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The spin-flop phase of a honeycomb antiferromagnet of Mn0.84Mg0.16TiO3 has been studied under magnetic field along normal direction to the honeycomb plane by neutron scattering. With increasing a m...

In two dimensional honeycomb ferromagnets, bosonic magnon quasiparticles (spin waves) may either behave as massless Dirac fermions or form topologically protected edge states. The key ingredient defining their nature is the next-nearest neighbor Dzyaloshinskii-Moriya (DM) interaction that breaks the inversion symmetry of the lattice and discriminates chirality of the associated spin-wave excitations. Using inelastic neutron scattering, we find that spin waves of the insulating honeycomb ferromagnet CrI$_3$ ($T_C=61$ K) have two distinctive bands of ferromagnetic excitations separated by a $\sim$4 meV gap at the Dirac points. These results can only be understood by considering a Heisenberg Hamiltonian with DM interaction, thus providing experimental evidence that spin waves in CrI$_3$ can have robust topological properties useful for dissipationless spintronic applications., Comment: 6 pages, 4 figures with supplemental information, accepted for publication in Phys. Rev. X

Ho Chung Jae, Jacquet Raphaël. Disparités régionales et capacités d'intervention de l'Etat en Chine populaire. In: Perspectives chinoises, n°60, 2000. pp. 40-55.

We use inelastic neutron scattering to explore the evolution of the low energy spin dynamics in the electron-doped cuprate Pr0.88LaCe0.12CuO4-d (PLCCO) as the system is tuned from its nonsuperconducting, as-grown antiferromagnetic (AF) state into an optimally-doped superconductor (Tc~24 K) without static AF order. The low temperature, low energy response of the spin excitations in under-doped samples is coupled to the presence of the AF phase, whereas the low-energy magnetic response for samples near optimal Tc exhibits spin fluctuations surprisingly insensitive to the sample temperature. This evolution of the low energy excitations is consistent with the influence of a quantum critical point in the phase diagram of PLCCO associated with the suppression of the static AF order. We carried out scaling analysis of the data and discuss the influence of quantum critical dynamics in the observed excitation spectrum., Comment: 11 Pages, 10 Figures. Minor changes to the text. Accepted by Phys. Rev. B and to appear in October 1st issue

Publication in the conference proceedings of EUSIPCO, Rhodes, Greece, 1998