Interpretation of the temperature-dependent resistivity ofK3C60 fulleride superconductors: an electron–phonon mechanism

Abstract

The temperature-dependent normal state resistivity of single crystalK3C60 is theoretically analysed within the framework of the electron–phonon model ofresistivity, i.e., the Bloch–Gruneisen model. Keeping in mind that a largeamount of impurities develop due to the doping of alkali metal in pureC60, zerotemperature limited resistivity has first been estimated. Due to the inherent intermolecular phonon(ωer) andintramolecular (ωra) phonon, the contributions to the resistivity have been estimated as a next step. Theintramolecular phonon yields a relatively larger contribution to the resistivitycompared to the contribution of intermolecular phonons above 260 K. In addition,below this temperature, the intermolecular phonon is a major source of resistivity.The estimated contribution to resistivity when subtracted from single crystaldata infers a quadratic temperature dependence till 200 K and there exists adeparture until near room temperature. The power temperature dependence ofρdiff = [ρexp−{ρ0+ρe−ph (= ρer+ρra)}] may be attributed to the contribution of the three dimensional transport mechanismand has been related to electron–electron interaction. We then emphasizedthe role of intramolecular phonons to estimate the transition temperatureTc, carbon isotopeeffect exponent α and pressure as well as the volume derivative ofTc and the results are consistent with the reported data. It therefore appears that bothelectron–electron and electron–phonon interaction play an important role in retracing thenormal state resistivity behaviour and some of the superconducting state properties.