ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
We report on electron-spin resonance on single crystals of YBa2Cu3O7−x and Bi4/3Pb2/3Sr2CaCu2O8+x at 9 GHz. While in the YBCO there was no observable ESR signal in the normal state (above Tc) or in the superconducting state (below Tc), we did observe a large microwave nonresonant absorption below Tc at low field values (H〈200 Oe). We attribute this form of absorption to fluxoid formation below Tc. In the BiPbSrCaCuO single crystals, a significantly different result was found in that an electron-spin-resonance signal was measured both above and below Tc, besides the low-field absorption occurring only below Tc. The g value was found to be 2.055 and reasonably constant with temperature from 300 to 4 K with H parallel to the c axis. We attributed the ESR line to Cu++ ion excitation. The ESR signal increased as T decreased from 300 K to Tc and the variation with temperature fits a Boltzmann statistics law. Below Tc the ESR signal remained constant as T was decreased below Tc. We explained this result in terms of two competing statistical effects. One effect is due to the fact that the ESR signal in the fluxoid region increases as the Boltzmann factor, but the fluxoid density decreases by the same factor. The net effect is that the ESR signal is constant with temperature below Tc. Hence, this is a clear demonstration of statistics involved in the formation of fluxoids.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.344671
