Human Dynamics

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Until now, the study of human dynamics has been done only qualitatively. Actually, the present possibility to have quantitative data on the kind and nature of social relationships through social networks is driving a rapid change in the field. Thanks to the emergence of detailed datasets that capture human behavior, we can now follow specific human actions in ultimate detail. One of the first measurable quantity with which one can describe the relationship between humans is the timing and order with which we perform specific tasks.… Read the rest

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Unconventional antiferromagnetism due to Dzyaloshinskii-Moriya interactions

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The relevance of antisymmetric superexchange interactions in spin Hamiltonians describing quantum antiferromagnetic (AF) systems has been acknowledged long ago by Dzyaloshinskii. Soon after, Moriya showed that such interactions arise naturally in perturbation theory due to the spin-orbit coupling in magnetic systems with low symmetry. Nowadays, a number of AF systems are known to belong to the class of Dzyaloshinskii-Moriya (DM) magnets, such as ?-Fe… Read the rest

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Random Lasers

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In a nutshell, a random laser is the coherent emission from active stochastic resonators.

In a series of articles around 1966, a Russian scientist V. S. Letokhov, of the Lebedev Physics Institute in Dubna considered the generation of light in the interstellar medium. In the presence of scatterers, as for example dust particles, photons diffuse like neutrons and, if some mechanism (following Letokhov a “negative absorption”) is able to increase their number, a sort of photonic reactor can be realized.… Read the rest

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Strongly Correlated Superconductivity: how can repulsion enhance Tc?

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In conventional superconductors, the repulsive interaction between electrons opposes to phonon-mediated pairing. We have shown that even phonon-mediated superconductivity can be favoured by repulsion under suitable conditions which are realized in fullerenes.

Trivalent alkali-doped fullerenes are almost certainly electron-phonon superconductors, and their critical temperature can reach around 40K. There are however many experimental evidences that seem to exclude a simple BCS (or Migdal-Eliashberg) scenario, since electron-electron correlations are likely to play a central role.… Read the rest

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Spin Glasses: a brief introduction

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Spin Glasses are dilute magnetic alloys where the interactions between spins are randomly ferromagnetic or anti-ferromagnetic, and are considered as paradigmatic examples of frozen disorder. The presence of disorder (the random interactions) induces frustration and a greater difficulty for the system to find optimal configurations. As a consequence, these systems exhibit non trivial thermodynamic and dynamic properties, different and richer than those observed in their non disordered counterpart.… Read the rest

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What is Econophysics?

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Collective phenomena in economics, social sciences and ecology are very attractive for statistical physicists, especially in view of the empirical abundance of non-trivial fluctuation patterns and statistical regularities — think of returns in financial markets or of allometric scaling in ecosystems — which pose intriguing theoretical challenges. On an abstract level, the problems at stake are indeed not too different from, say, understanding how spontaneous magnetization may arise in a magnetic system, since what one wants in both cases is to understand how the effects of interactions at the microscopic scale can build up to the macroscopic scale.… Read the rest

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Spin-orbit interaction and spintronics

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One of the new frontiers in condensed matter physics is development and engineering of electronic devices which carrier “bit” informations in the spin degree of freedom of the electronc instead of their charge. This research line is called indeed “spintronics”. Within this context the spin-or

Rashba band-spilling and spin ordering: from J. Sinova et al., Phys. Rev. Lett. 92, 126603 (2004).

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Inhomogeneities in Cuprates

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If the mechanism of high-Tc superconductivity is electronic, to understand the electronic excitation spectrum is as important as to understand phonons was important to develop BCS theory. In this regard charge and spin inhomogeneous states, often found in strongly correlated systems, are interesting because they can support new collective modes, “electronic phonons”, that would not be present in a weakly interacting fluid.… Read the rest

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Unconventional electron-phonon interaction and nonadiabatic effects

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The conventional understanding of the electron-phonon phenomenology in condensed matter strongly relies on the adiabatic assumption, i.e. that nuclei dynamics is much slower than the electron one. In solid crystals the validity of this assumption is usually related to the comparison of the phonon frequencies  with the Fermi energy EF. In conventional systems , assuring thus the reliability of the adiabatic assumption.… Read the rest

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