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Register a new userNon-Fermi liquid behavior and scaling of low frequency suppression in optical conductivity spectra of CaRuO$_3$
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Optical conductivity spectra $sigma_1(omega)$ of paramagnetic CaRuO$_3$ are investigated at various temperatures. At T=10 K, it shows a non-Fermi liquid behavior of $sigma_1(omega)sim 1/{omega}^{frac 12}$, similar to the case of a ferromagnet SrRuO$_3$. As the temperature ($T$) is increased, on the other hand, $sigma_1(omega)$ in the low frequency region is progressively suppressed, deviating from the $1/{omega}^{frac 12%}$-dependence. Interestingly, the suppression of $sigma_1(omega)$ is found to scale with $omega /T$ at all temperatures. The origin of the $% omega /T$ scaling behavior coupled with the non-Fermi liquid behavior is discussed.
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The reflectivity of the itinerant ferromagnet SrRuO_3 has been measured between 50 and 25,000 cm-1 at temperatures ranging from 40 to 300 K, and used to obtain conductivity, scattering rate, and effective mass as a function of frequency and temperature. We find that at low temperatures the conductivity falls unusually slowly as a function of frequency (proportional to omega^{-1/2}), and at high temperatures it even appears to increase as a function of frequency in the far-infrared limit. The data suggest that the charge dynamics of SrRuO_3 are substantially different from those of Fermi-liquid metals.
Infrared reflectivity measurements on 122 iron-pnictides reveal the existence of two electronic subsystems. The one gapped due to the spin-density-wave transition in the parent materials, such as EuFe$_2$As$_{2}$, is responsible for superconductivity in the doped compounds, like Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$. Analyzing the dc resistivity and scattering rate of this contribution, a hidden $T^2$ dependence is found, indicating that superconductivity evolves out of a Fermi-liquid state. The second subsystem gives rise to incoherent background, present in all 122 compounds, which is basically temperature independent, but affected by the superconducting transition.
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We report measurements of the bulk magnetic susceptibility and ^{29}Si nuclear magnetic resonance (NMR) linewidth in the heavy-fermion alloy CeRhRuSi_2. The linewidth increases rapidly with decreasing temperature and reaches large values at low temperatures, which strongly suggests the wide distributions of local susceptibilities chi_j obtained in disorder-driven theories of non-Fermi-liquid (NFL) behavior. The NMR linewidths agree well with distribution functions P(chi) which fit bulk susceptibility and specific heat data. The apparent return to Fermi-liquid behavior observed below 1 K is manifested in the vanishing of P(chi) as chi to infty, suggesting the absence of strong magnetic response at low energies. Our results indicate the need for an extension of some current theories of disorder-driven NFL behavior in order to incorporate this low-temperature crossover.
The electronic state and transport properties of hot dense iron are of the utmost importance to geophysics. Combining the density functional and dynamical mean field theories we study the impact of electron correlations on electrical and thermal resistivity of hexagonal close-packed $epsilon$-Fe at Earths core conditions. $epsilon$-Fe is found to behave as a nearly perfect Fermi liquid. The quadratic dependence of the scattering rate in Fermi liquids leads to a modification of the Wiedemann-Franz law with suppression of the thermal conductivity as compared to the electrical one. This significantly increases the electron-electron thermal resistivity which is found to be of comparable magnitude to the electron-phonon one. The implications of this effect on the dynamics of Earths core is discussed.
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