Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session Q12: Focus Session: Hidden Order and Heavy Fermions |
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Sponsoring Units: DCMP Chair: Lia Krusin-Elbaum, IBM T.J. Watson Research Center Room: Morial Convention Center 203 |
Wednesday, March 12, 2008 11:15AM - 11:51AM |
Q12.00001: Exotic Superconducting State Embedded in the Hidden Order Phase of URu$_2$Si$_2$ Invited Speaker: The heavy-Fermion compound URu$_2$Si$_2$ has mystified researchers since the superconducting state ($T_c$~=~1.5~K) is embedded within the ``hidden order" phase ($T_h$~=~17.5~K). According to several experimental observations, most of the carriers disappear below $T_h$ resulting in a density one order of magnitude smaller than in other heavy-Fermion superconductors. Superconductivity with such a low density is remarkable since the superfluid density is very low in some way reminiscent of underdoped cuprates; the superconductivity by itself is an exceptional case of pairing among heavy electrons with a long Fermi-wavelength in a nearly semimetallic system. Moreover, pressure studies reveal that the superconductivity coexists with the hidden order but is suppressed by antiferromagnetic ordering. Here, we report charge and thermal transport measurements on ultraclean single crystals of URu$_2$Si$_2$ ($RRR\sim700$) down to 30~mK ($T_c$/50), which reveal a number of unprecedented superconducting properties. The uniqueness is best highlighted by field-induced superconductor-insulator-like first-order transition at the upper critical fields, which is a direct consequence of the electronic structure imposed by the hidden order. The results provide strong evidence for a new type of unconventional superconductivity with two distinct gaps having different nodal topology. We propose a gap function with chiral $d$-wave form $ \Delta_{k} \propto k_z (k_x \pm i k_y ) $ [1]. We also report a distinct flux line lattice melting transition with outstanding characters and a formation of the quasiparticle Bloch state in the periodic flux line lattice in this ultraclean system [2]. The intriguing superconducting state of URu$_2$Si$_2$ adds a unique and exciting example to the list of unconventional superconductors.\\ ~ [1]~Y.~Kasahara {\it et al.} Phys. Rev. Lett. {\bf 99}, 116402 (2007). [2]~R.~Okazaki {\it et al.} arXiv:0710.2382 [Preview Abstract] |
Wednesday, March 12, 2008 11:51AM - 12:03PM |
Q12.00002: Neutron scattering studies of the quantum critical point of CeAuSb2 John Janik, Chris Wiebe, Haidong Zhou, Ben Ueland, Ying Chen, Jeff Lynn, Zachary Fisk, H. Le, Wei Bao, Youn-Jung Jo, Luis Balicas We present neutron scattering results on CeAuSb$_{2}$, a quantum critical material whose critical point in revealed in magnetic field. We find incommensurate ordering, indicative of itinerant electron physics. The incommensurate feature seem to be directly related to metamagnetic transitions. [Preview Abstract] |
Wednesday, March 12, 2008 12:03PM - 12:15PM |
Q12.00003: Magnetic and electrical transport study of single crystal YbAu$_{2}$ H. Ryu, E.D. Mun, S.L. Bud'ko, P.C. Canfield Single crystals of YbAu$_{2}$ grown by flux method are studied by low temperature and high magnetic field measurements of the electrical resistivity and magnetization. For zero field, three magnetic transitions at 1 K, 1.5 K and 2.8 K are observed in the resistivity data, the lower two transitions are suppressed by an applied magnetic field. At low temperatures metamagnetism is observed in the magnetization and magnetoresistance data. Strong anisotropy between the tetragonal ab plane and c-axis, is revealed in both magnetization and transport measurements. The $H-T$ phase diagram for applied field along the \textit{ab} plane is constructed by electrical transport measurements. The anisotropy can be explained with a crystalline electric field (CEF) model. YbAu$_{2}$ can be characterized as Kondo lattice compound with strong CEF splitting. [Preview Abstract] |
Wednesday, March 12, 2008 12:15PM - 12:27PM |
Q12.00004: A Novel Low-Temperature Phase in Strongly Correlated CePd$_{3}$Ga$_{8}$ Qing'An Li, J.F. Mitchell, K.E. Gray, Robin Macaluso The specific heat, C$_{p}$, of CePd$_{3}$Ga$_{8}$ strongly supports the presence of two phase transitions, which are consistent with magnetization data. The 11 K transition (suppressed for fields, B$>$3 T) is also seen in the resistivity, whereas the 6 K transition is not. The resistivity is anisotropic both with respect to field and current directions, while its temperature dependence is similar to UCd$_{11}$ and CeAuSb$_{2}$. Both resistivity and C$_{p}$ are affected by magnetic fields up to about 30 K and possible connections will be discussed. [Preview Abstract] |
Wednesday, March 12, 2008 12:27PM - 12:39PM |
Q12.00005: Is the Low-Temperature Phase in CePd$_{3}$Ga$_{8}$ Fascinating or Just Novel? K.E. Gray, J.F. Mitchell, H. Claus, Qing'An Li, Robin Macaluso Magnetization data for CePd$_{3}$Ga$_{8}$ strongly support the presence of two phase transitions, also seen in specific heat, C$_{p}$. The 11 K transition (suppressed for fields, B$>$3 T) has similarities to UCd$_{11}$ and CeAuSb$_{2}$, but the lower temperature phase (T$<$6 K, B$<$2.5 T) is novel and its nature is a mystery. Its uniaxial magnetic anisotropy implies that CePd$_{3}$Ga$_{8}$ is an effective Ising system for the Ce spins, likewise consistent with C$_{p}$. The phase diagram of this fascinating material will be discussed in terms of combined magnetization, conductivity, C$_{p}$ and neutron scattering data. [Preview Abstract] |
Wednesday, March 12, 2008 12:39PM - 12:51PM |
Q12.00006: Field-induced magnetic phase transition in antiferromagnetic YbPtSi Yuri Janssen, Yuen Yiu, Peter Khalifah, Meigan Aronson We have studied single crystals of the orthorhombic intermetallic compound YbPtSi. Here we present results of anisotropic field-and-temperature dependent magnetization and specific heat. Magnetization isotherms measured between 1.8 K and the ordering temperature of 4.65 K show a sudden anomalous increase in magnetization. This phase transition becomes sharper and takes place at progressively higher fields as temperature decreases. Measurements of field-and-temperature dependent specific heat above 0.4 K confirm this magnetic phase transition above 1.8 K, and allow us to draw anisotropic magnetic phase diagrams down to 0.4 K. These phase diagrams indicate that the magnetic phase transition in YbPtSi can be brought close to zero temperature in relatively modest applied fields, $\sim$ 3.5 T for the hard magnetization direction. The critical line is well described by $T_N(H)/T_N(0) = (1-(H_C(T)/H_C(0))^2)^{0.3}$, very different from quasi-one-dimensional or two-dimensional quantum critical antiferromagnets. [Preview Abstract] |
Wednesday, March 12, 2008 12:51PM - 1:03PM |
Q12.00007: Magnetic Order in single-crystalline YbPtSi Yuen Yiu, Yuri Janssen, Peter Khalifah, Meigan Aronson, Moosung Kim, Marcus Bennett We report the first measurements on YbPtSi, which we synthesized as single crystals by means of flux growth from Indium. Single crystal x-ray diffraction measurements find that the YbPtSi crystal structure is the orthorhombic Co$_{2}$Si-type, with one crystallographic site for Yb. Magnetic susceptibility measurements find Curie-Weiss behavior above 100 K with a moment of 4.35 $\mu _{B}$, close to the 4.54 $\mu _{B}$ expected for trivalent Yb.~ Measurements of the heat capacity find a mean field-like magnetic ordering transition at T=4.65K. DC-susceptibility measurements show substantial single ion anisotropy, but also exhibit a peak at 4.65 K, indicating possible~antiferromagnetic ordering. The electrical resistivity is metallic, and the magnetic ordering is accompanied by a change in slope. The magnetic entropy amounts to only about 65 {\%} of Rln2 expected from an ordering Yb ground state doublet at the ordering temperature, suggesting a possible role for the Kondo effect. Our measurements indicate that YbPtSi is an unusual example of an Yb-based Kondo lattice system, ordering at an unusually high temperature. [Preview Abstract] |
Wednesday, March 12, 2008 1:03PM - 1:15PM |
Q12.00008: Angle resolved photoemission studies of YbRh$_2$(Si$_{1-x}$Ge$_x$)$_2$ S.-K. Mo, K. Tanaka, N. Mannella, C. Capan, D.J. Kim, Z. Fisk, Z. Hussain, Z.-X. Shen YbRh$_2$(Si$_{1-x}$Ge$_x$)$_2$ has attracted a lot of attention as the first Yb-based system with a quantum critical point (QCP) at $x \sim 0.05$. The QCP can be tuned by either magnetic field or chemical substitution, and non Fermi liquid properties have been observed in the vicinity of it. We present high-resolution angle resolved photoemission data on this compound as a function of Ge-doping. The result will be discussed in conjunction with various theoretical proposals on the Fermi surface topology of this material. [Preview Abstract] |
Wednesday, March 12, 2008 1:15PM - 1:27PM |
Q12.00009: High Pressure Studies of CeIn$_{3}$ in High Magnetic Fields Kenneth Purcell, Jason Cooley, Rongwei Hu, Ross McDonald, Cedomir Petrovic, Stanley Tozer High pressure and strong magnetic fields are useful tools for studying the relationship between the antiferromagnetism and unconventional superconductivity observed in the heavy fermion superconductor CeIn$_{3}$.$^{1,2}$ We report high pulsed magnetic field (up to 55 T) pressure studies of single crystal CeIn$_{3}$ utilizing the change in the resonant frequency of a tunnel diode oscillator (TDO) as a contactless means of measuring the skin depth of the crystal. An anomaly in the skin depth was observed at $\sim $42 T and was found to be driven to lower fields with increasing pressure. The relationship of the observed anomaly with the nature of the Fermi surface and the formation of a superconducting state at $\sim $200 mK and 27 kbar will be discussed. 1. N. Harrison et al, preprint arXiv:07062387 2. N. D. Mathur et al, Nature, 394, 39 (1998) [Preview Abstract] |
Wednesday, March 12, 2008 1:27PM - 1:39PM |
Q12.00010: Effects of Rhenium doping on the high magnetic field versus temperature phase diagram of URu$_{2}$Si$_{2}$ Sonia Francoual, Neil Harrison, Marcello Jaime, Chuck Mielke, Alex Lacerda, Frederik Fabris, Nicholas Butch, Brian Maple Rhenium doping of URu$_{2}$Si$_{2}$ yields a heavy fermion compound U(Ru$_{1-x}$Re$_{x})_{2}$Si$_{2}$ in which the Hidden Order (T$_{N}$ = 17 K) is suppressed at x = 0.05 and ferromagnetism and non Fermi liquid behavior coexist below 10 K from x = 0.15. In the present study, low temperature and high magnetic field resistivity and magnetization measurements are carried out in U(Ru$_{1-x}$Re$_{x})_{2}$Si$_{2}$ single-crystal samples up to x = 0.15 in order to investigate the effects of rhenium doping on the robustness of the multiple ordered phases previously identified in URu$_{2}$Si$_{2}$ around the putative quantum critical point (QCP) at 37 $\pm $ 1 T and the properties of the underlying metamagnetic Fermi liquid as the ferromagnetic region is approached. It is shown that the dilute substitution of Re in place of Ru in URu$_{2}$Si$_{2}$ yields a complete suppression of the ordering at the QCP at x = 0.04 and postpones to higher field the metamagnetic transition in agreement with an increased hybridization of the f electrons with the conduction electrons. [Preview Abstract] |
Wednesday, March 12, 2008 1:39PM - 1:51PM |
Q12.00011: Unconventional Magnetic Scaling Exponents near a $T=0$ Transition in URu$_{2-x}$Re$_{x}$Si$_{2}$ Nicholas P. Butch, Benjamin T. Yukich, M. Brian Maple Substituting Re for Ru in the heavy fermion compound URu$_{2}$Si$_{2}$ suppresses the hidden order and superconducting transitions and gives rise to long range ferromagnetism. From electrical transport, specific heat, and magnetic susceptibility studies of single crystals of URu$_{2-x}$Re$_{x}$Si$_{2}$, $0 \leq x \leq 0.6$, it is apparent that the non-Fermi liquid behavior first observed in polycrystalline samples is indeed a robust phenomenon intrinsic to the bulk material. We present a recent investigation of the magnetization of URu$_{2-x}$Re$_{x}$Si$_{2}$ single crystals, wherein it is demonstrated that a scaled Arrott analysis can be performed to extract scaling exponents describing the magnetic transition from well into the ferromagnetic phase down to its onset. The variation of the exponents with $x$ is discussed within the context of the observed non-Fermi liquid behavior. [Preview Abstract] |
Wednesday, March 12, 2008 1:51PM - 2:03PM |
Q12.00012: The linear and non-linear magnetic susceptibility of $\mathrm{URu_{2}Si_{2}}$ in hydrostatic pressure G.J. MacDougall, G.M. Luke, T. Goko, J.D. Garrett The heavy-fermion material $\mathrm{URu_{2}Si_{2}}$ has long been a topic of interest due to the mysterious `hidden order' transition at $T_{0}$=17.5K. Though the exact nature of this order is still a matter of great debate, the transition has strong signatures in heat capacity, restivity and linear and non-linear magnetic susceptibility. Interest in the material has increased in recent years, as high-pressure measurements have revealed a first-order quantum phase transition to an antiferromagnetically ordered state. However, the fate of the hidden-order with pressure and how it relates to the anti-ferromagnetism is still unknown. With this in mind, we have measured the linear and nonlinear magnetic susceptibility of single-crystalline $\mathrm{URu_{2}Si_{2}}$ under hydrostatic pressure. We will report the results of these measurements, with particular emphasis placed on the signatures of hidden-order and how they evolve as the system is driven into the antiferromagnetic state. [Preview Abstract] |
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