Macroscopic evidence for quantum criticality and field-induced quantum   fluctuations in cuprate superconductors
  We present macroscopic experimental evidence for field-induced microscopic quantum fluctuations in different hole- and electron-type cuprate superconductors with varying doping levels and numbers of CuO$_2$ layers per unit cell. The significant suppression of the zero-temperature in-plane magnetic irreversibility field relative to the paramagnetic field in all cuprate superconductors suggests strong quantum fluctuations due to the proximity of the cuprates to quantum criticality. 
A. D. Beyer, V. S. Zapf, H. Yang, F. Fabris, M. S. Park, K. H. Kim,   S.-I. Lee, and N.-C. Yeh