Physics and Astronomy

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Browsing Physics and Astronomy by Author "Abrahams, Elihu"

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    Electron Correlation and Spin Dynamics in Iron Pnictides and Chalcogenides
    (arXiv, 2012) Yu, Rong; Si, Qimiao; Goswami, Pallab; Abrahams, Elihu
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    Magnetic and Ising quantum phase transitions in a model for isoelectronically tuned iron pnictides
    (American Physical Society, 2016) Wu, Jianda; Si, Qimiao; Abrahams, Elihu
    Considerations of the observed bad-metal behavior in Fe-based superconductors led to an early proposal for quantum criticality induced by isoelectronic P for As doping in iron arsenides, which has since been experimentally confirmed. We study here an effective model for the isoelectronically tuned pnictides using a large-N approach. The model contains antiferromagnetic and Ising-nematic order parameters appropriate for J1−J2 exchange-coupled local moments on an Fe square lattice, and a damping caused by coupling to itinerant electrons. The zero-temperature magnetic and Ising transitions are concurrent and essentially continuous. The order-parameter jumps are very small, and are further reduced by the interplane coupling; consequently, quantum criticality occurs over a wide dynamical range. Our results reconcile recent seemingly contradictory experimental observations concerning the quantum phase transition in the P-doped iron arsenides.
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    Spin dynamics of a J1- J2-K model for the paramagnetic phase of iron pnictides
    (American Physical Society, 2012) Yu, Rong; Wang, Zhentao; Goswami, Pallab; Nevidomskyy, Andriy H.; Si, Qimiao; Abrahams, Elihu
    We study the finite-temperature spin dynamics of the paramagnetic phase of iron pnictides within an antiferromagnetic J1-J2 Heisenberg model on a square lattice with a biquadratic coupling −K(Si · Sj )2 between the nearest-neighbor spins. Our focus is on the paramagnetic phase in the parameter regime of this J1-J2-K model where the ground state is a (π,0) collinear antiferromagnet. We treat the biquadratic interaction via a Hubbard-Stratonovich decomposition and study the resulting effective quadratic-coupling model using both modified spin wave and Schwinger boson mean-field theories; the results for the spin dynamics derived from the two methods are very similar. We show that the spectral weight of dynamical structure factor S(q,ω) is peaked at ellipses in the momentum space at low excitation energies.With increasing energy, the elliptic features expand towards the zone boundary and gradually split into two parts, forming a pattern around (π,π). Finally, the spectral weight is anisotropic, being larger along the major axis of the ellipse than along its minor axis. These characteristics of the dynamical structure factor are consistent with the recent measurements of the inelastic neutron scattering spectra of BaFe2As2 and SrFe2As2.