Interplay of the pseudogap and the BCS gap for heteropairs in 40^{40}K-6^6Li mixture

The description of heteropairs like $^{40}$K-$^6$Li near and in the superconducting state requires a fully selfconsistent theory [see Hanai and Ohashi, Phys. Rev. A 90, 043622 (2014)]. We derive analytic pseudogap Green's functions for the "normal" and superconducting states from the Luttinger-Ward theory with the T-matrix in the static separable approximation. The self-consistency in the closing loop of self-energy has two pronounced effects on the single-particle spectrum. First, the single-particle excitations decay before the asymptotic quasiparticle propagation is established, therefore the normal state is not a Fermi liquid. Second, the pseudogap has a V shape even for s-wave pairing. The V-shaped pseudogap and the U-shaped BCS gap interfere resulting in slope breaks of the gap walls and the in-gap states in the density of states. Various consequences of an incomplete self-consistency are demonstrated.Comment: Published versio

Thermal expansion of chromium-rich iron-based or iron/nickel-based alloys reinforced by tantalum carbides

Six alloys reinforced by TaC carbides based on iron (ferritic) or both iron and nickel (austenitic) were studied in thermal expansion between 100 and 1200°C for two microstructure orientations. The heating, isothermal and cooling parts of the dilatometry curves were characterized. The thermal expansion of the ferritic alloys is less important than that of the austenitic alloys. A compressive deformation of the matrix subjected to stresses applied by the carbides network was observed. The importance of this phenomenon seems depending more on the matrix nature than on the microstructure orientation.Досліджено шість сплавів на основі заліза (феритні та аустенітні) і нікелю, зміцнені карбідами TaC, та їх термічне розширення в інтервалі 100...1200°C для двох мікроструктурних орієнтацій. Проаналізовано ізотермічну та охолоджувальну ділянки на дилатометричних кривих. Термічне розширення феритних сплавів виражене не так чітко, як аустенітних. Стискальні деформації матриці призводять до напружень, які поширюються на колонії карбідів. Важливість цього явища вбачається у впливі фази матриці на мікроструктурні особливості сплаву загалом.Исследовано шесть сплавов на основе железа (ферритные и аустенитные) и никеля, упрочненных карбидами ТаС, и их термическое расширение в интервале 100... 1200°C для двух микроструктурных ориентаций. Проанализированы изотермический и охлаждающим участки на дилатометрических кривых. Термическое расширение ферритных сплавов выражено менее четко, нежели аустенитных. Сжимающие деформации матриц обуславливают напряжениям, которые распространяются на колонии карбидов. Важность этого явления видится во влиянии матричной фазы на микроструктурные особенности сплава в целом

Node-like excitations in superconducting PbMo6S8 probed by scanning tunneling spectroscopy

We present the first scanning tunneling spectroscopy study on the Chevrel phase PbMo6S8, an extreme type II superconductor with a coherence length only slightly larger than in high-Tc cuprates. Tunneling spectra measured on atomically flat terraces are spatially homogeneous and show well-defined coherence peaks. The low-energy spectral weight, the zero bias conductance and the temperature dependence of the gap are incompatible with a conventional isotropic s-wave interpretation, revealing the presence of low-energy excitations in the superconducting state. We show that our data are consistent with the presence of nodes in the superconducting gap.Comment: To appear in PRB; 5 pages, 4 figure

Hall effect in strongly correlated low dimensional systems

We investigate the Hall effect in a quasi one-dimensional system made of weakly coupled Luttinger Liquids at half filling. Using a memory function approach, we compute the Hall coefficient as a function of temperature and frequency in the presence of umklapp scattering. We find a power-law correction to the free-fermion value (band value), with an exponent depending on the Luttinger parameter $K_{\rho}$. At high enough temperature or frequency the Hall coefficient approaches the band value.Comment: 7 pages, 3 figure

Tunneling spectra of strongly coupled superconductors: Role of dimensionality

We investigate numerically the signatures of collective modes in the tunneling spectra of superconductors. The larger strength of the signatures observed in the high-Tc superconductors, as compared to classical low-Tc materials, is explained by the low dimensionality of these layered compounds. We also show that the strong-coupling structures are dips (zeros in the d2I/dV2 spectrum) in d-wave superconductors, rather than the steps (peaks in d2I/dV2) observed in classical s-wave superconductors. Finally we question the usefulness of effective density of states models for the analysis of tunneling data in d-wave superconductors.Comment: 8 pages, 6 figure

Multi-band Superconductivity in the Chevrel Phases SnMo6S8 and PbMo6S8

Sub-Kelvin scanning tunnelling spectroscopy in the Chevrel Phases SnMo6S8 and PbMo6S8 reveals two distinct superconducting gaps with Delta_1 = 3 meV, Delta_2 ~ 1.0 meV and Delta_1 = 3.1 meV, Delta_2 ~ 1.4 meV respectively. The gap distribution is strongly anisotropic, with Delta_2 predominantly seen when scanning across unit-cell steps on the (001) sample surface. The spectra are well-fitted by an anisotropic two-band BCS s-wave gap function. Our spectroscopic data are confirmed by electronic heat capacity measurements which also provide evidence for a twin-gap scenario.Comment: 5 pages, 4 figure

Bone mineral density in breast cancer patients treated with adjuvant letrozole, tamoxifen, or sequences of letrozole and tamoxifen in the BIG 1-98 study (SAKK 21/07)

Background: The risk of osteoporosis and fracture influences the selection of adjuvant endocrine therapy. We analyzed bone mineral density (BMD) in Swiss patients of the Breast International Group (BIG) 1-98 trial [treatment arms: A, tamoxifen (T) for 5 years; B, letrozole (L) for 5 years; C, 2 years of T followed by 3 years of L; D, 2 years of L followed by 3 years of T]. Patients and methods: Dual-energy X-ray absorptiometry (DXA) results were retrospectively collected. Patients without DXA served as control group. Repeated measures models using covariance structures allowing for different times between DXA were used to estimate changes in BMD. Prospectively defined covariates were considered as fixed effects in the multivariable models. Results: Two hundred and sixty-one of 546 patients had one or more DXA with 577 lumbar and 550 hip measurements. Weight, height, prior hormone replacement therapy, and hysterectomy were positively correlated with BMD; the correlation was negative for letrozole arms (B/C/D versus A), known osteoporosis, time on trial, age, chemotherapy, and smoking. Treatment did not influence the occurrence of osteoporosis (T score < −2.5 standard deviation). Conclusions: All aromatase inhibitor regimens reduced BMD. The sequential schedules were as detrimental for bone density as L monotherap

The Density of States in High-Tc Superconductors Vortices

We calculated the electronic structure of a vortex in a pseudogapped superconductor within a model featuring strong correlations. With increasing strength of the correlations, the BCS core states are suppressed and the spectra in and outside the core become similar. If the correlations are short-range, we find new core states in agreement with the observations in YBaCuO and BiSrCaCuO. Our results point to a common phenomenology for these two systems and indicate that normal-state correlations survive below Tc without taking part in the overall phase coherence.Comment: REVTeX 4, 5 pages, 2 EPS figures. Some changes to the text; new figures; references update

Influence of the Cr Content on the Corrosion Properties of a Series of Binary Cobalt-Chromium Alloys in Acidic Artificial Saliva

International audienceCobalt-based alloys are more and more considered for dental applications, instead the expensive noble alloys and the other predominantly based alloys based on the allergen element nickel. These alloys frequently contain chromium to allow good resistance against corrosion as this may take place in the buccal milieu. The most often chromium is present in high quantity, close to 30wt. %, but it is maybe possible to decrease a little its contents without losing corrosion resistance. The aim of this study is exploring how the corrosion behavior of a cobalt alloy may vary versus its chromium content. In order to simplify this investigation only Co-xCrbinary alloys were considered, with x decreasing from 30 to 0wt.% by slices of 5wt.%. A series of seven alloys was synthesized by foundry under inert atmosphere and their behavior in corrosion in an artificial saliva of simple composition (NaCl 9g/L) acidified to pH=2.3 was specified using various classical electrochemical techniques (open circuit potential follow-up, Stern-Geary, Tafel, cyclic polarization). It appeared that passivation of the alloys occurred during the first two hours of immersion when the chromium content was 10 wt. % or higher, with as result high corrosion potentials and low corrosion current densities

QED3 theory of pairing pseudogap in cuprates: From d-wave superconductor to antiferromagnet via "algebraic" Fermi liquid

High-$T_c$ cuprates differ from conventional superconductors in three crucial aspects: the superconducting state descends from a strongly correlated Mott-Hubbard insulator, the order parameter exhibits d-wave symmetry and superconducting fluctuations play an all important role. We formulate a theory of the pseudogap state in the cuprates by taking the advantage of these unusual features. The effective low energy theory within the pseudogap phase is shown to be equivalent to the (anisotropic) quantum electrodynamics in (2+1) space-time dimensions (QED$_3$). The role of Dirac fermions is played by the nodal BdG quasiparticles while the massless gauge field arises through unbinding of quantum vortex-antivortex degrees of freedom. A detailed derivation of this QED$_3$ theory is given and some of its main physical consequences are inferred for the pseudogap state. We focus on the properties of symmetric QED$_3$ and propose that inside the pairing protectorate it assumes the role reminiscent of that played by the Fermi liquid theory in conventional metals.Comment: 31 pages, 4 figures; replaced with revised versio