Anomalous temperature induced transition and convergence of thermal conductivity in germanene monolayer

SSP Chowdhury and S Thapliyal and S Mogurampelly, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 27, 20154-20162 (2025).

DOI: 10.1039/d5cp02975a

We report an anomalous temperature-induced transition in thermal conductivity in the germanene monolayer around a critical temperature Tc = 350 K. Equilibrium molecular dynamics simulations reveal a transition from kappa similar to T-2 scaling below the Tc to kappa similar to T-1/2 above, contrasting with conventional kappa similar to T-1 behavior. This anomalous scaling correlates with the long-scale characteristic timescale tau 2 obtained from double exponential fitting of the heat current autocorrelation function. Phonon mode analysis using normal mode decomposition indicates that a redshift in ZO phonons reduces the acoustic-optical phonon gap, causing an overlap, and enhances the phonon-phonon scattering, driving the anomalous scaling behavior. Moreover, non-equilibrium simulations find a convergent thermal conductivity of germanene with sample size, in agreement with mode coupling theory, owing to the high scattering of ZA phonons due to the inherent buckling of germanene.

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