Optical Conductivity of the t-J model within Cluster Dynamical Mean Field Theory

We study the evolution of the optical conductivity in the t-J model with temperature and doping using the Extended Dynamical Cluster Approximation. The cluster approach results in an optical mass which is doping independent near half filling. The transition to the superconducting state in the overdoped regime is characterized by a decrease in the hole kinetic energy, in contrast to the underdoped side where kinetic energy of holes increases upon superfluid condensation. In both regimes, the optical conductivity displays anomalous transfers of spectral weight over a broad frequency region.Comment: 4 pages, 3 figure

Simple Exactly Solvable Models of non-Fermi Liquids

We generalize the model of Hatsugai and Kohmoto [J. Phys. Soc. Jpn, 61, 2056 (1992)] and find ground states which do not show the properties of Fermi liquids. We work in two space dimensions, but it is straightforward to generalize to higher dimensions. The ground state is highly degenerate and there is no discontinuity in the momentum distribution; i.e., there is no Fermi surface. The Green's function generically has a branch cut.Comment: Revte

Studio Recital, Joy McIntyre, November 20, 1992

This is the concert program of the Studio Recital, Joy McIntyre performance on Friday, November 20, 1992 at 12:00 p.m., at the Concert Hall, 855 Commonwealth Avenue. Works performed were I Was Lonely and Forlorn by Benjamin Britten, Star Vicino by B. Britten, Wende Dich by Carl Phillipp Emanuel Bach, If Music Be the Food of Love by Henry Purcell, "Habanera" from "Carmen" by Georges Bizet, Jeune Fillette by J. B. Werkerlin, Demanten på marasnön by Jean Sibelius, Leave Me Loathsome Light by George Frideric Handel, "Hat man nicht auch Gold daneben" from "Fidelio" by Ludwig van Beethoven, Le papillon et la fleur by Gabriel Fauré, Die Zufriedenheit by Wolfgang Amadeus Mozart, "Quae Moerebat" from Stabat Mater by Giovanni Battista Pergolesi, Thou Didst Not Leave His Soul in Hell by George Frideric Handel, Sento Nel Core by Alessandro Scarlatti, Come Again, Sweet Love by Jown Dowland, Ganymed by Franz Schubert, The Maiden Blush by Roger Quilter, Nacht und Träume by F. Schubert, The Singer by Michael Head, Toglietimi by A. Scarlatti, Habanera by G. Bizet, Adieu by G. Fauré, Benedictus by Johann Sebastian Bach, Ah! Lève-toi by Charles Gounod, Chanson Triste by Henri Duparc, and "Il est doux" from Herodiade by Jules Massenet. Digitization for Boston University Concert Programs was supported by the Boston University Humanities Library Endowed Fund

From local to nonlocal Fermi liquid in doped antiferromagnets

The variation of single-particle spectral functions with doping is studied numerically within the t-J model. It is shown that corresponding self energies change from local ones at the intermediate doping to strongly nonlocal ones for a weakly doped antiferromagnet. The nonlocality shows up most clearly in the pseudogap emerging in the density of states, due to the onset of short-range antiferromagnetic correlations.Comment: 4 pages, 3 Postscript figures, revtex, submitted to Phys.Rev.Let

A micromorphological evaluation of pedogenesis on Isla Santa Cruz (Galápagos)

Thin sections of about 200 horizons or layers, representing 60 soil profiles in the coastal area and on the windward slopes of Isla Santa Cruz (Galápagos Islands) were analysed. Based on the fabric and the composition of the groundmass and the presence of pedofeatures in individual layers or horizons, clusters of similar material are made and 7 units and 3 subunits distinguished. Plotting these units on a survey map gives a good insight in the spatial distribution of soil materials, expressing different combinations of parent material and precipitation. In the coastal area and the lowest slopes, with a summer dry climate, respectively reddish and greyish and brown materials with a porphyric c/f related distribution pattern and striated b-fabrics, and often with fragmented illuvial clay coatings are observed. The coarse material contains mainly holocrystalline basalt fragments, unweathered in the coastal area, or basalt derived individual minerals. The micromass has a halloysitic-smectitic composition. On the higher slopes, with a permanent moist climate, materials have also a porphyric or fine monic c/f related distribution pattern, but the b-fabric is undifferentiated and no illuvial features are present, gibbsitic features sometimes occur and the micromass consists mainly of halloysite and gibbsite. Subunits are distinguished here according to the microstructure, and the quantity and type of coarse material. Mesocrystalline basalt, often vesicular, dominates over holocrystalline, pointing to the influence of scoria. Soils on the higher slopes are more strongly weathered than those on the drier lower slopes and the coastal area. In depressions in the higher areas, materials with a yellowish or brownish grey micromass with a striated b-fabric, and well developed limpid illuvial clay coatings and impregnative iron oxide nodules occur. The micromass has a halloysite-smectite composition. Contrary to existing hypotheses the reddish soils in the coastal area are not considered as palaeosoils (roots of tropical soils), but as modern soils developed in colluvium on the lower slopes, which was deposited on totally eroded surfaces (marine terraces?). On the slopes the distribution of units is not only determined by hypsometric zones, as suggested in literature, but is rather clustered according to types of parent material. The soils on Santa Cruz are supposed to be formed after the last interglacial period, different from the red soils of San Cristóbal which are older.<br>Se analizaron láminas delgadas de unos 200 horizontes o capas procedentes de 60 perfiles de suelos localizados en el área costera y en las laderas de barlovento de la Isla Santa Cruz (Islas Galápagos). En base a la contextura, la composición de la masa basal y la presencia de edaforasgos en las capas individuales u horizontes, se realizaron clusters de material similar y se distinguieron 7 unidades y 3 subunidades. La demarcación de estas unidades en un mapa permite obtener una buena perspectiva de la distribución espacial de los distintos materiales de suelo, que expresan diferentes combinaciones de material parental y precipitación. En la zona costera y en las laderas más bajas, con un clima con verano seco, se observan, respectivamente, materiales rojizos o grisáceos y materiales pardos con una distribución relacionada c/f tipo porfídica y contexturas birrefringentes estriadas, y frecuentemente aparecen con revestimientos de arcilla iluvial fragmentados. El material grueso contiene principalmente fragmentos de basalto holocristalino, sin meteorizar en la zona costera, o minerales individuales derivados de basalto. La micromasa tiene una composición haloisítico-esmectítica. En las laderas más elevadas, con un clima permanentemente húmedo, los materiales también tienen una distribución relacionada c/f tipo porfídica o mónica fina, pero la contextura birrefringente es indiferenciada y no aparecen rasgos iluviales, los rasgos gibsíticos aparecen alguna vez y la micromasa está formada fundamentalmente por haloysita y gibsita. En este caso las subunidades se distinguen en función de la microestructura y la cantidad y tipo de material grueso. El basalto mesocristalino, a menudo vesicular, domina sobre el holocristalino, indicando la influencia de las escorias. Los suelos sobre las laderas más elevadas están más fuertemente meteorizados que los que se encuentran en las laderas más bajas y más secas y en las zonas costeras. En las depresiones de las zonas elevadas aparecen materiales con una micromasa de amarillenta a pardo grisácea con una contextura birrefringente estriada, y revestimientos de arcilla límpida iluvial bien desarrollados y nódulos de óxidos de hierro. La micromasa está formada por haloisita y esmectita. Contrariamente a las hipótesis existentes, los suelos rojos en la zona costera no están considerados como paleosuelos (residuos de suelos tropicales) sino como suelos modernos desarrollados sobre materiales coluviales en las laderas más bajas, que fueron depositados sobre superficies totalmente erosionadas (¿terrazas marinas?). En las laderas la distribución de unidades no está solo determinada por zonas hipsométricas, tal y como sugiere la literatura, sino que está determinada sobre todo por el tipo de material original. Se supone que los suelos de Santa Cruz se han formado después del último periodo interglacial, diferentes de los suelos rojos más antiguos de San Cristóbal.<br>Lâminas delgadas de cerca de 200 horizontes ou camadas, que representam 60 perfis de solo na zona costeira e nas encostas de barlavento da Ilha de Santa Cruz (Ilhas Galápagos) foram analisadas. Com base na estrutura e composição do fundo matricial e na presença de pedocaracteres nas camadas individuais ou horizontes, podem-se estabelecer grupos de material semelhante e definir 7 unidades e 3 subunidades. Ao marcar estas unidades num mapa de levantamento, obtém-se uma boa perspectiva da distribuição espacial dos vários materiais do solo, que expressam diferentes combinações de material originário e de precipitação. Na zona costeira e encostas mais baixas, com um clima com verão seco, observam-se respectivamente materiais avermelhados ou acinzentados e materiais castanhos, com distribuição relacionada g/f porfírica e tessitura-b estriada, e muitas vezes com revestimentos de argila iluvial fragmentados. O material grosseiro contém principalmente fragmentos de basalto holocristalino, não meteorizado na zona costeira, ou minerais individuais derivados do basalto. A composição da micromassa é haloisítico-esmectítica. Nas encostas mais altas, com um clima permanentemente húmido, os materiais têm também uma distribuição relacionada g/f porfírica ou mónica fina, mas a tessitura-b é indiferenciada, não se observam pedocaracteres iluviais, pedocaracteres gibsíticos ocorrem algumas vezes e a micromassa consiste principalmente de haloisite e gibsite. Neste caso as subunidades são definidas de acordo com a microestrutura e a quantidade e tipo de material grosseiro. O basalto mesocristalino, frequentemente vesicular, é dominante relativamente ao basalto holocristalino, indicando a influência de escória. Os solos das encostas mais elevadas são mais fortemente meteorizados do que os das encostas mais baixas e mais secas e os da zona costeira. Em depressões nas áreas mais elevadas, encontram-se materiais com micromassa cinzenta amarelada ou acastanhada, tessitura-b estriada, revestimentos de argila límpida iluvial bem desenvolvidos e nódulos de óxido de ferro impregnativo. O micromassa é composta por haloisite e esmectite. Contrariamente às hipóteses existentes os solos avermelhados da zona costeira não são paleosolos (resíduos de solos tropicais), mas solos modernos desenvolvidos em material coluvial nas encostas mais baixas, que foi depositado sobre superfícies totalmente erodidas (terraços marinhos?). Nas encostas a distribuição de unidades não é apenas determinada pelas zonas hipsométricas, como sugerido na literatura, mas sobretudo determinada pelo tipo de material originário. Supõe-se que os solos em Santa Cruz se formaram após o último período interglacial, contrariamente aos solos vermelhos de San Cristóbal que são mais velhos

Dynamical Mean-Field Study of Metamagnetism in Heavy Fermion Systems

We investigate the metamagnetism in the periodic Anderson model with the $\bm{k}$-dependent $c-f$ mixing by using the dynamical mean-field theory combined with the exact diagonalization method. It is found that both effects of the $\bm{k}$-dependent $c-f$ mixing and strong correlation due to the Coulomb interaction between $f$ electrons are significant for determining both the magnetization and the mass enhancement factor. For the case away from the half-filling, the results is consistent with the metamagnetic behavior observed in CeRu$_2$Si$_2$.Comment: 3 pages, 4 figures, accepted in J. Phys. Soc. Jpn. 80 (2011) Suppl. (Proc. ICHE2010

Competition between electron-phonon attraction and weak Coulomb repulsion

The Holstein-Hubbard model is examined in the limit of infinite dimensions. Conventional folklore states that charge-density-wave (CDW) order is more strongly affected by Coulomb repulsion than superconducting order because of the pseudopotential effect. We find that both incommensurate CDW and superconducting phases are stabilized by the Coulomb repulsion, but, surprisingly, the commensurate CDW transition temperature is more robust than the superconducting transition temperature. This puzzling feature is resolved by a detailed analysis of perturbation theory.Comment: 13 pages in ReVTex including 3 encapsulated postscript files (embedded in the text). The encapsulated postscript files are compressed and uuencoded after the TeX file

Iterative Perturbation Theory for Strongly Correlated Electron Systems with Orbital Degeneracy

A new scheme of the iterative perturbation theory is proposed for the strongly correlated electron systems with orbital degeneracy. The method is based on the modified self-energy of Yeyati, et al. which interpolates between the weak and the strong correlation limits, but a much simpler scheme is proposed which is useful in the case of the strong correlation with orbital degeneracy. It will be also useful in the study of the electronic structures combined with the band calculations.Comment: 6 pages, 3 Postscript figures, to appear in J. Phys. Cond. Matte

Vertex Corrections and the Korringa Ratio in Strongly Correlated Electron Materials

We show that the Korringa ratio, associated with nuclear magnetic resonance in metals, is unity if vertex corrections for the dynamic spin susceptibility are negligible and the hyperfine coupling is momentum independent. In the absence of vertex corrections we also find a Korringa behaviour for $T_1$, the nuclear spin relaxation rate, i.e., $1/T_1\propto T$, and a temperature independent Knight shift. These results are independent of the form and magnitude of the self-energy (so far as is consistent with neglecting vertex corrections) and of the dimensionality of the system.Comment: 5 pages. accepted for publication in J. Phys.: Condens. Matte

Hot Spots and Pseudogaps for Hole- and Electron-Doped High-Temperature Superconductors

Using cluster perturbation theory, it is shown that the spectral weight and pseudogap observed at the Fermi energy in recent Angle Resolved Photoemission Spectroscopy (ARPES) of both electron and hole-doped high-temperature superconductors find their natural explanation within the t-t'-t''-U Hubbard model in two dimensions. The value of the interaction U needed to explain the experiments for electron-doped systems at optimal doping is in the weak to intermediate coupling regime where the t-J model is inappropriate. At strong coupling, short-range correlations suffice to create a pseudogap but at weak coupling long correlation lengths associated with the antiferromagnetic wave vector are necessary.Comment: RevTeX 4, 4 pages, 5 figures (2 in color