1. Berent, I. & Polturak, E. Phys. Rev. Lett. 81, 846–849 (1998).
2. Berent, I. & Polturak, E. J. Low-Temp. Phys. 112, 337–354 (1998).
3. 3.Polturak, E. et al. Physica B (in the press).
4. Schuster, I. et al. Europhys. Lett. 33, 623–628 (1996).
5. 5.Guyer, R. A. in Encyclopedia of Physics 2nd edn (eds Lerner, R. T. & Trigg, G. L.) 486-494 (VCH, New York, 1991).