A low-frequency torsional oscillator has been used to search for flux-lattice melting in an untwinned single crystal of ${\mathrm{Y}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. The damping of the oscillator was measured as a function of temperature, for applied magnetic fields in the range 0.1≤H≤2.3 T. A remarkably sharp damping peak has been located. It is suggested that the temperature of the peak corresponds to the melting point of the Abrikosov flux lattice.

• Received 13 May 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.1165