Specific heat, transport, and two-photon absorption (TPA) effects were studied in single crystalline magnetic semiconductors ${\mathrm{Pb}}_{1-x}{\mathrm{Yb}}_{x}X$ ($X=\mathrm{S},\mathrm{Se},\mathrm{Te}$ at $x=1–3\%$) near semiconductor-isolator phase transitions. It was shown that the TPA may be used as a sensitive tool for investigations of electron-phonon interactions near low temperature semiconductor-isolator phase transformation. Comparison with other methods of phase transition studies has shown more sharplike temperature dependence of the TPA. Particularly, comparison with piezo-optical and dilatometric methods shows on a better temperature resolution of the TPA with respect to the phase transitions. It was established as a correlation between the density of low-temperature phonon modes and values of the TPA. Particularly with increasing of the electron-phonon interactions defined by the temperature-dependent Debye term (parameter $\beta$) from the equation $C=\gamma T+\beta T^3+{\sum }_{i=1}^n{\delta }_i{T}^{2i+3}$, one can observe an increase of the TPA oscillator strengths. It was shown that only the low-temperature TPA behaviors might be determined by the features of the low-energy phonon modes related to the observed phase transformation. We also have discovered that low-temperature dependence of the specific heat $C_p$ in ${\mathrm{Pb}}_{1-x}{R}_x\mathrm{Te}$ $(R=\mathrm{Yb},\mathrm{Te})$ with $x=2.6\%$ and 1.65%, respectively, exhibits a nonmagnetic ordering caused by large value of electron-phonon contribution. Applying magnetic fields up to $2\mathrm{T}$ substantially modifies the temperature features of several phonon low-frequency modes, which may indicate a contribution of magnons.

• Received 23 March 2005

DOI:https://doi.org/10.1103/PhysRevB.73.035329