Anisotropy of Underdoped YBa-2Cu_3O_(6.5) Single Crystal

摘要

The c-axis anisotropy of an underdoped YBa_2Cu_3O_(6.5) single crystal has been investigated by the torque magnetometry. The underdoped crystal shows a super-conducting transition at 60 K. The torque was measured upon rotating the crystal around the b axis. The torque curve of the underdoped crystal was reversible except for angles near #theta#_(ca)= 90 deg under conditions of H = 60 kG and T = 50 K. The torque curve was analyzed by means of the anisotropic London model. We obtain that the anisotropy parameter #gamma#_(ca) = root m_c/m_a = 53, indicating areduced coupling between the adjacent CuO_2 layers compared to an optimum-doped crystal.