Quantum fluctuations in the effective pseudospin-1/2 model for magnetic pyrochlore oxides
Quantum fluctuations in the effective pseudospin-1/2 model for magnetic pyrochlore oxides
复制标题
DOI：
10.1103/physrevb.83.094411
复制
发表时间：
2011-03-14
影响因子：
3.7
通讯作者：
Tanaka, Yoichi
中科院分区：
文献类型：
--
作者：
Onoda, Shigeki;Tanaka, Yoichi
本文从理论上研究了磁性焦绿石氧化物中稀土相互作用的有效量子赝旋-1/2模型，该模型用原子二重态局域描述。从原子的非Kramers磁偶极子出发，对Pr4f和O2p电子之间的虚电子转移进行强耦合微扰展开，从微观上推导了Pr2TM2O7(Tm=Zr，Sn，Hf和Ir)中Pr3+4f局域磁矩.最近邻各向异性超旋-1/2哈密顿量的最一般形式也是由对称性构造出来的，它适用于Kramers离子Nd3+，Sm3+和Yb3+，潜在地显示出大的量子效应。然后用经典平均场理论和单个四面体上的精确对角化和16位团簇上的精确对角化研究了有效模型。这些计算揭示了在Pr3+的情况下，随着自旋冰的融化，可察觉到的量子涨落导致量子相变到四极态。该模型还显示了四面体上的合作四极矩和赝旋手性的形成。在耦合常数空间的有限区域内也发现了单重态量子自旋冰的符号。讨论了它与实验的相关性。
The effective quantum pseudospin-1/2 model for interacting rare-earth magnetic moments, which are locally described with atomic doublets, is studied theoretically for magnetic pyrochlore oxides. It is derived microscopically for localized Pr3+ 4f moments in Pr2TM2O7 (TM = Zr, Sn, Hf, and Ir) by starting from the atomic non-Kramers magnetic doublets and performing a strong-coupling perturbation expansion of the virtual electron transfer between the Pr 4f and the O 2p electrons. The most generic form of the nearest-neighbor anisotropic superexchange pseudospin-1/2 Hamiltonian is also constructed from the symmetry properties, which is applicable to Kramers ions Nd3+, Sm3+, and Yb3+, potentially showing large quantum effects. The effective model is then studied by means of a classical mean-field theory and the exact diagonalization on a single tetrahedron and on a 16-site cluster. These calculations reveal appreciable quantum fluctuations leading to quantum phase transitions to a quadrupolar state as a melting of spin ice for the Pr3+ case. The model also shows the formation of a cooperative quadrupole moment and pseudospin chirality on tetrahedrons. A sign of a singlet quantum spin ice is also found in a finite region in the space of coupling constants. The relevance to experiments is discussed.