D. Maurer

Evidence for ferroelectric phase transitions and excitonic high-Tc superconductivity in YBa2Cu3O7−δ from ultrasonic measurements

Abstract We report on pronounced anomalies of the absorption and dispersion of the sound-induced rf magnetic field in superconducting YBa 2 Cu 3 O 7−δ ( δ K T K and for a near coincidence of the superconducting transition and a ferroelectric phase transition at about 90 K.

Coexistence of high-Tc superconductivity and ferro- or antiferroelectricity in YBa2Cu3O7-δ

Abstract We report on pronounced anomalies of the absorption and dispersion of the sound-induced rf magnetic field in YBa2Cu3O7-δ. The experimental findings are highly indicative of a near-coincidence of the superconducting transition and an antiferrodistortive transition into either an antiferroelectric or improper ferroelectric state. To our knowledge the experimental technique presented here, so far is the only method which offers the possibility to show experimentally that both superconductivity and ferro-/antiferroelectricity may coexist. Furthermore, it is demonstrated that in YBa2Cu3O7-δ microtwinning plays an important role for the dielectric phase transition to become manifest. The possible relationship between our findings and high-Tc superconductivity is also discussed.

Sound Velocity and Ultrasonic Absorption in High-Tc-Superconductors

We report on strong hysteresis effects in the temperature dependence of the longitudinal ultrasonic attenuation and group-velocity in YBa2Cu3O7.

Evidence for coexistence of ferroelectricity and high-Tc superconductivity in YBa2Cu3O7-δ (δ < 0.15) from ultrasonic experiments

In order to determine the dielectric properties of the bound charges (soft dipoles) in superconducting YBa 2 Cu 3 O 7-δ (δ

Ultrasonic investigations of the kinetics of ordering in SbCl5-intercalated graphite

Abstract The unusual ultrasonic relaxation behaviour observed in the temperature range from 170 to 230 K is shown to depend strongly on the nucleation rate and not on the domain growth of the √39 × √39-phase only.

Influence of electron band structure on dipole-nuclear acoustic resonance

Abstract For an arbitrary Fermi surface a quantum theoretical treatment of dipole-nuclear acoustic resonance in cubic metals is presented for the first time. In contrast to current theories the validity of our results is not restricted to certain temperature regions.

Ultrasonic investigations of C60C70-compounds

Abstract We report on ultrasonic investigations of the frequency dependent and temperature dependent sound velocity in C60/C70 compounds. Although the wellknown phase transitions at about 260K and 155K are clearly seen in our experiments, concerning the absolute values of the sound velocity our results differ markedly from those found by means of low frequency vibrating reed techniques on C60 single crystals. Reasons for this unexpected behaviour are discussed briefly.

ULTRASONIC EXPERIMENTS ON THE HIGH-Tc-SUPERCONDUCTOR Y2-xBaxCuO4-δ

Abstract Sound velocity measurements on a mixed-phase sample Y 1.2 Ba 0.8 CuO 4−δ in high magnetic fields are reported. Like in normal metals, but in contrast to single-phase samples, the material is found to harden on cooling. In the vicinity of 95 K an elastic instability is observed which is referred to a semimetal-metal transition. For B 0 = 6T an anomalously large softening of ∼460 ppm is found at T c ( B 0 ). The importance of internal strains for the elastic behaviour and for the appearance of pronounced hysteresis effects in single-phase samples is discussed.

Influence of longitudinal and transverse magnetoresistivity on nuclear acoustic resonance in aluminium

By quantitative evaluation of the dipole NAR absorption lines in aluminum, it is shown for the first time that at low temperatures the NAR signal intensity is strongly affected by the dynamic longitudinal and transverse magnetoresistivity.

Elastic consequences of the dielectric behavior of Yba2Cu3O7-δ

Abstract Owing to the fact that superconductivity can be described as a dielectric phenomenon, where the screening of the repulsive electron-electron interaction is accounted for by introducing a temperature-dependent dielectric function ϵ(ω, k), in this paper emphasis is put on a brief discussion of values of ϵ consistent with high superconducting transition temperatures in principle as well as on experimental techniques which allow determination of the temperature-dependence of the dielectric function ϵ(ω, k).