We study angular-dependent magnetoresistance in a low Tc layered cuprate Bi2.15Sr1.9CuO 6+δ . The low Tc ∼ 4 K allows complete suppression of superconductivity by modest magnetic fields and facilitate accurate analysis of the upper critical field Hc2. We observe an universal exponential decay of fluctuation conductivity in a broad range of temperatures above Tc and propose a new method for extraction of Hc2(T ) from the scaling analysis of the fluctuation conductivity at T > Tc. Our main result is observation of a surprisingly low Hc2 anisotropy ∼ 2, which is much smaller than the effective mass anisotropy of the material ∼ 300. We show that the anisotropy is decreasing with increasing field and saturates at a small value when the field reaches the paramagnetic limit. We argue that the dramatic discrepancy of high field and low field anisotropies is a clear evidence for paramagnetically limited superconductivity.
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