Figure 1
Kinetic friction
(per unit length of the vortex) versus average velocity
for magnetic vortices in LSCO pristine superconductors (a) and theoretical results in (b). For vortices,
. In (a), (b):
exhibits a maximum and decreases with vortex density.
in (a), (c). For (c), (d):
for pristine and 200 MeV-iodine-irradiated (with equivalent field
,
is the average distance between defects) superconductors (c) and theory results in (d). For (c), (d): For low velocities,
(because the irradiation introduces defects that provide large potential barriers, hard to overcome at low velocities, increasing the friction). For high velocities,
, because the pristine sample has very many shallow (but steep) pinning sites, effectively providing a large pinning force. A similar broad maximum for
[in panels (a)–(d)] was also found for very different excitations: charge density waves (e). All of these properties are well explained [e.g., (b), (d)] with a simple model for overdamped particles discussed in the text. (e) Measured normalized kinetic friction versus driving electric field
(normalized by the threshold field
) for the CDW
. Note the similarities between the CDW in (e) and the pristine samples in (c) and (d). (f) Friction versus both: driving force
(upper axis) and versus
(lower axis). A sharp (smooth) transition from static to kinetic friction regimes for low (higher) temperatures is clearly seen. Note that
.
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