## 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 urn:nbn:de:hebis:30:3-492854 https://doi.org/10.1088/1367-2630/aaf81f 1367-2630 New journal of physics Dt. Physikalische Ges. ; IOP [Bad Honnef] ; [London] Article English 2019 2019/01/18 Universitätsbibliothek Johann Christian Senckenberg 2019/03/05 blue bronze; charge density wave; coherent emission; phonon; terahertz; time-resolved 21 Art. 013013 13 1 12 Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. 448056631 Physik / Physik 5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik Universitätspublikationen Physik Creative Commons - Namensnennung 3.0