Preparation and physical properties of single crystals of Hg-based cupric oxide superconductors

Hg基氧化铜超导体单晶的制备及物理性能

基本信息

批准号：
10640340
负责人：
HIROI Zenji
金额：
$ 1.79万
依托单位：
University of Tokyo (1999)Kyoto University (1998)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

A novel cuprate Volborthite, Cu_3V_2O_7(OH)_2・2H_2O, containing an S-1/2 (Cu^<2+> spin) kagome like lattice is studied by magnetic susceptibility, specific heat, and V NMR measurements. Signs for neither long-range order nor spin-gapped singlet ground states are detected down to 1.8 K, in spite of large antiferromagnetic couplings of-100 K between Cu spins fomrning a two-dimensional Kagome like network. It is suggested that Volborthite represents a system close to a quantum critical point between classical long-range ordered and quantum disordered phases.BaCu_2(Si_<1-x>Ge_x)_2O_7 comprising corrugated Cu-O chains has been found to be a spin-1/2 1D Heisenberg system with a linearly tunable exchange interaction from 290 K (x=0) to 580 K (x=l). The interchain interaction also shows a remarkable composition dependence varying from ferromagnetic (x=0) to antifer-romagnetic (x=l). These strong composition dependences have been found to lead to a rich magnetic phase diagram.Holes doped on edge-sharing CuO_2 chains are almost localized because of nearly orthogonal Cu-O-Cu bonds. Consequently, only spin degrees of freedom survive at low temperature, which sometimes presents unusual quantum magnetism. Quasi-one-dimensional cupric oxides Ca_<1-x>CuO_<2+d> and Sr_<14>Cu_<24>O_<41>, both containing 25-50% hole-doped edge-sharing CuO2 chains, are studied by uniform magnetic susceptibility and specific heat measurements on a series of polycrystalline samples with controlled metal and oxygen contents. Most of spins are dimerized always in Sr_<14>Cu_<24>O_<41>, while, in contrast, antiferromagnetic chains made of nearly 50% spins exist with the remainder forming dimers of variable density in Ca_<1-x>CuO_<2+d>.A two-sublattice model is proposed by considering that the nearest-neighbor couplings are negligibly small, due to both geometrical frustration and the special Cu-O-Cu bond angle of-95.

通过磁化率、比热和 V 核磁共振测量研究了一种新型铜酸盐伏硼铁矿，Cu_3V_2O_7(OH)_2·2H_2O，其含有 S-1/2 (Cu^<2+> 自旋) kagome 状晶格。 -尽管存在约 100 K 的大反铁磁耦合，但在低至 1.8 K 的范围内也能检测到自旋间隙单线态基态Cu 自旋之间形成二维 Kagome 状网络，表明 Volborthite 代表接近经典长程有序相和量子无序相之间的量子临界点的系统。BaCu_2(Si_<1-x>Ge_x)_2O_7 包含波纹。 Cu-O 链被发现是一个自旋 1/2 1D 海森堡系统，具有从 290 K (x=0) 到 290 K (x=0) 的线性可调交换相互作用。 580 K (x=l)。链间相互作用还显示出从铁磁 (x=0) 到反铁磁 (x=l) 的显着的成分依赖性，这些强烈的成分依赖性导致了丰富的磁性相图。由于测试的Cu-O-Cu键几乎正交，在共享边的CuO_2链上掺杂的空穴几乎是局域化的，在低温下仅存在自旋自由度，这有时会呈现出不寻常的量子磁性。研究了准一维氧化铜Ca_<1-x>CuO_<2+d>和Sr_<14>Cu_<24>O_<41>，两者均含有25-50%空穴掺杂共边CuO2链通过对一系列具有受控金属和氧含量的多晶样品进行均匀磁化率和比热测量，大多数自旋总是二聚化。 Sr_<14>Cu_<24>O_<41>，而相反，由近 50% 自旋组成的反铁磁链存在，其余部分在 Ca_<1-x>CuO_<2+d> 中形成不同密度的二聚体。考虑到由于几何挫败和特殊的 Cu-O-Cu 键角为-95，最近邻耦合可以忽略不计，提出了双子晶格模型。