Temperature dependence discontinuity of the phonon mode frequencies caused by a zero-gap state in HgCdTe alloys.

In the HgCdTe (MCT) alloys, a zero-gap state E(g)=Gamma(6)-Gamma(8)=0 may occur as the composition varies from HgTe to CdTe. This singular mechanism of the E(g) variation may be triggered by an external pressure or by a temperature. In this Letter, we present experimental data of the optical reflectivity in the far-infrared (FIR) domain in a wide interval of temperature (from 10 to 290 K) of the Hg1-xCdxTe (x=0.115) samples. Since the intensity of classical IR sources drops abruptly in this spectral region, a brilliant synchrotron radiation FIR source has been used. The results clearly show that frequencies of the optical phonon modes exhibit discontinuity in their temperature dependence when a zero-gap state occurs.