Noncentrosymmetric Metals Research Articles

Publisher's Note: Magnetostatics and optics of noncentrosymmetric metals [Phys. Rev. B88, 134514 (2013)

Received 6 November 2013DOI:https://doi.org/10.1103/PhysRevB.88.179902©2013 American Physical Society

Magnetostatics and optics of noncentrosymmetric metals

The current in noncentrosymmetric metals in the normal and superconducting states is found within the frame of linear response theory. In line with the usual terms corresponding to diamagnetic response, the Landau diamagnetism, and the Pauli paramagnetism, the general expression contains also terms corresponding to the spatial dispersion specific for a medium without space parity. This so-called gyrotropic current is calculated in the zero-frequency case as well as in the infrared frequency region. The static gyrotropic current yields a negligibly small correction to the London magnetostatics in a superconductor without inversion center, whereas the high-frequency response produces the natural optical activity revealed in the Kerr effect. The magnitude of the Kerr angle in the infrared frequency region is proved to be in a reasonable agreement with the recently reported observations of the Kerr effect in the pseudogap phase in several different high-${T}_{c}$ materials.

Optical activity of noncentrosymmetric metals

We describe the phenomenon of optical activity of noncentrosymmetric metals in their normal and superconducting states. The found conductivity tensor contains the linear in wave vector off diagonal part responsible for the natural optical activity. Its value is expressed through the ratio of light frequency to the band splitting due to the spin-orbit interaction. The Kerr rotation of polarization of light reflected from the metal surface is calculated. In the additional file "Erratum" I've pointed out the sign error in arXiv:1001.2113 ( PRB v.81, 094525 (2010)) that leads to the wrong statement about the Kerr effect in light reflection from the surface of media without space parity.

Recent Developments in Unconventional Superconductivity Theory

A review of recent developments in unconventional superconductivity theory is given. In the first part I consider the physical origin of the Kerr rotation polarization of light reflected from the surface of superconducting Sr2RuO4. Then a comparison of magneto-optical responses in superconductors with orbital and spin spontaneous magnetization is presented. The latter result is applied to the estimation of the magneto-optical properties of neutral superfluids with spontaneous magnetization. The second part is devoted to the natural optical activity or gyrotropy properties of noncentrosymmetric metals in their normal and superconducting states. The temperature behavior of the gyrotropy coefficient is compared with the temperature behavior of paramagnetic susceptibility determining the noticeable increase of the paramagnetic limiting field in noncentrosymmetric superconductors. In the last chapter I describe the order parameter and the symmetry of the superconducting state in the itinerant ferromagnet with orthorhombic symmetry. Finally the Josephson coupling between two adjacent ferromagnetic superconducting domains is discussed.

Spin–orbit coupling and semiclassical electron dynamics in noncentrosymmetric metals

Spin–orbit coupling of electrons with the crystal lattice plays a crucial role in materials without inversion symmetry, lifting spin degeneracy of the Bloch states and endowing the resulting nondegenerate bands with complex spin textures and topologically nontrivial wavefunctions. We present a detailed symmetry-based analysis of the spin–orbit coupling and the band degeneracies in noncentrosymmetric metals. We systematically derive the semiclassical equations of motion for fermionic quasiparticles near the Fermi surface, taking into account both the spin–orbit coupling and the Zeeman interaction with an applied magnetic field. Some of the lowest-order quantum corrections to the equations of motions can be expressed in terms of a fictitious “magnetic field” in the momentum space, which is related to the Berry curvature of the band wavefunctions. The band degeneracy points or lines serve as sources of a topologically nontrivial Berry curvature. We discuss the observable effects of the wavefunction topology, focusing, in particular, on the modifications to the Lifshitz–Onsager semiclassical quantization condition and the de Haas-van Alphen effect in noncentrosymmetric metals.

De Haas–van Alphen effect in metals without an inversion center

We show how the de Haas-van Alphen effect can be used to directly measure the magnitude of spin-orbit coupling in non-centrosymmetric metals, such as CePt3Si and LaPt3Si.

Order parameter in superconductors with nondegenerate bands

In noncentrosymmetric metals, the spin degeneracy of the electronic bands is lifted by spin-orbit coupling. We consider general symmetry properties of the pairing function Delta(k) in noncentrosymmetric superconductors with spin-orbit coupling (NSC), including CePt3Si, UIr and Cd2Re2O7. We find that Delta(k) = chi(k) t(k), where chi(k) is an even function which transforms according to the irreducible representations of the crystallographic point group and t(k) is a model dependent phase factor. We consider tunnelling between a NSC and a conventional superconductor. It is found that, in terms of thermodynamical properties as well as the Josephson effect, the state of NSC resembles a singlet superconducting state with gap function chi(k).