Spectroscopic Evidence of Low Energy Gaps Persisting Towards 120 Kelvin in Surface-Doped <i>p</i>-Terphenyl Crystals

The possibility of high temperature superconductivity in organic compounds has been discussed since the pioneering work of Little in 1964 [i], with unsatisfactory progress until the recent report of a weak Meissner shielding effect at 120 Kelvin in potassium-doped para-terphenyl samples [ii]. To date however, no other signals of the superconductivity have been shown, including the zero resistance state or evidence for the formation of the Cooper pairs that are inherent to the superconducting state. Here, using high-resolution photoemission spectroscopy on potassium surface-doped para-terphenyl crystals, we uncover low energy gaps that persist to approximately 120 K. Among a few potential origins for these gaps, we argue that the onset of electron pairing within molecules is most likely. And while pairing gaps are a prerequisite for high temperature superconductivity they do not guarantee it. Rather, the development of long-range phase coherence between the paired states on the molecules is necessary, requiring good wavefunction overlap between molecular states– something that is in general difficult for such weakly overlapping molecules.
[i]. W. A. Little, Phys. Rev. 134, A1416 (1964).
[ii]. R. S. Wang et al. Preprint at arXiv.1703.06641 (2017)