Features of electron states of compounds with strong electron correlations probed by radiation-induced disorder

Abstract

The radiation-disordering method is used for investigating features of electron states of two classes of systems with strong electron correlations: high-temperature superconductors (HTSCs) and heavy-fermion (HF) systems. At low temperatures, the electron states of these systems are formed in a strong interaction between conduction electrons and localized magnetic moments. To clarify the factors leading to a change in the properties of these compounds, the radiation-disordering effects are analyzed first in simpler systems: (I) superconducting (SC) intermetallic compounds MgB2 and MgCNi3; (II) compounds In x Bi2−x Te3 and HgSe with a relatively low charge-carrier concentration, pyrolytic graphite, and (i)-AlPdRe quasicrystal; and (III) oxide compounds K0.3WO3 and Sr2RuO4. It is shown that a number of essential properties of the electron states of the initial (ordered) compounds could be established when analyzing the experimental data within the framework of simple models. In systems with a carrier concentration n = (1017−1019) cm−3, the formation of radiation defects carrying an effective charge results in the Fermi-level shift that is the key factor for the observed changes in transport properties, while the scattering effects on additional defects are less significant. In the HTSC and HF systems, the observed disordering effects are qualitatively different. In this case, the presence of initial unique electron states formed through the interaction of electrons with localized magnetic moments and responsible for the “unusual” superconductivity is a more essential factor than the defect doping. The crystal order is very important for the existence of these low-temperature states and its damage results in their suppression. The nature of degradation of the HF states upon disordering depends on the effective mass m*: from the complete suppression for m*/m e > 100 to relatively weak changes in properties for m*/m e < 10. The decay of a coherent-electron system into two weakly interacting subsystems caused by disordering is a radiation defect common for the HTSC and HF systems, leading to a fast suppression of SC states. The crystal-order damage in these systems changes the type of interaction from collective to local, which can be considered as a continuous phase transition; this circumstance is often ignored when constructing the theoretical models for description of these fine quantum states.