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Université de Fribourg

Security and Human Rights – Mind the Balance! : On Security in International Human Rights Law and the Dangers of the Normalization of Emergency

Besson, Samantha

In: Quid? : Fribourg law review, 2017, p. 7-19

In this article, the author analyzes the issue of thebalance between human rights and security. More precisely, she addresses three specific questions:Firstly, should human rights be “balanced” against security per se? Secondly, considering that human rights may be restricted on security grounds in certain circumstances, should the Israeli practice of balancing human rights and security be...

Université de Fribourg

Phase diagram of two-dimensional hard rods from fundamental mixed measure density functional theory

Wittmann, René ; Sitta, Christoph E. ; Smallenburg, Frank ; Löwen, Hartmut

In: The Journal of Chemical Physics, 2017, vol. 147, no. 13, p. 134908

A density functional theory for the bulk phase diagram of two-dimensional orientable hard rods is proposed and tested against Monte Carlo computer simulation data. In detail, an explicit density functional is derived from fundamental mixed measure theory and freely minimized numerically for hard discorectangles. The phase diagram, which involves stable isotropic, nematic, smectic, and...

Université de Fribourg

Ultrafast electronic band gap control in an excitonic insulator

Mor, Selene ; Herzog, Marc ; Golež, Denis ; Werner, Philipp ; Eckstein, Martin ; Katayama, Naoyuki ; Nohara, Minoru ; Takagi, Hide ; Mizokawa, Takashi ; Monney, Claude ; Stähler, Julia

In: Physical Review Letters, 2017, vol. 119, no. 8, p. 086401

We report on the nonequilibrium dynamics of the electronic structure of the layered semiconductor Ta2NiSe5 investigated by time- and angle-resolved photoelectron spectroscopy. We show that below the critical excitation density of FC=0.2 mJ cm−2, the band gap narrows transiently, while it is enhanced above FC. Hartree-Fock calculations reveal that this effect can be explained by the presence...

Université de Fribourg

Tracing the nonequilibrium topological state of Chern insulators

Schüler, Michael ; Werner, Philipp

In: Physical Review B, 2017, vol. 96, no. 15, p. 155122

Chern insulators exhibit fascinating properties, which originate from the topologically nontrivial state characterized by the Chern number. How these properties change if the system is quenched between topologically distinct phases is, however, not fully understood. In this paper, we investigate the quench dynamics of the prototypical massive Dirac model for topological insulators in two...

Université de Fribourg

Magnetic moment evolution and spin freezing in doped BaFe 2 As 2

Pelliciari, Jonathan ; Huang, Yaobo ; Ishii, Kenji ; Zhang, Chenglin ; Dai, Pengcheng ; Chen, Gen Fu ; Xing, Lingyi ; Wang, Xiancheng ; Jin, Changqing ; Ding, Hong ; Werner, Philipp ; Schmitt, Thorsten

In: Scientific Reports, 2017, vol. 7, no. 1, p. 8003

Fe-K β X-ray emission spectroscopy measurements reveal an asymmetric doping dependence of the magnetic moments μbare in electron- and hole-doped BaFe2As2. At low temperature, μbare is nearly constant in hole-doped samples, whereas it decreases upon electron doping. Increasing temperature substantially enhances μbare in the hole-doped region, which is naturally explained by the...

Université de Fribourg

Hund’s coupling driven photocarrier relaxation in the two-band Mott insulator

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

In: Physical Review B, 2017, vol. 96, no. 16, p. 165104

We study the relaxation dynamics of photocarriers in the paramagnetic Mott insulating phase of the half-filled two-band Hubbard model. Using nonequilibrium dynamical mean-field theory, we excite charge carriers across the Mott gap by a short hopping modulation, and simulate the evolution of the photodoped population within the Hubbard bands. We observe an ultrafast charge-carrier relaxation...

Université de Fribourg

Anisotropic Harper-Hofstadter-Mott model: Competition between condensation and magnetic fields

Hügel, Dario ; Strand, Hugo U. R. ; Werner, Philipp ; Pollet, Lode

In: Physical Review B, 2017, vol. 96, no. 5, p. 054431

We derive the reciprocal cluster mean-field method to study the strongly interacting bosonic Harper-Hofstadter-Mott model. The system exhibits a rich phase diagram featuring band insulating, striped superfluid, and supersolid phases. Furthermore, for finite hopping anisotropy, we observe gapless uncondensed liquid phases at integer fillings, which are analyzed by exact diagonalization. The...

Université de Fribourg

Many-body localization phase in a spin-driven chiral multiferroic chain

Stagraczyński, S. ; Chotorlishvili, L. ; Schüler, Michael ; Mierzejewski, M. ; Berakdar, J.

In: Physical Review B, 2017, vol. 96, no. 5, p. 054440

Many-body localization (MBL) is an emergent phase in correlated quantum systems with promising applications, particularly in quantum information. Here, we unveil the existence and analyze this phase in a chiral multiferroic model system. Conventionally, MBL occurrence is traced via level statistics by implementing a standard finite-size scaling procedure. Here, we present an approach based on...

Université de Fribourg

Band gap formation and Anderson localization in disordered photonic materials with structural correlations

Froufe-Pérez, Luis S. ; Engel, Michael ; Sáenz, Juan José ; Scheffold, Frank

In: Proceedings of the National Academy of Sciences, 2017, vol. 114, no. 36, p. 9570–9574

Disordered dielectric materials with structural correlations show unconventional optical behavior: They can be transparent to long-wavelength radiation, while at the same time have isotropic band gaps in another frequency range. This phenomenon raises fundamental questions concerning photon transport through disordered media. While optical transparency in these materials is robust against...

Université de Fribourg

Information filtering based on corrected redundancy-eliminating mass diffusion

Zhu, Xuzhen ; Yang, Yujie ; Chen, Guilin ; Medo, Matúš ; Tian, Hui ; Cai, Shi-Min

In: PLOS ONE, 2017, vol. 12, no. 7, p. e0181402

Methods used in information filtering and recommendation often rely on quantifying the similarity between objects or users. The used similarity metrics often suffer from similarity redundancies arising from correlations between objects’ attributes. Based on an unweighted undirected object-user bipartite network, we propose a Corrected Redundancy-Eliminating similarity index (CRE) which is...