Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Y42: Superconductivity: Thermodynamic, Mechanical and Structural Properties |
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Sponsoring Units: DCMP Chair: George Crabtree, Argonne National Laboratory Room: D138 |
Friday, March 19, 2010 8:00AM - 8:12AM |
Y42.00001: High Field Specific Heat of the Cuprate Superconductor LSCO across the Phase Diagram Jonathon Kemper, Gregory Boebinger, Scott Riggs, Jon Betts, Albert Migliori Several samples of superconducting LSCO have been measured in specific heat experiments in magnetic fields up to 45 Teslas. The evolution of the electronic density of states is examined as a function of field and doping to reveal the nature of the vortex and normal state quasi-particle contributions within the zero-field superconducting regime. [Preview Abstract] |
Friday, March 19, 2010 8:12AM - 8:24AM |
Y42.00002: Quantum Oscillations in the Specific Heat of YBCO 6.55 Scott Riggs, Oskar Vafek, Jon Kemper, Greg Boebinger, Jon Betts, Albert Migliori, Ross McDonald, Doug Bonn, Walter Hardy, Ruixing Liang We measure the specific heat of underdoped YBCO 6.55 in magnetic fields up to 45T in order to provide a first study of the thermodynamics of the normal state in the high temperature superconducting cuprates. Our experiments are motivated by quantum oscillation measurements of resistivity and magnetization over the past several years that have been interpreted in the context of the standard Lifshitz-Kosevich (LK) formalism for conventional metals. We find quantum oscillations in the specific heat of the cuprates for the first time ever and reveal that the normal state exhibits a seemingly-contradictory mixture of conventional and unconventional behavior. We find that LK theory can quantitatively describe the temperature-dependence of the specific heat as well as the temperature- and field-dependence of the quantum oscillations in specific heat.~ However, the magnetic field dependence of the specific heat follows the sqrt(B) behavior of the superconducting state over our entire magnetic field range.~ As the superconducting state is suppressed (Tc --$>$ 0) at $\sim $30T in this sample, why does specific heat at 45T give evidence for a superconducting gap? Some ideas will be presented. [Preview Abstract] |
Friday, March 19, 2010 8:24AM - 8:36AM |
Y42.00003: $\mu$SR Study of Non-Magnetic Non-Centrosymmetric Superconductor LaRhSi$_3$ Alexandre Desilets-Benoit, Andrea Bianchi, Gabriel Seyfarth, Gerald Morris, Rob Kiefl, Sarah Dunsinger, Cigdem Capan, Zachary Fisk We report on results of $\mu$SR experiments in a transverse field geometry of the non-centrosymmetric non-magnetic superconductor LaRhSi$_3$. LaRhSi$_3$ crystallizes in the BaNiSn$_3$-type tetragonal structure (space group I4mm) and it has a critical temperature T$_c$ of 2.2 K. LaRhSi$_3$ is a type II superconductor which in magnetic fields presents an unusually sharp specific heat transition suggesting first order transitions. Under a field 250 G, LaRhSi$_3$ has a relatively low H$_{c2}$ in respect to its H$_{c1}$ of 90 G and a Pauli limit of 3.3 T. Surprisingly, at a field of 150 G we find the onset of depolarization of the muons to occur at a temperature which is a factor of 4 higher than the T$_c$ obtained from transport measurements. [Preview Abstract] |
Friday, March 19, 2010 8:36AM - 8:48AM |
Y42.00004: Calorimetric evidence for two-gap superconductivity in NbS$_{2}$ Peter Samuely, Jozef Kacmarcik, Zuzana Pribulova, Christophe Marcenat, Thierry Klein, Pierre Rodiere, L. Cario Concept of multiband/multigap superconductivity has been recently considered in several classes of novel superconductors but also older systems are reconsidered in this frame work. Here we show an evidence of two gaps in NbS$_{2}$ by the specific heat measurements in magnetic field. Our measurements are in a perfect agreement with the previous scanning tunneling spectroscopy of Guillamon et al., Phys. Rev. Lett. 101, 166407 (2008) on the same sample. The combination of the direct gap spectroscopy by surface sensitive STM and the thermodynamic specific heat probing the true bulk yield a strong confirmation of the existence of the two gap superconductivity in the system with strongly and weakly coupled Cooper pairs in a close analogy to MgB$_{2}$. From the specific heat measurements in a mixed state we have found that, again in analogy with MgB$_{2}$, the superconducting anisotropy of the upper critical field is temperature and field dependent but here in a qualitatively different way. [Preview Abstract] |
Friday, March 19, 2010 8:48AM - 9:00AM |
Y42.00005: Low temperature thermal conductivity of the noncentrosymmetric superconductor LaRhSi$_3$ C.F. Miclea, N. Kurita, C. Putzke, G. Seyfarth, C. Capan, A. Bianchi, Z. Fisk, Roman Movshovich We report results of low temperature thermalconductivity, $\kappa$, on single crystalline LaRhsi3. This compound crystallizes in tetragonal structure which lacks space- inversion symmetry. It is a moderate type II superconductor with a superconducting transition temperature of $T_c$=2.26 K, an upper critical field of only $H_{c2}=200$~Oe, and a first critical field $H_{c1}=120$~Oe. Immediately below $T_c$, the thermal conductivity has an exponential temperature dependence down to $T=0.4$~K. At low temperature $\kappa$ adopts a quadratic temperature dependence which changes suddenly to a cubic behavior only for fields around $H=H_{c1}$ and then becomes linear at higher fields. The magnetic field dependence of the residual linear term of thermal conductivity suggests an $s-$wave symmetry of the superconducting order parameter. [Preview Abstract] |
Friday, March 19, 2010 9:00AM - 9:12AM |
Y42.00006: Elastic Moduli of detwinned orthorhombic optimally doped LSCO (La$_{2-0.16 }$Sr$_{ 0.16 }$CuO$_{4})$ Victor Fanelli, Jonathan Betts, Albert Migliori, Yoko Suzuki, Jiaqiang Yan Accurate elastic modulus characterization of the superconducting phase transition (SC) in La$_{2-0.16 }$Sr$_{ 0.16 }$CuO$_{4}$ is difficult because the discontinuities in moduli are much smaller than fluctuations from twin boundary motion. Thus detwinning is required for a useful measurement and was achieved using mechanical stress along the tetragonal [110] direction (or equivalently, along the orthorhombic [100] direction) below the orthorhombic phase transition that is well below ambient temperature. Using resonant ultrasound spectroscopy (RUS) on the detwinned monocrystal, the discontinuities and moduli around the SC transition were measured. [Preview Abstract] |
Friday, March 19, 2010 9:12AM - 9:24AM |
Y42.00007: Intrinsic nature of oxygen isotope effect in La$_{2{\-}-x}$Sr$_{x}$CuO$_{4}$ using x{\-}-ray diffraction: no structural differences observed at low temperatures A.R. Moodenbaugh, D.E. Cox, M.K. Crawford High resolution synchrotron x-ray diffraction was used to study the structural transformations at low temperatures of La$_{2--x}$Sr$_{x}$CuO$_{4}$.\footnote{A. R. Moodenbaugh et al., Phys. Rev. B 58 (1998) 9549.} A fraction, estimated from diffraction intensities to be on the order of 10 percent, of Low Temperature Tetragonal (LTT) phase is observed in majority Low Temperature Orthorhombic (LTO1) phase for x$\sim $0.12. The remarkable superconducting oxygen isotope effects in these materials\footnote{M. K. Crawford et al., Science 250 (1990) 1390} has been firmly established, and still attracts great interest. We revisit the M=Sr materials x$\sim$0.12 to search for possible subtle structural differences in oxygen isotope exchanged sample pairs, which might contribute to transition temperature variations. Analyzed are both lattice parameters and ratio of LTT:LTO1 intensities. Preliminary results suggest that the low temperature structures of oxygen isotope exchanged pairs are indistinguishable at all temperatures. These results confirm the intrinsic nature of the observed isotope effects. [Preview Abstract] |
Friday, March 19, 2010 9:24AM - 9:36AM |
Y42.00008: Interplay between Superconductivity and Strain in Al and Nb from First-Principles: a Maximally Localized Wannier Functions Approach M. Salvetti, N. Bonini, D. Parks, N. Marzari, M. Calandra Phonon-mediated \textit{el-el} interactions are the microscopic basis of low temperature superconductivity. The Eliashberg-Migdal theory formulates the problem in terms of \textit{el-ph} matrix elements and corresponding \textit{el-ph} linewidths. In principle, \textit{ab-initio} DFT codes based on pseudo-potentials and plane-waves can provide an accurate prediction of the \textit{el-ph} linewidth spectrum over the entire Brillouin zone in bulk materials. In practice, fully converged calculations are often unattainable because of the required dense samplings of the Fermi surfaces and limitations in the available CPU time. In many cases, the reformulation of the \textit{el-ph} matrix problem using maximally localized Wannier functions reduces the time-consuming part of the calculation to the determination of the phonon frequencies via linear perturbation DFT and leads to a fully-physical based interpolation technique. Here, we present results on the superconducting critical temperature $T_{c}$ of Al and Nb crystals under various mechanically-strained configurations and show that even in such simple bulk systems the use of the Wannier basis approach is necessary to ensure accurate and reasonably fast calculations. [Preview Abstract] |
Friday, March 19, 2010 9:36AM - 9:48AM |
Y42.00009: Magnetic anisotropy of some cuprate superconductors. John Cooper, Marcin Matusiak, Ivan Kokanovic, Daniel Hills, Michael Sutherland, Timothy Benseman, John Loram We report magnetic anisotropy data obtained using cantilever torque or Squid magnetometry, for single crystals of YBa$_{2}$Cu$_{4}$O$_{8}$, YBa$_{2}$Cu$_{3}$O$_{6+x,}$ La$_{2-x}$Sr$_{x}$CuO$_{4}$ and Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8-x}$, grown by several different groups. At present the main results are: (1) The anisotropy far above $T_{c}$ is dominated by anisotropy in the spin susceptibility. By comparing data for YBa$_{2}$Cu$_{4}$O$_{8 }$and YBa$_{2}$Cu$_{3}$O$_{7 }$we show that the $T$-dependence is caused by the pseudogap. (2) At lower $T$, analysis in terms of weak, quasi-2D, Gaussian superconducting fluctuations gives values of the in-plane superconducting coherence length, and hence independent estimates of the Nernst coefficient above $T_{c}$. (3) Data for the field dependence of the fluctuations nearer $T_{c}$ are used to look for deviations from the above Gaussian picture. (4) There is some evidence from the magnetic susceptibility, Knight shift, susceptibility anisotropy and heat capacity, that the small pockets of carriers detected in high field quantum oscillation experiments on YBa$_{2}$Cu$_{4}$O$_{8 }$and$_{ }$YBa$_{2}$Cu$_{3}$O$_{6+x}$ are still present at low fields. [Preview Abstract] |
Friday, March 19, 2010 9:48AM - 10:00AM |
Y42.00010: Probing the gap symmetry by magnetic field in superconductors with anisotropic Fermi surfaces Ilya Vekhter, Anton Vorontsov Measurements of the thermal conductivity and specific heat under rotated magnetic fields aimed at determining the nodal directions in unconventional superconductors are being done on the ever-growing class of materials. Theoretical underpinnings of this method are by now well established for simple Fermi surfaces that are fully symmetric in the plane of field rotation. We show that in anisotropic materials the correct interpretation of experimental results requires knowledge of the shape and the topology of the Fermi surface as well as its curvature near the nodal points. We also investigate the dependence of the results on the strength of impurity scattering. We apply our results to the analysis of the thermal conductivity and heat capacity in two-dimensional organic superconductors, where recent experiments reignited the debate on the gap symmetry. [Preview Abstract] |
Friday, March 19, 2010 10:00AM - 10:12AM |
Y42.00011: Current induced transport properties in bulk YBCO and BSCCO George Zimmerman Simultaneous measurement of the electrical resistivity magnetic susceptibility as a function of current density of YBCO and BSCCO superconducting material reveals a resistivity maximum which is also reflected in the susceptibility. In addition to anomalies which appear at temperatures between 85K and 140K, the susceptibility seems to be affected by the electrical current up 200K. The electrical current, of density between 8 and 400 A/cm$^{2}$ seems to induce a lowered resistivity, which suggests a first order phase transition, possibly meta-stable, and persists despite the repeated cycling between 77K and 300K. The YBCO samples are bulk polycrystalline sintered rods with a density of 5.4 gm/cm$^{3}_{ . }$They were prepared by sintering and annealing from a powder. Most were 10 to 15 years old. The magnetic susceptibility shows a broad transition between 60K and 90K. The details of the measurements as a function of temperature, current density, and low magnetic field, and differences between YBCO and BSCCO will be described along with possible implications as to the nature of the pseudo-gap and other competing theories. [Preview Abstract] |
Friday, March 19, 2010 10:12AM - 10:24AM |
Y42.00012: Pauli blocking in low-dimensional Fermi systems at finite temperatures Francisco J. Sevilla, M. Fortes, M.A. Solis The chemical potential of an ideal Fermi gas for dimensions $d<2$ increases with temperature up to a maximum value [1], in sharp contrast with the monotonic decreasing behavior in the $d=3$ case [2]. The origin of this anomaly is examined in systems of non interacting fermions described by a more general energy-momentum dispersion relation $\epsilon\propto k^s$. We show that the abnormal behavior is caused by the interplay of the density of states as a function of $d/s$ and the exclusion principle producing a Pauli-blocking effect at finite temperatures. In the one-dimensional ideal Fermi gas, the effect is manifest up to temperatures as large as the Fermi temperature.\\[4pt] [1] M. Grether, M. de Llano, and M.A. Sol\'{\i}s, Eur. Phys. J. D 25, 287 (2003).\\[0pt] [2] G. Cook and R.H. Dickerson, Am. J. Phys. 63 (8), 737 (1995). [Preview Abstract] |
Friday, March 19, 2010 10:24AM - 10:36AM |
Y42.00013: The effect of multilayered Bi$_{1.8}$Pb$_{0.4}$Ca$_{2.2}$Sr$_{2}$Cu$_{3}$O$_{x}$/Ag on superconducting and microstructure properties of Bi$_{1.8}$Pb$_{0.4}$Ca$_{2.2}$Sr$_{2}$Cu$_{3}$O$_{x}$ Mustafa Akdogan, Cabir Terzioglu, Ibrahim Belenli A precursor powder with a nominal chemical composition of Bi$_{1.8}$Pb$_{0.4}$Ca$_{2.2}$Sr$_{2}$Cu$_{3}$O$_{x}$ was used to fabricate the multilayered Bi$_{1.8}$Pb$_{0.4}$Ca$_{2.2}$Sr$_{2}$Cu$_{3}$O$_{x}$/Ag samples (number of layers was 2, 4 and 8) using the powder-in-tube method (PIT). The density of powder increases during the drawing procedure and inside the composite wires of the final diameter is 3.54 mm. By an intermediate rolling, pressing and annealing procedure, the wires were rolled to obtain tapes. The rolling process was not effective in obtaining further substantially increase of the powder density, but greatly improved the orientation of ceramic grains inside the silver sheath. The sample is composed of a highly oriented Bi-2223 phase in the region near to the Ag layer. The eight-layered sample exhibits a rather high I$_{c}$ value of 110 A. T$_{c}$ and J$_{c}$ are enhanced by increasing the number of Ag layers. The formation of the dense oriented structure is near the interface between oxide and the Ag layer. This suggests that Ag plays an important role in the improvement of J$_{c}$. [Preview Abstract] |
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