Observation of van der Waals phonons in the single-layer cuprate (Bi,Pb)${}_2$(Sr,La)${}_2$CuO${}_{6+\delta }$

Abstract

Interlayer van der Waals (vdW) coupling is generic in two-dimensional materials such as graphene and transition metal dichalcogenides, which can induce very low-energy phonon modes. Using high-resolution inelastic hard x-ray scattering, we uncover the ultra-low energy phonon mode along the Cu-O bond direction in the high-$T_c$ cuprate (Bi,Pb)${}_2$(Sr,La)${}_2$CuO${}_{6+\delta }$ (Bi2201). This mode is independent of temperature, while its intensity decreases with doping in accordance with an increasing c-axis lattice parameter. We compare the experimental results to first-principles density functional theory simulations and identify the observed mode as a van der Waals phonon, which arises from the shear motion of the adjacent Bi-O layers. This shows that Bi-based cuprate has similar vibrational properties as graphene and transition metal dichalcogenides, which can be exploited to engineer novel heterostructures.

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Cited by in corpus (2)

• Signature of T${}_{\text{c}}$ above 111 K in Li-doped (Bi,Pb)-2223 superconductors: synergistic nature of hole concentration, coherence length and Josephson interlayer coupling
• The influence of phonon symmetry and electronic structure on the electron-phonon coupling momentum dependence in cuprates