The flux line lattice (FLL) elasticity and its anisotropic pinning have been investigated in a single crystalline La1.85Sr0.15CuO4 by ultrasonic measurements under high magnetic fields. The depinning activation energies are deduced from measurements under various settings of the directions of wave vector k, polarization vector u and magnetic fields H as Uac(0 K, 14 T) = 972 K for H⊥c, u∥c, Uab(0 K, 14 T) = 201 K for H⊥c, u∥(c × H) and Uca(0 K, 14 T) = 25 K for H∥c, u⊥c. The magnetic field dependence of U are also deduced as Uac ∝ H-0.3 and Uca ∝ H-1.5. The angular dependence of Uac is discussed on the basis of the intrinsic pinning mechanism.
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