Excitation of coherent phonons in the one-dimensional Bi(114) surface

TL;DR

This study investigates how optical excitation induces long-lived electronic and phononic coherent oscillations on a one-dimensional bismuth surface, revealing both bulk and surface phonon modes through time-resolved photoemission.

Contribution

It demonstrates the excitation of both bulk and surface coherent phonons in Bi(114), highlighting the role of electron-phonon coupling in a one-dimensional surface system.

Findings

Long-lived surface and bulk electronic states after excitation

Detection of a surface phonon mode at 0.72 THz

Observation of the bulk A1g phonon at 2.76 THz

Abstract

We present time-resolved photoemission experiments from a peculiar bismuth surface, Bi(114). The strong one-dimensional character of this surface is reflected in the Fermi surface, which consists of spin-polarized straight lines. Our results show that the depletion of the surface state and the population of the bulk conduction band after the initial optical excitation persist for very long times. The disequilibrium within the hot electron gas along with strong electron-phonon coupling cause a displacive excitation of coherent phonons, which in turn are reflected in coherent modulations of the electronic states. Beside the well-known A1g bulk phonon mode at 2.76 THz the time-resolved photoelectron spectra reveal a second mode at 0.72 THz which can be attributed to an optical surface phonon mode along the atomic rows of the Bi(114) surface.