Abstract
The London moment is the magnetic moment acquired by a rotating
superconductor. We propose that the London moment reveals the following
fundamental properties of the superconducting state: (i) superconductors
(unlike normal metals) know the $sign$ of the charge carriers, (ii) the
superconducting charge carriers are $free$ electrons, (iii) electrons are
expelled from the interior to the surface in the transition to the
superconducting state, (iv) superfluid electrons occupy orbits of radius
$2łambda_L$ ($łambda_L=$London penetration depth), and (v) a spin current
exists in the ground state of superconductors. These properties are consistent
with the Meissner effect, however the Meissner effect does not $directly$
reveal the sign of the charge carriers nor the fact that the carrier's mass is
the free electron mass nor the fact that a spin current exists in
superconductors. Note also that within the BCS theory of superconductivity none
of the key properties of superconductors listed above are predicted. Instead,
these properties are predicted by the theory of hole superconductivity.
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