We studied the impurity scattering on the Ϯs-wave superconductor ͑SC͒, with realistic parameters for the Fe pnictide SCs. Using the T-matrix method, generalized for the two bands, we found that the strong scattering limit of impurities forms an off-centered resonance state inside the superconducting ͑SC͒ gap, which modifies, surprisingly, the density of states ͑DOS͒ of a fully opened gap to a V-shaped DOS as if in the case of a d-wave SC. This behavior provides coherent explanations to the several conflicting experiments of the Fe-based SC: ͑1͒ the V-shaped DOS observed in photoemission and tunneling spectroscopy but with an isotropic gap; ͑2͒ the power-law behavior of the nuclear-spin-lattice relaxation rate ͑1 / T 1 ϳ T ␣ with ␣ ϳ 3͒ down to very low temperatures. We also extended the same T-matrix method to study the impurity suppression of the critical temperature T c of the Ϯs-wave pairing state. We found that both magnetic and nonmagnetic impurities suppress T c with a rate that is practically indistinguishable from the standard d-wave case despite a possibly large difference of the positive and the negative s-wave order parameter magnitudes.

We consider the minimal two-band model for the Fe-based superconductors with a phenomenological pairing interaction which mimics short-range antiferromagnetic (AFM) fluctuations. Two superconducting (SC) gap solutions are found to exist with the model: sign-changing s-wave gap ($\pm$s-wave) and double d-wave gap states. Both solutions hold the approximate relation $\Delta_{h} ^{max} N_h \approx \Delta_{e} ^{max} N_e$, a generic feature of two band model with a dominant interband pairing interaction. We carried out the calculations of the SC properties of the both SC states such as the density of states, temperature dependencies of spin-lattice relaxation rate $1/T_1$, Knight shift, and penetration depth, particularly taking into account of the interband coherence factors. The results are discussed in comparison with the currently available experimental data.Comment: Published version in Phys. Rev. B 78, 134523 (2008

We have measured the bulk properties as well as the elastic and inelastic neutron scattering of YMnO 3 in order to understand the static and dynamic properties of the Mn moments. Our measurements clearly show that above T N there are short range correlations between spins at the nearest neighbor and next nearest neighbor Mn sites, which also fluctuate in time. This, together with other bulk properties, demonstrates the presence of a spin liquid phase above T N arising from the geometrically frustrated Mn moments. Below T N , a well-defined spin wave develops and we can understand the experimentally measured spin wave spectrum in terms of a Heisenberg Hamiltonian with a small easy plane anisotropy. However, even in the ordered phase we have found evidence of short range spin correlations.

We interpret the giant infrared resonances observed in A6C60 (A K, Rb) by Fu etal. as being due to a classic charged-phonon effect in which the Ti"molecular vibration modes of C60 acquire electronic oscillator strength via coupling to virtual t I" t I"electronic transitions. For the compounds 8 C60 (x =3, 4, and 6), we predict, for weak electron-molecular-vibration coupling, that the softenings of the Ti"modes are proportional to x, but that the integrated oscillator strengths of their absorption bands are proportional to the square of x. Fu eral. ' have recently measured the infrared (IR) spectrum of AsCso (A =K, Rb) and find that several of the T~" infrared-active modes that appear in the spectrum of undoped crystalline C6o have acquired in the fully doped material anomalously large oscillator strengths and undergone softening.The oscillator strength enhancement of two of the modes is of order 10 . In this paper, we interpret these enhancements as being due to a classic charged-phonon effect in which the T~"vibrational modes of molecular C6o acquire electronic oscillator strength via coupling to virtual electronic transitions between the C60 t~"and t~g molecular orbitals. For weak electron-molecular-vibration (EMV) coupling, the theory we introduce to describe this effect predicts for the compounds A"Csp (x 3, 4, and 6) that the softening of the T~"modes is proportional to x, but that the integrated oscillator strength of their absorption bands is proportional to the square of x. The values of the dimensionless EMV coupling constants 0 ") which we are able to tentatively deduce from the data of Fu eral. are indicative of weak individual EMV coupling (A, "-0. 02) but fairly strong total EMV coupling. In fact, we deduce that the static electronic polarizability of C6O contributed by t~" t~g transitions is enhanced by a factor of 1.67 due to EMV coupling. We stress that the charged-phonon effect promises to be a means of yielding key experimental data for testing theoretical calculations of the electronic and vibrational structure of ionic C60, as well as providing a monitor of the charge state of the Cso molecule in doped fullerenes.The charged-phonon effect, or the borrowing of electronic oscillator strength by a vibrational mode from an electronic transition to which the mode has become coupled, is well known in physical chemistry.It is more spectacularly known in the physics of low-dimensional solids, where the conditions required to produce the coupling often arise from symmetry-breaking effects. ' In discussing its theory for the A C60 compounds we will introduce, in the present paper, four simplifying assumptions. First, we take the widths of the electronic bands in A"C60 to be zero so that we may work entirely within a molecular picture. In this limit x electrons occupy the threefold degenerate ti"molecular orbitals of each C60 ion, while the higher-lying t tg orbitals remain empty in the ground-state configuration. Electron-energy-loss spectroscopy studies of Sohrnen, Fink, and Kratschmer indicate that t...

PNI is an independent prognostic factor for predicting survival after nephrectomy in patients with RCC.

The extracted pairing interactions responsible for high-temperature superconductivity lead to a clear discrimination among theories.

Optical conductivity spectra σ1(ω) of paramagnetic CaRuO3 are investigated at various temperatures. At T = 10 K, it shows a non-Fermi liquid behavior of σ1(ω) ∼ 1/ω 1 2 , similar to the case of a ferromagnet SrRuO3. As the temperature (T ) is increased, on the other hand, σ1(ω) in the low frequency region is progressively suppressed, deviating from the 1/ω 1 2 -dependence. Interestingly, the suppression of σ1(ω) is found to scale with ω/T at all temperatures. The origin of the ω/T scaling behavior coupled with the non-Fermi liquid behavior is discussed.

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