Manifestation of anharmonicities in terms of Fano scattering and phonon lifetime of scissors modes in α-MoO3

Abstract

α-MoO₃ exhibits promising potential in the field of infrared detection and thermoelectricity owing to its exceptional characteristics of ultra-low-loss phonon polaritons (PhPs). It is of utmost importance to comprehend the phonon interaction exhibited by α-MoO₃ in order to facilitate the advancement of phonon-centric devices. The intriguing applications of α-MoO₃ for phonon-centric technology are found to be strongly dependent on scissors Raman modes. In this study, we have investigated the temperature-dependent asymmetric Raman line-shape characteristics of two scissors modes, A_g(1) and B_1g(1), in the orthorhombic phase of bulk α-MoO₃ within a temperature range spanning from 138 K to 498 K at 633 nm excitation wavelength. The Fano-Raman line-shape function was employed to analyze the asymmetry in terms of electron–phonon coupling strength, which varies from 0.050 to 0.313 and −0.017 to −0.192 for A_g(1) and B_1g(1) modes, respectively, with temperature. This asymmetric behavior of A_g(1) and B_1g(1) scissors modes are attributed to interference between the electronic energy continuum and discrete TO and LO phonon states, respectively. Therefore, the line-shape asymmetry in two scissors modes with increasing temperature stemming from the Fano resonance is also consistent with a 488 nm excitation wavelength. Additionally, anharmonicity caused by temperature results in redshift, and linewidth broadening of these two scissors modes through cubic-phonon decay has been observed. Moreover, the ultrashort lifetime of these optical phonons diminishes from ∼1.37 ps to ∼0.53 ps with increasing temperature due to the dominance of cubic-phonon decay over quartic-phonon decay. Our findings strongly emphasize the significance of investigating anharmonic interactions with Fano resonance to acquire an extensive comprehension of the vibrational characteristics of α-MoO₃ for novel functionalities.