Influence of an electron-phonon subsystem on specific heat and two-photon absorption of the semimagnetic semiconductors Pb_(1-x)Yb_xX (X=S, Se,Te) near the semiconductor-isolator phase transformation

摘要

Specific heat, transport, and two-photon absorption (TPA) effects were studied in single crystalline magnetic semiconductors Pb_(1-x)Yb_xX (X=S, Se,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 denned by the temperature-dependent Debye term (parameter β) from the equation C=γT+βT~3+Σ_i~n=1δ_iT~(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 Pb_(1-x)R_xxTe (R=Yb,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 T substantially modifies the temperature features of several phonon low-frequency modes, which may indicate a contribution of magnons.