@article{ab63bc8cf1f948cc8b7e07f418059380,
title = "Thickness-Dependent Coherent Phonon Frequency in Ultrathin FeSe/SrTiO3 Films",
abstract = "Ultrathin FeSe films grown on SrTiO3 substrates are a recent milestone in atomic material engineering due to their important role in understanding unconventional superconductivity in Fe-based materials. By using femtosecond time- and angle-resolved photoelectron spectroscopy, we study phonon frequencies in ultrathin FeSe/SrTiO3 films grown by molecular beam epitaxy. After optical excitation, we observe periodic modulations of the photoelectron spectrum as a function of pump-probe delay for 1-unit-cell, 3-unit-cell, and 60-unit-cell thick FeSe films. The frequencies of the coherent intensity oscillations increase from 5.00 ± 0.02 to 5.25 ± 0.02 THz with increasing film thickness. By comparing with previous works, we attribute this mode to the Se A1g phonon. The dominant mechanism for the phonon softening in 1-unit-cell thick FeSe films is a substrate-induced lattice strain. Our results demonstrate an abrupt phonon renormalization due to a lattice mismatch between the ultrathin film and the substrate. (Figure Presented).",
keywords = "Ultrathin films, coherent phonons, high-temperature superconductivity, time-resolved photoemission",
author = "Shuolong Yang and Sobota, {Jonathan A.} and Dominik Leuenberger and Kemper, {Alexander F.} and Lee, {James J.} and Schmitt, {Felix T.} and Wei Li and Moore, {Rob G.} and Kirchmann, {Patrick S.} and Shen, {Zhi Xun}",
note = "Publisher Copyright: {\textcopyright} 2015 American Chemical Society.",
year = "2015",
month = jun,
day = "10",
doi = "10.1021/acs.nanolett.5b01274",
language = "English",
volume = "15",
pages = "4150--4154",
journal = "Nano Letters",
issn = "1530-6984",
publisher = "American Chemical Society",
number = "6",
}