24 research outputs found
Featureless Mott Insulators
A family of the pair hopping models exhibiting the incompressible quantum
liquid at fractional filling is constructed in dimensional lattice.
Except in one dimension, the lattice is the generalized edge-shared triangular
lattice, for example the triangular lattice in two dimensions and tetrahedral
lattice in three dimensions. They obey the new symmetry, conservation of the
center-of-mass position proposed by Seidel et al..\cite{Seidel2005} The
uniqueness of the ground state is proved rigorously in the open boundary
condition. The finiteness of the excitation energy is calculated by the single
mode approximation.Comment: 12 pages, 5 figures, the detail version of Physical Review Letters
98, 066804 (2007
Modelling the Berezinskii-Kosterlitz-Thouless Transition in the NiGa_2S_4
In the two-dimensional superfluidity, the proliferation of the vortices and
the anti-vortices results in a new class of phase transition,
Berezinskii-Kosterlitz-Thouless (BKT) transition. This class of the phase
transitions is also anticipated in the two-dimensional magnetic systems.
However, its existence in the real magnetic systems still remains mysterious.
Here we propose a phenomenological model to illustrate that the novel
spin-freezing transition recently uncovered in the NMR experiment on the
NiGa_2S_4 compound is the BKT-type. The novel spin-freezing state observed in
the NiGa_2S_4 possesses the power-law decayed spin correlation.Comment: 4 pages, 6 figure
On the valence bond solid in the presence of Dzyaloshinskii-Moriya interaction
We examine the stability of the valence bond solid (VBS) phase against the
Dzyaloshinskii-Moriya (DM) interaction in the bipartite lattice. Despite the
VBS is vulnerable against the antiferromagnetic interaction, for example in the
Q-J model proposed by Sandvik, where the quantum phase transition occurs at
, we found that on the contrary the VBS is very stable against
the DM interaction. The quantum phase transition does not occur until D/Q goes
to infinity, where D is the strength of the DM interaction. The VBS in the ALKT
model and the Haldane gap system also exhibit the same property.Comment: 5 pages and 5 figure
Non-magnetic Stern-Gerlach Experiment from Electron Diffraction
Using the wave nature of the electrons, we demonstrate that a transverse spin
current can be generated simply by the diffraction through a single slit in the
spin-orbital coupling system of the two-dimensional electron gas. The
diffracted electron picks up the transverse momentum. The up spin electron goes
one way and the down spin electron goes the other, producing the coherent spin
current. In the system of spin-orbital coupling eVm, the
\emph{out-of-plane} component of the spin of the electron can be generated up
to 0.42 . Based on this effect, a novel device of grating to distill
spin is designed. Two first diffraction peaks of electron carry different
spins, duplicating the non-magnetic version of Stern-Gerlach experiment. The
direction of the spin current can be controlled by the gate voltage with low
energy cost.Comment: 4 pages, 4 figure