Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session B41: Heavy Fermion 115 Superconductors |
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Sponsoring Units: DMP DCMP Chair: Carlos Bolech, Rice University Room: 413 |
Monday, March 16, 2009 11:15AM - 11:27AM |
B41.00001: Penetration depth study of CeIrIn$_{5}$ Daniel Vandervelde, H.Q. Yuan, Y. Onuki, M.B. Salamon The heavy-Fermion compounds CeTIn$_{5}$, with T a transition metal, provide a fertile ground for studying the interplay between magnetism and superconductivity. The T = Co compound has a transition temperature $T_{c }$ = 2.4 K, and has a d-wave order parameter. As Ir is substituted for Co, the transition temperature decreases sharply to T$_{c}$ = 0.4 K. One report of the thermal conductivity of CeIrIn$_{5}$ supports a d-wave state, another argues in favor of a hybrid gap state with broken time-reversal symmetry. We report penetration depth studies of CeIrIn$_{5}$ to $T_{c}/$5 that supports the d-wave scenario. Converted to superconducting fraction, the data taken with the \textit{rf }measuring field along various crystallographic axes can be scaled to collapse to a single curve that matches a d-wave calculation with a zero-temperature gap of 2.5k$_{B}$T$_{c}$. [Preview Abstract] |
Monday, March 16, 2009 11:27AM - 11:39AM |
B41.00002: Magnetic-field induced quantum critical points of valence transition in Ce- and Yb-based heavy fermions Shinji Watanabe, Atsushi Tsuruta, Kazumasa Miyake, Jacques Flouquet Valence instability and its critical fluctuations have attracted much attention recently in the heavy-electron systems. Valence fluctuations are essentially charge fluctuations, and it is highly non-trivial how the quantum critical point (QCP) as well as the critical end point is controlled by the magnetic field. To clarify this fundamental issue, we have studied the mechanism of how the critical points of the first-order valence transitions are controlled by the magnetic field [1]. We show that the critical temperature is suppressed to be the QCP by the magnetic field and unexpectedly the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be a cooperative phenomenon of Zeeman effect and Kondo effect, which creates a distinct energy scale from the Kondo temperature. This mechanism explains a peculiar magnetic response in CeIrIn$_{5}$ and metamagnetic transition in YbXCu$_{4 }$for X=In as well as a sharp contrast between X=Ag and Cd. We present the novel phenomena under the magnetic field to discuss significance of the proximity of the critical points of the first-order valence transition. [1] S. Watanabe et al. PRL\textbf{100}, (2008) 236401. [Preview Abstract] |
Monday, March 16, 2009 11:39AM - 11:51AM |
B41.00003: Combined Effects of Magnetic Field and Uniaxial Pressure on CeCoIn$_5$ Rena Zieve, Scooter Johnson, Jason Cooley CeCoIn$_5$ exhibits unusual behavior in a magnetic field. The upper critical field is highly anisotropic, more than a factor of two larger for a field applied in the $ab$-plane than for a field along the $c$-axis. In both field orientations the superconducting transition changes from second-order to first-order with increasing field, and possible FFLO phases have been observed at high fields. Here we explore the influence of uniaxial pressure, applied along the crystal $c$-axis, on the temperature-field phase diagram. We find that a magnetic field suppresses the superconductivity far more sharply when the sample is also under pressure. We also examine the slope of the phase boundary near zero field and the nature of the transition at higher fields. [Preview Abstract] |
Monday, March 16, 2009 11:51AM - 12:03PM |
B41.00004: Dependence of Superconducting Transition Temperature on Uniaxial Pressure in CeCoIn$_5$ Scooter Johnson, Rena Zieve, Jason Cooley We apply uniaxial pressure up to 4 kbar along the $c$-axis of single crystal samples of CeCoIn$_5$ and measure how the transition temperature to the superconducting state changes. We mount the sample within an ac susceptibility coil and apply pressure through a helium bellows cell mounted on a dilution refrigerator. We find that pressure shifts the transition to lower temperatures at a rate of 22.5 mK per kbar. Our observation follows the general correlation between transition temperatures and lattice constants among 115 materials, where lower $T_c$'s typically correspond to smaller $c/a$ ratios. Pressure has the additional effect of broadening the transition well beyond what we expect from macroscopic pressure inhomogeneity. We are extending this work to measurements of CeCoIn$_5$ under $a$-axis pressure. [Preview Abstract] |
Monday, March 16, 2009 12:03PM - 12:15PM |
B41.00005: Optical Study of the Heavy Fermion Superconductor CeCoIn$_{5}$ T. Gebre, T. Tokumoto, J. Cherian, T. Murphy, S. Toszer, E. Palm, C. Wiebe, S. McGill We have performed dc magnetization and optical spectroscopy on flux-grown crystals of the heavy fermion superconductor, CeCoIn$_{5}$. We will discuss the growth technique and report results of low-temperature and high magnetic field measurements for different orientations of field and crystal axis. CeCoIn$_{5}$ is a strongly correlated system exhibiting superconductivity below 2.3 K and is believed to show a variety of magnetic field-induced phases near or below the critical temperature. [Preview Abstract] |
Monday, March 16, 2009 12:15PM - 12:27PM |
B41.00006: Coexistence of Superconducting and Magnetic Order in CeCoIn$_5$ Georgios Koutroulakis, Vesna Mitrovic, Mladen Horvatic, Claude Berthier, Gerard Lapertot, Jacques Flouquet The interplay between magnetic and superconducting order near a quantum critical point in heavy fermion materials has attracted intensive research interest in recent years. One of the most intriguing examples is that of CeCoIn$_5$, in which a novel phase within the superconducting phase is observed near the critical field at low temperature. Recent nuclear magnetic resonance [1] and neutron scattering [2] experiments showed that a static magnetic order is stabilized in this phase. The microscopic nature of this magnetic state will be discussed.\\[4pt] [1] B.-L. Young \textit{et al.}, Phys. Rev. Lett. \textbf{98}, 036402 (2007).\\[0pt] [2] M. Kenzelmann \textit{et al.}, Science \textbf{321}, 1652(2008). [Preview Abstract] |
Monday, March 16, 2009 12:27PM - 12:39PM |
B41.00007: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 12:39PM - 12:51PM |
B41.00008: Local Structure and Site Occupancy in Cd- and Hg-doped Ce$T$In$_{5}$ ($T$=Co, Rh, Ir) C.H. Booth, E.D. Bauer, F. Ronning, V. Sidorov, T. Park, J.D. Thompson, J.L. Sarrao, A.D. Bianchi, Z. Fisk Local structure measurements using the extended x-ray absorption fine-structure (EXAFS) technique were performed from the In $K$, Cd $K$, and Hg $L_3$ edges on samples of CeCo(In$_{1-x}$Cd$_x$)$_5$ (0.5\%$\geq x \geq$3.1\%) and Ce$T$(In$_{1-x}$Hg$_x$)$_5$ ($T$=Co, Rh, Ir, 0.7\%$\geq x \geq$3.5\%). Fits indicate no measurable change in the bulk local structure with these substituents. In contrast, the local structure data around the substituent atoms indicates about $f_{Cd}^{Co}=44(3)\%$ of Cd atoms reside on In(1) sites, similar to previous results [$f_{Sn}^{Co}=55(5)\%$] for Sn in CeCo(In$_{1-x}$Sn$_x$)$_5$. Mercury has an even stronger preference for the In(1) site, with $f_{Hg}^{Co}=71(5)\%$, $f_{Hg}^{Rh}=97(3)\%$, and $f_{Hg}^{Ir}=55(5)\%$, although other phases appear to be present in the CeIr(In$_{1-x}$Hg$_x$)$_5$ material. Small distortions from the parent structure are also observed around the substituent atoms. These results will be related to the sharp decrease in the superconducting transition temperature with $x$. [Preview Abstract] |
Monday, March 16, 2009 12:51PM - 1:03PM |
B41.00009: Cd and Sn doping effects on Pauli limiting and HFLT state in CeCoIn$_5$ R. Movshovich, Y. Tokiwa, N. Kurita, F. Ronning, E.D. Bauer, P. Papin, J.D. Thompson, A.D. Bianchi, J.F. Rauscher, S.M. Kauzlarich, Z. Fisk , I. Vekhter We investigated the effect of Cd and Sn doping on the superconducting (SC) transition temperature $T_c$, the superconducting critical field $H_{c2}$, and the High-Field-Low- Temperature (HFLT) phase in heavy fermion superconductor CeCoIn$_5$. $T_c$ decreases monotonically for both dopants, whereas $H_{c2}$ rises initially with Cd substitution, while dropping for Sn doping. Analysis of the magnetization data suggests that these effects are caused by weakening of the Pauli limiting in CeCoIn$_5$ with Cd doping, most likely due to changes of susceptibility of the normal state. Both Cd (leading to AFM ground state at higher concentrations) and Sn impurities, at a very low level of a few hundred ppm, suppress the HFLT phase. We interpret these results as supporting the superconducting origin of the HFLT phase. [Preview Abstract] |
Monday, March 16, 2009 1:03PM - 1:15PM |
B41.00010: Kondo coherence and superconductivity in Yb doped CeCoIn$_5$ Andrea Bianchi, Gabriel Seyfarth, Bobby Prevost, Sjoerd Roorda, Dan Hurt, Cigdem Capan, Zachary Fisk We have studied the effect of Yb doping on superconductivity in the unconventional heavy fermion superconductor CeCoIn$_5$ in a doping series spanning from pure CeCoIn$_5$ to the paramagnetic metal YbCoIn$_5$, which is isostructural with CeCoIn$_5$. By replacing Ce by Yb, we are at the same time removing carriers as well as disrupting the Kondo lattice of CeCoIn$_5$, which is thought to be responsible for superconductivity in this compound. This will give us insight into how the Kondo coherence and Cooper pair breaking in CeCoIn$_5$ are affected by Yb substitution. Our doping series shows that the unit cell volume stays approximately constant up to a Yb concentration of about 40~\%. At higher Yb concentrations the unit cell volume begins to shrink gradually to the value of YbCoIn$_5$. However, is superconductivity in the doped system is remarkably resilient against Yb substitution: At low doping the superconducting transition temperature $T_c$ is only gradually suppressed from the value of 2.24~K of pure CeCoIn$_5$, and only with a Yb concentration of 60~\% $T_c$ is suppressed below 0.3~K. [Preview Abstract] |
Monday, March 16, 2009 1:15PM - 1:27PM |
B41.00011: Conductance asymmetry in point-contact junctions on the heavy-fermion compounds CeMIn$_{5}$ (M=Co, Rh, Ir) L.H. Greene, W.K. Park, E.D. Bauer, J.L. Sarrao, J.D. Thompson The Ce-based 1-1-5 heavy-fermion compounds, CeMIn$_{5}$ (M=Co, Rh, Ir), continue to draw much attention from the community. One of the key questions is how the localized discrete states acquire itinerancy over the conduction electron continuum. As a probe of the evolutionary behavior of the Kondo lattice, we take differential conductance spectra from nanoscale metallic junctions on CeMIn$_{5}$ single crystals over wide temperature ranges. A striking common feature is the systematic development of an asymmetry in the background conductance [1]. Conventional models including the heating model with large Seebeck coefficients of heavy fermions do not account for this behavior. We propose a phenomenological model based on a possible Fano interference effect [2] between two conductance channels, one into the heavy electron liquid (hybridized f-band) and the other into the conduction electrons without hybridization. [1] W. K. Park et al., Phys. Rev. Lett. \textbf{100}, 177001 (2008). [2] U. Fano, Phys. Rev. \textbf{124}, 1866 (1961). [Preview Abstract] |
Monday, March 16, 2009 1:27PM - 1:39PM |
B41.00012: The Fano effect in the point contact spectroscopy of heavy electron materials Yi-feng Yang Recent experiments on CeCoIn$_5$ reveal similar temperture dependence of the conductance asymmetry in the point contact spectroscopy and the Knight shift anomaly. This suggests a common origin of both anomalies and supports a previously proposed phenomenological two-fluid model that predicts the emergence of a heavy fluid, or Kondo liquid, in heavy electron materials. Here we propose a phenomenological formula for the point contact spectroscopy and describe the spectra by a Fano effect of tunneling electrons due to the Kondo liquid emergence. Our formula explains quantitatively the experimental data of several heavy electron materials. [Preview Abstract] |
Monday, March 16, 2009 1:39PM - 1:51PM |
B41.00013: Evidence for magnetic field-tuned quantum criticality below $H_{c2}$ in CeCoIn$_5$ J. Paglione, J.-P. Reid, M.A. Tanatar, L. Taillefer, C. Petrovic The existence of a magnetic field-tuned quantum critical point coinciding with the upper critical field for superconductivity in the heavy-fermion superconductor CeCoIn$_5$ has remained a puzzling fact, and has proven difficult to study due to the onset of superconductivity. Here we present low temperature thermal conductivity measurements which probe the approach to the quantum critical point in CeCoIn$_5$ as a function of field from within the superconducting state, revealing new evidence for field- tuned quantum criticality. [Preview Abstract] |
Monday, March 16, 2009 1:51PM - 2:03PM |
B41.00014: Insulating Vortex Core near QCP in CeCoIn$_5$ H. Xiao, T. Hu, C. C. Almasan, T. A. Sayles, M. B. Maple We have investigated the vortex core of the superclean unconventional heavy fermion superconductor CeCoIn$_5$ by studying the flux flow dissipation in the mixed state for two magnetic field orientations, i.e., $H \parallel c$ axis and $H \parallel ab $ plane, at temperatures down to 1.8 K. The vortex core in the mixed state of CeCoIn$_5$ is insulator-like, in contrast to the metallic behavior of CeCoIn$_5$ in its normal state, at temperatures $T$ larger than the supercondcting transition temperature $T_c$. Moreover, the abnormal insulating behavior of the vortex core is strongly suppressed when CeCoIn$_5$ is tuned away from the quantum critical point (QCP) by applying pressure. This latter result gives firm evidence that quantum criticality plays an important role in the interaction between superconductivity and magnetism, hence is responsible for the emergence of unconventional superconductivity. A scaling law of the flux flow resistivity has also been found and will be discussed. [Preview Abstract] |
Monday, March 16, 2009 2:03PM - 2:15PM |
B41.00015: The effect of Yb substitution in the heavy-fermion superconductor CeCoIn$_{5}$ Lei Shu, E. Gonzales, K. Huang, T.A. Sayles, J. Paglione, M.B. Maple The discovery of a new family of heavy-fermion superconductors with the formula CeMIn$_{5}$ (M=Co, Rh, Ir ) provides an interesting playground to understand the relation between unconventional superconductivity and quantum criticality. CeCoIn$_{5}$, with the highest ambient pressure superconducting transition temperature of all heavy-fermion compounds, exhibits a magnetic field-tuned quantum critical point. The peculiar magnetic properties of CeCoIn$_{5}$ are determined by the interaction between the magnetic moments of the Ce$^{3+}$ ions and the spins of conduction electrons. Through systematic studies of Ce$_{1-x}$Yb$_{x}$CoIn$_{5}$ alloys, where the magnetic Ce ions (4$f^{1}$ configuration) are diluted by Yb (hole analogue; 4$f^{13}$ configuration), it allows us to study the nature of intersite interactions. Lattice constant, magnetic susceptibility, and electrical resistivity data of Ce$_{1-x}$Yb$_{x}$CoIn$_{5}$ alloys throughout the range $0\leq x \leq 1$ will be reported. [Preview Abstract] |
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