Frequency-dependent tunneling effect

The effect of a larger A that suppresses tunnelling is also seen in the greatly reduced diffusion of H in the Nb-V alloys compared with H in either of the pure metals. Another case where the formulae above for the transition rates of H tunnelling in a two-well potential can quantitatively explain the observed effects, is the temperature and frequency dependence of the NMR spin-lattice relaxation peak around 60 K of H in... 

This suggests to exploit tunneling as an experimental tool to detect crystal field levels of RE-impurities (Fulde et al., 1970). The physical process which should enable this is the energy dependent life time of the conduction electrons. This leads to a frequency dependent superconducting order parameter. The latter causes a structure in the tunneling density of states which can be measured. In order to demonstrate the crystal-field effects we have plotted in fig. 17.25a the tunneling density of states of a superconductor containing RE-... 

The temperature dependence of this rate constant was measured by Al-Soufi et al. [1991], and is shown in Figure 6.17. It exhibits a low-temperature limit of rate constant kc = 8x 105 s 1 and a crossover temperature 7 C = 80K. In accordance with the discussion in Section 2.5, the crossover temperature is approximately the same for hydrogen and deuterium transfer, showing that the low-temperature limit appears when the low-frequency vibrations, whose masses are independent of tunneling mass, become quantal at Tisotope effect increases with decreasing temperature in the Arrhenius region by about two orders of magnitude and approaches a constant value kH/kD = 1.5 x 103 at T[Pg.174]

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