Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Y38: Nanostructures of Correlated Materials |
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Sponsoring Units: DCMP Chair: Aditi Mitra, New York University Room: F149 |
Friday, March 19, 2010 8:00AM - 8:12AM |
Y38.00001: Quantum ripples in strongly correlated metals Eric Andrade, Eduardo Miranda, Vladimir Dobrosavljevic Abstract We study how well-known effects of the long-ranged Friedel oscillations are affected by strong electronic correlations. We first show that their range and amplitude are significantly suppressed in strongly renormalized Fermi liquids. We then investigate the interplay of elastic and inelastic scattering in the presence of these oscillations. In the singular case of two-dimensional systems, we show how the anomalous ballistic scattering rate is confined to a very restricted temperature range even for moderate correlations. In general, our analytical results indicate that a prominent role of Friedel oscillations is relegated to weakly interacting systems. [Preview Abstract] |
Friday, March 19, 2010 8:12AM - 8:24AM |
Y38.00002: Two-band electronic metal and neighboring spin liquid (spin Bose-metal) on a zigzag strip with longer-ranged repulsion Hsin-Hua Lai, Olexei I. Motrunich We consider an electronic model for realizing the Spin Bose-metal (SBM) phase on a 2-leg triangular strip -- a spin liquid phase found by D.~N.~Sheng~\textit{et~al.} [Phys. Rev. B {\bf 79}, 205112 (2009)] in a spin-1/2 model with ring exchanges. Starting from a two-band ``C2S2'' metal, the SBM can be viewed as a ``C1S2'' Mott insulator with gapped overall conducting charge mode. We consider extended repulsive interactions motivated by the ab initio derivation of an electronic model for $\kappa$-ET spin liquid material [K.~Nakamura~\textit{et~al.}, J. Phys. Soc. Jpn. {\bf 78}, 083710(2009)]. Using weak coupling renormalization group analysis, we find that such interactions allow much wider C2S2 metallic phase than in the Hubbard model with on-site repulsion only. We identify a valid eight-fermion Umklapp term that is crucial for producing a Mott insulator and use Bosonization to study phases obtained out of the C2S2 metal upon increasing overall repulsion strength, finding that the SBM phase is a natural outcome for extended interactions. [Preview Abstract] |
Friday, March 19, 2010 8:24AM - 8:36AM |
Y38.00003: Charge Fractionalization in a Mesoscopic Ring Wade DeGottardi, Siddhartha Lal, Smitha Vishveshwara In interacting one-dimensional systems, Luttinger liquid theory predicts the existence of fractionally charged quasiparticles whose properties depend on the Luttinger parameter. Recent experiments performed on quantum wires suggest the observation of such fractionalization. A complication that needs to be carefully considered in these geometries is that all measurements ultimately involve electrons that have tunneled outside the one-dimensional system into leads. Here, we propose a means of bypassing this complication by introducing a ring geometry and focusing on the non-invasive measurement of the time averaged power dissipated in a pickup loop proximate to the ring. We show that signatures of fractionalization of an electron that has tunneled into the ring are present in the dissipated power profile around the ring. As an independent measurement, we also show that the Luttinger parameter in the ring geometry can be derived from Coulomb blockade resonances controlled by both a tunable chemical potential and an Aharonov-Bohm flux. [Preview Abstract] |
Friday, March 19, 2010 8:36AM - 8:48AM |
Y38.00004: Quantum criticality and non-Fermi-liquid behavior in a two-level two-lead quantum dot Xin Wang, Andrew J. Millis We investigate the possibility of occupation switching and quantum criticality in a model of two quantum impurities coupled to two leads, using analytical and quantum Monte Carlo techniques. For spinless electrons, no phase transition is found, in agreement with previous numerical renormalization group calculations. For electrons with spin, we have found that in the weakly interacting regime, all properties vary smoothly with parameters; while in the strongly interacting regime, occupation numbers vary discontinuously at zero temperature as level energies are changed. The discontinuity point is characterized by non-Fermi-liquid behavior, visible in self-energies and correlation functions. [Preview Abstract] |
Friday, March 19, 2010 8:48AM - 9:00AM |
Y38.00005: Quantum-critical transitions and dissipation in double quantum dots Kevin Ingersent A device consisting of two quantum dots---one strongly interacting and tuned to its Kondo regime, the other effectively a noninteracting resonant level---coupled in parallel to two leads, can be mapped onto a single-impurity Anderson model with a pseudogapped effective density of states [1]. The finite-temperature conductance contains signatures of a quantum phase transition between local-moment and Kondo-screened phases [2]. In this talk I consider possible effects of environmental dissipation, introduced through the coupling of the interacting dot to a bosonic bath characterized by a power-law spectrum. The coupling takes place either via the dot's charge or via one component of its spin. Dissipation tends to suppress internal fluctuations on the interacting dot, and (depending on the bath spectral exponent) may completely destroy Kondo physics. The phase diagrams of the charge- and spin-coupled models will presented, along with thermodynamic and transport properties. \\[4pt] [1] L.G.G.V. Dias da Silva et al., PRL 97, 096603 (2006).\\[0pt] [2] L.G.G.V. Dias da Silva et al., PRB 78, 153304 (2008). [Preview Abstract] |
Friday, March 19, 2010 9:00AM - 9:12AM |
Y38.00006: Spectrum and screening cloud in the central spin model Sebastian Eggert, Michael Bortz, Joachim Stolze We consider an electronic spin in a quantum dot, coupled to the surrounding nuclear spins via inhomogeneous antiferromagnetic hyperfine interactions and subject to a uniform field, which is described by Gaudin's central spin model. We study spectral properties, the two-point correlation functions, and the magnetization profile in the ground state and in low-lying exci ted states, which characterizes the structure of the cloud of nuclear spins screening the electron spin. A close connection to the pair occupation probability in the BCS-model is established. Using the exact Bethe Ansatz solution of that model and arguments of integrability, we can distinguish between contributions from purely classical physics and from quantum fluctuations. [Preview Abstract] |
Friday, March 19, 2010 9:12AM - 9:24AM |
Y38.00007: Nonequilibrium dynamics in a two-channel Kondo system due to a quantum quench Zurab Ratiani, Aditi Mitra Recent experiments by Potok et al. have demonstrated a remarkable tunability between a single-channel Fermi liquid fixed point and a two-channel non-Fermi liquid fixed point. Motivated by this we study the nonequilibrium dynamics due to a sudden quench of the parameters of a Hamiltonian from a single-channel to a two-channel anisotropic Kondo system. We find a distinct difference between the long time behavior of local quantities related to the impurity spin as compared to that of bulk quantities related to the total (conduction electrons + impurity) spin of the system. In particular, the local impurity spin and the local spin susceptibility are found to equilibrate, but in a very slow power-law fashion which is peculiar to the non-Fermi liquid properties of the Hamiltonian. In contrast, we find a lack of equilibration in the two particle expectation values related to the total spin of the system. [Preview Abstract] |
Friday, March 19, 2010 9:24AM - 9:36AM |
Y38.00008: First-principles Calculations of Engineered Surface Kondo Atom Chiung-Yuan Lin, Barbara Jones In recent STM experiments, a surface Kondo atom (Co) is studied under the influence of a second magnetic atom or magnetic anisotropy on a specially designed CuN/Cu(100) surface. The Kondo properties of Co on such a surface were not studied before. We have done density functional calculation of this system, and obtain several properties that is important for the surface Kondo effect. We calculated the Co's surrounding local density of states and the on-site Coulomb $U$, and compare and contrast the behavior of Co and Mn. Our calculations also confirm that the Co spin of this structure is 3/2, as also measured indirectly by STM. [Ref. of experiments: Nature Physics, \underline {4}, 847 (2008); Phys. Rev. Lett. \underline {103}, 107203 (2009).] [Preview Abstract] |
Friday, March 19, 2010 9:36AM - 9:48AM |
Y38.00009: Search for nanoscale electronic phase separation in lightly doped CuO using STM Francoise Kidwingira, Ko Munakata, Malcolm Beasley High temperature superconductivity is widely believed to come from the CuO planes of the quasi-two-dimensional cuprate compounds. It is therefore a natural to ask to what extend their properties are shared with the 3 dimensional cuprate CuO. Static electronic phase separation seems to be one of these shared properties: charge stripes have been observed in a number cuprates, most notably LSCCO, and more recently in CuO single crystals. We report here STM measurements of lightly doped thin films of Cu and observe strong evidence for electronic inhomogeneity on the nanometer scale. Work supported by BES-DoE. [Preview Abstract] |
Friday, March 19, 2010 9:48AM - 10:00AM |
Y38.00010: Non-Fermi-Liquid Behavior in Gold Nanowires on Ge(001) Rene Matzdorf, Christian Blumenstein, Joerg Schaefer, Sebastian Meyer, Sebastian Mietke, Melanie Klinke, Tatjana Podlich, Ralph Claessen In the recently discovered self-organized Au atomic nanowires on Ge(001) a power-law behavior in the density of states (DOS) has been discovered by low-temperature scanning tunneling spectroscopy (STS). We present temperature dependent STS data in a temperature range from T = 5K to T = 50K that show energy and temperature dependence as expected for Luttinger-liquids. The structure of the system has been studied by low-temperature scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). A subtle four-fold periodicity along the chains is found, lacking lateral phase correlation. An energy gap relating to a charge density wave is not observed. [Preview Abstract] |
Friday, March 19, 2010 10:00AM - 10:12AM |
Y38.00011: Evidence of Joule heat and carriers injection from temperature-dependent IV characteristics on VO$_2$ sub-micron devices Juan Ramirez, Amos Sharoni, Maria Gomez, Ivan Schuller Temperature dependence of the current-induced Metal-Insulator Transition (MIT) of thin VO$_2$ films was measured for devices ranging from macroscopic size down to 1 micron length. While the V vs. I characteristics of macroscopic VO$_2$ device showed smooth transition, due to Joule heating, the small, 1 $\mu$m, device exhibit a completely different behavior. We find an V vs. I exhibiting negative differential resistance with many discrete voltage jumps. The jumps range from a few millivolts to a few volts, similar to resistance jumps we observed in the temperature driven transition of nanoscale VO$_2$ devices. From the temperature dependence of these jumps we can differentiate between MIT induced by Joule heating or due to carrier injection. These results are consistent with previous works indicating a phase separation across MIT in VO$_2$ thin films and could shed light on the VO$_2$ MIT mechanism. [Preview Abstract] |
Friday, March 19, 2010 10:12AM - 10:24AM |
Y38.00012: Direct correlation of structural domain formation with the metal-insulator transition in VO$_{2 }$nanobeams Shixiong Zhang, Jungyen Chou, Lincoln J. Lauhon While the metal-insulator transition in VO$_{2}$ bulk and thin films has been investigated for decades, recent studies of nanobeams have provided new insights into nature of the phase transition, in particular the relationship between inhomogeneous strain and metal/insulator domain formation. We have used Raman spectroscopy mapping of single nanobeam electrical devices at varying temperatures to directly correlate the domain structure with electrical resistance. With increasing temperature, clamped nanobeams transform from the insulating monoclinic M$_{1}$ phase to a mixture of the metastable Mott-insulating M$_{2}$ phase and the metallic rutile phase. Domain fractions were used to extract the temperature dependent resistivity of the M$_{2}$ phase, which shows an activated behavior consistent with the expected Mott-Hubbard gap. A metallic monoclinic M$_{2}$ phase was also produced by direct injection of charge into the device, providing evidence of an insulator-to-metal transition without a structural phase transformation. [Preview Abstract] |
Friday, March 19, 2010 10:24AM - 10:36AM |
Y38.00013: ABSTRACT HAS BEEN MOVED TO H38.00011 |
Friday, March 19, 2010 10:36AM - 10:48AM |
Y38.00014: Valence transitions and nanoscale Kondo-like behavior in Yb organometallic molecules C.H. Booth, W.W. Lukens, D. Kazhdan, Y.-J. Hu, R.A. Andersen, E.D. Bauer, L. Maron, O. Eisenstein When a material exhibiting Kondo behavior is reduced in size to the nanoscale, quantum confinement effects are dramatic, but still poorly understood. If the system is small enough, complex many-body calculations should no longer be necessary to describe the physics, and an understanding of the Kondo effect at the nanoscale can be attacked from a different direction. We present experimental and calculational results on Me-substituted complexes of Cp$_2^*$Yb(bipy) that demonstrate the efficacy of this approach. In particular, these molecules exhibit temperature-independent paramagnetism and intermediate valence of the Yb. Moreover, the first excited state can be lowered below room temperature, generating temperature-dependent Yb valence behavior, and even first-order valence transitions. CASSCF calculations demonstrate the importance of $\pi^*$ orbitals in obtaining appropriate ground states, and are able to reproduce trends in the excited state energies and the Yb valence. These results have direct implications for understanding not only nanoscale Kondo behavior, but also the general concept of valence tautomerism, and the importance of $f$-orbitals in bonding for lanthanide organometallics. [Preview Abstract] |
Friday, March 19, 2010 10:48AM - 11:00AM |
Y38.00015: The Realization of Artificial Kondo Lattices in Nanostructured Arrays Deepak Singh, Mark Tuominen Kondo lattice systems are described by intermetallic compounds of rare earth elements which contain a chemically ordered lattice of local moments that are coupled to the compound's conduction electrons via Kondo interaction. We will present a simple method to artificially create Kondo lattice systems in nanostructured arrays. Artificial Kondo lattices were fabricated using thin Nb film (10 nm thickness) with magnetic impurities, Co, embedded in a periodic (28 nm) hexagonal matrix. By controlling the percentage of magnetic impurities embedded in the thin film, we were able to control the strength of exchange coupling interaction between magnetic impurity's moments and conduction electrons spins. Electrical transport measurements and magnetoresistivity measurements of artificial lattices reflected the Kondo lattice properties found in rare-earth element compounds. Experimental data will be discussed in the wake of present theoretical models. An interesting observation of normalized logarithmic behavior of resistivity as a function of temperature will also be discussed. [Preview Abstract] |
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