Magneto-Optical Tools to Study Effects in Dirac and Weyl Semimetals

Abstract

Research regarding topological Dirac and Weyl semimetals contributes to our understanding not only of the field of solid-state physics, but also the field of high-energy physics as the physics of Dirac and Weyl semimetals resembles the physics of Dirac and Weyl massless fermions. In condensed matter physics, the Weyl nodes are detached in momentum space and may be realized as emergent quasiparticles with a distinct chirality, left-handed or right-handed. These states lead to phenomena like the chiral anomaly and the anomalous Hall effect (AHE). Furthermore, the combination of quantum effects and magnetic effects in magnetic Weyl semimetals is very intriguing. Magneto-optical tools, which are usually used to study magnetic phenomena, also contribute to magnetic Weyl semimetals. Moreover, with the magneto-optical technique, it is possible to follow the dynamics of the processes and to study the lifetime of the Weyl states. In this work, we review and discuss the effects of using magneto-optical tools for studying quantum effects like the chiral anomaly or magnetic effects in magnetic Weyl and Dirac systems using the magneto-optical Kerr effect (MOKE) or Faraday systems including a single detection and imaging. Examples of using magneto-optical systems in the research of ultrafast magnetic dynamics of thin polycrystalline nickel and permaloy are reviewed as are the magnetic spatial dynamics by employing magneto-optical Kerr or Faraday microscopy tools with ferromagnetic thin films. Interestingly, the excitation of a circularly polarized femtosecond laser pulse could lead to the breakage of time-reversal symmetry and to the transformation of the Dirac state to the Floquet–Weyl semimetal state. The development of a suitable ultrafast magneto-optical system for Weyl systems is discussed, and the practical difficulties for the realization of such a system are considered.

Strong Magneto-Optical Kerr Effects in Ni-Doped ZnO Nanolaminate Structures Obtained by Atomic Layer Deposition

“…The prospects of the possible magnetism implication with soft magnetic behavior under an applied magnetic field in undoped ZnO is usually analyzed within the framework of the defect-induced d0 mechanism [45]. Тhe net spin polarization is mediated by interrelated structural and stoichiometric deviations such as anion (oxygen VO) or cation (Zink VZn) vacancies as well as surface and interface/substrate effects [31][32][33]. The complexity of magnetic effects expands even more when room temperature ferromagnetism [2,46] is achieved via TM magnetic doping effects, as in the case of ZnO:Ni with further alteration of the chemical phase composition and possible foreign magnetic clusters embedded in the main ZnO matrix.…”

“…The prospects of the possible magnetism implication with soft magnetic behavior under an applied magnetic field in undoped ZnO is usually analyzed within the framework of the defect-induced d 0 mechanism [45]. The net spin polarization is mediated by interrelated structural and stoichiometric deviations such as anion (oxygen VO) or cation (Zink VZn) vacancies as well as surface and interface/substrate effects [31][32][33].…”

“…MO Kerr microscopy is an irreplaceable tool for studying and visualizing the spin system dynamics, magnetic domain textures and quasiparticles (such as skyrmions). Some of the state-of-the-art developments are related to the novel antiferromagnetic spintronics, magneto-plasmonics, and 2D and topological materials and are especially focused on the improvement of spatial, temporal, and spectral resolution [28][29][30][31][32]. In addition, the recent advancements in the field of topological insulators can give new impulse for a revival of MOKE-based memory drive technology [33].…”

Magneto-optical Kerr effect in Weyl semimetals with broken inversion and time-reversal symmetries

“…The topological nature of the band structure of a WSM leads to a number of interesting transport and optical properties such as an anomalous Hall effect 3 , the chiralmagnetic effect 4 , Fermi arcs 5 , a chiral anomaly leading to a negative longitudinal negative magnetoresistance 6 and to a plasmon 7 whose frequency increases with the magnetic field B as √ B. Valuable information on the band structure and topological properties of WSMs can be obtained by magnetooptical methods such as the magneto-optical Kerr effect (MOKE) 8 which is a powerful probe of the magnetic and electronic properties of a material. The MOKE is a noncontact technique that measures the rotation of the polarization vector and the ellipticity of an electromagnetic wave reflected from the surface of a material.…”