Positron annihilation study in SmFeAsO and SmFeAsO0.82F0.18

Abstract

SmFeAsO 1 − x F x polycrystalline samples were first studied by positron annihilation lifetime spectroscopy and Doppler-broadening spectroscopy, combined with the calculated results of positron lifetime. The experimental results agree well with the calculated positron bulk lifetime in SmFeAsO and SmFeAsF crystals. The temperature dependence of S-parameter shows a remarkable difference between the parent and superconductor. An abrupt jump of S-parameter is detected around 150 K in parent sample, however, two different slopes were shown below and above superconducting transition. The linearity S-T plot determines one-type of defects through the superconducting transition which must play an important role in superconductivity.

Acoustic birefringence via non-Eulerian metamaterials

“…The recently developed field of metamaterials , however, has offered the intriguing possibility of acquiring artificial structures that, once engineered, can bring about desired bulk properties. In fact, such composites have allowed realization of materials with exotic features such as negative refractive index, offering platforms for various unconventional wave phenomena such as wave cloaking [44], focusing [45], imaging [46] and wavefront modulation [47]. Interestingly, they also have enabled synthesis of electromagnetic artificial composites supporting two, or even an arbitrary large number of low-frequency modes [48].…”