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Recently, a novel material with bilayer kagome lattice Ca10Cr7O28 was proposed to be a gapless quantum spin liquid, due to the lack of long-range magnetic order and the observation of broad diffuse excitations. Here, we present the ultralow-temperature thermal conductivity measurements on single crystals of Ca10Cr7O28 to detect its low-lying magnetic excitations. At finite temperatures, with increasing the magnetic fields, the thermal conductivity exhibits a clear dip around 6 T, which may correspond to a crossover in the magnetic ground state. At the zero-temperature limit, no residual linear term is found at any fields, indicating the absence of gapless itinerant fermionic excitations. Therefore, if the spinons do exist, they are either localized or gapped. In the gapped case, the fitting of our data gives a small gap ∆ ∼ 0.27(2) K. These results put strong constraints on the theoretical description of the ground state in this quantum spin liquid candidate. arXiv:1803.03515v1 [cond-mat.str-el]

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The Fe 0.95 Co 0.05 Si 2 semiconducting film has been successfully grown on glass substrate by magnetron sputtering at substrate temperature of 637 K and then thermal annealing at 823 K for one hour in high vacuum. The Raman data and high Seebeck coefficient suggested that the β-Fe 0.95 Co 0.05 Si 2 semiconducting film was achieved. Room temperature ferromagnetism was observed, and the ferromagnetic phase transition was at about * Corresponding author. 1250097-1 Mod. Phys. Lett. B 2012.26. Downloaded from www.worldscientific.com by NEW YORK UNIVERSITY on 02/06/15. For personal use only. Y. P. Han et al. 380 K. The possible reason for the ferromagnetism of the β-Fe 0.95 Co 0.05 Si 2 semiconducting film was discussed.