Order-disorder transition induced by deformation of vortex lines at the   twin boundaries in YBa$_2$Cu$_3$O$_{7-\delta}$-crystals: test of the   Lindemann criteria
  We show that rotation of the magnetic field off the plane of twin boundaries (TB's) induces transition of an ordered vortex solid phase to a disordered one. This transition arises due to appearance of transverse deformations of vortex lines near the TB's, $u_{t,TB}$, the amplitude of which satisfies the Lindemann criteria, $u_{t,rp}=c_La_0$. This order-disorder transition is accompanied by an increase in the depinning current, by crossover from an elastic creep to plastic one, and by appearance of the $S$-shaped voltage-current characteristics. 
Yu. T. Petrusenko, A. V. Bondarenko, A. A. Zavgorodniy, M. A.   Obolenskii, V. I. Beletskii