# Exotic Quantum Phenomena of the Spin Nanotubes

Toru Sakai, JAEA SPring-8, Hyogo, Japan

25.11.2013 at 14:00

Recently some quantum spin systems on tube lattices, so called spin nanotubes, have been synthesized. They are expected to be interesting low-dimensional systems like the carbon nanotubes. As the first step of theoretical study on the spin nanotube, we investigate the S=1/2 three-leg spin tube, which is the simplest one, using the density matrix renormalization group (DMRG) and the numerical exact diagonalization (ED), conbined with a precise finite-size scaling analysis named level spectroscopy[2].

The spin gap, which is one of the most interesting macroscopic quantum effects, was revealed to be open for any finite rung exchange couplings, in contrast to the three-leg spin ladder system which is gapless. It is consistent with the previous effective Hamiltonian approach. We also found a new quantum phase transition caused by an asymmetric rung interaction. When one of the three rung coupling constants is changed, the spin gap would vanish. In addition we theoretically predict some new field-induced quantum phase transitions. A chiraliy-mediated

novel superconductivity mechanism will be also proposed[2,3].

[1] T. Sakai et al., J. Phys.: Condens. Matter 22 (2010) 403201.

[2] T. Sakai et al., Phys. Rev. B 78 (2008) 184415.

[3] K. Okunishi et al., Phys. Rev. B 85 (2012) 054416.

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