It is often convenient to fit the measured asymmetry spectrum in a
``rotating reference frame'' (RRF). To do this, one
multiplies the complex muon polarization by a
function
.
The RRF frequency
is chosen to be slightly lower than
the average Larmor-precession frequency
of
the muon in the sample.
There are two important benefits from this procedure.
The first is that the quality of the fit
can be visually inspected.
The precession signal viewed in this rotating reference frame has only
low frequency components on the order of
, where
is the average precession frequency in the lab frame.
Second and most important, it allows
the data to be packed into much fewer bins, greatly enhancing the
speed of fitting.
Further details of the
SR technique may be found elsewhere (e.g. see
Refs. [47,46,49,50]).
The essential
point is that the muon accurately probes the local distribution of
magnetic fields
in the bulk of the superconductor.
The resulting
SR line shape contains considerable information.
Of particular interest, are the magnetic penetration depth
,
the coherence length
and the vortex-lattice structure.
Unfortunately, the
SR
line shape also contains information not generally wanted--such as
the effects of flux lattice disorder and additional fields such as those
due to nuclear dipolar moments.
Furthermore, extracting quantities such as
and
from
the data requires some modelling of the internal field distribution.
This is the major difficulty in employing the
SR technique.