Remarkable transition from rocksalt/perovskite layered structure to fluorite/rocksalt layered structure in rapidly cooled Ln2CuO4

This work was supported by EPSRCLanthanide cuprates of formula Ln2CuO4 exist in two principal forms, T and T′ which are renowned for their exhibition at low temperatures of hole and electronic types of superconductivity, respectively. These structures differ primarily in the arrangement of oxygen between the perovskite layers and also in nature of the copper oxygen planes. The Cu-O distance in the T structure (~1.90 Å) is much shorter than the T′ (1.97Å), reflecting a transition between partial Cu+ and partial Cu3+ character. In seeking to find compositions that bridge these two structure/electron carrier types, we observed the transition from a T structure to a T′ type structure, resulting in the metastable form T″ with slightly larger volume but similar character to T′. This transition from T to T″ is associated with 5% increase in a and a 5% decrease in c parameters of the tetragonal unit cells, which results in disintegration of ceramic bodies.Publisher PDFPeer reviewe

Determination of the magnetic penetration depth of the high T_c superconductor YBa₂Cu₃O_7-x by polarised neutron reflection

Flecher and co-workers in their work on superconducting films niobium, lead and lead-bismuth, have used the reflection of spin-polarized slow neutrons to obtain a direct and absolute measurement of the magnetic penetration depth. In this paper, the authors report the first such measurement of the penetration depth in a sample of yBa//2Cu//3O//7// minus //x. At a temperature of 4. 8 K and in an applied magnetic field of 350 oersteds they obtain a value, which represents an upper limit, of 225 plus or minus 75 Angstroms, which is small compared with penetration depths in conventional superconductors, and with the recently quoted values for YBa//2Cu//3O//7// minus //x and La//1//. //8//5Ba//0//. //1//5CuO//4

Hidden phase in a two-dimensional Sn layer stabilized by modulation hole doping

Semiconductor surfaces and ultrathin interfaces exhibit an interesting variety of two-dimensional quantum matter phases, such as charge density waves, spin density waves and superconducting condensates. Yet, the electronic properties of these broken symmetry phases are extremely difficult to control due to the inherent difficulty of doping a strictly two-dimensional material without introducing chemical disorder. Here we successfully exploit a modulation doping scheme to uncover, in conjunction with a scanning tunnelling microscope tip-assist, a hidden equilibrium phase in a hole-doped bilayer of Sn on Si(111). This new phase is intrinsically phase separated into insulating domains with polar and nonpolar symmetries. Its formation involves a spontaneous symmetry breaking process that appears to be electronically driven, notwithstanding the lack of metallicity in this system. This modulation doping approach allows access to novel phases of matter, promising new avenues for exploring competing quantum matter phases on a silicon platform