Electronic Structure and the Fermi Surface ofPuCoGa5and

Abstract

By using a relativistic linear augmented-plane-wave method, we clarify energy band structures and Fermi surfaces of recently discovered plutonium-based superconductor PuCoGa5. We find several cylindrical sheets of Fermi surfaces with large volume, very similar to CeMIn5 (M=Ir and Co) isostructural with PuCoGa5, in spite of different f -electron numbers between Ce 3+ and Pu 3+ ions. The similarity is understood by a concept of electron-hole conversion in a tight binding model constructed based on the j-j coupling scheme. Based on the present results, we provide a possible scenario to explain why a transition temperature is so high as 18.5K in PuCoGa5. PACS numbers: 74.25.Jb, 74.70.Tx, 71.18.+y, 71.15.Rf Recently it has been discovered that PuCoGa 5 exhibits superconductivity [1]. Surprisingly its superconducting transition temperature T c is 18.5K, which is the highest among those yet observed f -electron materials and high enough even compared with other well-known intermetallic compounds. It has been also found that PuRhGa 5 becomes superconducting with T c =8.6K [2]. These plutonium intermetallic compounds PuMGa 5 have the same HoCoGa 5 -type tetragonal structure as CeMIn 5 , a family of cerium-based heavy fermion superconductors [3]. Note, however, that superconductivity occurs for M=Ir (T c =0.4K) and Co (2.3K) in CeMIn 5 , while antiferromagnetic (AFM) phase has been found for M=Rh at ambient pressure. Another isostructural material including uranium is UMGa 5 [4], but superconductivity has not been found yet. These HoCoGa 5 -type compounds are frequently referred to as "115".Regarding superconducting mechanism in the 115 compounds, first let us consider Ce-115. It has been widely considered that it is unconventional d-wave superconductor induced by AFM spin fluctuations. In fact, there are some evidences such as T 3 behavior in nuclear relaxation rate [5] and node structure measured by thermal conductivity [6]. For the phase diagram of Ce(Co,Rh,Ir)In 5 [7], AFM phase is found to exist in adjacent to the superconducting phase. Those experimental facts remind us of high-T c cuprates, but a clear difference from cuprates should be remarked. Namely, high-T c superconductivity in cuprates occurs by hole doping into AFM insulators, while in Ce-115, no hole doping is needed. To understand the appearance of superconductivity induced by AFM spin fluctuations without hole doping, a crucial role of orbital degree of freedom has been pointed out by Takimoto et al. [8].Concerning Pu-115, it is still premature to draw a definitive conclusion about the mechanism of superconductivity, but we notice that some normal-state properties in PuMGa 5 seem to be dominated by AFM spin fluctuations, e.g., the Curie-Weiss behavior in magnetic susceptibility and electric resistivity in proportion to T 1.35 [1]. Thus, it may be natural to consider that superconductivity in Pu-based compounds is also induced by AFM fluctuations. However, several problems still exist, even if d-wave superconductivity is confirmed in both Ce-115 and Pu...

Thermodynamic and transport properties of single-crystallineUMGa5(M=Fe,Moreno1, Bauer2, Sarrao3 et al. 2005Phys. Rev. B334210View full textAdd to dashboardCite

“…8,9 Although less is known about these plutonium-based materials, the underlying physics appears to be similar 10 to that of CeMIn 5 and, in particular, seems to rely on the existence of at least partially localized f electrons. [11][12][13] A family of uranium-based analogues of CeMIn 5 and PuMGa 5 was reported some time ago. 14 UMGa 5 crystallizes in the same tetragonal HoGoGa 5 -type structure as the Ce and Pu variants for M = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt.…”

Photoemission and the Electronic Structure ofPuCoGa5

“…Here we have δ -Pu as the parent cubic phase structure with Ga substituting on the face centers to form PuGa 3 and insertion of the CoGa 2 layer into the cubic structure to form PuCoGa 5 in the tetragonal phase. With the discovery of superconductivity in PuRhGa 5 [17] it does indeed seem reasonable that the PuMGa 5 family of compounds is following systematics much like the CeMIn 5 family of superconducting compounds.Since the discovery of PuCoGa 5 there are currently three computational frameworks to describe the electronic structure of PuCoGa 5 nominally within the framework of DFT[18,19,20]. The theoretical efforts for PuCoGa 5 are following the path set forth in δ -Pu, with conventional DFT pushing the 5f-electron intensity up against the Fermi level[18] or magnetic solutions [19] which serve to effectively localize some of the Pu 5f intensity below the Fermi level(E F ).…”

Probing the population of the spin–orbit split levels in the actinide 5f states

“…A recent surge of interest in the actinides has occurred, driven by the variety of exotic behaviors exhibited in 5f metals and compounds [1][2][3][4][5][6][7][8][9][10][11], such as the discovery of Pu-based superconductivity [8][9][10], and the unique phonon dispersion observed in -U [6,7] and -Pu [3][4][5]. Along the actinide series a volume anomaly occurs near Pu, due to a change in the bonding behavior of the valence states (see Figure 1 [11]).…”