Search

We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe_{4}As_{4}. In contrast to the related CaFe_{2}As_{2} compounds, CaKFe_{4}As_{4} has a high T_{c} of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearly isotropic (within the explored portions of the Brillouin zone), but are significantly different for each of the Fermi surface (FS) sheets. Most importantly, we find that the momentum dependence of the gap magnitude plotted across the entire Brillouin zone displays a strong deviation from the simple cos(k_{x})cos(k_{y}) functional form of the gap function, proposed by the scenario of Cooper pairing driven by a short range antiferromagnetic exchange interaction. Instead, the maximum value of the gap is observed on FS sheets that are closest to the ideal nesting condition, in contrast to previous observations in other ferropnictides. These results provide strong support for the multiband character of superconductivity in CaKFe_{4}As_{4}, in which Cooper pairing forms on the electron and the hole bands interacting via a dominant interband repulsive interaction, enhanced by band nesting.

In this study, we use angle resolved photoemission spectroscopy, Raman spectroscopy, low energy electron diffraction, and x-ray scattering to reveal an unusual electronically mediated charge density wave (CDW) in K0.9Mo6O17. Not only does K0.9Mo6O17 lack signatures of electron-phonon coupling, but it also hosts an extraordinary surface CDW, with TS_CDW = 220 K nearly twice that of the bulk CDW, TB_CDW = 115 K. While the bulk CDW has a BCS-like gap of 12 meV, the surface gap is 10 times larger and well in the strong coupling regime. Strong coupling behavior combined with the absence of signatures of strong electron-phonon coupling indicates that the CDW is likely mediated by electronic interactions enhanced by low dimensionality.

We use our high resolution He-lamp based, tunable laser-based ARPES measurements and density functional theory calculations to study the electronic properties of LaBi, a binary system that was proposed to be a member of a new family of topological semimetals. Both bulk and surface bands are present in the spectra. The dispersion of the surface state is highly unusual. It resembles a Dirac cone, but upon closer inspection we can clearly detect an energy gap. The bottom band follows roughly a parabolic dispersion. The dispersion of the top band remains very linear, "V" shape like, with the tip approaching very closely to the extrapolated location of Dirac point. Such asymmetric mass acquisition is highly unusual and opens a possibility of a new topological phenomena that has yet to be understood., 14 pages 4 figures

We investigate the effect of isotope substitution on the electron-phonon interaction in the multi-band superconductor MgB2 using tunable laser based Angle Resolved Photoemission Spectroscopy. The kink structure around 70 meV in the $\sigma$ band, which is caused by electron coupling to the E2g phonon mode, is shifted to higher binding energy by ~3.5 meV in Mg(10)B2 and the shift is not affected by superconducting transition. These results serve as the benchmark for investigations of isotope effects in known, unconventional superconductors and newly discovered superconductors where the origin of pairing is unknown., Comment: 5 pages, 4 figures

In a type I Dirac or Weyl semimetal, the low-energy states are squeezed to a single point in momentum space when the chemical potential μ is tuned precisely to the Dirac/Weyl point. Recently, a type II Weyl semimetal was predicted to exist, where the Weyl states connect hole and electron bands, separated by an indirect gap. This leads to unusual energy states, where hole and electron pockets touch at the Weyl point. Here we present the discovery of a type II topological Weyl semimetal state in pure MoTe

In a type I Dirac or Weyl semimetal, the low energy states are squeezed to a single point in momentum space when the chemical potential Ef is tuned precisely to the Dirac/Weyl point. Recently, a type II Weyl semimetal was predicted to exist, where the Weyl states connect hole and electron bands, separated by an indirect gap. This leads to unusual energy states, where hole and electron pockets touch at the Weyl point. Here we present the discovery of a type II topological Weyl semimetal (TWS) state in pure MoTe2, where two sets of WPs (W2+-, W3+-) exist at the touching points of electron and hole pockets and are located at different binding energies above Ef. Using ARPES, modeling, DFT and calculations of Berry curvature, we identify the Weyl points and demonstrate that they are connected by different sets of Fermi arcs for each of the two surface terminations. We also find new surface "track states" that form closed loops and are unique to type II Weyl semimetals. This material provides an exciting, new platform to study the properties of Weyl fermions., 16 pages, 4 figures

We study magnetic domains in ${\text{Nd}}_{2}{\text{Fe}}_{14}\text{B}$ single crystals using high resolution magnetic force microscopy (MFM). Previous MFM studies and small angle neutron scattering experiments suggested the presence of nanoscale domains in addition to optically detected micrometer-scale ones. We find, in addition to the elongated, wavy nanodomains reported by a previous MFM study, that the micrometer-sized, star-shaped fractal pattern is constructed of an elongated network of nanodomains $\ensuremath{\sim}20$ nm in width, with resolution-limited domain walls thinner than 2 nm. While the microscopic domains exhibit significant resilience to an external magnetic field, some of the nanodomains are sensitive to the magnetic field of the MFM tip.

We use angle resolved photoemission spectroscopy, Raman spectroscopy, low energy electron diffraction, and x-ray scattering to reveal an unusual electronically mediated charge density wave (CDW) in K_{0.9}Mo_{6}O_{17}. Not only does K_{0.9}Mo_{6}O_{17} lack signatures of electron-phonon coupling, but it also hosts an extraordinary surface CDW, with T_{S_CDW}=220 K nearly twice that of the bulk CDW, T_{B_CDW}=115 K. While the bulk CDW has a BCS-like gap of 12 meV, the surface gap is 10 times larger and well in the strong coupling regime. Strong coupling behavior combined with the absence of signatures of strong electron-phonon coupling indicates that the CDW is likely mediated by electronic interactions enhanced by low dimensionality.

We use ultrahigh resolution, tunable, vacuum ultraviolet laser angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of WTe$_2$, a material that was predicted to be a type-II Weyl semimetal. The Weyl fermion states in WTe2 were proposed to emerge at the crossing points of electron and hole pockets; and Fermi arcs connecting electron and hole pockets would be visible in the spectral function on (001) surface. Here we report the observation of such Fermi arcs in WTe2 confirming the theoretical predictions. This provides strong evidence for type-II Weyl semimetallic states in WTe2., Comment: 5 pages, 4 figures

In order to understand the origin of high-temperature superconductivity in copper oxides, we must understand the normal state from which it emerges. Here, we examine the evolution of the normal state electronic excitations with temperature and carrier concentration in Bi2Sr2CaCu2O8 using angle-resolved photoemission. In contrast to conventional superconductors, where there is a single temperature scale Tc separating the normal from the superconducting state, the high- temperature superconductors exhibit two additional temperature scales. One is the pseudogap scale T*, below which electronic excitations exhibit an energy gap. The second is the coherence scale Tcoh, below which sharp spectral features appear due to increased lifetime of the excitations. We find that T* and Tcoh are strongly doping dependent and cross each other near optimal doping. Thus the highest superconducting Tc emerges from an unusual normal state that is characterized by coherent excitations with an energy gap., Comment: 5 pages, 4 figures. Published in Proc. Nat. Acad. Sci. vol. 108 pp 9346 (2011). Free to download

The pseudogap state in the cuprate superconductors shows signs of electronic pair formation above the superconducting temperature. Is it just a ‘precursor’ state or a separate (and competing) state? In fact, both interpretations seem to be correct.

A study shows that in electron-doped Ba(Fe1−xCox)2As2, the presence or absence of superconductivity and antiferromagnetism can be linked directly to changes in the Fermi surface—as measured by angle-resolved photoemission spectroscopy.

In a classical Bardeen-Cooper-Schrieffer superconductor, pairing and coherence of electrons are established simultaneously below the critical transition temperature (T(c)), giving rise to a gap in the electronic energy spectrum. In the high-T(c) copper oxide superconductors, however, a pseudogap extends above T(c). The relationship between the pseudogap and superconductivity is one of the central issues in this field. Spectral gaps arising from pairing precursors are qualitatively similar to those caused by competing electronic states, rendering a standard approach to their analysis inconclusive. The issue can be settled, however, by studying the correlation between the weights associated with the pseudogap and superconductivity spectral features. Here we report a study of two spectral weights using angle-resolved photoemission spectroscopy. The weight of the superconducting coherent peak increases away from the node following the trend of the superconducting gap, but starts to decrease in the antinodal region. This striking non-monotonicity reveals the presence of a competing state. We demonstrate a direct correlation, for different values of momenta and doping, between the loss in the low-energy spectral weight arising from the opening of the pseudogap and a decrease in the spectral weight associated with superconductivity. We therefore conclude that the pseudogap competes with the superconductivity by depleting the spectral weight available for pairing.

We present a muon-spin rotation study of the optimally doped cuprate superconductor (BiPb)2(SrLa)2 CuO6+δ . The measured magnetic field dependence of the in-plane magnetic penetration λ ab suggests superconductivity with a dominant d-wave order parameter. The comparison of the temperature dependence of λ ab with calculations, assuming the angular gap symmetry as obtained from photoemission measurements, is consistent with a partial suppression of the quasi-particle weight towards the anti-nodal region of the Fermi surface. This suggests that the superconducting and the pseudogap state are dominated by different parts of the Fermi surface.

We use tunable laser-based angle-resolved photoemission spectroscopy to study the electronic structure of the multiband superconductor ${\mathrm{MgB}}_{2}$. These results form the baseline for detailed studies of superconductivity in multiband systems. We find that the magnitude of the superconducting gap on both $\ensuremath{\sigma}$ bands follows a BCS-like variation with temperature with ${\mathrm{\ensuremath{\Delta}}}_{0}\ensuremath{\sim}7\phantom{\rule{0.28em}{0ex}}\mathrm{meV}$. The value of the gap is isotropic within experimental uncertainty and in agreement with a pure $s$-wave pairing symmetry. We also observe in-gap states confined to ${k}_{F}$ of the $\ensuremath{\sigma}$ band that occur at some locations of the sample surface. The energy of this excitation, $\ensuremath{\sim}3$ meV, is somewhat larger than the previously reported gap on $\ensuremath{\pi}$ Fermi sheet and therefore we cannot exclude the possibility of interband scattering as its origin.

We use ultra-high resolution, tunable, VUV laser-based, angle-resolved photoemission spectroscopy (ARPES) and temperature and field dependent resistivity and thermoelectric power (TEP) measurements to study the electronic properties of WTe2, a compound that manifests exceptionally large, temperature dependent magnetoresistance. The temperature dependence of the TEP shows a change of slope at T=175 K and the Kohler rule breaks down above 70-140 K range. The Fermi surface consists of two electron pockets and two pairs of hole pockets along the X-Gamma-X direction. Upon increase of temperature from 40K, the hole pockets gradually sink below the chemical potential. Like BaFe2As2, WTe2 has clear and substantial changes in its Fermi surface driven by modest changes in temperature. In WTe2, this leads to a rare example of temperature induced Lifshitz transition, associated with the complete disappearance of the hole pockets. These dramatic changes of the electronic structure naturally explain unusual features of the transport data., Comment: 5 pages, 3 figures

We use angle-resolved photoemission spectroscopy (ARPES) to study the 2D heavy fermion superconductor, Ce₂RhIn₈. The Fermi surface is rather complicated and consists of several hole and electron pockets with one of the sheets displaying strong nesting properties with a q-vector of (0.32, 0.32) π/a. We do not observe kz dispersion of the Fermi sheets, which is consistent with the expected 2D character of the electronic structure. Comparison of the ARPES data to band structure calculations suggests that a localized picture of the f-electrons works best. While there is some agreement in the overall band dispersion and location of the Fermi sheets, the model does not reproduce all observed bands and is not completely accurate for those it does. As a result, our data paves the way for improving the band structure calculations and the general understanding of the transport and thermodynamical properties of this material.

We use a tunable laser ARPES to study the electronic properties of the prototypical multiband BCS superconductor MgB2. Our data reveal a strong renormalization of the dispersion (kink) at ~65 meV, which is caused by coupling of electrons to the E2g phonon mode. In contrast to cuprates, the 65 meV kink in MgB2 does not change significantly across Tc. More interestingly, we observe strong coupling to a second, lower energy collective mode at binding energy of 10 meV. This excitation vanishes above Tc and is likely a signature of the elusive Leggett mode., 10 figs

The loss of single-particle coherence going from the superconducting state to the normal state in underdoped cuprates is a dramatic effect that has yet to be understood. Here, we address this issue by performing angle resolved photoemission spectroscopy (ARPES) measurements in the presence of a transport current. We find that the loss of coherence is associated with the development of an onset in the resistance, in that well before the midpoint of the transition is reached, the sharp peaks in the ARPES spectra are completely suppressed. Since the resistance onset is a signature of phase fluctuations, this implies that the loss of single-particle coherence is connected with the loss of long-range phase coherence., Comment: 7 pages, 7 figures

The response of a material to external stimuli depends on its low-energy excitations. In conventional metals, these excitations are electrons on the Fermi surface—a contour in momentum (k) space that encloses all of the occupied states for non-interacting electrons. The pseudogap phase in the copper oxide superconductors, however, is a most unusual state of matter1. It is metallic, but part of its Fermi surface is ‘gapped out’ (refs 2, 3); low-energy electronic excitations occupy disconnected segments known as Fermi arcs4. Two main interpretations of its origin have been proposed: either the pseudogap is a precursor to superconductivity5, or it arises from another order competing with superconductivity6. Using angle-resolved photoemission spectroscopy, we show that the anisotropy of the pseudogap in k-space and the resulting arcs depend only on the ratio T/T*(x), where T*(x) is the temperature below which the pseudogap first develops at a given hole doping x. The arcs collapse linearly with T/T*(x) and extrapolate to zero extent as T→0. This suggests that the T=0 pseudogap state is a nodal liquid—a strange metallic state whose gapless excitations exist only at points in k-space, just as in a d-wave superconducting state.

X-ray powder diffraction (XRD), magnetic susceptibility $\ensuremath{\chi}$, isothermal magnetization $M$, heat capacity ${C}_{\mathrm{p}}$, and in-plane electrical resistivity $\ensuremath{\rho}$ measurements as a function of temperature $T$ and magnetic field $H$ are presented for ${\mathrm{CaCo}}_{1.86}{\mathrm{As}}_{2}$ single crystals. The electronic structure is probed by angle-resolved photoemission spectroscopy (ARPES) measurements of ${\mathrm{CaCo}}_{1.86}{\mathrm{As}}_{2}$ and by full-potential linearized augmented-plane-wave calculations for the supercell ${\mathrm{Ca}}_{8}{\mathrm{Co}}_{15}{\mathrm{As}}_{16}$ (${\mathrm{CaCo}}_{1.88}{\mathrm{As}}_{2}$). Our XRD crystal structure refinement is consistent with the previous combined refinement of x-ray and neutron powder diffraction data showing a collapsed-tetragonal ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type structure with 7(1)% vacancies on the Co sites corresponding to the composition ${\mathrm{CaCo}}_{1.86}{\mathrm{As}}_{2}$ [D. G. Quirinale et al., Phys. Rev. B 88, 174420 (2013)]. The anisotropic $\ensuremath{\chi}(T)$ data are consistent with the magnetic neutron diffraction data of Quirianale et al. that demonstrate the presence of A-type collinear antiferromagnetic order below the N\'eel temperature ${T}_{\mathrm{N}}=52$(1) K with the easy axis being the tetragonal $c$ axis. However, no clear evidence from the $\ensuremath{\rho}(T)$ and ${C}_{\mathrm{p}}(T)$ data for a magnetic transition at ${T}_{\mathrm{N}}$ is observed. A metallic ground state is demonstrated from the band calculations and the $\ensuremath{\rho}(T)$, ${C}_{\mathrm{p}}(T)$, and ARPES data, and spin-polarized calculations indicate a competition between the A-type AFM and FM ground states. The ${C}_{\mathrm{p}}(T)$ data exhibit a large Sommerfield electronic coefficient reflecting a large density of states at the Fermi energy $\mathcal{D}({E}_{\mathrm{F}})$ that is enhanced compared with the band structure calculation where the bare $\mathcal{D}({E}_{\mathrm{F}})$ arises from Co $3d$ bands. At 1.8 K, the $M(H)$ data for $H\ensuremath{\parallel}c$ exhibit a well-defined first-order spin-flop transition at an applied field of 3.5 T. The small ordered moment of $\ensuremath{\approx}$$0.3{\ensuremath{\mu}}_{\mathrm{B}}$/Co obtained from the $M(H)$ data at low $T$, the large exchange enhancement of $\ensuremath{\chi}$ and the lack of a self-consistent interpretation of the $\ensuremath{\chi}(T)$ and $M(H,T)$ data in terms of a local moment Heisenberg model together indicate that the magnetism of ${\mathrm{CaCo}}_{1.86}{\mathrm{As}}_{2}$ is itinerant.

We use angle-resolved photoemission spectroscopy and density functional theory calculations to study the electronic structure of CaFe${}_{2}$As${}_{2}$ in the collapsed tetragonal (CT) phase. This unusual phase of iron arsenic high-temperature superconductors was hard to measure as it exists only under pressure. By inducing internal strain, via the postgrowth thermal treatment of single crystals, we were able to stabilize the CT phase at ambient pressure. We find significant differences in the Fermi surface topology and band dispersion data from the more common orthorhombic-antiferromagnetic or tetragonal-paramagnetic phases, consistent with electronic structure calculations. The top of the hole bands sinks below the Fermi level, which destroys the nesting present in parent phases. The absence of nesting in this phase, along with an apparent loss of Fe magnetic moment, are now clearly experimentally correlated with the lack of superconductivity in this phase.

We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather then preformed pairs. Pairing does occur below Tpair~150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scattering creates "artificial" Fermi arcs for Tc, Comment: 18 pages, 8 figures

Angle-resolved photoemission data in the superconducting state of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ show a kink in the dispersion along the zone diagonal, which is related via a Kramers-Kr\"onig analysis to a drop in the low energy scattering rate. As one moves towards $(\ensuremath{\pi},0)$, this kink evolves into a spectral dip. The occurrence of these anomalies in the dispersion and line shape throughout the zone indicates the presence of a new energy scale in the superconducting state.

We have performed a systematic doping-dependent angle-resolved photoemission spectroscopy (ARPES) of Pb-substituted Bi2201 (Bi1.80Pb0.38Sr2.01CuO6-delta) With high energy (7-11 meV) and momentum (0.01 Angstrom (-1)) resolutions. We found that all the samples show a large hole-like Fermi surface centered at (pi,pi), whose volume changes systematically as a function of doping. The superconducting gap exhibits a d(x2-y2)-like anisotropy with a typical gap value of 10-15 meV near (pi ,0). By comparing with Bi2Sr2CaCu2O8 (Bi2212), we found that the size of superconducting gap is well scaled with the maximum T-c (T-c(max)) Doping-dependence of spectral line shape at (pi ,0) is very similar between Bi2201 and Bi2212, while its energy scale is different by a factor of 4, corresponding to the ratio of T-c(max) between the two compounds. These indicate that the superconducting and pseudogap properties are characterized by T-c(max) irrespective of the number of CuO2 layers or the BiO superstructure. (C) 2000 Elsevier Science Ltd. All rights reserved.

The doping dependence of the low-temperature spectral function is precisely determined from angle resolved photoemision (ARPES) measurements. It is found that, as the doping decreases, the maximum of the superconducting gap increases, but the slope of the gap near the nodes decreases. Though consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple cos(kx)-cos(ky) form. We suggest that this arises due to the increasing importance of long range interactions as one approaches the insulator. It is also shown that the shape of the spectral function at the (π, 0) point below T c can be explained by the interaction of the electrons with a collective mode whose energy matches that of the magnetic resonance as obtained by inelastic neutron scattering data, and points to the intimate relation of magnetic correlatins to high Tc superconductivity.

We have performed a systematic high energy (7–11 meV) and momentum (0.01 A −1 ) resolution angle-resolved photoemission spectroscopy (ARPES) on superstructure-free Bi 1.80 Pb 0.38 Sr 2.01 CuO 6−δ with various dopings. All the samples from overdoped T c = 0K to underdoped T c = 18K possess a large hole-like Fermi surface centered at X point, whose volume shows a systematic evolution with doping. The superconducting gap exhibits a d x 2 − y 2 -like anisotropy with a typical gap value of 10–15 meV. By comparing with Bi 2 Sr 2 CaCu 2 O 8 , we found that the size of superconducting gap and the ARPES spectral feature near E F are well scaled with the maximum T c ( T c max ). This suggests that the superconducting properties are characterized by T c max irrespective of the number of CuO 2 layers or the structural modulation in BiO layer.

We study the Fermi surface of Bi2Sr2CaCu2O8 using angle resolved photoemission spectroscopy (ARPES) with a momentum resolution of approximately 0.01 of the Brillouin zone. We show that, contrary to recent suggestions, the ARPES derived Fermi surface is a large hole barrel centered at (pi,pi), independent of the incident photon energy. We caution that the photon energy and k dependence of the matrix elements, if not properly accounted for, can lead to misinterpretation of ARPES intensities.

The photoemission line shape near (pi, 0) in Bi(2)Sr(2)CaCu(2)O(8+delta) below T(c) is characterized by a sharp peak, followed at higher energy by a dip and hump. We study the evolution of this line shape as a function of momentum, temperature, and doping. We find the hump scales with the peak and persists above T(c) in the pseudogap state. We present strong evidence that the peak-dip-hump structure arises from the interaction of electrons with a collective mode of wave vector (pi, pi). The inferred mode energy and its doping dependence agree well with a magnetic resonance observed by neutron scattering.

Comparing photoemission measurements on Bi2212 with penetration depth data, we show that a description of the nodal excitations of the d-wave superconducting state in terms of noninteracting quasiparticles is inadequate, and we estimate the magnitude and doping dependence of the Landau interaction parameter which renormalizes the linear T contribution to the superfluid density. Furthermore, although consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple coskx 2 cosky form, which suggests an increasing importance of long range interactions as the insulator is approached.

We use the gradient of the energy-integrated angle resolved photoemission (ARPES) intensity in order to define precisely the Fermi surface (FS) in BSCCO superconductors. We show that, independent of the photon energy, the FS is a hole barrel centered at ({pi},{pi}), Then, the superconducting gap along the FS is precisely determined from ARPES measurements on over-doped and underdoped samples of Bi2212. As the doping decreases, the maximum gap increases, but the slope of the gap near the nodes decreases. Though consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple cos(k{sub x})-cos(k{sub y}) form. A comparison of our ARPES results with available penetration depth data indicates that the renormalization of the linear T suppression of the superfluid density at low temperatures due to quasiparticle excitations around the d-wave nodes is large and doping dependent.

OBJECTIVE: The rs1333049, rs10757278 and rs4977574 are single nucleotide polymorphisms (SNPs) of chromosome 9p21 locus that are associated with prevalence of acute coronary syndromes (ACS). The rs1333049 SNP was also associated with cardiac outcome 6 months post ACS. No data concerning their association with long term prognosis after myocardial infarction is available. The aim of our study was to investigate the association of the 9p21.3 locus with 5-year overall mortality in patients with ST-elevation myocardial infarction (STEMI) treated invasively. MATERIALS AND METHODS: We performed a retrospective analysis of data collected prospectively in a registry of consecutive patients with STEMI treated with primary PCI. Genotyping was performed with a TaqMan method. The analyzed end-point was total 5-year mortality. RESULTS: The study group comprised 589 patients: 25.3% of females (n = 149), mean age 62.4±11.9 years, total 5-year mortality 16.6% (n = 98). When all the study group was analyzed, no significant differences in mortality were found between the genotypes. However, in high-risk patients (Grace risk score ≥155 points, n = 238), low-risk homozygotes had significantly better 5-year survival compared to other genotypes. The hazard ratio associated with high-risk genotype (high-risk homozygote or heterozygote) was: HR = 2.9 (95%CI 1.4-6.1) for the rs4977574 polymorphism, HR = 2.6 (1.25-5.3) for the rs1333049 one and HR = 2.35 (1.2-4.6) for the rs10757278 one (Cox proportional hazards model). CONCLUSIONS: The 9p21.3 locus is associated with 5-year mortality in high-risk patients with STEMI. This finding, due to very high effect size, could potentially be applied into clinical practice, if appropriate methods are elaborated.

We use angle-resolved photoemission spectroscopy and full-potential linearized augmented-plane-wave (FP-LAPW) calculations to study the electronic structure of BaCo${}_{2}$As${}_{2}$. The Fermi surface (FS) maps and the corresponding band dispersion data (at 90 and 200 K) reveal a small electron pocket at the center and a large electron pocket at the corner of the Brillouin zone. Therefore the nesting between electron and hole FS pockets is absent in this compound, in contrast to the parent compounds of FeAs-based high-$T$${}_{\mathrm{c}}$ superconductors. The electron pockets at the center of the zone are surrounded by two sets of four smaller electron pockets. The electronic structure at about 500 meV binding energy is very similar to features at the chemical potential in BaFe${}_{2}$As${}_{2}$. This indicates that complete substitution of Co for Fe causes a nearly rigid shift in the chemical potential by adding two electrons per formula unit at higher binding energies. However at lower binding energies $\ensuremath{\sim}$270 meV, the electron pocket at the center of the zone is absent, unlike in the Co-substituted Fe-based materials. This demonstrates that the rigid band picture is valid only at higher binding energies and breaks down closer to the chemical potential in BaCo${}_{2}$As${}_{2}$. We also observed the presence of a flat band near the Fermi energy that may have consequences for transport and thermodynamical properties. The experimental FS topology as well as band dispersion data are in reasonable agreement with the FP-LAPW calculations.

We use angle-resolved photoemission spectroscopy and a new quantitative approach based on the partial density of states to study properties of seemingly disconnected portions of the Fermi surface (FS) that are present in the pseudogap state of cuprates called Fermi arcs. We find that the normal state FS collapses very abruptly into Fermi arcs at the pseudogap temperature (${T}^{*}$). Surprisingly, the length of the Fermi arcs remains constant over an extended temperature range between ${T}^{*}$ and ${T}_{\mathrm{pair}}$, consistent with the presence of an ordered state below ${T}^{*}$. These arcs collapse again at the temperature below which pair formation occurs (${T}_{\mathrm{pair}}$) either to a point or a very short arc, whose length is limited by our experimental resolution. The tips of the arcs span between points defining a set of wave vectors in momentum space, which are the fingerprints of the ordered state that causes the pseudogap.

Formation energies of native defects in Bi${}_{2}$(Te${}_{x}$Se${}_{3\ensuremath{-}x}$), with comparison to ideal Bi${}_{2}$Te${}_{2}$S, are calculated in density-functional theory to assess transport properties. Bi${}_{2}$Se${}_{3}$ is found to be $n$ type for both Bi- and Se-rich growth conditions, while Bi${}_{2}$Te${}_{3}$ changes from $n$ to $p$ type going from Te- to Bi-rich conditions, as observed. Bi${}_{2}$Te${}_{2}$Se and Bi${}_{2}$Te${}_{2}$S are generally $n$ type, explaining observed heavily doped $n$-type behavior in most samples. A (0/\ensuremath{-}) transition level at 16 meV above valence-band maximum for Bi on Te antisites in Bi${}_{2}$Te${}_{2}$Se is related to the observed thermally active transport gap causing a $p$-to-$n$ transition at low temperature. Bi${}_{2}$(Te${}_{x}$Se${}_{3\ensuremath{-}x}$) with $xg2$ are predicted to have high bulk resistivity due to effective carrier compensation when approaching the $n$-to-$p$ crossover. Predicted behaviors are confirmed from characterization of our grown single crystals.

We have performed detailed studies of the temperature evolution of the electronic structure in $\mathrm{Ba}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}{)}_{2}{\mathrm{As}}_{2}$ using angle resolved photoemission spectroscopy. Surprisingly, we find that the binding energy of both hole and electron bands changes significantly with temperature in both pure and Ru substituted samples. The hole and electron pockets are well nested at low temperature in unsubstituted (${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$) samples, which likely drives the spin density wave and resulting antiferromagnetic order. Upon warming, this nesting is degraded as the hole pocket shrinks and the electron pocket expands. Our results demonstrate that the temperature dependent nesting may play an important role in driving the antiferromagnetic-paramagnetic phase transition.

Magnesium diboride, MgB2, has the highest transition temperature (T(c) = 39 K) of the known metallic superconductors. Whether the anomalously high T(c) can be described within the conventional BCS (Bardeen-Cooper-Schrieffer) framework has been debated. The key to understanding superconductivity lies with the 'superconducting energy gap' associated with the formation of the superconducting pairs. Recently, the existence of two kinds of superconducting gaps in MgB2 has been suggested by several experiments; this is in contrast to both conventional and high-T(c) superconductors. A clear demonstration of two gaps has not yet been made because the previous experiments lacked the ability to resolve the momentum of the superconducting electrons. Here we report direct experimental evidence for the two-band superconductivity in MgB2, by separately observing the superconducting gaps of the sigma and pi bands (as well as a surface band). The gaps have distinctly different sizes, which unambiguously establishes MgB2 as a two-gap superconductor.

We use angle-resolved photoemission spectroscopy to study a nontrivial surface state in a pseudobinary Bi2Te2.8Se0.2 topological insulator. We show that, unlike previously studied binaries, this is an intrinsic topological insulator with the conduction bulk band residing well above the chemical potential. Our data indicate that under a good vacuum condition there are no significant aging effects for more than two weeks after cleaving. We also demonstrate that the shift of the Kramers point at low temperature is caused by UV-assisted absorption of molecular hydrogen. Our findings pave the way for applications of these materials in devices and present an easy scheme to tune their properties.

The Fermi surfaces (FS's) and band dispersions of EuRh2As2 have been investigated using angle-resolved photoemission spectroscopy. The results in the high-temperature paramagnetic state are in good agreement with the full potential linearized augmented plane wave calculations, especially in the context of the shape of the two-dimensional FS's and band dispersion around the Gamma (0,0) and X (pi,pi) points. Interesting changes in band folding are predicted by the theoretical calculations below the magnetic transition temperature Tn=47K. However, by comparing the FS's measured at 60K and 40K, we did not observe any signature of this transition at the Fermi energy indicating a very weak coupling of the electrons to the ordered magnetic moments or strong fluctuations. Furthermore, the FS does not change across the temperature (~ 25K) where changes are observed in the Hall coefficient. Notably, the Fermi surface deviates drastically from the usual FS of the superconducting iron-based AFe2As2 parent compounds, including the absence of nesting between the Gamma and X FS pockets.

The compound ${\mathrm{BaMn}}_{2}{\mathrm{As}}_{2}$ with the tetragonal ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$ structure is a local-moment antiferromagnetic insulator with a N\'eel temperature ${T}_{\mathrm{N}}=625\text{ }\text{ }\mathrm{K}$ and a large ordered moment $\ensuremath{\mu}=3.9{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Mn}$. We demonstrate that this compound can be driven metallic by partial substitution of Ba by K while retaining the same crystal and antiferromagnetic structures together with nearly the same high ${T}_{\mathrm{N}}$ and large $\ensuremath{\mu}$. ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ is thus the first metallic ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type $M\mathrm{As}$-based system containing local $3d$ transition metal $M$ magnetic moments, with consequences for the ongoing debate about the local-moment versus itinerant pictures of the FeAs-based superconductors and parent compounds. The ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ class of compounds also forms a bridge between the layered iron pnictides and cuprates and may be useful to test theories of high ${T}_{\mathrm{c}}$ superconductivity.

We used angle-resolved photoemission spectroscopy and thermoelectric power to study the poorly explored, highly overdoped side of the phase diagram of Ba(Fe${}_{1\ensuremath{-}x}$Co${}_{x}$)${}_{2}$As${}_{2}$ high-temperature superconductor. Our data demonstrate that several Lifshitz transitions---topological changes of the Fermi surface---occur for large $x$. The central hole barrel changes to ellipsoids that are centered at $Z$ at $x\ensuremath{\sim}0.11$ and subsequently disappear around $x\ensuremath{\sim}0.2$; changes in thermoelectric power occur at similar $x$ values. ${T}_{c}$ decreases and goes to zero around $x\ensuremath{\sim}0.15$---between the two Lifshitz transitions. Beyond $x=0.2$ the central pocket becomes electron-like and superconductivity does not exist. Our observations reveal the importance of the underlying Fermiology in electron-doped iron arsenides. We speculate that a likely necessary condition for superconductivity in these materials is the presence of the central hole pockets rather than nesting between central and corner pockets.

Rare-earth platinum bismuth ($R$PtBi) has been proposed recently as a potential topological insulator. In this paper, we present measurements of the metallic surface electronic structure in three members of this family, using angle-resolved photoemission spectroscopy (ARPES). Our data show clear spin-orbit splitting of the surface bands and the Kramers' degeneracy of spins at the $\mathrm{\ensuremath{\Gamma}\ifmmode \bar{}\else \={}\fi{}}$ and $\mathrm{M\ifmmode \bar{}\else \={}\fi{}}$ points, which is reproduced nicely with our full-potential linearized augmented plane wave calculation for a surface electronic state. Topologically nontrivial behavior is signified by band inversion in the calculated bulk electronic structures, yet no direct indication of such behavior is detected by ARPES except for a weak Fermi crossing detected in close proximity to the $\mathrm{\ensuremath{\Gamma}\ifmmode \bar{}\else \={}\fi{}}$ point, making the total number of Fermi crossings odd. In the surface band calculation, however, this crossing is explained by a Kramers pair of bands that are very close to each other. The classification of this family of materials as topological insulators remains an open question.

We have investigated the electronic states in quasi-one-dimensional CuO chains by microprobe angle resolved photoemission spectroscopy. We find that the quasiparticle Fermi surface consists of six disconnected segments, consistent with recent theoretical calculations that predict the formation of narrow, elongated Fermi surface pockets for coupled CuO chains. In addition, we find a strong renormalization effect with a significant kink structure in the band dispersion. The properties of this latter effect [energy scale (∼40 meV), temperature dependence, and behavior with Zn-doping] are identical to those of the bosonic mode observed in CuO2 planes of high-temperature superconductors, indicating they have a common origin. © 2010 The American Physical Society

We measured the electronic structure of an iron arsenic parent compound LaFeAsO using angle resolved photoemission spectroscopy (ARPES). By comparing with a full-potential Linear Augmented PlaneWave calculation we show that the extra large Gamma hole pocket measured via ARPES comes from electronic structure at the sample surface. Based on this we discuss the strong polarization dependence of the band structure and a temperature-dependent hole-like band around the M point. The two phenomena give additional evidences for the existence of the surface-driven electronic structure., 6 pages, 6 figures

The superfluid density ρs in underdoped (Tc≃23 K), optimally doped (Tc≃35 K), and overdoped (Tc≃29 K) single-crystalline (Bi,Pb)2(Sr,La)2CuO6+δ samples was studied by means of muon spin rotation (μSR). By combining the μSR data with the results of angle-resolved photoemission spectroscopy measurements on similar samples [T. Kondo et al., Nature (London) 457, 296 (2009)] good self-consistent agreement is obtained between two techniques concerning the temperature and the doping evolution of ρs. © 2010 The American Physical Society