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Register a new userOrigin of the Large Anisotropy in the chi_3 Anomaly in URu_2Si_2
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Motivated by recent quantum oscillations experiments on URu_2Si_2, we discuss the microscopic origin of the large anisotropy observed many years ago in the anomaly of the nonlinear susceptibility in this same material. We show that the magnitude of this anomaly emerges naturally from hastatic order, a proposal for hidden order that is a two-component spinor arising from the hybridization of a non-Kramers Gamma_5 doublet with Kramers conduction electrons. A prediction is made for the angular anisotropy of the nonlinear susceptibility anomaly as a test of this proposed order parameter for URu_2Si_2.
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$alpha$-RuCl$_3$ is drawing much attention as a promising candidate Kitaev quantum spin liquid. However, despite intensive research efforts, controversy remains about the form of the basic interactions governing the physics of this material. Even the sign of the Kitaev interaction (the bond-dependent anisotropic interaction responsible for Kitaev physics) is still under debate, with conflicting results from theoretical and experimental studies. The significance of the symmetric off-diagonal exchange interaction (referred to as the $Gamma$ term) is another contentious question. Here, we present resonant elastic x-ray scattering data that provides unambiguous experimental constraints to the two leading terms in the magnetic interaction Hamiltonian. We show that the Kitaev interaction ($K$) is ferromagnetic, and that the $Gamma$ term is antiferromagnetic and comparable in size to the Kitaev interaction. Our findings also provide a natural explanation for the large anisotropy of the magnetic susceptibility in $alpha$-RuCl$_3$ as arising from the large $Gamma$ term. We therefore provide a crucial foundation for understanding the interactions underpinning the exotic magnetic behaviours observed in $alpha$-RuCl$_3$.
We develop a Landau Ginzburg theory of the hidden order phase and the local moment antiferromagnetic phase of URu_2Si_2. We unify the two broken symmetries in a common complex order parameter and derive many experimentally relevant consequences such as the topology of the phase diagram in magnetic field and pressure. The theory accounts for the appearance of a moment under application of stress and the thermal expansion anomaly across the phase transitions. It identifies the low energy mode which is seen in the hidden order phase near the conmensurate wavector (0,0, 1) as the pseudo-Goldstone mode of the approximate U(1) symmetry.
We have investigated the nature of the antiferromagnetic (AF) phase induced by uniaxial stress sigma in URu2Si2, by performing elastic neutron scattering measurements up to 0.4 GPa. We have found that the AF Bragg-peak intensity shows a clear hysteresis loop with sigma under the zero-stress cooling condition. The result strongly suggests that the sigma-induced AF phase is metastable and separated from the coexisting hidden ordered phase by a first-order phase transition. We also present the analyses of the crystalline strain effects, and suggest that the c/a ratio plays an important role in the competition between these two phases.
A dramatic temperature dependent enhancement of U 5f spectral weight at $E_F$ is observed in angle-resolved photoemission measurements of $URu_2Si_2$ at the center of an X-point hole-pocket. Comparison of this temperature dependent behavior for excitation both at and below the U $5d to 5f$ resonant threshold is presented.
We study low temperature properties in the metallic magnets, considering the itinerant electron mediated ferromagnetism. Applying the Monte Carlo simulations to the extended double exchange model, we discuss reorientation phase transition and anisotropy field for the metallic magnets.
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