Point-contact measurements of CeB6 and CeCu6 in high magnetic fields

Epitaxial YBa₂Cu₄O₇-thin films with thec-axis oriented perpendicular to the film plane were prepared bydc-sputtering from a single stoichiometric target on (100) SrTiO₃-substrates. Typical values of the inductively measured superconducting transitions were about 90 K with a width less than 0.5 K. Critical current densities were measured on 5 to 10 m wide strips as function of magnetic field and temperature. The temperature dependences ofj _c follow a universal functionj _c(B,T)=j _c ^* (T=0,B)·(1–T/T _c (B)) with =1.5±0.1. ForB=0 andT=77 K we obtainedj _c =4·10⁶ A/cm². The field dependence of the resistive transitions was measured with the magnetic field parallel to thec-axis. The slope of the upper critical fieldB _c2 (T) was determined for different criteria. The carrier concentration evaluated from Hall-effect measurements was found to decrease linearly from one per unit cell at 240 K with decreasing temperature extrapolating nearly through zero forT=0. Highly resolved angular dependent measurements of the critical current density withB perpendicular to the current but tilted from thec-axis show a very strong and sharp enhancement ofj _c for the magnetic field parallel to the (CuO₂)-layers (Bc). Additionally to this phenomenon, which is caused by an intrinsic pinning mechanism due to the layered structure of high-T _c -superconductors the influence of the anisotropy of the upper critical field onj _c (B, T, ) is evident nearT _c .     

Transverse electron focusing as a way of studying surface crystallography

Conduction electrons represent a unique probe for studying surfaces (and interfaces) due to their extremely low excitation energies and to the fact that they impinge upon the surface from inside the sample. Focusing of conduction electrons by means of a transverse homogeneous magnetic field—transverse electron focusing (TEF)—provides a means for probing the atomic structure and composition of surfaces and interfaces, including both regular and irregular roughness. This article explains what TEF is, reviews what has been learned from it about surface structure, and describes what can be learned in the future.     

Magnetic domains in non-ferromagnetic metals: The non-linear de Haas-van Alphen effect

This review is devoted to an exposition of the principles of the physics of magnetic domains in non-ferromagnetic metals and diamagnetic phase transitions, which lead to the formation of the so-called Condon domains during magnetic oscillations in a three-dimensional electron gas. One of the goals of the review is to provide a deeper insight into the nature of this instability of the electron gas in normal metals and improve the understanding of this type of non-spin magnetism. We discuss theoretical aspects of the physics underlying magnetic ordering of conduction electrons in bulk metals and in thin films, and describe the behaviour of the susceptibility, thermal expansion, specific heat, compressibility, sound velocity, magnetic induction bifurcation, the order parameter, domain formation, wetting of domain walls, nucleation and kinetics of diamagnetic phase transitions. In the vicinity of diamagnetic phase transitions the results obtained coincide with those following from the Landau theory of phase transitions. The existence of the critical sample size for the diamagnetic phase transition in thin films is considered. We place special emphasis on the problem of the order of diamagnetic phase transitions. The survey is partly motivated as complementary to the recent review by G. Solt and V. Egorov describing the experimental situation in the field. Contents PAGE 1. Introduction 386 2. Diamagnetic phase transitions and Condon domains 390 2.1. Shoenberg's and Condon's consideration of the phenomena 390 2.2. Phase diagrams for one de Haas-van Alphen cycle 395 3. Critical phenomena at second-order diamagnetic phase transitions in three-dimensional metals 397 3.1. Introduction 397 3.2. Order parameter and susceptibility 397 3.3. Specific heat jump 403 3.4. Phase diagrams 407 3.5. Finite-size effects 410 3.6. Compressibility, thermal expansion and sound velocity 414 4. Condon domains and resonance methods of their investigation 417 4.1. Introduction 417 4.2. Nuclear magnetic resonance and Condon domains 418 4.3. Muon spin resonance spectroscopy and Condon domains 420 4.4. Critical exponents at diamagnetic phase transitions in silver and beryllium 426 4.5. Helicon resonance and Condon domains 428 4.6. Critical dynamics of the diamagnetic phase transition in aluminium 430 5. First-order diamagnetic phase transitions 431 5.1. Introduction 431 5.2. Domain formation 433 5.3. Kinetics 436 5.4. Wetting 441 5.5. Nucleation 442 5.6. Order of diamagnetic phase transitions 444 5.7. Hysteresis and Condon domains 445 6. Summary 446 7. Some open issues 448 Acknowledgements 450 References 451     

Anisotropy of the magnetoelectric effect in terbium molybdate

Anisotropy of the nonlinear magnetoelectric effect in a single-crystal, single-domain sample of the β′ metastable ferroelectric paramagnetic phase of terbium molybdate Tb₂(MoO₄)₃ was studied experimentally in dc magnetic fields of up to 6 T at temperatures of 4.2 and 1.8 K. It was shown that the existing models of the magnetoelectric effect cannot explain the experimental dependences of magnetic field-induced electric polarization on the direction of the applied magnetic field. A model of the magnetoelectric effect is proposed that qualitatively describes the observed angular dependence of the magnetic field-induced electric polarization.     

Far-infrared absorption of superconducting films with spatially varying order parameter

We have measured the far-infrared absorption of superconducting films in situations, where the order parameter varies spatially. The variation is induced by a perpendicular magnetic field or with a proximity effect contact. The measurements are analysed on the basis of a local model, combining a spatial variation of the order parameter with the Abrikosov-Gorkov solutions of a homogeneous superconductor under pair-breaking conditions.