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Anomalous spectral weight transfer at the superconducting transition of single-crystalline Bi2Sr2CaCu208+5 was observed by high-resolution angle-resolved photoemission spectroscopy. As the sample goes superconducting, not only is there spectral weight transfer from the gap region to the pileup peak as in BCS theory, but along the T-M direction there is also some spectral weight transfer from higher binding energies in the form of a dip. In addition, we note that at the superconducting transition there is a decrease (increase) in the occupied spectral weight for the spectra taken along T-M (T-X).PACS numbers: 74.65.+n, 71.20.Cf, 79.60.Cn In the BCS theory for traditional superconductors the electron Fermi sea is unstable to attractive interactions mediated by phonons. A superconducting gap is formed when the near-Fermi-edge electrons condense to form pairs at low temperatures. As illustrated in the inset of Fig.

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The electronic structure of the first Pu-based superconductor PuCoGa 5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Exceptional agreement between calculation and experiment defines a path forward for understanding electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. The results for PuCoGa 5 clearly indicate 5f electron behavior on the threshold between localized and itinerant. Comparisons to delta phase Pu metal show a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant. PACS: 71.27.+a,71.28.+d, The recent discovery of PuCoGa 5 , the first Pu-based superconductor, with a T C =18.5 K and unconventional superconductivity demonstrates the rich and complex nature of Pu-based materials [1]. The role of the 5f electrons in bonding and hybridization is intimately intertwined with the wide range of ground state properties found in actinide materials including enhanced mass, magnetism, superconductivity, as well as spin and charge density waves. Within the actinide series, Pu occupies the position between the clearly hybridized 5f states of uranium [2] and clearly localized 5f states of americium[3] which due to its J=0 ground state is a superconductor. Pu defines the localized/itinerant boundary for the 5f electrons in the actinides [4,5]. There have been several recent papers reporting photoemission [6,8,7,9] and electronic structure calculations [4,5,10,11,12,13,14] for the fcc (δ ) phase of Pu metal. A classic failure of density functional theory (DFT) within the local density approximation (LDA) or generalized gradient approximation (GGA) is observed in the case of δ -Pu with the volume from LDA falling over 25% short (GGA only slightly better) of the experimental volume in the largest discrepancy to date in DFT for a crystal.To accommodate the large volume of the delta phase of Pu metal, there have been magnetically ordered electronic structures proposed which, to some degree, effectively localize 5f electrons, reducing the contribution to the chemical bonding and increasing the volume[10], however there is no experimental evidence for magnetism in δ -Pu [15]. Another approach used for δ -Pu is the dynamical mean field theory (DMFT) which may offer promise with further development [11]. Currently the agreement between DMFT and experiment is weak with the PES shown in Ref.[11] being more of an idealized representation than actual data. The link between δ -Pu metal and PuCoGa 5 is strong and follows the same path as the family of Ce-based heavy fermion-superconductors (CeMIn 5 , M=Co, Rh, Ir) [16] having the cubic CeIn 3 as the root crystal structure. 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 s...

High-resolution angle-resolved photoelectron spectroscopic measurements were made of the Fermi edge of a single crystal of Bi2Sr2CaCu2O8 at 90 K along several directions in the Brillouin zone. The resultant Fermilevel crossings are consistent with local-density band calculations, including a point calculated to be of Bi-O character. Additional measurements were made where bands crossed the Fermi level between 100 and 250 K, along with measurements on an adjacent Pt foil. The Fermi edges of both materials agree to within the noise. Below the Fermi level the spectra show correlation effects in the form of an increased effective mass, but the essence of the single-particle band structure is retained. The shape of the spectra can be explained by a lifetime-broadened photohole and secondary electrons. The effective inverse photohole lifetime is linear in energy.

Detailed studies indicate a superconducting gap in the high-temperature superconductor Bi(2)Sr(2)CaCu(2)O(8). Photoemission measurements with high energy and angle resolution isolate the behavior of a single band as it crosses the Fermi level in both the normal and superconducting states, giving support to the Fermi liquid picture. The magnitude of the gap is 24 millielectron volts.