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Infrared ellipsometry study of the charge dynamics in K3p-terphenyl

Authors :
He, Qi
Marsik, P.
Mardelé, F. Le
Xu, B.
Sharma, Meenakshi
Pinto, N.
Perali, A.
Di Nicola, C.
Pettinari, C.
Baeriswyl, D.
Bernhard, C.
Publication Year :
2023

Abstract

We report an infrared ellipsometry study of the charge carrier dynamics in polycrystalline Kxp-terphenyl samples with nominal $x=3$, for which signatures of high-temperature superconductivity were previously reported. The infrared spectra are dominated by two Lorentzian bands with maxima around 4 000 cm$^{-1}$ and 12 000 cm$^{-1}$ which, from a comparison with calculations based on a H\"uckel model are assigned to intra-molecular excitations of $\pi$ electrons of the anionic p-terphenyl molecules. The inter-molecular electronic excitations are much weaker and give rise to a Drude peak and a similarly weak Lorentzian band around 220 cm$^{-1}$. A dc resistivity of about 0.3 $\Omega$ cm at 300 K is deduced from the IR data, comparable to values measured by electrical resistivity on a twin sample. The analysis of the temperature dependence of the low-frequency response reveals a gradual decrease of the plasma frequency and the scattering rate of the Drude peak below 300 K that gets anomalously enhanced below 90 K. The corresponding missing spectral weight of the Drude peak appears blue-shifted towards the Lorentz-band at 220 cm$^{-1}$. This characteristic blue-shift signifies an enhanced localization of the charge carriers at low temperatures and contrasts the behavior expected for a bulk superconducting state for which the missing spectral weight would be redshifted to a delta-function at zero frequency that accounts for the loss-free response of the superconducting condensate. Our data might still be compatible with a filamentary superconducting state with a volume fraction well below the percolation limit for which the spatial confinement of the condensate can result in a plasmonic resonance at finite frequency.<br />Comment: 12 pages, 7 figures

Details

Database :
arXiv
Publication Type :
Report
Accession number :
edsarx.2302.10097
Document Type :
Working Paper
Full Text :
https://doi.org/10.1103/PhysRevB.107.094520