Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M46: Hidden Order, URu2Si2 and Other U-Based Heavy-Fermion Systems |
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Sponsoring Units: DCMP Chair: Nick Butch, National Institute of Standards and Technology Room: Mile High Ballroom 4E |
Wednesday, March 5, 2014 11:15AM - 11:27AM |
M46.00001: Magnetic Nematicity in the Hidden Ordered Compound URu2Si2 Peter Riseborough, S.G. Magalhaes, E.J. Calegari The Hund's rule exchange interaction promotes a second-order phase transition to a coupled spin and orbital density wave state in the underscreened Anderson Lattice Model. The spin-flip part of the Hund's rule coupling stabilizes a spontaneous spin-dependent mixing of 5f quasiparticle bands which, in the normal state, have pure orbital characters. The transition breaks the spin-rotational invariance and leads to an asymmetric pseudo-gap forming in the density of states. When a magnetic field is applied, the electronic dispersion relations become dependent on the relative orientation of the field and the spontaneously chosen quantization axis. We show that this results in the magnetic susceptibility becoming anisotropic below the critical temperature, but without the development of a static magnetization. [Preview Abstract] |
Wednesday, March 5, 2014 11:27AM - 11:39AM |
M46.00002: Absence of a static in-plane magnetic moment in the `hidden-order' phase of URu$_2$Si$_2$ Pinaki Das, R.E. Baumbach, E.D. Bauer, M. Janoschek, K. Huang, M.B. Maple, Y. Zhao, J.S. Helton, J.W. Lynn We have carried out a careful magnetic neutron scattering study of the heavy fermion compound URu$_2$Si$_2$ to probe the possible existence of a small magnetic moment parallel to the tetragonal basal plane in the `hidden-order' phase. This small in-plane component of the magnetic moment $S_\parallel$ on the uranium sites has been postulated by two recent models (rank-5 superspin/hastatic order) aiming to explain the hidden-order phase, in addition to the well-known out-of-plane component $S_\perp \approx 0.01-0.04 ~\mu_B${/}U. $S_\parallel$ and $S_\perp $ components were separated by using the fact that only the components of the magnetic structure that are perpendicular to the scattering vector $Q$ contribute to the magnetic neutron scattering. We find no evidence for an in-plane magnetic moment $S_\parallel$. Based on the statistics of our measurement, we establish that the upper experimental limit for the size of any possible in-plane component is $S_{\parallel}^{max} \approx 1\times10^{-3} ~\mu_B${/}U. Analysis of diffuse neutron scattering shows no presence of short-range magnetic correlations within the measured limit. [Preview Abstract] |
Wednesday, March 5, 2014 11:39AM - 11:51AM |
M46.00003: The Hidden Order Gap and In-Gap Excitation Mode in URu$_2$Si$_2$ Revealed by Electronic Raman Scattering Hsiang-Hsi Kung, Ryan Baumbach, Eric Bauer, John A. Mydosh, Weilu Zhang, Verner K. Thorsm{\O}lle, Kristjan Haule, Girsh Blumberg The heavy fermion compound URu$_2$Si$_2$ displays a phase transition into the so called ``hidden order'' state at $T_{HO}=17.5\,$K. Using polarized electronic Raman scattering, we show that the Raman response in the $A_{2g}$ symmetry channel ($D_{4h}$): (1)~at high temperatures can be described by a Drude-like continuum with the scattering rate decreasing from 46\,cm$^{-1}$ at 300\,K to 16\,cm$^{-1}$ at 70\,K; (2)~develops a low energy peak due to spectral weight transfer through Fano interference in the temperature range of 70-20\,K; (3)~below $T_{HO}$ develops a gap of about 55\,cm$^{-1}$ in the continuum, and a sharp in-gap mode centered at 14\,cm$^{-1}$. In addition, we show that the real part of the static Raman susceptibility in the $A_{2g}$ symmetry is proportional to the \textit{c}-axis static magnetic susceptibility above $T_{HO}$. The implication of these observations will be discussed in the talk. [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:03PM |
M46.00004: Microwave Conductivity Measurements of URu$_2$Si$_2$ James Day, Mahyad Aghigh, Jordan Baglo, Ryan Baumbach, Eric Bauer, Doug Bonn Narrow, free-carrier spectra occur in the heavy fermion metals, in which the high quasiparticle effective mass renormalizes the width of the Drude conductivity peak from infrared frequencies, where it is found in more typical metals, down to the microwave region. This narrow peak has been observed [1] in a thin film of UPd$_2$Al$_3$, occurring with a Lorentzian lineshape due to the dominant defect-scattering in the film. We have taken microwave conductivity measurements on URu$_2$Si$_2$ in a temperature range in which the sample has entered into its hidden order state but above the superconducting transition. These measurements exhibit a narrow Lorentzian lineshape, indicating high sample purity and considerably reduced impurity scattering. If the inelastic scattering is sufficiently low, there is the possibility for an observation of electron-electron scattering. Results to date will be presented. \\[4pt] [1] Scheffler, M. $\textit{et al.}$, $\textit{Nature}$ $\textbf{438}$, 1135 (2005). [Preview Abstract] |
Wednesday, March 5, 2014 12:03PM - 12:15PM |
M46.00005: Optical study of the hidden order state in URu$_2$Si$_2$ Thomas Timusk, Jesse Hll, Toomas R{\~o}{\~o}m, Urmas Nagel, Taaniel Uleksin, Ricardo Lobo, Chris Homes We discuss recent optical experiments [1,2] both in the normal state above the hidden order transition at 17.5 K in URu$_2$Si$_2$ and in the hidden order state itself. In the normal state the focus is on the development of coherence as shown by the Drude peak and the pseudo-hybridization gap that develops at 12 meV. In the hidden order state a gap opens up with $2\Delta=6$ meV but its temperature evolution is not that of a mean field transition. To gain insight into the nature of the transitions we discuss the transfer of spectral weight between the various features in the optical conductivity spectrum as the temperature is changed. \\[4pt] [1] U. Nagel {\it et al.} PNAS {\bf 109} 19161 (2012).\\[0pt] [2] J. Hall {\it t al.} Phys. Rev. B {\bf 86}, 035132 (2012). [Preview Abstract] |
Wednesday, March 5, 2014 12:15PM - 12:27PM |
M46.00006: Anomalous Nernst effect of the heavy-fermion superconductor URu$_{2}$Si$_{2}$ Takuya Yamashita, Sho Tonegawa, Yugo Tsuruhara, Hiroaki Sumiyoshi, Satoshi Fujimoto, Tatsuma Matsuda, Yoshinori Haga, Etsuji Yamamoto, Yoshichika Onuki, Takasada Shibauchi, Yuji Matsuda The heavy-fermion material URu$_{2}$Si$_{2}$ exhibits the ``hidden order'' and superconducting phase transitions at T$_{\rm{HO}}$ = 17.5 K and T$_{\rm{SC}}$ = 1.4 K, respectively. Below T$_{\rm{HO}}$ a significant decrease of carrier density has been observed, and the remaining carriers condense into the superconducting state below T$_{\rm{SC}}$. The superconducting symmetry is suggested to be chiral d-wave with time reversal symmetry breaking. We have recently measured the Nernst coefficient ${\nu}$(T) in an ultraclean single crystal of URu$_{2}$Si$_{2}$ with RRR $\sim$ 700, which is much larger than the previous report [1]. We observed an increase of in $\nu$(T) below T$_{\rm{HO}}$ which shows an additional steep increase below $\sim$ 3T$_{\rm{SC}}$. The magnitude of $\nu$(T) is much larger than the previous report and reaches $\sim$ 200 $\mu$V/KT at 1 T. We show that such a giant Nernst effect in an ultraclean sample cannot be explained by conventional Gaussian superconducting fluctuations. Possible origins including fluctuations of exotic chiral superconductivity will be discussed.\\[4pt] [1] R. Bel $\it{et}$ $\it{al}$., Phys. Rev. B $\bf{70}$, 220501 (2004). [Preview Abstract] |
Wednesday, March 5, 2014 12:27PM - 12:39PM |
M46.00007: $^{29}$Si NMR study of the paramagnetic state of URu$_2$Si$_2$ under pressure Kent Shirer, Jason Haraldsen, Adam Dioguardi, John Crocker, Ching Lin, Marc Janoschek, Kevin Huang, Noravee Kanchanavatee, Brian Maple, Matthias Graf, Alexander Balatsky, Nicholas Curro We report $^{29}$Si nuclear magnetic resonance measurements in a single crystal of URu$_2$Si$_2$ in the hidden order, antiferromagnetic, and paramagnetic phases under pressure. We find evidence for partial suppression of the density of states below 30 K at ambient pressure. We study how this behavior varies under pressure as hidden order gives way to antiferromagnetism. We analyze the data in light of various recent models. [Preview Abstract] |
Wednesday, March 5, 2014 12:39PM - 12:51PM |
M46.00008: Abrupt electronic structure changes in URu$_{2}$Si$_{2}$ at the Hidden Order transition J.D. Denlinger, J.W. Allen, L. Dudy, Jeongsoo Kang, N.P. Butch, M.B. Maple In recent years, high-resolution angle-resolved photoemission (ARPES) measurements of URu$_{2}$Si$_{2}$ [1] have attempted to characterized the temperature dependent behavior of $f$-states close to the Fermi level in the range of photon energies of 7-31 eV and in a narrow $k$-space range around the surface zone center revealing varying ways in which energy shifts, backfolding of states and/or spectral weight sharpening correlate to the hidden order transition at 17.5K. In this study we expand the temperature dependent ARPES measurements to a broader range of photon energy and emission angles in order to probe the full 3-dimensional electronic structure. We find particular $k$-space regions close to incommensurate wave vector separation that exhibit dramatic electronic structure changes that are abrupt at the hidden order transition and whose evolution to higher temperatures correlates to a gradual Kondo coherence transition below $\sim$50K. A critical assessment of these electronic structure changes in relation to LDA band structure predictions is discussed. \\[4pt] [1] A.F. Santander-Syro, Nat. Phys. 2009; R. Yoshida, PRB 2010; G.L. Dakovski, PRB 2011; F.L. Boariu, PRL 2013; S. Chatterjee, PRL 2013; J.Q. Meng, PRL 2013. [Preview Abstract] |
Wednesday, March 5, 2014 12:51PM - 1:03PM |
M46.00009: Hybridization in Kondo lattice heavy fermions via quasiparticle scattering spectroscopy (QPS) Sanjay Narasiwodeyar, Matt Dwyer, Laura Greene, Wan Kyu Park, Eric Bauer, Paul Tobash, Ryan Baumbach, Filip Ronning, John Sarrao, Joe Thompson, Paul Canfield Band renormalization in a Kondo lattice via hybridization of the conduction band with localized states has been a hot topic over the last several years. In part, this has to do with recently reignited interest in the hidden order problem in URu$_{2}$Si$_{2}$. Despite recent developments regarding the electronic structure in this compound, it remains to be resolved whether the hidden order phase transition is related to the opening of a hybridization gap. Our quasiparticle scattering spectroscopy (QPS) has shown they are not related directly [1]. This can be understood naturally since in principle band renormalization does not involve symmetry breaking. To deepen our understanding, we extend to other Kondo lattice compounds. For instance, when applied to YbAl$_{3}$, a vegetable heavy-fermion system, QPS reveals conductance signatures for hybridization in a Kondo lattice such as asymmetric Fano background along with characteristic energy scales. Presenting new results on these materials, we will discuss a broader picture.\\[4pt] [1] W. K. Park \textit{et al}., PRL \textbf{108}, 246403 (2012). [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:15PM |
M46.00010: Temperature Dependence of the London Penetration Depth and Nodal Gap Structure of UPt$_3$ from Small Angle Neutron Scattering W.P. Halperin, W.J. Gannon, C. Rastovski, K.J. Schlesinger, C. Steiner, M.R. Eskildsen, A.B. Vorontsov, J. Hlevyack, J. Gavilano, U. Gasser, G. Nagy Despite the fact that the heavy-fermion superconductor UPt$_3$ has attracted substantial experimental and theoretical attention for nearly thirty years, the nature of the unconventional superconducting order parameter is not settled. There are many theories that attempt to explain the superconducting state, all of which differ in the nodal structure of the superconducting gap. Our recent measurements of the temperature dependence of the small angle neutron scattering from the superconducting vortex lattice provides a bulk measurement of the anisotropic temperature dependence of the London penetration depth and thus a direction specific probe of quasi particle excitations sensitive to gap nodes. Our measurements and their theoretical analysis favor an odd parity, time reversal symmetry breaking order parameter with $E_{2u}$ symmetry. [Preview Abstract] |
Wednesday, March 5, 2014 1:15PM - 1:27PM |
M46.00011: History Dependence of the Vortex Lattice Rotation in the B-phase of UPt$_3$ M.R. Eskildsen, W.J. Gannon, W.P. Halperin, C. Rastovski, C. Steiner, U. Gasser, G. Nagy, J.L. Gavilano The unconventional superconductor UPt$_3$ is widely believe to be a triplet superconductor, where the low temperature superconducting B-phase is a chiral state. We have performed small angle neutron scattering from the vortex lattice (VL) of UPt$_3$ in the B-phase with magnetic fields parallel to the hexagonal $c$-axis. Our field dependent measurements show scattering from multiple VL domains, with a subtle magnetic field history dependence of the domain orientation; VL's prepared with the magnetic field parallel or antiparallel with respect to the angular momentum from the circulating screening currents show different field history dependence. These results indicate a coupling of a chiral superconducting order parameter with the applied magnetic field, in agreement with other recent results. [Preview Abstract] |
Wednesday, March 5, 2014 1:27PM - 1:39PM |
M46.00012: NMR, Thermodynamics and Magnetic Disorder in Kondo Intermetallics: UCu4Pd and UCu4Ni Oscar Bernal, Ariana Valdez, D.E. MacLaughlin, G.R. Stewart We compare and contrast the static magnetic character of UCu4Pd and UCu4Ni as probed by local Cu-NMR and bulk thermodynamic measurements. For the Pd case, evidence for magnetic disorder has been well established by most bulk (magnetization, specific heat, etc.) and local measurements, particularly Cu-NMR. For the Ni case, on the contrary, the local Cu-NMR data appear to suggest that thermodynamic divergences are not directly controlled by static magnetic inhomogeneity, even though the Ni material possesses a higher degree of structural disorder than UCu4Pd. We discuss to what extent Cu-NMR can be used to elucidate differences between the two systems and shed light on the notion of disorder-driven quantum criticality. [Preview Abstract] |
Wednesday, March 5, 2014 1:39PM - 1:51PM |
M46.00013: Low Temperature Specific heat of U$_{2}$PtC$_{2}$ Roman Movshovich, Franziska Weickert, Eric D. Bauer, Joe D. Thompson, Ni Ni, Filip Ronning We present specific heat data of the moderately heavy superconductor U$_{2}$PtC$_{2}$ with T$_{\mathrm{c}} =$ 1.34 K, and normal state Sommerfeld coefficient $\gamma =$ C/T $\approx $ 150 mJ/mol K$^{2}$, at temperatures down to below 100 mK and in fields up to 9 T, exceeding the superconducting critical field. Zero-field data show systematic deviation from the weak-coupling BCS fit, with excess contribution at low temperature. The field evolution of the residual $\gamma _{0}$(T$=$0) shows $\surd $H dependence for H \textless 1 T. Together, these results suggest an unconventional nature of superconductivity in this compound. [Preview Abstract] |
Wednesday, March 5, 2014 1:51PM - 2:03PM |
M46.00014: Superconductivity and magnetism in the doping series U$_{2}$Rh$_{\mathrm{x}}$Pt$_{\mathrm{(1-x)}}$C$_{2}$ Nicholas Wakeham, Ni Ni, Darrick Williams, Eric Bauer, Joe Thompson, Filip Ronning U$_{2}$PtC$_{2}$ has been known for many years to exhibit nearly-heavy-fermion behavior, as well as superconductivity, T$_{\mathrm{c}}$ $\sim$ 1.5 K. Little is known about the nature of the superconductivity, but many other uranium based heavy fermion superconductors, such as UPt$_{3}$ and UBe$_{13}$, have been shown to be unconventional. U$_{2}$RhC$_{2}$ also shows nearly-heavy-fermion behavior, but it is non-superconducting and reported to be antiferromagnetic, T$_{\mathrm{N}}$ $\sim$ 18 K. These observations have motivated our study of the doping series of U$_{2}$Rh$_{\mathrm{x}}$Pt$_{\mathrm{(1-x)}}$C$_{2}$ in order to investigate the evolution from the antiferromagnetic to the superconducting groundstate, as well as the role of the antiferromagnetism in the superconductivity. Through measurement of the resistivity, magnetic susceptibility and heat capacity of polycrystalline samples, we show the suppression of antiferromagnetism, the presence of competing ferromagnetism, and emergence of superconductivity with doping. Furthermore, we present evidence that the emergence of superconductivity, which deviates from single-gap BCS theory, is not directly related to the suppression of antiferromagnetism. [Preview Abstract] |
Wednesday, March 5, 2014 2:03PM - 2:15PM |
M46.00015: The Fermi volume as a probe of hidden order Alix McCollam, Bohdan Andraka, Stephen Julian Quantum oscillations are a highly sensitive probe of electronic structure, and provide valuable information about the Fermi surface and quasiparticle properties. We demonstrate that the volume of the Fermi surface, measured very precisely using de Haas-van Alphen (dHvA) oscillations, can be used to probe changes in the nature and occupancy of localized electronic states. In systems with unconventional ordered states, this allows an underlying electronic order parameter to be followed to very low temperatures. PrOs$_4$Sb$_{12}$ has an unusual antiferroquadrupolar (AFQ) ordered phase that forms at low temperature and high magnetic field. We find that the phase of dHvA oscillations is sensitively coupled, through the Fermi volume, to the configuration of Pr f-electron states that are responsible for AFQ order. Specifically, a given sheet of the Fermi surface expands or shrinks as the occupancy of competing localized Pr crystal field states changes. In addition, the low temperature sensitivity of the dHvA effect reveals a strong and previously unrecognized influence of hyperfine coupling on the order parameter below 300mK within the AFQ phase. Our approach to quantum oscillations in PrOs$_4$Sb$_{12}$ might be more widely applicable and provide new insights in hidden order systems. [Preview Abstract] |
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