Phonon softening and higher-order anharmonic effect in the superconducting topological insulator SrxBi2Se3

Abstract

We report the anharmonic effect of the Raman-scattering spectrum in the low-carrier density superconductor SrxBi2Se3, which is dominated by the quartic term. Compared to the parent Bi2Se3, the superconducting SrxBi2Se3 crystals show obvious phonon softening in the three optical phonon modes , , and . Based on the simulations by the Fano function, we present compelling evidence of the enhanced electron–phonon coupling in SrxBi2Se3 for its smaller asymmetric parameter q. Moreover, an anomalous broadening and intensity antiresonance in the characteristic Raman peaks were observed as the temperature decreased to around 160 K. Thus, the superconducting topological material SrxBi2Se3 represents a counterintuitive example where the electron–phonon interaction is strengthened by the accumulation of electron carriers.