Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session J38: Heavy Fermions II: Ce-based 115 and 122 Systems |
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Sponsoring Units: DCMP Chair: Johnpierre Paglione, University of Maryland Room: F149 |
Tuesday, March 16, 2010 11:15AM - 11:27AM |
J38.00001: Change in anisotropic scattering by quantum fluctuations in CeCoIn$_5$ under pressure Hanoh Lee, Eunsung Park, Tuson Park, E.D. Bauer, J.D. Thompson A recent study of CeRhIn$_{5}$ under pressure showed that electronic scattering is most isotropic near its local quantum critical point (QCP) and becomes more anisotropic as pressure tunes it away from the QCP.\footnote{T. Park, et al., \textit{Nature} \textbf{456}, 366 (2008).} We have measured the a- and c-axis resistivity of CeCoIn$_{5}$ at pressures up to 1.7 GPa to determine evolution of the anisotropy in this quantum critical metal. The effective mass and scattering rate, deduced from the slope of the upper critical field and resistivity, decrease with increasing pressure, indicating that the system moves away from its QCP as pressure increases. Temperature dependence of the anisotropy is almost constant down to 14 K (=T$_{0})$ at ambient pressure, but applied pressure shifts the deviation temperature T$_{0}$ to a higher temperature, which is consistent with the presence of a QCP near ambient pressure. Analysis of these data and a comparison with CeRhIn$_{5}$ will be presented to discuss nature of the quantum critical fluctuations in this compound. [Preview Abstract] |
Tuesday, March 16, 2010 11:27AM - 11:39AM |
J38.00002: High-Pressure Electrical and Structural Characterization of CeCoIn$_5$ Nathaniel Brady, Georgiy Tsoi, Tesfaye Gebre, Eric Palm, Stanley Tozer, Timothy Murphy, Yogesh Vohra, David Hilton We have performed both electrical and structural characterizations of the heavy fermion, CeCoIn$_5$, in a \emph{high-pressure} designer diamond anvil cell (0 to 60 GPa). First, we performed four-point probe measurements of the electrical resistivity as a function of temperature (10 K to 300 K) over this pressure range. We observe a resistance peak (Kondo) that shifts to higher temperatures as pressure is increased from 0 to ~5.4 GPa. Above 5.4 GPa, we observe no peak resistance between 10 K and 300 K. Additionally, we have performed an x-ray diffraction measurement in a diamond anvil cell at 300 K and have observed a novel structural phase transition at 15 GPa. In this talk, we will discuss the origins of the electrical resistivity of CeCoIn$_5$ and its relation to this structural phase transition. [Preview Abstract] |
Tuesday, March 16, 2010 11:39AM - 11:51AM |
J38.00003: Superconductivity and non-Fermi-liquid behavior in Ce$_{1-x}$Yb$_{x}$CoIn$_{5}$ L. Shu, E. Gonzales, K. Huang, T.A. Sayles, R.E. Baumbach, J.J. Hamlin, D.A. Zocco, C.A. McElroy, M.B. Maple, J. Paglione, J. O'Brien, P.-C. Ho Single-crystals of Ce$_{1-x}$Yb$_{x}$CoIn$_{5}$ were investigated by specific heat $C_{\rm P}(T)$, electrical resistivity $\rho(T)$, and magnetic susceptibility $\chi(T)$ measurements as a function of $x$. As Yb is substituted for Ce, $T_{c}(x)$ is gradually suppressed to 0.9 K at $x=0.8$. In the low Yb concentration region near $x = 0.1$, there is a feature in the lattice constants and residual resistivity, a crossover in the anisotropy of $\chi(T)$, the development of NFL $T$-dependences of $\chi(T)$ and $C_{\rm P} (T)$ in the normal state,indicating the existence of a quantum critical point, and a plateau in $T_c(x)$. In the high Yb concentration region near $x=0.8$, there is an abrupt drop in the lattice parameters that is accompanied by a precipitous drop in $T_c(x)$. The features in the physical properties at $x=0.1$ and $0.8$ indicate the occurrence of some incipient electronic phase transitions, possibly involving the Ce and Yb valences at these compositions. [Preview Abstract] |
Tuesday, March 16, 2010 11:51AM - 12:03PM |
J38.00004: Physics of diluted dense Kondo lattices Zachary Fisk, Cigdem Capan, Daniel Hurt, Eric Bauer, Yi-feng Yang, Joe Thompson, Andrea Bianchi, Nicholas apRoberts-Warren, Nicholas Curro, Adam Dioguardi, David Pines, Abby Shockley A thermodynamic analysis of the specific heat of superconducting Ce$_{1-x}$La$_{x}$CoIn$_{5}$ and related materials suggests that the superconducting fraction in the alloys is proportional to 1-x. This gives the picture of holes in the dense Kondo metallic state surrounding the La sites, a picture which is consistent with other aspects of the physics of these doped systems. [Preview Abstract] |
Tuesday, March 16, 2010 12:03PM - 12:15PM |
J38.00005: Field dependence of antiferromagnetic spin fluctuations in the heavy fermion superconductor CeCoIn$_5$ S. E. Brown, H. Sakai, S.-H. Baek, F. Ronning, E. D. Bauer, J. D. Thompson Magnetic fields are proposed as a tuning parameter for quantum
critical fluctuations in the heavy fermion superconductor
CeCoIn$_5$, with a critical point close to the superconducting
$B_{c2}$. Here, $^{59}$Co NMR spin lattice relaxation is used to
study the effect of magnetic field applied on the amplitude,
dimensionality, and anisotropy of antiferromagnetic spin
fluctuations for temperatures covering $T$=100mK-100K and $B=$5-10T
($\parallel {\mathbf c}$). Spin fluctuations are evident for
temperatures below $T\sim40$K, below which $[T_1T]^{-1}$ increases
markedly for all fields. At lower temperatures, a significant
dependence on magnetic field is observed. For fields $B>B_{c2}=$5T,
$[T_1T]^{-1}\to$constant for $T |
Tuesday, March 16, 2010 12:15PM - 12:27PM |
J38.00006: Towards a solution for the puzzle of the high-field, low-temperature phase in CeCoIn$_5$: An NMR investigation Georgios Koutroulakis, Michael D. Stewart Jr., Vesna F. Mitrovic, Mladen Horvatic, Claude Berthier, Gerard Lapertot, Jacques Flouquet The unravelling of long range magnetic order within the superconducting phase of CeCoIn$_5$, limited in a narrow region of the phase diagram near $H_{c_2}$, has opened a new window for the understanding of the interplay between magnetic and superconducting orders. Nevertheless, essential questions regarding the exact nature of the magnetic structure and the superconducting order parameter, as well as the driving mechanisms of their coexistence, remain unanswered. In this talk, we attempt to shed some light on these puzzles by analyzing the results of our detailed high-field, low-temperature Nuclear Magnetic Resonance study. [Preview Abstract] |
Tuesday, March 16, 2010 12:27PM - 12:39PM |
J38.00007: Knight Shift Probe of Onset of Coherence in Heavy Electron Superconductor CeIrIn5 Abigail Shockley, Nicholas Curro, Adam Dioguardi, Nicholas apRoberts-Warren, Peter Klavins The CeMIn$_{5}$ compounds, where M = Co, Ir, Rh, are a novel class of superconductors discovered about 10 years ago. The 115 compounds are Kondo lattice materials: the compound's conduction electrons are coupled to an ordered lattice of local moments through the Kondo effect. These materials have a large effective electronic mass at low temperatures. We present new NMR Knight shift data in single crystals of CeIrIn5 between 2K and 120K. We find that the Knight shift of the In(1) site in this material is proportional to the bulk magnetic susceptibility above a temperature T* $\sim $ 30$^{\circ}$K. Below this temperature, the Knight shift fails to track the susceptibility. We interpret these results in terms of the two-fluid model, in which the susceptibility of the heavy electron component, chi{\_}cf, grows in intensity with decreasing temperature. We find that K{\_}cf $\sim $ chi{\_}cf $\sim $ log(T/T*), in agreement with other heavy fermion compounds. Our results confirm the predictions of the dynamical mean field theory calculations of Haule et al. for the onset of coherence in this compound. [Preview Abstract] |
Tuesday, March 16, 2010 12:39PM - 12:51PM |
J38.00008: Magnetic excitations in heavy fermion materials: Superconductivity and hidden magnetic quantum critical fluctuations Yi-feng Yang, Ricardo Urbano, Nicholas Curro, David Pines, Eric Bauer We report Knight shift experiments on the superconducting heavy electron material CeCoIn$_5$ that allow one to track with some precision the behavior of the heavy electron Kondo liquid in the superconducting state with results in agreement with BCS theory. An analysis of the $^{115}$In nuclear quadrupole resonance spin-lattice relaxation rate $T_1^{-1}$ measurements under pressure reveals the presence of $2d$ magnetic quantum critical fluctuations in the heavy electron component that are a promising candidate for the pairing mechanism in this material. Our results are consistent with an antiferromagnetic quantum critical point located at slightly negative pressure in CeCoIn$_5$ and provide additional evidence for significant similarities between the heavy electron materials and the high $T_c$ cuprates. [Preview Abstract] |
Tuesday, March 16, 2010 12:51PM - 1:03PM |
J38.00009: Point-contact Spectroscopy in Heavy-Fermion Superconductors Mikael Fogelstrom, Matthias J. Graf We present a minimal theoretical model for tunneling into heavy-fermion materials. In particular, we apply this model to point-contact spectroscopy (PCS) on CeCoIn5. The model assumes that electrons from a normal-metal tip tunnel into a heavy-fermion material via two interfereing channels: i) directly into conduction band(s), and ii) indirectly via localized f-electron levels. The model naturally reproduces the asymmetric Fano-shaped normal-state tunneling conductance seen in several PCS experiments. Additionally, in the superconducting state (CeCoIn5 with Tc=2.3K) we compute the PCS conductance. Here, we find that we can reproduce the experimentally obtained dI/dV-spectra accounting for an Andreev signal, i.e. the enhanced sub-gap conductance. Our theory is fully consistent with the typical $\sim$10\% increase with respect to the normal state conductance. Unlike other theories we don't require renormalization of Fermi velocities or scattering potentials at the NS interface to account for the strongly suppressed Andreev reflection in heavy-fermion materials. Finally, in the superconducting state we compare our results with those of the conventional BTK theory and extract information about the pairing symmetry for CeCoIn5. [Preview Abstract] |
Tuesday, March 16, 2010 1:03PM - 1:15PM |
J38.00010: Epitaxial thin films of heavy-Fermion superconductor CeCoIn$_5$ T. Shibauchi, H. Shishido, K. Yasu, Y. Mizukami, T. Terashima, Y. Matsuda Experimental studies of heavy-Fermion superconductors have been mainly concentrated in measurements using bulk crystals so far. Thin film fabrication process is a key to open new approaches to study fundamental physics, such as phase-sensitive measurements of order parameter using Josephson junctions, and controlling dimensionality of heavy Fermions by superlattices. Despite several attempts using different techniques and various substrates [1-3], epitaxial growth of Ce-based heavy-Fermion superconductors has been a challenging issue. Here we report on the first successful growth of epitaxial thin films of heavy-Fermion superconductor CeCoIn$_5$. By the combination of a ultra-high vacuum deposition technique using molecular beam epitaxy and the choice of proper substrate material with very good lattice matching with CeCoIn$_5$, we are able to fabricate epitaxial films whose transport properties reproduce the characteristic features of the bulk CeCoIn$_5$, including a sharp superconducting transition at 2.3 K. [1] O.\,K. Soroka {\it et al.}, J.\,Phys.: Condens.\,Matter {\bf 19}, 056006 (2007). [2] M. Izaki {\it et al.}, Appl. Phys. Lett. {\bf 91}, 122507 (2007). [3] A.\,G. Zaitsev {\it et al.}, Physica C {\bf 469}, 52 (2009). [Preview Abstract] |
Tuesday, March 16, 2010 1:15PM - 1:27PM |
J38.00011: Electronic structure of the heavy-fermion superconductor PuCoGa$_{5}$ probed via the dynamics of photoinduced quasiparticles. Diyar Talbayev, K.S. Burch, E.E.M. Chia, S.A. Trugman, J.-X. Zhu, E.D. Bauer, J.A. Kennison, J.N. Mitchell, J.D. Thompson, J.L. Sarrao, A.J. Taylor We studied the relaxation of photoinduced quasiparticles in the heavy-fermion superconductor PuCoGa$_{5}$ using pump-probe spectroscopy. The relaxation time of photoinduced reflectance in the normal state allows an estimate of the electron-phonon coupling constant $\lambda $ =0.20-0.26, which is incompatible with the measured T$_{c}$ and speaks against phonon-mediated superconducting pairing. Upon lowering the temperature in the normal state (T$>$T$_{c})$, we find an order-of-magnitude increase of the relaxation time -- evidence for the presence of a hybridization gap in the electronic density of states. The relaxation slows down due to a coupling of quasiparticle population to a slowly decaying non-equilibrium high-frequency phonon population. A kinetic model that describes the coupled quasiparticle and phonon populations allows the estimate of the hybridization gap magnitude to be $\sim $90 K. Our measurement provides the first evidence for the presence of a hybridization gap in PuCoGa$_{5}$. The observed dynamics in the superconducting state confirms that the heavy quasiparticles detected in the normal state also participate in the superconducting pairing. [Preview Abstract] |
Tuesday, March 16, 2010 1:27PM - 1:39PM |
J38.00012: CeM2Si2 (M=Cu, Ru, Rh, Pd, and Au,): a spectroscopic investigation of the crystal-field schemes applying polarized soft XAS and neutron scattering. Andrea Severing, Devashibhai Adroja, Thomas Willers, Zhiwei Hu, Liu Hao Tjeng We have investigated the crystal field schemes of the CeM2Si2 series (M=Cu, Ru, Rh, Pd and Au) with linear polarized soft x-ray absorption spectroscopy (XAS) and inelastic neutron scattering. Within the series the ground states are antiferromagnetic, itinterant and/or superconducting at ambient or applied pressure. Soft-XAS at the Ce M4,5 edges can be used as a complementary technique to neutron scattering: while inelastic neutron scattering gives the crystal-field transition energies, the polarization dependence of XAS reflects the symmetry of the initial state and gives therefore direct information about the Jz admixtures of the ground state wave function. Crystal-field investigations of rare earth with XAS are not limited by energy resolution in contrast to what had been perceived in the past. This way we can provide spectroscopic information of the crystal-field schemes even in the presence of strong correlations. [Preview Abstract] |
Tuesday, March 16, 2010 1:39PM - 1:51PM |
J38.00013: Neutron study of crystal field excitations in single crystal CeCu$_{2}$Ge$_{2}$ Michael Loewenhaupt, Enrico Faulhaber, Astrid Schneidewind, Micha Deppe, Klaudia Hradil CeCu$_{2}$Ge$_{2}$ is the counterpart of the heavy-fermion superconductor CeCu$_{2}$Si$_{2}$. CeCu$_{2}$Ge$_{2}$ is a magnetically ordering (T$_{N}$= 4.1 K) Kondo lattice with a moderate Sommerfeld coefficient of 140 mJ/molK$^{2}$ [1]. Inelastic neutron measurements on a polycrystalline sample revealed a doublet ground state and a quasi-quartet at 16.5 meV [1] though a splitting of the 4f$^{1}$ (J=5/2) ground state multiplet into 3 doublets is expected from the point symmetry of the Ce$^{3+}$ ions. We performed detailed inelastic neutron scattering experiments on the thermal triple-axis spectrometer PUMA at FRM II at temperatures between 10 K and 300 K and for different crystallographic directions from low to high momentum transfers. In this way we obtained a reliable separation of magnetic and phonon contributions. From our results we infer that the quasi-quartet consists in fact of two doublets at 17 and 18 meV which exhibit a strong directional dependence of their transition matrix elements to the ground state doublet. Finally we will present a new set of crystal field parameters and their implications on other magnetic properties. [1] G. Knopp et al., Z. Physik B 77 (1989) 95 [Preview Abstract] |
Tuesday, March 16, 2010 1:51PM - 2:03PM |
J38.00014: Observation of Magnetic Field-Tuned Quantum Phase Transition in Intermetallic CeAg$_{2}$Ge$_{2}$ Deepak Singh, Arumugam Thamizhavel, Sung Chang, Jeffrey Lynn Quantum phase transition arises either due to the competition between Kondo screening and long range RKKY-type interaction or, the spin density wave (SDW) instability of the Fermi surface at the quantum critical point. We have performed neutron scattering measurements on single crystal CeAg2Ge2 and observed the SDW-type quantum phase transition with magnetic field as tuning parameter. CeAg2Ge2 crystallizes in a ThCr2Si2-type tetragonal crystal structure and undergoes an antiferromagnetic transition at TN = 4.6 K. Detail measurements of Q-vectors associated with long-range order and the numerical modeling of the data revealed the propagation of amplitude modulated spin density wave in this compound. With magnetic field as tuning parameter, the variation of magnetic ordering moment across 2 T field was clearly observed. Experimental data of CeAg$_{2}$Ge$_{2}$ will be discussed along with other Ce-based rare earth heavy fermion compounds which exhibit quantum criticality at low temperature. [Preview Abstract] |
Tuesday, March 16, 2010 2:03PM - 2:15PM |
J38.00015: ABSTRACT WITHDRAWN |
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