T. Oguchi

Local density band approach to f-electron systems - heavy fermion superconductor UPt3

Abstract A fully relativistic, local density band calculation for the heavy fermion superconductor UPt 3 is presented. The calculated band structure is in excellent agreement with angle resolved photoemission spectra of Arko et al. An analysis of the Fermi surface and the electron-phonon interaction provides a consistent picture which explains several unusual properties of UPt 3 .

Structural, electronic and magnetic properties of NiAl and FeAl alloys☆

Abstract Local density total energy and electronic structure calculations for NiAl, Ni 3 Al, FeAl and Fe 3 Al yield lattice constants which agree well with experiment. We find for Ni 3 Al the Cu 3 Au structure, and for Fe 3 Al the DO 3 structure as their ground states, NiAl is paramagnetic, Fe 3 Al ferromagnetic, and Ni 3 Al and FeAl show weak itinerant magnetic phases.

Local density total energy description of ground and excited state properties of the rare earth metals

Abstract Ground and excited state properties of rare-earth metals are investigated by means of total energy calculations in the local density approximation using the linearized muffin-tin orbital band structure method. Equilibrium lattice constants, bulk moduli and cohesive energies obtained for the rare-earth series are found to be in good agreement with experimental trends. The localization of the 4f electrons in the rare-earths is discussed and compared with that of the 5f electrons in the actinides. The relation between the structural sequence observed in the rare-earths and d-band occupancy is examined. The 4f excitation energies and intra-atomic Coulomb correlations—obtained by taking the difference in total energy of the appropriate final states—are compared with the results of photoemission and inverse photoemission experiments. A comparison of the localization of the 4f electrons in the rare-earths with that of the 5f electrons in the actinides is presented using additional results obtained for the actinide metals with the same approach.

Magnetically induced tetragonal lattice distortion in antiferromagnetic fcc Mn

Abstract The magnetically induced tetragonal lattice distortion observed in an antiferromagnetic metal, γMn, is studied using a total energy local spin density band theory approach. Good agreement is obtained with experiment for both the magnetic moment (2.3μ B ) and the size of the tetragonal distortion. The origin of the distortion is explained in terms of a directional property of the d-band bonding introduced by the antiferromagnetic ordering. Generalizing the results, any strong antiferromagnet with uniaxial magnetic structure is predicted to distort via a contraction perpendicular to the ferromagnetic lattice plane.

Electronic and structural properties of rare earth metals at normal and high pressures: Eu and Yb

Abstract Ground state properties of the divalent rare earth metals Eu and Yb at ambient and high pressures are investigated by calculating their band structures and total energies using the linearized muffin-tin orbital method. To monitor the strengths of the 4f interactions in the local density approximation the hybridization of the 4f electrons is either fully included (itinerant model) or completely neglected (localized model). The effects of spin-polarization are also included for Eu. Divalent to trivalent valence transitions under pressure are discussed and compared with recent X-ray absorption experiments. For Yb, the structural stability of its fcc, bcc and hcp phases is investigated and results are presented.

Electronic structure of UPd3 — A localized f compound

Abstract Various experiments on UPd 3 , the analogue of the heavy fermion superconductor, UPt 3 , have ascertained that there are two f electrons per U which are localized in a magnetic singlet state. Recently, both photoemission (PES) and de Haas-van Alphen (dHvA) experiments have been reported on UPd 3 . To complement this experimental work, local density energy band calculations have been performed on UPd 3 where the f electrons have been treated as core states. The resulting density of states is found to be in good agreement with photoemission data. The theoretical Fermi surface is found to be more complex than current dHvA data indicate, but one can still unambiguously assign theoretical extremal orbits to the experimental data. Thus again, the data is consistent with a local f 2 configuration. Since the band calculations can explain the dHvA data in heavy fermion UPt 3 with the f electrons treated as band states, one finds that the Kohn-Sham ansatz for treating the f electrons as Bloch states breaks down between these two cases. This finding is confirmed by recent U(Pd x Pt 3- x ) alloy experiments which show a sudden decrease in the specific heat coefficient when alloying these two compounds.

Hybridization, electronic structure and properties of uranium intermetallics: URu3, URh3, UPd3, UIr3 and UPt3

Abstract Results of fully-relativistic local density energy band calculations for uranium intermetallics, URu 3 URh 3 , UPd 3 , UIr 3 and UPt 3 , are presented. These include energy bands projected by angular momentum and atom type, total and projected densities of states, specific heat mass enhancement factors and Stoner factors, Systematic variations in hybridization between uranium and transition-metal (X) states,particularly U-f and X-d, are found. The effects of crystal structure on the electronic structure of UPt 3 are examined. The f-d hybridization in the observed hexagonal UPt 3 phase is larger than that in the cubic phase. It is shown by inspecting the wavefunctions on the Fermi surface that the large k -dependence of the hybridization results in strong anistropy of the Fermi surface.

Predictions of anisotropic superconductivity in UIr3 and UPt3

Abstract Anisotropic singlet state superconductivity is predicted for UIr3 (an itinerant non-heavy fermion intermetallic) as was done earlier for UPt3 (perhaps the prototype heavy fermion system). In both, this arises from strong Uf-Xd hybridization which yields a highly anisotropic (i) Fermi surface (now confirmed by dHvA experiments of Taillefer et al. on UPt3), (ii) electron-phonon interaction, and (iii) superconducting energy gap.

Interface magnetism of metallic superlattices: CrAu

Abstract Magnetism of CrAu(001) superlattices is investigated using local spin density energy band approach. Sizable ferromagnetic moments (3μB) are found on Cr in superlattices with monolayer Cr, independent of Au thickness. For thicker Cr layers, the moment of the interface Cr is reduced but remains much larger than the bulk value.

Magnetism and electronic structure of bimetallic superlattices: Cr/Fe

Abstract The electronic and magnetic properties of Cr/Fe(110) coherent modulated superlattices (CMS) with various layer thicknesses were studied using the local spin density linear muffin-tin orbital method. In agreement with experiment, we find that the magnetic moments of the Fe layers are not significantly affected by the Cr layers and to have almost the same magnitude as in bulk bcc Fe, even in the case of an Fe monolayer in the Cr/Fe(110) CMS. Only a small moment (≤0.4μ B ) is found for the Cr layers aligned antiparallel to the n.n. Fe moments. The Cr moment alignment is determined by a delicate balance between the different magnetic interactions (Fe-Fe, Fe-Cr and Cr-Cr); the Cr magnetic moment always prefers to align antiparallel to the n.n. Fe and Cr moments.