Superconducting stiffness
and coherence length
are usually determined by measuring the penetration depth
of a magnetic field and the upper critical field
of a superconductor (SC), respectively. However, in magnetic SC, which is iron-based, this could
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Superconducting stiffness
and coherence length
are usually determined by measuring the penetration depth
of a magnetic field and the upper critical field
of a superconductor (SC), respectively. However, in magnetic SC, which is iron-based, this could lead to erroneous results, since the internal field could be very different from the applied one. To overcome this problem in Fe
Se
Te
with
and
(FST), we measured both quantities with the Stiffnessometer technique. In this technique, one applies a rotor-free vector potential
to a superconducting ring and measures the current density
via the ring’s magnetic moment
.
and
are determined from London’s equation,
, and its range of validity. This method is particularly accurate at temperatures close to the critical temperature
. We find weaker
and longer
than existing literature reports, and critical exponents which agree better with expectations based on the Ginzburg–Landau theory.
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