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According to previous theoretical work, the binary oxide CuO can become a room temperature multiferroic via tuning of the superexchange interactions by application of pressure. Thus far, however, there has been no experimental evidence for the predicted room-temperature multiferroicity.Here, we show by neutron diffraction that the multiferroic phase in CuO reaches 295 K with the application of 18.5 GPa pressure. We also develop a spin Hamiltonian based on density functional theory and employing superexchange theory for the magnetic interactions, which can reproduce the experimental results. The present study provides a stimulus to develop room-temperature multiferroic materials by alternative methods based on existing low temperature compounds, such as epitaxial strain, for tunable multifunctional devices and memory applications.

The layered two-dimensional material MoTe 2 in the T d crystal phase is a semimetal which has theoretically been predicted to possess topologically nontrivial bands corresponding to Weyl fermions. Clear experimental evidence by angle-resolved photoemission spectroscopy (ARPES) is, however, lacking, which calls for a careful examination of the relation between ground state band structure calculations and ARPES intensity plots. Here we report a study of the near-Fermi-energy band structure of MoTe 2 (T d ) by means of ARPES measurements, density functional theory, and one-step-model ARPES calculations. Good agreement between theory and experiment is obtained. We analyze the orbital character of the surface bands and its relation to the ARPES polarization dependence. We find that light polarization has a major effect on which bands can be observed by ARPES. For s-polarized light, the ARPES intensity is dominated by subsurface Mo d orbitals, while p-polarized light reveals the bands mainly derived from Te p orbitals. Suitable light polarization for observing either an electron or hole pocket are determined.

A computational method is devised for calculating angle-resolved photoelectron spectra using a plane-wave basis and repeated-slab geometry. The method is tested with a one-dimensional model with a rectangular potential well. The model parameters are adjusted to reproduce electronic structure of graphene at the Γ point of the Brillouin zone, as obtained from density functional theory. Photoemission final states with proper boundary conditions are constructed from linear combinations of supercell eigenstates such as to match the free wave at the center of the vacuum region. These states, calculated with a moderate plane-wave cut-off, agree very well with the exact wave function. The computed photoemission intensity differs strongly from the popular (single) plane-wave approximation and shows a pronounced energy dependence.