Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session R44: Experimental Studies of 115 Materials |
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Sponsoring Units: DCMP Chair: J. Sarrao, Los Alamos National Laboratory Room: Baltimore Convention Center 347 |
Wednesday, March 15, 2006 2:30PM - 2:42PM |
R44.00001: Hidden magnetism and quantum criticality in the heavy fermion superconductor CeRhIn$_{5}$ J.D. Thompson, T. Park, F. Ronning, H.Q. Yuan, M.B. Salamon, R. Movshovich, J.L. Sarrao We report the dependence on pressure and magnetic field of the specific heat and electrical resistivity of the pressure-tuned heavy-fermion superconductor CeRhIn$_{5}$. Above a critical pressure, where long-range antiferromagnetic order (AFM) abruptly disappears, application of a field brings back magnetism inside the superconducting state. As a function of pressure at low temperatures, the set of fields required to induce magnetism defines a line of quantum-phase transitions that separates a phase of coexisting AFM and SC from a purely unconventional superconducting phase. This quantum-transition line and the upper critical field boundary, above which superconductivity is suppressed, merge at a quantum tetracritical point where another quantum-phase boundary separates magnetically ordered and disordered normal phases. The quasiparticle mass diverges as this normal-state quantum boundary is approached, and crossing it produces a change in the Fermi-surface volume. [1] [1] H. Shishido et al., J. Phys. Soc. Jpn. \textbf{74}, 1103 (2005). [Preview Abstract] |
Wednesday, March 15, 2006 2:42PM - 2:54PM |
R44.00002: NMR Studies of CeCoIn$_5$ below 1K N. Curro, B.-L. Young, R. Urbano, R. Movshovich, J. Sarrao We present new NMR data in the normal and superconducting states of CeCoIn$_5$ below 1K and in fields up to 12T. The temperature dependence of the Knight shift anomalies exhibited by the Co and the two In sites is field dependent in the normal state, and may be related to the presence of a field-tuned quantum critical point. The spectra and relaxation rates exhibit dramatic changes in the superconducting and Fulde-Ferrell-Larkin- Ovchinnikov states. [Preview Abstract] |
Wednesday, March 15, 2006 2:54PM - 3:06PM |
R44.00003: Hall Effect under pressure in CeCoIn5 S. Singh, C. Capan, S. Wirth, M. Nicklas, A. Gladun, H. Lee, Z. Fisk, J. F. DiTusa, F. Steglich Important deviations from Landau Fermi Liquid theory are observed in many rare-earth compounds known as heavy fermion compounds. These anomalies can be ascribed to the presence of a quantum critical point (QCP) separating two different ground states in the phase diagram of these compounds. A quantum phase transition is a continuous ground state transformation driven by quantum fluctuations. In this context, CeCoIn5, a recently discovered heavy fermion superconductor, has been at the focus of intensive investigations. In this material, thermodynamic and transport properties point to a field-tuned QCP, whose origin remains elusive. At ambient pressure, this QCP is close to the superconducting upper critical field, and a Sn-doping study has failed to separate the two. We present new results on Hall Effect under pressure in a single crystal CeCoIn5 and discuss the origin of the QCP and its evolution with pressure. [Preview Abstract] |
Wednesday, March 15, 2006 3:06PM - 3:18PM |
R44.00004: Far-Infrared Properties of CeCoIn$_{5}$ G.V. Sudhakar Rao, S. Ocadlik, F.S. Razavi, M. Reedyk, C. Petrovic Measurements of the optical response of far-infrared radiation on single crystals of heavy fermion superconductor CeCoIn$_{5}$ have been made at various temperatures from 0.5 K to 2.5 K using a step- and- integrate Martin-Puplett type polarizing interferometer. An energy gap-like structure reminiscent of that observed in antiferromagnetic Cr was observed below 12 cm$^{-1}$ in the superconducting state. The size of this gap feature reduces with the increase of temperature to the normal state. This observation suggests the possibility of the role of magnetic excitations in pairing the electrons in the superconducting state.. [Preview Abstract] |
Wednesday, March 15, 2006 3:18PM - 3:30PM |
R44.00005: Is quantum criticality relevant to upper critical field ($H_{c2}$) scaling in the heavy-fermion compound CeRhIn$_5$? Tuson Park, John L. Sarrao, Joe D. Thompson We report disparate forms of upper critical field ($H_{c2}$) scaling below and above a critical pressure $P_{c1}$, where long- range antiferromagnetic order (AFM) abruptly disappears in the pressure-tuned heavy-fermion superconductor CeRhIn$_5$. For $P > P_{c1}$, $h_{c2} = H_{c2}/H_{c2}(T=0$~K) shows normal two- fluid type scaling with $t = T/T_c$, i.e., $h_{c2} = (1-t^2)(1- at^2)$, where $T_c$ is superconducting transition temperature at zero field and a is a fitting parameter. In this regime, the Maki parameter $\alpha$, a measure of Pauli limiting effects, is large, suggesting that an inhomogeneous superconducting state (FFLO) may be observable. For $P < P_{c1}$, in stark contrast, $h_{c2}$ linearly increases with decreasing $t$ down to $t = 0.1 $ and the specific heat discontinuity $\Delta C/C_N$ at $T_c$ is much smaller than the BCS value (=1.43). These observations manifest the interplay between superconductivity and antiferromagnetic fluctuations that exist in the vicinity of $P_ {c1}$. [Preview Abstract] |
Wednesday, March 15, 2006 3:30PM - 3:42PM |
R44.00006: $\mu $SR measurement of the superconducting penetration depth in aged PuCoGa$_{5}$ R. H. Heffner, K. Ohishi, W. Higemoto, T. Ito, G. D. Morris, M. J. Fluss, D. E. MacLauglin, L. Shu, E. D. Bauer, J. L. Sarrao The superconductor PuCoGa$_{5}$ possesses a relatively high critical temperature (T$_{c}$ = 18.5 K), a moderate mass enhancement (Sommerfeld coefficient $\cong $ 80 mJ/mol-K$^{2})$ and exhibits behavior consistent with spin-fluctuation-induced d-wave superconductivity [1]. It is also radioactive, with its dominant radioisotope $^{239}$Pu having a half-life of 2.4 x 10$^{4}$ yrs. We report $\mu $SR measurements of the temperature and field dependence of the magnetic field penetration depth $\lambda $(T,H) in a 400 day-old sample of PuCoGa$_{5}$ (T$_{c}$ = 15 K), and compare these results to data obtained on the same sample approximately one year earlier. In 600 Oe applied field both measurements show a linear low-temperature behavior for $\lambda $(T) - $\lambda $(0) = bT for T/T$_{c} \quad <$ 0.5 with the same coefficient b. The magnitude of $\lambda $(0) in the aged sample has increased by a factor of about 1.8. The results are discussed in terms of the effects of radiation damage on the postulated d-wave superconducting order parameter. [1] J. L. Sarrao \textit{et al.}, Nature \underline {420}, 297 (2002); N. J. Curro et al., Nature \underline {434}, 622 (2005). [Preview Abstract] |
Wednesday, March 15, 2006 3:42PM - 3:54PM |
R44.00007: NMR investigation of Sn-doped CeRhIn$_{5}$ R. R. Urbano, N. J. Curro, E. D. Bauer, D. Mixson, J. L. Sarrao, J. D. Thompson We have studied the local environment of the In(1) sites in the paramagnetic (PM) and antiferromagnetic (AFM) states of the heavy fermion compound CeRhIn$_{5-x}$Sn$_{x}$ ($0.0\le x\le 0.4)$ using Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) measurements. The AFM state can be continuously suppressed by Sn doping such that the Neel temperature $T_N $ goes to zero at $x_c \cong 0.4$. $^{115}$In NQR data in the PM state reveal that the suppression of $T_N $ as a function of $x$ is accompanied by a frequency shift and a broadening of the line. We also report spin-lattice relaxation rate $T_1^{-1} $ as a function of $x$ and $T$. [Preview Abstract] |
Wednesday, March 15, 2006 3:54PM - 4:06PM |
R44.00008: In-plane Torque Measurement on CeCoIn$_5$ Single Crystals T. Hu, H. Xiao, C. C. Almasan, T. A. Sayles, M. B. Maple We report in-plane torque measurements on single crystals of the heavy fermion superconductor CeCoIn$_5$ performed in the normal state at 1.9, 3, 6, and 10 K, as a function of angle and applied magnetic field. The measurements at constant angle were done in sweeping the magnetic field up to 14 T. The measured torque has a reversible and an irreversible component, with the former larger than the latter. The reversible component can be expressed as $\tau_{rev} (\theta) = \tau_{2}sin2\theta + \tau_{4}sin4\theta$ ($\theta$ is the angle between the applied field and the a-axis of the crystal), which is typical of systems with long range magnetic order. However, it has been reported that the heavy fermion superconductor CeCoIn$_{5}$ has no long range magnetic order, but only short range antiferromagntic fluctuations. The temperature and magnetic field dependence of the coefficients $\tau_{2}$ and $\tau_{4}$ will be discussed. The torque vs field curves at fixed angles show De-Hass Van-Alphen effect at temperatures as high as 10 K. The possible reasons behind this will also be discussed. [Preview Abstract] |
Wednesday, March 15, 2006 4:06PM - 4:18PM |
R44.00009: NMR Study of the Possible FFLO State in CeCoIn$_5$ V. F. Mitrovi{\'c}, M. Horvati{\'c}, C. Berthier, G. Knebel, G. Lapertot , J. Flouquet We report nuclear magnetic resonance (NMR) measurements of the heavy-fermion superconductor CeCoIn$_5$ in the vicinity of the superconducting critical field $H_{C2}$ for a magnetic field applied perpendicular to the $c$ axis. A possible inhomogeneous superconducting state, Fulde-Ferrel-Larkin- Ovchinnikov (FFLO), is stabilized in this part of the phase diagram. In 11 T applied magnetic field, we observe clear signatures of the two phase transitions. We show that a higher temperature transition is clearly associated with the transition to the homogeneous superconducting state. The low temperature phase cannot be characterized by a simple FFLO state, viewed as a stack of static, and spatially well separated, superconducting and normal regions. Alternative explanations of the nature of the low temperature phase are discussed. [Preview Abstract] |
Wednesday, March 15, 2006 4:18PM - 4:30PM |
R44.00010: Angular Dependent Torque Measurements on CeCoIn$_5$ Single Crystals H. Xiao, T. Hu, C. C. Almasan, T. A. Sayles, M. B. Maple Angular dependent torque measurements were performed on single crystals of CeCoIn$_5$ heavy fermion superconductor ($T_{c0}$ = 2.3 K) in the temperature $T$ range 1.9 K $\leq T \leq $ 20 K and magnetic fields $H$ up to 14 T. Large paramagnetic effect is found in the normal state due to magnetic moment of the magnetic ion Ce$^{3+}$. Torque measurements in the mixed state were also performed. The torque curves show sharp hysteresis peaks at $\theta = 90^{o}$ ($\theta$ is the angle between $H$ and the $c-$axis of the crystal), a result of intrinsic pinning of vortices. The anisotropy $\gamma \equiv \sqrt{m_{c}/m_{a}}$ in the mixed state was determined from the reversible part of the vortex contribution to the torque signal using Kogan's model [Phys. Rev. B \textbf{38}, 7049 (1988)]. The anisotropy $\gamma$ decreases with increasing magnetic field and temperature. The fact that $\gamma$ is not a constant points towards a multiband scenario in this heavy fermion material. [Preview Abstract] |
Wednesday, March 15, 2006 4:30PM - 4:42PM |
R44.00011: Penetration Depth Studies of Tin Doped CeCoIn$_{5}$ Daniel Vandervelde, H.Q. Yuan, M.B. Salamon, E.D. Bauer, N. Hur, F. Ronning, M.J. Graf, J.D. Thompson, J.L. Sarrao, R. Movshovich The heavy fermion superconductor CeCoIn$_{5}$ has attracted much attention recently. Its high T$_{C}$ ($\sim $2.3K), nearby antiferromagnetic phases, and evidence of line nodes in the superconducting gap indicative of a d-wave order parameter have made it an interesting topic of study. Here we present measurements of the AC magnetic field penetration depth ($\Delta \lambda $(T)) undertaken on the same material, but with an impurity doping of Sn (CeCoIn$_{5-X}$Sn$_{X})$ at three concentrations x=0.03, x=0.06, and x=0.09. Our findings support the assertion that CeCoIn$_{5}$ is a nonlocal, d-wave superconductor, but that as impurity concentration is increased, scattering quickly becomes the dominant mechanism. All data was modeled as a quadratic, scattering-dominated temperature dependence that crosses over to a linear regime reminiscent of the pure sample at a temperature$^{1 }$T*. The observed value of T* increases with the concentration of impurities as is predicted in the impurity model by Hirschfield and Goldenfeld (T*$\sim \surd $n$_{i})$.$^{1}$ This dependence on the concentration of a nonmagnetic impurity adds further confirmation of the d-wave nature of the superconducting state. $^{1}$ P.J. Hirschfield and N. Goldenfeld, Phys Rev. B \textbf{48}, 4219 (1993) [Preview Abstract] |
Wednesday, March 15, 2006 4:42PM - 4:54PM |
R44.00012: Gap structure of heavy-fermion superconductor CeIrIn5 from heat transport Hamideh Shakeripour, S.Y. Li, N. Doiron-Leyraud , Louis Taillefer, C. Petrovic We present measurements of the in-plane and out-plane thermal conductivity of heavy-fermion superconductor CeIrIn5 down to temperatures approaching Tc/10, throughout the vortex state. We use the observed anisotropy in residual linear term and response to a magnetic field to shed light on the nodal structure of the superconducting gap. We compare our results to existing theoretical calculations and discuss the possibility of multi-band superconductivity, observed recently in the related material CeCoIn5 [1]. \newline \newline [1] M.A. Tanatar et al., Phys. Rev. Lett. 95, 067002 (2005). [Preview Abstract] |
Wednesday, March 15, 2006 4:54PM - 5:06PM |
R44.00013: Non-local Magnetic Field-tuned Quantum Criticality in Cubic CeIn$_{3-x}$Sn$_x$ ($x=$~0.25) Neil Harrison, Alejandro Silhanek, Marcelo Jaime, Victor Fanelli, Cristian Batista, Takao Ebihara, Koji Tezuka We show that antiferromagnetism in lightly Sn-doped CeIn$_3$ terminates at a critical field $\mu_0H_{\rm c}=$~38~$\pm$~1~T. Electrical transport, specific heat and magnetization measurements reveal that $m^\ast$ does not diverge, suggesting that cubic CeIn$_3$ is representative of a critical spin-density wave (SDW) scenario, unlike the local quantum critical points observed in lower-symmetry systems such as CeCu$_{6-x}$Au$_x$ and YbRh$_2$Si$_{2-x}$Ge$_x$. The existence of a maximum in $m^ast$ at a lower field $\mu_0H_{\rm x}=$~30~$\pm$~1~T may be interpreted as a field-induced crossover from local moment to SDW behavior as the magnitude of the antiferromagnetic order parameter falls below the Fermi bandwidth. [Preview Abstract] |
Wednesday, March 15, 2006 5:06PM - 5:18PM |
R44.00014: Correlation induced phase transition in fcc Pu Shao-Ping Chen The density functional theory calculations (GGA+U) of fcc Pu indicate that as the Hubbard on-site Coulomb repulsion U increases the fcc Pu system goes through a sharp phase transition. Accompanying this transition are sharp drops of the bulk moduli, and large values and even negative values of pressure derivatives of the bulk moduli. Some evidence of these effects were consistent with current experimental observations. [Preview Abstract] |
Wednesday, March 15, 2006 5:18PM - 5:30PM |
R44.00015: Phonon mechanisms for structural phase transitions in Pu Avadh Saxena, Turab Lookman, R.C. Albers As a function of temeprature, pressure and alloying (Ga or Al) plutonium undergoes a series of structural transitions. Based on crystallography and symmetry we identify possible phonon mechanisms for various phase transitions. Coupling of shuffle modes corresponding to the specific phonons (primary order parameter) to the relevant strain tensor components (secondary order parameter) we develop Ginzburg-Landau free energies for some of the important structural transitions such as $\delta\rightarrow \alpha$ (FCC to simple monoclinic), $\delta\rightarrow\beta$ (FCC to side centered monoclinic) and $\beta\rightarrow \alpha$ (side centered monoclinic to simple monoclinic). We use these free energies to explore certain parts of the Pu phase diagram and relate to experimental structural and thermodynamic data such as specific heat and thermal expansion for the cases available. We also enumerate the orientational relationships between parent and product phases in these transitions. [Preview Abstract] |
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