G. Güntherodt

Elastic and magnetoelastic effects in CeB6

Elastic constants of CeB6 were redetermined by ultrasonic and Brillouin scattering measurements. We found all elastic constants to be positive, especiallyc12. The temperature and magnetic field dependence of the elastic modesc44 and (c11-c12)/2 is explained on the basis of the newly proposed crystalline-electric-field level scheme for CeB6 with theΓ7 level 545 K above theΓ8 ground state. The deduced quadrupolar coupling constants give an antiferroquadrupolar ordering temperature of 3.3 K in agreement with experiment.

Brillouin scattering from collective spin waves in magnetic superlattices (invited)

We report on the observation and the analysis of collective magnetostatic spin‐wave excitations in magnetic superlattices. The influence of interface anisotropies, which can become dominant for small modulation wavelengths, is discussed. For the system Fe/Pd we show that Brillouin spectroscopy experiments in combination with the measurement of the saturation magnetization by a SQUID magnetometer give evidence for a magnetic polarization of the Pd spacer layers, as well as for a small negative out‐of‐plane interface anisotropy constant of Ks =−0.15 erg/cm2.

Raman spectroscopy as a function of the oxygen content in YBa2Cu3O7-x

Abstract We report on Raman spectroscopy of YBa 2 Cu 3 O 7-x samples with different oxygen contents. Besides other phonon modes we reproducibly observe a lattice mode at 641 cm −1 , which appears for superconducting samples and disappears if the samples are rapidly quenched from 800 °C. We conclude that the 641 cm −1 peak has to be related to vibrations of the CuO chains in YBa 2 Cu 3 O 7-x .

Tunneling and point-contact spectroscopy of high-Tc superconductors M−Ba2Cu3O7 (M=Y, La, Eu)

Tunneling and point-contact measurements have been performed on different high-Tc superconductors M−Ba2Cu3O7 with M=Y, La, Eu. The average energy gaps deduced from the tunneling spectra are about 2Δ=33 meV for the Y- and La-type samples and about 2Δ=38 meV for the Eu-type samples, which give ratios 2Δ/kBTc in the range from 4 to 6. The point-contact characteristics show a distinct minimum in the differential resistance about zero bias and additional sharp spikes up to 40 mV. From these pointcontacts we can give an estimate of the critical current, yielding values in the range from 0.2 to 3 mA.

Electron tunneling into intermediate valence intermetallics

Abstract Electron tunneling into Intermediate-Valent (IV) intermetallics (YbInAu 2 , YbAl 2 , CeCu 2 Si 2 and CeRu 2 ) has been investigated by GaAs Schottky barrier point-contact tunneling. No IV-related asymmetries or indications for a strongly renormalized tunneling density of states are found. The IV superconductor CeRu 2 ( T c = 6 K ) shows a strongly enlarged gap of 2Δ = (3.3±0.3 meV).

Inelastic electronic excitations in CePd3 observed by Raman scattering and luminescence emission

Abstract In intermediate valent CePd 3 the intraionic J = 5 2 → J = 7 2 excitation of the 4f 1 ( 2 F J ) configuration and the interconfigurational 4f 1 → 4f 0 + e - excitation energy have been observed near 256 and 325 meV, respectively, by means of electronic Raman scatterring. A narrow d-like band is identified near 2.4 eV above E F by d → f luminescence emission.

Resonant electron-phonon coupling in CeAl2

Abstract The resonant coupling of the Γ + 5 phonon to the Γ 7 -Γ 8 CEF excitations in CeAl 2 is probed by Raman scattering via the simultaneous observation of the renormalized (Γ + 6 ) phonon and the phonon bound state. This represents the “phononic analogue” to the instantaneous observation of electronic charge fluctuations by XPS in intermediate valence compounds.

Raman scattering from spin fluctuations and phonons in the heavy-fermion superconductor UPt3

Abstract Quasielastic scattering from spin fluctuations has been observed in UPt3 by Raman spectroscopy. The experiments for wave vectors q≈0 show a nearly temperature independent linewidth for 5 K ⩽ T ⩽ 300 K Complementary to neutron scattering results this establishes the q independence of the spin relaxation rate, indicating the localized nature of the spin fluctuations. A Raman-active phonon near 79 cm-1 (10 meV) shows a drastic increase in line-width with decreasing temperature, demonstrating strong electron-phonon coupling.

Light scattering in metallic compounds and thin supported layers

Recent progress of light scattering in metals is reviewed by selected highlights: Raman scattering in CeB6 has established a new crystalline electric field (CEF) level scheme with aΓ8 ground state. The resonant CEF-phonon coupling has been identified in CeAl2. The ionic model description of intermediate valence of rare earth (RE) ions in metals could directly be proved by Raman spectroscopy in EuPd2Si2. Brillouin scattering from elastic surface wave excitations of bulk metals or supported thin layers can now be used for the reliable determination of their elastic constants. For very thin metallic layers light scattering has been very successful in observing the dispersion of standing spin waves and their elastic analogue, the Sezawa waves. From the standing spin waves the exchange constant can be determined most directly. The investigation of Au clusters deposited on NaCl has revealed a new localized acoustic surface mode (“cluster mode”). Its frequency crosses with increasing Au deposition the frequency of the transverse acoustic phonon mode of the substrate at the percolation threshold.

Collective spin waves in Fe/Pd and Fe/W multilayers

In Fe/Pd and Fe/W multilayers the complete, theoretically predicted band of collective magnetostatic spin‐wave excitations has been observed. Despite the large number of bilayers (49–90) discrete spin‐wave modes have been found in the upper half of the band. For Fe/Pd multilayers the saturation magnetization shows a monotonic reduction of up to 30% with decreasing modulation wavelength (down to 33 A), which is not found in the Fe/W multilayer.