A NMR study of vortex melting in YBa_2Cu_4O_8

摘要

The temperature dependence of ~(17)O and ~(63)Cu nuclear magnetic resonance (NMR) spectra has been measured in the mixed state of superconducting YBa_2Cu_4O_8. The line width in Hperpendicularc begins to increase just below T_c. On the other hand, the increase of line width in H//c occurs below 50K, which indicates the vortex melting transition. The coexistence region of solid and liquid vortices is not observed in our measurements.