Excited-state band structure mapping

M Puppin,R P Xian,C Monney,S Dong,A Dominguez,J Feldl,M Wolf,R Ernstorfer,H Hübener,C W Nicholson,L Rettig,Y Deng,A Rubio

doi:10.1103/physrevb.105.075417

Abstract

Angle-resolved photoelectron spectroscopy is an extremely powerful probe of materials to access the occupied electronic structure with energy and momentum resolution. However, it remains blind to those dynamic states above the Fermi level that determine technologically relevant transport properties. In this work, we extend band structure mapping into the unoccupied states and across the entire Brillouin zone by using a state-of-the-art high repetition rate, extreme ultraviolet fem- tosecond light source to probe optically excited samples. The wide-ranging applicability and power of this approach are demonstrated by measurements on the 2D semiconductor WSe2, where the energy-momentum dispersion of valence and conduction bands are observed in a single experiment. This provides a direct momentum-resolved view not only on the complete out-of-equilibrium band gap but also on its renormalization induced by electron-hole interaction and screening. Our work establishes a new benchmark for measuring the band structure of materials, with direct access to the energy-momentum dispersion of the excited-state spectral function.

Highlights

In this work we extend band structure mapping into the unoccupied states and across the entire Brillouin zone by using a state-of-the-art high repetition rate, extreme ultraviolet femtosecond light source to probe optically excited samples
The wideranging applicability and power of this approach are demonstrated by measurements on the two-dimensional semiconductor WSe2, where the energy-momentum dispersion of valence and conduction bands are observed in a single experiment
This results in XUV pulses at an energy of 21.7 eV and with characteristic time-bandwidth products of approximately 20 fs × 110 meV [23], which are temporally short enough to access the excited states before significant carrier energy relaxation has occurred and, at the same time, have an energy bandwidth sufficiently narrow to resolve the excited-state energy features. Time-resolved angle-resolved photoemission spectroscopy (trARPES) experiments were performed on single-crystalline samples of bulk WSe2 cleaved in ultrahigh vacuum conditions

Summary

Introduction

Functionality in electronic and optoelectronic devices is based on the control of the flow of charge carriers under outof-equilibrium conditions. Charge transport and device operation rely upon generating nonequilibrium electron distributions controlled by external fields to achieve the desired electronic response. The propagation of electrons in a crystal and the evolution of their energy distributions are governed by the details of the electronic structure, as well as the efficiency of elastic and inelastic scattering processes. Time-resolved angle-resolved photoemission spectroscopy (trARPES) addresses this problem by observing the spec-

Methods

Results

Conclusion