Morfill, G. E., Konopka, U., Kretschmer, M., Rubin-Zuzic, M., Thomas, H. M., Zhdanov, S. K., et al. (2006). The 'classical tunnelling effect'—observations and theory. New Journal of Physics, 8: 7. doi:10.1088/1367-2630/8/1/007.