We present an exhaustive analysis of transport measurements performed intwinned YBa2Cu3O7 single crystals which stablishes that the vortex solid-liquidtransition is first order when the magnetic field H is applied at an angletheta away from the direction of the twin planes. We show that the resistivetransitions are hysteretic and the V-I curves are non-linear, displaying acharacteristic s-shape at the melting line Hm(T), which scales asepsilon(theta)Hm(T,theta). These features are gradually lost when the criticalpoint H*(theta) is approached. Above H*(theta) the V-I characteristics show alinear response in the experimentally accessible V-I window, and the transitionbecomes reversible. Finally we show that the first order phase transition takesplace between a highly correlated vortex liquid in the field direction and asolid state of unknown symmetry. As a consequence, the available data supportthe scenario for a vortex-line melting rather than a vortex sublimation asrecently suggested [T.Sasagawa et al. PRL 80, 4297 (1998)].
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机译：我们提出了对缠绕的YBa2Cu3O7单晶进行的输运测量的详尽分析，该分析确定了当磁场H以远离双平面方向的角度θ施加时，涡旋固液过渡是一阶的。我们表明，电阻跃变是滞后的，V-I曲线是非线性的，在熔解线Hm（T）上显示出特征性的s形，该熔断线缩放了asepsilonθHm（T，theta）。当接近临界点H *θ时，这些特征逐渐消失。在H *θ之上，V-I特性在实验可访问的V-I窗口中显示出线性响应，并且转变是可逆的。最后，我们表明，一阶相变发生在场方向上高度相关的涡旋液体与未知对称性的固态之间。结果，可用数据支持了涡旋线融化而不是最近提出的涡旋升华的场景[T.Sasagawa等人。 PRL 80，4297（1998）]。
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