Effects of nonorthogonality in the time-dependent current through tunnel junctions

A theoretical technique which allows to include contributions from non-orthogonality of the electron states in the leads connected to a tunneling junction is derived. The theory is applied to a single barrier tunneling structure and a simple expression for the time-dependent tunneling current is derived showing explicit dependence of the overlap. The overlap proves to be necessary for a better quantitative description of the tunneling current, and our theory reproduces experimental results substantially better compared to standard approaches.Comment: 4 pages, 1 table, 1 figur

Experimental Study of Active Magnetic Regenerator (AMR) Composed of Spherical GdN

Presented at the 16th International Cryocooler Conference, held May 17-20, 2008 in Atlanta, Georgia.An experimental study of an active magnetic regenerator (AMR) employing GdN was carried out. Spherical GdN material was synthesized by the hot isostatic pressing (HIP) method. The specific heat was measured and the magnetic entropy change ΔS and adiabatic temperature change ΔTad were calculated. The refrigeration with an AMR cycle was tested in the temperature range between 48 and 66 K with the field swinging from 1.2 to 3.7 T at upper side and from 2.0 to 4.0 T at lower side of the regenerator bed filled with GdN spheres. A temperature span, ΔTspan,was found to develop soon after starting the cycle and became more than 4.7 degree in steady state. This temperature span ΔTspan was at least 1.5 times as large as the adiabatic temperature change ΔTad

Critical Properties of Condensation of Field-Induced Triplet Quasiparticles

A review on the field-induced magnetic ordering is given, together with some results of a quantum Monte Carlo simulation focused on the critical behevior near the quantum critical point.Comment: Proceedings of SPQS, Sendai, 200