AbstractDetailed measurements of the in-plane resistivity were performed in a high-quality Ba($$\hbox {Fe}_{1-x}\hbox {Co}_{{x}}$$
Fe
1
-
x
Co
x
)$$_2\hbox {As}_2$$
2
As
2
($$x=0.065$$
x
=
0.065
) single crystal, in magnetic fields up to 9 T and with different orientations $$\theta$$
θ
relative to the crystal c axis. A significant $$\rho (T)_{H,\theta }$$
ρ
(
T
)
H
,
θ
rounding is observed just above the superconducting critical temperature $$T_c$$
T
c
due to Cooper pairs created by superconducting fluctuations. These data are analyzed in terms of a generalization of the Aslamazov-Larkin approach, that extends its applicability to high reduced-temperatures and magnetic fields. This method allows us to carry out a criterion-independent determination of the angular dependence of the upper critical field, $$H_{c2}(\theta )$$
H
c
2
(
θ
)
. In spite of the relatively small anisotropy of this compound, it is found that $$H_{c2}(\theta )$$
H
c
2
(
θ
)
presents a significant deviation from the single-band 3D anisotropic Ginzburg-Landau (3D-aGL) approach, particularly for large $$\theta$$
θ
(typically above $$\sim 60^o$$
∼
60
o
). These results are interpreted in terms of the multiband nature of these materials, in contrast with other proposals for similar $$H_{c2}(\theta )$$
H
c
2
(
θ
)
anomalies. Our results are also consistent with an effective anisotropy factor almost temperature independent near $$T_c$$
T
c
, a result that differs from the ones obtained by using a single-band model.
Determination of the Upper Critical Field of a Single Crystal LiFeAs: The Magnetic Torque Study up to 35 Tesla
