Browsing by Author "Browne, D. A."

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    Helical magnetic order and Fermi surface nesting in non-centrosymmetric ScFeGe
    (American Physical Society, 2021) Karna, Sunil K.; Tristant, D.; Hebert, J. K.; Cao, G.; Chapai, R.; Phelan, W. A.; Zhang, Q.; Wu, Y.; Dhital, C.; Li, Y.; Cao, H. B.; Tian, W.; Dela Cruz, C. R.; Aczel, A. A.; Zaharko, O.; Khasanov, A.; McGuire, M. A.; Roy, A.; Xie, W.; Browne, D. A.; Vekhter, I.; Meunier, V.; Shelton, W. A.; Adams, P. W.; Sprunger, P. T.; Young, D. P.; Jin, R.; DiTusa, J. F.; Physics, School of Science
    An investigation of the structural, magnetic, thermodynamic, and charge transport properties of noncentrosymmetric hexagonal ScFeGe reveals it to be an anisotropic metal with a transition to a weak itinerant incommensurate helimagnetic state below 𝑇𝑁=36 K. Neutron diffraction measurements discovered a temperature and field independent helical wave vector 𝒌 = (0 0 0.193) with magnetic moments of 0.53 𝜇𝐵 per Fe confined to the 𝑎⁢𝑏 plane. Density functional theory calculations are consistent with these measurements and find several bands that cross the Fermi level along the 𝑐 axis with a nearly degenerate set of flat bands just above the Fermi energy. The anisotropy found in the electrical transport is reflected in the calculated Fermi surface, which consists of several warped flat sheets along the 𝑐 axis with two regions of significant nesting, one of which has a wave vector that closely matches that found in the neutron diffraction. The electronic structure calculations, along with a strong anomaly in the 𝑐 -axis conductivity at 𝑇𝑁, signal a Fermi surface driven magnetic transition, similar to that found in spin density wave materials. Magnetic fields applied in the 𝑎⁢𝑏 plane result in a metamagnetic transition with a threshold field of ≈6.7 T along with a sharp, strongly temperature dependent discontinuity and a change in sign of the magnetoresistance for in-plane currents. Thus, ScFeGe is an ideal system to investigate the effect of in-plane magnetic fields on a helimagnet with a 𝑐 -axis propagation vector, where the relative strength of the magnetic interactions and anisotropies determine the topology and magnetic structure.
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    Quantum Oscillations with Angular Dependence in PdTe2 Single Crystals
    (IOP, 2020-10-16) Chapai, Ramakanta; Browne, D. A.; Graf, David E.; DiTusa, J. F.; Jin, Rongying; Physics, School of Science
    The layered transition-metal dichalcogenide PdTe2 has been discovered to possess bulk Dirac points as well as topological surface states. By measuring the magnetization (up to 7 T) and magnetic torque (up to 35 T) in single crystalline PdTe2, we observe distinct de Haas-van Alphen (dHvA) oscillations. Eight frequencies are identified with H||c, with two low frequencies (Fα= 8 T and Fβ= 117 T) dominating the spectrum. The effective masses obtained by fitting the Lifshitz-Kosevich (LK) equation to the data are mα*=0.059m0 and mβ*=0.067m0 where m0 is the free electron mass. The corresponding Landau fan diagrams allow the determination of the Berry phase for these oscillations resulting in values of ∼0.67π for the 3D α band (hole-type) (down to the 1st Landau level) and ∼0.23π-0.73π for the 3D β band (electron-type) (down to the 3rd Landau level). By investigating the angular dependence of the dHvA oscillations, we find that the frequencies and the corresponding Berry phase (ΦB) vary with the field direction, with a ΦB∼ 0 when H is 10°-30° away from the a b plane for both α and β bands. The multiple band nature of PdTe2 is further confirmed from Hall effect measurements.