Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session W11: Focus Session: Transport Properties of Nanostructures VI: Kondo Phenomena |
Hide Abstracts |
Sponsoring Units: DMP Chair: Aditi Mitra, New York University Room: 305 |
Thursday, March 19, 2009 11:15AM - 11:27AM |
W11.00001: Very high Kondo temperature ($T_{K}\sim $ 80 K) in single self-assembled InAs quantum dots coupled to metallic nanogap electrodes Kenji Shibata, Kazuhiko Hirakawa We have studied electron tunneling through single self-assembled InAs quantum dots (QDs) laterally coupled to metallic nanogap electrodes. Lateral electron tunneling structures were fabricated by forming nanogap metallic electrodes directly upon single self-assembled InAs QDs grown on GaAs surfaces. The n-type substrate was used as a backgate electrode. Although no intentional tunneling barriers were introduced, the fabricated samples worked as single electron transistors and exhibited Coulomb blockade effect. Furthermore, a clear spin-half Kondo effect was observed when strong coupling between the electrodes and the QDs was realized using a large QD with a diameter of $\sim $100 nm. From the temperature dependence of the linear conductance at the Kondo valley, the Kondo temperature, $T_{K}$, was determined to be $\sim $ 81 K. This is the highest $T_{K}$ ever reported for artificial semiconductor nanostructures. This high Kondo temperature is due to strong QD-electrode coupling and large charging/orbital-quantization energies in our self-assembled InAs QD structures. [Preview Abstract] |
Thursday, March 19, 2009 11:27AM - 11:39AM |
W11.00002: Reduced Kondo conductance in a quantum dot by a high-biased quantum point contact nearby Kenichi Hitachi, Akira Oiwa, Seigo Tarucha A quantum point contact (QPC) near a quantum dot (QD) can be used for detecting the charge state in a QD. Also a single spin in a QD can be monitored by pulsed gate operation. However it has been shown that applied QPC source-drain bias voltage induces undesirable charge and spin fluctuations in a QD, such as photon-assisted like tunneling in a Coulomb blockade regime or suppressing conductance at spin-half Kondo valley. In this experiment, we examined the influence of Kondo valley and inelastic cotunneling at Coulomb valley in detail. We found that decreasing conductance at Kondo valley can be explained by the increase of local temperature, which is estimated by the conductance at inelastic cotunneling. We predict that this local increase of temperature is caused by the back-action between a QD and a QPC. This gives an alternative explanation of suppressing conductance at Kondo valley, which was thought to be the effect of dephasing a spin singlet between the dot and the lead. [Preview Abstract] |
Thursday, March 19, 2009 11:39AM - 11:51AM |
W11.00003: A magnetic field-induced crossover to a non-universal regime in a Kondo dot Andrei Kogan, Tai-Min Liu, Bryan Hemingway, Steven Herbert, Michael Melloch We have measured the magnetic splitting, $\Delta_K$, of a Kondo peak in the differential conductance of a Single-Electron Transistor while tuning the Kondo temperature, $T_K$, along two different paths in the parameter space: varying the dot-lead coupling at a constant dot energy, and vice versa. At a high magnetic field, $B$, the changes of $\Delta_K$ with $T_K$ along the two paths have opposite signs, suggesting that $\Delta_K$ is not a universal function of $T_K$. At low $B$, we observe a decrease in $\Delta_K$ with $T_K$ along both paths. Detailed $\Delta_K(B)$ data for two different $T_K$ show consistency for the splitting onset. Furthermore, we find $\Delta_K/\Delta<1$ at low $B$ and $\Delta_K/\Delta>1$ at high $B$, where $\Delta$ is the Zeeman energy of the bare spin. We discuss an approximate scaling of $\Delta_K$ with $B/T_K$ at low $B$ and compare the findings to previous measurements and theory. [Preview Abstract] |
Thursday, March 19, 2009 11:51AM - 12:03PM |
W11.00004: Correlated Wavefunction Description of Kondo States on Metal Surfaces Sahar Sharifzadeh, Patrick Huang, Emily A. Carter At low temperatures, a variety of magnetic impurities adsorbed on metal surfaces form a Kondo state, where the conduction electrons are thought to screen out the spin on the impurity to yield a many-body singlet, based on analogy with bulk Kondo physics in which magnetic quenching is observed at low temperatures.~ In scanning tunneling spectroscopy (STS), this state manifests as a narrow resonance in the density of states at the Fermi level.~ However, qualitative differences in the Kondo resonance lineshape are seen between specific adatom-substrate systems, for reasons that are not understood.~ We present a many-body correlated wavefunction study of Co on transition metal surfaces.~ We apply an embedded configuration interaction (CI) approach, where a finite cluster containing the impurity is described by a many-body CI wavefunction, while the effects of the extended background are included via a periodic density functional theory-based embedding potential.~ We discuss the nature of the correlated wavefunction and impurity orbital structure on different surfaces, and discuss implications for the observed STS data. [Preview Abstract] |
Thursday, March 19, 2009 12:03PM - 12:15PM |
W11.00005: Kondo effect in single-molecule magnet transistors Gabriel Gonzalez, Michael Leuenberger, Eduardo Mucciolo We present a careful and thorough microscopic derivation of the anisotropic Kondo Hamiltonian for single-molecule magnet (SMM) transistors. When the molecule is strongly coupled to metallic leads, we show that by applying a transverse magnetic field it is possible to topologically induce or quench the Kondo effect in the conductance of a SMM with either an integer or a half-integer spin S$>$1/2. This topological Kondo effect is due to the Berry-phase interference between multiple quantum tunneling paths of the spin. We calculate the renormalized Berry-phase oscillations of the two Kondo peaks as a function of a transverse magnetic field by means of the poor man's scaling approach. We illustrate our findings with the SMM Ni4, which we propose as a possible candidate for the experimental observation of the conductance oscillations. [Preview Abstract] |
Thursday, March 19, 2009 12:15PM - 12:27PM |
W11.00006: Frequency-dependent Full Counting Statistics of Electron Transport in Double Quantum Dots Ramon Aguado, David Marcos, Clive Emary, Tobias Brandes Full Counting Statistics is a powerful tool to study correlations in stochastic processes. It has been applied in the last years to characterize nanoscale transport. We present a technique that allows to calculate finite frequency high-order correlators of the electronic current through an interacting nanostructure. We illustrate our technique by calculating the frequency-dependent shot noise (second order) and skewness (third order) of a double quantum dot. Our results demonstrate that the frequency- dependent skewness contains useful information about the internal quantum dynamics of the nanostructure in bias voltage regimes where the second-order correlations are dominated by thermal fluctuations. [Preview Abstract] |
Thursday, March 19, 2009 12:27PM - 12:39PM |
W11.00007: Transport properties of a superconducting single-electron transistor coupled to a nanomechanical oscillator Verena Koerting, T.L. Schmidt, C.B. Doiron, C. Bruder, B. Trauzettel Superconducting single-electron transistors (SSETs) are known to constitute a very sensitive probe for the position measurement of a nanomechanical resonator (NR) which can provide near quantum-limited accuracy. The laws of quantum mechanics, however, also require a backaction of the SSET on the resonator, which limits the sensitivity. Recent experiments have confirmed that the backaction gives rise to an effective thermal bath which has the potential to cool or drive the resonator. Our research attempts to gain a better understanding of this system by examining the action of the NR on the SSET. In particular, we investigate the effect on transport properties of the SSET. We focus on the double Josephson quasiparticle (DJQP) resonance where an especially strong back-action can be observed due to the appearance of two coherent Cooper pair tunneling events. We argue that a measurement of for example the current, the charge noise and the shot noise (Fano factor) provides a direct way of gaining information on the state of the NR. In addition to an analytical discussion of the linear response regime we discuss results of higher order approximation schemes and a full numerical solution. [Preview Abstract] |
Thursday, March 19, 2009 12:39PM - 12:51PM |
W11.00008: Spin-dependent tunneling and the Kondo effect in quantum dots.* S. E. Ulloa, A. Ngo, E. Vernek Many-body effects have a significant role in electronic transport of nanoscale systems. Particular interesting systems are quantum dots coupled to electronic reservoirs via quantum point contacts. Due to strong spin-orbit interactions [1,2], quantum point contacts can exhibit spin dependent hybridization of the QD states, opening the possibility for generating spin-polarized transport. In this work we study electronic transport of a single level quantum dot connected to polarizing quantum point contacts (QPCs) in both the Coulomb blockade and Kondo regimes. We study how QPCs generate spin-polarized currents by using scattering matrix methods and the equations-of-motion technique. We calculate the electronic Green's function, conductance and spin polarization in different parameter regimes. Our results show that both Hubbard and Kondo regimes exhibit high spin-polarized conductance. We analyze how the spin-dependent hybridization of the QPC modifies the Kondo resonance, as well as the density of states of the system. These effects are controllable by lateral gate voltages applied on QPCs, as in recent experiments [2]. [1] A. Reynoso \textit{et al.,} Phys. Rev, B \textbf{75}, 085321 (2007). [2] P. Debray \textit{et al.}, unpublished (2008). * Supported by NSF-DMR WMN. [Preview Abstract] |
Thursday, March 19, 2009 12:51PM - 1:03PM |
W11.00009: Andreev transport through side-coupled double quantum dots Yoichi Tanaka, Norio Kawakami, Akira Oguri We study the transport through side-coupled double quantum dots, connected to normal and superconducting (SC) leads with a T-shape configuration, using the numerical renormalization group. We find that the Coulomb interaction in the side dot suppresses the destructive interference effect typical of the T-shape geometry, and enhances the conductance substantially in the Kondo regime. This behavior stands in stark contrast to a wide Kondo valley seen in the normal transport. Moreover, the SC proximity penetrating into the interfacial dot pushes the Kondo clouds, which screens the local moment in the side dot, towards the normal lead to make the singlet bond long. The conductance shows a peak of the unitary limit as the cloud expands. It is further elucidated that two separate Fano structures appear in the gate-voltage dependence of the Andreev transport, and the corresponding line shape is quite different from the Fano-Kondo plateau observed in the normal transport. [Preview Abstract] |
Thursday, March 19, 2009 1:03PM - 1:15PM |
W11.00010: Zeeman vs resonance splitting effects in a double quantum dot system N. Sandler, E. Vernek, L.G.G.V. Dias da Silva, K. Ingersent, S.E. Ulloa Electron correlations in quantum dot (QD) systems have many intriguing consequences. At low temperatures, the coupling between confined and conduction electrons is known to realize the Kondo effect. This phenomenon exhibits new and interesting features when electrons in an interacting QD hybridize with a non-flat conduction band. For example, when the QD is side-connected to external leads via a second large (noninteracting) QD, the effective density of states coupling to the interacting QD can have a peak at or near the Fermi level. In this regime, interference between the many-body Kondo state in the interacting dot and the single-particle resonance on the other dot causes splitting of the Kondo resonance [1] Here, we use the numerical renormalization group method to study this double-QD system in the presence of an external \textit{in-plane} magnetic field. We explore the interplay between different energy scales and discuss the behavior of the Kondo resonance in the presence of competing interactions. The in-plane field suppresses the Kondo effect, although this requires a stronger field than for a single QD, and the conductance decreases with field in a non-universal fashion. [1] L. G. G. V. Dias da Silva \textit{et al.}, Phys. Rev. Lett.\textbf{ 9}7, 096603 (2006). [Preview Abstract] |
Thursday, March 19, 2009 1:15PM - 1:27PM |
W11.00011: Shot noise in a Mn-doped quantum dot nanomagnet L.D. Contreras-Pulido, J. Fernandez-Rossier, R. Aguado A single-electron transistor (SET) based upon a II-IV semiconductor quantum dot doped with a single Mn ion behaves as a nanomagnet whose magnetic properties can be controlled electrically, and the effective exchange between the Mn and the carriers depends whether the SET is operated in the electron or the hole region. For holes, the Ising coupling for symmetric dots in absence of spin-flip Mn-hole exchange, results in Coulomb Blockade oscillations which depend on the spin state of the Mn atom [1]. We extended such analysis and studied finite-frequency shot noise through the SET [2]. Shot noise shows various regimes which, as a function of gate and bias voltages, reflect different magnetic configurations of the nanomagnet. We find super-Poissonian noise in a region of bias and gate voltages where the competing dynamics between slow and fast channels (corresponding to different orientations between the hole and the Mn ion) results in bunching. This behavior appears as a resonance around zero frequency, reflecting charge relaxation dynamics. We also discuss the role of transverse spin-flip terms. [1] J. Fernandez-Rossier and R. Aguado, Phys. Rev. Lett. 98, 106805 (2007) [2] D. Contreras-Pulido, J. Fernandez-Rossier and R. Aguado, in preparation [Preview Abstract] |
Thursday, March 19, 2009 1:27PM - 1:39PM |
W11.00012: Kondo effects in triangular triple quantum dots Akira Oguri, Takahide Numata, Yunori Nisikawa, A.C. Hewson We study the conductance through a triangular triple quantum dot, which is connected to two noninteracting leads, using the numerical renormalization group (NRG). It is found that the system shows a variety of Kondo effects depending on the filling of the triangle. The SU(4) Kondo effect occurs at half-filling, and a sharp conductance dip due to a phase lapse appears in the gate-voltage dependence. Furthermore, when four electrons occupy the three sites on average, a local $S=1$ moment, which is caused by the Nagaoka mechanism, is induced along the triangle. The temperature dependence of the entropy and spin susceptibility of the triangle shows that this moment is screened by the conduction electrons via two separate stages at different temperatures. The two-terminal and four-terminal conductances show a clear difference at the gate voltages, where the SU(4) or the $S=1$ Kondo effects occur[1]. We will also discuss effects of deformations of the triangular configuration, caused by the inhomogeneity in the inter-dot couplings and in the gate voltages. \\[4pt] [1] T.Numata, Y.Nisikawa, A.Oguri, and A.C.Hewson: arXiv:0808.3496. [Preview Abstract] |
Thursday, March 19, 2009 1:39PM - 1:51PM |
W11.00013: Interference in triple quantum dot systems George Martins, Edson Vernek, Carlos Busser, Enrique Anda, Sergio Ulloa, Nancy Sandler Transport properties of an interacting triple quantum dot system coupled to three leads in a triangular geometry has been studied in the Kondo regime. Applying mean-field finite-U slave boson and embedded cluster approximations to the calculation of transport properties of this system unveils a set of very rich features associated to its particular symmetry. In the case where just two leads are present, interference effects between degenerate molecular levels are studied, as well as an $S=1$ Kondo effect. The introduction of a third lead does not affect the coherence of propagating electrons, but rather results in an `amplitude leakage' phenomenon, which alters the interference effects. There is a good overall agreement between the two techniques employed. [Preview Abstract] |
Thursday, March 19, 2009 1:51PM - 2:03PM |
W11.00014: Bloch oscillations in lateral periodic nanostructure arrays W. Pan, S.K. Lyo, J.L. Reno, J.A. Simmons, D. Li, S.R.J. Brueck In a periodic structure of electron potential, under an external electric field $E$, if an electron can reach the boundary of the Brillouin zone (BZ) without being scattered, it undergoes Bragg reflection, passing back into the BZ on the opposite side. This results in a high frequency oscillation of electrons, i.e., Bloch oscillation (BO). Recently, BO has gained a renewed interest, as a Bloch$^{ }$oscillator can be utilized as a frequency-tunable THz source. Work on BO has mainly been carried out in quantum well superlattices. On the other hand, a surface superlattices patterned into a two dimensional electron system has long been proposed as an alternative structure to generate BO. Here, we report our experimental results on the negative differential conductance and Bloch oscillation induced edge magnetoplasma resonance in a series of lateral superlattices. Results from the so-called reversed Bloch oscillations measurements and bolometric measurements will also be presented and discussed. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the US Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. The facilities of the NSF-sponsored NNIN node at UNM were used for the fabrication. [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. |
© 2022 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
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700