Hijii, Keigo, Miyashita, Seiji
We study structure of the gapless points (diabolical points) at zero magnetic field ($H_z=0$) of single-spin models with spin anisotropies. Nontrivial appearance of diabolical points at finite...
Phase diagram of S=1 XXZ chain with next-nearest neighbor interaction (2004)
Murashima, Takahiro, Hijii, Keigo, Nomura, Kiyohide, Tonegawa, Takashi
The one dimensional S=1 XXZ model with next-nearest-neighbor interaction $\alpha$ and Ising-type anisotropy $\Delta$ is studied by using a numerical diagonalization technique. We discuss the ground...
Staggered dimer order in S=1/2 quantum spin ladder system with four spin exchange (2003)
Hijii, Keigo, Qin, Shaojin, Nomura, Kiyohide
We study the S=1/2 quantum spin ladder system with the four-spin exchange, using density matrix renormalization group method and an exact diagonalization method. Recently, the phase transition in...
Universality class of S=1/2 quantum spin ladder system with the four spin exchange (2001)
Hijii, Keigo, Nomura, Kiyohide
We study s=1/2 Heisenberg spin ladder with the four spin exchange. Combining numerical results with the conformal field theory(CFT), we find a phase transition with central charge c=3/2. Since this...