An alternative measure of correlation strength is the width of the gap (the narrower it is the stronger the correlations), but experimentally determined gap magnitudes have typically differed strongly depending on the quantity they were extracted from. In that case, the knowledge of the charge carrier concentration is needed to estimate the mass enhancement from experimental values of γ, A, or χ 0. The above Fermi liquid relations may still be meaningful if effects such as doping or off-stoichiometry move the Fermi level from within the gap into the conduction or valence band, or even into a conductive impurity band. The periodic Anderson and Kondo lattice models are also known to exhibit such gaps at half filling, where the lower hybridized band is fully occupied and the upper hybridized band is empty, a Kondo insulator results. In a simple mean-field picture, the insulating state arises due to the hybridization of the conduction electrons with the localized electrons, and the Fermi level lies within this hybridization gap. They are typically referred to as Kondo insulators. Whereas most heavy fermion compounds are indeed metallic, there is a smaller subset of materials that display semiconducting properties. It is important to note that the above relations hold for metals. Upon approaching a quantum critical point, situated at T = 0 and, these temperature dependences hold in ever narrower temperature ranges as they give way to non-Fermi liquid behavior emerging at the quantum critical point and extending in a fan-like shape into the phase diagram. for the electronic specific heat, for the electrical resistivity, or for the magnetic susceptibility of the conduction electrons, where the Sommerfeld coefficient γ, the resistivity A coefficient, and the Pauli susceptibility χ 0 are all related to the effective mass. The effective mass can then be determined by comparison with the corresponding theoretical Fermi liquid expression, e.g. The standard method to experimentally determine effective masses of heavy fermion metals is to measure a physical property at sufficiently low temperatures such that it exhibits Fermi liquid behavior. Particularly drastic enhancements appear when approaching a quantum critical point where, at a critical value δ c of the control parameter, a second-order (typically antiferromagnetic (AFM)) phase transition is just suppressed to T = 0. Small variations of an external (nonthermal) control parameter δ such as pressure or magnetic field lead to strong changes in the effective mass. They are also known for their ready tunability. They are best known for the heavy effective masses of their charge carriers, the property that gave this class of materials its name. Heavy fermion compounds are materials where itinerant and localized (typically 4 f or 5 f) electrons coexist and, at low enough temperatures T, strongly interact via the Kondo effect. We hope that our work will guide the search for new Weyl–Kondo semimetals and correlated topological semimetals in general, and also trigger new theoretical work. They suggest that the topological Hall response is maximized by strong correlations and small carrier concentrations. We also put forward scaling plots of the intrinsic Berry-curvature-induced Hall response vs the inverse Weyl velocity-a measure of correlation strength, and vs the inverse charge carrier concentration-a measure of the proximity of Weyl nodes to the Fermi level. This allows for a substantiated assessment of other Weyl–Kondo semimetal candidate materials. We summarize its key characteristics and use them to construct a prototype Weyl–Kondo semimetal temperature-magnetic field phase diagram. We take the time-reversal symmetric Weyl semimetal as an example because it is expected to have clear (albeit nonquantized) topological signatures in the Hall response and because the first strongly correlated representative, the noncentrosymmetric Weyl–Kondo semimetal Ce 3Bi 4Pd 3, has recently been discovered. In this perspective paper, we focus on correlation-driven gapless phases. How strong correlations and topology interplay is a topic of great current interest.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |