Macroscopic quantum phenomena in high-Tcsuperconducting material

The observation of macroscopic quantum phenomena in a high-$T_c$ superconducting material [${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{9\mathrm{-}\mathrm{y}}$ (Y-Bu-Cu-O), $T_c$=93.4 K] is reported. Relationships between current, voltage, and magnetic fields of Sn–Y-Ba-Cu-O and Y-Ba-Cu-O–Y-Ba-Cu-O point contracts were measured. In both cases the critical current is periodic in the magnetic field, which is typical for double point contacts (dc superconducting quantum interference devices). In the Sn–Y-Ba-Cu-O contacts the oscillations were observed below the $T_c$ of tin. In the Y-Ba-Cu-O–Y-Ba-Cu-O contacts the oscillations were observed at temperatures up to 66 K, clearly demonstrating macroscopic quantum phemonena in this high-$T_c$ material.