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Université de Fribourg

Enhancing speed of pinning synchronizability: low-degree nodes with high feedback gains

Zhou, Ming-Yang ; Zhuo, Zhao ; Liao, Hao ; Fu, Zhong-Qian ; Cai, Shi-Min

In: Scientific Reports, 2015, vol. 5, p. 17459

Controlling complex networks is of paramount importance in science and engineering. Despite recent efforts to improve controllability and synchronous strength, little attention has been paid to the speed of pinning synchronizability (rate of convergence in pinning control) and the corresponding pinning node selection. To address this issue, we propose a hypothesis to restrict the control cost,...

Université de Fribourg

Superconductivity from emerging magnetic moments

Hoshino, Shintaro ; Werner, Philipp

In: Physical Review Letters, 2015, vol. 115, no. 24, p. 247001

Multiorbital Hubbard models are shown to exhibit a spatially isotropic spin-triplet superconducting phase, where equal-spin electrons in different local orbitals are paired. This superconducting state is stabilized in the spin-freezing crossover regime, where local moments emerge in the metal phase, and the pairing is substantially assisted by spin anisotropy. The phase diagram features a...

Université de Fribourg

Nonthermal Melting of Néel Order in the Hubbard Model

Balzer, Karsten ; Wolf, F. Alexander ; McCulloch, Ian P. ; Werner, Philipp ; Eckstein, Martin

In: Physical Review X, 2015, vol. 5, no. 3, p. 031039

Symmetry-broken states such as magnetic order and superconductivity are the hallmark of complex properties in solids. An intriguing new direction in condensed-matter physics is to manipulate these properties on the fastest possible time scales using ultrashort laser pulses. Theoretically, however, the collective many-particle dynamics that is responsible for the formation and melting of...

Université de Fribourg

Double-expansion impurity solver for multiorbital models with dynamically screened $U$ and $J$

Steiner, Karim ; Nomura, Yusuke ; Werner, Philipp

In: Physical Review B, 2015, vol. 92, no. 11, p. 115123

We present a continuous-time Monte Carlo impurity solver for multiorbital impurity models which combines a strong-coupling hybridization expansion and a weak-coupling expansion in the Hund's coupling parameter J. This double-expansion approach allows to treat the dominant density-density interactions U within the efficient segment representation. We test the approach for a two-orbital model with...

Université de Fribourg

Beyond the Hubbard bands in strongly correlated lattice bosons

Strand, Hugo U. R. ; Eckstein, Martin ; Werner, Philipp

In: Physical Review A, 2015, vol. 92, no. 6, p. 063602

We investigate features in the single-particle spectral function beyond the Hubbard bands in the strongly correlated normal phase of the Bose-Hubbard model. There are two distinct classes of additional peaks generated by the bosonic statistics. The first type is thermally activated Hubbard “sidebands”, with the same physical origin as the zero-temperature Hubbard bands, but generated by...

Université de Fribourg

Fidelity susceptibility perspective on the Kondo effect and impurity quantum phase transitions

Wang, Lei ; Shinaoka, Hiroshi ; Troyer, Matthias

In: Physical Review Letters, 2015, vol. 115, no. 23, p. 236601

The Kondo effect is a ubiquitous phenomenon appearing at low temperature in quantum confined systems coupled to a continuous bath. Efforts in understanding and controlling it have triggered important developments across several disciplines of condensed matter physics. A recurring pattern in these studies is that the suppression of the Kondo effect often results in intriguing physical phenomena...

Université de Fribourg

Charge-spin-orbital fluctuations in mixed valence spinels: Comparative study of ${\mathrm{AlV}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$

Uehara, Amane ; Shinaoka, Hiroshi ; Motome, Yukitoshi

In: Physical Review B, 2015, vol. 92, no. 19, p. 195150

Mixed valence spinels provide a fertile playground for the interplay between charge, spin, and orbital degrees of freedom in strongly correlated electrons on a geometrically frustrated lattice. Among them, AlV2O4 and LiV2O4 exhibit contrasting and puzzling behavior: self-organization of seven-site clusters and heavy fermion behavior. We theoretically perform a comparative study of...

Université de Fribourg

Lifetime of fluorescent dye molecules in dense aqueous suspensions of polystyrene nanoparticles

Scalia, Giuseppe ; Scheffold, Frank

In: Optics Express, 2015, vol. 23, no. 23, p. 29342

We study the lifetime of two common fluorescent dye molecules from the Alexa Fluor NHS Ester family dissolved in water in an opaque aqueous dispersion of dielectric polystyrene nanoparticles. We investigate the role of the dispersion composition by varying the particle concentration and adding SDS (sodium dodecyl sulfate) surfactant molecules. The observed strong changes in lifetime of Alexa 430...

Université de Fribourg

Localized magnetic plasmons in all-dielectric $\ensuremath{\mu}<0$ metastructures

Paniagua-Domínguez, R. ; Froufe-Pérez, Luis S. ; Sáenz, J. J. ; Sánchez-Gil, J. A.

In: Physical Review B, 2015, vol. 91, no. 23, p. 235120

Metamaterials are known to exhibit a variety of electromagnetic properties nonexisting in nature. We show that an all-dielectric (nonmagnetic) system consisting of deep-subwavelength, high-permittivity resonant spheres possesses effective negative magnetic permeability (dielectric permittivity being positive and small). Due to the symmetry of the electromagnetic wave equations in classical...

Université de Fribourg

Subshell-selective x-ray studies of radiative recombination of ${\mathrm{U}}^{92+}$ ions with electrons for very low relative energies

Banaś, D. ; Pajek, M. ; Surzhykov, A. ; Stöhlker, Th. ; Brandau, C. ; Gumberidze, A. ; Kozhuharov, C. ; Beyer, H. F. ; Böhm, S. ; Bosch, F. ; Czarnota, M. ; Chatterjee, S. ; Dousse, Jean-Claude ; Fritzsche, S. ; Hagmann, S. ; Liesen, D. ; Mokler, P. H. ; Müller, A. ; Kumar, A. ; Reuschl, R. ; Sierpowski, D. ; Spillmann, U. ; Szlachetko, Jakoub ; Tashenov, S. ; Trotsenko, S. ; Verma, P. ; Warczak, A.

In: Physical Review A, 2015, vol. 92, no. 3, p. 032710

Radiative recombination (RR) into the K shell and L subshells of U92+ ions interacting with cooling electrons has been studied in an x-ray RR experiment at the electron cooler of the Experimental Storage Ring at GSI. The measured radiative recombination rate coefficients for electron-ion relative energies in the range 0–1000 meV demonstrate the importance of relativistic effects. The observed...