This review presents a summary and evaluation of the experimental properties of unconventional superconductivity in ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ as they were known in the spring of 2002. At the same time, the paper is intended to be useful as an introduction to the physics of spin-triplet superconductivity. First, the authors show how the normal-state properties of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ are quantitatively described in terms of a quasi-two-dimensional Fermi liquid. Then they summarize its phenomenological superconducting parameters in the framework of the Ginzburg-Landau model, and discuss the existing evidence for spin-triplet pairing. After a brief introduction to the vector order parameter, they examine the most likely symmetry of the triplet state. The structure of the superconducting energy gap is discussed, as is the effect of symmetry-breaking magnetic fields on the phase diagram. The article concludes with a discussion of some outstanding issues and desirable future work. Appendixes on additional details of the normal state, difficulty in observing the bulk Fermi surface by angle-resolved photoemission, and the enhancement of superconducting transition temperature in a two-phase ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}\ensuremath{-}\mathrm{Ru}$ system are included.

The superconductivity of Sr 2 RuO 4 and the physics of spin-triplet pairing

The contribution that the technique of ferromagnetic resonance (FMR) has made to the understanding of the magnetic behaviour of ultrathin single films is reviewed. Experimental methods to measure FMR in situ in ultrahigh vacuum are presented. The temperature dependence of the magnetization, of the magnetic relaxation rate in the vicinity of the Curie temperature, and of the second- and fourth-order magnetic anisotropy energy (MAE) constants can be measured by FMR in situ for magnetic monolayers. Using the cases of Ni/Cu(001) and Gd/W(110) as examples, the role of the MAE for the quantitative description of temperature- and thickness-dependent reorientation transitions of the magnetization is discussed. Initial results for the anisotropy of the g-factor which is related to the anisotropy of the orbital moment (and the MAE) are presented.

https://iopscience.iop.org/article/10.1088/0034-4885/61/7/001/pdf

Ferromagnetic resonance of ultrathin metallic layers

Dans V3Si les atomes de vanadium sont disposes suivant des chaines lineaires denses et on peut appliquer aux electrons d l'approximation des liaisons fortes a une dimension. On constate que l'energie electronique ainsi calculee s'abaisse par deformation de la maille. Ceci peut constituer une explication, par un effet Jahn-Teller de bandes, du changement de phase cubique → tetragonale observe a basse temperature.

https://hal.archives-ouvertes.fr/jpa-00206382/document

Instabilité électronique et changement de phase cristalline des composés du type V3Si à basse température

A consistent explanation of the unusual combination of anisotropies of the Knight shifts and relaxation rates of Cu(1) and Cu(2) nuclei in YBa2Cu3O7 is given. The key features are an anisotropic on-site hyperfine coupling to local Cu2+ electronic spins and an isotropic transferred hyperfine coupling to the neighboring Cu2+-spins. We use a quantum chemical model of the Cu-O hybridization to estimate the strength of these hyperfine interactions. Good agreement is found between our estimated parameters and experiment.

Analysis of magnetic resonance experiments in YBa2Cu3O7

Recent studies of charge-transfer salts of the ion bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) are reviewed, focusing in particular on experimental techniques which involve high magnetic fields and on data obtained since 1996. Novel experimental techniques developed in the past few years, including angle-dependent magnetoresistance oscillations, periodic orbit resonances and Fermi-surface traversal resonances are described in detail; briefer descriptions of more traditional techniques such as the Shubnikov-de Haas effect are also included. The applications of these techniques to the ?, ?, ? and ?'' BEDT-TTF salts is described. Theoretical developments related to the experimental data are also mentioned.

https://iopscience.iop.org/article/10.1088/0034-4885/63/8/201/pdf

Studies of quasi-two-dimensional organic conductors based on BEDT-TTF using high magnetic fields

Measurements of the magnitude, sign, and temperature dependence of the Knight shift and susceptibility in platinum are used to determine the contributions to each arising from the spin paramagnetism of the $s$ and $d$ bands, the orbital paramagnetism and the core diamagnetism. A complete expression for the orbital contribution to the Knight shift in a transition metal is derived, including spin-orbit coupling. We show that in the tight-binding limit, as in the free ion, a simple relation exists between the orbital susceptibility and the orbital hyperfine field. The relation of the enhancement of the $d$-spin susceptibility over its specific heat value to the possible occurrence of superconductivity is discussed.

Interpretation of Knight Shifts and Susceptibilities of Transition Metals: Platinum

Nuclear Spin Relaxation in Transition Metals; Core Polarization

The cross sections for Raman scattering by electrons and holes in a semiconductor subjected to a magnetic field are calculated. A number of processes in which the Landau level number changes by $\ensuremath{\Delta}n=2$, as well as a spin-flip process with $\ensuremath{\Delta}n=0$, are considered. Except for the $\ensuremath{\Delta}n=2$ process in the conduction band, the matrix elements are independent of the strength of the magnetic field. Scattering cross sections are estimated for InSb (incident photon energy 0.12 eV) and InP (incident photon energy 1.17 eV). The magnitude of these cross sections suggests that it may be possible to use Raman scattering to measure effective masses.

Y. Yafet

Papers

Interpretation of Knight Shifts and Susceptibilities of Transition Metals: Platinum

Nuclear Spin Relaxation in Transition Metals; Core Polarization

Raman Scattering by Carriers in Landau Levels

Orbital Paramagnetism and the Knight Shift of D-Band Superconductors

Orbital Paramagnetism and the Knight Shift in Transition Metal Superconductors