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Korea Superconducting Tokamak Advanced Research (KSTAR) program has made significant advances in the development of long pulse and high-performance plasma scenarios, utilizing the advantages of the fully superconducting tokamak. Ten years of KSTAR operation have produced outstanding progress in plasma control, extending the operating window of the plasma discharges, and achieving the H-mode up to 1.2 MA in plasma current, up to 90 s at top duration, and up to 2.16 in elongation. The unique features of the KSTAR device also produced a record 30 s long pulse in H-mode operation without an edge-localized-mode (ELM) crash, and progress in the fundamental transport physics through systematic study, using unique diagnostic capabilities. Therefore, the next near-term research focus will be on how to extend the high performance plasmas up to 300 s by overcoming scientific and engineering obstacles to steady state operation. For fusion reactors, the tokamak device needs to sustain a permanent plasma current. It is also known that the bootstrap current should play an important role in the plasma current for an efficient fusion reactor, and its contribution should be over as high as possible. An internal transport barrier discharge based on the reverse shear profile of the safety factor is one of the promising candidates for enhancing the bootstrap current. However, even in reverse shear mode, an additional external off axis current drive (CD) should be provided to control the current profile, as well as to supplement the plasma current. KSTAR has pursued steady state to operation, aiming for a fully non inductive state, based on real time (RT) plasma control by maximizing the long pulse capabilities of the superconducting machine. In order to deposit current at an arbitrary position, the first requirement is to have many highly efficient CD actuators capable of profile diversity. KSTAR has prepared several RF CD portfolios in addition to a conventional on and off axis CD neutral beam injection (NBI) system. The final target of an off axis current drive will be a 4 MW off-axis NB, 8 MW on-axis NB, 6 MW electron cyclotron heating (ECH), and 4 MW radio frequency heating and current drive (RFHCD) (ion cyclotron (IC), lower hybrid (LH), Helicon CD). In addition, as a long-term goal, demonstrating a long pulse core edge compatible plasma in a reactor relevant condition is important in present medium size tokamak, since it is expected to sustain a very high pressure pedestal height plasma using super H-mode, with parallel upgrades of the superconducting toroidal field (TF) coils.

General characteristics of a fishbone mode in KSTAR are investigated. Fishbone activities are observed with a Mirnov coil, an electron cyclotron emission radiometer (from the core to the edge of plasmas) and an beam emission spectroscopy system (core or edge plasmas) which are measuring fluctuations of poloidal magnetic fields, electron temperatures, and densities, respectively. Temporal evolutions of these fluctuations are similar to the observations from other tokamaks. An interesting and notable feature found in KSTAR fishbone modes is that radial coherence structures of electron temperature and density with respect to magnetic fluctuations are non-monotonic that they have a local minimum at [Formula: see text] and a maximum at [Formula: see text] in addition to the usual global peak near the q = 1 surface, where r/ a is the normalized minor radius and q is the safety factor. Furthermore, the associated temporal evolution of the electron temperatures in slow-time scale, i.e., less than 1 kHz, with the fishbone activities show that there exist a drop in temperature or increase in temperature depending on inside or outside the q = 1 surface, respectively, from the core to the edge plasmas except that there are almost no temperature changes in the intermediate region which seems to be correlated with the non-monotonic coherence profile. Such a non-monotonic structure and the slow temporal evolution of temperatures are explained with barely trapped resonating fast ions with the banana orbit widths of the order of the minor radius, so that they transit the core and the edge regions simultaneously without trespassing the mid-plane intermediate region.

The electronic structures of Gd-substituted Bi2−xGdxTe3 single crystals have been investigated by employing synchrotron-radiation spectroscopies, such as soft X-ray absorption spectroscopy (XAS), soft X-ray magnetic circular dichroism (XMCD), photoemission spectroscopy (PES), and scanning photoelectron microscopy (SPEM). SPEM measurements confirm that Gd ions are substituted homogeneously in Bi2−xGdxTe3 crystals. The measured Gd 3d XAS and XMCD spectra provide evidence that the substituted Gd ions are trivalent and magnetic. The hν-dependence of the valence-band (VB) PES spectra are described well by the hν-dependent contributions of the Te 5p and Bi 6p states. A good agreement is found between the measured VB PES spectra of Bi2−xGdxTe3 and the calculated partial densities of states, revealing that the Te 5p states will play an important role in determining the thermoelectric and topological properties of Bi2−xGdxTe3.

Previous high-resolution angle-resolved photoemission (ARPES) studies of URu$_2$Si$_2$ have characterized the temperature-dependent behavior of narrow-band states close to the Fermi level ($E_\mathrm{F}$) at low photon energies near the zone center, with an emphasis on electronic reconstruction due to Brillouin zone folding. A substantial challenge to a proper description is that these states interact with other hole-band states that are generally absent from bulk-sensitive soft x-ray ARPES measurements. Here we provide a more global $k$-space context for the presence of such states and their relation to the bulk Fermi surface topology using synchrotron-based wide-angle and photon energy-dependent ARPES mapping of the electronic structure using photon energies intermediate between the low-energy regime and the high-energy soft x-ray regime. Small-spot spatial dependence, $f$-resonant photoemission, Si 2$p$ core-levels, x-ray polarization, surface-dosing modification, and theoretical surface slab calculations are employed to assist identification of bulk versus surface state character of the $E_\mathrm{F}$-crossing bands and their relation to specific U- or Si-terminations of the cleaved surface. The bulk Fermi surface topology is critically compared to density functional theory and to dynamical mean field theory calculations. In addition to clarifying some aspects of the previously measured high symmetry $\Gamma$, Z and X points, incommensurate 0.6a* nested Fermi-edge states located along Z-N-Z are found to be distinctly different from the density functional theory Fermi surface prediction. The temperature evolution of these states above $T_{HO}$, combined with a more detailed theoretical investigation of this region, suggests a key role of the N-point in the hidden order transition., Comment: topical review 47 pages, 12 figures, proof edits, hyperlinked TOC

By employing soft X-ray magnetic circular dichroism (XMCD) and soft X-ray absorption spectroscopy (XAS), we have investigated the temperature (T)-dependent valence and spin states of Cr ions in half-metallic ferromagnet CrO2 nanorod powder. The lineshape-analysis of both the Cr 2 p XAS and XMCD spectra of CrO2 reveals that the Cr ions in bulk CrO2 have both Cr 4 + t 2 g 2 ↑ and Cr 3 + t 2 g 3 ↑ valence configurations. This work provides the direct experimental evidence for the Cr 3 + - Cr 4 + mixed-valent states in bulk CrO2 ( Cr 3.8 + ) , demonstrating that the half-metallic ferromagnetism in CrO2 originates from the double-exchange interaction. The T-dependent intensity variation of the Cr 2 p XMCD spectrum agrees well with the bulk magnetization M(T) and the Curie temperature, indicating that the measured Cr 2 p XMCD data represent the intrinsic bulk ferromagnetism in CrO2, and support the above finding of the XMCD lineshape analysis.

We have investigated the angle-dependent orbital and spin magnetic moments of the [Co/Pd] multilayer (ML) films with intervening CoO layers under annealing by employing angle-dependent soft X-ray magnetic circular dichroism (XMCD). After annealing, the orbital magnetic moments of Co ions are found to be enhanced, with the maximum values along the perpendicular direction of [Co/Pd] ML, providing evidence for the origin of the improved perpendicular magnetic anisotropy (PMA) being the interface spin–orbit coupling. The induced Pd polarization was observed after annealing, demonstrating the strong Co-Pd hybridization arising from the Co-Pd alloy formation near the interface. The angle-dependent coercivity follows the 1 / cos θ behavior, suggesting that the magnetization reversal in the hysteresis curve in [Co/Pd] ML occurs mainly through the pinning mechanism.

The electronic structures of the layered rare-earth chalcogenide compounds of CeTe2, PrTe2, and PrTe3, which have the charge-density wave (CDW) transition and possibly the chiral transition, have been investigated by employing soft X-ray absorption spectroscopy (XAS) and angle-resolved photoemission spectroscopy (ARPES). R 3d XAS measurements show that the valence states of Ce and Pr ions are nearly trivalent in all the compounds. Similar band dispersions are observed in their measured ARPES data, but with the band positions in PrTe3 being shifted up in energy compared to those in CeTe2 and PrTe2. These findings suggest that their Te 5p band structures are determined mainly by the 2D interactions in the Te(2)/Te(3) sheets, but with a larger number of holes in the Te 5p bands in PrTe3 than in CeTe2 and PrTe2. The measured constant energy maps of CeTe2, PrTe2, and PrTe3 for high binding energies are similar to one another, reflecting the Te 5p band structures of the Te(2)/Te(3) square nets. In contrast, the Fermi surfaces (FSs) of CeTe2 and PrTe3 exhibit extra features, different from the FS of the ideal Te(2)/Te(3) square nets, which arise from the CDW-induced FS reconstruction in the Te(2)/Te(3) sheets.

The electronic structure of a M\"obius Kondo insulator candidate of CeRhSb has been investigated by employing angle-resolved photoemission spectroscopy, density functional theory (DFT) band calculations, and dynamical mean-field theory (DMFT) band calculations. Fermi surfaces (FSs) and band structures are successfully measured for three orthogonal crystallographic directions. A sharp Ce $4f$ peak is observed at the Fermi level (${E}_{\text{F}}$), and its temperature ($T$) evolution agrees with that of the Ce $4f$ Kondo resonance. The metallic FSs are obtained for all three different (100), (010), and (001) planes. The Ce $4f$ FSs are described properly by the unfolded DFT calculations considering the reduced Ce-only unit cell. The $T$ dependence of Ce $4f$ states as well as the dispersive coherent Ce $4f$ bands are described well by the DMFT calculations and reveal the anisotropic $c\text{\ensuremath{-}}f$ hybridization. The photon energy dependence of the Fermi-edge states in CeRhSb reveals the three-dimensional character, consistent with the bulk states dispersing to ${E}_{\text{F}}$ over a larger energy scale rather than the predicted M\"obius topological surface states.

Highly insulated envelope or external insulation systems are being applied in recent energy saving buildings to reduce the heat loss through envelope. Internal insulation systems are applied to most apartments in Korea because they are inexpensive and convenient to construct. However, the internal insulation systems have poor performance because of the heat bridges through structures such as slabs. The external insulation systems have better thermal performance because the heat bridges through the structure are rarely formed. However, it has problems regarding the external insulator separation because of strong winds, spread of fire because of insulator combustion in case of fire, formation of heat bridges through the connectors between structure and external insulation. In this study, the thermal performance of the sandwich insulation system for apartment buildings was evaluated according to the shear connectors and insulation materials.

Evaluation of the thermal performance of a fenestration system during the cooling season is based on heat gains by temperature difference and solar radiation, characterised by thermal transmittance (U-value) and solar heat gain coefficient, respectively. While U-value testing and calculation methods have been long established, solar heat gain coefficient has been evaluated only by calculation under the lack of any established testing method. However, calculation alone cannot yield exact solar heat gain coefficient values for various types of fenestration. To address this problem, this study aims to develop a solar heat gain coefficient apparatus for measuring the energy performance of fenestration in terms of U-value and solar heat gain coefficient, and to evaluate that system. The proposed measurement system can be used in measuring U-values and solar heat gain coefficient values for fenestration with complicated shapes, such as an awning device.

Lately, constructions of large and high-rise buildings are steadily increasing, and various building envelope systems were developed in accordance with this trend. However, insulation methods applied to the building envelope may cause interior condensation, energy loss and discoloration of walls. In this study, ventilated insulation system was applied simultaneously considering conduction, convection and radiation of heat. This research performed a field experiment to evaluate insulating performance comparing ventilated insulation system with non-ventilated insulation system.

Ca3CoXO6 (X = Co, Rh) is a low-dimensional system of materials with (CoXO6)∞ chains separated by Ca ions and packed in a triangular fashion. For Ca3Co2O6, each chain has CoO6 octahedra alternating with CoO6 trigonal prisms by sharing the triangular face; in the case of Ca3CoRhO6, most of the Co ions in the octahedral sites are replaced by Rh ions. We have studied Ca3CoXO6 (X = Co, Rh) by carrying out thorough measurements of its magnetic properties, high-resolution neutron powder diffraction, and X-ray absorption spectroscopy. Ferromagnetic ordering along the chain’s direction (c-axis) appears at T c1 ~ 25 K in Ca3Co2O6 while it occurs at a much higher temperature ~90 K in Ca3CoRhO6. The magnetic order in the packing ab-plane, which results from the interaction between neighboring ferromagnetic chains, is found to change from a partiallydisordered antiferromagnetic to a ferrimagnetic and then to a ferromagnetic one under an applied magnetic field in both Ca3Co2O6 and Ca3CoRhO6. For Ca3CoRhO6 with a higher T c1, a controllable parameter, that is, the degree of the Co-Rh cation site ordering exists within a chain, which affects the magnetic properties in a major way. This cation site order can be controlled experimentally by varying the rate of cooling to room temperature after the final sintering in the sample’s synthesis procedures. In the samples air-quenched at a cooling rate of several hundred K/min, T c1 was decreased to ~80 K from 90 K for normal samples with a 2-K/min cooling rate, and the ferrimagnetic region in the H -T phase diagram shrunk. In contrast, the Tc1 of the ones that were slow cooled at a cooling rate of ~0.5 K/min was increased to a higher temperature of ~100 K, and the ferrimagnetic region in the H - T phase diagram correspondingly became enlarged. For comparison, Ca3Co2O6 samples with different cooling rates were also investigated, and their magnetic properties were found to be independent of the synthesis conditions. We discuss the present results in terms of the disorder, frustration, and dimensionality of the Ca3CoXO6 system.

The electronic structures of the magnetic topological insulator candidates of Ce-substituted Bi2–xCexSe3 (x ≤ 0.12) have been investigated through angle-resolved photoemission spectroscopy (ARPES), soft X-ray absorption spectroscopy (XAS), and soft X-ray magnetic circular dichroism (XMCD) measurements on high-quality single crystals. Ce 3d XAS and XMCD measurements provide evidence that the substituted Ce ions in Bi2–xCexSe3 are trivalent and magnetic, confirming the purely magnetic effect of the Ce-substitution. ARPES measurements reveal the formation of an energy gap (Δ) for x > 0, indicating that the finite Δ arises from the broken time-reversal symmetry due to the substituted magnetic Ce impurities.

The electronic structure of a charge density wave (CDW) system PrTe3 and its modulated structure in the CDW phase have been investigated by employing ARPES, XAS, Pr 4 f RPES, and first-principles band structure calculation. Pr ions are found to be nearly trivalent, supporting the CDW instability in the metallic Te sheets through partial filling. Finite Pr 4 f spectral weight is observed near the Fermi level, suggesting the non-negligible Pr 4 f contribution to the CDW formation through the Pr 4 f -Te 5p hybridization. The two-fold symmetric features in the measured Fermi surface (FS) of PrTe3 are explained by the calculated FS for the assumed 7 × 1 CDW supercell formation in Te sheets. The shadow bands and the corresponding very weak FSs are observed, which originate from both the band folding due to the 3D interaction of Te sheets with neighboring Pr-Te layers and that due to the CDW-induced FS reconstruction. The straight vertical FSs are observed along kz , demonstrating the nearly 2D character for the near-EF states. The observed linear dichroism reveals the in-plane orbital character of the near-EF Te 5p states.

To finally resolve the controversial issue of whether or not the electronic structure of YbB_{6} is nontrivially topological, we have made a combined study using angle-resolved photoemission spectroscopy (ARPES) of the nonpolar (110) surface and density functional theory (DFT). The flat-band conditions of the (110) ARPES avoid the strong band bending effects of the polar (001) surface and definitively show that YbB_{6} has a topologically trivial B 2p-Yb 5d semiconductor band gap of ∼0.3 eV. Accurate determination of the low energy band topology in DFT requires the use of a modified Becke-Johnson exchange potential incorporating spin-orbit coupling and an on-site Yb 4f Coulomb interaction U as large as 7 eV. The DFT result, confirmed by a more precise GW band calculation, is similar to that of a small gap non-Kondo nontopological semiconductor. Additionally, the pressure-dependent electronic structure of YbB_{6} is investigated theoretically and found to transform into a p-d overlap semimetal with small Yb mixed valency.

The electronic structures of SrRu 1 − xIr xO 3 films ( 0 ≤ x ≤ 1) have been investigated by employing polarization-dependent soft X-ray absorption spectroscopy. In SrIrO 3, the coherent quasi-particle peak at the Fermi level ( E F) is clearly observed, reflecting the spin-orbit-coupled correlated metallic nature of SrIrO 3. X-ray linear dichroism signals for x = 0 and x = 1 are negligibly weak, demonstrating the pseudo-cubic structure for SrRuO 3 and the strong spin-orbit coupling in SrIrO 3. In contrast, finite linear dichroism is observed for the intermediate x regime, indicating that the narrow d x z ↓ and d y z ↓ bands close to E F are occupied less than the wide d x y ↓ band due to the enhanced in-plane hopping.The electronic structures of SrRu 1 − xIr xO 3 films ( 0 ≤ x ≤ 1) have been investigated by employing polarization-dependent soft X-ray absorption spectroscopy. In SrIrO 3, the coherent quasi-particle peak at the Fermi level ( E F) is clearly observed, reflecting the spin-orbit-coupled correlated metallic nature of SrIrO 3. X-ray linear dichroism signals for x = 0 and x = 1 are negligibly weak, demonstrating the pseudo-cubic structure for SrRuO 3 and the strong spin-orbit coupling in SrIrO 3. In contrast, finite linear dichroism is observed for the intermediate x regime, indicating that the narrow d x z ↓ and d y z ↓ bands close to E F are occupied less than the wide d x y ↓ band due to the enhanced in-plane hopping.

The electronic structures of Co-based potential thermoelectric (TE) oxides, including \(\hbox{Ca}_3\hbox{Co}_4\hbox{O}_9\) and \(\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}\) (y = 8 + δ) single crystals and polycrystalline \(\hbox{Ca}_3\hbox{Co}_2\hbox{O}_6\), have been investigated by employing soft x-ray absorption spectroscopy (XAS) and photoemission spectroscopy (PES). Co 2p XAS measurements show that Co ions are nearly trivalent (\(\hbox{Co}^{3+}\)) in all of these Co-based TE oxides with a small mixture of \(\hbox{Co}^{4+}\) ions in \(\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}\). Valence-band PES and O 1s XAS measurements show that the occupied Co 3d states are located at the top of the valence bands and that the lowest unoccupied states have the primarily Co 3d character, respectively. These findings suggest the importance of the Co 3d electronic structures in determining TE properties of these Co-based oxides.

The electronic structures of a charge density wave (CDW) system $R{\mathrm{Te}}_{2}$ $(R=\text{Ce},\text{Pr})$ have been investigated by employing angle-resolved photoemission spectroscopy (ARPES) and the first-principles band structure method. The $R$ $4f$ hybridization peak $(4{f}^{n}{c}^{m\ensuremath{-}1})$ in the $R$ $4f$ PES spectrum is located deeper in ${\mathrm{PrTe}}_{2}$ than in ${\mathrm{CeTe}}_{2}$ and $R$ $4f$ spectral intensity near ${E}_{F}$ is much weaker in ${\mathrm{PrTe}}_{2}$ than in ${\mathrm{CeTe}}_{2}$, implying the importance of the hybridization between Ce $4f$ and Te(1) $5p$ electrons. For both ${\mathrm{CeTe}}_{2}$ and ${\mathrm{PrTe}}_{2}$, the metallic states crossing the Fermi level $({E}_{F})$ are observed below the CDW transition temperature, indicating the existence of the partially ungapped Fermi surfaces (FSs). The zigzag features having the fourfold rotational symmetry are observed near the $X$ point in the FS of ${\mathrm{CeTe}}_{2}$, but not in the FS of ${\mathrm{PrTe}}_{2}$. The tight-binding model calculations show that the zigzag FS features in ${\mathrm{CeTe}}_{2}$ can be described as the CDW-induced FS reconstruction due to the $4\ifmmode\times\else\texttimes\fi{}4$ CDW supercell structure. The effect of the linear dichroism is observed in ARPES, suggesting that the ${E}_{F}$-crossing states have mainly the in-plane orbital character. The photon-energy maps for the near-${E}_{F}$ states exhibit the straight vertical dispersions for both ${\mathrm{CeTe}}_{2}$ and ${\mathrm{PrTe}}_{2}$, demonstrating the dominant two-dimensional character in $R{\mathrm{Te}}_{2}$ $(R=\text{Ce},\text{Pr})$.

The electronic structure of CeTe2 has been investigated by performing high-resolution photoemission spectroscopy (PES) measurements on high-quality stoichiometric single crystals of CeTe2. The Ce 3d XAS measurement indicates that the Ce ions are trivalent. The Ce 4f PES spectrum reveals two-peak structures with the Ce 4f bulk hybridization peak located around 0.8 eV below EF. The high-resolution, high-energy, bulk-sensitive PES study of CeTe2 provides evidence for a metallic density of states near EF. The carriers near EF consist mainly of Ce 5d and Te(1) 5p states, while the contribution from the Ce 4f and Te(2) 5p states is negligible. This finding agrees with the CDW instability in the Te(1) sheets.

Electronic structures of La-doped Ba 2 FeMoO 6 double perovskite oxides have been investigated using photoemission spectroscopy and soft x-ray absorption spectroscopy. The ground states of Ba 2-x La x FeMoO 6 are found to be in the Fe 2+ -Fe 3+ mixed-valent states and the Fe valence state increases toward 3+ with increasing x. The states close to E F consist of the degenerate Mo-Fe t 2g ↓ states. The LSDA + U calculations for Ba 2-x La x FeMoO 6 (x = 0, 1) show a larger occupied bandwidth of the Mo t 2g ↓ states for x = 1 than for x = 0, which is consistent with the higher T C value predicted in a type of the double exchange mechanism.

The electronic structure of epitaxial thin films of La0.7Ce0.3MnO3 (LCeMO) has been investigated using photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The measured valence-band PES, Ce 3d PES, and Ce 3d XAS spectra for LCeMO consistently indicate that the localized Ce 4f orbitals are almost unoccupied so that the Ce valence is nearly tetravalent. The Mn 2p XAS spectrum suggests Mn2+ and Mn3+ mixed-valent states of Mn ions in LCeMO. The LSDA + U calculation agrees better with the measured PES/XAS spectra than the LSDA calculation (U: the on-site Coulomb interaction). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Valence states and electronic structures of Cr-doped Nd½A½MnO₃ (NAMO; A=Ca, Sr) manganites have been investigated using x-ray absorption spectroscopy (XAS) and high-resolution photoemission spectroscopy (PES). All the Cr-doped NAMO systems exhibit the clear metallic Fermi edges in the Mn e_g PES spectra near E_F. The spectral intensity at E_F is higher for Cr-doped Nd½Sr½MnO₃ (NSMO) than for Cr-doped Nd½Ca½MnO₃ (NCMO), reflecting the stronger metallic nature for NSMO than for NCMO. The measured Cr 2p XAS spectra are found to be very similar to that of Cr₂O₃, indicating that Cr ions in Cr-doped NAMO are in the trivalent Cr³+ states (t³_(2g)). The Cr 2p XAS data are consistent with the Cr 3d PES spectra located at ~1.3 eV below EF and having no emission near E_F.

The electronic structures of the quenched superconductivity system Y 1-x Pr x Ba 2 Cu 3 O 7-δ (YPrBCO; x = 0, 0.4, 0.8) have been investigated by angle-resolved photoemission spectroscopy (ARPES). With increasing x, the ARPES spectra along Γ → S exhibit a binding energy shift away from E F and a pronounced decrease in the density of electronic states near E F , suggesting an enhanced size of the Fermi wave vector k F from S for x = 0.4, as compared to x = 0. The ARPES results have been compared with the LSDA + U electronic structure calculations incorporating the spin-orbit interaction for PrBa 2 Cu 3 O 7 .

Isothermal solidification of conventional Cu/Sn diffusional couples was performed to form thin (30 µm) joints consisting of Cu-Sn intermetallics. During initial stages of isothermal solidification, both Cu6Sn5 and Cu3Sn phases grow, even though the former is the dominant. After consumption of all available Sn, the Cu3Sn phase grows reactively at the expense of Cu and Cu6Sn5. Finally, we obtain solder joints that consist of only Cu3Sn. Indentation fracture-toughness measurements show that Cu3Sn is superior to Cu6Sn5. Furthermore, indentations of Cu3Sn exhibit the presence of shear bands, which are not observed in Cu6Sn5, implying that the former is more ductile than the latter. Ductile intermetallic-based joints formed by isothermal solidification are promising candidates to form thin (as thin as 5–10 µm or less) solder joints, as they are thermally and thermodynamically stable compared to conventional solder joints. Excess copper in the interconnect provides ductility to the interconnect.

We have investigated the surface states of a potential mixed-valent topological insulator ${\mathrm{SmB}}_{6}$ based on first-principles density functional theory slab band structure analysis. We have found that metallic surface states are formed in the bulk band gap region, providing evidence for the topological insulating nature of ${\mathrm{SmB}}_{6}$. The obtained surface in-gap states are quite different from those in existing reports in that they are formed differently depending on the Sm or ${\mathrm{B}}_{6}$ surface termination, and are composed of mainly the Sm $4f$ state indicating the essentiality of including $f$ electrons in describing the surface states. We have obtained the spin chiral structures of the Fermi surfaces, which are also in accordance with the topological insulating nature of ${\mathrm{SmB}}_{6}$.

The electronic structure of La0.7Ce0.3MnO3 (LCeMO) has been investigated by using photoemission spectroscopy. A very weak 4f resonance is observed and the Ce 3d spectrum of LCeMO is very similar to that of CeO2, indicating that Ce ions are far from being trivalent. The Mn 2p core-level spectrum of LCeMO is essentially the same as that of hole-doped La0.7Sr0.3MnO3, but different from that of MnO. The local spin-density approximation (LSDA) electronic structure calculations for LCeMO show that the Mn 3d states contribute a large peak around -2 eV and a weak structure between -2 eV and EF, and that the O 2p states are spread between -3 eV and -9 eV, with negligible contribution near EF. The LSDA calculations for LCeMO and hole-doped La0.7Ba0.3MnO3 reveal that the calculated Mn 3d density of states at EF in LCeMO is larger, reflecting the effect of electron doping with Ce ions.

The electronic structure of the electron-doped manganite La0.7Ce0.3MnO3 (LCeMO) has been investigated by performing the band calculations with the local spin-density functional approximation (LSDA), which are then compared to the photoemission spectroscopy (PES) data. In order to investigate the effect of the Mn 3d on-site Coulomb correlation on the electronic structure of LCeMO, we have calculated the Mn 3d partial density of states (PDOS) by performing the LSDA+U calculations. Our calculations show that the Mn 3d on-site Coulomb correlation accounts for the major features in the experimental PES spectra, such as the peak positions and the reduced spectral weight near the Fermi level.

The electronic structures of Pr 1− x Sr x MnO 3 (PSMO; x =1/3, 1/2, 2/3) have been investigated by performing photoemission spectroscopy measurements and the LSDA band-structure calculations. The partial yield spectra and the constant-initial-state spectra near the Pr 4 d absorption edge provide evidence that the Pr ions are nearly trivalent in PSMO. The Pr 4 f and Mn 3 d partial spectral weight (PSW) distributions of PSMO are found to be insensitive to x , reflecting the small overlap between Mn 3 d and Pr 4 f orbitals. The spectrum near the Fermi level exhibits evidence for the metal–insulator transitions with varying x , as well as a charge gap formation for x =1/2.

The electronic structures of amorphous a-Fe100-xZrx and a-(Fe1-yMy)33Zr67 alloys (M = Co, Ni, Cu) have been investigated by using x-ray photoemission spectroscopy. For a-Fe100-xZrx, the linewidths of both the Fe 2p and Zr 3d core-level spectra become narrower with increasing x. Systematic line-shape analysis reveals that such a trend could be either due to the decrease in the Auger recombination process or due to the decrease in the exchange splitting of core-hole electrons. The broad Zr 3d spectrum for x = 10 is decomposed into two peaks, suggesting a localized nature of the Zr 4d electrons in a-Fe90Zr10. For a-(Fe1-yMy)33Zr67 (M = Co, Ni), the Fe 2p spectrum becomes narrower and the shoulder-like satellite structure becomes more pronounced with increasing y, reflecting the increasingly localized nature of the Fe 3d electrons. In contrast, the M 2p spectra of a-(Fe1-yMy)33Zr67 remain essentially unchanged with varying y, implying that the M 2p spectra of a-M100-xZrx are much less sensitive to the M ion species than to the fractional concentrations of M and Zr ions. As M varies from Fe to Co and Ni in a-M33Zr67, the Zr 3d spectrum exhibits a small shift toward higher binding energy and a slight increase in the linewidth. Band-structure calculations for ordered MZr2 (M = Fe, Co, Ni, Cu) predict that both the density of states at the Fermi level N(EF) and the total number of valence electrons increase as M varies from Fe to Co and Ni, which is consistent with the measured Zr 3d spectra of a-M33Zr67.

Highly epitaxial CrSi 2 films were grown on Si(111) substrate by Cr deposition on Si(111)-(7×7) surface at 450°C followed by in situ annealing at 900–1100°C in ultrahigh vacuum. CrSi 2 (001) plane was grown parallel to the Si(111) plane with a CrSi 2 // Si matching face relationship. The valence band (VB photoemission for the 1200-Å-thick CrSi 2 was measured at room temperature and 20 K by using synchrotron radiation (hν=20–120 eV). Overall shapes of the two energy distribution curves (EDC's) were similar. Two peaks were observed in the EDC's corresponding to the bonding and the nonbonding Cr -d states in the CrSi 2. The onset of the VB photoemission measured at 20 K was located at about 0.32 eV below Fermi level, due to the energy band gap opening at low temperature.

A resonant photoemission study has been performed for Pr{sub 1{minus}x}Sr{sub x}MnO{sub 3}thinsp(x=1/3,1/2) and the partial spectral weight (PSW) distributions of both Pr 4f and Mn 3d electrons have been determined. With varying temperature ({ital T}) and {ital x}, metal-insulator transitions are observed in the photoemission data. The Pr ions in Pr{sub 1{minus}x}Sr{sub x}MnO{sub 3} are trivalent, and Pr 4f PSW exhibits a dominant hybridization peak indicating large Pr 4f{minus}Othinsp2p mixing. The Mn 3d PSW at low {ital T} shows a charge gap for x=1/2, and a reduced spectral intensity near E{sub F} for x=1/3, suggesting the localized nature due to the lattice polaron formation. thinsp {copyright} {ital 1999} {ital The American Physical Society}

Mn-based Heusler alloys of NiMnSb and PtMnSb have been predicted to be half-metallic ferromagnetic metals, with 100% spin-polarized conduction electrons at the Fermi level. In this study, the valence-band and Sb 4d core levels of the XMnSb-type Heusler alloys (X = Mi, Pd, Pt) have been investigated using synchrotron-radiation photoemission spectroscopy. Samples were made by melting the appropriate amount of constituent elements in vacuum-sealed quartz tubes at 1100 °C, and subsequent annealing at 600 °C for one week. Photoemission measurements were performed on the Mark V beamline at the Synchrotron Radiation Center at the University of Wisconsin-Madison. Polycrystalline samples were fractured in situ and measured at about 60 K in a vaccum better than 4 × 10−11 Torr. The instrumental resolution of the system is about 0.2 eV at hν=40 eV and about 0.4 eV at hν = 150 eV, respectively. The incident photon flux was monitored by the yield from a gold mesh and all the spectra were normalized to the incident phot...

Photoemission study has been performed for a high-quality single crystal of ${\mathrm{CeRu}}_{2},$ including resonant photoemission near the Ce $4\stackrel{\ensuremath{\rightarrow}}{d}4f$ absorption edge and high-resolution photoemission at a low-photon energy. Resonant photoemission study provides evidence for the large hybridization between Ce $4f$ and conduction electrons, indicating mixed-valence in ${\mathrm{CeRu}}_{2}.$ It is found that the line shape of the high-resolution spectrum near the Fermi level depends on the experimental conditions and the sample surface treatment. Comparison of photoemission data to the calculated density of states reveals that band calculations provide a reasonably good description of the electronic structure of ${\mathrm{CeRu}}_{2}.$

The valence band (VB) electronic structures of CrSi2 were studied by synchrotron radiation photoemission. Overall features of the VB photoemission spectra measured at room temperature (RT) and 20 K by using synchrotron radiation (photon energy, hν=20–120 eV) were similar. Two characteristic emissions were observed corresponding to the bonding and the nonbonding Cr-d partial density of states (PDOS) in the CrSi2. The onset of the VB photoemission measured at 20 K was located at about 0.32 eV below Fermi level, due to the energy band gap of CrSi2 more than 0.32 eV.

The electronic structures of Sr 2 - x K x FeMoO 6 ( x = 0 , 0.1 , 0.2 ) double perovskites have been investigated by employing photoemission spectroscopy (PES), soft X-ray absorption spectroscopy (XAS), and soft X-ray magnetic circular dichroism (XMCD) near the Fe 2 p absorption edge. The substitution of K + ions for Sr 2 + ions causes the increasing Fe 2 + component in the Fe 2 + – Fe 3 + mixed-valent states, but little difference in the Fe 2p XMCD spectra. As x increases, the photoemission intensity near the Fermi level decreases, which indicates the decreasing carriers and the decreasing bandwidth of the itinerant t 2 g ↓ states.

Electronic structures of AgNi 1 - x Co x O 2 ( 0 ⩽ x ⩽ 1 ) delafossite oxides have been investigated by using photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS). T 2p XAS ( T = Co , Ni) spectra of AgNi 1 - x Co x O 2 show that the valence states of Co ions are trivalent and do not change with x . In contrast, Ni ions are in the Ni 2 + – Ni 3 + mixed-valent states and the trivalent component increases with increasing x . This finding suggests that the metallic nature of AgNi 1 - x Co x O 2 for low values of x arises from the divalent Ni ions. The valence-band PES study of AgNi 1 - x Co x O 2 reveals that the Ni 3d states are more metallic like than the Co 3d states.

The electronic structure of single crystalline CeNiSn has been investigated using photoemission spectroscopy. The extracted Ce 4f spectrum exhibits three peak structures; the typical Fermi level and 2 eV peaks, and another between them, {approximately}0.9 eV below the Fermi level E{sub F}. The near-E{sub F} peak reflects a substantial Ce 4f-Sn sp hybridization, whereas the 0.9 eV peak arises from the Ce 4f-Ni 3d and Ce 5d-Ni 3d hybridization. A Ni 3d satellite feature is observed about 6 eV below the Ni 3d main band, indicating a strong Ni 3d Coulomb correlation in CeNiSn. The high-resolution photoemission study indicates a finite metallic density of states at E{sub F}, implying a semimetallic ground state. The electronic states near E{sub F} are found to have mixed character from the Sn sp, Ce 5d, Ce 4f, and Ni 3d electrons. Constant-initial-state and constant-final-state yield spectra across the 4d{r_arrow}4f threshold indicate the Ce valence to be close to 3+. {copyright} {ital 1998} {ital The American Physical Society}

The electronic structures of $R$ $4f$ and Fe $3d$ states of $R$Fe${}_{2}$O${}_{4}$ ($R=\text{Er}$, Tm, Lu) have been investigated by employing soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism at the Fe $2p$ and $R$ $3d$ absorption edges. It is found that the valence states of Fe and $R$ ions are nearly Fe${}^{2.5+}$ and ${R}^{3+}$, and that the net magnetic moments of Fe${}^{2+}$ and Fe${}^{3+}$ ions are antiparallel to each other. Both $R$ $3d$ and O $1s$ XAS spectra show that the localized $R$ $4f$ states do not contribute to the multiferroicity of $R$Fe${}_{2}$O${}_{4}$. On the other hand, the magnetization data for $R$Fe${}_{2}$O${}_{4}$ at low temperature ($T$) reveal the cluster glass behavior for $R=\text{Tm}$ and Lu, but not for $R=\text{Er}$. This work suggests that the $T$-dependent structural differences among $R$Fe${}_{2}$O${}_{4}$, caused by different $R$ ions, are closely related to the magnetoelectricity at low temperature.

We have investigated the band structure and the band symmetry of mixed-valence insulator SmB$_{6}$ systematically within the density functional theory (DFT). We have analyzed the symmetries and characters of Sm $4f$ and $5d$ bands near the Fermi level ($E_F$) in terms of the non-relativistic real cubic bases as well as the relativistic complex bases incorporating the spin-orbit coupling and the cubic crystal field. Further, we have found that the semi-core band located at $\sim 15$ eV below $E_F$ has the mixed parity and thereby affects the parity eigenvalues of the special ${\bf k}$-points considerably. We have discussed the possible surface states and topological class of SmB$_{6}$, based on the bulk parity tables., Comment: 6 pages, 8 figures, 1 table

Recent renewed interest in the mixed valent insulator SmB6 comes from topological theory predictions and surface transport measurements of possible in-gap surface states whose existence is most directly probed by angle-resolved photoemission spectroscopy (ARPES). Early photoemission leading up to a recent flurry of ARPES studies of in-gap states is reviewed. Conflicting interpretations about the nature of the Sm 4f-5d hybridization gap and observed X-point bands between the f-states and the Fermi level are critically assessed using the important tools of photon polarization and spatial dependence which also provide additional insight into the origin of the more ambiguous {\Gamma}-point in-gap states., Comment: 10 pages, 6 figures, SCES2013 proceedings; references updated

Auger electron spectroscopy, x‐ray photoelectron spectroscopy, and x‐ray diffraction (XRD) were employed to investigate the stoichiometry and texture of the indium‐oxide films. The films were prepared by the reactive evaporation and reactive ion plating of pure indium in an oxygen atmosphere of ∼10−4 Torr. Standard In and In2O3 grains were used to estimate the atomic concentration of the indium‐oxide films and to identify the film orientation. We correlated the electrical and optical properties of the films with their atomic concentration and texture. It was found that the films exhibiting low resistivity have atomic ratios of O to In of 1.29–1.31 and full widths at half‐maximum for (222) XRD peaks of 0.32°–0.34°.

Electronic structure of epitaxial Co films on Pd(111) has been investigated as a function of the Co overlayer thickness, by using angle-resolved photoemission spectroscopy (ARPES). It is found that experimental band structures for Pd(111) and work functions for Co/Pd(111) agree reasonably well with the results of band structure calculations. Compared to Pd(111), valence band ARPES spectra of Co/Pd(111) support the existence of the induced magnetic polarization of Pd atoms near the interface, suggesting large hybridization between Co 3d and Pd 4d states near the interface.

Electronic structures of the valence band and Sb 4d core levels of the XMnSb-type Heusler alloys (where X=Pt,Pd,Ni) have been investigated systematically using photoemission spectroscopy (PES) and self-consistent spin-polarized band structure calculations. The extracted Mn 3d PSW of XMnSb (where X=Pt, Pd) are found to be almost identical. Interestingly, they are quite different from those of Mn metal, but are analogous to those of MnO, suggesting that the role of the Sb 5p electrons in XMnSb may be similar to that of the O 2p electrons in MnO. A comparison of the PSW with the corresponding theoretical angular momentum projected density of states (PLDOS) shows a fairly good agreement for the Pt and Pd d states, but large discrepancies for the Mn and Ni 3d states. The calculated X d and Mn 3d PLDOS reveal that the hybridization between the Mn 3d and X d states increases from X=Pt to Pd and Ni. In the Sb 4d core level PES spectra, a broader and less structureless line shape is observed for X=Pd than for X=Pt and Ni. A detailed analysis of their line shapes indicates that it is due to a larger lifetime broadening for X=Pd than for X=Pt and Ni.

Electronic structures of amorphous Fe x Zr 100− x alloys ( x = 90,91) have been investigated by using X-ray photoelectron spectroscopy (XPS) at room temperature. It is found that large energy scale features of the Fe 2p and 3s core level XPS spectra of these alloys are essentially identical to those of Fe metal, suggesting that local electronic structures around Fe atoms in these alloys are similar to those in Fe metal. It is expected that the basic mechanism for the magnetism in a-Fe x Zr 100− x alloys ( x ≈ 90) is same as that in Fe metal. On the other hand, core level shifts and much broader linewidths are observed in the Zr 3d core level XPS spectra of these alloys, as compared to Zr metal. The line shape analysis of the Zr 3d core level XPS spectra reveals that each spin—orbit-split component in a-Fe x Zr 100− x alloys ( x = 90,91) consists of two peaks, causing a broader total linewidth than in Zr metal. Possible origins for such composite structures might be two final states screened by different numbers of localized Zr 4d electrons and the existence of Zr atoms with different local environments.

The electronic structure of spinel FeV${}_{2}$O${}_{4}$, which contains two Jahn-Teller active Fe and V ions, has been investigated by employing soft x-ray absorption spectroscopy (XAS), soft x-ray magnetic circular dichroism (XMCD), and nuclear magnetic resonance (NMR). XAS indicates that V ions are trivalent and Fe ions are nearly divalent. The signs of V and Fe $2p$ XMCD spectra are opposite to each other. It is found that the effect of the V $3d$ spin-orbit interaction on the V $2p$ XMCD spectrum is negligible, indicating that the orbital ordering of V ${t}_{2g}$ states occurs from the real orbital states and that the orbital moment of a V${}^{3+}$ ion is mostly quenched. NMR shows that V spins are canted to have a Yafet-Kittel-type triangular spin configuration.

Electronic structures of a charge-density wave (CDW) system CeTe${}_{2\ensuremath{-}x}$Sb${}_{x}$ ($x=0$, 0.05) have been investigated by employing angle-resolved photoemission spectroscopy (ARPES) and the first-principles electronic and phonon band-structure methods. The observed Fermi surface (FS) agrees very well with the calculated FS for the undistorted CeTe${}_{2}$ both in shapes and sizes. The metallic states crossing the Fermi level (${E}_{F}$) are observed in ARPES even in the CDW state. The carriers near ${E}_{F}$ have mainly the Te(1) $5p$ character, with a negligible contribution from Ce $4f$ states. The supercell (shadow) bands and the corresponding very weak FSs are found to arise from band folding due to the interaction of Te(1) layers with Ce-Te(2) layers. We found that the CDW modulation vector is along $\ensuremath{\Gamma}$-$X$ (${\mathbf{Q}}_{\text{CDW}}\ensuremath{\approx}X$), which is not coincident with the most prominent FS nesting vector.

Co/Pd multilayered films with ultrathin layers of Co were prepared by alternating deposition in an ultrahigh‐vacuum physical‐vapor‐deposition system. The individual layer thicknesses of the samples were estimated making use of the angular positions of x‐ray diffraction peaks. The magnetic and magneto‐optical properties were found to vary depending on Pd buffer layer and Pd sublayer thicknesses, as well as Co sublayer thickness. Some of the films showed good properties for magneto‐optical medium, such as large perpendicular magnetic anisotropy and Kerr rotation, and perfect squareness of the magnetic hysteresis loop. The Pd‐predeposited films were found to have a remarkably high coercivity of 4723 Oe and a greatly enhanced interfacial magnetic anisotropy of 0.72 mJ/m2. The transition from in‐plane to perpendicular magnetic anisotropy took place at a Co sublayer thickness of 8.2 A for the multilayer with Pd predeposition. Kerr rotation was inversely proportional to the Pd/Co sublayer thickness ratio, showing the maximum value of 0.12°. The magnetic and magneto‐optical properties were correlated systematically to the structural parameters of the multilayered films.