Spin fluctuations, Fermi surface hotspots and nesting in PuCoGa 5
- PDF / 3,457,355 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 47 Downloads / 401 Views
Spin fluctuations, Fermi surface hotspots and nesting in PuCoGa5 Matthias J. Graf, Tanmoy Das and Jian-Xin Zhu Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A. ABSTRACT Surprisingly little is known about the mechanism and symmetry of superconducting pairing in PuCoGa5. A common thread with other unconventional superconductors is the presence of spin fluctuations in the normal state, which in this particular case is controlled by strong spin–orbit coupling split bands. The many and anisotropic Fermi surfaces make the guessing of the potential spin-fluctuation nesting vector and resulting symmetry of the pairing function a nontrivial task. To provide much needed guidance for the identification of the pairing symmetry in this multiband superconductor, we perform first-principles based magnetic spin susceptibility calculations to identify the dominant nesting vectors that potentially give rise to interband pairing with nodal d- or s±-wave gap functions. INTRODUCTION The nature of the pairing in the unconventional superconductor PuCoGa5 is still unknown, though it was proposed early on that it is most likely due to spin fluctuations [1-3]. This was further corroborated by the fact that two of its Fermi surfaces are quasi-twodimensional (quasi-2D) and located at the M point of the Brillouin zone [4-7]. Thus it was quite natural to draw analogies with the copper-oxide high-temperature superconductors, where power laws in the temperature behavior of many physical observables were shown to be consistent with d-wave pairing and nodes in the gap function on the Fermi surface. Lacking phase-sensitive probes to determine the sign of the superconducting gap function in PuCoGa5, so far virtually all experiments have been interpreted in terms of an oversimplified single-band d-wave theory, which can account remarkably well for reported power laws and Andreev reflection [1-3,8]. An important question to be asked is whether other pairing symmetries within a multiband theory of superconductivity can equally well describe existing experiments, as well as propose discriminating future experiments. It is thus natural to explore the mechanism of spin fluctuations as the mediating glue for spin-singlet superconductivity in this material. As we know from our earlier work, PuCoGa5 possesses a strong particle-hole continuum spectrum of spin fluctuations in the normal state, which therefore should give rise to unconventional pairing and even exotic pairing symmetries in a multiband scenario of superconductivity considering the presence of anisotropic Fermi surfaces [9,10]. By studying the magnetic spin susceptibility, we will address the question of whether the spin-fluctuation theory of superconductivity can account for gapless behavior or nodal quasiparticle states in the excitation spectrum. For comparison, the existence of nodal quasiparticle states is well established in copper-oxide and some heavyfermion superconductors, but not in iron-based superconductors [11].
THEORY In previous work, we presented
Data Loading...
