Electronic structure and possible pseudogap behavior in iron based superconductors

Starting from the simplified analytic model of electronic spectrum of iron - pnictogen (chalcogen) high - temperature superconductors close to the Fermi level, we discuss the influence of antiferromagneting (AFM)scattering both for stoichiometric case and the region of possible short - range order AFM fluctuations in doped compounds. Qualitative picture of the evolution of electronic spectrum and Fermi surfaces (FS) for different dopings is presented, with the aim of comparison with existing and future ARPES experiments. Both electron and hole dopings are considered and possible pseudogap behavior connected with partial FS "destruction" is demonstrated, explaining some recent experiments.Comment: 5 pages, 4 figures, published versio

Contrast of LiFeAs with isostructural, isoelectronic, and non-superconducting MgFeGe

Stoichiometric LiFeAs at ambient pressure is an 18 K superconductor while isoelectronic MgFeGe is not, despite their extremely similar electronic structures. To investigate possible sources of this distinctively different superconducting behavior, we quantify the differences using first principles density functional theory, establishing first that the Fe total 3d occupations are identical in the two compounds. Individual 3d orbital occupations also differ very little ($\sim 0.01$). The differences in Fermi surfaces (FSs) do not seem significant; however a redistribution of bands just above the Fermi level does represent a possibly significant distinction. Because the bands and FSs of LiFeAs are less in agreement with experiment than for other iron-pnictides, we study the effects of additional exchange-correlations effects beyond GGA (the generalized gradient approximation) by applying the modified Becke-Johnson potential (mBJ) exchange potential, which gives much improved bandgaps in insulators compared to GGA and might be useful for semimetals such as the Fe-based superconductors. Overall, we conclude that the mBJ corrections do not improve the description of LiFeAs as compared to experiment

Building light nuclei from neutrons, protons, and pions

In these lectures I first explain, in a rather basic fashion, the construction of effective field theories. I then discuss some recent developments in the application of such theories to two- and three-nucleon systems.Comment: 54 pages, uses czjphys.cls. Lectures given at 14th Summer School "Understanding the Structure of Hadrons", Prague, July 2001. To appear in Czechoslovak Journal of Physic

Clinicoepidemiologic features of tuberculosis among HIV-infected children living in Sverdlovsk Region

Social and economic events happened the 90s resulted in the increase of sickness rate of tuberculosis among children. In addition, in the last years the number of HIV-infected has increased among adults and childrenas well as sickness rate of tuberculosis among HIV-infected including children. The article gives the data of the analysis of the epidemiological and clinical features of tuberculosis among HIV-infected children (20 children) in comparison with non- HIV-infected children (16 children). All HIV-infected children were infected by vertical way, but when tuberculosis has developed, the III-IV stages of HIV-infection were diagnosed more often. It was revealed that 65% of children in this group had family contact with tubercular patients. More than half (60 %) patients had complications in tuberculosis course; a third (30%) had bacterioexcretion. Mantoux test showed positive result in 65% of the cases, Diaskintest had diagnostic value at 7 children out of 8 ones.Социально-экономические потрясения 90-х годов привели к увеличению показателей заболеваемости детей туберкулезом. Кроме того, в последние годы наблюдается увеличение доли инфицированных ВИЧ среди взрослого и детского населения, рост заболеваемости туберкулезом среди ВИЧ-инфицированных лиц, в том числе - детей. В статье приведены данные анализа эпидемиологических и клинических особенностей туберкулеза у ВИЧ-инфицированных детей (20 детей) в сравнении с не инфицированными ВИЧ (16 детей). Все ВИЧ-инфицированные дети были заражены вертикальным путем, при развитии туберкулеза чаще диагностировалась III-IV стадии ВИЧ-инфекции. У 65% детей данной группы был выявлен семейный контакт с больными туберкулезом. Более чем у половины (60%) пациентов туберкулез протекал осложненно, у трети (30%) наблюдалось бактерио-выделение. Проба Манту лишь в 65% случаев была положительной, Диаскинтест у 7 детей из 8 имел диагностическую ценность

Electronic Structure Calculation by First Principles for Strongly Correlated Electron Systems

Recent trends of ab initio studies and progress in methodologies for electronic structure calculations of strongly correlated electron systems are discussed. The interest for developing efficient methods is motivated by recent discoveries and characterizations of strongly correlated electron materials and by requirements for understanding mechanisms of intriguing phenomena beyond a single-particle picture. A three-stage scheme is developed as renormalized multi-scale solvers (RMS) utilizing the hierarchical electronic structure in the energy space. It provides us with an ab initio downfolding of the global band structure into low-energy effective models followed by low-energy solvers for the models. The RMS method is illustrated with examples of several materials. In particular, we overview cases such as dynamics of semiconductors, transition metals and its compounds including iron-based superconductors and perovskite oxides, as well as organic conductors of kappa-ET type.Comment: 44 pages including 38 figures, to appear in J. Phys. Soc. Jpn. as an invited review pape

Pairing symmetry and properties of iron-based high temperature superconductors

Pairing symmetry is important to indentify the pairing mechanism. The analysis becomes particularly timely and important for the newly discovered iron-based multi-orbital superconductors. From group theory point of view we classified all pairing matrices (in the orbital space) that carry irreducible representations of the system. The quasiparticle gap falls into three categories: full, nodal and gapless. The nodal-gap states show conventional Volovik effect even for on-site pairing. The gapless states are odd in orbital space, have a negative superfluid density and are therefore unstable. In connection to experiments we proposed possible pairing states and implications for the pairing mechanism.Comment: 4 pages, 1 table, 2 figures, polished versio

Nuclear magnetic relaxation and superfluid density in Fe-pnictide superconductors: An anisotropic \pm s-wave scenario

We discuss the nuclear magnetic relaxation rate and the superfluid density with the use of the effective five-band model by Kuroki et al. [Phys. Rev. Lett. 101, 087004 (2008)] in Fe-based superconductors. We show that a fully-gapped anisotropic \pm s-wave superconductivity consistently explains experimental observations. In our phenomenological model, the gaps are assumed to be anisotropic on the electron-like \beta Fermi surfaces around the M point, where the maximum of the anisotropic gap is about four times larger than the minimum.Comment: 10 pages, 8 figures; Submitted versio

Coulomb repulsion and correlation strength in LaFeAsO from Density Functional and Dynamical Mean-Field Theories

LDA+DMFT (Local Density Approximation combined with Dynamical Mean-Field Theory) computation scheme has been used to calculate spectral properties of LaFeAsO -- the parent compound for new high-T$_c$ iron oxypnictides. Coulomb repulsion $U$ and Hund's exchange $J$ parameters for iron 3d electrons were calculated using \textit {first principles} constrained density functional theory scheme in Wannier functions formalism. Resulting values strongly depend on the number of states taken into account in calculations: when full set of O-$2p$, As-$4p$, and Fe-3d orbitals with corresponding bands are included, computation results in $U=3\div$4 eV and J=0.8 eV. In contrast to that when the basis set is restricted to Fe-3d orbitals and bands only, computation gives much smaller parameter values $F^0$=0.8 eV, $J$=0.5 eV. However, DMFT calculations with both parameter sets and corresponding to them choice of basis functions result in weakly correlated electronic structure that is in agreement with experimental X-ray and photoemission spectra.Comment: 13 pages, 9 figure

Doclinical pathology of the rear eye cut-off in patients with tuberculosis and pulmonary localization sarcoidosis

The method of optical coherence tomography provides valuable information about pathological changes in the anterior segment of the eye, in the central parts of the fundus, and also significantly complements the diagnostic capabilities of angiographic studies in various forms of retinal pathology. The caliber of the retinal vessels provides information on the state of microcirculation and is prognostically significant in relation to the development of severe damage to the organ of vision in people with various pathologies. A study of the state of the fundus vessels in patients with tuberculosis and pulmonary sarcoidosis was carried out. The results are obtained: pathology of the fundus vessels is present in patients with tuberculosis and sarcoidosis, but with sarcoidosis it is accompanied by clinical manifestations in the form of a decrease in visual acuity. The OCT method can be proposed for screening patients to detect preclinical fundus lesions.Метод оптической когерентной томографии позволяет получить ценную информацию о патологических изменениях в переднем сегменте глаза, в центральных отделах глазного дна, а также существенно дополняет диагностические возможности ангиографических исследований при различных формах патологии сетчатки. Калибр сосудов сетчатки глаза дает информацию о состоянии микроциркуляции и является прогностически значимым в отношении развития тяжелых поражений органа зрения у лиц с различной патологией. Проведено исследование состояния сосудов глазного дна у пациентов с туберкулезом и саркоидозом легочной локализации. Получены следующие результаты: патология сосудов глазного дна имеется у пациентов с туберкулезом и саркоидозом, но при саркоидозе сопровождается клиническими проявлениями в виде снижения остроты зрения. Метод ОКТ может быть предложен для скринингового обследования пациентов для выявления доклинических поражений глазного дна

Enteroureteroplasty in tuberculosis and other deseases

Results of intestinal reconstruction of the ureter in 25 patients are analysed. Ileal graft was used in 23 cases, appendix - in 2. Before surgery hydrourete-ronephrosis was diagnosed in all patients, renal insufficiency (stage I or II) - in 9 (36,0%). Percutaneous puncture nephrostomy as the first step of surgical treatment performed in 22 (88,0%) patients. The evaluation of complications and metabolic disorders was done in early and long-term postoperative period (6-12 months) in 25 and 21 patients respectively. Upper tract dilatation had improved or stabilized in all patients. Ileal loop necrosis occurred in 1 (4,0%) case, ileal anastomotic insufficiency — in 1 (4,0%)). Chlorine blood level was 107,2+2,3 mmol/l in early postoperative period and 106,8+1,9-6-12 months later, base deficit (BD) -1,43+1,8 and -2,15+1,9 respectively. Loopogram stu-dies revealed 2 cases of reflux and 1 - nephrosclerosis. The quality of life (QOL) study using the SF-36 survey showed significant improvement of all its components 6-12 months after the operation.Энтероуретеропластике подвергнуто 25 пациентов: 23 - илео-, 2 - аппендикоуретеропластике. У всех больных до операции имел место гидроуретеронефроз (ГУН), у 9 (36,0%) - хроническая почечная недостаточность. У 22 (88,0%) пациентов предварительно выполнена чрескожная пункционная нефростомия. Проведен анализ ранних и поздних осложнений (через 6-12 месяцев), оценка метаболических нарушений. Отмечено 2 (8,0%) осложнения (1 некроз трансплантата и 1 несостоятельность межкишечного анастомоза), раннего послеоперационного периода и 3 (14,3%) - позднего (пузырно­мочеточниковый рефлюкс -1 ; нефросклероз -1 ). Содержание хлора в крови составило 107,2+2,3 ммоль/л в ближайшие после операции сроки и 106,8 ±1,9 - в отдаленные, дефицит оснований (BE) - -1,43+1,8 и -2,15+1,9 соответственно. Отмечено существенное улучшение качества жизни через 6-12 мес. по всем показателям шкалы SF-36 (р<0,05)