Anisotropic thermal expansion of p-Terphenyl: a self-assembled supramolecular array of poly-p-phenyl nanoribbons

TL;DR

This study investigates the anisotropic thermal expansion of p-Terphenyl, revealing a nanoscale network of nanoribbons and phase transition behaviors that are relevant for understanding its superconducting properties.

Contribution

It provides the first detailed analysis of the temperature-dependent anisotropic thermal expansion and structural phase transitions in p-Terphenyl, supporting the existence of a nanoribbon network.

Findings

Anisotropic thermal expansion observed in the ab plane.

Phase transition at 193 K with power law behavior.

Evidence of a nanoscale network of nanoribbons.

Abstract

The recent discovery of superconductivity in a metallic aromatic hydrocarbon, alkali-doped p-Terphenyl, has attracted considerable interest. The critical temperature Tc ranges from few to 123 K, the record for organic superconductors, due to uncontrolled competition of multiple phases and dopant concentration. In the proposed mechanism of Fano resonance in a superlattice of quantum wires with coexisting polarons and Fermi particles, the lattice properties play a key role. Here we report a study of the temperature evolution of the parent compound p-Terphenyl crystal structure proposed to be made of a self-assembled supramolecular network of nanoscale nanoribbons. Using temperature dependent synchrotron radiation x-ray diffraction we report the anisotropic thermal expansion in the ab plane, which supports the presence of a nanoscale network of one-dimensional nanoribbons running in the b-axis direction in the P21/a structure. Below the enantiotropic phase transition at 193 K the order parameter of the C-1 structure follows a power law behaviour with the critical exponent 0.34 and the thermal expansion of the a-axis and b-axis show major changes supporting the formation of a two-dimensional bonds network. The large temperature range of the orientation fluctuations in a double well potential of the central phenyl has been determined.