Chemical effects of alkali atoms on critical temperature in superconducting alkali-doped fullerides

• Published in: Physica. C, Superconductivity Vol. 546; pp. 34 - 43
• Main Authors: Hetfleisch, F., Gunnarsson, O., Srama, R., Han, J.E., Stepper, M., Roeser, H.-P., Bohr, A., Lopez, J.S., Mashmool, M., Roth, S.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.03.2018; Elsevier BV
• Subjects: Alkali metals; Alkalies; Atoms & subatomic particles; Chemical effects; Critical temperature; Fullerides; Parameters; Superconductors
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2017.12.005

•A broad overview to existing lattice parameter—TC data is presented.•A chemical effect of the alkali metals is revealed, besides a known spacing effect.•Several mechanisms for this effect are examined.•The size of this chemical effect is non negligible for fullerides.•Analog impact to other Hubbard Model like systems is expected. Alkali metal doped fullerides (A3C60) are superconductors with critical temperatures, Tc, extending up to 38 K. Tc is known to depend strongly on the lattice parameter a, which can be adjusted by physical or chemical pressure. In the latter case an alkali atom is replaced by a different sized one, which changes a. We have collected an extensive data base of experimental data for Tc from very early up to recent measurements. We disentangle alkali atom chemical effects on Tc, beyond the well-known consequences of changing a. It is found that Tc, for a fixed a, is typically increased as smaller alkali atoms are replaced by larger ones, except for very large a. Possible reasons for these results are discussed. Although smaller in size than the lattice parameter contribution, the chemical effect is not negligible and should be considered in future physical model developments.