Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon

Abstract

Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons.

Temperature-dependent Brillouin light scattering spectra of magnons in yttrium iron garnet and permalloy

“…The laser and instrument contributions do not change with sample heating, where the wave vector range does increase due to an increase in refractive index with temperature. The change in refractive index is on the order of 1%, leading the change in wave vector range to be negligible 16,25 .Thus, the increase in BLS linewidth observed results from an increase in the intrinsic linewidth. Magnon linewidth is expected to increase with increasing temperature due to increased magnon scattering.…”

“…Finally, the corrected BLS intensity temperature dependence is related to the magnon population just for the magnon mode being probed. In local thermal equilibrium the magnon population is determined by the Bose-Einstein distribution, and thus offers the possibility to uniquely measure the temperature of a single magnon mode, as similarly concluded for phonons in a previous study 16 . It should be noted the corrected BLS intensity can only measure relative temperature changes, not absolute temperatures.…”

“…The temperature of this mode uniquely determines the magnon population under local thermal equilibrium. Previous light scattering measurements of phonons, specifically Raman and BLS, have shown that the integrated intensity is proportional to the population of the probed phonon 16,42 . Population, or occupancy of a mode, is, in fact, a more general concept that is valid under both equilibrium and non-equilibrium conditions.…”

“…Brillouin light scattering (BLS) is an inelastic light scattering technique that has been used to study magnons and acoustic phonons [11][12][13][14][15] . BLS measurements are not only able to distinguish magnons and phonons, but also able to distinguish between different modes of the carriers, such as between backward-volume and Damond-Eshbach magnon modes, and between longitudinal and transverse acoustic phonon modes [16][17][18] . The BLS spectra are generally characterized by three parameters: frequency, linewidth, and integrated intensity (further referred to simply as intensity).…”

“…Previous BLS experiments have solely used the frequency shift to determine the temperature of magnons 11,19 . In a different study, it was shown that frequency shift, linewidth, and intensity of BLS spectra of acoustic phonons in silicon all provide temperature sensing capabilities, though each probes different ranges of the acoustic phonon spectrum 16 . In this letter, we report systematic changes in BLS spectra of prototypical magnetic insulators and metals, i.e., yttrium iron garnet (YIG) and permalloy (Py) as the sample is uniformly heated.…”