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 This is a few days late from its intended posting.  This should have been part of the month celebration of Superconductivity.

Superconductivity research in the Philippines only started in 1987 as a playful and curiosity-based inquiry on high temperature superconductors at the National Institute of Physics.  The first publication came in 1991 from the Condensed Matter Physics group and 10 years after, the same group published its most cited paper to date. The paper has at least a citation every year.

The paper explains the effect of phase drifts on AC magnetic susceptibility measurements. The phase drifts, according to Sarmago et. al.[1], cause the projection of both the Meissner and AC loss signals to be measured by the lock-in amplifier in the in-phase and out-of-phase traces.  This paper is frequently cited since it somewhat resolves conflicting results on using AC techniques.

Here is the abstract:

R.V Sarmago, K.L.C Molina and L.J.D Guerra, A new perspective to AC magnetic susceptibility measurements in an unbalanced mutual inductance bridge, Physica C: Superconductivity 364-365, 2001. doi: 10.1016/S0921-4534(01)00762-6

Abstract

AC magnetic susceptibility measurements using an unbalanced mutual inductance bridge were performed on a bulk YBa2Cu3O7−δ superconductor at frequencies f=110–800 Hz and AC fields B=0.2–2 mT. By deliberately leaving the bridge unbalanced, the effect of phase drift on the measurements is shown. Because of this phase drift, we found that the hump appearing in the in-phase measurements (associated with χ) is the same AC loss peak appearing in the out-of-phase measurements (associated with χ). In addition, since the behavior of the AC susceptibility data we obtained is in agreement with the literature, conflicting results by other groups can be resolved by a simple consideration of this phase drift.

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[1] R.V Sarmago, K.L.C Molina and L.J.D Guerra, A new perspective to AC magnetic susceptibility measurements in an unbalanced mutual inductance bridge, Physica C: Superconductivity 364-365, 2001. doi: 10.1016/S0921-4534(01)00762-6
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