Doping evolution of the absolute value of the London penetration depth and superfluid density in single crystals of Ba(Fe1-xCox)2As2

The zero-temperature value of the in-plane London penetration depth, lambda(ab)(0), has been measured in single crystals of Ba(Fe1-xCox)(2)As-2 as a function of the Co concentration, x, across both the underdoped and over-doped superconducting regions of the phase diagram. For x >= 0.047, lambda(ab)(0) has been found to have values between 120+/-50 and 300+/-50 nm. A pronounced increase in lambda(ab)(0), to a value as high as 950+/-50 nm, has been observed for x <= 0.047, corresponding to the region of the phase diagram where the itinerant antiferromagnetic and superconducting phases coexist and compete. Direct determination of the doping-dependent lambda(ab)(0) has allowed us to track the evolution of the temperature-dependent superfluid density, from which we infer the development of a pronounced superconducting gap anisotropy at the edges of the superconducting dome.