Coherent photo-induced phonon emission in the charge-density-wave state of K0.3MoO3

  • We report on the observation of coherent terahertz (THz) emission from the quasi-one-dimensional charge-density wave (CDW) system, blue bronze (K0.3MoO3), upon photo-excitation with ultrashort near-infrared optical pulses. The emission contains a broadband, low-frequency component due to the photo-Dember effect, which is present over the whole temperature range studied (30–300 K), as well as a narrow-band doublet centered at 1.5 THz, which is only observed in the CDW state and results from the generation of coherent transverse-optical phonons polarized perpendicular to the incommensurate CDW b-axis. As K0.3MoO3 is centrosymmetric, the lowest-order generation mechanism which can account for the polarization dependence of the phonon emission involves either a static surface field or quadrupolar terms due to the optical field gradients at the surface. This phonon signature is also present in the ground-state conductivity, and decays in strength with increasing temperature to vanish above $T\sim 100\,{\rm{K}}$, i.e. significantly below the CDW transition temperature. The temporal behavior of the phonon emission can be well described by a simple model with two coupled modes, which initially oscillate with opposite polarity.
Author:Kaneez Rabia, Fanqi MengORCiD, Mark David Thomson, Maxim Bykov, Roberto Merlin, Sander van Smaalen, Hartmut RoskosORCiDGND
Parent Title (English):New journal of physics
Publisher:Dt. Physikalische Ges. ; IOP
Place of publication:[Bad Honnef] ; [London]
Document Type:Article
Year of Completion:2019
Date of first Publication:2019/01/18
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2019/03/05
Tag:blue bronze; charge density wave; coherent emission; phonon; terahertz; time-resolved
Issue:Art. 013013
Page Number:13
First Page:1
Last Page:12
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Institutes:Physik / Physik
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik
Licence (German):License LogoCreative Commons - Namensnennung 3.0