Pseudogap evidenced by Cu EPR in the normal state of Ortho-III   YBa2Cu3O7-x
  The temperature dependences of g factors of underdoped YBa2Cu3O7-x (Tc approximates 86.5K) indicate that the pseudogap onset temperature T*( approximates 190 K) coincides with the phase boundary established by resistivity, Nernst effect, neutron diffraction and ultrasound measurements in YBCO phase diagram. The obtained empirical relationship between g factors and pseudogap is appropriate for the entire charactering temperature range of Ortho-III YBCO. The EPR signals are ascribed to the localized Cu2+(1) sites based on the quantitative calculations of the g factors by involving the local structures of the paramagnetic copper (1) sites. The present work provides another potential spectroscopic probe for the pseudogap in underdoped high Tc superconductors and the origin of EPR and related mechanisms in YBCO which are still controversial. 
Min-Quan Kuang, Shao-Yi Wu, Hong-Kuan Yuan, Li-Dan Wang, Shu-Kai Duan,   An-Long Kuang, and Guo-Qing Li
cond-mat.supr-con