Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session W13: Thermodynamic Properties of Superconductors |
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Sponsoring Units: DCMP Chair: Donald Naugle, Texas A&M University Room: LACC 402B |
Thursday, March 24, 2005 2:30PM - 2:42PM |
W13.00001: Anomalous normal state Nernst effect in electron doped Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$ P. Li, H. Balci, Y. Dagan, W. Yu, R. L. Greene We present systematic studies of the normal state Nernst effect in thin films of the electron doped superconductor Pr$_{2-x}$Ce$_{x} $CuO$_{4-y}$ (x=0.05, 0.11, 0.13, 0.15, 0.17, 0.19 and 0.21). A large \textbf{\textit{positive}} normal state Nernst signal appears at all doping levels with different magnitude and temperature dependence. The off-diagonal Peltier term $\alpha _{xy}$ is derived from the Nernst, resistivity and thermoelectric power and Hall effect, and its dependence on charge carrier density and relaxation time $\tau $ will be presented. Our results are compatible with a two band (ambipolar) model. Possible explanations for the temperature dependence of the Nernst effect will be presented. \textbf{(This work is supported by NSF Grant DMR-0352735)} [Preview Abstract] |
Thursday, March 24, 2005 2:42PM - 2:54PM |
W13.00002: Evidence of Nodal Superconductivity in Na0.35CoO2$\cdot$1.3H2O:A Specific Heat Study H. D. Yang, J.-Y. Lin, C. P. Sun, Y. C. Kang, C. L. Huang, K. Takada, T. Sasaki, H. Sakurai, E. Takayama-Muromachi Comprehensive low-temperature specific heat data $C(T$,$H)$ of Na$_{0.35}$CoO$_{2}$ยท$1.3$H$_{2}$O with temperature $T$ down to 0.6 K and the magnetic field $H$ up to 8 T are presented. A very sharp superconducting anomaly was observed at $T_{c}$=4.5 and \textit{$\gamma $}$_{n}$=13.94 mJ/mol K$^{2}$ and $\Theta _{D}$=362 K are derived. In the superconducting state, the electronic contribution $C_{es}$ at$ H$=0 can be well described by the model of the line nodal order parameter. In low $H$, $\delta $\textit{$\gamma $}($H)\propto H^{1/2}$ which is also a manifestation of the line nodes. The behaviors of both $T_{c}(H)$ and \textit{$\gamma $}($H)$ suggest the anisotropy of $H_{c2}$ or possible crossovers or transitions occurring in the mixed state. Collaborated with NCTU$^{\ast }$, TAIWAN and NIMS$^{\# }$, JAPAN [Preview Abstract] |
Thursday, March 24, 2005 2:54PM - 3:06PM |
W13.00003: 3$\omega$ Thermal Conductivity Measurement of La$_{2-x}$Sr$_{x}$CuO$_{4}$ in pulsed high magnetic field Dongkyun Kim, Jon Betts, Fedor Balakirev, Albert Migliori, Bo Soo Kang, Quanxi Jia, Jia-Qiang Yan, J. B. Goodenough It is difficult to study the normal state behavior of High T$_{C}$ superconductors below T$_{C}$, because high magnetic field is required to suppress the superconducting state. National High Magnetic Field Laboratory in Los Alamos has a high magnetic field facility up to 75T using pulsed magnets. Users can perform a variety of measurements including resistivity, Hall effect, magnetization, photo-luminescence, and specific heat. Recently, we developed thermal conductivity measurement in high magnetic field utilizing the 3$\omega $ technique. La$_{2-x}$Sr$_{x}$CuO$_{4}$ is reported to have enhanced thermal conductivity in the superconducting state. By applying magnetic field, this enhancement is reduced. The intriguing feature is that the temperature T$_{K}$ below which thermal conductivity is reduced by magnetic field is higher than T$_{C}$. Furthermore, it was shown that small substitution of Cu by Zn prevents this reduction. In this talk we will report the recent thermal conductivity data of La$_{2-x}$Sr$_{x}$CuO$_{4}$ in high magnetic field to shed lights on this subject, by totally suppressing the superconducting state. [Preview Abstract] |
Thursday, March 24, 2005 3:06PM - 3:18PM |
W13.00004: The phonon contribution to the low-temperature thermal conductivity in overdoped cuprates: a probe of electron-phonon coupling David Hawthorn, Shiyan Li, Fil Ronning, Mike Sutherland, Robert Hill, Makariy Tanatar, Johnpierre Paglione, Darren Peets, Ruixing Liang, Doug Bonn, Walter Hardy, N. Kaneko, Martin Greven, Louis Taillefer In the cuprates, past investigations of the low-temperature ($T < 1$K) thermal conductivity ($\kappa$) have focused on the electronic contribution to $\kappa$. Here we examine the phonon contribution to the thermal conductivity in two families of overdoped cuprates: Tl-2201 and Bi-2201. We find $\kappa_{ph}$ to be proportional to $T^2$ with a magnitude that is independent of sample size (not determined by boundary scattering of the phonons). In Tl2201, $\kappa_{ph}$ is shown to grow with increasing doping. We argue that this term in $\kappa_{ph}$ arises from phonon-electron scattering, providing a measure of electron-phonon coupling in the cuprates. The increase in $\kappa_{ph}$ with increasing doping is indicative of a decrease in the electron-phonon coupling with increasing doping. [Preview Abstract] |
Thursday, March 24, 2005 3:18PM - 3:30PM |
W13.00005: Strongly enhanced diamagnetism and the vortex-Nernst effect in Bi2Sr2CaCu2O8+x Yayu Wang, Lu Li, Mike Naughton, Genda Gu, S. Uchida, Nai-Phuan Ong The magnetization of the Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ (Bi-2212) cuprates has been measured using high-resolution cantilever magnetometer. In underdoped Bi-2212, the fluctuation-induced diamagnetism onsets at temperatures much higher than the critical temperature $T_{c0}$. Both the temperature and field dependence of the diamagnetic signals closely match the vortex-Nernst effect measured on the same sample. These new results strongly support the previous finding of the Nernst effect: the vortex-liquid state extends to temperatures well above $T_{c}$ in underdoped cuprates. The transition at $T_{c}$ is caused by the loss of long-range phase coherence among the Cooper pairs. *Supported by NSF (DMR 02-13706). [Preview Abstract] |
Thursday, March 24, 2005 3:30PM - 3:42PM |
W13.00006: Sub-microgram differential AC calorimetry Andreas Rydh, R. Xie, S. Smith, J. E. Pearson, R. Divan, U. Welp, W. K. Kwok, M. R. Eskilden We have developed a differential, steady-state AC microcalorimeter based on a Si$_{3}$N$_{4}$-membrane with thin film heaters and thermocouples for studies of sub-microgram samples. The calorimeter shows good absolute accuracy down to 1 K and excellent performance with high resolution, $\Delta C/C < 10^{-5}$, without temperature smearing. This is exemplified by measurements of the superconducting transition of a 650 ng YBCO single crystal. The addenda heat capacity is found to be less than 1 $\mu$J/K at room temperature and decreasing steadily with decreasing temperature to below a few nJ/K at 1 K. Key features of the microcalorimeter include constantan heater meanders, Au- 2.1$\%$Co versus Cu film thermocouples, and a novel, differential measurement method. The small size and differential design makes the device ideal for characterizations of tiny single crystals in strong magnetic fields, but the potential of the calorimeter to be used for studies of bio-organic liquid droplets will also be discussed. Support from Fulbright, the Sweden-America Foundation, and U.S. Department of Energy, Basic Energy Science under Contract W-31-109-ENG-38 is acknowledged. [Preview Abstract] |
Thursday, March 24, 2005 3:42PM - 3:54PM |
W13.00007: Isotope effects in HTS cuprates: pressure, anisotropy, impurities and pseudogap. Jeffery Tallon, James Storey, Grant Williams, Nswamy Suresh The oxygen isotope effect on Tc and the superfluid density in high-Tc superconductor cuprates has been investigated as a function of pressure, anisotropy, impurity scattering and pseudogap correlations. The doping dependent effects observed are fully consistent with the calculated behaviour in the presence of scattering and depleted normal-state electronic density of states. Like so many other physical properties they reveal a critical doping state where the pseudogap abruptly closes. [Preview Abstract] |
Thursday, March 24, 2005 3:54PM - 4:06PM |
W13.00008: Thermal Conductivity of YBa$_2$Cu$_3$O$_7$ Dale R. Harshman, John D. Dow It is widely, but incorrectly, believed that the thermal conductivity of YBa$_2$Cu$_3$O$_7$ can only be explained in terms of a d-wave model. We show that an s-wave model of hole- pairing, combined with muon spectra that are observed to be s- wave, specific heat data with an observed zero-field linear-T term, superconductivity determined to be in the BaO layers, and non-superconducting CuO$_2$-plane bands describe the YBa$_2 $Cu$_3$O$_7$ data better than any d-wave model. Unlike any d- wave model, the s-wave explanation is also consistent with the superconductivity of Cu-doped Sr$_2$YRuO$_6$ and Ba$_2$YRuO$_6$, at $\approx$49~K and $\approx$83~K, despite these compounds having no cuprate-planes, and the superconductivity of GdSr$_2 $Cu$_2$RuO$_8$ and Gd$_{2-z}$Ce$_z$Sr$_2$Cu$_2$RuO$_{10}$ occurring at $\approx$40~K, despite the fact that their cuprate- planes are either antiferromagnetic or weakly ferromagnetic. In all of these compounds, the superconducting layer is the SrO or BaO layer. The errors which led to the widely believed erroneous concept of cuprate-plane superconductivity are discussed. [Preview Abstract] |
Thursday, March 24, 2005 4:06PM - 4:18PM |
W13.00009: Scaling law of the thermal conductivity in nodal superconductors H. Won, K. Maki The scaling law of the thermal conductivity in d-wave superconductors in the vortex state has been considered by Simon-Lee$^{1}$ and K\"{u}bert-Hirschfeld$^2$. Here we present simple expressions of $\kappa_{xx}$ and $\kappa_{xy}$ for a class of nodal superconductors in the clean limit (i.e. $\Gamma \ll v\sqrt{eH}$, $T \ll \Delta$ where $\Gamma$ is the quasi-particle scattering rate, $v$ the Fermi velocity of quasiparticle and $T$ the temperature). When the above condition is satisfied, $\kappa_{xx}$ and $\kappa_{xy}$ are simple function of $v\sqrt {eH} /T$. The present result is compared with the recent thermal conductivity data of the heavy fermion superconductor CePt$_3$Si by Izawa et al. \par\noindent [1] S.H. Simon and P.A. Lee, PRL 78, 1548 (1997). \par\noindent [2] C. K\"{u}bert and P.J. Hirschfeld, PRL 80, 4963 (1998). [Preview Abstract] |
Thursday, March 24, 2005 4:18PM - 4:30PM |
W13.00010: High-pressure behaviors of a niobium nitride single crystal Xiao-Jia Chen, Viktor V. Struzhkin, Zhigang Wu, Ronald E. Cohen, Ho-kwang Mao, Russell J. Hemley, Axel N{\O}rlund Christensen We report the measurements of the high-pressure lattice structures, Raman-scattering spectra, and superconducting transition temperatures up to 50 GPa on a non-stoichiometric niobium nitride single crystal. The material remains the simple $B1$ NaCl structure over the whole pressure range with a bulk modulus of 348 GPa, comparable to that of cubic boron nitride. The pressure-induced phonon frequency shifts are obtained based on the Raman-scattering data. These results together with the calculated electronic density of states are used to explain our observed constant superconducting transtion at 12.6 K under pressures in this material. [Preview Abstract] |
Thursday, March 24, 2005 4:30PM - 4:42PM |
W13.00011: LaOs4Sb12 and LaRu4Sb12, a contrast with the unconventional behavior of PrOs4Sb12 Daniel Vandervelde, M. B. Salamon, Elbert Chia, H. Sugawara, H. Sato Recent measurements of the penetration depth $\lambda ({\rm T})$ in single crystals of PrOs$_{4}$Sb$_{12}$ have revealed unconventional behavior in the order symmetry of the superconducting energy gap$^{[1]}$. We present, for contrast, high precision measurements undertaken of LaOs$_{4}$Sb$_{12}$ and LaRu$_{4}$Sb$_{12}$, under analogous conditions, where we observe fully gapped behavior. These results show that the substitution of La for Pr yields similar behavior as that seen in the fully gapped superconductor PrRu$_{4}$Sb$_{12} \quad ^{[2] }$These materials appear to have SC electron densities, $\rho $, characteristic of s-wave, BCS superconductors with the data exhibiting a fit to $\rho $ of exponential at low temperature. All measurements were done at temperatures from 0.1K to 0.9K for LaOs$_{4}$Sb$_{12}$, and to 3.8K for LaRu$_{4}$Sb$_{12}$ using a self-inductive oscillator technique. Fits of $\rho $ were made assuming specific heat jumps of 1.74$\gamma $T$_{c}$ and 1.81$\gamma $T$_{c}$ respectively with T$_{c}$'s of 0.76K and 3.6K respectively. Measurements have been performed on Pr(Os$_{1-x}$Ru$_{x})_{4}$Sb$_{12} \quad ^{[3]}$ to map it's transition from fully gapped to unconventional behavior, and so we propose future work of mapping a similar transition in a series of Pr$_{1-x}$La$_{x}$Os$_{4}$Sb$_{12}$ materials. [1]Elbert E.M. Chia \underline {\textit{et al.}}, Phys. Rev. Lett. 91, 247003 (2003) [2] Elbert E.M. Chia \underline {\textit{et al.}}, Phys. Rev. B 69 180509(R) (2004) [3] Elbert E.M. Chia \underline {\textit{et al.}}, condmat/0411395 [Preview Abstract] |
Thursday, March 24, 2005 4:42PM - 4:54PM |
W13.00012: Effects of anisotropic impurity scattering on thermal conductivity and thermoelectric effect in unconventional superconductors Mikael Fogelstrom, Tomas Lofwander We report analytic and numerical results for the thermal conductivity and thermoelectric effect in unconventional superconductors with a dilute random distribution of impurities. We present new results for the effects of anisotropic impurity scattering. For low temperatures we present analytic results for the universal limit asymptotics and the $T^3$ corrections. Only the $T\rightarrow 0$ value of the thermal conductivity remains universal (independent of the impurity scattering potential). All other quantities depend on the phase shifts and vertex corrections. [Preview Abstract] |
Thursday, March 24, 2005 4:54PM - 5:06PM |
W13.00013: Heat Capacity of the Magnetic Superconductors R$_{2-x}$Ce$_x$RuSr$_2$CuO$_{10-\delta}$ Donald Naugle, K. D. D. Rathnayaka, Maryna Anatska, Israel Felner The interplay of superconductivity and magnetism is one of the fundamental problems in condensed matter physics. One of the most interesting systems to display such behavior is the R$_{2-X}$Ce$_{X}$Ru Sr$_{2}$Cu$_{2}$ O$_{10-\delta}$ family (Ru-2122) with R=Gd or Eu. Magnetic ordering, usually antiferromagnetic, can occur at a temperature approximately four times that of superconductivity, which may be as high as 50K. Onset of weak ferromagnetism is observed well above T$_{c}$, suggesting coexistence of ferromagnetic and superconducting order. Recent thermal conductivity measurements [1] show a large jump in thermal conductivity precisely at the onset of superconductivity in the Ru-2122 compound with Eu$_{1.5}$Ce$_{0.5}$, a behavior inconsistent with typical superconductors. Heat capacity measurements on ruthenate samples were carried out to probe the behavior of this material above and below its superconducting transition temperature. Work supported by the Robert A. Welch Foundation (A-0514) and the National Science Foundation (DMR-0103455) [1] B.D. Hennings et.al, Physica C370, 253 (2002) [Preview Abstract] |
Thursday, March 24, 2005 5:06PM - 5:18PM |
W13.00014: In-plane anisotropy of Seebeck coefficient in slightly doped YBa$_2$Cu$_3$O$_y$ Kouji Segawa, Yoichi Ando In order to observe one-dimensionality, which can be direct evidence for self-organization of electrons into charge stripes, we developed a detwinning technique for YBa$_2$Cu$_3$O$_y$ (YBCO) for a wide range of doping down to non-superconducting compositions. The temperature dependence and the doping dependence of the in-plane resistivity indicates that the observed anisotropy is not due to the Cu-O chains but due to an electron self-organization in the CuO$_2$ planes [1]. The in- plane anisotropy is also observed in the optical conductivity. The frequency dependence of the conductivity spectra indicates that the plasma frequency is isotropic and the resistivity anisotropy is caused by an anisotropic scattering rate [2]. In the present work we measured in-plane anisotropy of the Seebeck coefficient in slightly doped YBCO. From the isotropic plasma frequency, which is proportional to $n/m^\ast$ in the Drude model, one expects that the Seebeck coefficient is isotropic. However, it turns out that $S_a$ is larger than $S_b$ in slightly doped samples. This result cannot be accounted for by the simple Drude picture, and thus the observed anisotropy highlights another peculiar aspect of the self-organization of electrons in cuprates. [1] Ando et al., PRL 88, 137005 (2002). [2] Y.-S. Lee et al., PRB 70, 014518 (2004). [Preview Abstract] |
Thursday, March 24, 2005 5:18PM - 5:30PM |
W13.00015: Low Temperature Heat Capacity of Superconducting Zn Nanowires James Kurtz, Bob Johnson, Mingliang Tian, Nitesh Kumar, Zhigang Ma, Moses H.W. Chan Thermodynamic measurements on superconducting nanostructures are notoriously difficult. Nanowires electrodeposited in porous alumina offer unusually high wire density and length compared to other systems, yielding samples massive enough to measure. In this work, low temperature heat capacity measurements have been carried out on ensembles of parallel Zn nanowires in porous alumina. Samples with wire diameters ranging from 28nm to 150nm were measured. The temperature and field dependence of the heat capacity will be presented and compared to bulk data and to transport measurements in similar wire ensembles. Key features to be discussed are the height and width of the heat capacity peak at the transition for increasingly smaller wire diameters. \newline This work was supported by Penn State MRSEC NSF grant number DMR0213623. [Preview Abstract] |
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