Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session H4: New Developments in Heavy Electron Superconductivity |
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Sponsoring Units: DCMP Chair: Joe Thompson, Los Alamos National Laboratory Room: 306/307 |
Tuesday, March 17, 2009 8:00AM - 8:36AM |
H4.00001: New developments in our understanding of superconductivity in the 115 materials Invited Speaker: Is a quantum critical point (QCP) pertinent to unconventional superconductivity? There are several heavy-fermion compounds in which unconventional superconductivity emerges in proximity to a spin-density-type quantum-critical point (1). The absence of superconductivity in prime candidates for a local or Kondo-breakdown quantum criticality, however, raises the question of whether this type of criticality could benefit superconductivity (2). Using the heavy-fermion antiferromagnet CeRhIn$_{5}$ as an example (3), we present the first evidence that critical modes associated with the Kondo-breakdown criticality can provide a new route to unconventional superconductivity. At a local QCP, accessed by applied pressure, magnetic and charge fluctuations coexist and produce electronic scattering that is maximal at the optimal pressure for unconventional superconductivity. References: (1) Mathur et al., Nature 394, 39 (1998); Monthoux et al., Nature 450, 1177 (2007). (2) Gegenwart et al., Nat. Phys. 4, 186 (2008). (3) T. Park et al., Nature 440, 65 (2006); T. Park et al. Proc. Nat. Acad. Sci. 105, 6825 (2008). [Preview Abstract] |
Tuesday, March 17, 2009 8:36AM - 9:12AM |
H4.00002: Unconventional superconductivity of NpPd$_5$Al$_2$ Invited Speaker: The 5f electrons in actinide compounds has an intermediate character between the 4f-localized state and the 3d-itinerant state. This leads to a variety of exotic phenomena, such as non-Fermi liquid behavior, multipole ordering, hidden order state and unconventional superconductivity. The discovery of superconductivity in PuCoGa$_5$ and PuRhGa$_5$ with high critical temperatures provides a new perspective on the physics of actinide compounds. It is generally believed that Np compounds have more 5f-itinerant characteristic features like d-electron metals compared with U compounds. In fact, the results of dHvA experiments in Np-115 compounds are in good agreement with the 5f-itinerant band model. However, the complicated magnetic properties in Np-115 are well explained by the mean field theory including the orbital ordering based on the 5f-localized model. This indicates the dual nature of 5f electrons. NpPd$_5$Al$_2$ is the first Np-based heavy fermion superconductor with the ZrNi$_2$Al$_5$-type tetragonal structure. The superconductivity was found below $T_{\rm sc}=5\,{\rm K}$. The non-Fermi liquid behavior and the large specific heat coefficient ($\gamma=200\,{\rm mJ/K^2 mol}$) were detected. The upper critical field $H_{\rm c2}$ at $0\,{\rm K}$ is large and highly anisotropic: $37\,{\rm kOe}$ for $H \parallel [100]$ and $143\,{\rm kOe}$ for $H \parallel [001]$. $H_{\rm c2}$ is strongly suppressed by the magnetic field in the $H_{\rm c2}$--$T$ phase diagram for both field direction, indicating the strong Pauli paramagnetic effect. The d-wave spin-singlet superconductivity is most likely realized. The large specific heat jump $\Delta C/\gamma T_{\rm sc} = 2.33$ suggests the superconductivity with strong coupling. The results are compared with the well known heavy fermion superconductor CeCoIn$_5$. [Preview Abstract] |
Tuesday, March 17, 2009 9:12AM - 9:48AM |
H4.00003: Heavy electrons and symplectic symmetry of a spin Invited Speaker: Motivated by the recent discovery of the heavy fermion materials NpPd5Al$_2$ [1] and PuCoGa$_5$ [2] which transform directly from Curie paramagnets into superconductors, we have developed a novel theory of these materials based on the idea of composite pairing between local moments and electron pairs. This talk will discuss a simple model of this kind of pairing that can be solved exactly in a large-N limit [3]. The talk will discuss how this concept enables us to understand the giant entropy of condensation, the symmetry of the order parameter as well as an enhancement of the Andreev reflection in tunneling measurements and an upturn in the NMR relaxation rate above Tc. \\[0pt] [1] D. Aoki et al., Jour. Phys. Soc. of Japan 76, 063701 (2007).\\[0pt] [2] J. Sarrao et al., Nature (London) 420, 297 (2002).\\[0pt] [3] R. Flint, M. Dzero and P. Coleman, Nature Physics 4, 643 (2008). [Preview Abstract] |
Tuesday, March 17, 2009 9:48AM - 10:24AM |
H4.00004: Quantum Criticality and Superconductivity in $\beta $-YbAlB$_{4}$ Invited Speaker: Heavy fermion systems have provided a number of prototypical compounds to study unconventional superconductivity and non-Fermi-liquid (NFL) states. A long standing issue in the research of heavy fermion superconductivity in 4$f$ intermetallics is the dramatically different behavior between the electron like Ce (4$f^{1})$ and hole like Yb (4$f^{13})$ compounds. While superconductivity has been found in a number of Ce based heavy fermion compounds, no superconductivity has been reported for the corresponding Yb systems. In this talk, I present our recent finding of the superconductivity in the new heavy fermion system $\beta $-YbAlB$_{4}$ [1-3]. The superconducting transition temperature is 80 mK, and above it, the system exhibits pronounced NFL behavior in the transport and thermodynamic properties [2,3]. Furthermore, the magnetic field dependence of the NFL behavior indicates that the system is a rare example of a pure metal that displays quantum criticality at ambient pressure and under zero magnetic field. Using our latest results, we discuss the detailed properties of superconductivity and quantum criticality. This is the work performed in collaboration with K. Kuga, Y. Matsumoto, T. Tomita, Y. Machida, T. Tayama, T. Sakakibara, Y. Karaki, H. Ishimoto, S. Yonezawa, Y. Maeno, E. Pearson, G. G. Lonzarich, L.Balicas, H. Lee, and Z. Fisk. \\[4pt] [1] Robin T. Macaluso, Satoru Nakatsuji, Kentaro Kuga, Evan Lyle Thomas, Yo Machida, Yoshiteru Maeno, Zachary Fisk, and Julia Y. Chan, Chem. Mater$. $\textbf{19} 1918 (2007). \\[0pt] [2] S. Nakatsuji, K.Kuga, Y. Machida, T. Tayama, T. Sakakibara, Y. Karaki, H. Ishimoto, S. Yonezawa, Y. Maeno, E. Pearson, G. G. Lonzarich, L.Balicas, H. Lee, and Z. Fisk, Nature Phys \textbf{4}, 603-607 (2008). \\[0pt] [3] K. Kuga, Y. Karaki, Y. Matsumoto, Y. Machida, and S. Nakatsuji, Phys. Rev. Lett. \textbf{101}, 137004 (2008). [Preview Abstract] |
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