We experimentally demonstrate an ultra high Q/V nanocavity on SOI substrate. The design is based on modal adaptation within the cavity and allows to measure a quality factor of 58.000 for a modal volume of 0.6(lambda/n)(3) . This record Q/V value of 10(5) achieved for a structure standing on a physical substrate, rather than on membrane, is in very good agreement with theoretical predictions also shown. Based on these experimental results, we show that further refinements of the cavity design could lead to Q/V ratios close to 10(6).

We have studied the magnetic interactions of single-crystalline CePd 2 Si 2 by measurements of the electrical resistivity, specific heat, thermal expansion, magnetic susceptibility, and elastic and inelastic neutron scattering. In the paramagnetic phase the system is characterized by Kondo-type spin fluctuations which give rise to a strong quasielastic signal in the inelastic neutron scattering cross section. Below the antiferromagnetic ordering temperature (T N ϭ8.5 K͒, the quasielastic signal coexists with spin-wave excitations. The spin waves are strongly dispersive, with a minimum energy of 0.83 meV at the magnetic zone center kϭ(1/2,1/2,0). The dispersion can be described in terms of a two-sublattice model with a reduced magnetic exchange interaction and a strong damping of the spin waves due to Kondo screening. The volume dependence of the magnetic interactions has been analyzed using the Grüneisen parameters in order to study the magnetic interactions close to the quantum critical point, which is reached at an applied pressure of about 30 kbar.

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