Muon-spin-rotation measurements of the penetration depth of the infinite-layer electron-doped Sr0.9La0.1CuO2 cuprate superconductor

Muon spin rotation (µSR) measurements of the in-plane penetration depthab have been per- formed in the electron-doped infinite layer high-Tc superconductor (HTS) Sr0.9La0.1CuO2. Absence of the magnetic rare-earth ions in this compound allowed to measure for the first time the abso- lute value ofab(0) in electron-doped HTS using µSR. We foundab(0)=116(2) nm. The zero- temperature depolarization rate �(0)/ 1/� 2(0)=4.6(1) µs 1 is more than four times higher than expected from the Uemura line. Therefore this electron-doped HTS does not follow the Uemura relation found for hole-doped HTS. PACS numbers: 74.72.-h, 76.75.+i, 74.25.Dw, 74.25.Ha The high-Tc cuprate superconductors are obtained by doping holes or electrons into the antiferromagnetic (AF) insulating state. Both electron and hole-doped cuprates share a common building block, namely the copper- oxygen plane and one would expect that the same pairing mechanism is applicable. There are a number of impor- tant differences, however, between the generic phase di- agrams of the electron-doped and hole-doped materials. In order to elucidate the mechanism of high-Tc super- conductivity (HTS), it is very important to clarify the origin of similarities and differences between hole-doped (p-type) and electron-doped (n-type) cuprates. The magnetic field penetration depthis one of the fundamental lengths of a superconductor, related to the superfluid phase stiffnesss ∝ 1/� 2 , or what is often re- ferred to as superfluid density ns/m ∗ ∝ 1/� 2 (supercon- ducting carrier concentration ns divided by the effective mass m ∗ ). Accurate and precise measurements of the absolute value of �(T → 0) are very important for un- derstanding superconductivity in cuprates. The muon- spin-rotation (µSR) technique provides a powerful tool to measurein type II superconductors. Detailed µSR investigations of polycrystalline HTS have demonstrated thatcan be obtained from the muon spin depolarization rate �(T) ∝ 1/� 2 (T), which probes the second moment of the magnetic field distribution in the mixed state (1). One of the most interesting result of µSR investigations in HTS is a remarkable proportionality between Tc and the zero-temperature depolarization rate �(0) ∝ 1/� 2 (0) for a wide range of p-type underdoped HTS (so-called Uemura line) (2, 3). This observation indicates that the superfluid density is an important quantity which deter- mines Tc in HTS. This is not expected in conventional BCS theory and therefore the Uemura relation has an