case, the interaction of an Iron(II) ion with a 1nm silicon nanoparticle (Si29H24). In the ground state the iron atom is found to sit below a six membered silicon ring on the particle surface. The effect on the molecular orbitals and charge distribution is presented, and time dependent density functional theory is used to investigate the excited state energy levels and oscillator strengths compared to the silicon nanoparticle alone. Absorption measurements of Iron(II) ions in solution with silicon nanoparticles are made for comparison. [Preview Abstract] |
Wednesday, March 17, 2010 9:24AM - 9:36AM |
P9.00008: Statistical properties of electron levels in quantum dot Branislav Vlahovic, Sergei Matinyan, Igor Filikhin Spherical shaped Si quantum dots (QDs) embedded into the SiO$_{2}$ substrate are considered in the single sub-band effective mass approach. The electron and heavy hole sub-bands are taken into account. The energy dependence of electron effective mass is applied for small size QD (I. Filikhin et al. PRB 73, 205332 (2006)). Calculations of low-lying single electron and hole energy levels are performed. The PL exciton data are reproduced well by our model calculations for QD with diameter D$<$6 nm. For weak confinement regime (size D$>$10 nm), when the number of confinement levels is limited by several hundred, we considered the statistical properties of the electron confinement. Distribution function for the electron levels is calculated for various QD shapes. Evidence of chaotic properties is discussed. [Preview Abstract] |
Wednesday, March 17, 2010 9:36AM - 9:48AM |
P9.00009: Inter-dot Effects in a Chain of CdS/CdSe/CdS Quantum Well Quantum Dots Joseph Pingenot, Kieran J. Mullen Although individual quantum well quantum dots (QWQD)s have been studied extensively, regular arrays of QWQDs have not received as much attention. Previous theoretical work on single electrons in a regular array of rings has shown antiferroelectric electron ordering, indicating the possibility of creating systems with antiferroelectric ordering in systems such as QWQDs. We have studied theoretically a chain of identical CdS/CdSe/CdS QWQDs with well thicknesses between 42nm and 10nm, with an external barrier width of 14nm. QWQD cores were between 14nm and 38nm, respectively. Valence and conduction states were calculated for a single QWQD using 8-band k-dot-p theory on a realspace grid using a program developed by Pryor[2]. The potential from the two nearest neighbors was found from the conduction state. For electron-hole interactions, the uppermost valence state of all 3 QWQDs were included. The holes were much more localized than the electrons, causing a large potential around them. A nonsimple potential arises from the combined states. The states were sensitive to the roughness of the sphere. [1]PRB 78 075411 [2] PRB 72 205311 [Preview Abstract] |
Wednesday, March 17, 2010 9:48AM - 10:00AM |
P9.00010: STM Exploration of Binary Nanocrystals Chenggang Tao, Marilena Longobardi, Matt Sheldon, Bryce Sadtler, A. Paul Alivisatos, Michael F. Crommie Multi-component nanocrystals provide an exciting platform for creating flexibly tailored electronic nanodevices due to their ``built-in'' heterojunction interface. Such systems are potentially useful for creating inexpensive energy-conversion devices from abundant materials. Using scanning tunneling microscopy and spectroscopy, we have investigated the structural and electronic properties of binary CdS/Cu2S nanorods bound to a metal surface. We will present spectroscopic results that provide new insight into energy level alignment within these dual-phase nanocrystals. [Preview Abstract] |
Wednesday, March 17, 2010 10:00AM - 10:12AM |
P9.00011: Continuous analytical solutions for strain applied to quantum dot and rings James Nimmo, Igor Filikhin, Vladimir Suslov, Branislav Vlahovic Several analytical strain matrix component solutions for quantum dot (QD) various geometries have been derived using principles of continuous mechanics. These strain calculations were used to determine the shift in electron energies for various QD and ring configurations and sizes (see, for instance, M. Grundmann et al. PRB 52, 11969 (1995)). In the presented work we propose simplified strain approximation for such calculations. This approximation is accompanied by the band gap model given in I. Filikhin et al. PRB 73, 205332 (2006). The results of our calculation are compared to those of previous ones. Besides, comparisons are made between 2D and 3D electron energy calculations. Finally the limits of continuous strain calculations are discussed. [Preview Abstract] |
Wednesday, March 17, 2010 10:12AM - 10:24AM |
P9.00012: Transport properties of few-electron quantum dots in gated InGaAs/InP and InAsP structures Ghislain Granger, S.A. Studenikin, A. Kam, A.S. Sachrajda, P.J. Poole, G.C. Aers, R.L. Williams Electron transport experiments are conducted on gated quantum dots formed in InGaAs/InP and InAsP/InP quantum well (QW) structures. These ridge-shape structures are grown by chemical beam epitaxy on pre-patterned substrates, and the InGaAs or InAsP QW are inserted at specific locations. In this system, quantum dots are formed underneath of submicron gate electrodes. Devices with split gate patterns are also under investigation. Standard Coulomb-blockade diamonds are observed up to 6 K, and a never-ending diamond indicates that the quantum dot can be completely emptied. With a bias across the dot and in the transport window corresponding to the addition of the second electron to the quantum dot, the triplet excited state becomes accessible, and the singlet-triplet transition is observed at 5 T. The observation of photon-assisted tunneling at microwave frequencies up to 50 GHz will also be presented. Due to their unique properties, such quantum dots could be useful for quantum computing experiments. [Preview Abstract] |
Wednesday, March 17, 2010 10:24AM - 10:36AM |
P9.00013: Electrical control of Kondo effect and superconducting transport in a sidegated InAs quantum dot Josephson junction Yasushi Kanai, Russell Deacon, Akira Oiwa, Katuharu Yoshida, Kenji Shibata, Kazuhiko Hirakawa, Seigo Tarucha Transport through a quantum dot Josephson junction exhibits the novel interplay between the superconductivity and Kondo screening. The important energy scales for the interaction between Kondo effect and superconductivity are captured in the scaling parameter t$_{K}$ = k$_{B}$T$_{K}$/$\Delta $ determined by the superconducting gap energy ($\Delta )$ and Kondo temperature (T$_{K})$. Here, we demonstrate that an additional sidegate electrode placed laterally to the InAs QD can tune smoothly t$_{K}$, because it imposes an additional anisotropic electrostatic potential on the QD. Using the sidegate we study the non-dissipative and dissipative transport through the QD Josephson junction as a function of t$_{K}$. When t$_{K}$ is tuned through unity we find a drastic change in the Josephson current as shown. We measure a `switching current' I$_{sw}$ defined by the current value at the maximum differential resistance instead of a critical current. For t$_{K} \quad >>$ 1, I$_{sw}$ is large while for t$_{K} \quad <<$ 1 I$_{sw}$ is strongly suppressed. These results suggest that the junction is tuned from a 0-junction in which the supercurrent is enhanced by Kondo correlations to a $\pi $-junction in which the magnetic moment is unscreened and switching current is suppressed. We find that the transition occurs at t$_{K}\sim $1.1. [Preview Abstract] |
Wednesday, March 17, 2010 10:36AM - 10:48AM |
P9.00014: Polarization-induced charge carrier separation in GaN quantum dots on polar and nonpolar surfaces Oliver Marquardt, Tilmann Hickel, Joerg Neugebauer Wurtzite III-nitride quantum dots (QDs) show a strongly reduced light emission efficiency when grown in the polar direction, due to strong built-in potentials which spatially separate electrons and holes, leading to weak recombination rates. To overcome this problem, QDs grown on nonpolar substrates have received much research interest, recently. We have compared GaN QDs grown on polar and nonpolar surfaces using an eight-band $\mathbf{k}\cdot\mathbf{p}$ model, employing geometries observed in recent experimental studies. Our studies indicate that the spatial separation of electrons and holes is even larger in QDs on nonpolar surfaces than in polar ones of comparable size, leading to even weaker recombination rates. A systematic investigation of various modifications on the above reference systems allowed us to identify the size of nonpolar QDs as the key parameter to achieve a higher efficiency in light emission processes. In particular, it has been found that this effect is stronger in nonpolar than in polar QDs by several orders of magnitude, making nonpolar QDs a promising research object for future light emission devices. [Preview Abstract] |
Wednesday, March 17, 2010 10:48AM - 11:00AM |
P9.00015: Quantum Phase Transition in Quadruple Quantum Dots Dong E. Liu, Shailesh Chandrasekharan, Harold U. Baranger We find a quantum phase transition between an Ising symmetry broken phase and an SU(4) Kondo screened phase in quadruple quantum dots. The dots are in a square configuration and coupled only capacitively. In response to tuning the inter-dot interaction, a Kosterlitz-Thouless (KT) type transition between the two phases occurs when the 4 dots are occupied by 2 spin polarized electrons. The SU(4) Kondo screened state is an orbital Kondo state described by the 6-dimensional representation of SU(4). In the Ising symmetry broken phase, the two electrons reside in dots at opposite diagonals. A similar quantum phase transition is also found in a spinfull system with a different configuration in which there is non-zero electron tunneling between the two pairs of dots. Quantum Monte Carlo simulation with directed loop update along with finite size scaling analysis is employed to obtain the thermodynamic properties of the system. We determine the range of experimentally realizable parameters where the system exhibits such a KT type quantum phase transition. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700