Small-Angle X-ray and neutron scattering from diamond single crystals

Results of Small-Angle Scattering study of diamonds with various types of point and extended defects and different degrees of annealing are presented. It is shown that thermal annealing and/or mechanical deformation cause formation of nanosized planar and threedimensional defects giving rise to Small-Angle Scattering. The defects are often facetted by crystallographic planes 111, 100, 110, 311, 211 common for diamond. The scattering defects likely consist of clusters of intrinsic and impurity-related defects; boundaries of mechanical twins also contribute to the SAS signal. There is no clear correlation between concentration of nitrogen impurity and intensity of the scattering.Comment: 6 pages, 5 figures; presented at SANS-YuMO User Meeting 2011, Dubna, Russi

The Resonance Peak in Sr2_2RuO4_4: Signature of Spin Triplet Pairing

We study the dynamical spin susceptibility, $\chi({\bf q}, \omega)$, in the normal and superconducting state of Sr$_2$RuO$_4$. In the normal state, we find a peak in the vicinity of ${\bf Q}_i\simeq (0.72\pi,0.72\pi)$ in agreement with recent inelastic neutron scattering (INS) experiments. We predict that for spin triplet pairing in the superconducting state a {\it resonance peak} appears in the out-of-plane component of $\chi$, but is absent in the in-plane component. In contrast, no resonance peak is expected for spin singlet pairing.Comment: 4 pages, 4 figures, final versio

Incorporating Inertia Into Multi-Agent Systems

We consider a model that demonstrates the crucial role of inertia and stickiness in multi-agent systems, based on the Minority Game (MG). The inertia of an agent is introduced into the game model by allowing agents to apply hypothesis testing when choosing their best strategies, thereby reducing their reactivity towards changes in the environment. We find by extensive numerical simulations that our game shows a remarkable improvement of global cooperation throughout the whole phase space. In other words, the maladaptation behavior due to over-reaction of agents is removed. These agents are also shown to be advantageous over the standard ones, which are sometimes too sensitive to attain a fair success rate. We also calculate analytically the minimum amount of inertia needed to achieve the above improvement. Our calculation is consistent with the numerical simulation results. Finally, we review some related works in the field that show similar behaviors and compare them to our work.Comment: extensively revised, 8 pages, 10 figures in revtex

Probing the role of Nd3+ ions in the weak multiferroic character of NdMn2O5 by optical spectroscopies

Raman and infrared spectroscopies are used as local probes to study the dynamics of the Nd-O bonds in the weakly multiferroic NdMn2O5 system. The temperature dependence of selected Raman excitations reveals the splitting of the Nd-O bonds in NdMn2O5. The Nd3+ ion crystal field (CF) excitations in NdMn2O5 single crystals are studied by infrared transmission as a function of temperature, in the 1800-8000 cm-1 range, and under an applied magnetic field up to 11 T. The frequencies of all 4Ij crystal-field levels of Nd3+ are determined. We find that the degeneracy of the ground-state Kramers doublet is lifted ({\Delta}0 ~7.5 cm-1) due to the Nd3+-Mn3+ interaction in the ferroelectric phase, below TC ~ 28 K. The Nd3+ magnetic moment mNd(T) and its contribution to the magnetic susceptibility and the specific heat are evaluated from {\Delta}0(T) indicating that the Nd3+ ions are involved in the magnetic and the ferroelectric ordering observed below ~ 28 K. The Zeeman splitting of the excited crystal field levels of the Nd3+ ions at low temperature is also analyzed.Comment: This paper is accepted for publication as a Regular Article in Physical Review