Structural and magnetic phase diagram of CeFeAsO(1- x)F(x) and its relation to high-temperature superconductivity

Recently, high-transition-temperature (high-Tc) superconductivity was discovered in the iron pnictide RFeAsO(1-x)F(x) (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO(1-x)F(x) as the system is tuned from a semimetal to a high-Tc superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x=0.10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x>0.06, resulting in an electronic phase diagram remarkably similar to that of the high-Tc copper oxides. Comparison of the structural evolution of CeFeAsO(1-x)F(x) with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-Tc superconductivity in these Fe pnictides.

Glutathione therapy: from prodrugs to genes

Glutathione (GSH; L-gamma-glutamyl-L-cysteineglycine) is found in almost all mammalian cells, and liver has very high intracellular levels of GSH. It has many cellular functions, such as being a coenzyme, maintaining thiol/disulfide status, protection against toxic compounds and oxidative stress. GSH levels have been reported to be low in a number of pathological conditions; thus methods for increasing GSH levels are desirable. GSH may be increased by supplying its amino acid precursor cysteine, in the form of prodrugs, such as N-acetylcysteine (NAC) and 2-oxothiazolidine-4-carboxylate (OTC). It may also be increased by giving gamma-glutamylcysteine, a dipeptide precursor GSH monoester and GSH diester are effective GSH delivery drugs. Such compounds may be therapeutically useful. Gene therapy may be useful for longer term therapy of GSH deficiency.

Knock-in mice with a chimeric human/murine p53 gene develop normally and show wild-type p53 responses to DNA damaging agents: a new biomedical research tool

The high prevalence and great diversity of p53 tumor suppressor gene mutations in human tumors call for development of therapeutic molecules that rescue function of aberrant p53 protein. P53 mutations also offer new approaches to the study of the origins of mutations in human cancer. An experimental mouse model with a genetically modified but normal functioning p53 gene harboring the human rather than the murine core domain, would be of considerable benefit to research on both cancer therapeutics and etiology; however, it is uncertain whether such mice would permit biological functions of p53 to be retained. Using a Cre/lox P gene-targeting approach, we have constructed a human p53 knock-in (hupki) mouse strain in which exons 4-9 of the endogenous mouse p53 allele were replaced with the homologous, normal human p53 gene sequence. The chimeric p53 allele (p53(KI)) is properly spliced, transcribed in various tissues at levels equivalent to wild-type mice, and yields cDNA with the anticipated sequence, that is, with a core domain matching that of humans. The hupki p53 protein binds to p53 consensus sequences in gel mobility shift assays and accumulates in the nucleus of hupki fibroblasts in response to UV irradiation, as is characteristic of wild-type p53. Induction of various p53-regulated genes in spleen of gamma-irradiated homozygous hupki mice (p53(KI/KI)), and the kinetics of p53-dependent apoptosis in thymocytes are similar to results with wild-type (p53(+/+)) mice, further indicating normal p53 pathway function in the hupki strain. The mice are phenotypically normal and do not develop spontaneous tumors at an early age, in contrast to knock-out (p53(-/-)) strains with a defective p53 gene. The chimeric (p53(KI)) allele thus appears to provide a biological equivalent to the endogenous murine (p53(+)) gene. This strain is a unique tool for examining in vivo spontaneous and induced mutations in human p53 gene sequences for comparison with published human tumor p53 mutation spectra. In addition, the hupki strain paves the way for mouse models in pre-clinical testing of pharmaceuticals designed to modulate DNA-binding activity of human p53.

Skeletal muscle glutathione is depleted in critically ill patients

OBJECTIVE

To investigate the concentrations of reduced and total glutathione in relation to the muscle free amino acid pattern in critically ill patients and matched healthy controls.

DESIGN

Prospective case control.

SETTING

University hospital intensive care unit (ICU).

PATIENTS

Eleven critically ill patients in the intensive care unit were studied after a stay of at least 4 days. Eleven age- and gender-matched metabolically healthy patients undergoing elective surgical procedures served as controls.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Reduced and total glutathione concentrations were determined in skeletal muscle, in plasma, and in whole blood, together with muscle free amino acid concentrations. In the ICU group, reduced and total glutathione values were 57% and 62%, respectively, of the values seen in the control group (p < .001). In addition, a decreased ratio between reduced and total glutathione compared with the controls was seen (0.80 as compared with 0.91, p < .001). The glutamine concentration in skeletal muscle in the ICU group was 72% lower compared with that value seen in healthy controls (p < .001). Correlations were found between the concentrations of glutamine and the total muscle glutathione (r2 = .46, p < .001), as well as between glutamine and the ratio of reduced and total glutathione (r2 = .45, p < .001) in skeletal muscle, suggesting that the redox status of glutathione and the glutamine status of the tissue are related.

CONCLUSIONS

Critical illness is associated with alterations in muscle glutathione metabolism. The muscle-reduced glutathione concentrations decrease and, in addition, the ratio between reduced and total glutathione decreases, indicating a situation of oxidative stress in this tissue. This decrease may impair the defense of muscle against oxygen free radicals and influence amino acid transport, thus contributing to the loss of balance between protein synthesis and protein degradation that is characteristic of protein catabolism.

Skeletal muscle glutathione after surgical trauma

OBJECTIVE

The authors investigate the effect of surgical trauma on skeletal muscle concentrations of glutathione in patients undergoing selective abdominal surgery.

SUMMARY BACKGROUND DATA

The posttraumatic state is accompanied by characteristic changes in the pattern of free amino acids and a decline of protein synthesis in human skeletal muscle. Glutathione has multiple metabolic functions that are involved in cellular homeostasis. It is unknown how surgical trauma affects the glutathione metabolism of skeletal muscle in surgical patients.

METHODS

Eight patients undergoing elective abdominal surgery were investigated. Percutaneous muscle biopsies and blood samples were taken before operation and at 6, 24, and 48 hours after operation. The concentrations of glutathione were determined in muscle tissue, plasma, and whole blood, as well as the concentrations of the related amino acids in muscle and plasma.

RESULTS

In skeletal muscle, the levels of both reduced and total glutathione decreased by 40% (p<0.01) at 24 hours and remained low at 48 hours after operation compared with the preoperative values. The glutathione concentration in plasma was 20% lower after operation compared with the concentration before operation (p<0.05). There were no changes at the whole blood levels of glutathione. Tissue glutamate and glutamine decreased significantly after operation (p<0.001), whereas intracellular cysteine and glycine remained unchanged.

CONCLUSIONS

Skeletal muscle glutathione deficiency occurs after surgical trauma. This may lead to an increase in the susceptibility to intracellular oxidative injury.

Determination of intracellular glutathione in human skeletal muscle by reversed-phase high-performance liquid chromatography

A chromatographic method for the specific determination of cellular low molecular mass thiols has been applied to human muscle tissue. The method is based on the derivatisation of thiols using monobromobimane, which is a specific reagent for the sulphydryl group. The glutathione and cysteine bimane adducts were separated by reversed-phase HPLC, whilst quantitation of the cysteine and glutathione adducts was achieved by fluorescence spectroscopy. The method was found to yield a quantitative recovery of glutathione (ca. 96%), to be sensitive (down to 20 pmol glutathione/per injection) and reveal a low intra-individual coefficient of variation (C.V. < 5%) of the glutathione concentrations in human skeletal muscle. The concentrations of reduced and total glutathione were 1320 +/- 37 mumol/kg wet weight (mean +/- S.E.M.) and 1525 +/- 66 mumol/kg wet weight, respectively. The method was also applied to tissues from nine healthy volunteers to determine if fluctuations in glutathione level occurred over a 24-h period. No diurnal variation of glutathione level in human skeletal muscle was observed.

Pressure induced superconductivity on the border of magnetic order in MnP

We report the discovery of superconductivity on the border of long-range magnetic order in the itinerant-electron helimagnet MnP via the application of high pressure. Superconductivity with T(sc)≈1  K emerges and exists merely near the critical pressure P(c)≈8  GPa, where the long-range magnetic order just vanishes. The present finding makes MnP the first Mn-based superconductor. The close proximity of superconductivity to a magnetic instability suggests an unconventional pairing mechanism. Moreover, the detailed analysis of the normal-state transport properties evidenced non-Fermi-liquid behavior and the dramatic enhancement of the quasiparticle effective mass near P(c) associated with the magnetic quantum fluctuations.

Synergism of Electrochemical and Mechanical Factors in Erosion−Corrosion

A theoretical model was developed on basis of nonequilibrium thermodynamics, dislocation kinetics, and electrochemistry, which may lead to the quantitative assessment of material loss produced by the synergism of mechanical and electrochemical factors in an erosion-corrosion process, As predicted by this model, the synergistic effect results mainly from the interaction of two irreversible fluxes, namely, the anodic dissolution current density and the plastic flowing in the surface layer caused by dynamic plastic deformation. An enhanced anodic dissolution flux is induced by the dynamic surface plastic deformation resulting from the impingement of solid particles, which can be correlated to the wastage rate due to the mechanical erosion. Meanwhile, the anodic current present at the electrode surface, in turn, can increase the mobility of dislocation and reduce the resistance in the surface layer against plastic deformation. Such an effect is demonstrated by the hardness degradation of metals in corrosive media. Theoretical analysis indicates that the corrosion-induced hardness degradation is a linear function of the logarithm of anodic current density. The degradation of mechanical erosion resistance with decreasing hardness suggests that the corrosion-enhanced erosion may result from the degradation in hardness of target material induced by the anodic dissolution and the corresponding wastage is also a linear function of the logarithm of anodic current density. The theoretical predictions were compared with the experimental results of carbon steels obtained form the slurry-erosion tests and the micro-hardness measurements. The results indicate that the hardness degradation in corrosive media is mainly controlled by the anodic current density and is almost independent of the polarization behavior of steels.

Superconductivity at 41 K and its competition with spin-density-wave instability in layered CeO1-xFxFeAs

A series of layered CeO1-xFxFeAs compounds with x=0 to 0.20 are synthesized by the solid state reaction method. Similar to the LaOFeAs, the pure CeOFeAs shows a strong resistivity anomaly near 145 K, which was ascribed to the spin-density-wave instability. F doping suppresses this instability and leads to the superconducting ground state. Most surprisingly, the superconducting transition temperature could reach as high as 41 K. Such a high T_{c} strongly challenges the classic BCS theory based on the electron-phonon interaction. The closeness of the superconducting phase to the spin-density-wave instability suggests that the magnetic fluctuation plays a key role in the superconducting pairing mechanism. The study also reveals that the Ce 4f electrons form local moments and are ordered antiferromagnetically below 4 K, which could coexist with superconductivity.

Observation of Dirac cone electronic dispersion in BaFe2As2

We performed an angle-resolved photoemission spectroscopy study of BaFe2As2, which is the parent compound of the so-called 122 phase of the iron-pnictide high-temperature superconductors. We reveal the existence of a Dirac cone in the electronic structure of this material below the spin-density-wave temperature, which is responsible for small spots of high photoemission intensity at the Fermi level. Our analysis suggests that the cone is slightly anisotropic and its apex is located very near the Fermi level, leading to tiny Fermi surface pockets. The bands forming the cone show an anisotropic leading edge gap away from the cone that suggests a nodal spin-density-wave description.

Glutathione status in critically-ill patients: possibility of modulation by antioxidants

Muscle tissue serves as a protein reservoir which is mobilized to meet the specific metabolic needs associated with various catabolic conditions in human subjects, such as trauma and critical illness. Glutathione is one of the most abundant short-chain peptides and a major source of non-protein thiol in the body, and tissue glutathione concentration is related to its oxidative capacity. Skeletal muscle is relatively unique with respect to a variety of metabolic properties, such as oxidative potential, patterns of amino acid utilization, and antioxidant enzyme activity. The glutathione concentration is not influenced by food intake, or by food deprivation. Moreover, there is no diurnal variation on muscle glutathione levels. Following elective surgery the muscle concentration of GSH (the reduced form) decreases by 40% 24 h post-operatively, while the concentration of GSSG (the oxidized form) remains unaltered. During critical illness a similar decrease in the GSH concentration is seen, but in addition a change in the redox status indicative of an elevated GSSG level occurs. Furthermore, correlations between the concentrations of glutamine as well as glutamate and GSH exist in these patients. From available evidence accumulated it is clear that glutathione plays a pivotal role in the maintenance of the intracellular redox status, the antioxidant vitamin levels, and the antioxidant enzyme functions under various metabolic conditions. The effectiveness of glutathione protection in the individual tissue depends on the tissue concentration of glutathione as well as the capacity of the tissue to import GSH and to export GSSG. The mechanisms by which catabolism regulates tissue glutathione levels and the enzyme activities associated with the gamma-glutamyl cycle are not completely understood and further studies need to be conducted.

Surgical trauma decreases glutathione synthetic capacity in human skeletal muscle tissue

To gain insight into cellular metabolism underlying the glutathione (GSH) alterations induced by surgical trauma, we assessed postoperative skeletal muscle GSH metabolism and its redox status in 10 patients undergoing elective abdominal surgery. Muscle biopsy specimens were taken from the quadriceps femoris muscle before and at 24 and 72 h after surgery. GSH concentrations decreased by 40% at 24 h postoperatively compared with the paired preoperative values (P < 0.001) and remained low at 72 h (P < 0.01). The concentration of GSH disulfide (GSSG) did not significantly change throughout the study period, whereas the total GSH (as GSH equivalent) concentration decreased after surgery. Of the GSH constituent amino acids, the concentration of cysteine remained unchanged throughout the study period (from 28.2 +/- 10.1 preoperatively to 29.4 +/- 13.9 at 24 h postoperatively and to 28.3 +/- 15.6 micromol/kg wet wt at 72 h postoperatively). Despite a reduction in glutamate concentration by 40% 24 h after surgery, no correlation was established between GSH and glutamate concentrations postoperatively. Activity of gamma-glutamylcysteine synthetase did not change significantly after surgery, whereas GSH synthetase activity decreased postoperatively (from 66.4 +/- 19.1 preoperatively to 41.0 +/- 10.5 24 h postoperatively, P < 0.01, and to 46.0 +/- 11.7 microU/mg protein 72 h postoperatively, P < 0.05). The decrease of GSH was correlated to the reduced GSH synthetase activity seen at 24 h postoperatively. These results indicate that the skeletal muscle GSH pool is diminished in patients after surgical trauma. The depletion of the GSH pool is associated with a decreased activity of GSH synthetase, indicating a decreased GSH synthetic capacity in skeletal muscle tissue.

Superconducting properties of the Fe-based layered superconductor LaFeAsO0.9F0.1-delta

We have employed a new route to synthesize single phase F-doped LaOFeAs compound and confirmed the superconductivity above 20 K in this Fe-based system. We show that the new superconductor has a rather high upper critical field of over 50 T. A clear signature of superconducting gap opening below T(c) was observed in the far-infrared reflectance spectra, with 2Delta/kT(c) approximately 3.5-4.2. Furthermore, we show that the new superconductor has electron-type conducting carriers with a rather low-carrier density.

Resistance to HSP90 inhibition involving loss of MCL1 addiction

Inhibition of the chaperone heat-shock protein 90 (HSP90) induces apoptosis, and it is a promising anti-cancer strategy. The mechanisms underpinning apoptosis activation following HSP90 inhibition and how they are modified during acquired drug resistance are unknown. We show for the first time that, to induce apoptosis, HSP90 inhibition requires the cooperation of multi BH3-only proteins (BID, BIK, PUMA) and the reciprocal suppression of the pro-survival BCL-2 family member MCL1, which occurs via inhibition of STAT5A. A subset of tumour cell lines exhibit dependence on MCL1 expression for survival and this dependence is also associated with tumour response to HSP90 inhibition. In the acquired resistance setting, MCL1 suppression in response to HSP90 inhibitors is maintained; however, a switch in MCL1 dependence occurs. This can be exploited by the BH3 peptidomimetic ABT737, through non-BCL-2-dependent synthetic lethality.

Spiral magnetic order and pressure-induced superconductivity in transition metal compounds

Magnetic and superconducting ground states can compete, cooperate and coexist. MnP provides a compelling and potentially generalizable example of a material where superconductivity and magnetism may be intertwined. Using a synchrotron-based non-resonant X-ray magnetic diffraction technique, we reveal a spiral spin order in MnP and trace its pressure evolution towards superconducting order via measurements in a diamond anvil cell. Judging from the magnetostriction, ordered moments vanish at the quantum phase transition as pressure increases the electron kinetic energy. Spins remain local in the disordered phase, and the promotion of superconductivity is likely to emerge from an enhanced coupling to residual spiral spin fluctuations and their concomitant suppression of phonon-mediated superconductivity. As the pitch of the spiral order varies across the 3d transition metal compounds in the MnP family, the magnetic ground state switches between antiferromagnet and ferromagnet, providing an additional tuning parameter in probing spin-fluctuation-induced superconductivity.

The relationship between magnetic order and superconductivity is one of the central issues in unconventional superconductors. Here, Wang et al. report a spiral spin order in MnP and trace its pressure evolution towards superconducting order, suggesting variable spiral pitch as a mechanism to tune spin-fluctuation-induced superconductivity.

Origin of the spin density wave instability in AFe2As2 (A=Ba,Sr) as revealed by optical spectroscopy

We performed optical spectroscopy measurement on single crystals of BaFe2As2 and SrFe2As2, the parent compounds of FeAs-based superconductors. Both are found to be quite metallic with fairly large plasma frequencies at high temperature. Upon entering the spin-density-wave state, the formation of partial energy gaps was clearly observed with the surprising presence of two different energy scales. A large part of the Drude component was removed by the gapping of Fermi surfaces. Meanwhile, the carrier scattering rate was even more dramatically reduced. We elaborate that the spin-density-wave instability is more likely to be driven by the Fermi surface nesting of itinerant electrons than a local-exchange mechanism.

Novel kinetics of mammalian glutathione synthetase: characterization of gamma-glutamyl substrate cooperative binding

Glutathione (GSH) synthetase [L-gamma-glutamyl-L-cysteinyl:glycine ligase (ADP-forming), EC 6.3.2.3] catalyzes the final step in GSH biosynthesis. Mammalian glutathione synthetase is a homodimer with each subunit containing an active site. We report the detailed kinetic data for purified recombinant rat glutathione synthetase. It has the highest specific activity (11 micromol/min/mg) reported for any mammalian glutathione synthetase. The apparent K(m) values for ATP and glycine are 37 and 913 microM, respectively. The Lineweaver-Burk double reciprocal plot for gamma-glutamyl substrate binding revealed a departure from linearity indicating cooperative binding. Quantitative analysis of the kinetic results for gamma-glutamyl substrate binding gives a Hill coefficient (h) of 0. 576, which shows the negative cooperativity. Neither ATP, the other substrate involved in forming the enzyme-bound gamma-glutamyl phosphate intermediate, nor glycine, which attacks this intermediate to form GSH, exhibit any cooperativity. The cooperative binding of gamma-glutamyl substrate is not affected by ATP concentration. Thus, mammalian glutathione synthetase is an allosteric enzyme.

Cooperative binding of gamma-glutamyl substrate to human glutathione synthetase

Human glutathione synthetase is responsible for catalyzing the final step in glutathione biosynthesis. It is a homodimer with a monomer subunit MW of 52 kDa. Kinetic analysis reveals a departure from linearity of the Lineweaver-Burk double reciprocal plot for the binding of gamma-glutamyl substrate, indicating cooperative binding. The measured apparent K(m) values for gamma-glutamyl-alpha-aminobutyrate (an analog of gamma-glutamyl-alpha-aminobutyrate) are 63 and 164 microM, respectively. Neither ATP (K(m) of 248 microM) nor glycine (K(m) of 452 microM) exhibits such cooperative binding behavior. Although ATP is proposed to play a key role in the sequential binding of gamma-glutamyl substrate to the enzyme, the cooperative binding of the gamma-glutamyl substrate is not affected by alterations of ATP concentration. Quantitative analysis of the kinetic results for gamma-glutamyl substrate binding gives a Hill coefficient (h) of 0.75, indicating negative cooperativity. Our studies, for the first time, show that human glutathione synthetase is an allosteric enzyme with cooperative binding for gamma-glutamyl substrate.

Origin of the spin density wave instability in AFe2As2 (A=Ba,Sr) as revealed by optical spectroscopy

We performed optical spectroscopy measurement on single crystals of BaFe2As2 and SrFe2As2, the parent compounds of FeAs-based superconductors. Both are found to be quite metallic with fairly large plasma frequencies at high temperature. Upon entering the spin-density-wave state, the formation of partial energy gaps was clearly observed with the surprising presence of two different energy scales. A large part of the Drude component was removed by the gapping of Fermi surfaces. Meanwhile, the carrier scattering rate was even more dramatically reduced. We elaborate that the spin-density-wave instability is more likely to be driven by the Fermi surface nesting of itinerant electrons than a local-exchange mechanism.

Fermi surface topology and low-lying quasiparticle dynamics of parent Fe1+xTe/Se superconductor

We report the first photoemission study of Fe1+xTe-the host compound of the newly discovered iron-chalcogenide superconductors (maximum Tc approximately 27 K). Our results reveal a pair of nearly electron-hole compensated Fermi pockets, strong Fermi velocity renormalization, and an absence of a spin-density-wave gap. A shadow hole pocket is observed at the "X" point of the Brillouin zone which is consistent with a long-range ordered magnetostructural ground state. No signature of Fermi surface nesting instability associated with Q=(pi/2,pi/2) is observed. Our results collectively reveal that the Fe1+xTe series is different from the undoped phases of the high Tc pnictides and likely harbor an unusual mechanism for superconductivity and magnetic order.

Capillary zone electrophoresis/mass spectrometry of 5-aminolaevulinic acid and porphobilinogen

A capillary zone electrophoresis/electrospray ionisation mass spectrometry (CZE/ESI-MS) method has been developed for the separation and detection of 5-aminolaevulinic acid (ALA) and porphobilinogen (PBG). Capillaries were 70 cm long with an inner diameter of 75 micrometer and outer diameter of 375 micrometer. The buffer used was aqueous ammonium acetate (50mM, pH 5.2) with a co-axial 'make-up' flow of methanol/aqueous 0.1% formic acid (1:1 v/v) at a flowrate of 6 microL/min. A voltage of 20 kV was used for CZE and an ESI voltage of 3.5 kV. Full scan data was acquired over the range m/z 100-500 in positive ion mode, from which selected ion electropherograms were extracted; at m/z 132 for the protonated molecular ion of ALA and m/z 210 for the methylenepyrrolenine fragment ion of PBG. The protonated molecular ion of PBG, m/z 227, was found to be too facile to monitor, easily losing ammonia in the electrospray source and better sensitivity was achieved by monitoring the resulting fragment ion. The detection limits were circa 100 attomoles of ALA and 10 attomoles of PBG at a signal-to-noise ratio (S/N) better than 10, providing sufficient sensitivity for clinical use and offering advantages over existing techniques.

Determination of 5-aminolaevulinic acid dehydratase activity in erythrocytes and porphobilinogen in urine by micellar electrokinetic capillary chromatography

A micellar electrokinetic capillary chromatographic (MECC) method has been developed and optimised for the separation of 5-aminolaevulinic acid (ALA) and porphobilinogen (PBG). The running buffer consisted of a mixture of 20 mM sodium phosphate and 20 mM sodium borate containing 50 mM sodium dodecyl sulphate (SDS) adjusted to pH 9.5 with 1 M NaOH. The running voltage and temperature were 20-25 kV and 30 degrees C, respectively. The MECC method for the analysis of PBG is fast and simple and is useful for the screening of PBG in the urine of patients suspected to have acute intermittent porphyria (AIP), and for the confirmation of lead exposure by measuring red-cell ALA-dehydratase (ALA-D) activity with ALA as the enzyme substrate.

Multiple phase transitions in single-crystalline Na_{1-delta}FeAs

Specific heat, resistivity, susceptibility, and Hall coefficient measurements were performed on high-quality single-crystalline Na_{1-delta}FeAs. This compound is found to undergo three successive phase transitions at around 52, 41, and 23 K, which correspond to structural, magnetic, and superconducting transitions, respectively. The Hall effect result indicates the development of energy gap at low temperature due to the occurrence of spin-density-wave instability. Our results provide direct experimental evidence of the magnetic ordering in the nearly stoichiometric NaFeAs.

Band structure and fermi surface of an extremely overdoped iron-based superconductor KFe2As2

We have performed high-resolution angle-resolved photoemission spectroscopy on heavily overdoped KFe_{2}As_{2} (transition temperature T_{c} = 3 K). We observed several renormalized bands near the Fermi level with a renormalization factor of 2-4. While the Fermi surface around the Brillouin-zone center is qualitatively similar to that of optimally doped Ba_{1-x}K_{x}Fe_{2}As_{2} (x = 0.4; T_{c} = 37 K), the Fermi surface topology around the zone corner (M point) is markedly different: the two electron Fermi surface pockets are completely absent due to an excess of hole doping. This result indicates that the electronic states around the M point play an important role in the high-T_{c} superconductivity of Ba_{1-x}K_{x}Fe_{2}As_{2} and suggests that the interband scattering via the antiferromagnetic wave vector essentially controls the T_{c} value in the overdoped region.

Probing the superconducting energy gap from infrared spectroscopy on a Ba0.6K0.4Fe2As2 single crystal with Tc=37 K

We performed optical spectroscopy measurement on a superconducting Ba0.6K0.4Fe2As2 single crystal with T{c}=37 K. Formation of the superconducting energy gaps in the far-infrared reflectance spectra below T{c} is clearly observed. A flat and close to unity reflectance is observed roughly below 150 cm;{-1} for T<<T{c}, following an s-wave pairing line shape. A more rapid decrease occurs near 200 cm;{-1}, leading to a peak in the ratio of the reflectance at T<<T{c} over that for T>or=T{c}. We determined the absolute value of the penetration depth at 10 K as lambda approximately 2000+/-80 A. A spectral weight analysis shows that the Ferrell-Glover-Tinkham sum rule is satisfied at low energy scale, less than 6Delta.