Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session A23: Strongly Correlated Electrons I |
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Sponsoring Units: GMAG Chair: Chris Stock, John Hopkins University Room: Baltimore Convention Center 320 |
Monday, March 13, 2006 8:00AM - 8:12AM |
A23.00001: High magnetic field thermal-expansion and magnetostriction of URu$_2$Si$_2$ V\'ictor Correa, Timothy Murphy, Eric Palm, Stanley Tozer, Peter Sharma, Neil Harrison, Marcelo Jaime, George Schmiedeshoff, John Mydosh We present high magnetic field (up to 45 T) thermal-expansion and magnetostriction results on URu$_2$Si$_2$ single crystals. The volume change associated with the transition to the ``hidden'' order phase becomes increasingly discontinous as the magnetic field is raised above 30 T. This confirms recent thermal conductivity and specific heat experiments indicating a strong coupling between the ``hidden'' order parameter and the lattice which suggest some sort of charge ordered state. Several other transitions are observed at higher fields, many of them showing hysteresis, while a change in the sign of the magnetostriction coefficient is observed at the metamagnetic transition ($B_M$ $\sim$ 38 T). [Preview Abstract] |
Monday, March 13, 2006 8:12AM - 8:24AM |
A23.00002: Phonon Thermal Transport of URu$_{2}$Si$_{2}$: Broken Translational Symmetry and Strong-Coupling of the ``Hidden Order'' to the Lattice Peter Sharma, N. Harrison, M. Jaime, Y.S. Oh, K.H. Kim, C.D. Batista, H. Amitsuka, J.A. Mydosh A dramatic increase in the total thermal conductivity ($k)$ is observed in the Hidden Order (HO) state of single crystal URu$_{2}$Si$_{2}$. Through measurements of the thermal Hall conductivity, we explicitly show that the electronic contribution to $k$ is extremely small, so that this large increase in $k$ is dominated by phonon conduction. An itinerant BCS/mean-field model describes this behavior well: the increase in $k$ is associated with the opening of a large energy gap at the Fermi Surface, thereby decreasing electron-phonon scattering. Our analysis implies that the ``Hidden Order'' parameter is strongly coupled to the lattice, suggestive of a broken symmetry involving charge degrees of freedom. [Preview Abstract] |
Monday, March 13, 2006 8:24AM - 8:36AM |
A23.00003: On Heavy Fermion Superconductivity and Quantum Criticality in the 115 series Kenneth Burch We have performed a detailed analysis of the optical properties of the 1-1-5 series (CeTIn5 where T=Co,Ir,Rh), revealing the hybridization gap ($\Delta$) as key to understanding their rich phase diagram. Surprisingly we find that $\Delta$ for only one of the four bands crossing the Fermi surface determines the properties of the system. Furthermore, these carriers are the lightest and produce the smallest $\Delta$. Additionally we discuss connections between this $\Delta$, the superconducting transition temperature and the symmetry of the superconducting gap. This study demonstrates an experimental link between superconductivity and the parameter governing the magnetic Quantum Critical Point. [Preview Abstract] |
Monday, March 13, 2006 8:36AM - 8:48AM |
A23.00004: Quantum Criticality in CeMIn$_{5-x}$Sn$_x$ (M = Rh, Co) Filip Ronning, Ed Bauer, C. Capan, Y. Tokiwa, J.D. Thompson, J.L. Sarrao, R. Movshovich Non-Fermi liquid behavior, as characterized by a T-linear resistivity and a T log(T) behavior in specific heat, is observed in zero field in the heavy fermion system CeCoIn$_5$. The application of magnetic field has revealed a field tuned quantum critical point surprisingly coincident with the superconducting H$_{c2}$. We present data that shows the application of pressure reduces the critical field H$_{QCP}$ more rapidly than H$_{c2}$ is suppressed. We also investigate doping studies which show an anisotropically field tuned QCP in CeRhIn$_{5-x}$Sn$_x$ at x=1.0, the critical doping where antiferromagnetism is suppressed, while results on CeCoIn$_{5-x} $Sn$_x$ maintains that the quantum critical field and the superconducting upper critical field are intimately connected. We attempt to reconcile whether all the critical behavior in the CeMIn$_5$ family can have a common origin. [Preview Abstract] |
Monday, March 13, 2006 8:48AM - 9:00AM |
A23.00005: Superconducting properties of Ce$_{2}$CoIn$_{8}$ N. Hur, T. Park, E. D. Bauer, J. D. Thompson, J. L. Sarrao The new family of Ce-based heavy-fermion compounds with the general formula Ce$_{n}$TIn$_{3n+2}$ (T=transition metal) have attracted sparked interest in recent years owing to their various interesting phenomena, such as pressure induced superconductivity, quantum criticality, and non-Fermi liquid behaviors. However, among n=2 compounds, Ce$_{2}$CoIn$_{8}$ has not been studied sufficiently mainly because of the difficulty in the synthesis of crystals of decent size. Herein, we report the successful reproduction of Ce$_{2}$CoIn$_{8}$ single crystals and present their magnetic, thermal and transport properties. Observed anomalies in resistivity and their magnetic field dependence will be explained within the context of a filamentary superconductivity. The nature and possible origin of the resistivity transition is discussed in comparison with that in CeIrIn$_{5}$. [Preview Abstract] |
Monday, March 13, 2006 9:00AM - 9:12AM |
A23.00006: Point Contact Spectroscopy Study of the Heavy Fermion Superconductor Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$ C. S. Turel, J. Y. T. Wei, N. A. Frederick, W. M. Yuhasz, S. K. Kim, J. Paglione, M. B. Maple The recent discovery of superconductivity in the heavy fermion material Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$ has generated widespread interest. In particular, there is evidence for the existence of two competing superconducting order parameters, at least one of which is believed to have nodes. We have performed point-contact spectroscopy measurements on single crystals of Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$, using Pt-Ir tips in a dilution refrigerator with a pulsed technique to minimize Joule heating. We present differential conductance spectra down to 100 mK, along with the magnetic field evolution. We discuss the implications of our data in relation to recently proposed pairing symmetries. [Preview Abstract] |
Monday, March 13, 2006 9:12AM - 9:24AM |
A23.00007: de Haas van Alphen perspective on the origin of heavy fermions in UPt$_3$ Patrick Rourke, Alix McCollam, Greg McMullan, Mike Norman, Stephen Julian, Andrew Huxley Precise de Haas van Alphen (dHvA) oscillation measurements on the heavy fermion superconductor UPt$_3$ are available as a function of magnetic field angle. It was recently proposed that the heavy quasiparticles in this material arise from the localization of two of the three 5f electrons of the U ions [Zwicknagl et al., PRB 65, 081103R (2002)]. The predicted Fermi surface topology however differs from traditional bandstructure calculations. We will focus on the experimentally observed angle dependence of the hole-like $\delta$-orbit, as this appears difficult to reconcile with the Fermi surface of Zwicknagl et al. [Preview Abstract] |
Monday, March 13, 2006 9:24AM - 9:36AM |
A23.00008: NMR measurement of spin-spin relaxation (T$_{2})$ of URu$_{2}$Si$_{2}$ Tod Caldwell, Nicholas Curro We report detailed temperature dependences of the 29Si spin-spin relaxation rate T2 in the heavy fermion superconductor URu$_{2}$Si$_{2}$ as a function of field and temperature.~ All experimental work was carried out on an aligned powder sample.~ Both Carr-Purcell-Meiboom-Gill (CPMG) and Hahn-Echo pulse sequence techniques were employed to examine differences in spin-spin relaxation.~ We find unusual enhancements of the relaxation rate near the hidden order transition, and will discuss our results in the context of various theoretical scenarios. [Preview Abstract] |
Monday, March 13, 2006 9:36AM - 9:48AM |
A23.00009: Indications of a Field Dependent Vortex Core Size in CeCoIn$_5$ L. DeBeer-Schmitt, M. R. Eskildsen, C. D. Dewhurst, B. W. Hoogenboom, C. Petrovic Using Small-Angle Neutron Scattering, we have imaged the flux- line lattice (FLL) in the {\em d}-wave, heavy fermion superconductor CeCoIn$_5$. At low fields, a hexagonal FLL is observed which undergoes a first order transition to a rhombic (distorted square) symmetry as the field is increased above 0.55 T. As the field is increased futher, the FLL approaches a square symmetry. Measurements of the FLL reflectivity yields a constant form factor independent of the applied magnetic field, in stark contrast to the exponential decrease usually observed. The field-independent form factor may indicate a field dependent vortex core size, $\xi$ $\propto$ $H^{-1/2}$, in qualitative agreement with recent theoretical predictions for ultra-clean, high-$\kappa$ superconductors [V.G. Kogan and N.V. Zhelezina, PRB {\bf 71}, 134505 (2005)]. [Preview Abstract] |
Monday, March 13, 2006 9:48AM - 10:00AM |
A23.00010: Quantum Criticality in Itinerant Antiferromagnet Cr$_{0.965}$V$_{0.035}$ D.A. Sokolov, G. Strycker, M.C. Aronson, M.C. Bennett, S.E. Nagler, M. Lumsden We report results of triple-axis neutron scattering experiments, in which we studied the development of the magnetic fluctuations in the quantum critical itinerant antiferromagnet Cr$_{0.965}$V$_ {0.035}$. Unexpectedly, we found temperature dependent elastic scattering at the incommensurate wavevector q$^{\ast}$=(001$\pm\delta$)2 $\pi$/a, which corresponds to the spin density wavevector in pure Cr and no elastic scattering at the commensurate wavevector q=(001)2 $\pi$/a. We propose an electronic phase separation scenario to account for the observed elastic scattering. Temperature independent inelastic scattering was observed at the commensurate wavevector q. This scattering showed a linear increase with energy transfer E$_{t} $, saturating at E$_{t}$=18 meV, which we interpret as a characteristic energy scale expected for the Fermi liquid. The wave vector dependence of the scattering at q$^{*}$ is Lorentzian, with an intensity which decreases with increasing energy transfer, and is temperature independent below 100 K. The Lorentzian linewidth approaches the spectrometer resolution at the lowest temperatures and energy transfers. These observations suggest that the susceptibility underlying the incommensurate scattering is maximized, and is perhaps critical, for q=q$^{\ast}$, E$\rightarrow$0, and T$\rightarrow$0, as has been observed near other antiferromagnetic quantum critical points. Work at the University of Michigan supported by the National Science Foundation. [Preview Abstract] |
Monday, March 13, 2006 10:00AM - 10:12AM |
A23.00011: Attractive electron-electron interaction induced by the Bloch band topological field Junren Shi, Qian Niu We demonstrate a new possibility for the occurrence of the attractive electron-electron interaction in ferromagnetic metals. Unlike that of the conventional origin via the boson-exchange (spin fluctuation), this attractive interaction is induced by the Bloch band topological field, which transforms the Coulomb repulsion to a direct attractive interaction between electrons, resulting in unconventional superconductivity with the isotropic $p$--wave pairing. Our study highlights the fundamental effects of the Bloch band topological field, which presents in a large class of crystalline materials. It also provides a plausible alternative theory for the recently discovered ferromagnetic superconductors UGe$_{2}$ and ZrZn$_{2}$. [Preview Abstract] |
Monday, March 13, 2006 10:12AM - 10:24AM |
A23.00012: Theory of the helical spin crystal. A candidate for the partially ordered state of MnSi Benedikt Binz, Ashvin Vishwanath, Vivek Aji MnSi is an itinerant magnet which at low temperatures develops a helical spin density wave. Under pressure it undergoes a transition into an unusual partially ordered state whose nature is debated. Here we propose that the helical spin crystal (the magnetic analog of a solid) is a useful starting point to understand partial order in MnSi. We consider helical spin crystals with BCC structure (composed of superpositions of six different helical spin-density waves) and determine conditions under which they may be energetically favored. We introduce a Landau theory to study the properties of these states, in particular the effect of crystal anisotropy, magnetic field and disorder. These results compare favorably with existing data on MnSi from neutron scattering and magnetic susceptibility measurements. Future experiments to test this scenario are also proposed. [Preview Abstract] |
Monday, March 13, 2006 10:24AM - 10:36AM |
A23.00013: Anomalous quasiparticle transport in the superconducting state of CeCoIn$_{5}$ Yuichi Kasahara, Yasuyuki Nakajima, Koichi Izawa, Kamran Behnia, Yuji Matsuda, Hiroaki Shishido, Rikio Settai, yoshichika Onuki To investigate the quasiparticle dynamics in the superconducting state of quasi-two dimensional heavy fermion superconductor CeCoIn$_ {5}$, the thermal Hall conductivity $\kappa_{xy}$ is measured. In zero magnetic field, thermal Hall angle shows up a steep increase below $T_{c}$, indicating that the quasiparticle mean free path is strongly enhanced. In spite of the presence of a periodic vortex lattice, this enhancement is easily suppressed by a very weak magnetic field. We found that the density states of the delocalized quasiparticles $N_{\mathrm{del}} $, which is obtained from $\kappa_ {xx}$ and $\kappa_{xy}$, exhibits a $\sqrt{H}$- dependence, indicating a Volovik effect. Moreover, $\kappa_{xy}$ reveals the scaling relation with respect to $T/\sqrt{H}$, which is expected for $d $-wave symmetry. These results provide a further support for $d$-wave superconducting symmetry in CeCoIn$_{5}$. We also argue that a small Fermi energy, a short coherence length, and a long quasiparticle mean free path all indicate CeCoIn$_{5}$ is in the superclean regime. These results highlight that CeCoIn$_{5}$ is unique among superconductors. [Preview Abstract] |
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