tag:blogger.com,1999:blog-1590521830913540202018-03-05T19:25:33.480-08:00cond-mat.other - Other Condensed MatterSite for <a href="http://communitypeerreview.blogspot.com/">Community Peer Review</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.comBlogger980125tag:blogger.com,1999:blog-159052183091354020.post-16749402865120181042013-08-06T00:00:00.003-07:002013-08-06T00:00:56.225-07:001308.0823 (H. Schenck et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0823">Vector chiral phases in frustrated 2D XY model and quantum spin chains</a> [<a href="http://arxiv.org/pdf/1308.0823">PDF</a>]</h2>H. Schenck, V. L. Pokrovsky, T. Nattermann<a name='more'></a><blockquote class="abstract">The phase diagram of the frustrated 2D XY model is calculated analytically. The chiral (Ising) transition is described by three independent critical exponents which are calculated in $d=5/2-\epsilon$ dimensions. Vortex interaction is short range on small and logarithmic on large scales, if compared with the chiral correlation length $\xi$. The vortex unbinding transitions is triggered by the increase of $\xi$ and occurs before the chiral transition takes place. In a narrow region close to the Lifshitz point a reentrant quasi-ferromagnetic phase appears. Application to antiferromagnetic quantum spin chains and multiferroics are discussed.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0823">http://arxiv.org/abs/1308.0823</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-30257160031348580032013-08-06T00:00:00.001-07:002013-08-06T00:00:55.083-07:001308.0913 (Yu. A. Freiman et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0913">Sound velocities in H_2, He, and H_2-He solid mixtures under pressure</a> [<a href="http://arxiv.org/pdf/1308.0913">PDF</a>]</h2>Yu. A. Freiman, Alexei Grechnev, S. M. Tretyak, A. F. Goncharov, C. -s. Zha, R. J. Hemley<a name='more'></a><blockquote class="abstract">Bulk and shear sound velocities in solid hydrogen, helium and hydrogen-helium mixtures under pressure are calculated using two complementary approaches: semi-empirical lattice dynamics based on the many-body intermolecular potentials and density-functional theory in generalized gradient approximation. The thermodynamics of the He-H$_2$ mixture has been treated within the additive-volume approximation. Our results are compared with the first-principle diffusion Monte-Carlo calculation of Alavi {\it et al.} (Science {\bf 269}, 1252 (1995)) and the semi-empirical work of Duffy {\it et al.} (Science {\bf 263}, 1590 (1994)) which employs the two-body Young-Ross potential. It is shown that the stiffer the potential is, the more the sound velocity is overestimated. Comparison with the data obtained from the observation of global oscillations of Jupiter is also made.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0913">http://arxiv.org/abs/1308.0913</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-83803398182450522082013-08-04T00:01:00.005-07:002013-08-04T00:01:22.876-07:000912.5379 (Bo Xiong et al.)<h2 class="title"><a href="http://arxiv.org/abs/0912.5379">Distortion of Interference Fringes and the Resulting Vortex Production<br /> of Merging Bose-Einstein Condensates</a> [<a href="http://arxiv.org/pdf/0912.5379">PDF</a>]</h2>Bo Xiong, Tao Yang, Keith A. Benedict<a name='more'></a><blockquote class="abstract">We investigate the effects of interatomic interactions and expansion on the distortion of interference fringes of a pair of initially well-separated, but coherent, condensate clouds trapped in a harmonic trap. The distortion of interference fringes, which can lead to the spontaneous formation of vortices in the atom clouds, depends crucially on two relevant parameters: the center-of-mass velocity and peak density of the initial state. We identify three qualitatively distinct regimes for the interfering condensates: collision, expansion, and merging, by the spatial and temporal features of the fringe spacings. Using a comprehensive set of numerical simulations based on the Gross-Pitaevskii equation, we specify the cross-overs between these regimes and propose the optimal the system parameters required for dynamical instabilities and vortex creation.</blockquote>View original: <a href="http://arxiv.org/abs/0912.5379">http://arxiv.org/abs/0912.5379</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-109590746884117082013-08-04T00:01:00.003-07:002013-08-04T00:01:21.832-07:001308.0003 (O. A. Ponomarev et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0003">Hole Conductivity in Heterogeneous DNA Fragments</a> [<a href="http://arxiv.org/pdf/1308.0003">PDF</a>]</h2>O. A. Ponomarev, A. S. Shigaev, A. I. Zhukov, V. D. Lakhno<a name='more'></a><blockquote class="abstract">The characteristics of cation radical (hole) migration in heterogeneous DNA were investigated on the basis of Kubo formula, in which correlation functions were obtained from solutions of systems of Bogoliubov hierarchy. The cutting of Bogoliubov hierarchy was carried out by excepting correlations of the third and higher order. The obtained system of non-linear differential equations was investigated both analytically and numerically. The environment polarization, caused by interaction of holes with base pairs vibrations, was shown to play the key role in transport processes. The energy of the interaction can ten-fold exceed vibration energy. The transfer rate between adjacent DNA bases in one-dimensional case was shown to be almost independent of the nature and behavior of more distant pairs. The charge probability amplitude oscillates in the picosecond timescale. Nonetheless, the rates of hole transfer, obtained by averaging over these oscillations, turned out to be very close to the experimental data. The calculated dependence of the hole transfer rate between two guanine bases on the number of intervening adenine bases was also in good agreement with the experimental data. Besides, the temperature dependence of the transfer rate was investigated. Hopping mechanism was shown to make the main contribution to the hole transport process at 300 K.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0003">http://arxiv.org/abs/1308.0003</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-41690822088214716162013-08-04T00:01:00.001-07:002013-08-04T00:01:20.728-07:001308.0004 (H. Razmi et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0004">The Casimir Atomic Pendulum</a> [<a href="http://arxiv.org/pdf/1308.0004">PDF</a>]</h2>H. Razmi, M. Abdollahi<a name='more'></a><blockquote class="abstract">We want to introduce an atomic pendulum whose driving force (torque) is due to the quantum vacuum fluctuations. Applying the well-known Casimir-Polder effect to a special configuration (a combined structure of an atomic nanostring and a conducting plate), an atomic pendulum (Casimir atomic pendulum) is designed. Using practically acceptable data corresponding to the already known world of nanotechnology and based on reasonable/reliable numerical estimates, the period of oscillation for the pendulum is computed. This pendulum can be considered as both a new Micro (Nano)-Eelectromechanical system and a new simple vacuum machine. Its design may be considered as a first step towards realizing the visualized vacuum (Casimir) clock!</blockquote>View original: <a href="http://arxiv.org/abs/1308.0004">http://arxiv.org/abs/1308.0004</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-60111028655666857972013-08-02T00:45:00.001-07:002013-08-02T00:45:21.472-07:001307.8219 (Swathi S. Hegde et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.8219">Freezing a Quantum Magnet by Repeated Quantum Interference: An<br /> Experimental Realization</a> [<a href="http://arxiv.org/pdf/1307.8219">PDF</a>]</h2>Swathi S. Hegde, Hemant Katiyar, T. S. Mahesh, Arnab Das<a name='more'></a><blockquote class="abstract">We experimentally demonstrate the phenomenon of dynamical many-body freezing in a periodically driven quantum Ising magnet within an NMR simulation scheme. The phenomenon is essentially a result of repeated quantum interference between the amplitudes of the fundamental excitations of the many-body system. The degree of freezing exhibits surprising non-monotonic behavior with respect to the driving frequency. At the points of maximal freezing, the population dynamics of all the quasi-particle modes are frozen very strongly for all time, which renders the freezing occurring independent of initial state and visible for almost all system sizes. Magnetization measured for our finite spin system gives direct access to the time-evolution of the underlying fermionic excitations in momentum space.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8219">http://arxiv.org/abs/1307.8219</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-34615995787038303332013-07-31T00:16:00.001-07:002013-07-31T00:16:22.097-07:001307.7775 (Manan Mehta et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7775">A Hybrid Analog/Digital Phase-Locked Loop for Frequency Mode Non-contact<br /> Scanning Probe Microscopy</a> [<a href="http://arxiv.org/pdf/1307.7775">PDF</a>]</h2>Manan Mehta, Venkat Chandrasekhar<a name='more'></a><blockquote class="abstract">Non-contact scanning probe microscopy (SPM) has developed into a powerful technique to image many different properties of samples. The conventional method involves monitoring the amplitude, phase or frequency of a cantilever oscillating at or near its resonant frequency as it is scanned across the surface of a sample. For high Q factor cantilevers, monitoring the resonant frequency is the preferred method in order to obtain reasonable scan times. This can be done by using a phase-locked-loop (PLL). PLLs can be obtained as commercial integrated circuits, but these do not have the frequency resolution required for SPM. To increase the resolution, all-digital PLLs requiring sophisticated digital signal processors or field programmable gate arrays have also been implemented. We describe here a hybrid analog/digital PLL where most of the components are implemented using discrete analog integrated circuits, but the frequency resolution is provided by a direct digital synthesis chip controlled by a simple PIC microcontroller. The PLL has excellent frequency resolution and noise, and can be controlled and read by a computer via a USB connection.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7775">http://arxiv.org/abs/1307.7775</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-89352335135461102792013-07-30T00:02:00.009-07:002013-07-30T00:02:39.330-07:001305.2106 (Hrachya B. Nersisyan et al.)<h2 class="title"><a href="http://arxiv.org/abs/1305.2106">Second-order Born approximation for the scattering phase shifts:<br /> Application to the Friedel sum rule</a> [<a href="http://arxiv.org/pdf/1305.2106">PDF</a>]</h2>Hrachya B. Nersisyan, José M. Fernández-Varea<a name='more'></a><blockquote class="abstract">Screening effects are important to understand various aspects of ion-solid interactions and, in particular, play a crucial role in the stopping of ions in solids. In this paper the phase shifts and scattering amplitudes for the quantum-mechanical elastic scattering within up to the second-order Born (B2) approximation are revisited for an arbitrary spherically-symmetric electron-ion interaction potential. The B2 phase shifts and scattering amplitudes are then used to derive the Friedel sum rule (FSR) involving the second-order Born corrections. This results in a simple equation for the B2 perturbative screening parameter of an impurity ion immersed in a fully degenerate electron gas which, as expected, turns out to depend on the ion atomic number $Z_{1}$ unlike the first-order Born (B1) screening parameter reported earlier by some authors. Furthermore, our analytical results for the Yukawa, hydrogenic, Hulth\'{e}n, and Mensing potentials are compared, for both positive and negative ions and a wide range of one-electron radii, to the exact screening parameters calculated self-consistently by imposing the FSR requirement. It is shown that the B2 screening parameters agree excellently with the exact values at large and moderate densities of the degenerate electron gas, while at lower densities they progressively deviate from the exact numerical solutions but are nevertheless more accurate than the prediction of the B1 approximation. In addition, a simple Pad\'{e} approximant to the Born series has been developed that improves the performance of the perturbative FSR for any negative ion as well as for $Z_{1}=+1$.</blockquote>View original: <a href="http://arxiv.org/abs/1305.2106">http://arxiv.org/abs/1305.2106</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-73176432675942038452013-07-30T00:02:00.007-07:002013-07-30T00:02:38.323-07:001307.7453 (V I Kruglov et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7453">A dense Bose fluid at zero temperature: condensation and clusters in<br /> liquid He-4</a> [<a href="http://arxiv.org/pdf/1307.7453">PDF</a>]</h2>V I Kruglov, M J Collett<a name='more'></a><blockquote class="abstract">We present a full set of wave equations describing a dense Bose fluid, applicable both to non- ideal gases and to liquid 4He. The phonon spectrum in liquid 4He is found and the fraction of condensed particles is calculated at zero temperature for a wide range of densities. The theory also yields the ground-state energy for the quantum liquid 4He in agreement to high accuracy with Monte Carlo simulations and experimental data at low pressure. We also present the derivation of a generalized Hartree-Fock equation describing roton clusters in low temperature liquid 4He, allowing us to confirm that, at low enough temperatures and for a wide range of pressures, the stable clusters consist of 13 bound atoms.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7453">http://arxiv.org/abs/1307.7453</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-1274263896699438112013-07-30T00:02:00.005-07:002013-07-30T00:02:37.314-07:001307.7599 (M. Mootz et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7599">Pair-excitation energetics of highly correlated many-body states</a> [<a href="http://arxiv.org/pdf/1307.7599">PDF</a>]</h2>M. Mootz, M. Kira, S. W. Koch<a name='more'></a><blockquote class="abstract">A microscopic approach is developed to determine the excitation energetics of highly correlated quasi-particles in optically excited semiconductors based entirely on a pair-correlation function input. For this purpose, the Wannier equation is generalized to compute the energy per excited electron-hole pair of a many-body state probed by a weak pair excitation. The scheme is verified for the degenerate Fermi gas and incoherent excitons. In a certain range of experimentally accessible parameters, a new stable quasi-particle state is predicted which consists of four to six electron-hole pairs forming a liquid droplet of fixed radius. The energetics and pair-correlation features of these "quantum droplets" are analyzed.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7599">http://arxiv.org/abs/1307.7599</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-92081574038055659412013-07-30T00:02:00.003-07:002013-07-30T00:02:36.388-07:001307.7679 (Venkat Chandrasekhar et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7679">A real-time software simulator for scanning force microscopy</a> [<a href="http://arxiv.org/pdf/1307.7679">PDF</a>]</h2>Venkat Chandrasekhar, Manan Mehta<a name='more'></a><blockquote class="abstract">We describe software that simulates the hardware of a scanning force microscope. The essential feature of the software is its real-time response, which is critical for mimicking the behavior of real scanning probe hardware. The simulator runs on an open-source real time Linux kernel, and can be used to test scanning probe microscope control software as well as theoretical models of different types of scanning probe microscopes. We describe the implementation of a tuning-fork based atomic force microscope and a dc electrostatic force microscope, and present representative images obtained from these models.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7679">http://arxiv.org/abs/1307.7679</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-12419072235552195862013-07-30T00:02:00.001-07:002013-07-30T00:02:33.623-07:001307.7686 (Ariel Haziot et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7686">Critical dislocation speed in helium-4 crystals</a> [<a href="http://arxiv.org/pdf/1307.7686">PDF</a>]</h2>Ariel Haziot, Andrew Fefferman, Fabien Souris, John Beamish, Humphrey Maris, Sébastien Balibar<a name='more'></a><blockquote class="abstract">Our experiments show that in $^4$He crystals, the binding of $^3$He impurities to dislocations does not necessarily imply their pinning. Indeed, in these crystals, there are two different regimes of the motion of dislocations when impurities bind to them. At lowdriving strain $\epsilon$ and frequency $\omega$, where the dislocation speed is less than a critical value (45 $\mu$m/s), dislocations and impurities apparently move together. Impurities really pin the dislocations only at higher values of $\omega$. The critical speed separating the two regimes is two orders of magnitude smaller than the average speed of free $^3$He impurities in the bulk crystal lattice.We obtained this result by studying the dissipation of dislocation motion as a function of the frequency and amplitude of a driving strain applied to a crystal at low temperature. Our results solve an apparent contradiction between some experiments, which showed a frequency-dependent transition temperature from a soft to a stiff state, and other experiments or models where this temperature was assumed to be independent of frequency. The impurity pinning mechanism for dislocations appears to be more complicated than previously assumed.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7686">http://arxiv.org/abs/1307.7686</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-90211555215089341422013-07-26T00:46:00.007-07:002013-07-26T00:46:20.314-07:001307.6632 (Michikazu Kobayashi et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.6632">Kelvin modes as Nambu-Goldstone modes along superfluid vortices and<br /> relativistic strings: finite volume size effects</a> [<a href="http://arxiv.org/pdf/1307.6632">PDF</a>]</h2>Michikazu Kobayashi, Muneto Nitta<a name='more'></a><blockquote class="abstract">We study Kelvin modes and translational zero modes excited along a quantized vortex and relativistic global string in superfluids and a relativistic field theory, respectively, by constructing the low-energy effective theory of these modes. We find that they become exact gapless Nambu-Goldstone modes only in a system with the infinite volume limit. On the other hand, in a system with the finite volume, we find an imaginary massive gap causing the tachyonic instability above some critical wavelength in the relativistic theory. We also find in the non-relativistic theory that Kelvin modes with wavelengths longer than some critical value propagate in the direction opposite to those with shorter length, contrary to conventional understanding. The number of Nambu-Goldstone modes also saturate the equality of the Nielsen-Chadha inequality for both relativistic and non-relativistic theories.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6632">http://arxiv.org/abs/1307.6632</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-32288220989792985912013-07-26T00:46:00.005-07:002013-07-26T00:46:19.374-07:001307.6640 (Jean-Nicolas Longchamp et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.6640">Low-energy electron holographic imaging of ultraclean graphene-supported<br /> gold-nanorods</a> [<a href="http://arxiv.org/pdf/1307.6640">PDF</a>]</h2>Jean-Nicolas Longchamp, Conrad Escher, Tatiana Latychevskaia, Hans-Werner Fink<a name='more'></a><blockquote class="abstract">An ideal support for electron microscopy shall be as thin as possible and interact as little as possible with the primary electrons. Since graphene is atomically thin and made up of carbon atoms arranged in a honeycomb lattice, the potential to use graphene as substrate in electron microscopy is enormous. Until now graphene has hardly ever been used for this purpose because the cleanliness of freestanding graphene before or after deposition of the objects of interest was insufficient. We demonstrate here by means of low-energy electron holographic imaging that freestanding graphene prepared with the Platinum-metal catalysis method remains ultraclean even after re-exposure to ambient conditions and deposition of gold-nanorods from the liquid phase. In the holographic reconstruction of the gold particles the organic shell surrounding the objects is imaged while it is not detectable in SEM images of the very same sample, demonstrating the tremendous potential of low-energy electron holography for the imaging of graphene-supported single biomolecules.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6640">http://arxiv.org/abs/1307.6640</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-67932859163386714772013-07-26T00:46:00.003-07:002013-07-26T00:46:18.732-07:001307.6667 (Patrizia Monachesi et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.6667">Electronic structure and magnetic properties of Mn, Co, and<br /> Ni-substitution of Fe in Fe4N</a> [<a href="http://arxiv.org/pdf/1307.6667">PDF</a>]</h2>Patrizia Monachesi, Torbjörn Björkman, Thomas Gasche, Olle Eriksson<a name='more'></a><blockquote class="abstract">The magnetic properties of Mn, Co and Ni substituted Fe4N are calculated from first principles theory. It is found that the generalized gradient approximation reproduces with good accuracy the magnetic moment and equilibrium volume for the parent Fe4N structure, with the atomic moment largest for the Fe atom furthest away from the N atom (Fe I site), approaching a value of 3 muB/atom, whereas the Fe atom closer to the N atom (Fe II site) has a moment closer to that of bcc Fe. Substitution of Fe for Mn, Co or Ni, shows an intricate behavior in which the Mn substitution clearly favors the Fe II site, Ni favors substitution on the Fe I site and Co shows no strong preference for either lattice site. Ni and Co substitution results in a ferromagnetic coupling to the Fe atoms, whereas Mn couples antiferromagnetically on the Fe II site and ferromagnetically on the Fe I site. For all types of doping, the total magnetic moment is enhanced compared with Fe4N only in the energetically very unfavorable case of Mn doping at the Fe I site.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6667">http://arxiv.org/abs/1307.6667</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-66424750308602665682013-07-26T00:46:00.001-07:002013-07-26T00:46:17.762-07:001307.6782 (P. J. Heikkinen et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.6782">Relaxation of Bose-Einstein Condensates of Magnons in Magneto-Textural<br /> Traps in Superfluid 3He-B</a> [<a href="http://arxiv.org/pdf/1307.6782">PDF</a>]</h2>P. J. Heikkinen, S. Autti, V. B. Eltsov, J. J. Hosio, M. Krusius, V. V. Zavjalov<a name='more'></a><blockquote class="abstract">In superfluid 3He-B externally pumped quantized spin-wave excitations or magnons spontaneously form a Bose-Einstein condensate in a 3-dimensional trap created with the order-parameter texture and the polarizing field minimum. The condensation is manifested by coherent precession of the magnetization with a common frequency in a large sample volume. The trap shape is controlled by the profile of the applied magnetic field and by the condensate itself via the spin-orbit interaction. The trapping potential can be experimentally determined with the spectroscopy of the magnon levels in the trap. We have measured the decay of the ground-level condensates after switching the pumping off in the temperature range (0.14{\div}0.2)Tc at 0.5 bar pressure. Two contributions to the relaxation are identified: spin-diffusion with the diffusion coefficient proportional to the density of thermal quasiparticles and the approximately temperature-independent radiation damping caused by the losses in the NMR pick-up circuit. The measured dependence of the relaxation on the shape of the trapping potential is in a good agreement with our calculations based on the magnetic field profile and the magnon-modified texture shape. The obtained values of the spin diffusion coefficient at low temperatures agree with the theoretical prediction and earlier measurements at temperatures above 0.5Tc.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6782">http://arxiv.org/abs/1307.6782</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-71799880059261994932013-07-23T00:01:00.007-07:002013-07-23T00:01:21.800-07:001307.3186 (C. -I. Chou et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.3186">Localization and Recurrence of Quantum Walk in Periodic Potential on a<br /> Line</a> [<a href="http://arxiv.org/pdf/1307.3186">PDF</a>]</h2>C. -I. Chou, C. -L. Ho<a name='more'></a><blockquote class="abstract">We present a model of quantum walk in periodic potential on the line. We take the simple view that different potentials affect differently the way the coin state of the walker is changed. Thus we suppose the coin state is changed according to a coin operator $C_0$ when there is no potential, and $C_p$ when the field is present. For simplicity and definiteness, we choose in this work $C_0=I$ and $C_p=H$. This means that the walker's coin state is unaffected at sites without potential, and is rotated in an unbiased way according to Hadamard matrix at sites with potential. This is the simplest and most natural model of a quantum walk in a periodic potential with two coins. Six generic cases of such quantum walks were studied numerically. It is found that of the six cases, four cases display significant localization effect, where the walker is confined in the neighborhood of the origin for sufficiently long times. Associated with such localization effect is the recurrence of the probability of the walker returning to the neighborhood of the origin. In these four cases, the number of points with Hadamard coin is "sufficiently" larger than the number of points with identity coin. This implies the existence of critical values of period $N$ for these cases.</blockquote>View original: <a href="http://arxiv.org/abs/1307.3186">http://arxiv.org/abs/1307.3186</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-81428073957627936592013-07-23T00:01:00.005-07:002013-07-23T00:01:20.588-07:001307.5573 (Shingo Kobayashi et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.5573">Topological influence and back-action between topological excitations</a> [<a href="http://arxiv.org/pdf/1307.5573">PDF</a>]</h2>Shingo Kobayashi, Nicolas Tarantino, Masahito Ueda<a name='more'></a><blockquote class="abstract">Topological objects can influence each other if the underlying homotopy groups are non-Abelian. Under such circumstances, the topological charge of each individual object is no longer a conserved quantity and can be transformed to each other. Yet, we can identify the conservation law by considering the back-action of topological influence. We develop a general theory of topological influence and back-action based on the commutators of the underlying homotopy groups. We illustrate the case of the topological influence of a half-quantum vortex on the sign change of a point defect and point out that the topological back-action from the point defect is such twisting of the vortex that the total twist of the vortex line carries the change in the point-defect charge to conserve the total charge. We use this theory to classify charge transfers in condensed matter systems and show that a non-Abelian charge transfer can be realized in a spin-2 Bose-Einstein condensate.</blockquote>View original: <a href="http://arxiv.org/abs/1307.5573">http://arxiv.org/abs/1307.5573</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-18852932327318155172013-07-23T00:01:00.003-07:002013-07-23T00:01:19.428-07:001307.5584 (I. H. Neumann et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.5584">Vortex pinning by surface geometry in superfluid helium</a> [<a href="http://arxiv.org/pdf/1307.5584">PDF</a>]</h2>I. H. Neumann, R. J. Zieve<a name='more'></a><blockquote class="abstract">We present measurements of how a single vortex line in superfluid helium interacts with a macroscopic bump on the chamber wall. At a general level our measurements confirm computational work on vortex pinning by a hemispherical bump, but not all the details agree. Rather than observing a unique pin location, we find that a given applied velocity field can support pinning at multiple sites along the bump, both near its apex and near its edge. We also find that pinning is less favorable than expected. A vortex can pass near or even traverse the bump itself with or without pinning, depending on its path of approach to the bump.</blockquote>View original: <a href="http://arxiv.org/abs/1307.5584">http://arxiv.org/abs/1307.5584</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-77372223445996429482013-07-23T00:01:00.001-07:002013-07-23T00:01:18.336-07:001307.5656 (Jean-François Camenen et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.5656">Confined packings of frictionless spheres and polyhedra</a> [<a href="http://arxiv.org/pdf/1307.5656">PDF</a>]</h2>Jean-François Camenen, Yannick Descantes, Patrick Richard<a name='more'></a><blockquote class="abstract">By means of numerical simulations, we study the influence of confinement on three-dimensional random close packed (RCP) granular materials subject to gravity. The effects of grain shape (spherical or polyhedral) and polydispersity on this dependence are investigated. In agreement with a simple geometrical model, the solid fraction is found to decrease linearly for increasing confinement no matter the grain shape. This decrease remains valid for bidisperse sphere packings although the gradient seems to reduce significantly when the proportion of small particles reaches 40% by volume. The aforementioned model is extended to capture the effect of the confinement on the coordination number.</blockquote>View original: <a href="http://arxiv.org/abs/1307.5656">http://arxiv.org/abs/1307.5656</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-16861102552413024192013-07-22T00:00:00.001-07:002013-07-22T00:00:56.767-07:001307.5282 (Laurent Boué et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.5282">Analytic solution of the dynamics of quantum vortex reconnection</a> [<a href="http://arxiv.org/pdf/1307.5282">PDF</a>]</h2>Laurent Boué, Dmytro Khomenko, Victor S. L'vov, Itamar Procaccia<a name='more'></a><blockquote class="abstract">Experimental and simulational studies of the dynamics of vortex reconnections in quantum fluids showedthat the distance $d$ between the reconnecting vortices is close to a universal time dependence $d=D[\kappa|t_0-t|]^\alpha$ with $\alpha$ fluctuating around 1/2 and $\kappa=h/m$ is the quantum of circulation. Dimensional analysis, based on the assumption that the quantum of circulation $\kappa=h/m$ is the only relevant parameter in the problem, predicts $\alpha=1/2$. The theoretical calculation of the dimensionless coefficient $D$ in this formula remained an open problem. In this Letter we present an analytic calculation of $D$ in terms of the given geometry of the reconnecting vortices. We start from the numerically observed generic geometry on the way to vortex reconnection and demonstrate that the dynamics is well described by a self-similar analytic solution which provides the wanted information.</blockquote>View original: <a href="http://arxiv.org/abs/1307.5282">http://arxiv.org/abs/1307.5282</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-27169992105077334312013-07-19T00:45:00.001-07:002013-07-19T00:45:56.872-07:001307.4892 (A. I. Karasevskii)<h2 class="title"><a href="http://arxiv.org/abs/1307.4892">An energy gap in the spectrum of atomic excitations systems</a> [<a href="http://arxiv.org/pdf/1307.4892">PDF</a>]</h2>A. I. Karasevskii<a name='more'></a><blockquote class="abstract">It is shown that atoms in the system can be treated as quantum particles localized in potential wells, created by atomic potentials of neighboring atoms. As a result, the state of atoms in the liquid is characterized by wave functions and the discrete energy spectrum resulting in formation of s and p - zones corresponding to the ground and excited states of helium atoms, respectively, separated by a gap. The width of the gap in system equals ~8.5 K at T=0. Formation of the gap in the energy spectrum of atomic excitations in helium systems allows us to draw the analogy between the physical mechanisms of superfluidity and classical superconductivity.</blockquote>View original: <a href="http://arxiv.org/abs/1307.4892">http://arxiv.org/abs/1307.4892</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-31477341524699014812013-07-18T00:31:00.009-07:002013-07-18T00:31:05.805-07:001307.4513 (Manuel Valiente et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.4513">Effective field theory of interactions on the lattice</a> [<a href="http://arxiv.org/pdf/1307.4513">PDF</a>]</h2>Manuel Valiente, Nikolaj T. Zinner<a name='more'></a><blockquote class="abstract">We consider renormalization of effective field theory interactions by discretizing the continuum on a tight-binding lattice. After studying the one-dimensional problem, we address s-wave collisions in three dimensions and relate the bare lattice coupling constants to the continuum coupling constants. Our method constitutes a very simple avenue for the systematic renormalization in effective field theory, and is especially useful as the number of interaction parameters increases.</blockquote>View original: <a href="http://arxiv.org/abs/1307.4513">http://arxiv.org/abs/1307.4513</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-33966023727243717712013-07-18T00:31:00.007-07:002013-07-18T00:31:04.910-07:001307.4548 (Markus Sproll et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.4548">Low-amplitude magnetic vortex core reversal by non-linear interference<br /> between azimuthal spin waves and the vortex gyromode</a> [<a href="http://arxiv.org/pdf/1307.4548">PDF</a>]</h2>Markus Sproll, Matthias Noske, Hans Bauer, Matthias Kammerer, Ajay Gangwar, Georg Dieterle, Markus Weigand, Hermann Stoll, Christian H. Back, Gisela Schütz<a name='more'></a><blockquote class="abstract">We demonstrate a non-linear interference due to an active 'dual frequency' excitation of both, the sub-GHz vortex gyromode and multi-GHz magneto-static spin waves in ferromagnetic micrometer sized platelets in the vortex state. When the sub-GHz vortex gyromode is excited simultaneously a significant broadband reduction of the switching threshold for spin wave mediated vortex core reversal is observed in both, experiments and micromagnetic simulations. Consequently, the magnetic field amplitudes required for vortex core reversal can be lowered by nearly one order of magnitude. Moreover, additional spin wave resonance frequencies are found which emerge only if the vortex gyromode is actively excited simultaneously which can be explained by frequency doubling and by the broken symmetry of the vortex state.</blockquote>View original: <a href="http://arxiv.org/abs/1307.4548">http://arxiv.org/abs/1307.4548</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-159052183091354020.post-4842944467608080892013-07-18T00:31:00.005-07:002013-07-18T00:31:03.904-07:001307.4559 (Xuetao Zhu et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.4559">Electron-Phonon Coupling on the Surface of Topological Insulators</a> [<a href="http://arxiv.org/pdf/1307.4559">PDF</a>]</h2>Xuetao Zhu, Colin Howard, Jiandong Guo, Michael El-Batanouny<a name='more'></a><blockquote class="abstract">Topological insulators (TIs) are materials that have a bulk electronic band gap like an ordinary insulator but have protected conducting states on their surface. One of the most interesting properties of TIs is their spin helicity, whereby the spin is locked normal to the wave vector of the surface electronic state. The topological surface states should be very stable in TIs, since these spin-textured surface states are robust against spin-independent backscattering. Scattering from defects and other lattice imperfections is possible provided the spin is not completely flipped. However, the quality of TI crystals can be controlled by careful growth, whereas phonons will exist in even the most perfect crystals. Consequently, electron-phonon coupling (EPC) should be the dominant scattering mechanism for surface electronic states at finite temperatures. Hence, the study of EPC in TIs is of exceptional importance in assessing any potential applications. In this article both experimental and theoretical studies of the EPC on the surface of TIs are reviewed, with the contents mainly focused on the typical strong three dimensional TIs, such as Bi2Se3 and Bi2Te3.</blockquote>View original: <a href="http://arxiv.org/abs/1307.4559">http://arxiv.org/abs/1307.4559</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0