M. Enderle

Quantum dynamics and entanglement of spins on a square lattice.

Bulk magnetism in solids is fundamentally quantum mechanical in nature. Yet in many situations, including our everyday encounters with magnetic materials, quantum effects are masked, and it often suffices to think of magnetism in terms of the interaction between classical dipole moments. Whereas this intuition generally holds for ferromagnets, even as the size of the magnetic moment is reduced to that of a single electron spin (the quantum limit), it breaks down spectacularly for antiferromagnets, particularly in low dimensions. Considerable theoretical and experimental progress has been made in understanding quantum effects in one-dimensional quantum antiferromagnets, but a complete experimental description of even simple two-dimensional antiferromagnets is lacking. Here we describe a comprehensive set of neutron scattering measurements that reveal a non-spin-wave continuum and strong quantum effects, suggesting entanglement of spins at short distances in the simplest of all two-dimensional quantum antiferromagnets, the square lattice Heisenberg system.

Evidence of a bond-nematic phase in LiCuVO4.

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.

Magnetic order and dynamics of the charge-ordered antiferromagnet La 1.5 Sr 0.5 CoO 4

We describe neutron-scattering experiments performed to investigate the magnetic order and dynamics of half-doped

Nature of the magnetic order in the charge-ordered cuprate La1.48Nd0.4Sr0.12CuO4.

{text{La}}_{1.5}{text{Sr}}_{0.5}{text{CoO}}_{4}

Spin dynamics in stripe-ordered La 5 / 3 Sr 1 / 3 NiO 4

. This layered perovskite exhibits a near-ideal checkerboard pattern of

Spin reorientation transition in the incommensurate stripe-ordered phase ofLa3/2Sr1/2NiO4

{text{Co}}^{2+}/{text{Co}}^{3+}

Spin dynamics of half-doped La 3 ∕ 2 Sr 1 ∕ 2 Ni O 4

charge order at temperatures below

Stripe order and magnetic transitions inLa2−xSrxNiO4

ensuremath{sim}800text{ }text{K}

Inward dispersion of the spin excitation spectrum of stripe-ordered La 2NiO 4+δ

. Magnetic correlations are observed at temperatures below

Ferromagnetic excitations inLa0.82Sr0.18CoO3observed using neutron inelastic scattering

ensuremath{sim}60text{ }text{K}