Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session H5: CeMIn5 (115 ) Heavy Electron Materials: A Rosetta Stone for the Kondo Lattice? |
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Sponsoring Units: DCMP Chair: Zachary Fisk, University of California, Irvine Room: Morial Convention Center RO1 |
Tuesday, March 11, 2008 8:00AM - 8:36AM |
H5.00001: Angle-resolved Photoemission of CeCoIn$_5$: Detailed Comparison to LDA and LDA+DMFT Invited Speaker: Highly-automated photon-dependent angle resolved photoemission spectroscopy (ARPES) in the energy range of 80-200 eV has been used to characterize the three dimensional (3D) Fermi surface (FS) topology and electronic band structure of cleaved single crystals of CeCoIn$_5$. The sample temperature of $\approx26$K is well below the lattice coherence onset temperature of $\approx45$K found in a recent ``two fluid'' analysis of transport data. Detailed comparison of ARPES FS contours to LDA calculations for the Ce 4f electrons treated as itinerant or confined to the core reveals remarkable agreement to fine topological details of the f-core calculations. Also in agreement to the f-core calculations is the experimental absence of extra electron-like contours predicted in the f-itinerant calculation, originating from $\alpha$ and $\beta$ bands re-entrant below $E_F$ along Z-A. Finally, the areas enclosed by FS contours for the $\alpha$ and $\beta$ bands are significantly smaller than are found in very low temperature CeCoIn$_5$ de Haas van Alphen data that agrees generally with the f-itinerant calculation. It is concluded that clear signatures of coherence in the transport data can develop at temperatures for which the f-electrons are not yet included in the FS. In this connection, comparison will also be made to recent T-dependent LDA+DMFT calculations for CeIrIn$_5$. This work was done in collaboration with J. D. Denlinger, Feng Wang, R. S. Singh, K. Rossnagel, S. Elgazzar, P. M. Oppeneer, V. S. Zapf and M. B. Maple, and was supported by the U.S. DOE (DE-AC03-76SF00098 at the ALS, DE-FG02-07ER46379 at UM for current work, DE FG02-04ER-46105 at UCSD), by the U.S. NSF (DMR-03-02825 at UM for initial work, DMR-03-35173 at UCSD) and by the Swedish Research Council (VR) and the European Commission (JRC-ITU). [Preview Abstract] |
Tuesday, March 11, 2008 8:36AM - 9:12AM |
H5.00002: Modeling the Localized to Itinerant Electronic Transition in the Heavy Fermion System CeIrIn5 Invited Speaker: Within the ab-inition calculation we adress the crossover from localized to itinerant state of a heavy fermion material CeIrIn5. The temperature evolution of the one electron spectra and the optical conductivity is predicted from first principles. The buildup of coherence in the form of a dispersive many body feature is followed in detail and its effects on the conduction electrons of the material is revealed. We find multiple hybridization gaps and link them to the crystal structure of the material. Our theoretical approach explains the multiple peak structures observed in optical experiments and the sensitivity of CeIrIn5 to substitutions of the transition metal element and may provide a microscopic basis for the more phenomenological descriptions currently used to interpret experiments in heavy fermion systems. [Preview Abstract] |
Tuesday, March 11, 2008 9:12AM - 9:48AM |
H5.00003: Andreev reflection in heavy fermions and the superconducting order parameter in CeCoIn$_{5}$ Invited Speaker: Andreev reflection, a retro-reflection of an incoming electron as a hole at a normal-metal/superconductor interface, is well understood in conventional superconductors. For heavy-fermion superconductors, the microscopic consequences of the heavy electronic mass remain an open question. According to the Blonder-Tinkham-Klapwijk (BTK) theory, no Andreev process is allowed because of the large mismatch in the Fermi velocities [1]. However, conductance enhancement due to Andreev reflection, albeit reduced, has been frequently observed in heavy-fermion superconductors [2]. In this talk, I will present such conductance spectra obtained along three different crystallographic orientations of the heavy-fermion superconductor CeCoIn$_{5}$ [3]. Qualitative analysis using the extended BTK model shows the first spectroscopic evidence for $d_{\mbox{x}^2-\mbox{y}^2} $-wave (instead of $d_{xy}$-wave) symmetry, resolving the controversy over the node locations. In order to explain the reduced Andreev signal and the conductance asymmetry, both commonly observed in heavy-fermion superconductors, we propose a conductance model based on the two-fluid phenomenology [4] and an assumed energy-dependent density of states. I will discuss the significance of this model and possible clues for developing it into a microscopic theory. [1] G. E. Blonder, M. Tinkham, and T. M. Klapwijk, Phys. Rev. B \textbf{25}, 4515 (1982); G. E. Blonder and M. Tinkham, \textit{ibid}. \textbf{27}, 112 (1983). [2] Yu. G. Naidyuk and I. K. Yanson, J. Phys.: Condens. Matter \textbf{10}, 8905 (1998). [3] W. K. Park \textit{et al}., arXiv:0709.1246 (submitted to Phys. Rev. Lett.). [4] S. Nakatsuji, D. Pines, and Z. Fisk, Phys. Rev. Lett. \textbf{92}, 016401 (2004). This work is done in collaboration with L. H. Greene, H. Stalzer, J. L. Sarrao, J. D. Thompson, Z. Fisk, and P. Canfield. [Preview Abstract] |
Tuesday, March 11, 2008 9:48AM - 10:24AM |
H5.00004: Universal behavior in heavy electron materials Invited Speaker: I describe improvements in the phenomenological two-fluid theory that enable one to reconcile the thermal and magnetic measurements of the collective deconfinement of localized spins in Kondo lattice materials that begins at T* and leads to the formation of a new quantum state of matter - the heavy electron Kondo Liquid (KL). The resulting phenomenological KL density of states provides a good fit to the theoretical results for Ir 115 and its experimental measurement in Knight shift and Hall effect anomalies, tunneling experiments, and Raman scattering in the 115 materials. I discuss the relationship between T* and the single ion Kondo temperature and present an updated version of the Doniach diagram for heavy electron materials. [Preview Abstract] |
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