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Soft Phonon Mode and the Anomalous Temperature Dependence of Band Gap in AgGaS 2
Author(s) -
Choi InHwan,
Eom SungHwan,
Yu P. Y.
Publication year - 1999
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/(sici)1521-3951(199909)215:1<99::aid-pssb99>3.0.co;2-#
Subject(s) - phonon , raman spectroscopy , raman scattering , band gap , condensed matter physics , blueshift , materials science , soft modes , mode (computer interface) , observable , optics , physics , optoelectronics , photoluminescence , computer science , dielectric , ferroelectricity , operating system , quantum mechanics
We report the first observation of a low energy phonon mode in the low‐temperature and resonantly‐enhanced Raman spectra of AgGaS 2 . This mode appears as sidebands of one‐phonon Raman modes at T < 100 K. Its frequency is 8.0 cm —1 at T = 3.4 K and decreases to 5.7 cm —1 at 90 K. The mode becomes overdamped and difficult to resolve as T is increased to 100 K. We tentatively attribute this “soft mode” with a zone‐edge phonon which is observable in two‐phonon combination Raman scattering. When alloyed with Cu both the soft mode and the anomalous blue‐shift of the band gap in AgGaS 2 are suppressed. We propose that this soft mode is responsible for the anomalous blue‐shift of the band gap in AgGaS 2 at low temperature.