Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session P20: Focus Session: Carbon Nanotubes: Electron Transport |
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Sponsoring Units: DMP Chair: Saiful Khondaker, University of Central Florida Room: C120-C122 |
Wednesday, March 17, 2010 8:00AM - 8:12AM |
P20.00001: Kondo Box in a Carbon Nanotube Ivan Borzenets, Yuriy Bomze, Henok Mebrahtu, Gleb Finkelstein We realize the Kondo box in a carbon nanotube quantum dot interacting with an extra electron. We study the electronic transport through the nanotube in a regime where it has an odd number of electrons. We found that the zero-bias conductance is suppressed due to the antiferromagnetic exchange interaction between the nanotube and the extra electron. We characterize the excitations of the Kondo box system in magnetic field and determine the spin of the first few eigenstates. [Preview Abstract] |
Wednesday, March 17, 2010 8:12AM - 8:24AM |
P20.00002: Few-electron physics in single- and double quantum dots in carbon nanotubes Bernhard Wunsch, Javier von Stecher, Ana Maria Rey, Eugene Demler We study the few-electron eigenspectrum of single- and double quantum dots in carbon-nanotubes. The interplay between spin-orbit coupling and electron-electron interaction strongly modifies the two-particle spectrum. In particular, we find a transition to a spin- and valley polarized ground state at small magnetic fields even for a single quantum dot. We discuss manifestations of this break-down of the constant interaction model in the transport characteristics of double dots, and analyze when Pauli-blockade of the current can occur. [Preview Abstract] |
Wednesday, March 17, 2010 8:24AM - 8:36AM |
P20.00003: Transport and Strong-Correlation Phenomena in Carbon Nanotube Quantum Dots in a Magnetic Field George Martins, Eugene Kim, M. Mizuno Transport through carbon nanotube (CNT) quantum dots (QDs) in a magnetic field is discussed. The evolution of the system from the ultraviolet to the infrared is analyzed; the strongly correlated (SC) states arising in the infrared (due to the Kondo effect) are investigated. Experimental consequences of the physics are presented -- the SC states arising at various fillings are shown to be drastically different; these differences have distinct signatures in the conductance and, in particular, the noise. Besides CNT QDs, our results are also relevant to double QD systems. [Preview Abstract] |
Wednesday, March 17, 2010 8:36AM - 8:48AM |
P20.00004: Carbon Nanotubes: from SU4 to Dicke effect Carlos A. B\"usser, G.B. Martins, P. Orellana, E. Vernek, G.A. Lara, E.H. Kim, E.V. Anda Single electron transistors can be manufactured by coupling a Carbon Nanotubes (CNT) to metal leads. In this case the Kondo effect may arise. The difference between the Kondo effect in CNT and the same effect in quantum dots (QD) comes from the degeneracy of the chiral states of the CNT. While in QDs the Kondo effect is related to the SU(2) symmetry, in CNTs the spins with different chirality can give rise to a SU(4) Kondo effect with a larger $T_K$. On the other hand we have the so called bound states in the continuum (BICs) or Dicke effect. In this effect a localised state at the CNT is decoupled from the metal reservoirs. When this state cross the Fermi level is filled abruptly changing the many body physics of the CNT thus the transport properties. In this talk we discuss the possibility to find BICs in a CNT and the influence of this effect over the Kondo regime and the transport properties of the CNT at zero-bias. [Preview Abstract] |
Wednesday, March 17, 2010 8:48AM - 9:00AM |
P20.00005: Wigner molecules in carbon-nanotube quantum dots Massimo Rontani, Andrea Secchi The paradigm of few-electron complexes in quantum dots (QDs) relies on the ``particle-in-a-box'' idea that lowest-energy orbitals are filled according to Pauli's exclusion principle. If Coulomb repulsion is sufficiently strong to overcome the kinetic energy cost of localization, a different scenario is predicted: a ``Wigner'' molecule (WM) forms, made of electrons frozen in space according to a geometrical pattern. Despite considerable experimental effort, evidence of the WM in semiconductor QDs has been elusive so far. Here we demonstrate theoretically that WMs occur in gate-defined QDs embedded in typical semiconducting carbon nanotubes (CNTs). Their signatures must be searched ---and indeed have already been observed [Deshpande and Bockrath, Nature Phys. {\bf 4,} 314 (2008)] --- in tunneling spectra. Through exact diagonalisation (ED) calculations, we unveil the inherent features of the electron molecular states. We show that, like nuclei in a usual molecule, electrons have localized wave functions and hence negligible exchange interactions. The molecular excitations are vibrations around the equilibrium positions of electrons. ED results are well reproduced by an ansatz vibrational wave function, which provides a simple theoretical model for transport experiments in ultraclean CNTs. [Preview Abstract] |
Wednesday, March 17, 2010 9:00AM - 9:12AM |
P20.00006: Scanning gate microscopy of metallic carbon nanotubes Jiamin Xue, Brian LeRoy The one dimensional nature of metallic single-walled carbon nanotubes (SWCNTs) causes their low energy properties to be described by Luttinger liquid theory. Using low-temperature scanning probe microscopy and electrical transport measurements, we have investigated the electronic properties of metallic SWCNTs. An AFM operating at 300 mK was used to probe the SWCNTs using scanning gate microscopy. Using a voltage on the AFM tip, we are able to probe the spatial dependence of the conductance. Spatially resolved images of conductance show rings with a modulation as a function of AFM tip position, which is consistent with Luttinger liquid theory. The ability to perform simultaneous electrical transport and scanning probe microscopy measurements allows us to test theoretical predictions about Luttinger liquids including spin-charge separation. [Preview Abstract] |
Wednesday, March 17, 2010 9:12AM - 9:24AM |
P20.00007: Scanning gate microscopy of electronic inhomogeneities in single-walled carbon nanotube (SWCNT) devices Steven R. Hunt, Phillip G. Collins The electronic properties of graphitic carbon devices are primarily determined by the contact metal and the carbon band structure. However, inhomogeneities such as substrate imperfections, surface defects, and mobile contaminants also contribute and can lead to transistor-like behaviors. We experimentally investigate this phenomena in the 1-D limit using metallic single-walled carbon nanotubes (SWCNTs) before and after the electrochemical creation of sidewall defects. While scanning gate microscopy readily identifies the defect sites, the energy-dependence of the technique allows quantitative analysis of the defects and discrimination of different defect types. This research is partly supported by the NSF (DMR 08-xxxx). [Preview Abstract] |
Wednesday, March 17, 2010 9:24AM - 9:36AM |
P20.00008: Electronic transport at van Hove Singularities in a large diameter carbon nanotube Yanfei Yang, Georgy Fedorov, Serhii Shafraniuk, Rupert Lewis, Benjamin Cooper, Christopher Lobb, Paola Barbara Carbon nanotube field-effect transistors (CNFET) with high transparency contacts show maxima of differential conductance at zero bias voltage [1]. These zero-bias anomalies (ZBAs) occur at large negative gate voltages and in narrow gate voltage ranges. Here we report on observation of pronounced ZBAs in devices made with a large diameter nanotube, at values of gate voltages corresponding to van Hove singularities of the nanotube density of states. We report the modulation of ZBAs by Fabry-Perot oscillations and distinct characterizations of these effects at low temperature and in magnetic field. Our proposed explanation is superconductivity in the nanotubes, occurring when the gate voltage shifts the Fermi level into van Hove singularities of the electronic density of states [1]. \\[4pt] [1] J. Zhang, A. Tselev, Y. Yang, K. Hatton, P. Barbara, S. Shafraniuk, Phys. Rev. B, \textbf{74}, 155414 (2006). [Preview Abstract] |
Wednesday, March 17, 2010 9:36AM - 9:48AM |
P20.00009: Theoretical study of nanoscale four-probe measurements: the effects of resonant scattering by localized states at the probe-sample contacts Asako Terasawa, Keiji Tobimatsu, Tomofumi Tada, Takahiro Yamamoto, Satoshi Watanabe Quantum effects on multi-probe conduction are one of the topics of growing importance in nanoscience and nanotechnology. Interesting features are reported in nanoscale four-probe measurements such as the resistance oscillation and the negative four-probe resistance [1]. We investigated the behavior of nanoscale four-probe resistance theoretically, and found that the oscillation of four-probe resistance of nanowires can be understood in terms of the interference caused by multiple reflections between voltage probes [2]. In the present work, we have further analyzed the relation between the resistance oscillation and interference on the basis of the spectrum of the peak spacing in resistance oscillation. We have found anomalous dips in the peak spacing spectra. We show that they can be attributed to the resonant scattering by localized states at the probe-sample contacts. The author was supported through the Global COE Program, ``Global Center of Excellence for Mechanical Systems Innovation,'' by the Ministry of Education, Culture, Sports, Science and Technology. \\[4pt] [1] B. Gao et al., Phys. Rev. Lett. 95, 196802 (2005).\\[0pt] [2] A. Terasawa et al., Phys. Rev. B 79, 195436 (2009). [Preview Abstract] |
Wednesday, March 17, 2010 9:48AM - 10:00AM |
P20.00010: Measurements on quantum capacitance of individual single walled carbon nanotubes Junfeng Dai, Jung Yul Li, Hualing Zeng, Xiaodong Cui We report measurements of the quantum capacitance of individual semiconducting and small band gap single walled carbon nanotubes (SWNTs). The observed quantum capacitance, 82 aF/$\mu $m for a semiconducting SWNT with chiral index (16,8) and 10.3 aF/$\mu $m for a small band gap SWNT upon Fermi level lying at the first subband are remarkably smaller than those originating from the density of states. We attribute the discrepancy to a strong electron correlation in SWNTs and derive the Luttinger parameter $g $of 0.25--0.3 for the (16,8) SWNT and of 0.32 for a small band gap SWNT. [Preview Abstract] |
Wednesday, March 17, 2010 10:00AM - 10:12AM |
P20.00011: Electronic focusing in carbon nanotubes Patricio H\"{a}berle, Samuel Hevia, Rodrigo Segura Slow electrons traveling close to a surface exhibit modifications of their trajectories due to the polarization charge they induce on the surface. This image charge interaction, in the case of carbon nanotubes (CNTs), is responsible for focusing electrons traveling in the vicinity of a nanotube. The consequences of this effect on the electronic trajectories are more significant for both low kinetic energies and small tube diameters. Numerical calculations indicate low energy electron spectroscopies are especially sensitive to this phenomenon. We have observed evidence of this electronic focusing in inverse photoemission spectroscopy from different CNTs samples. [Preview Abstract] |
Wednesday, March 17, 2010 10:12AM - 10:24AM |
P20.00012: Signatures of Luttinger liquid effects in the conductance of clean pn-junctions Wei Chen We study corrections to the conductance of a pn-junction in an armchair carbon nanotube, which is induced by the upmklapp and e-ph scattering. The correction scales as a power of temperature, with the exponent that depennds on the Luttinger interaction parameter. [Preview Abstract] |
Wednesday, March 17, 2010 10:24AM - 10:36AM |
P20.00013: Order-N electron transport calculation from ballistic to diffusive regimes by time-dependent wave-packet diffusion method -Application to carbon nanotubes- Hiroyuki Ishii, Nobuhiko Kobayashi, Kenji Hirose Using a time-dependent wave-packet diffusion method[1], which treats the quantum electron transport problems of huge systems of up to 80 million atoms, combining with molecular dynamics simulations, we study the electron transport of carbon nanotubes from ballistic to diffusive regimes from an atomistic viewpoint in the unified way. We can simulate the effects of electron- phonon couplings on the transport properties of the nanotubes at various temperatures. We confirm that the obtained mean free path and mobility agree well with recent experimental observations and theoretical calculations, and succeed in evaluating the resistance in entire regime between ballistic and diffusive transport limits. We clarify the resistance is remarkably different from that at the two transport limits, when the length of nanotubes is comparable to the mean free path. [1]H.Ishii, N.Kobayashi, and K.Hirose, Appl.Phys.Express 1(2008) 123002. [Preview Abstract] |
Wednesday, March 17, 2010 10:36AM - 10:48AM |
P20.00014: Individual carbon nanotube Schottky diode rectifiers characterized at microwave frequencies Enrique Cobas, Steven Anlage, Michael Fuhrer Carbon nanotube Schottky diodes (CNT-SDs) are predicted to have very high cut-off frequencies due to small junction capacitances. Additionally, carbon nanotube (CNT) conductors are expected to exhibit signatures of Tomonaga-Luttinger Liquid states in their frequency-dependent conductivity. We have measured the rectification of microwave signals by CNT-SDs as a function of frequency, power, and dc bias voltage. Horizontally aligned CNTs were grown by chemical vapor deposition on high-frequency compatible quartz substrates. Dissimilar metal contacts were created in coplanar waveguide geometries via photolithography. The diodes were subjected to microwave signals from 100MHz to 40GHz. A frequency-independent rectified dc current of approximately 100$\mu $A / W was observed throughout this frequency range, consistent with the expected intrinsic cut-off frequency of the devices of order 1THz. [Preview Abstract] |
Wednesday, March 17, 2010 10:48AM - 11:00AM |
P20.00015: Spin Dependent Scattering in Nanotubes Yonatan Abranyos, Godfrey Gumbs Using a continuum model, we obtain analytical expressions for the spin-split energy bands for electrons on the surface of nanotubes in the presence of Spin-Orbit Interaction. Each energy level could then be used to accommodate the two types of spin. We calculate the scattering amplitude from a barrier around the axis of the nanotube into various spin-dependent states. [Preview Abstract] |
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