Scaling of the physical properties in Ba(Fe,Ni)2As2 single crystals: Evidence for quantum fluctuations
Résumé
We report on local magnetization, tunnel diode oscillators, and specific-heat measurements in a series of Ba(NixFe1−x)2As2 single crystals (0.26≤x≤0.74). We show that the London penetration depth λ(T)=λ(0)+Δλ(T) scales as λ(0)∝1/Tc^0.85±0.2, Δλ(T)∝T^2.3±0.3 (for T≤T_c/3) and $\partial\Delta\lambda/\partial T^2\propto 1/T_c^{2.8\pm0.3}$ in both underdoped and overdoped samples. Moreover, the slope of the upper critical field ($H'_{c2}=-(dH_{c2}/dT)_{|T\rightarrow T_c}$) decreases with $T_c$ in overdoped samples but increases with decreasing $T_c$ in underdoped samples. The remarkable variation of $\lambda(0)$ with $T_c$ and the non exponential temperature dependence of $\Delta\lambda$ 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 3D superconducting critical points.
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