title: Branch-cut singularities in thermodynamics of Fermi liquid systems.
abstract: The recently measured spin susceptibility of the two-dimensional electron gas exhibits a strong dependence on temperature, which is incompatible with the standard Fermi liquid phenomenology. In this article, we show that the observed temperature behavior is inherent to ballistic two-dimensional electrons. Besides the single-particle and collective excitations, the thermodynamics of Fermi liquid systems includes effects of the branch-cut singularities originating from the edges of the continuum of pairs of quasiparticles. As a result of the rescattering induced by interactions, the branch-cut singularities generate nonanalyticities in the thermodynamic potential that reveal themselves in anomalous temperature dependences. Calculation of the spin susceptibility in such a situation requires a nonperturbative treatment of the interactions. As in high-energy physics, a mixture of the collective excitations and pairs of quasiparticles can effectively be described by a pole in the complex momentum plane. This analysis provides a natural explanation for the observed temperature dependence of the spin susceptibility, both in sign and in magnitude.
authors.affiliation: Department of Condensed Matter Physics, The Weizmann Institute of Science, Rehovot 76100, Israel. arcadi.shehter@weizmann.ac.il
authors.forename: Arkady
authors.initials: A
authors.lastname: Shekhter
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Finkel'stein