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CeMIn[sub 5](M=Co,Ir,Rh) heavy fermion superconductors and the utility of high magnetic field.

Description: We review the properties of the recently discovered CeMIn5 (M=Co, Ir, Rh) heavy fermion superconductors and discuss the present state of our understanding of these materials. A particular focus is the role that magnetic fields have played in elucidating the properties of these materials. Specifically, we discuss quantum oscillation measurements on CeMIn5, the influence of applied field on the linear coefficient of specific heat, {gamma}, and the nature of the HT phase diagrams in both the normal and superconducting states of these materials.
Date: January 1, 2001
Creator: Sarrao, John L.,
Partner: UNT Libraries Government Documents Department

Temperature dependent 5f-states in URu2Si2

Description: A dramatic temperature dependent enhancement of U 5f spectral weight at EF is observed in angle-resolved photoemission measurements of URu{sub 2}Si{sub 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->5f resonant threshold is presented.
Date: November 1, 2001
Creator: Denlinger, Jonathan D.; Gweon, Gey-Hong; Allen, James W. & Sarrao, John L.
Partner: UNT Libraries Government Documents Department

Magnetotransport studies of cerium iridium indium (5) and cerium cobalt indium(5).

Description: Magnetotransport measurements have shed additional light on the behavior of CeRhIn5.[1] In an effort to more fully understand the systematic relationship between CeRhIns and the other members of the CeMIn5 (M = Co, Rh, Ir) series of heavy fermion superconductors we have extended our studies to CeCoIns and CeIrIn5 . To that end, we have investigated the magnetotransport in Ce-based heavy fermion superconductors CeIrIns and CeCoIn5 from 1 .4 - 300 K as a function of applied magnetic fields to 18 T utilizing the 20 T superconducting magnetic located at the Los Alamos campus of the National High Magnetic Field Laboratory. Our results indicate that the magnetoresistance in both materials is smaller than antiferromagnetic CeRhIns. In CeIrIn5, the sign of the magnetoresistance is dependent on the direction of applied magnetic field with the negative magnetoresistance corresponding to a single impurity-like regime extending down to lower temperature with the applied field along the c-axis than with the field applied along the basal plane . In CeCoIns, a similar behavior occurs in which a negative magnetoresistance is observed at higher temperatures for the field applied along the c-axis, but by 25 K the magnetoresistance is positive, independent of field direction . A negative magnetoresistance is recovered in the low temperature regime in which the superconductivity has been destroyed by an applied field.
Date: January 1, 2003
Creator: Christianson, A. D. (Andrew D.); Lacerda, A. H. (Alex H.); Pagliuso, P. J. (Pascoal J.); Sarrao, John L., & Kern, S.
Partner: UNT Libraries Government Documents Department

Spin dynamics of Li Doped La[sub 2]CuO[sub 4]with a disordered ground state

Description: Only 3% hole doping by Li is sufficient to suppress the long-range antiferromagnetic order in LazCu04. Spin dynamics in the disordered state was investigated by measuring the dynamic magnetic structure factor, S(q,w), as a function of temperature, using cold neutron spectroscopy, on La2Cuo.96Lio.0404a nd La{approx}Cuo.gLio.104s ingle crystals. The details of observed spin dynamics of the quantum disordered spin liquid were compared to the theoretical results of the nonlinear u model for a two dimensional Heisenberg antiferromagnet, which predicts a phase crossover upon cooling from a quantum critical regime of a quantum spin liquid to its quantum paramagnetic regime.
Date: January 1, 2002
Creator: Chen, Y.; Bao, W. (Wei); Sarrao, John L.,; Park, S.-H. L. (Park, S.-H. Lee) & Lorenzo, J. E.
Partner: UNT Libraries Government Documents Department

Crystal structure, superconductivity and magnetism of the quasi-2D heavy fermion materials CeTIn[sub 5] (T = Co, Rh, Ir).

Description: The crystal structure of the recently discovered heavy-fermion (HF) superconductor CeCoIn{sub 5} (T{sub c} = 2.3 K) has been determined by high-resolution neutron powder diffraction. It is tetragonal (space group P4/mmm), with lattice parameters a = 4.61292(9) {angstrom} and c = 7.5513(2) {angstrom} at ambient conditions. Whereas CeCoIn{sub 5} is isostructural with the HF aniferromagnet CeRhIn{sub 5} and the HF superconductor CeIrIn{sub 5}, its cell constants and its only variable positional parameter, zIn2, differ significantly from the corresponding ones of CeRhIn{sub 5} and CeIrIn{sub 5}. As a result, the distortions of the cuboctahedron [CeIn{sub 3}], which is the key structural unit in all three materials, are different in CeCoIn{sub 5} from the ones in CeRhIn{sub 5} and CeIrIn{sub 5}. The compounds CeCoIn{sub 5} and CeIrIn{sub 5}, which contain the most distorted (in one or another way) [CeIn{sub 3}] cuboctahedra exhibit superconductivity at ambient pressure below 2.3 K and 0.4 K, respectively. On the other hand, CeRhIn{sub 5}, in which [CeIn{sub 3}] cuboctahedra are the less distorted, and the cubic HF CeIn{sub 3} are antiferromagnets at ambient pressure with T{sub N} = 3.8 K and 10 K respectively; they become superconductors under pressure of 16 kbar and 25 kbar with T{sub c} = 2.1 and 0.2 K respectively.
Date: January 1, 2001
Creator: Sarrao, John L.,; Pagliuso, P. J. (Pascoal J.); Moreno, N. O.; Thompson, J. D. (Joe David); Fisk, Zachary & Moshopoulou, E. G.
Partner: UNT Libraries Government Documents Department

Absence of X-point band overlap in divalent hexaborides and variability of the surface chemical potential

Description: Angle-resolved photoemission measurements of divalent hexaborides reveals a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. While the global ARPES band structure and gap size observed are consistent with the results of bulk-sensitive soft x-ray absorption and emission boron K-edge spectroscopy, the surface-sensitive photoemission measurements also show a variation with cation, surface and time of the position of the surface chemical potential in the band structure.
Date: November 4, 2001
Creator: Denlinger, Jonathan D.; Gweon, Gey-Hong; Mo, Sung-Kwan; Allen, James W.; Sarrao, John L.; Bianchi, Adrian D. et al.
Partner: UNT Libraries Government Documents Department

Possibility of minimal surface contributions to low photon energy angle-resolved photoemission of CeRu{sub 2}Si{sub 2}

Description: Surface-related effects in angle-resolved valence spectra of CeRu{sub 2}Si{sub 2} at the Ce 4d {yields} 5f resonance threshold for different cleaved surfaces are presented and compared to angle-integrated valence spectra and to bulk-sensitive Ce 3d-edge valence spectra. Evidence that Ce 4d-edge photoemission spectroscopy on ideal cleaved surfaces is dominated by bulk Ce 4f states is presented.
Date: November 1, 2001
Creator: Denlinger, Jonathan D.; Gweon, Gey-Hong; Allen, James W. & Sarrao, John L.
Partner: UNT Libraries Government Documents Department

Bulk band gaps in divalent hexaborides

Description: Complementary angle-resolved photoemission and bulk-sensitive k-resolved resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. This semiconducting gap implies that carriers detected in transport measurements arise from defects, and the measured location of the bulk Fermi level at the bottom of the conduction band implicates boron vacancies as the origin of the excess electrons. The measured band structure and X-point gap in CaB6 additionally provide a stringent test case for proper inclusion of many-body effects in quasi-particle band calculations.
Date: August 1, 2002
Creator: Denlinger, Jonathan; Clack, Jules A.; Allen, James W.; Gweon, Gey-Hong; Poirier, Derek M.; Olson, Cliff G. et al.
Partner: UNT Libraries Government Documents Department

Local structure and site occupancy of Cd and Hg substitutions in CeTIn_5 (T=Co, Rh, Ir)

Description: The CeTIn_5 superconductors (T=Co, Rh, or Ir) have generated great interest due to their relatively high transition temperatures, non-Fermi liquid behavior, and their proximity to antiferromagnetic order and quantum critical points. In contrast to small changes with the T-species, electron doping in CeT(In_1-x M_x)_5 with $M$=Sn and hole doping with Cd or Hg have a dramatic effect on the electronic properties at very low concentrations. The present work reports local structure measurements usingthe extended x-ray absorption fine-structure (EXAFS) technique that address the substituent atom distribution as a function of T, M, and x, in the vicinity of the superconducting phase. Together with previous measurements for M=Sn, the proportion of the $M$ atom residing on the In(1) site, f_\textrm In(1), increases in the order M=Cd, Sn, and Hg, ranging from about 40\percent to 70percent, showing a strong preference for each of these substituents to occupy the In(1) site (random occupation = 20percent). In addition, f_In(1) ranges from 70percent to 100percent for M=Hg in the order T=Co,Rh, and Ir. These fractions track the changes in the atomic radii of the various species, and help explain the sharp dependence of $T_c$ on substituting into the In site. However, it is difficult to reconcile the small concentrations of M with the dramatic changes in the ground state in the hole-doped materials with only an impurity scattering model. These results therefore indicate that while such substitutions have interesting local atomic structures with important electronic and magnetic consequences, other local changes in the electronic and magnetic structure are equally important in determining the bulk properties of these materials.
Date: April 22, 2009
Creator: Booth, Corwin H.; Bauer, Eric. D.; Bianchi, Andrea D.; Ronning, Fillip; Thompson, Joe D.; Sarrao, John L. et al.
Partner: UNT Libraries Government Documents Department

Coexistence of antiferromagnetic order and superconductivity in CeRh[sub 1[minus]x]M[sub x]In[sub 5](M=Ir and Co)

Description: We report a systematic neutron diffraction study on the coexistence of long-range magnetic order and superconductivity in heavy fermion compounds CeRhl-,M,Ins (M=Ir,Co). In addition to the incommensurate antiferromagnetic component in pure CeRhIn5, new type of antiferromagnetic component is found to concur with appearance of superconductivity in the Ir and Co alloy series. There is no detectable effect of the superconducting transition on magnetic order parameters. We compare those results with similar studies we performed on CeRhIn:, under pressure. We also discuss possible theoretical scenarios.
Date: December 4, 2002
Creator: Llobet-Megias, A. (Anna); Christianson, A. D. (Andrew D.); Bao, W. (Wei); Gardner, J. S.; Pagliuso, P. J. (Pascoal J.); Moreno, N. O. et al.
Partner: UNT Libraries Government Documents Department

Discovery of plutonium-based superconductivity

Description: The discovery of superconductivity in single crystals of PuCoGa{sub 5} with transition temperature T{sub c}=18.5 K is discussed. The existing data lead to the speculation that the superconductivity in PuCoGa{sub 5} may be unconventional. In such a scenario the properties of PuCoGa{sub 5} would be intermediate between those of isostructural UCoGa{sub 5} and CeCoIn{sub 5}, more heavily studied f-electron materials.
Date: January 1, 2002
Creator: Sarrao, John L.,; Thompson, J. D. (Joe David); Moreno, N. O.; Morales, L. A. (Luis A.); Wastin, F. (Franck); Rebizant, J. et al.
Partner: UNT Libraries Government Documents Department

Superconductivity in PuCoGa5.

Description: When randomly oriented columnar defects (CDs) are added to Hg-1223 and Tl-2212 superconductors, their vortex state equilibrium magnetization Meq decreases substantially. Meq progressively deviates from the usual London ln(B) dependence and the curves become S-shaped. Vortex-defect interactions quantitatively account for this behavior.
Date: January 1, 2003
Creator: Thompson, J. D. (Joe David); Sarrao, John L.,; Morales, L. A. (Luis A.); Wastin, F. (Franck); Rebizant, J.; Boulet, P. et al.
Partner: UNT Libraries Government Documents Department