Time reversal symmetry breaking in cuprates induced by the spiral spin order

We propose a new interpretation of the spontaneous time reversal symmetry breaking (TRSB) observed recently in a pseudogap state of cuprate (Kaminsky et al.). It is shown that the TRSB dichroism in ARPES signal may be connected with the local spiral spin structures in system. It may be caused by a spin-orbit interaction and by spin polarization of electrons at various sections of Fermi surface in spiral state. Angular dependence of dichroism signal is studied in schematic KKR approximation. Tests are proposed to check an existence of the local spiral spin structure and to distiguish it from the TRSB state with micro-currents constructed by Varma.Comment: 7 pages, Revtex, 4 figure

Metal-insulator transition in a doubly orbitally degenerate model with correlated hopping

In the present paper we propose a doubly orbitally degenerate narrow-band model with correlated hopping. The peculiarity of the model is taking into account the matrix element of electron-electron interaction which describes intersite hoppings of electrons. In particular, this leads to the concentration dependence of the effective hopping integral. The cases of the strong and weak Hund's coupling are considered. By means of a generalized mean-field approximation the single-particle Green function and quasiparticle energy spectrum are calculated. Metal-insulator transition is studied in the model at different integer values of the electron concentration. With the help of the obtained energy spectrum we find energy gap width and criteria of metal-insulator transition.Comment: minor revisions, published in Phys. Rev.

Structural and thermoelectric properties of n-type isocubanite CuFe2S3

International audienceAn effective strategy to enhance thermoelectric performance consists of scattering phonons by point defects, such as the ones intrinsic to the n-type isocubanite CuFe2S3. In this structure, the TEM evidences a random distribution of vacancies, and copper and iron ions of the 4c and 4d sites naturally reduce the phonon lifetime. Furthermore, orthorhombic and cubic cubanite are usually found in their natural states intimately intergrown with other sulfides such as chalcopyrite (CuFeS2) and pyrrhotite (Fe7S8). We performed comprehensive studies of Rietveld analysis of X-ray diffraction, transmission electron microscopy, and thermoelectric transport measurements of the n-type isocubanite CuFe2S3, and we obtained a maximum ZT value of 0.14 at 700 K in this environmentally friendly compound. Our electronic structure calculations support the fact that chalcopyrite CuFeS2 is an antiferromagnetic insulator, together with a higher degree of covalency of sulfide compared to oxides. The weak temperature dependence of the resistivity points towards strong disorder in the 4c and 4d sites of the isocubanite

Structural and thermoelectric properties of n-type isocubanite CuFe2S3

International audienceAn effective strategy to enhance thermoelectric performance consists of scattering phonons by point defects, such as the ones intrinsic to the n-type isocubanite CuFe2S3. In this structure, the TEM evidences a random distribution of vacancies, and copper and iron ions of the 4c and 4d sites naturally reduce the phonon lifetime. Furthermore, orthorhombic and cubic cubanite are usually found in their natural states intimately intergrown with other sulfides such as chalcopyrite (CuFeS2) and pyrrhotite (Fe7S8). We performed comprehensive studies of Rietveld analysis of X-ray diffraction, transmission electron microscopy, and thermoelectric transport measurements of the n-type isocubanite CuFe2S3, and we obtained a maximum ZT value of 0.14 at 700 K in this environmentally friendly compound. Our electronic structure calculations support the fact that chalcopyrite CuFeS2 is an antiferromagnetic insulator, together with a higher degree of covalency of sulfide compared to oxides. The weak temperature dependence of the resistivity points towards strong disorder in the 4c and 4d sites of the isocubanite

Preoperative Peak Oxygen Uptake in Lung Cancer Subjects With Neoadjuvant Chemotherapy: A Cross-Sectional Study.

BACKGROUND: In non-small-cell lung cancer patients, high peak oxygen uptake (peak V̇O2 ) predicts lower rates of postoperative complications and better long-term survival. Neoadjuvant chemotherapy (NAC) may negatively impact peak V̇O2 . METHODS: Cardiopulmonary exercise testing (CPET) was performed in 34 consecutive stage IIIA/IIIB non-small-cell lung cancer subjects scheduled for elective lung surgery. Using multivariate linear regression adjusted for potential confounders, we compared CPET results in subjects receiving or not receiving NAC (NAC+, n = 19; NAC-, n = 15). RESULTS: Adjusted peak V̇O2 was lower in NAC + compared with NAC- subjects (-5.3 mL/min/kg [95% CI -8.3 to -2.2], P = .01). Likewise, oxygen pulse, maximal work load, and ventilatory threshold were also lower in NAC+ subjects, whereas peak heart rate and breathing reserve were similar. NAC+ subjects presented lower values of diffusion capacity for carbon monoxide (DLCO) (P = .035) and hemoglobin concentrations (P < .001). DLCO was strongly correlated with peak V̇O2 (r(2) = 0.56). Adjustment for DLCO reduced the effect of NAC on peak V̇O2 without suppressing it. CONCLUSIONS: NAC was associated with lower preoperative peak V̇O2 in subjects with non-small-cell lung cancer. This lower aerobic fitness may result from NAC-induced reduction in pulmonary gas exchange or heart toxicity. Since lower fitness is linked to poorer outcome, the decision for NAC may have to be balanced with its possible toxicity