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Physical review materials 5(10), 104403 (2021). doi:10.1103/PhysRevMaterials.5.104403, Hybridization of electronic states and orbital symmetry in transition metal oxides are generally considered key ingredients in the description of both their electronic and magnetic properties. In the prototypical case of La$_{0.65}$Sr$_{0.35}$MnO$_3$ (LSMO), a landmark system for spintronics applications, a description based solely on Mn 3d and O 2p electronic states is reductive. We thus analyzed elemental and orbital distributions in the LSMO valence band through a comparison between density functional theory calculations and experimental photoelectron spectra in a photon energy range from soft to hard x rays. We reveal a number of hidden contributions, arising specifically from La 5p, Mn 4s, and O 2s orbitals, considered negligible in previous analyses; our results demonstrate that all these contributions are significant for a correct description of the valence band of LSMO and of transition metal oxides in general., Published by APS, College Park, MD

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We present a combined polarized neutron and x-ray scattering study on two enantiopure langasite single crystals aimed at the determination of their absolute structural and magnetic chiralities and the coupling between them. Our respective data sets unambiguously reveal two samples of opposite structural chirality, where the magnetic handedness is pinned by the structural one. Simple energy considerations of the magnetic exchange and single-ion anisotropy parameters reveal that it is not the Dzyaloshinskii-Moriya interaction but the local single-ion anisotropy on a triangular plaquette which plays a key role in stabilizing one of the two magnetic helices.

The tetragonal phase of chromium (III) oxide, although unstable in the bulk, can be synthesized in epitaxial heterostructures. The theoretical investigation by density functional theory predicts an antiferromagnetic ground state for this compound. We demonstrate experimentally antiferromagnetism up to 40 K in ultrathin films of t-Cr2O3 by electrical measurements exploiting interface effect within a neighboring ultrathin Pt layer. We show that magnetotransport in Pt is affected by both spin-Hall magnetoresistance and magnetic proximity effect while we exclude any role of magnetism for the low-temperature resistance anomaly observed in Pt., 23 pages, 5 figures, Accepted in PRB (2019)

Currently, there is a flurry of research interest on materials with an unconventional electronic structure, and we have already seen significant progress in their understanding and engineering towards real-life applications. The interest erupted with the discovery of graphene and topological insulators in the previous decade. The electrons in graphene simulate massless Dirac Fermions with a linearly dispersing Dirac cone in their band structure, while in topological insulators, the electronic bands wind non-trivially in momentum space giving rise to gapless surface states and bulk bandgap. Weyl semimetals in condensed matter systems are the latest addition to this growing family of topological materials. Weyl Fermions are known in the context of high energy physics since almost the beginning of quantum mechanics. They apparently violate charge conservation rules, displaying the "chiral anomaly", with such remarkable properties recently theoretically predicted and experimentally verified to exist as low energy quasiparticle states in certain condensed matter systems. Not only are these new materials extremely important for our fundamental understanding of quantum phenomena, but also they exhibit completely different transport phenomena. For example, massless Fermions are susceptible to scattering from non-magnetic impurities. Dirac semimetals exhibit non-saturating extremely large magnetoresistance as a consequence of their robust electronic bands being protected by time reversal symmetry. These open up whole new possibilities for materials engineering and applications including quantum computing. In this review, we recapitulate some of the outstanding properties of WTe$_2$, namely, its non-saturating titanic magnetoresistance due to perfect electron and hole carrier balance up to a very high magnetic field observed for the very first time. (Continued. Please see the main article)., 33 pages, 7 figures

Erratum

The development of high efficiency perovskite solar cells has sparked a multitude of measurements on the optical properties of these materials. For the most studied methylammonium(MA) PbI3 perovskite, a large range (6-55 meV) of exciton binding energies has been reported by various experiments. The existence of excitons at room temperature is unclear. For the MAPbX(3) perovskites we report on relativistic Bethe-Salpeter Equation calculations (GW-BSE). This method is capable to directly calculate excitonic properties from first-principles. At low temperatures it predicts exciton binding energies in agreement with the reported 'large' values. For MAPbI(3), phonon modes present in this frequency range have a negligible contribution to the ionic screening. By calculating the polarization in time from finite temperature molecular dynamics, we show that at room temperature this does not change. We therefore exclude ionic screening as an explanation for the experimentally observed reduction of the exciton binding energy at room temperature and argue in favor of the formation of polarons.

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We present a comprehensive experimental and theoretical study of the electronic and magnetic properties of two quasi-two-dimensional (2D) honeycomb lattice monoclinic compounds A3Ni2SbO6(A=Li,Na). Magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long-range order with Néel temperatures of ∼14 and 16 K for Li3Ni2SbO6 and Na3Ni2SbO6, respectively. The effective magnetic moments of 4.3μB/f.u.(Li3Ni2SbO6) and 4.4μB/f.u.(Na3Ni2SbO6), where f.u. is formula units, indicate that Ni2+ is in a high-spin configuration (S=1). The temperature dependence of the inverse magnetic susceptibility follows the Curie-Weiss law in the high-temperature region and shows positive values of the Weiss temperature, ∼8K (Li3Ni2SbO6) and ∼12 K (Na3Ni2SbO6), pointing to the presence of nonnegligible ferromagnetic interactions, although the system orders antiferromagnetically at low temperatures. In addition, the magnetization curves reveal a field-induced (spin-flop type) transition below TN that can be related to the magnetocrystalline anisotropy in these systems. These observations are in agreement with density functional theory calculations, which show that both antiferromagnetic and ferromagnetic intralayer spin exchange couplings between Ni2+ ions are present in the honeycomb planes, supporting a zigzag antiferromagnetic ground state. Based on our experimental measurements and theoretical calculations, we propose magnetic phase diagrams for the two compounds. © 2015 American Physical Society. ©2015 American Physical Society.

Mn5Ge3(001) thin films grown on Ge(111) were studied by angle-and spin-resolved photoemission using synchrotron radiation in the 17-40 eV photon energy range. The photoelectron spectra were simulated starting from a first-principles band-structure calculation for the ground state, using the free-electron approximation for the final states, taking into account photohole lifetime effects and k(perpendicular to) broadening plus correlation effects, but ignoring transition matrix elements. The measured spin polarizations for the various k points investigated in the Gamma MLA plane of the Brillouin zone are found to be in fair enough agreement with the simulated ones, providing a strong support to the ground-state band-structure calculations. Possible origins for the departures between either simulations and experiments or previous and present experiments are discussed.

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We present a study based on several advanced first-principles methods of the recently synthesized PbNiO3 [J. Am. Chem. Soc. 133, 16920 (2011)], a rhombohedral antiferromagnetic insulator, which crystallizes in the highly distorted R3c crystal structure. We find this compound electrically polarized with a very large electric polarization of similar to 100 mu C/cm(2), thus, even exceeding the polarization of well-known BiFeO3. PbNiO3 is a proper ferroelectric with polarization driven by large Pb-O polar displacements along the [111] direction. Contrary to naive expectations, a definite ionic charge of 4+ for the Pb ion cannot be assigned, and, in fact, the large Pb 6s-O 2p hybridization drives the ferroelectric distortion through a lone-pair mechanism similar to that of other Pb- and Bi-based multiferroics.