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Luminescent, Film, and Cryogenic Detectors
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
The seminal paper that began the flurry of interest in these detectors is that by Day et al. [2003], upon which most of the following discussion is based. Recall that in a superconductor a DC supercurrent, carried by Cooper pairs, flows without resistance. A Cooper pair, which is bound together by electron-phonon interactions, has a binding energy wq<1.7ϵgTc. However, superconductors have a non-zero impedance for AC currents. An electric field applied near the surface of a superconductor accelerates the Cooper pairs and, thereby stores energy in the superconductor in the form of kinetic energy. Because the supercurrent is non-dissipative, the stored energy may be extracted by reversing the electric field. Similarly, energy may be stored in the magnetic field inside the superconductor, which penetrates only a short distance, λ ≃ 50 nm, from the surface. Consequently, a superconductor has a surface inductance Ls = μoλ caused by the reactive energy flow between the superconductor and the electromagnetic field. The surface impedance Zs = Rs + jωLs35 includes a surface resistance Rs to account for AC losses at angular frequency ω caused by the small fraction of electrons that are not in Cooper pairs, i.e., the quasiparticles. For temperatures T ≪ Tc we find that Rs ≪ ωLs, thereby having negligible losses in the resonance circuit [Baselmans 2011].
Introduction to Refractory Josephson Junctions
Published in Edward Wolf, Gerald Arnold, Michael Gurvitch, John Zasadzinski, Josephson Junctions, 2017
The Josephson effect entails a tunneling supercurrent density J=Josinφ $$ {\mathbf{J}} = {\mathbf{Jo}}sin\varphi ~~~~ $$
Vibrating reed magnetometer studies of superconducting and magnetic materials
Published in Philosophical Magazine, 2020
L. E. De Long, A. P. Kaphle, B. Farmer
Improvements in VRM by the UKG have facilitated precision studies of the mixed state of SC materials far below Hc2(T). VR data for thin-film, single-crystal and ceramic (Ba0.6K0.4)BiO3 samples demonstrated the sensitivity of VRM to subtle sample inhomogeneities, as shown in Figures 8–10. Data for an epitaxial (Ba0.6K0.4)BiO3 film had particularly high SNR, especially considering the sample was optically transparent with small dimensions (thickness ∼ 50 nm and area ∼ 2 mm2)! A peak in dissipation (imaginary part m” of m) is generally observed as temperature is decreased just below the sample SC TC, due to competition between the decreasing penetration depth λ(T) and increasing supercurrent density [12,17]. The 1/Q peak of the film is narrower than that of fine-grained, bulk ceramic samples [43,64], reflecting a surprisingly high compositional homogeneity of the film. In contrast, a nominal single crystal that appeared to be of high quality when characterised by DC and AC SQUID magnetometry (see Figure 8) yielded broad, multi-peaked 1/Q data from VRM (see Figure 10), indicating significant composition gradients and growth defects were present in apparently ‘clean’, bulk samples. This work served as an early warning that SC materials with moderate-to-high TC’s may have a general tendency to phase separate or break up into an intrinsic N/SC domain structures [65] with length scales comparable to the coherence length ξo [19].