Anomalous Pressure Dependences of the Superconducting Transition Temperature of Graphite Intercalation Compounds

Abstract

ABSTRACTMeasurements of the pressure (P) dependence of the superconducting transition temperature Tc of KHgC4, KHgC8, KTℓ1.5C4 and KC8 are reported. KC24 was found to be nonsuperconducting to a limiting temperature T ≈ 0.07 K for P ≤ 10 kbar, and RbC8 was found to be nonsuperconducting to T ≈ 1.30 K for P ≤ 22 kbar. The Tc of KHgC8 was found to monotonically decrease at a rate dTc/dP = −6.5 × 10−5 K/bar from a zero pressure Tc = 1.850 K. The Tc of KTℓ1.5C4 initially decreases at a rate dTc/dP≤ −4.5 × 10−5 K/bar from a zero pressure Tc = 2.54 K. KHgC4 displayed a broad zero pressure superconducting transition with an onset at T ≈ 1.42 K, followed by an abrupt narrowing of the transition and rapid decrease of Tc at a rate dTc/dP = −5 × 10−5 K/bar at p > 1 kbar. The Tc of KC8 was observed to jump from a zero pressure value of 0.13 K to a broad transition with an onset at ˜ 1.7 K for P > 2 kbar.