The family of superconducting fullerides (NH/sub 3/)/sub x/NaK/sub 2/C/sub 60/ shows an anomalous correlation between T/sub c/ and lattice parameter. To better understand the origin of this anomaly we have studied a representative x=0.72 compound using superconducting quantum interference device (SQUID) magnetometry and muon spin rotation spectroscopy. The lower critical field H/sub c1/, measured by the trapped magnetization method, is less than 1 G, a very small value as compared with that of other fullerides. Muon spin depolarization in the superconducting phase shows also quite small local-field inhomogeneities, of the order of those arising from nuclear dipolar fields. On the other hand, the 40-T value for H/sub c2/, as extracted from magnetometry data, is comparable to that of other fullerides. We show that these observations cannot be rationalized within the framework of the Ginzburg-Landau theory of superconductivity. Instead, the anomalous magnetic properties could be interpreted taking into account the role played by polaronic instabilities in this material.
Muon spin rotation and SQUID investigation of superconductivity in (NH/sub 3/)/sub x/NaK/sub 2/C/sub 60/ (x~0.7)
Bolzoni F
2003
Abstract
The family of superconducting fullerides (NH/sub 3/)/sub x/NaK/sub 2/C/sub 60/ shows an anomalous correlation between T/sub c/ and lattice parameter. To better understand the origin of this anomaly we have studied a representative x=0.72 compound using superconducting quantum interference device (SQUID) magnetometry and muon spin rotation spectroscopy. The lower critical field H/sub c1/, measured by the trapped magnetization method, is less than 1 G, a very small value as compared with that of other fullerides. Muon spin depolarization in the superconducting phase shows also quite small local-field inhomogeneities, of the order of those arising from nuclear dipolar fields. On the other hand, the 40-T value for H/sub c2/, as extracted from magnetometry data, is comparable to that of other fullerides. We show that these observations cannot be rationalized within the framework of the Ginzburg-Landau theory of superconductivity. Instead, the anomalous magnetic properties could be interpreted taking into account the role played by polaronic instabilities in this material.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
