High-energy heavy-ion irradiation is known to produce effective vortex pinning centers in the high-T_(c) cupratesuperconductors, as amorphous columnar tracks. However, while the beneficial effects on pinning has been ...High-energy heavy-ion irradiation is known to produce effective vortex pinning centers in the high-T_(c) cupratesuperconductors, as amorphous columnar tracks. However, while the beneficial effects on pinning has been wellestablished through dc and low-frequency characterizations, the same analysis in the high-frequency regime isfar from complete. Even less investigated are the effects of heavy ion irradiation on the microwave propertiesof metallic low-T_(c) superconducting films. Here, we report on the effects of 1.15 GeV Pb irradiation on the highfrequency properties of YBa_(2)Cu_(3)O_(7−x)(YBCO) and Nb_(3)Sn thin films. The microwave analysis, performed in therange 7-8 GHz, allows obtaining the fundamental properties of both the materials, as the London penetrationdepth and gap values, and of the main pinning parameters, through the determination of the Campbell lengthby measurements in dc magnetic fields up to 4 T. GeV heavy-ion irradiation confirmed to be extremely effectivefor YBCO also in the high frequency regime, enhancing both the pinning constant and the depinning frequency,thus pushing the critical current density to about 30% of the depairing current density. On the other hand, thediscontinuous but correlated defects produced in Nb_(3)Sn was found to be ineffective to enhance the pinningproperties (the pinning constant in fact decreases), while the observed increment of the depinning frequencyis ascribed to the reduction of the vortex viscosity, in turn due to the growth of the normal state resistivity.展开更多
文摘High-energy heavy-ion irradiation is known to produce effective vortex pinning centers in the high-T_(c) cupratesuperconductors, as amorphous columnar tracks. However, while the beneficial effects on pinning has been wellestablished through dc and low-frequency characterizations, the same analysis in the high-frequency regime isfar from complete. Even less investigated are the effects of heavy ion irradiation on the microwave propertiesof metallic low-T_(c) superconducting films. Here, we report on the effects of 1.15 GeV Pb irradiation on the highfrequency properties of YBa_(2)Cu_(3)O_(7−x)(YBCO) and Nb_(3)Sn thin films. The microwave analysis, performed in therange 7-8 GHz, allows obtaining the fundamental properties of both the materials, as the London penetrationdepth and gap values, and of the main pinning parameters, through the determination of the Campbell lengthby measurements in dc magnetic fields up to 4 T. GeV heavy-ion irradiation confirmed to be extremely effectivefor YBCO also in the high frequency regime, enhancing both the pinning constant and the depinning frequency,thus pushing the critical current density to about 30% of the depairing current density. On the other hand, thediscontinuous but correlated defects produced in Nb_(3)Sn was found to be ineffective to enhance the pinningproperties (the pinning constant in fact decreases), while the observed increment of the depinning frequencyis ascribed to the reduction of the vortex viscosity, in turn due to the growth of the normal state resistivity.
