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Abstract:
We have measured the resistive upper critical field of overdoped single
crystals of Tl2Ba2CuO6 from the zero-field transition temperature T(c)
(approximately 20 K) to temperatures as low as 12 mK, corresponding to
less than 0.001 T(c). In sharp contrast to the predictions of standard
theories of superconductivity, the critical field is found to rise
steeply with positive curvature as the temperature is reduced, and no
sign of saturation is observed down to the lowest temperatures reached.
