Figure 1
The Raman response spectra of an
crystal in the normal (red) and SC (blue) states for the
(top row) and
(bottom row) scattering channels. The
channel is accessed by RL (a)–(c) or VH (d) polarization and the
channel by RR (e)–(h) polarization. The low temperature data are acquired at 5–8 K. The normal state has been achieved either by increasing the crystal temperature to 40 K (d) or by applying a 5 T magnetic field parallel to the
-axis [(a)–(c), (e)–(h)] [
32]. The columns are arranged in the order of increasing excitation energy
. Solid lines are fits to the data points. The normal state continuum is fitted with
function. The data in the SC state is decomposed into a sum of a gapped normal state continuum with temperature broadened
gap cutoff, the SC coherence peak at
(shaded in violet), and the collective modes at
and
(shaded in dark and light green). The solid hairline is the sum of both modes. To fit the observed shapes the theoretical BCS coherence peak singularity
is broadened by convolution with a Lorentzian with
of
[
22]. The collective mode
is fitted with the response function shown in Fig. 3. Panels (d) and (h) also show the high energy part of spectra for respective symmetries. The broad
band at 79 meV is the boron stretching mode, the only phonon that exhibits renormalization below
[
25]. For the
channel the spectra are dominated by two-phonon scattering.
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