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Comment: Title changed; 9 pages, 2 figures
We present a $^{63,65}$Cu and $^{29}$Si NMR study of the quasi-2D coupled spin 1/2 dimer compound BaCuSi$_2$O$_6$ in the magnetic field range 13-26 T and at temperatures as low as 50 mK. NMR data in the gapped phase reveal that below 90 K different intra-dimer exchange couplings and different gaps ($\Delta_{\rm{B}}/\Delta_{\rm{A}}$ = 1.16) exist in every second plane along the c-axis, in addition to a planar incommensurate (IC) modulation. $^{29}$Si spectra in the field induced magnetic ordered phase reveal that close to the quantum critical point at $H_{\rm{c1}}$ = 23.35 T the average boson density $\bar{n}$ of the Bose-Einstein condensate is strongly modulated along the c-axis with a density ratio for every second plane $\bar{n}_{\rm{A}}/\bar{n}_{\rm{B}} \simeq 5$. An IC modulation of the local density is also present in each plane...
Comment: revised, section V about exact diagonalization is extensively rewritten, 17 pages, 11 figures, RevTex 4, accepted by Phys. Rev. B
Band structure calculations within the local spin-density approximation are presented in order to investigate the electronic and magnetic properties of the zigzag spin-chain compound In$_2$VO$_5$. The essential structural feature of the system is a double chain of VO$_6$-octahedra, which leads to competing intrachain and interchain magnetic couplings. Frustration of the spin-chains is expected for the proposed antiferromagnetic ordering at low temperatures. However, the band calculations show that the experimental room temperature crystal structure is incompatible with antiferromagnetism. Both the intrachain and interchain coupling is found to be ferromagnetic.
Spin- and angle-resolved resonant (Ce $4d\to4f$) photoemission spectra of a monolayer Ce on Fe(110) reveal spin-dependent changes of the Fermi-level peak intensities. That indicate a spin-dependence of $4f$ hybridization and, thus, of $4f$ occupancy and local moment. The phenomenon is described in the framework of the periodic Anderson model by $4f$ electron hopping into the exchange split Fe 3d derived bands that form a spin-gap at the Fermi energy around the $\bar{\Gamma}$ point of the surface Brillouin zone.
Ferroelectric spiral magnets DyMnO3 and TbMnO3 show similar behavior of electric polarization in applied magnetic fields. Studies of the field dependence of lattice modulations on the contrary show a completely different picture. Whereas in TbMnO3 the polarization flop from P||c to P||a is accompanied by a sudden change from incommensurate to commensurate wave vector modulation, in DyMnO3 the wave vector varies continuously through the flop transition. This smooth behavior may be related to the giant magnetocapacitive effect observed in DyMnO3.
We propose a novel experimental probe for cold atomic gases analogous to the scanning tunnelling microscope (STM) in condensed matter. This probe uses the coherent coupling of a single particle to the system. Depending on the measurement sequence, our probe allows to either obtain the \emph{local} density, with a resolution on the nanometer scale, or the single particle correlation function in real time. We discuss applications of this scheme to the various possible phases for a two dimensional Hubbard system of fermions in an optical lattice.
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