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Polarized and unpolarized neutron scattering experiments on the frustrated ferromagnetic spin-1/2 chain LiCuVO4 show that the phase transition at H(Q) of 8 T is driven by quadrupolar fluctuations and that dipolar correlations are short range with moments parallel to the applied magnetic field in the high-field phase. Heat-capacity measurements evidence a phase transition into this high-field phase, with an anomaly clearly different from that at low magnetic fields. Our experimental data are consistent with a picture where the ground state above H(Q) has a next-nearest neighbor bond-nematic order along the chains with a fluidlike coherence between weakly coupled chains.

We report a 51 V nuclear magnetic resonance investigation of the frustrated spin-1/2 chain compound LiCuVO4, performed in pulsed magnetic fields and focused on high-field phases up to 55 T. For the crystal orientations H c and H b we find a narrow field region just below the magnetic saturation where the local magnetization remains uniform and homogeneous, while its value is field dependent. This behavior is the first microscopic signature of the spin-nematic state, breaking spin-rotation symmetry without generating any transverse dipolar order, and is consistent with theoretical predictions for the LiCuVO4 compound.PACS numbers: 75.10. Kt, 75.30.Kz, The search for new states of quantum matter is one of the most active research fields in condensed-matter physics. In this respect frustrated magnetic systems attract a lot of interest as they accommodate various unconventional quantum states, having no direct classical analogues, ordered and disordered, induced by the competing interactions [1]. One particularly interesting state is the spin-nematic phase, in which the quantum magnet behaves like a liquid crystal. Taking an external magnetic field H as the reference direction, a spin-nematic phase is defined as a state without any transverse dipolar (i.e., vector-type) order, (−1) i S + i + H.c. = 0, but possessing instead a transverse quadrupolar (tensor-type) order,The quadrupolar order parameter develops on the bonds between neighboring spins and can be described as a condensate of two-magnon pairs. It breaks the spin-rotational symmetry about the magnetic field, but only partially as π-rotations transform the order parameter into itself. The also broken translational symmetry of the order parameter is invisible in the dipolar channel. There is also an analogy between the spin-nematic phase and the superconducting state: the nematic phase can be considered as a "bosonic" superconductor formed as a result of two-magnon condensation [1,2].The concept of a spin-nematic state was developed by Andreev and Grishchuk more than 30 years ago [3], which incited intense search for a realization in real materials. However, a definite experimental proof for the existence of such a phase has not been provided yet. Several magnetic insulators have been proposed as possible candidates, including the two-dimensional magnet NiGa 2 S 4 (spin-1 system) [4-6] and thin films of 3 He [7][8][9].In the past 10 years a large number of theoretical studies have supported the formation of the spinnematic phase in frustrated zig-zag 1D (chain) systems [10][11][12][13][14]. Amongst these, orthorhombic LiCuVO 4 is one of the most promising candidates [15,16]. It consists of spin-1/2 Cu 2+ chains along the orthorhombic b axis with a dominant nearest-neighbor ferromagnetic interaction J 1 = −1.6 meV, a frustrated next-nearest-neighbor antiferromagnetic interaction J 2 = 3.8 meV, and an interchain coupling J = −0.4 meV [17,18]. At zero magnetic field an incommensurate planar spiral structure is realized below T N = 2.3 K, having the moments lying...

We have studied the magnetic structure of the ferroelectric frustrated spin-1/2 chain material LiCuVO4 in applied electric and magnetic fields using polarized neutrons. A symmetry and mean-field analysis of the data rules out the presence of static Dzyaloshinskii-Moriya interaction, while exchange striction is shown to be negligible by our specific-heat measurements. The experimentally observed magnetoelectric coupling is in excellent agreement with the predictions of a purely electronic mechanism based on spin supercurrents.Comment: 4 pages, 3 figures, final versio

Field-induced magnetic ordering in the Haldane chain compound SrNi2V2O8 and effect of anisotropy have been investigated using single crystals. Static susceptibility, inelastic neutron scattering, high-field magnetization, and low temperature heat-capacity studies confirm a non-magnetic spin-singlet ground state and a gap between the singlet ground state and triplet excited states. The intra-chain exchange interaction is estimated to be J ∼ 8.9±0.1 meV. Splitting of the dispersions into two modes with minimum energies 1.57 and 2.58 meV confirms the existence of single-ion anisotropyThe value of D is estimated to be −0.51±0.01 meV and the easy axis is found to be along the crystallographic c-axis. Field-induced magnetic ordering has been found with two critical fields [µ0H . Field-induced three-dimensional magnetic ordering above the critical fields is evident from the heat-capacity, susceptibility, and high-field magnetization study. The Phase diagram in the H-T plane has been obtained from the high-field magnetization. The observed results are discussed in the light of theoretical predictions as well as earlier experimental reports on Haldane chain compounds.