FeTi$_2$O$_5$: a spin Jahn-Teller transition tuned by cation substitution
Physical Review B American Physical Society 100 (2019) 094401
Abstract:
We have used muon-spin rotation, heat capacity and x-ray diffraction measurements in combination with density functional theory and dipole field calculations to investigate the crystal and magnetic structure of FeTi$_2$O$_5$. We observe a long range ordered state below 41.8(5) K with indications of significant correlations existing above this temperature. We determine candidate muon stopping sites in this compound, and find that our data are consistent with the spin Jahn-Teller driven antiferromagnetic ground state with k=(1/2,1/2,0) reported for CoTi$_2$O$_5$. By comparing our data with calculated dipolar fields we can restrict the possible moment size and directions of the Fe$^{2+}$ ions.Manifold of spin states and dynamical temperature effects in LaCoO3: Experimental and theoretical insights
Physical Review B American Physical Society (APS) 100:5 (2019) 054306
Spin-orbit excitons in CoO
Physical Review B American Physical Society (APS) 100:7 (2019) 075143
Topological Lifshitz transitions and Fermi arc manipulation in Weyl semimetal NbAs.
Nature communications 10:1 (2019) 3478
Abstract:
Surface Fermi arcs (SFAs), the unique open Fermi-surfaces (FSs) discovered recently in topological Weyl semimetals (TWSs), are unlike closed FSs in conventional materials and can give rise to many exotic phenomena, such as anomalous SFA-mediated quantum oscillations, chiral magnetic effects, three-dimensional quantum Hall effect, non-local voltage generation and anomalous electromagnetic wave transmission. Here, by using in-situ surface decoration, we demonstrate successful manipulation of the shape, size and even the connections of SFAs in a model TWS, NbAs, and observe their evolution that leads to an unusual topological Lifshitz transition not caused by the change of the carrier concentration. The phase transition teleports the SFAs between different parts of the surface Brillouin zone. Despite the dramatic surface evolution, the existence of SFAs is robust and each SFA remains tied to a pair of Weyl points of opposite chirality, as dictated by the bulk topology.Selective probing of magnetic order on Tb and Ir sites in stuffed Tb2Ir2O7 using resonant x-ray scattering
Journal of Physics: Condensed Matter IOP Publishing 31:34 (2019) 344001