Y.-L. Mathis

Terapascal static pressure generation with ultrahigh yield strength nanodiamond

Terapascal static pressure generation is enabled in laboratory due to implementation of nanocrystralline diamond microballs. Studies of materials’ properties at high and ultrahigh pressures lead to discoveries of unique physical and chemical phenomena and a deeper understanding of matter. In high-pressure research, an achievable static pressure limit is imposed by the strength of available strong materials and design of high-pressure devices. Using a high-pressure and high-temperature technique, we synthesized optically transparent microballs of bulk nanocrystalline diamond, which were found to have an exceptional yield strength (~460 GPa at a confining pressure of ~70 GPa) due to the unique microstructure of bulk nanocrystalline diamond. We used the nanodiamond balls in a double-stage diamond anvil cell high-pressure device that allowed us to generate static pressures beyond 1 TPa, as demonstrated by synchrotron x-ray diffraction. Outstanding mechanical properties (strain-dependent elasticity, very high hardness, and unprecedented yield strength) make the nanodiamond balls a unique device for ultrahigh static pressure generation. Structurally isotropic, homogeneous, and made of a low-Z material, they are promising in the field of x-ray optical applications.

Terahertz Radiation at ANKA, the New Synchrotron Light Source in Karlsruhe

ANKA is a new synchrotron light source atthe Karlsruhe Research Center in southwestGermany. The acronym stands for Ångstrøm Source Karlsruhe.The ANKA-IR beamline provides a highbrilliance infrared beam through the near,mid and far-infrared range. Thefar-infrared range is of particularinterest, since at frequencies lower thanaround 200 cm-1 (6 THz) synchrotronlight begins to outperform conventionalthermal sources in terms of total intensityas well as brilliance. The extraction ofthe entire flux is a challenge in the THzrange, since the natural verticaldivergence of synchrotron radiationincreases with wavelength and the openingangle for collection is limited by designconstraints. At ANKA-IR, this problem issolved by the collection of radiationemitted from a bending magnet edge source,which has a much smaller verticaldivergence than conventional synchrotronradiation emitted from the constantmagnetic field region within the dipolemagnet. Edge radiation at ANKA permits theextraction of the entire infrared flux downto around 100 cm-1 (3 THz) while withconventional synchrotron radiation thiswould only be the case for frequencies downto 2500 cm-1. ANKA-IR provides usableintensity down to 4 cm-1 (120 GHz).

Nonthermal response of YBa2Cu3O7−δthin films to picosecond THz pulses

The photoresponse of YBaCuO thin film microbridges with thicknesses between 15 and 50 nm was studied in the optical and terahertz frequency range. The voltage transients in response to short radiation pulses were recorded in real time with a resolution of a few tens of picoseconds. The bridges were excited by either femtosecond pulses at a wavelength of 0.8 μm or broadband (0.1–1.5 THz) picosecond pulses of coherent synchrotron radiation. The transients in response to optical radiation are qualitatively well explained in the framework of the two-temperature model with a fast component in the picosecond range and a bolometric nanosecond component whose decay time depends on the film thickness. The transients in the THz regime showed no bolometric component and had amplitudes up to three orders of magnitude larger than the two-temperature model predicts. Additionally THz field-dependent transients in the absence of DC bias were observed. We attribute the response in the THz regime to a rearrangement of vortices caused by high-frequency currents.

Infrared Spectro/Microscopy at SSLS — Edge Effect Source in a Compact Superconducting Storage Ring

Singapore Synchrotron Light Source (SSLS) is commissioning its new beamline for Infrared Spectro/Microscopy (ISMI). The infrared light is extracted from the edge region of dipole D1 of the compact superconducting electron storage ring Helios 2. The nominal source point is located at half the maximum field, i.e., at 2.25 T. The end station comprises both, a medium and a high resolution Fourier transform infrared spectrometer (FTIR), the former featuring an infrared microscope as well as a UHV chamber for catalysis experiments. Synchrotron Radiation Workshop (SRW) calculations and a preliminary experimental evaluation of ISMI show the capability of this beamline to deliver a bright flux of photons in the Far and Mid infrared spectral regions.

FLUTE: A versatile linac-based THz source

A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short (~1 ps) THz pulses (up to ~4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range (~100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments.

Giant exciton Fano resonance in quasi-one-dimensional Ta2NiSe5

This work was partly supported by JSPS KAKENHI Grants No. 24224010, No. 15H05852, and No. 17H01140.

In situ synchrotron far-infrared spectromicroscopy of a copper electrode at grazing incidence angle.

Synchrotron far-infrared spectroscopy in situ was successfully carried out on a copper microelectrode using a grazing-angle objective attached to a Bruker IRscope II microscope. The thin-layer spectroelectrochemical cell was constructed out of Teflon and fitted with a 20 microm-thick Mylar window; the copper electrode was 500 microm in diameter. Measurements were carried out in 0.1 M NaOH solution as a function of applied potential between -1.4 and 0 V versus a Hg/Hg2SO(4) reference electrode. Results demonstrate that with the present technique it is possible to obtain in situ spectra with excellent signal-to-noise ratio for surface oxide films formed electrochemically with less than 1 nL of active solution volume. The surface film on copper at 0 V consisted mainly of CuO with possibly some Cu(OH)2 also present. This interpretation is consistent with previous works and thermodynamic calculations.

Optical anisotropy of the Jeff=1/2 Mott insulator Sr2IrO4

We report the complex dielectric function along and perpendicular to the IrO2 planes in the layered perovskite Sr2IrO4 determined by spectroscopic ellipsometry in the spectral range from 12 meV to 6 eV. Thin high quality single crystals were stacked to measure the c-axis optical conductivity. In the phonon response we identified 10 infrared-active modes polarized within the basal plane and only four modes polarized along the c-axis, in full agreement with first-principle lattice dynamics calculations. We also observed a strong optical anisotropy in the near-infrared spectra arising from direct transitions between Ir 5d t2g Jeff = 1/2 and Jeff = 3/2 bands, which transition probability is highly suppressed for light polarized along the c-axis. The spectra are analyzed and discussed in terms of relativistic LSDA+U band structure calculations.

Far Infrared Coherent Synchrotron Edge Radiation at ANKA

The region of the electromagnetic spectrum between 0.3 and 20 THz is a “frontier region” of spectroscopy in physics, chemistry, biology, material sciences, and medicine [1]. Radiation in the THz range allows the investigation and excitation of phenomena with time constants of about 1 ps. Examples on this time scale are atomic electron orbits in highly excited Rydberg states, rotations of small molecules and modes of collective oscillations of proteins and polar liquids like water. Resonances of electrons in semiconductor nanostructures and band gaps of superconductors can equally be studied with THz radiation. The THz region lies above the frequencies of traditional electronics but below the range of optical and infrared generators. Until now, possibilities to generate sufficiently intense and brilliant radiation at the wavelengths in question were scarce and the region was therefore named the “THz gap” (Figure 1). In accelerators such highly intense coherent THz radiation can be generated under special conditions when the electron bunch length is comparable to the wavelength of the emitted radiation [2,3]. Since the emission of long wavelengths is suppressed by shielding effects of the vacuum chamber, the bunch length needs to be sufficiently short in order to yield observable intensities.

Far-infrared spectroscopy of interlayer vibrations of Cu(II), Mg(II), Zn(II), and Al(III) intercalated muscovite

In this study the intercalation behavior of di- and trivalent cations like Cu(II), Mg(II), Zn(II), and Al(III) into the interlayers of muscovite was investigated by X-ray diffraction and far-infrared spectroscopy. The X-ray diffractometry shows that the original material is a muscovite 2M1. During the metal cation treatment, new peaks occur at about 1.1 and 2.2 nm, while the original peaks strongly decrease. This gives evidence for the formation of a strongly modified mica structure. The occurrence of bands at low wavenumbers (93 cm−1 and 104 cm−1) in the far-infrared spectra show that the untreated material was partly dehydroxylated. The strong decrease of the band at 93 cm−1 and the occurrence of a band at 110 cm−1 during the intercalation are strong hints about the rehydroxylation of the mineral. The strong increase of the band intensity at 88 cm−1 and the occurrence of a band at 119 cm−1 in the treated muscovites prove the formation of a new, strongly modified mica phase that has both the new cations and the potassium incorporated into the interlayer space.