Spontaneous plaquette formation in the SU(4) Spin-Orbital ladder

The low-energy properties of the SU(4) spin-orbital model on a two-leg ladder are studied by a variety of analytical and numerical techniques. Like in the case of SU(2) models, there is a singlet-multiplet gap in the spectrum, but the ground-state is two-fold degenerate. An interpretation in terms of SU(4)-singlet plaquettes is proposed. The implications for general two-dimensional lattices are outlined.Comment: 4 pages, 5 Postscript figure

Spin-mechanics with levitating ferromagnetic particles

We propose and demonstrate first steps towards schemes where the librational mode of levitating ferromagnets is strongly coupled to the electronic spin of Nitrogen-Vacancy (NV) centers in diamond. Experimentally, we levitate ferromagnets in a Paul trap and employ magnetic fields to attain oscillation frequencies in the hundreds of kHz range with Q factors close to $10^4$. These librational frequencies largely exceed the decoherence rate of NV centers in typical CVD grown diamonds offering prospects for sideband resolved operation. We also prepare and levitate composite diamond-ferromagnet particles and demonstrate both coherent spin control of the NV centers and read-out of the particle libration using the NV spin. Our results will find applications in ultra-sensitive gyroscopy and bring levitating objects a step closer to spin-mechanical experiments at the quantum level.Comment: Lengthened to 11 pages. To appear in PR

Industrial applications of heavy ions beams at GANIL

International audienceAfter a year of research and development, BSI and GANIL started an industrial production of microporous membranes. The status of the technical and commercial problems is given. With the collaboration of industrial firms, other applications are studied, like : non reflecting surfaces, ion implantation, surface treatment, radiation damage..

Formation of energy gap in higher dimensional spin-orbital liquids

A Schwinger boson mean field theory is developed for spin liquids in a symmetric spin-orbital model in higher dimensions. Spin, orbital and coupled spin-orbital operators are treated equally. We evaluate the dynamic correlation functions and collective excitations spectra. As the collective excitations have a finite energy gap, we conclude that the ground state is a spin-orbital liquid with a two-fold degeneracy, which breaks the discrete spin-orbital symmetry. Possible relevence of this spin liquid state to several realistic systems, such as CaV$_4$V$_9$ and Na$_2$Sb$_2$Ti$_2$O, are discussed.Comment: 4 pages with 1 figur

SU(4) Spin-Orbital Two-Leg Ladder, Square and Triangle Lattices

Based on the generalized valence bond picture, a Schwinger boson mean field theory is applied to the symmetric SU(4) spin-orbital systems. For a two-leg SU(4) ladder, the ground state is a spin-orbital liquid with a finite energy gap, in good agreement with recent numerical calculations. In two-dimensional square and triangle lattices, the SU(4) Schwinger bosons condense at (\pi/2,\pi/2) and (\pi/3,\pi/3), respectively. Spin, orbital, and coupled spin-orbital static susceptibilities become singular at the wave vectors, twice of which the bose condensation arises at. It is also demonstrated that there are spin, orbital, and coupled spin-orbital long-range orderings in the ground state.Comment: 5 page

N\'eel and Spin-Peierls ground states of two-dimensional SU(N) quantum antiferromagnets

The two-dimensional SU(N) quantum antiferromagnet, a generalization of the quantum Heisenberg model, is investigated by quantum Monte Carlo simulations. The ground state for $N\le 4$ is found to be of the N\'eel type with broken SU(N) symmetry, whereas it is of the Spin-Peierls type for $N\ge 5$ with broken lattice translational invariance. No intermediate spin-liquid phase was observed in contrast to previous numerical simulations on smaller lattices [Santoro et al., Phys. Rev. Lett. {\bf 83} 3065 (1999)].Comment: 4 pages, 4 figure