Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session G19: URu2Si2 Hidden Order and other U-based Systems |
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Sponsoring Units: DCMP Chair: Jason Jeffries, Lawrence Livermore National Lab Room: 321 |
Tuesday, March 19, 2013 11:15AM - 11:27AM |
G19.00001: Precursor Hidden Order Fluctuations in URu$_2$Si$_2$ Peter Riseborough It has been proposed that the Hidden Order phase in URu$_2$Si$_2$ is a combined spin-orbit density wave, which is stabilized by the effect of the spin-flip part of the inter-orbital Hund's rule exchange. The transition involved the nesting of bands with different orbital characters and results in a partial gapping of the Fermi-surface. Above the transition temperature, the system exhibits combined spin and orbital fluctuations whose lifetimes and amplitudes increase as the temperature is reduced towards the critical temperature. These fluctuations produces hot-spots on the Fermi-surface, modifies the electronic structures as precursor to the opening of the gap. We examine the dependence of precritical fluctuations on the transition temperature. As the critical temperature is reduced to zero, it is found that the nature of the transition changes from second-order to first-order. [Preview Abstract] |
Tuesday, March 19, 2013 11:27AM - 11:39AM |
G19.00002: Charge-$2e$ Skyrmion condensate in a hidden order state Chen-Hsuan Hsu, Sudip Chakravarty A higher angular momentum ($l=2$) $d$-density wave, a mixed triplet and a singlet, interestingly, admits skyrmionic textures. The Skyrmions carry charge $2e$ and can condense into a spin-singlet $s$-wave superconducting state. In addition, a charge current can be induced by a time-dependent inhomogeneous spin texture, leading to quantized charge pumping. The quantum phase transition between this mixed triplet $d$-density wave and skyrmionic superconducting condensate likely leads to deconfined quantum critical points. We suggest connections of this exotic state to electronic materials that are strongly correlated, such as the heavy fermion URu$_2$Si$_2$. At the very least, we provide a concrete example in which topological order and broken symmetry are intertwined, which can give rise to non-BCS superconductivity. [Preview Abstract] |
Tuesday, March 19, 2013 11:39AM - 11:51AM |
G19.00003: Evidence for an orbital moment in the superconducting state of URu$_2$Si$_2$ Gang Li, Qiu Zhang, Daniel Rhodes, Bin Zheng, Pallab Goswami, P. Tobash, Filip Ronning, Joe D. Thompson, Eric D. Bauer, Luis Balicas URu$_2$Si$_2$ was suggested to be a chiral \emph{d}-wave superconductor with a $k_z (k_x \pm ik_y)$ orbital component for the Cooper pair wave-function. This state breaks time-reversal symmetry due to the orbital moment associated with this pair wave-function. Here, we report torque magnetometry in URu$_2$Si$_2$ at high fields and very low temperatures revealing a change in the sign of the magnetic hysteresis for $H \rightarrow H_{c2}$, and for angles $15^{\circ}$ away from the \emph{ab}-plane, i.e. from a clear diamagnetic response dominated by the pinning of vortices to a state with a much smaller but paramagnetic-like hysteretic response which \emph{disappears} at $H_{c2}$. If diamagnetism results from screening super-currents, we conclude that this hysteretic paramagnetic response must result from super-currents circulating in the opposite sense which generate an effective moment as expected for a chiral superconductor. [Preview Abstract] |
Tuesday, March 19, 2013 11:51AM - 12:03PM |
G19.00004: Global k-space perspective of temperature-dependent U f-states in URu$_{2}$Si$_{2}$ J.D. Denlinger, L. Dudy, J.-S. Kang, J.W. Allen, N.P. Butch, M.B. Maple In recent years, high-resolution angle-resolved photoemission (ARPES) measurements [1] have identified a narrow band of $f$-states close to the Fermi level in URu$_{2}$Si$_{2}$ whose temperature dependent spectral weight and/or energy shifts correlate to the hidden order transition at 17.5K. These $f$-states have been observed close to normal emission at a few select photon energies of $\sim$ 6, 21 and 30 eV corresponding to momentum space locations close to Z, $\Gamma $ and Z points respectively. We attempt to provide a more global $k$-space context for the presence of such $f$-states and their relation to the bulk Fermi surface topology using synchrotron-based wide-angle and photon energy-dependent ARPES mapping of the electronic structure. In addition, x-ray polarization and small-spot spatial dependences are exploited to assist identification of these narrow-band $f$-states and their relation to specific U- or Si-terminations of the cleaved surface.\\[4pt] [1] A.F. Santander-Syro, Nat. Phys. 2009; R. Yoshida, Phys. Rev. B 2010; G.L. Dakovski, Phys. Rev. B 2011. [Preview Abstract] |
Tuesday, March 19, 2013 12:03PM - 12:15PM |
G19.00005: Formation of coherent heavy fermion states at the hidden order transition in URu$_2$Si$_2$, as seen by ARPES Shouvik Chatterjee, Jan Trinckauf, Torben Hanke, Daniel Shai, John Harter, Travis Williams, Graeme Luke, Jochen Geck, Kyle Shen We present high-resolution angle-resolved photoemission (ARPES) spectra that allow us to delineate the evolution of the low energy electronic structure of the heavy-fermion superconductor URu$_2$Si$_2$ across the hidden order (HO) transition. By employing a range of excitation photon energies, we are able to disentangle various features in the electronic structure which, to date, have not been clearly identified. In contrast to the conventional Kondo lattice scenario, we find that precisely at T$_{\mathrm{HO}}$, the low energy electronic structure changes due to hybridization from incoherent and localized f states to a coherent heavy fermion liquid. We also observe a sharp drop in the scattering rate upon cooling through T$_{\mathrm{HO}}$, suggesting that the large scattering rate is caused by fluctuations in the order parameter. Our findings place clear constraints on the possible theoretical models for the HO state while clarifying a few of the apparently inconsistent observations of the previous ARPES measurements. [Preview Abstract] |
Tuesday, March 19, 2013 12:15PM - 12:27PM |
G19.00006: Heavy fermion phases probed by temperature dependent tunneling spectroscopy Ana Maldonado, Isabel Guillam\'on, Jose Gabriel Rodrigo, Hermann Suderow, Sebasti\'an Vieira, Dai Aoki, Jacques Flouquet Heavy fermions offer a rich physical phenomenology at very low temperatures, exhibiting different phase transitions on cooling that determine their electronic properties. Their ground states cover many electronic interactions, such as Kondo effect, superconducting or long range magnetic ones and, eventually, their coexistence. Thus, exploring the local electronic properties of these systems using scanning tunneling microscopy/spectroscopy (STM/S) at different temperatures is essential. In this communication, tunneling spectroscopy measurements using a superconducting tip of Al in the superconducting phase of URu$_{2}$Si$_{2}$\footnote{A. Maldonado et al., \textit{Phys. Rev. B} $\mathbf{85}$, 214512 (2012)} and using one of Au in the paramagnetic and antiferromagnetic phases of, respectively, CeRu$_{2}$Si$_{2}$ and CeRh$_{2}$Si$_{2}$\footnote{A. Maldonado et al., Accepted in \textit{J. Phys.: Condens. Matter}} will be discussed. The features found in the tunneling spectroscopy of each compound at 0.15K and their respective thermal evolution reflect the formation of different electronic ground states. [Preview Abstract] |
Tuesday, March 19, 2013 12:27PM - 12:39PM |
G19.00007: From hidden order to magnetic order: Optical conductivity reveals new behavior in URu$_2$Si$_2$ Jesse Hall, Noravee Kanchanavatee, Marc Janoschek, Kevin Huang, Nicholas Butch, Brian Maple, Thomas Timusk As a new generation of experimental techniques is brought to bear against the heavy-Fermion compound URu$_2$Si$_2$, striking new details about the electronic structure changes at the mysterious hidden order (HO) transition are becoming clear. Far infrared optical conductivity measurements were performed on oriented samples of URu$_2$Si$_2$ doped with both Fe and Re. While Re-doping pushes the material towards ferromagnetism, Fe-doping substitutes for hydrostatic pressure and enhances the temperature of the HO transition slightly before pushing the material into antiferromagnetism. Optical conductivity measurements have revealed new information about the charge dynamics at the transition, and how these evolve with doping. Both the structure and energy of the gap are altered as the material is pushed towards magnetic ordering. Comparison is made between the gap seen in optical conductivity and the charge gaps seen in scanning tunneling spectroscopy and ARPES, as well as the gaps in the magnetic excitation spectrum seen in neutron scattering. [Preview Abstract] |
Tuesday, March 19, 2013 12:39PM - 12:51PM |
G19.00008: NMR Evidence for psuedogap in URu$_2$Si$_2$ Kent Shirer, Adam Dioguardi, John Crocker, Nicholas apRoberts-Warren, Abigail Shockley, Ching Lin, David Nisson, Jason Cooley, Brian Maple, Jason Haraldsen, Matthias Graf, Nicholas Curro We report $^{29}$Si NMR measurements in single crystals and aligned powders of URu$_2$Si$_2$ in the hidden order and paramagnetic phases. In the paramagnetic phase, the spin lattice relaxation data reveal evidence of spin fluctuations of U moments. Furthermore, we find evidence for partial suppression of density of states below 30 K. [Preview Abstract] |
Tuesday, March 19, 2013 12:51PM - 1:03PM |
G19.00009: Spin Correlations in the Different Phases of URu$_2$Si$_2$ Travis J. Williams, H. Barath, Z. Yamani, J.A. Rodriguez-Rivera, J.B. Leao, J.D. Garrett, G.M. Luke, W.J.L. Buyers, C. Broholm We report a neutron scattering study of the magnetic excitation spectrum in three temperature and pressure driven phases of URu$_2$Si$_2$: the paramagnetic, `hidden order' and antiferromagnetic phases. The experiment was conducted using the novel neutron scattering spectrometer MACS at the NIST Center for Neutron Research[1]. Wide-angle detector coverage offers comprehensive scattering data covering an entire plane in momentum space with excellent energy resolution. The ambient pressure data show a magnetic excitation spectrum characteristic of Fermi surface nesting in the paramagnetic phase and the development of a gap in the excitation spectrum upon cooling through the T$_C$~=~17.5~K phase transition. The efficiency of MACS allowed a comprehensive data set in the high-pressure phase. Throughout the (H0L) scattering plane we find qualitatively similar excitations as in the hidden order phase though with a substantial reduction in the overall spectral weight and an upward shift in energy. These data should allow a critical evaluation of recent theoretical work to understand the small and large moment phases of URu$_2$Si$_2$. [1] J.A. Rodriguez-Rivera, Meas. Sci. Technol. 19, 034023 (2008). [Preview Abstract] |
Tuesday, March 19, 2013 1:03PM - 1:15PM |
G19.00010: Phonon Behavior in the Hidden Order state of the Heavy Fermion Superconductor URu$_2$Si$_2$ Dillon Gardner, Craig Bonnoit, Travis Williams, Graeme Luke, Young Lee The heavy fermion compound URu$_2$Si$_2$ has generated much interest after the initial discovery of coexisting superconductivity and magnetism. Subsequent measurements revealed a phase transition at T=17.5 K into what is referred to as the ``hidden order'' state. The order parameter of this state remains unknown. Anomalous behavior in both the lattice component of thermal conductivity and thermal expansion parameters suggest that the phonons may also exhibit anomalous behavior that can shed light on the nature of the Hidden Order. We present inelastic X ray scattering measurements of lattice dynamics in both the hidden order phase and high temperature phase. [Preview Abstract] |
Tuesday, March 19, 2013 1:15PM - 1:27PM |
G19.00011: Anisotropic phonon softening in URu$_{2}$Si$_{2}$ Nicholas Butch, Michael Manley, Jason Jeffries, Marc Janoschek, Kevin Huang, Brian Maple, Jeffrey Lynn We studied the low-energy phonons of URu$_{2}$Si$_{2}$ via inelastic neutron scattering. At the wave-vectors associated with magnetic excitations, the phonons show surprisingly little modification. However, we find important temperature and direction dependence of the phonons in the basal plane. Possible ramifications for the symmetry of the hidden order will be discussed. [Preview Abstract] |
Tuesday, March 19, 2013 1:27PM - 1:39PM |
G19.00012: High-magnetic field magnetostriction and thermal expansion in URu$_2$Si$_2$ V.F. Correa, S. Francoual, M. Jaime, N. Harrison, A. Lacerda, T.P. Murphy, E.C. Palm, S.W. Tozer, P.A. Sharma, J.A. Mydosh We report high magnetic field (up to $\mu_0$H = 45 T) $c$-axis thermal expansion and magnetostriction experiments on URu$_2$Si$_2$ single crystals. The sample length change $\Delta$L$_c$(T$_{HO}$)/L$_c$ associated with the transition to the ``hidden order'' phase becomes increasingly discontinous as the magnetic field is raised above 25 T. The re-entrant ordered phase III is clearly observed in both the thermal expansion $\Delta$L$_c$(T)/L$_c$ and magnetostriction $\Delta$L$_c$(B)/L$_c$ above 36 T, in good agreement with previous results. The sample length is also discontinous at the boundaries of this phase, mainly at the upper boundary. A change in the sign of the coefficient of thermal-expansion is observed at the metamagnetic transition (B$_M$ ? 38 T) which is likely related to the existence of a quantum critical end point. See V.F. Correa et al., Phys. Rev. Lett. (in the press). [Preview Abstract] |
Tuesday, March 19, 2013 1:39PM - 1:51PM |
G19.00013: Revealing the electronic structure of USb$_{2}$ using femtosecond optical pulses Jingbo Qi, Tomasz Durakiewicz, E. Bauer, R. Baumbach, K. Gofryk, T. Klimczuk, P. Riseborough, Antoinette Taylor, Rohit Prasankumar USb$_{2}$ is a very interesting moderately heavy system, as it displays dispersive 5f bands as well as the first example of a clear kink structure in f-electron systems. This material also exhibits a renormalized zone-centered hole-like band, driven by boson-mediated interband scattering processes. Employing ultrafast optical spectroscopy, we explored the nature of the boson participating in this band renormalization, and explicitly characterized the gap structures near the Fermi surface in USb$_{2}$ for the first time. Our results reveal new physical properties of this material, which have not previously been unveiled by other experimental methods. [Preview Abstract] |
Tuesday, March 19, 2013 1:51PM - 2:03PM |
G19.00014: Non-Fermi vs. Inhomogeneous-Fermi Liquid behaviour in UCu$_4$Ni in the context of the Kondo Disorder Model Ariana Valdez, Oscar Bernal, G.R. Stewart, J.S. Kim UCu$_4$Ni is a site-disordered material with diverging thermodynamic and anomalous transport properties. Local nuclear magnetic resonance (NMR) experiments in combination with bulk magnetic susceptibility $\chi$ measurements performed on the same samples indicate that the low-temperature divergence of $\chi$ might be due in part to the presence of paramagnetic impurities. In this contribution, we describe the magnetization in terms of a Kondo disorder model and extract a set of parameters of the distribution of Kondo temperatures, which indicate that the low temperature side of the distribution does not have sufficient area to accommodate a non-Fermi liquid divergence. We use the same parameters to subsequently calculate the specific heat $C$ and to extrapolate to low temperatures, which allows us to compare with the known divergence of the magnetic contribution to $C/T$ below 10~K. We discuss to what extent the physics of this material is that of a non-Fermi liquid as opposed to an inhomogeneous Fermi fluid. [Preview Abstract] |
Tuesday, March 19, 2013 2:03PM - 2:15PM |
G19.00015: The Effects of Grinding on the Magnetic Susceptibility of UCu$_{3.95}$Ni$_{1.05}$ Carlos Sanchez, Carmen Quen, Edith Soto, Oscar Bernal, G.R. Stewart The effects of grinding on the magnetic susceptibility of UCu$_{3.95}$Ni$_{1.05}$ were studied in order to understand magnetization measurements in this material. Substantial information was recovered from these experiments, which were done at temperatures ranging from 3K to 300K and magnetic fields from 500 Oe to 4.75 kOe. For instance, a new and unexpected ferromagnetic (FM) phase transition was found at about 150~K in both ingot and powder samples. Similarly the magnetic properties of the powder seem to differ slightly from the ingot's. The powder's magnetic susceptibility $\chi_{\rm pwd}$ appears greater than the ingot's $\chi_{\rm ing}$ at all temperatures measured, with the difference $\Delta\chi=\chi_{\rm pwd}-\chi_{\rm ing}$ increasing with decreasing temperature. We analyze the observed $\Delta\chi$ in terms of two potential sources: impurities added to the powder during the grinding process and the effects of sample geometries in combination with the presence of a second (FM) phase in the studied material. We discuss how the measured differences might affect the study of the physics of this non-Fermi liquid/quantum critical compound. [Preview Abstract] |
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