Anisotropic magnetism, resistivity, London penetration depth and magneto-optical imaging of superconducting K0.80Fe 1.76Se2 single crystals

摘要

Single crystals of K0.80Fe1.76Se2 were successfully grown from a ternary solution. We show that, although crystals form when cooling a near-stoichiometric melt, crystals are actually growing out of a ternary solution that remains liquid to at least 850 °C. We investigated their chemical composition, anisotropic magnetic susceptibility and resistivity, specific heat, thermoelectric power, London penetration depth and flux penetration via magneto-optical imaging. Whereas the samples appear to be homogeneously superconducting at low temperatures, there appears to be a broadened transition range close to Tc ～ 30K that may be associated with small variations in stoichiometry.