Magnetic Field as an Important Tool in Exploring the Strongly Correlated Fermi Systems and Their Particle–Hole and Time-Reversal Asymmetries

Abstract

In this review, we consider the impact of magnetic field on the properties of strongly correlated heavy-fermion compounds such as heavy-fermion metals and frustrated insulators with quantum spin liquid. Magnetic field B can be considered a universal tool, allowing the exploration of the physics controlling the remarkable properties of heavy-fermion compounds. These vivid properties are T/B scaling, exhibited under the application of magnetic field B and at fixed temperature T, and the emergence of Landau Fermi liquid behavior under the application of magnetic field. We analyze the influence of quasiparticle–hole asymmetry on the properties of heavy-fermion (HF) compounds such as the universal scaling behavior of the thermopower S/T exhibited under the application of magnetic field B. We show that universal scaling is demonstrated by different HF compounds such as β-YbAlB4, YbRh2Si2, and strongly correlated layered cobalt oxide [BiBa0.66K0.36O2]CoO2. Analyzing YbRh2Si2, we show that the T/B scaling behavior of S/T is violated at the antiferromagnetic phase (AF) transition. The residual resistivity ρ0 and the density of states N0 experience jumps at the AF transition, causing two jumps in the thermopower and its sign reversal. Our consideration is based on the flattening of the single-particle spectrum that strongly affects ρ0 and N0 and leads to the violation of particle–hole symmetry. The particle–hole asymmetry generates the asymmetrical part Δσd(V) of tunneling differential conductivity σd(V), Δσd(V)=σd(V)−σd(−V), where V is the voltage bias. We demonstrate that in the presence of magnetic field, the quasiparticle–hole asymmetry vanishes, the LFL behavior is restored, and the asymmetry disappears. Our calculations of the mentioned properties of HF compounds, based on the fermion condensation theory, are in good agreement with the experiment and support our conclusion that the fermion condensation theory is capable of describing the properties of HF compounds, including those exhibited under the application of magnetic field.

Transport Properties of Strongly Correlated Fermi Systems

“…Thus, under the application of a magnetic field, the LFL behavior is restored, and the NFL one exhibited by optical conductivity is violated so that the scaling behavior following from Equations ( 30) and ( 35) vanishes. These measurement confirm both our theoretical consideration of the optical conductivity and the role of the magnetic field when studying the HF compounds [40]. We note that this role of the magnetic field is missed in the frameworks of marginal Fermi liquid, Kondo lattice, etc.…”

“…It is worth noting that the transition from the NFL behavior to the LFL taking place under the application of the magnetic field, as it is seen in Figures 2 and 3, is the special property of the topological FCQPT and described by Equation (7) [7,39]. This important property is in a good agreement with experimental facts and allows one to use it as the versatile tool to explore the physics of HF compounds, including the violation of both the particle-hole symmetry and the time invariance symmetry; this violation is directly related to the concept of flat bands [7,40], see Sections 5 and 6. In contrast, these properties are not considered in a number of theories, including the theory of marginal Fermi liquid, see e.g., [35].…”

“…It is seen from Equations ( 6), ( 15) and ( 16) that both LMR and the the muon spinlattice relaxation rate are diminishing functions of magnetic field B. This result is the vivid feature of the fermion condensation theory that allows one to evaluate the behavior of the effective mass under the application of magnetic fields; see [7,40]. ρ N was extracted from the LMR of YbRh 2 Si 2 at different temperatures [28,29] listed in the legend.…”