tag:blogger.com,1999:blog-38172933552940965212017-02-08T20:57:03.286-08:00cond-mat.mes-hall - Mesoscale and Nanoscale PhysicsSite for <a href="http://communitypeerreview.blogspot.com/">Community Peer Review</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.comBlogger7055125tag:blogger.com,1999:blog-3817293355294096521.post-24398235826569235392013-08-06T00:01:00.059-07:002013-08-06T00:01:31.807-07:001111.4918 (Sarah Goler et al.)<h2 class="title"><a href="http://arxiv.org/abs/1111.4918">Revealing the atomic structure of the buffer layer between SiC(0001) and<br /> epitaxial graphene</a> [<a href="http://arxiv.org/pdf/1111.4918">PDF</a>]</h2>Sarah Goler, Camilla Coletti, Vincenzo Piazza, Pasqualantonio Pingue, Francesco Colangelo, Vittorio Pellegrini, Konstantin V. Emtsev, Stiven Forti, Ulrich Starke, Fabio Beltram, Stefan Heun<a name='more'></a><blockquote class="abstract">On the SiC(0001) surface (the silicon face of SiC), epitaxial graphene is obtained by sublimation of Si from the substrate. The graphene film is separated from the bulk by a carbon-rich interface layer (hereafter called the buffer layer) which in part covalently binds to the substrate. Its structural and electronic properties are currently under debate. In the present work we report scanning tunneling microscopy (STM) studies of the buffer layer and of quasi-free-standing monolayer graphene (QFMLG) that is obtained by decoupling the buffer layer from the SiC(0001) substrate by means of hydrogen intercalation. Atomic resolution STM images of the buffer layer reveal that, within the periodic structural corrugation of this interfacial layer, the arrangement of atoms is topologically identical to that of graphene. After hydrogen intercalation, we show that the resulting QFMLG is relieved from the periodic corrugation and presents no detectable defect sites.</blockquote>View original: <a href="http://arxiv.org/abs/1111.4918">http://arxiv.org/abs/1111.4918</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-81078975287020477072013-08-06T00:01:00.057-07:002013-08-06T00:01:30.404-07:001305.2272 (Maxim Breitkreiz et al.)<h2 class="title"><a href="http://arxiv.org/abs/1305.2272">Transport anomalies due to anisotropic interband scattering</a> [<a href="http://arxiv.org/pdf/1305.2272">PDF</a>]</h2>Maxim Breitkreiz, P. M. R. Brydon, Carsten Timm<a name='more'></a><blockquote class="abstract">Unexpected transport behavior can arise due to anisotropic single-particle scattering in multiband systems. Specifically, we show within a semiclassical Boltzmann approach beyond the relaxation-time approximation that anisotropic scattering between electronlike and holelike Fermi surfaces generically leads to negative transport times, which in turn cause negative magnetoresistance, an extremum in the Hall coefficient, and a reduction of the resistivity. The anisotropy required for this to occur decreases with increasing mismatch between the Fermi-surface radii.</blockquote>View original: <a href="http://arxiv.org/abs/1305.2272">http://arxiv.org/abs/1305.2272</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-91246183983677508392013-08-06T00:01:00.055-07:002013-08-06T00:01:29.347-07:001305.2820 (E. J. König et al.)<h2 class="title"><a href="http://arxiv.org/abs/1305.2820">Interaction and disorder effects in 3D topological insulator thin films</a> [<a href="http://arxiv.org/pdf/1305.2820">PDF</a>]</h2>E. J. König, P. M. Ostrovsky, I. V. Protopopov, I. V. Gornyi, I. S. Burmistrov, A. D. Mirlin<a name='more'></a><blockquote class="abstract">A theory of combined interference and interaction effects on the diffusive transport properties of 3D topological insulator surface states is developed. We focus on a slab geometry (characteristic for most experiments) and show that interactions between the top and bottom surfaces are important at not too high temperatures. We treat the general case of different surfaces (different carrier densities, uncorrelated disorder, arbitrary dielectric environment, etc.). In order to access the low-energy behavior of the system we renormalize the interacting diffusive sigma model in the one loop approximation. It is shown that intersurface interaction is relevant in the renormalization group (RG) sense and the case of decoupled surfaces is therefore unstable. An analysis of the emerging RG flow yields a rather rich behavior. We discuss realistic experimental scenarios and predict a characteristic non-monotonic temperature dependence of the conductivity. In the infrared (low-temperature) limit, the systems flows into a metallic fixed point. At this point, even initially different surfaces have the same transport properties. Investigating topological effects, we present a local expression of the $\mathbb Z_2$ theta term in the sigma model by first deriving the Wess-Zumino-Witten theory for class DIII by means of non-abelian bosonization and then breaking the symmetry down to AII. This allows us to study a response of the system to an external electromagnetic field. Further, we discuss the difference between the system of Dirac fermions on the top and bottom surfaces of a topological insulator slab and its non-topological counterpart in a double-well structure with strong spin-orbit interaction.</blockquote>View original: <a href="http://arxiv.org/abs/1305.2820">http://arxiv.org/abs/1305.2820</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-49619995190190799202013-08-06T00:01:00.053-07:002013-08-06T00:01:28.487-07:001305.2888 (I. S. Burmistrov et al.)<h2 class="title"><a href="http://arxiv.org/abs/1305.2888">Multifractality at Anderson transitions with Coulomb interaction</a> [<a href="http://arxiv.org/pdf/1305.2888">PDF</a>]</h2>I. S. Burmistrov, I. V. Gornyi, A. D. Mirlin<a name='more'></a><blockquote class="abstract">We explore mesoscopic fluctuations and correlations of the local density of states (LDOS) near localization transition in a disordered interacting electronic system. It is shown that the LDOS multifractality survives in the presence of Coulomb interaction. We calculate the spectrum of multifractal dimensions in $2+\epsilon$ spatial dimensions and show that it differs from that in the absence of interaction. The multifractal character of fluctuations and correlations of the LDOS can be studied experimentally by scanning tunneling microscopy of two-dimensional and three-dimensional disordered structures.</blockquote>View original: <a href="http://arxiv.org/abs/1305.2888">http://arxiv.org/abs/1305.2888</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-69510114384104381272013-08-06T00:01:00.051-07:002013-08-06T00:01:27.251-07:001308.0603 (Johannes Bauer et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0603">Realizing a Kondo-correlated state with ultracold atoms</a> [<a href="http://arxiv.org/pdf/1308.0603">PDF</a>]</h2>Johannes Bauer, Christophe Salomon, Eugene Demler<a name='more'></a><blockquote class="abstract">We propose a novel realization of Kondo physics with ultracold atomic gases. It is based on a Fermi sea of two different hyperfine states of one atom species forming bound states with a different species, which is spatially confined in a trapping potential. We show that different situations displaying Kondo physics can be realized when Feshbach resonances between the species are tuned by a magnetic field and the trapping frequency is varied. We illustrate that a mixture of ${}^{40}$K and ${}^{23}$Na atoms can be used to generate a Kondo correlated state and that momentum resolved radio frequency spectroscopy can provide unambiguous signatures of the formation of Kondo resonances at the Fermi energy. We discuss how tools of atomic physics can be used to investigate open questions for Kondo physics, such as the extension of the Kondo screening cloud.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0603">http://arxiv.org/abs/1308.0603</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-42153043705835997142013-08-06T00:01:00.049-07:002013-08-06T00:01:26.284-07:001308.0633 (Adam T. Neal et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0633">Magneto-Transport in MoS2: Phase Coherence, Spin Orbit Scattering and<br /> the Hall Factor</a> [<a href="http://arxiv.org/pdf/1308.0633">PDF</a>]</h2>Adam T. Neal, Han Liu, Jiangjiang Gu, Peide D. Ye<a name='more'></a><blockquote class="abstract">We have characterized phase coherence length, spin orbit scattering length, and the Hall factor in n-type MoS2 2D crystals via weak localization measurements and Hall-effect measurements. Weak localization measurements reveal a phase coherence length of ~50 nm at T = 400 mK for a few-layer MoS2 film, decreasing as T^-1/2 with increased temperatures. Weak localization measurements also allow us, for the first time without optical techniques, to estimate the spin orbit scattering length to be 430 nm, pointing to the potential of MoS2 for spintronics applications. Via Hall-effect measurements, we observe a low temperature Hall mobility of 311 cm2/Vs at T = 1 K which decreases as a power law with a characteristic exponent {\gamma}=1.5 from 10 K to 60 K. At room temperature, we observe Hall mobility of 24 cm2/Vs. By determining the Hall factor for MoS2 to be 1.35 at T = 1 K and 2.4 at room temperature, we observe drift mobility of 420 cm2/Vs and 56 cm2/Vs at T = 1 K and room temperature, respectively.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0633">http://arxiv.org/abs/1308.0633</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-31424695240973053632013-08-06T00:01:00.047-07:002013-08-06T00:01:25.366-07:001308.0671 (Tomasz M Rusin et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0671">Super-Zitterbewegung oscillations of electrons in monolayer graphene</a> [<a href="http://arxiv.org/pdf/1308.0671">PDF</a>]</h2>Tomasz M Rusin, Wlodek Zawadzki<a name='more'></a><blockquote class="abstract">Electrons in monolayer graphene in the presence of an electromagnetic (or electric) wave are considered theoretically. It is shown that the electron motion is a nonlinear combination of Zitterbewegung (ZB, trembling motion) resulting from the periodic potential of graphene lattice and the driving field of the wave. This complex motion is called "Super-Zitterbewegung". The theory is based on the time-dependent two-band Hamiltonian taking into account the graphene band structure and interaction with the wave. Our theoretical treatment includes the rotating wave approximation and high-driving-frequency approximation for narrow wave packets, as well as numerical calculations for packets of arbitrary widths. Different regimes of electron motion are found, depending on relation between the ZB frequency $\omega_Z$ and the driving frequency $\omega_D$ for different strengths of the electron-wave interaction. Frequencies and intensities of the resulting oscillation modes are calculated. The nonlinearity of the problem results in a pronounced multi-mode behavior. Polarization of the medium is also calculated relating our theoretical results to observable quantities. The presence of driving wave, resulting in frequencies directly related to $\omega_Z$ and increasing the decay time of oscillations, should facilitate observations of the Zitterbewegung phenomenon.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0671">http://arxiv.org/abs/1308.0671</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-68209083112661078182013-08-06T00:01:00.045-07:002013-08-06T00:01:24.010-07:001308.0688 (Weihang Zhou et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0688">Exciton-phonon Bound Complex in Single-walled Carbon Nanotubes Revealed<br /> by High-field Magneto-optical Spectroscopy</a> [<a href="http://arxiv.org/pdf/1308.0688">PDF</a>]</h2>Weihang Zhou, Tatsuya Sasaki, Daisuke Nakamura, Hiroaki Saito, Huaping Liu, Hiromichi Kataura, Shojiro Takeyama<a name='more'></a><blockquote class="abstract">High-field magneto-optical spectroscopy was conducted on highly-selected chiral (6,5) specific single-walled carbon nanotubes. Spectra of phonon sidebands in both 1st and 2nd sub-bands were observed to be unchanged by the application of an external magnetic field up to 52 T. Our analyses led to the conclusion that both phonon sidebands in respective sub-band originate from the dark K-momentum singlet (D-K-S) excitons. Moreover, while the relative ordering between the bandedge bright exciton and its zero-momentum anti-bonding counterpart was found to be opposite for the 1st and 2nd sub-bands, the relative ordering between the D-K-S exciton and the band-edge bright exciton was clarified to be the same for both sub-bands. Energy of these D-K-S excitons was estimated to be ~ 21.5 and ~ 37.3 meV above the band-edge bright exciton for the 1st and 2nd sub-bands, respectively.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0688">http://arxiv.org/abs/1308.0688</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-86207070582737233082013-08-06T00:01:00.043-07:002013-08-06T00:01:23.486-07:001308.0696 (D. Lagarde et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0696">Carrier and polarization dynamics in monolayer MoS2</a> [<a href="http://arxiv.org/pdf/1308.0696">PDF</a>]</h2>D. Lagarde, L. Bouet, X. Marie, C. R. Zhu, B. L. Liu, T. Amand, B. Urbaszek<a name='more'></a><blockquote class="abstract">In monolayer MoS2 optical transitions across the direct bandgap are governed by chiral selection rules, allowing optical valley initialization. In time resolved photoluminescence experiments we find that both the polarization and emission dynamics do not change from 4K to 300K within our time resolution. The created polarization remains stable during the exciton emission time on the order of 4ps. We show that the decrease of the time-integrated polarization with increasing temperature is not due to a shortening of the polarization lifetime induced by intervalley scattering, but due to a more and more non-resonant excitation as the bandgap shifts with temperature. By compensating this change in bandgap energy with the excitation laser energy an emission polarization of 40% is recovered at room temperature, close to the maximum emission polarization for this sample at 4K.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0696">http://arxiv.org/abs/1308.0696</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-79582434754740972792013-08-06T00:01:00.041-07:002013-08-06T00:01:22.427-07:001308.0713 (Pilkyung Moon et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0713">Optical probing of the Hofstadter butterfly</a> [<a href="http://arxiv.org/pdf/1308.0713">PDF</a>]</h2>Pilkyung Moon, Mikito Koshino<a name='more'></a><blockquote class="abstract">We investigate the optical absorption spectrum and the selection rule for the Hofstadter butterfly in twisted bilayer graphene under magnetic fields. We demonstrate that the absorption spectrum exhibits a self-similar recursive pattern reflecting the fractal nature of the energy spectrum. We find that the optical selection rule has a nested self-similar structure as well, and it is governed by the conservation of the total angular momentum summed over different hierarchies.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0713">http://arxiv.org/abs/1308.0713</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-84724007421938579322013-08-06T00:01:00.039-07:002013-08-06T00:01:21.159-07:001308.0714 (William Paul et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0714">FIM tips in SPM: Apex orientation and temperature considerations on atom<br /> transfer and diffusion</a> [<a href="http://arxiv.org/pdf/1308.0714">PDF</a>]</h2>William Paul, David Oliver, Yoichi Miyahara, Peter Grütter<a name='more'></a><blockquote class="abstract">Atoms transferred to W(111) and W(110) tip apices from the Au(111) surface during tunneling and approach to mechanical contact experiments in STM are characterized in FIM at room temperature and at 158 K. The different activation energies for diffusion on the (111) and (110) tip planes and the experiment temperature are shown to be important factors controlling the extent of changes to the atomic structure of the tip. W(111) tips are much better suited to scanning probe studies which require the characterization of an atomically defined tip and subsequent verification of its integrity in FIM. The statistics of the observed spikes in the tunneling current when the tips are approached to Au(111) are interpreted using a simple model of adatoms diffusing through the STM junction.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0714">http://arxiv.org/abs/1308.0714</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-18359774074225466572013-08-06T00:01:00.037-07:002013-08-06T00:01:19.903-07:001308.0756 (Adrian E. Feiguin et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0756">Hermitian and non-Hermitian thermal Hamiltonians</a> [<a href="http://arxiv.org/pdf/1308.0756">PDF</a>]</h2>Adrian E. Feiguin, Israel Klich<a name='more'></a><blockquote class="abstract">Thermal density matrices can be described by a pure quantum state within the thermofield formalism. Here we show how to construct a class of Hamiltonians realizing a thermofield state as their ground state. These Hamiltonians are frustration-free, and can be Hermitian or non-Hermitian, allowing one to use ground-state methods to understand the thermodynamic properties of the system. In particular this approach gives an explicit mapping of thermal phase transitions into quantum phase transitions. In the non-Hermitian case, the quantum phase transition is not accompanied by a change in the spectrum of the Hamiltonian, which remains gapped. We illustrate these ideas for the classical 2D Ising model.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0756">http://arxiv.org/abs/1308.0756</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-72072319425157387012013-08-06T00:01:00.035-07:002013-08-06T00:01:18.840-07:001308.0760 (V. G. Karpov et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0760">Hot spot runaway in thin film photovoltaics and related structures</a> [<a href="http://arxiv.org/pdf/1308.0760">PDF</a>]</h2>V. G. Karpov, A. Vasko, A. Vijh<a name='more'></a><blockquote class="abstract">We show that thin film diode structures, such as photovoltaics and light emitting arrays, can undergo zero threshold localized thermal runaway leading to thermal and electrical nonuniformities spontaneously emerging in originally uniform systems. The linear stability analysis is developed for a system of thermally and electrically coupled two discrete diodes, and for a distributed system. These results are verified with numerical modeling that is not limited to small fluctuations. The discovered instability negatively affects the device performance and reliability. It follows that these problems can be mitigated by properly designing the device geometry and thermal insulation.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0760">http://arxiv.org/abs/1308.0760</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-78040232402981265952013-08-06T00:01:00.033-07:002013-08-06T00:01:17.779-07:001308.0811 (I. A. Fyodorov et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0811">Limitations on the number of plasmons in nanoparticles</a> [<a href="http://arxiv.org/pdf/1308.0811">PDF</a>]</h2>I. A. Fyodorov, V. M. Parfenyev, G. T. Tartakovsky, S. S. Vergeles, A. K. Sarychev<a name='more'></a><blockquote class="abstract">In this letter, we address the thermal processes occurring in plasmonic nanoparticles. We determine constrains imposed upon the plasmonic excitation in such nanoparticle by the resulting heat generation. Taking into account temperature dependence of the metal losses, we predict the existence of the critical number of plasmons in the nanoparticle. We also allow for the temperature dependencies of the thermal-conductivity coefficient of the environment and the Kapitza heat boundary resistance. We show that the latter can dominate the overall heat resistance in the system. Strength limitations caused by the action of electric forces are also considered. Obtained results provide instruments for the heat and strength management in the plasmonic engineering.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0811">http://arxiv.org/abs/1308.0811</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-91104028793466729322013-08-06T00:01:00.031-07:002013-08-06T00:01:16.800-07:001308.0815 (F. Caruso et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0815">Solving a two-electron quantum dot model in terms of polynomial<br /> solutions of a Biconfluent Heun Equation</a> [<a href="http://arxiv.org/pdf/1308.0815">PDF</a>]</h2>F. Caruso, J. Martins, V. Oguri<a name='more'></a><blockquote class="abstract">The effects on the non-relativistic dynamics of a system compound by two electrons interacting by a Coulomb potential and with an external harmonic oscillator potential, confined to move in a two dimensional Euclidean space, are investigated. In particular, it is shown that it is possible to determine exactly and in a closed form a finite portion of the energy spectrum and the associated eigeinfunctions for the Schr\"odinger equation describing the relative motion of the electrons.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0815">http://arxiv.org/abs/1308.0815</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-15339887984483095362013-08-06T00:01:00.029-07:002013-08-06T00:01:15.536-07:001308.0826 (A. Barfuss et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0826">Elemental Topological Insulator with a Tunable Fermi Level: Strained<br /> α-Sn on InSb(001)</a> [<a href="http://arxiv.org/pdf/1308.0826">PDF</a>]</h2>A. Barfuss, L. Dudy, M. R. Scholz, H. Roth, P. Höpfner, C. Blumenstein, G. Landolt, J. H. Dil, N. C. Plumb, M. Radovic, A. Bostwick, E. Rotenberg, A. Fleszar, G. Bihlmayer, D. Wortmann, G. Li, W. Hanke, R. Claessen, J. Schäfer<a name='more'></a><blockquote class="abstract">We report on the epitaxial fabrication and electronic properties of a topological phase in strained \alpha-Sn on InSb. The topological surface state forms in the presence of an unusual band order not based on direct spin-orbit coupling, as shown in density functional and GW slab-layer calculations. Angle-resolved photoemission including spin detection probes experimentally how the topological spin-polarized state emerges from the second bulk valence band. Moreover, we demonstrate the precise control of the Fermi level by dopants.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0826">http://arxiv.org/abs/1308.0826</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-58902670141728021612013-08-06T00:01:00.027-07:002013-08-06T00:01:14.575-07:001308.0828 (H. Soller et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0828">Signatures in the conductance for phase transitions in excitonic systems</a> [<a href="http://arxiv.org/pdf/1308.0828">PDF</a>]</h2>H. Soller, D. Breyel<a name='more'></a><blockquote class="abstract">We analyse two phase transitions in exciton bilayer systems: a topological phase transition to a phase which hosts Majorana fermions and a phase transition to a Wigner crystal. Using generic simple models for the different phases we discuss the conductance properties of the latter when contacted to metallic leads and demonstrate the possibility to observe the different phase transitions by simple conductance measurements.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0828">http://arxiv.org/abs/1308.0828</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-27278194164948620102013-08-06T00:01:00.025-07:002013-08-06T00:01:13.395-07:001308.0866 (B. Y. Sun et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0866">Negative differential transmission in graphene</a> [<a href="http://arxiv.org/pdf/1308.0866">PDF</a>]</h2>B. Y. Sun, M. W. Wu<a name='more'></a><blockquote class="abstract">By using the Kubo linear response theory with the Keldysh Green function approach, we investigate the mechanism leading to the negative differential transmission in system with the equilibrium electron density much smaller than the photon-excited one. It is shown that the negative differential transmission can appear at low probe-photon energy (in the order of the scattering rate) or at high energy (much larger than the scattering rate). For the low probe-photon energy case, the negative differential transmission is found to come from the increase of the intra-band conductivity due to the large variation of electron distribution after the pumping. As for the high probe-photon energy case, the negative differential transmission is shown to tend to appear with the hot-electron temperature being closer to the equilibrium one and the chemical potential higher than the equilibrium one but considerably smaller than half of the probe-photon energy. We also show that this negative differential transmission can come from both the inter- and the intra-band components of the conductivity. Especially, for the inter-band component, its contribution to the negative differential transmission is shown to come from both the Hartree-Fock self-energy and the scattering. Furthermore, the influence of the Coulomb-hole self-energy is also addressed.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0866">http://arxiv.org/abs/1308.0866</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-66138917849460147282013-08-06T00:01:00.023-07:002013-08-06T00:01:12.309-07:001308.0875 (Nam Lyong Kang et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0875">Derivation of line shape function in the optical conductivity by a new<br /> diagram method</a> [<a href="http://arxiv.org/pdf/1308.0875">PDF</a>]</h2>Nam Lyong Kang, Sang Don Choi<a name='more'></a><blockquote class="abstract">A new diagram method to derive line shape function in the optical conductivity formula is introduced and the result obtained applying the method to an electron-phonon system is compared with that derived using the projection-reduction method. The result satisfies the population criterion, which states that the distribution functions for electrons and phonons should be combined in multiplicative forms, and gives physical intuition to quantum dynamics of electrons in a solid. This method can be called the "KC diagram" method because it originates from the proper application of the Kang-Choi reduction identity and a state-dependent projection operator.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0875">http://arxiv.org/abs/1308.0875</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-90032761037761915742013-08-06T00:01:00.021-07:002013-08-06T00:01:11.213-07:001308.0928 (H. Ochoa et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0928">Spin memory and spin-lattice relaxation in two-dimensional hexagonal<br /> crystals</a> [<a href="http://arxiv.org/pdf/1308.0928">PDF</a>]</h2>H. Ochoa, F. Guinea, V. I. Fal'ko<a name='more'></a><blockquote class="abstract">We propose a theory of spin relaxation of electrons and holes in two-dimensional hexagonal crystals such as atomic layers of transition metal dichalcogenides (MoS2, WSe2, etc). We show that even in intrinsically defectless crystals, their flexural deformations are able to generate spin relaxation of carriers. Based on symmetry analysis, we formulate a generic model for spin-lattice coupling between electrons and flexural deformations, and use it to determine temperature and material-dependent spin lifetimes in atomic crystals in ambient conditions.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0928">http://arxiv.org/abs/1308.0928</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-14405977709566819662013-08-06T00:01:00.019-07:002013-08-06T00:01:10.183-07:001308.0930 (Per Lunnemann et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0930">Calibrating and Controlling the Quantum Efficiency Distribution of<br /> Inhomogeneously Broadened Quantum Rods Using a Mirror Ball</a> [<a href="http://arxiv.org/pdf/1308.0930">PDF</a>]</h2>Per Lunnemann, Freddy T. Rabouw, Relinde J. A. van Dijk-Moes, Francesca Pietra, Daniël Vanmaekelbergh, A. Femius Koenderink<a name='more'></a><blockquote class="abstract">We demonstrate that a simple silver coated ball lens can be used to accurately measure the entire distribution of radiative transition rates of quantum dot nanocrystals. This simple and cost-effective implementation of Drexhage's method that uses nanometer-controlled optical mode density variations near a mirror, not only allows to extract calibrated ensemble-averaged rates, but for the first time also to quantify the full inhomogeneous dispersion of radiative and non radiative decay rates across thousands of nanocrystals. We apply the technique to novel ultra-stable CdSe/CdS dot-in-rod emitters. The emitters are of large current interest due to their improved stability and reduced blinking. We retrieve a room-temperature ensemble average quantum efficiency of 0.87+-0.08 at a mean lifetime around 20 ns. We confirm a log-normal distribution of decay rates as often assumed in literature and we show that the rate distribution-width, that amounts to about 30% of the mean decay rate, is strongly dependent on the local density of optical states.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0930">http://arxiv.org/abs/1308.0930</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-54096977945230472342013-08-06T00:01:00.017-07:002013-08-06T00:01:09.095-07:001308.0937 (Gowrishankar Seshadri et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0937">Optimum Size of Nanorods for Heating Application</a> [<a href="http://arxiv.org/pdf/1308.0937">PDF</a>]</h2>Gowrishankar Seshadri, Rochish Thaokar, Anurag Mehra<a name='more'></a><blockquote class="abstract">Magnetic nanoparticles (MNP's) have become increasingly important in heating applications such as hyperthermia treatment of cancer due to their ability to release heat when a remote external alternating magnetic field is applied. It has been shown that the heating capability of such particles varies significantly with the size of particles used. In this paper, we theoretically evaluate the heating capability of rod-shaped MNP's and identify conditions under which these particles display highest efficiency. For optimally sized monodisperse particles, the power generated by rod-shaped particles is found to be equal to that generated by spherical particles. However, for particles which have a dispersion in size, rod-shaped particles are found to be more effective in heating as a result of the greater spread in the power density distribution curve. Additionally, for rod-shaped particles, a dispersion in the radius of the particle contributes more to the reduction in loss power when compared to a dispersion in the length. We further identify the optimum size, i.e the radius and length of nanorods, given a bi-variate log-normal distribution of particle size in two dimensions.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0937">http://arxiv.org/abs/1308.0937</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-2476715155197625932013-08-06T00:01:00.015-07:002013-08-06T00:01:08.414-07:001308.0965 (D. Wang et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0965">Magnonic momentum transfer force on domain walls confined in space</a> [<a href="http://arxiv.org/pdf/1308.0965">PDF</a>]</h2>D. Wang, Xi-guang Wang, Guang-hua Guo<a name='more'></a><blockquote class="abstract">Momentum transfer from incoming magnons to a Bloch domain wall is calculated using one dimensional continuum micromagnetic analysis. Due to the confinement of the wall in space, the dispersion relation of magnons is different from that of a single domain. This mismatch of dispersion relations can result in reflection of magnons upon incidence on the domain wall, whose direct consequence is a transfer of momentum between magnons and the domain wall. The corresponding counteraction force exerted on the wall can be used for the control of domain wall motion through magnonic linear momentum transfer, in analogy with the spin transfer torque induced by magnonic angular momentum transfer.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0965">http://arxiv.org/abs/1308.0965</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-59746516535155243742013-08-06T00:01:00.013-07:002013-08-06T00:01:07.371-07:001308.0972 (Jürg Diemand et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0972">Large Scale Molecular Dynamics Simulations of Homogeneous Nucleation</a> [<a href="http://arxiv.org/pdf/1308.0972">PDF</a>]</h2>Jürg Diemand, Raymond Angélil, Kyoko K. Tanaka, Hidekazu Tanaka<a name='more'></a><blockquote class="abstract">We present results from large-scale molecular dynamics (MD) simulations of homogeneous vapor-to-liquid nucleation. The simulations contain between one and eight billion Lennard-Jones (LJ) atoms, covering up to 1.2 {\mu}s (56 million time-steps). They cover a wide range of supersaturation ratios, S=1.55 to 10^4, and temperatures from kT = 0.3 to 1.0 {\epsilon} (where {\epsilon} is the depth of the LJ potential, and k the Boltzmann constant). We have resolved nucleation rates as low as 10^{17} cm^{-3} s^{-1} (in the argon system), and critical cluster sizes as large as 100 atoms. Recent argon nucleation experiments probe nucleation rates in an overlapping range, making the first direct comparison between laboratory experiments and molecular dynamics simulations possible: We find very good agreement within the uncertainties, which are mainly due to the extrapolations of argon and LJ saturation curves to very low temperatures. The self-consistent, modified classical nucleation model of Girshick and Chiu [J. Chem. Phys. 93, 1273 (1990)] underestimates the nucleation rates by up to 9 orders of magnitudes at low temperatures, and at kT = 1.0 {\epsilon} it overestimates them by up to 10^5. The predictions from a semi-phenomenological model by Laaksonen et al. [Phys. Rev. E 49, 5517 (1994)] are much closer to our MD results, but still differ by factors of up to 104 in some cases. At low temperatures, the classical theory predicts critical clusters sizes, which match the simulation results (using the first nucleation theorem) quite well, while the semi-phenomenological model slightly underestimates them. At kT = 1.0 {\epsilon} the critical sizes from both models are clearly too small. (abridged)</blockquote>View original: <a href="http://arxiv.org/abs/1308.0972">http://arxiv.org/abs/1308.0972</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-3817293355294096521.post-51483721110483560352013-08-06T00:01:00.011-07:002013-08-06T00:01:05.785-07:001308.0976 (D. Wang et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0976">Unified description of laser induced magnetization dynamics in<br /> ferromagnetic metals</a> [<a href="http://arxiv.org/pdf/1308.0976">PDF</a>]</h2>D. Wang, A. J. Schellekens, B. Koopmans<a name='more'></a><blockquote class="abstract">Laser induced ultrafast demagnetization in ferromagnetic metals was discovered almost 20 years ago, but currently there is still lack of consensus on the microscopic mechanism responsible for the corresponding transfer of angular momentum and energy between electron, lattice and spin subsystems. A distinct, but intrinsically correlated phenomenon occurring on a longer timescale is the magnetization oscillation after the ultrafast demagnetization process, if a magnetic field is applied to tilt the magnetization vector away from its easy direction. Based on a microscopic three temperature model, which adapts the Elliott-Yafet scattering between electrons and phonons to explain the ultrafast demagnetization process, a unified theoretical description of both phenomena is proposed. In our unified description, the ultrafast demagnetization is mediated by the Elliott-Yafet scattering, while the resultant change of anisotropy is responsible for the following magnetization oscillation. Theoretical prediction with plausible parameters are in excellent agreement with experimental data measured using time resolved magneto-optical Kerr effect in an in-plane magnetized Pt/Co/Pt thin film with perpendicular interface anisotropy. This agreement between theory and experiment provides more insight into the microscopic mechanism behind the ultrafast demagnetization process. Furthermore, the model proposed here could also be used to study the magnetization dynamics triggered by the modification of anisotropy field through ultrafast laser heating.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0976">http://arxiv.org/abs/1308.0976</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0