Coherent dynamics of the charge density wave gap in tritellurides.

L Rettig,U Bovensiepen,I R Fisher,M Wolf,J.-H Chu

doi:10.1039/c4fd00045e

Abstract

The dynamics of the transient electronic structure in the charge density wave (CDW) system RTe3 (R = rare-earth element) is studied using time- and angle-resolved photoemission spectroscopy (trARPES). Employing a three-pulse pump-probe scheme we investigate the effect of the amplitude mode oscillations on the electronic band structure and, in particular, on the CDW energy gap. We observe coherent oscillations in both lower and upper CDW band with opposite phases, whereby two dominating frequencies are modulating the CDW order parameter. This demonstrates the existence of more than one collective amplitude mode, in contrast to a simple Peierls model. Coherent control experiments of the two amplitude modes, which are strongly coupled in equilibrium, demonstrate independent control of the modes suggesting a decoupling of both modes in the transient photoexcited state.

Highlights

Cooperative effects in low-dimensional materials represent a fascinating topic of condensed matter research
Coherent control experiments of the two amplitude modes, which are strongly coupled in equilibrium, demonstrate independent control of the modes suggesting a decoupling of both modes in the transient photoexcited state
Using a three-pulse pump–probe scheme in time- and angle-resolved photoemission experiments we demonstrated the effect of the amplitude mode oscillations on the electronic band structure in the prototypical charge-density wave compounds RT33

Summary

Introduction

Cooperative effects in low-dimensional materials represent a fascinating topic of condensed matter research. Various interactions of the electronic, orbital, spin and lattice degrees of freedom can lead to instabilities and broken-symmetry ground states leading to new emergent properties, which are of both fundamental and technological interest. Examples for such low-temperature broken-symmetry phases are superconducting, charge density wave (CDW) or magnetically ordered states, which are connected to other typically lower symmetry states by phase transitions as function of temperature, pressure, external elds, or are induced by optical excitation. The energy gap D(k) is a direct measure of the order parameter of the CDW phase and can be determined by appropriate spectroscopic tools from the occupied and unoccupied single-particle band structure

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