Abstract
Careful investigation of the angular dependence of resistivity
ρ
(
θ
) (
θ
is the angle between the magnetic field and the
ab
-planes) and the temperature dependence of resistivity
ρ
(
T
) within the superconducting transition in an applied magnetic field
B
up to 1 T for a series of YBa
2
Cu
3
O
7−
δ
(YBCO) thin films revealed a large variation of intrinsic anisotropy factor
γ
. The series of films studied included both optimally doped and underdoped samples of different
T
c
, critical current density
J
c
, film thickness, and preparation techniques. The variation in the shape and depth of the minimum measured for
ρ
(
θ
) near
θ
=0° could be directly correlated to the intrinsic anisotropy of the YBCO films. The results of fitting of
ρ
(
θ
) using Bardeen–Stephen theory allowed a quantitative determination of the value of
γ
which varies between 7 and 230, and is independent of
T
c
, film thickness, or
J
c
. The sharper the minimum in
ρ
(
θ
) around
θ
=0° the larger is the anisotropy. For highly anisotropic film,
ρ
(
θ
) showed an identical behavior for
B
∥
J
and
B
⊥
J
(i.e.,
ρ
(
θ
) is independent of the angle
θ
between
B
and
J
for this film). The large variation in
γ
could be attributed to the “buckling” of the CuO
2
planes.