Browsing by Author "Walker, H.C."

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    Anomalous Metamagnetism in the Low Carrier Density Kondo Lattice YbRh3Si7
    (American Physical Society, 2018) Rai, Binod K.; Chikara, S.; Ding, Xiaxin; Oswald, Iain W.H.; Schönemann, R.; Loganathan, V.; Hallas, A.M.; Cao, H.B.; Stavinoha, Macy; Chen, T.; Man, Haoran; Carr, Scott; Singleton, John; Zapf, Vivien; Benavides, Katherine A.; Chan, Julia Y.; Zhang, Q.R.; Rhodes, D.; Chiu, Y.C.; Balicas, Luis; Aczel, A.A.; Huang, Q.; Lynn, Jeffrey W.; Gaudet, J.; Sokolov, D.A.; Walker, H.C.; Adroja, D.T.; Dai, Pengcheng; Nevidomskyy, Andriy H.; Huang, C.-L.; Morosan, E.
    We report complex metamagnetic transitions in single crystals of the new low carrier Kondo antiferromagnet YbRh3Si7. Electrical transport, magnetization, and specific heat measurements reveal antiferromagnetic order at TN=7.5 K. Neutron diffraction measurements show that the magnetic ground state of YbRh3Si7 is a collinear antiferromagnet, where the moments are aligned in the ab plane. With such an ordered state, no metamagnetic transitions are expected when a magnetic field is applied along the c axis. It is therefore surprising that high-field magnetization, torque, and resistivity measurements with H∥c reveal two metamagnetic transitions at μ0H1=6.7 T and μ0H2=21 T. When the field is tilted away from the c axis, towards the ab plane, both metamagnetic transitions are shifted to higher fields. The first metamagnetic transition leads to an abrupt increase in the electrical resistivity, while the second transition is accompanied by a dramatic reduction in the electrical resistivity. Thus, the magnetic and electronic degrees of freedom in YbRh3Si7 are strongly coupled. We discuss the origin of the anomalous metamagnetism and conclude that it is related to competition between crystal electric-field anisotropy and anisotropic exchange interactions.
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    Spin Waves in Detwinned BaFe2As2
    (American Physical Society, 2018) Lu, Xingye; Scherer, Daniel D.; Tam, David W.; Zhang, Wenliang; Zhang, Rui; Luo, Huiqian; Harriger, Leland W.; Walker, H.C.; Adroja, D.T.; Andersen, Brian M.; Dai, Pengcheng
    Understanding magnetic interactions in the parent compounds of high-temperature superconductors forms the basis for determining their role for the mechanism of superconductivity. For parent compounds of iron pnictide superconductors such as AFe_{2}As_{2} (A=Ba, Ca, Sr), although spin excitations have been mapped out throughout the entire Brillouin zone, the respective measurements were carried out on twinned samples and did not allow for a conclusive determination of the spin dynamics. Here we use inelastic neutron scattering to completely map out spin excitations of ∼100% detwinned BaFe_{2}As_{2}. By comparing observed spectra with theoretical calculations, we conclude that the spin excitations can be well described by an itinerant model when taking into account moderate electronic correlation effects.
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    Weaker nematic phase connected to the first order antiferromagnetic phase transition inﾠSrFe2As2ﾠcompared toﾠBaFe2As2
    (American Physical Society, 2019) Tam, David W.; Wang, Weiyi; Zhang, Li; Song, Yu; Zhang, Rui; Carr, Scott V.; Walker, H.C.; Perring, Toby G.; Adroja, D.T.; Dai, Pengcheng
    Understanding the nature of the electronic nematic phase in iron pnictide superconductors is important for elucidating its impact on high-temperature superconductivity. Here we use transport and inelastic neutron scattering to study spin excitations and in-plane resistivity anisotropy in uniaxial pressure detwinned BaFe2As2 and SrFe2As2, the parent compounds of iron pnictide superconductors. While BaFe2As2 exhibits weakly first-order tetragonal-to-orthorhombic structural and antiferromagnetic (AF) phase transitions below Ts>TN≈138K, SrFe2As2 has strongly coupled first-order structural and AF transitions below Ts=TN≈210K. We find that the direct signatures of the nematic phase persist to lower temperatures above the phase transition in the case of SrFe2As2 compared to BaFe2As2. Our findings support the conclusion that the strongly first-order nature of the magnetic transition in SrFe2As2 weakens the nematic phase and resistivity anisotropy in the system.