Phase diagram and dependence of the critical temperature T_c on the pressure for Tl_{0.5}Pb_{0.5}Sr_2Ca_{1-x}Y_xCu_2)_7

Using a mean-field BCS-like approach on the bidimensional extended Hubbard Hamiltonian we calculate the superconducting transition temperature Tc as a function of the hole content nh, for the d-wave and extended-s wave gap symmetries. To describe the pressure effect on Tc we assume it induces a change in the magnitude V of the attractive superconductor potential. This assumption yields an explanation for the intrinsic term, and together with the well known change in nh, we set the critical temperature as Tc=Tc(nh(P),V(P)). With this we obtain a general expansion of Tc in terms of the pressure P and the hole content nh. We apply this expansion to the Tl_{0.5}Pb_{0.5}Sr_2Ca_{1-x}Y_xCu_2)_7 system

Theoretical high-TcT_c d-wave superconducting gap in an inhomogeneous medium

We perform theoretical calculations to obtain a distribution of local d-wave superconducting gaps $\Delta_0({r})$ for a high temperature superconducting (HTSC) series in a disordered superconductor with an average doping level $$. To reproduce the inhomogeneous medium a nonmagnetic random potential $V^{imp}$, within a Bogoliubov-de Gennes (BdG) formalism, is considered. First the phase diagram $\Delta_0 x$ for the LSCO HTSC series, with V^{imp}=0, is obtained. Then, we perform calculations considering a fixed value of the disorder strength $V^{imp}$ and obtain a distribution of local superconducting gaps $\Delta_0({r})$, and local density of charge carriers $\rho({r})$. It is shown that the underdoped compounds are more inhomogeneous than the overdoped ones, which is in accordance with experimental findings. Also, the spatial variation of $\Delta_0({r})$ indicates that as increases, the system becomes more homogeneous.Comment: 6 pages and 6 fig

A Theory for High-TcT_c Superconductors Considering Inhomogeneous Charge Distribution

We propose a general theory for the critical $T_c$ and pseudogap $T^*$ temperature dependence on the doping concentration for high-$T_c$ oxides, taking into account the charge inhomogeneities in the $CuO_2$ planes. The well measured experimental inhomogeneous charge density in a given compound is assumed to produce a spatial distribution of local $\rho(r)$. These differences in the local charge concentration is assumed to yield insulator and metallic regions, possibly in a stripe morphology. In the metallic region, the inhomogeneous charge density yields also spatial distributions of superconducting critical temperatures $T_c(r)$ and zero temperature gap $\Delta_0(r)$. For a given sample, the measured onset of vanishing gap temperature is identified as the pseudogap temperature, that is, $T^*$, which is the maximum of all $T_c(r)$. Below $T^*$, due to the distribution of $T_c(r)$'s, there are some superconducting regions surrounded by insulator or metallic medium. The transition to a superconducting state corresponds to the percolation threshold among the superconducting regions with different $T_c(r)$'s. To model the charge inhomogeneities we use a double branched Poisson-Gaussian distribution. To make definite calculations and compare with the experimental results, we derive phase diagrams for the BSCO, LSCO and YBCO families, with a mean field theory for superconductivity using an extended Hubbard Hamiltonian. We show also that this novel approach provides new insights on several experimental features of high-$T_c$ oxides.Comment: 7 pages, 5 eps figures, corrected typo

Theory of the Diamagnetism Above the Critical Temperature for Cuprates

Recently experiments on high critical temperature superconductors has shown that the doping levels and the superconducting gap are usually not uniform properties but strongly dependent on their positions inside a given sample. Local superconducting regions develop at the pseudogap temperature ($T^*$) and upon cooling, grow continuously. As one of the consequences a large diamagnetic signal above the critical temperature ($T_c$) has been measured by different groups. Here we apply a critical-state model for the magnetic response to the local superconducting domains between $T^*$ and $T_c$ and show that the resulting diamagnetic signal is in agreement with the experimental results.Comment: published versio

Pressure Studies on a High-TcT_c Superconductor Pseudogap and Critical Temperatures

We report simultaneous hydrostatic pressure studies on the critical temperature $T_c$ and on the pseudogap temperature $T^*$ performed through resistivity measurements on an optimally doped high-$T_c$ oxide $Hg_{0.82}Re_{0.18}Ba_2Ca_2Cu_3O_{8+\delta}$. The resistivity is measured as function of the temperature for several different applied pressure below 1GPa. We find that both $T_c$ and $T^*$ increases linearly with the pressure. This result demonstrate that the well known intrinsic pressure effect on $T_c$ is also present at $T^*$ and both temperatures are originated by the same superconducting mechanism.Comment: 4 pages and 2 figures in eps, final versio

Upper critical field Hc2H_{c2} calculations for the high critical temperature superconductors considering inhomogeneities

We perform calculations to obtain the $H_{c2}$ curve of high temperature superconductors (HTSC). We consider explicitly the fact that the HTSC possess intrinsic inhomogeneities by taking into account a non uniform charge density $\rho(r)$. The transition to a coherent superconducting phase at a critical temperature $T_c$ corresponds to a percolation threshold among different superconducting regions, each one characterized by a given $T_c(\rho(r))$. Within this model we calculate the upper critical field $H_{c2}$ by means of an average linearized Ginzburg-Landau (GL) equation to take into account the distribution of local superconducting temperatures $T_c(\rho(r))$. This approach explains some of the anomalies associated with $H_{c2}$ and why several properties like the Meissner and Nernst effects are detected at temperatures much higher than $T_c$.Comment: Latex text, add reference

Does hepatocellular carcinoma in non-alcoholic steatohepatitis exist in cirrhotic and non-cirrhotic patients?

Non-alcoholic steatohepatitis (NASH) has been associated with hepatocellular carcinoma (HCC) often arising in histologically advanced disease when steatohepatitis is not active (cryptogenic cirrhosis). Our objective was to characterize patients with HCC and active, histologically defined steatohepatitis. Among 394 patients with HCC detected by ultrasound imaging over 8 years and staged by the Barcelona Clinic Liver Cancer (BCLC) criteria, we identified 7 cases (1.7%) with HCC occurring in the setting of active biopsy-proven NASH. All were negative for other liver diseases such as hepatitis C, hepatitis B, autoimmune hepatitis, Wilson disease, and hemochromatosis. The patients (4 males and 3 females, age 63 ± 13 years) were either overweight (4) or obese (3); 57% were diabetic and 28.5% had dyslipidemia. Cirrhosis was present in 6 of 7 patients, but 1 patient had well-differentiated HCC in the setting of NASH without cirrhosis (fibrosis stage 1) based on repeated liver biopsies, the absence of portal hypertension by clinical and radiographic evaluations and by direct surgical inspection. Among the cirrhotic patients, 71.4% were clinically staged as Child A and 14.2% as Child B. Tumor size ranged from 1.0 to 5.2 cm and 5 of 7 patients were classified as early stage; 46% of all nodules were hyper-echoic and 57% were <3 cm. HCC was well differentiated in 1/6 and moderately differentiated in 5/6. Alpha-fetoprotein was <100 ng/mL in all patients. HCC in patients with active steatohepatitis is often multifocal, may precede clinically advanced disease and occurs without diagnostic levels of alpha-fetoprotein. Importantly, HCC may occur in NASH in the absence of cirrhosis. More aggressive screening of NASH patients may be warranted

Search for fingerprints of disoriented chiral condensates in cosmic ray showers

Although the generation of disoriented chiral condensates (DCCs), where the order parameter for chiral symmetry breaking is misaligned with respect to the vacuum direction in isospin state, is quite natural in the theory of strong interactions, they have so far eluded experiments in accelerators and cosmic rays. If DCCs are formed in high-energy nuclear collisions, the relevant outcome are very large event-by-event fluctuations in the neutral-to-charged pion fraction. In this note we search for fingerprints of DCC formation in observables of ultra-high energy cosmic ray showers. We present simulation results for the depth of the maximum ($X_{max}$) and number of muons on the ground, evaluating their sensitivity to the neutral-to-charged pion fraction asymmetry produced in the primary interaction.Comment: 7 pages, 4 figure