ABSENCE OF SUPERCONDUCTIVITY IN THE DOPED ANTIFERROMAGNETIC SPIN LADDER COMPOUND (LA,SR)CUO2.5

A SPIN-1/2 Heisenberg antiferromagnetic ladder is a model system compr ising parallel chains of interacting elemental spins. Spin ladders hav ing an even number of chains have been predicted(1-6) to exhibit inter esting dynamics, including superconductivity, when unoccupied spin sit es are introduced along the chain (that is, when the chains are doped with holes). Spin-ladder models thus provide a novel potential mechani sm for high-temperature superconductivity in real materials. But unfor tunately materials with spin-ladder structure are quite rare(4-10), an d the few known compounds have not previously been doped successfully with holes. Here we report the high-pressure synthesis of a new hole-d oped two-chain ladder compound, La1-xSrxCuO2.5. We have observed a mar ked insulator-to-metal transition in this compound with increased dopi ng, but no superconducting transition down to 5 K. The absence of supe rconductivity in this material must be reconciled with theoretical pre dictions based on ideal hole-doped spin-ladder models.