Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G2: Focus Session: Quantum Control of Molecular, Nano, and Plasmonic Materials IV |
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Sponsoring Units: DCP Chair: Thomas Weinacht, Stony Brook University Room: 102 |
Tuesday, March 4, 2014 11:15AM - 11:51AM |
G2.00001: TDDFT and RPA for mesoscopic systems with thousands to millions of electrons: understating the red-shift in silver clusters absorption around 5nm Invited Speaker: Daniel Neuhauser Two quantum approaches for describing mesoscopic quantum systems with TDDFT will be described: The first, in collaboration with G. Lu and colleagues, is a single-orbital Madelung-like TDDFT propagation incorporating the correct homogenous electron gas dependence of the susceptibility on frequency, wavevector and density. We used this approach to understand the red-shift in the absorption of silver clusters around 5nm diameters. The second, in collaboration with R. Baer and E. Rabani, obtains the exact TDDFT and RPA results by stochastic averaging where the system's time-dependent density and potential is obtained by propagating small set of randomly chosen stochastic-orbitals, each of which is initially a random combination of the system's occupied orbitals. For large systems $\sim$ 10-40 orbitals are sufficient to get the correct dynamics regardless of the number of electrons. [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:03PM |
G2.00002: Binary Platinum-Based Nanoclusters: A Density Functional Theory Investigation Juarez L.F. Da Silva, Ricardo K. Nomiyama, Maur\'Icio J. Piotrowski, Diego Guedes Sobrinho, Anderson S. Chaves Binary Ptatinum-based nanoclusters have attracted great attention in the last years due to the possibility to improve the chemical and physical properties of Pt nanoclusters. In this work, we will report a theoretical study of the structure and electronic properties of the Pt$_n$TM$_{55-n}$ (TM = Fe, Co, Ni, Cu, Zn, Rh, Au) nanoclusters using density functional theory as implemented in the Vienna Ab-Initio Simulation Package (VASP). We found negative values for the excess energy for all systems, except for TM = Au, which indicates a gain in stability of the nanoclusters in comparison to the parent systems, i.e., Pt$_{55}$ and TM$_{55}$. We observed that platinum has a strong preference to occupy the nanocluster surface, except for TM = Au, which can be explained by the large atomic radius of Pt atoms compared with with the Fe, Co, Ni, Cu, and Zn atoms. Our results indicate that the core-shell configuration, in which the core (13 TM atoms) and shell (42 Pt atoms) are from different chemical species, has greater stability compared with other compositions for all systems (except for TM = Au). Furthermore, we studied the average effective coordination, bond lengths, magnetic, and electronic properties of all those systems as a function of the composition. [Preview Abstract] |
Tuesday, March 4, 2014 12:03PM - 12:15PM |
G2.00003: First principles theory for surface plasmon generation and decay to hot carriers Ravishankar Sundararaman, Prineha Narang, Adam Jermyn, Harry A. Atwater, William A. Goddard III Plasmonic resonances provide a promising pathway for efficiently capturing infrared photons from solar radiation and boosting photo-catalytic activity via local temperature enhancements and hot carrier generation. Previous calculations of plasmon decay to excited carriers employing a fully quantized model Hamiltonian \footnote{A. Jermyn, P. Narang and H. A. Atwater, \emph{(under preparation)}} indicate strong plasmon polarization dependence and momentum anisotropy of the generated carriers, in contrast with classical theories. An accurate first principles calculation for this process must account for microscopic details at the atomic scale for the electronic states as well as the effect of the 10-100~nm length scale particle and antennae geometries on the plasmon resonances. Here, we present a first-principles multi-scale model of plasmonics combining electronic density-functional theory with electromagnetic models on longer length-scales, and investigate the role of electronic structure and geometry on plasmonic light absorption, decay and hot carrier generation. [Preview Abstract] |
Tuesday, March 4, 2014 12:15PM - 12:27PM |
G2.00004: High Field Optomagnetic (OM) Polarization-Phase Selective (PPS) Monitoring of Structures and Controlling Reaction Agents Mechanisms in Complex Molecular Systems Kresimir Rupnik Using OM techniques, including new high filed 25T Split-Florida magnet at NHMF Laboratory, we have recently observed unusual metal cluster structures and electron transfer patterns in complex molecular systems of biomedical and material science interest. We report here some of the new technological solutions and (many) challenges that face OM and (quantum) control research. Of particular interest is identification of fast (10-100s fs) highly correlated electrons spin and vibrational coupling interpreted using adaptive molecular-photonic interaction models. Our observations question interpretations of previously proposed electron spin structure models and mechanisms and$_{\mathrm{\thinspace }}$indicate possible new controlling mechanisms through highly selective coupled channels that combine different specific redox and photonic agents. [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 1:03PM |
G2.00005: Strong Field Coherent Control at the Space-Time Limit Invited Speaker: Tamar Seideman Strong field coherent control has proven advantageous for control of molecular dynamics largely since it is able to benefit from the advanced Ti-Sapphire technology available at 800 nm wavelength. Although the most popular and versatile of the class of strong field, induced dipole coherent control methods is molecular alignment, related techniques that rely on similar concepts, including torsional control and molecular focusing, have been shown similarly successful. Here we suggest that the strong field approach to will prove yet more advantageous for coherent control of nanoscale material systems. One reason is the naturally available strong field and strong field orientational and translational gradients in nanoscale plasmonic environments, such as light-triggered molecular conduction junctions and tip--molecule--surface systems. Another is the enhancement of the polarizability of molecules adsorbed onto a metal construct as compared to isolated molecules. In the talk, we will combine plasmonics physics with concepts and tools borrowed from coherent control of molecular dynamics with two goals in mind. One is to introduce new function into nanoplasmonics, including ultrafast elements and broken symmetry elements. The second is to develop coherent nanoscale sources and apply them to strong field coherent control of both mechanical motions and electric transport in the nanoscale. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G2.00006: Charge transfer and quantum coherence in solar cells and artificial light harvesting system Christoph Lienau In artificial light harvesting systems the conversion of light into electrical or chemical energy happens on the femtosecond time scale, and is thought to involve the incoherent jump of an electron from the optical absorber to an electron acceptor. Here we investigate the primary dynamics of the photoinduced electronic charge transfer process in two prototypical structures: (i) a carotene-porphyrin-fullerene triad, a prototypical elementary component for an artificial light harvesting system and (ii) a polymer:fullerene blend as a model system for an organic solar cell. Our approach [1] combines coherent femtosecond spectroscopy and first-principles quantum dynamics simulations. Our experimental and theoretical results provide strong evidence that the driving mechanism of the primary step within the current generation cycle is a quantum-correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds. We furthermore highlight the fundamental role played by the flexible interface between the light-absorbing chromophore and the charge acceptor in triggering the coherent wavelike electron-hole splitting. \\[4pt] [1] C. A. Rozzi et al., Nature Comm. \textbf{4}, 1602 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G2.00007: High photoreactivity in a non-fluorescent photocleavable ligands on gold Hans D. Robinson, Chalongrat Daengngam, Stefan V. Stoianov, Steven B. Thorpe, Xi Guo, Webster L. Santos, John R. Morris We report on the photo-patterning of a gold surface functionalized with a self-assembled monolayer of an {\em o}-nitrobenzyl-based photocleavable ligand bound to the gold surface with a thiol anchor. We find that the dose of UV light required to induce the photoreaction on gold is very similar to the dose in an alcohol solution, even though many optical phenomena are strongly suppressed on metal surfaces. We attribute this finding to a combination of the large skin depth in gold at UV wavelengths, the high speed of the photoreaction, and the spatially indirect nature of the lowest excited singlet. Any photoreactive compound where the quantum efficiency of fluorescence is sufficiently low, preferably no larger than about $10^{-5}$ in the case of gold surfaces, will show a similarly high photoreactivity in metal-surface monolayers. The implications of this result for optically driven self-assembly in plasmonic systems will be discussed. [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G2.00008: The effect of Coulomb interactions on thermoelectric properties of quantum dots Natalya Zimbovskaya, Valery Kuzmin Thermoelectric effects in a quantum dot coupled to the source and drain charge reservoirs are explored using a nonequilibrium Green's functions formalism beyond the Hartree-Fock approxomation. We concentrate on theoretical analysis of the influence of Coulomb interactions on thermopower and the figure of merit $ZT. $ Obtained results show that Coulomb interactions between charge carriers on the dot significantly contribute to its thermoelectric properties. In the present work, we trace the transition from the Coulomb blockade regime to Kondo regime in the thermoelectric properties of the quantum dot which occurs when we gradually strengthen the coupling of the dot to the charge reservoirs. We show that within the Coulomb blockade regime (when the coupling of the dot to the leads is weak compared to the characteristic strength of the charge carriers interactions) thermoelectric characteristics of the dot display distinct features caused by Coulomb interactions. These features indicate possibilities of enhancement of thermoelectric efficiency of the considered systems. Within the Kondo regime, when the couplings of the dot to the leads became stronger, the influence of Coulomb interactions declines bringing a decrease in the the thermoelectric efficiency. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 2:15PM |
G2.00009: Quantum Control of Electrons in Atoms, Molecules and Materials - from Femtosecond to Attosecond to Zeptosecond Timescales Invited Speaker: Margaret Murnane This talk will discuss strong field quantum control in atomic, molecular and materials systems with applications across a broad range of chemical, physical and materials sciences. Using mid-infrared femtosecond lasers to drive the high harmonic (HHG) frequency upconversion process, strong time-gated phase matching results in bright \textit{coherent} keV soft X-ray beams on a tabletop for the first time [1]. The new photon energy range accessed of 0.2--1.6 keV (corresponding to wavelengths of 1 -- 6 nm) is of particular interest for applications in chemical and materials spectroscopy and imaging. X-rays can penetrate thick (opaque) samples and achieve high spatial resolution (2--50nm) imaging, with the added advantage of elemental and chemical specificity by employing characteristic elemental X-ray absorption edges and chemically-induced fine structure at these edges. Moreover, when atoms are ionized by mid-infrared light, the electron liberated during the HHG process can be driven back to the parent ion multiple times, resulting in quantum interferences and zeptosecond x-ray waveforms [2]. We also recently demonstrated that we can precisely control molecular dynamics on both nuclear (i.e. femtosecond) and electronic (i.e. attosecond) timescales [3,4]. Using vacuum ultraviolet light pulses that are tunable in wavelength and time structure, it is possible to switch population between electronic excited states on attosecond timescales, and use this ability to select specific pathways for ionization or dissociation of a molecule. Ultrafast lasers can also be used to switch the dissociation pathways of molecules as they explode after irradiation by ionizing light. Finally, we used ultrafast x-rays to capture coherent processes in materials, such how fast a material can change its electronic or magnetic state,... or how fast spin currents can control and enhance magnetization in materials.\\[4pt] [1] Popmintchev et al., Science \textbf{336}, 1287 (2012).\\[0pt] [2] Hernandez-Garcia et al., PRL \textbf{111},~033002 (2013).\\[0pt] [3] Zhou et al., Nature Phys. \textbf{8}, 232 (2012).\\[0pt] [4] Ranitovic at al., submitted (2013).\\[0pt] [5] S. Mathias et al., PNAS \textbf{109}, 4792 (2012).\\[0pt] [6] Rudolf et al., Nat. Comm. \textbf{3}, 1037 (2012).\\[0pt] [7] Turgut et al., PRL \textbf{110}, 197201 (2013). [Preview Abstract] |
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