Evidence from Mechanical Measurements for Flux-Lattice Melting in Single-Crystal Y<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ba</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>7</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Bi</mml:mi></mml:mrow><mml:mrow><mml:mn>2.2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Sr</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ca</mml:mi></mml:mrow><mml:mrow><mml:mn>0.8</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>8</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>
Аннотация
We have studied flux-lattice melting in single crystals of Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and ${\mathrm{Bi}}_{2.2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{0.8}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8}$ using a high-$Q$ mechanical oscillator. In Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ with an applied magnetic field $\mathbf{H}\ensuremath{\perp}\stackrel{^}{\mathbf{c}}$, flux-lattice melting occurs at ${H}_{c2}$ as in a conventional three-dimensional superconductor. However, for $\mathbf{H}\ensuremath{\parallel}\stackrel{^}{\mathbf{c}}$ flux-lattice melting occurs 3.2 K below ${H}_{c2}$. We believe that this is evidence for a transition into a vortex-liquid state similar to that seen in two-dimensional superconducting films. For ${\mathrm{Bi}}_{2.2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{0.8}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8}$ the effect is even more pronounced; with a bulk superconducting transition of 75 K, the flux-lattice melting in this material occurs in both orientations near 30 K.
Перевод пока недоступен