“Unconventional low-energy excitations in cuprate superconductors” N.-C. Yeh and A. D. Beyer, invited review article, Int. J. Mod. Phys. B 23, 4543 (2009). [arxiv:0909.0322]
http://www.worldscientific.com/doi/abs/10.1142/S021797920905403X
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