Effects of In-Plane Impurity Substitution in Sr2RuO4

We report comparative substitution effects of nonmagnetic Ti^(4+) and magnetic Ir^(4+) impurities for Ru^(4+) in the spin-triplet superconductor Sr2RuO4. We found that both impurities suppress the superconductivity completely at a concentration of approximately 0.15%, reflecting the high sensitivity to translational symmetry breaking in Sr2RuO4. In addition, a rapid enhancement of residual resistivity is in quantitative agreement with unitarity-limit scattering. Our result suggests that both nonmagnetic and magnetic impurities in Sr2RuO4 act as strong potential scatterers, similar to the nonmagnetic Zn^(2+) impurity in the high-Tc cuprates.Comment: 4 pages, 2 figures. submitted to Journal of the Physical Society of Japa

Effect of Na doping on flux pinning of YBa1.9Na0.1Cu3O7-d

We have prepared Na-doped YBa2Cu3Oy (YBa1.9Na0.1Cu3Oy +40mol%Y211) (YBNCO) and Na-free YBa2Cu3Oy (YBCO) samples by the Melt-Textured Growth (MTG) method to study the effect of doped Na ion on flux pinning. The ac susceptibility curves (acs) as well as the hysteresis loops were measured for the samples. Then the effective pinning energy (U(T,Hdc,J)), irreversibility line (Hirr(T)) and critical current density (jc(Hdc)) were determined, where T, Hdc and J are temperature, dc magnetic field and current density, respectively. We found that, with Na doping, the Hirr(T) line shifted to lower temperature while the Jc(Hdc) and U(T,Hdc,J) became smaller. It indicates that the Na ions play a negative role in the flux pinning of YBCO. The appearance of the second peak in the Jc(Hdc) curves and the enhancement of anisotropy in YBNCO further support this finding.Comment: 7 pages, 7figures. Submited to Physica.

Effects of Uniaxial Stress on Antiferromagnetic Moment in the Heavy Electron Compound URu_2Si_2

We have performed the elastic neutron scattering experiments under uniaxial stress \sigma along the tetragonal [100], [110] and [001] directions for URu2Si2. For \sigma // [100] and [110], the antiferromagnetic moment \mu_o is strongly enhanced from 0.02 \mu_B (\sigma=0) to 0.22 \mu_B (\sigma=2.5 kbar) at 1.5 K. The rate of increase d\mu_o/d\sigma is roughly estimated to be ~ 0.1 \mu_B/kbar, which is much larger than that for the hydrostatic pressure (~ 0.025 \mu_B/kbar). Above 2.5 kbar, \mu_o shows a tendency to saturate similar to the behavior in the hydrostatic pressure. For \sigma // [001], on the other hand, \mu_o shows only a slight increase to 0.028 \mu_B (\sigma = 4.6 kbar) with a rate of ~ 0.002 \mu_B/kbar. The observed anisotropy suggests that the competition between the hidden order and the antiferromagnetic state in URu2Si2 is strongly coupled with the tetragonal four-fold symmetry and the c/a ratio, or both.Comment: 3 pages, 3 eps figures, Proceedings of Int. Conf. on Strongly Correlated Electrons with Orbital Degrees of Freedom (Sendai, Japan, September 11-14, 2001

Ferromagnetism in the Strong Hybridization Regime of the Periodic Anderson Model

We determine exactly the ground state of the one-dimensional periodic Anderson model (PAM) in the strong hybridization regime. In this regime, the low energy sector of the PAM maps into an effective Hamiltonian that has a ferromagnetic ground state for any electron density between half and three quarters filling. This rigorous result proves the existence of a new magnetic state that was excluded in the previous analysis of the mixed valence systems.Comment: Accepted in Phys. Rev.

Propagation inhibition and wave localization in a 2D random liquid medium

Acoustic propagation and scattering in water containing many parallel air-filled cylinders is studied. Two situations are considered and compared: (1) wave propagating through the array of cylinders, imitating a traditional experimental setup, and (2) wave transmitted from a source located inside the ensemble. We show that waves can be blocked from propagation by disorders in the first scenario, but the inhibition does not necessarily imply wave localization. Furthermore, the results reveal the phenomenon of wave localization in a range of frequencies.Comment: Typos in Fiures are correcte

Incoherent non-Fermi liquid scattering in a Kondo lattice

One of the most notorious non-Fermi liquid properties of both archetypal heavy-fermion systems [1-4] and the high-Tc copper oxide superconductors [5] is an electrical resistivity that evolves linearly with temperature, T. In the heavy-fermion superconductor CeCoIn5 [5], this linear behaviour was one of the first indications of the presence of a zero-temperature instability, or quantum critical point. Here, we report the observation of a unique control parameter of T-linear scattering in CeCoIn5, found through systematic chemical substitutions of both magnetic and non-magnetic rare-earth, R, ions into the Ce sub-lattice. We find that the evolution of inelastic scattering in Ce1-xRxCoIn5 is strongly dependent on the f-electron configuration of the R ion, whereas two other key properties -- Cooper-pair breaking and Kondo-lattice coherence -- are not. Thus, T-linear resistivity in CeCoIn5 is intimately related to the nature of incoherent scattering centers in the Kondo lattice, which provides insight into the anomalous scattering rate synonymous with quantum criticality [7].Comment: 4 pages, 3 figures (published version

Localization in a random phase-conjugating medium

We theoretically study reflection and transmission of light in a one-dimensional disordered phase-conjugating medium. Using an invariant imbedding approach a Fokker-Planck equation for the distribution of the probe light reflectance and expressions for the average probabilities of reflection and transmission are derived. A new crossover length scale for localization of light is found, which depends on the competition between phase conjugation and disorder. For weak disorder, our analytical results are in good agreement with numerical simulations.Comment: RevTex, 4 pages, 4 figure

Neutron Scattering Study on Competition between Hidden Order and Antiferromagnetism in U(Ru_{1-x}Rh_x)_2Si_2 (x <= 0.05)

We have performed elastic and inelastic neutron scattering experiments on the solid solutions U(Ru_{1-x}Rh_x)_2Si_2 for the Ru rich concentrations: x=0, 0.01, 0.02, 0.025, 0.03, 0.04 and 0.05. Hidden order is suppressed with increasing x, and correspondingly the onset temperature T_m (~ 17.5 K at x=0) of weak antiferromagnetic (AF) Bragg reflection decreases. For x=0.04 and 0.05, no magnetic order is detected in the investigated temperature range down to 1.4 K. In the middle range, 0.02 <= x <= 0.03, we found that the AF Bragg reflection is strongly enhanced. At x=0.02, this takes place at ~ 7.7 K (=T_M), which is significantly lower than T_m (~ 13.7 K). T_M increases with increasing x, and seems to merge with T_m at x=0.03. If the AF state is assumed to be homogeneous, the staggered moment \mu_o estimated at 1.4 K increases from 0.02(2) \mu_B/U (x=0) to 0.24(1) \mu_B/U (x=0.02). The behavior is similar to that observed under hydrostatic pressure (\mu_o increases to ~ 0.25 \mu_B/U at 1.0 GPa), suggesting that the AF evolution induced by Rh doping is due to an increase in the AF volume fraction. We also found that the magnetic excitation observed at Q=(1,0,0) below T_m disappears as T is lowered below T_M.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp

Anomalous Low Temperature Behavior of Superconducting Nd(1.85)Ce(0.15)CuO(4-y)

We have measured the temperature dependence of the in-plane London penetration depth lambda(T) and the maximum Josephson current Ic(T) using bicrystal grain boundary Josephson junctions of the electron-doped cuprate superconductor Nd(1.85)Ce(0.15)CuO(4-y). Both quantities reveal an anomalous temperature dependence below about 4 K. In contrast to the usual monotonous decrease (increase) of lambda(T) (Ic(T)) with decreasing temperature, lambda(T) and Ic(T) are found to increase and decrease, respectively, with decreasing temperature below 4 K resulting in a non-monotonous overall temperature dependence. This anomalous behavior was found to be absent in analogous measurements performed on Pr(1.85)Ce(0.15)CuO(4-y). From this we conclude that the anomalous behavior of Nd(1.85)Ce(0.15)CuO(4-y) is caused by the presence of the Nd3+ paramagnetic moments. Correcting the measured lambda(T) dependence of Nd(1.85)Ce(0.15)CuO(4-y) for the temperature dependent susceptibility due to the Nd moments, an exponential dependence is obtained indicating isotropic s-wave pairing. This result is fully consistent with the lambda(T) dependence measured for Pr(1.85)Ce(0.15)CuO(4-y).Comment: 4 pages including 4 figures, to appear in Phys. Rev. Let

Diffusive and localization behavior of electromagnetic waves in a two-dimensional random medium

In this paper, we discuss the transport phenomena of electromagnetic waves in a two-dimensional random system which is composed of arrays of electrical dipoles, following the model presented earlier by Erdogan, et al. (J. Opt. Soc. Am. B {\bf 10}, 391 (1993)). A set of self-consistent equations is presented, accounting for the multiple scattering in the system, and is then solved numerically. A strong localization regime is discovered in the frequency domain. The transport properties within, near the edge of and nearly outside the localization regime are investigated for different parameters such as filling factor and system size. The results show that within the localization regime, waves are trapped near the transmitting source. Meanwhile, the diffusive waves follow an intuitive but expected picture. That is, they increase with travelling path as more and more random scattering incurs, followed by a saturation, then start to decay exponentially when the travelling path is large enough, signifying the localization effect. For the cases that the frequencies are near the boundary of or outside the localization regime, the results of diffusive waves are compared with the diffusion approximation, showing less encouraging agreement as in other systems (Asatryan, et al., Phys. Rev. E {\bf 67}, 036605 (2003).)Comment: 8 pages 9 figure