Experimental evidence for vortex lines in the vortex-liquid phase ofYBa2Cu3O6.95in a geometry of tilted vortices

Using a transport method with a geometry of tilted magnetic field, we have studied the direction of the electric field generated by the motion of vortices. This experiment gives evidence of uncut vortex lines in slightly overdoped untwinned ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.95}$ above the melting first order transition, showing that the first order transition does not correspond to a decoupling of the vortex lines. The gradual loss of the line correlation appears close to $T_{c2\mathrm{}}$ on a width which is typically that of the critical fluctuations. Those results are similar to what we have found previously in a heavily twinned sample and lead to the conclusion that the twin planes are not necessary to induce uncut vortex lines in the liquid phase, even in a thick sample. Moreover, we observe a nonzero transverse voltage below the critical current, which is not explained unless referring to surface nondissipative currents.