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Register a new userDetermination of the infrared complex magneto-conductivity tensor in itinerant ferromagnets from Faraday and Kerr measurements
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M.-H. Kim
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We present measurement and analysis techniques that allow the complete complex magneto-conductivity tensor to be determined from mid-infrared (11-1.6 micron; 100-800 meV) measurements of the complex Faraday (theta_F) and Kerr (theta_K) angles. Since this approach involves measurement of the geometry (orientation axis and ellipticity of the polarization) of transmitted and reflected light, no absolute transmittance or reflectance measurements are required. Thick film transmission and reflection equations are used to convert the complex theta_F and theta_K into the complex longitudinal conductivity sigma_xx and the complex transverse (Hall) conductivity sigma_xy. theta_F and theta_K are measured in a Ga_(1-x)Mn_xAs and SrRuO_3 films. The resulting sigma_xx is compared to the values obtained from conventional transmittance and reflectance measurements, as well as the results from Kramers-Kronig analysis of reflectance measurements on similar films.
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By studying the rotations of the polarization of light propagating in right and left handed films, with emphasis on the transmission (Faraday effect) and reflec- tions (Kerr effect) of light and through the use of complex values representing the rotations, it can be shown that the real portions of the complex angle of Faraday and Kerr rotations are odd functions with respect to the refractive index n and that the respective imaginary portions of the angles are an even function of n. Multiple reflections within the medium lead to the maximums of the real portions of Faraday and Kerr effects to not coincide with zero ellipticity. It will also be shown that in the thin film case with left handed materials there are large resonant enhancements of the reflected Kerr angle that could be obtained experimentally.
We measure the band structure of nickel along various high-symmetry lines of the bulk Brillouin zone with angle-resolved photoelectron spectroscopy. The Gutzwiller theory for a nine-band Hubbard model whose tight-binding parameters are obtained from non-magnetic density-functional theory resolves most of the long-standing discrepancies between experiment and theory on nickel. Thereby we support the view of itinerant ferromagnetism as induced by atomic correlations.
We investigate the unusual magnetic properties of nearly-critical, weakly-itinerant ferromagnets with general formula UTX, where T=Rh,Co and X=Ge,Si. As a unique feature about these systems, we show that changes in the V_{df} hybridization control their proximity to a ferromagnetic instability, and determine the evolution of: the ground state magnetization, M_0, the Curie Temperature, T_C, the density of states at the Fermi level, N(E_F), the T^2 resistivity coefficient, A, and the specific heat coefficient, gamma. The universal aspect of our findings comes from the dependence on only two parameters: the T_d bandwidth, W_d, and the distance between T_d and U_f band centers, C_{T_d}-C_{U_f}.
We propose an experiment to use the magneto-optical Faraday effect to probe the dynamic Hall conductivity of spin liquid candidates. Theory predicts that an external magnetic field will generate an internal gauge field. If the source of conductivity is in spinons with a Fermi surface, a finite Faraday rotation angle is expected. We predict the angle to scale as the square of the frequency rather than display the standard cyclotron resonance pattern. Furthermore, the Faraday effect should be able to distinguish the ground state of the spin liquid, as we predict no rotation for massless Dirac spinons. We give a semiquantitative estimate for the magnitude of the effect and find that it should be experimentally feasible to detect in both $kappa$-(ET)$_2$Cu$_2$(CN)$_3$ and, if the spinons form a Fermi surface, Herbertsmithite. We also comment on the magneto-optical Kerr effect and show that the imaginary part of the Kerr angle may be measurable.
Direct coupling between gapless bosons and a Fermi surface results in the destruction of Landau quasiparticles and a breakdown of Fermi liquid theory. Such a non-Fermi liquid phase arises in spin-orbit coupled ferromagnets with spontaneously broken continuous symmetries due to strong coupling between rotational Goldstone modes and itinerant electrons. These systems provide an experimentally accessible context for studying non-Fermi liquid physics. Possible examples include low-density Rashba coupled electron gases, which have a natural tendency towards spontaneous ferromagnetism, or topological insulator surface states with proximity-induced ferromagnetism. Crucially, unlike the related case of a spontaneous nematic distortion of the Fermi surface, for which the non-Fermi liquid regime is expected to be masked by a superconducting dome, we show that the non-Fermi liquid phase in spin-orbit coupled ferromagnets is stable.
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