Abstract
We report on local magnetization, tunnel diode oscillators, and specific-heat measurements in a series of Ba(NiFe)As single crystals (). We show that the London penetration depth scales as , (for ), and in both underdoped and overdoped samples. Moreover, the slope of the upper critical field [] decreases with in overdoped samples but increases with decreasing in underdoped samples. The remarkable variation of with and the nonexponential temperature dependence of clearly indicates that pair-breaking effects are important in this system. We show that the observed scalings strongly suggest that those pair-breaking effects could be associated with quantum fluctuations near three-dimensional superconducting critical points.
- Received 22 December 2011
DOI:https://doi.org/10.1103/PhysRevB.85.214506
©2012 American Physical Society