Ultra-high Energy Resolution Research Articles

Ultrahigh-resolution and angle-resolved photoemission study of SmB 6

The photoemission spectra with the ultrahigh-energy resolution reveal the small gap formation at lower temperatures than the characteristic coherent temperature T coh. In addition, the temperature dependence of the density of states at Fermi level clearly shows a simple scaling relationship with T coh. The narrow 4f-band with a very small dispersion just below E F are observed by angle-resolved spectra at the first time.

Low-Temperature High-Resolution Resonant Photoemission Study of Kondo Insulator Ce3Bi4Pt3

High-resolution Ce 4d-4f resonant photoemission spectroscopy has been performed on the Kondo insulator Ce3Bi4Pt3 at 12 K. By subtracting the off-resonance spectrum (hν=114 eV) from the on-resonance spectrum (hν=122 eV), a measure of Ce 4f partial density of state is obtained. Temperature-dependent Ce 4f spectra very close to EF are measured with ultrahigh-energy resolution (ΔE∼6 meV) and a clear depression of intensity is observed at 6 K, indicating a (pseudo)gap opening at low tempera tures.

Determination of profile parameters of a Fano resonance without an ultrahigh-energy resolution

A deconvolution procedure is proposed to determine the resonant width $\ensuremath{\Gamma}$, the asymmetry parameter $q$, and the background cross section ${\ensuremath{\sigma}}_{b}$ of a Fano-type resonance in the absence of an ultrahigh-energy resolution. This procedure enables a direct extrapolation to infinite energy resolution using a set of explicit analytical relations in terms of the ratio between the width $\ensuremath{\Gamma}$ and the experimental energy resolution $\ensuremath{\Omega}$ in the limit of $\ensuremath{\Gamma}/\ensuremath{\Omega}\ensuremath{\ll}1$.

Electronic Structure of Icosahedral Alloys Studied by Ultrahigh Energy Resolution Photoemission Spectroscopy.

The results of a systematic ultrahigh resolution ultraviolet photoemission study of the electronic structure of stable icosahedral alloys ${\mathrm{Al}}_{64}$${\mathrm{Cu}}_{24}$${\mathrm{Fe}}_{12}$, ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Fe}}_{15}$, ${\mathrm{Al}}_{70}$${\mathrm{Pd}}_{20}$${\mathrm{Mn}}_{10}$, and ${\mathrm{Al}}_{70.5}$${\mathrm{Pd}}_{21}$${\mathrm{Re}}_{8.5}$ are presented. It is shown that all icosahedral alloys have a clearly developed Fermi edge and are thus metallic down to the temperature of measurement (14-45 K). A marked decrease of the spectral intensity towards the Fermi level in these alloys is demonstrated to be consistent with the existence of the theoretically predicted pseudogap. With an experimental resolution of 6 meV, no evidence of the theoretically predicted spikiness of the density of states could be observed.

A Note on the Dynamical Critical Phenomena at the Structural Phase Transition inKDCO3

The dynamical behavior of the order parameter at structural phase transition in KDCO 3 is investigated theoretically. In particular, recent experimental results on ultra high energy resolution neutron spectroscopy using TASSE (triple axis spin echo spectroscopy) technique are analyzed and compared with the results of the ultrasonic measurements. It is verified that analysis based on generalized-Langvein equation of motion of pseudospin-phonon coupled system can give overall agreements with the results of both neutron scattering and ultrasonic measurements.

Electron-ion recombination using the modified cryring electron cooler

Recent electron-ion recombination experiments at the heavy-ion syncrotron storage ring CRYRING are described. These experiments include state selective radiative recombination into mid- n levels of deuterons and dielectronic recombination of Ar 13+. Modifications to the CRYRING electron cooler have reduced the transverse electron temperature to a few tenths of an meV/ k B. The ultrahigh energy resolution achieved is demonstrated in the recent experiments. The widths of the Ar 13+ Δn = 0 dielectronic recombination resonances are resolved to 30 meV FWHM. Detailed calculation of the electron-ion interaction energies has allowed a determination of the peak positions to ± 30 meV.

Observation of an "extended" Van Hove singularity in YBa2Cu4O8 by ultrahigh energy resolution angle-resolved photoemission.

We characterize the nature of the Van Hove singularity near the Fermi energy ([ital E][sub [ital F]]) in YBa[sub 2]Cu[sub 4]O[sub 8] using ultrahigh energy resolution (10 meV) angle-resolved photoemission spectroscopy, together with corresponding first-principles spectra intensity computations. The singularity, related to CuO[sub 2] planes, is located about 19 meV below [ital E][sub [ital F]] at the [ital Y] point in the Brillouin zone and arises from a band which is nearly dispersionless along the [Gamma] to [ital Y] direction. Such an extended'' saddle point would render the band structure quasi-1D and yield a power law divergence in the density of states, allowing the occurrence of [ital T][sub [ital c]]'s of order 100 K even in a weak coupling BCS scheme.

Structure determination of the NiSi 2(111) surface with medium-energy ion backscattering from individual monolayers

The surface structure of the epitaxial NiSi 2/Si(111) system has been determined applying new ion scattering methods. By detection of backscattered ions with ultrahigh energy resolution the signals from successive atomic layers are separated. Angular distributions of the yield of ions mainly backscattered from a single Ni monolayer directly provide the (sub)surface atom coordinates. In addition, analysis of the energy losses in the first atomic layer, which depend on the specific ion trajectories, allows an independent structure determination. Using either of the two methods, the NiSi 2(111) surface is found to have a bulklike topology, i.e. it is terminated by a SiNiSi triple layer. Other surface structure models, such as termination by a Si double layer, are ruled out. The outermost NiNi and NiSi interlayer spacings are found to be contracted with respect to their bulk values in the strained silicide by 0.05 ± 0.02 and 0.12 ± 0.02 Å, respectively.

Ultra-High Resolution Inelastic Neutron Scattering.

Two types of ultra high energy resolution neutron scattering instruments, the backscattering spectrometer and the spin echo spectrometer, are described. Examples of the types of research which can be done with these instruments are given and plans for a cold neutron backscattering spectrometer which will be built in the NIST Cold Neutron Research Facility (CNRF) are discussed. It is hoped that this information will be of use to researchers considering neutron scattering experiments at NIST.

Developments in superconducting tunnel junction detectors

Superconducting tunnel junctions (STJs) have a large possibility of being utilized as radiation detectors of ultrahigh energy resolution. In fact, Sn/SnO x /Sn junctions as X-ray detectors have aready shown about three times higher energy resolution than Si detectors. Recently, in addition to Sn junctions, studies of new-type STJ detectors are in progress. Research into STJ detectors, including our recent studies on Nb/AlAlO x /Nb junctions witha single crystal Nb film and on series-connected STJ detectors, are briefly reviewed.

CoSi2/Si(111) interface: Determination of the interfacial metal coordination number.

The morphology and the surface and interface structure of flat ${\mathrm{CoSi}}_{2}$ films (thickness \ensuremath{\sim}2 Si-Co-Si triple layers) epitaxially grown on Si(111) have been investigated using medium-energy ion scattering with ultrahigh energy resolution. The data show that the silicide is attached to the substrate through Co-Si bonds rather than through Si-Si bonds. At the interface, the silicide is terminated by a full Si-Co-Si triple layer. The interface metal atoms are thus eightfold coordinated. The silicide-substrate distance is expanded by 0.16\ifmmode\pm\else\textpm\fi{}0.08 \AA{}. The first Si substrate layer is relaxed outward by 0.08\ifmmode\pm\else\textpm\fi{}0.08 \AA{}. The length of the Co-Si interface bond is thus dilated by 0.08 \AA{}. At the silicide surface, the first Co-Si interplanar distance is found to be relaxed inward by 0.14\ifmmode\pm\else\textpm\fi{}0.04 \AA{}. Our measurements suggest that the silicide lattice strain is almost fully relaxed. We propose that such relaxation occurs through a high density of microcracks in the film. The average spacing between cracks is then smaller than roughly 50 \AA{}.

Monolayer resolution in medium-energy ion-scattering experiments on the NiSi2(111) surface.

The surface structure of the epitaxial ${\mathrm{NiSi}}_{2}$/Si(111) system has been determined applying a new ion-scattering method. Detecting backscattered ions with ultrahigh energy resolution we resolve the signals from successive atomic layers. From both their intensity and energy, which depends on the specific ion trajectories, we directly deduce the (sub)surface atom coordinates. Applying this new approach, we find that the ${\mathrm{NiSi}}_{2}$(111) surface has a bulklike topology, i.e., it is terminated by a Si-Ni-Si triple layer. The outermost Ni-Si and Ni-Ni interlayer distances are relaxed from their bulk values.