Existence of a phase transition under finite magnetic field in the long-range RKKY Ising spin glass Dyx_{x}Y1−x_{1-x}Ru2_{2}Si2_{2}

A phase transition of a model compound of the long-range Ising spin glass (SG) Dy$_{x}$Y$_{1-x}$Ru$_{2}$Si$_{2}$, where spins interact via the RKKY interaction, has been investigated. The static and the dynamic scaling analyses reveal that the SG phase transition in the model magnet belongs to the mean-field universality class. Moreover, the characteristic relaxation time in finite magnetic fields exhibits a critical divergent behavior as well as in zero field, indicating a stability of the SG phase in finite fields. The presence of the SG phase transition in field in the model magnet strongly syggests that the replica symmetry is broken in the long-range Ising SG.Comment: 4 pages, 4 figures, to be published in JPSJ (2010

Localization length of a soliton from a non-magnetic impurity in a general double-spin-chain model

A localization length of a free-spin soliton from a non-magnetic impurity is deduced in a general double-spin-chain model ($J_0-J_1-J_2-J_3$ model). We have solved a variational problem which employs the nearest-neighbor singlet-dimer basis. The wave function of a soliton is expressed by the Airy function, and the localization length $(\xi)$ is found to obey a power law of the dimerization $(J_2-J_3)$ with an exponent -1/3; $\xi\sim (J_2-J_3)^{-1/3}$. This explains why NaV_2O_5 does not show the antiferromagnetic order, while CuGeO_3 does by impurity doping. When the gap exists by the bond-dimerization, a soliton is localized and no order is expected. Contrary, there is a possibility of the order when the gap is mainly due to frustration.Comment: 4 pages, REVTeX, Figures are in eps-file

Quark and lepton masses and mixing in SO(10) with a GUT-scale vector matter

We explore in detail the effective matter fermion mass sum-rules in a class of renormalizable SUSY SO(10) grand unified models where the quark and lepton mass and mixing patterns originate from non-decoupling effects of an extra vector matter multiplet living around the unification scale. If the renormalizable type-II contribution governed by the SU(2)_L-triplet in 54_H dominates the seesaw formula, we obtain an interesting correlation between the maximality of the atmospheric neutrino mixing and the proximity of y_s/y_b to V_cb in the quark sector.Comment: 13 pages, 1 figure, 2 tables; v2: major update, references adde