We investigate a new method to search for keV-scale sterile neutrinos that could account for Dark Matter. Neutrinos trapped in our galaxy could be captured on stable 163Dy if their mass is greater than 2.83 keV. Two experimental realizations are studied, an integral counting of 163Ho atoms in dysprosium-rich ores and a real-time measurement of the emerging electron spectrum in a dysprosium-based detector. The capture rates are compared to the solar neutrino and radioactive backgrounds. An integral counting experiment using several kilograms of 163Dy could reach a sensitivity for the sterile-to-active mixing angle sin(theta)2 of 10-5 significantly exceeding current laboratory limits. Smaller mixing angles may be explored with a real-time experiment.
We study the dynamics of a two-dimensional ensemble of randomly distributed classical Heisenberg spins with isotropic RKKY and weaker anisotropic dipole-dipole couplings. Such ensembles may give rise to the flux noise observed in SQUIDs with a 1/f^α power spectrum (α≲1). We solve numerically the Landau-Lifshiftz-Gilbert equations of motion in the dissipationless limit. We find that Ising type fluctuators, which arise from spin clustering close to a spin-glass critical behavior with T_c=0, give rise to 1/f^α noise. Even weak anisotropic interactions lead to a crossover from the Heisenberg-type criticality to the much stronger Ising-type criticality. The temperature dependent exponent α(T)≲1 grows and approaches unity when the temperature is lowered. This mechanism acts in parallel to the spin diffusion mechanism. Whereas the latter is sensitive to the device geometry, the spin-clustering mechanism is largely geometry independent.
Based on the paper:
Juan Atalaya, John Clarke, Gerd Schön, Alexander Shnirman
Phys. Rev. B 90, 014206 (2014)
