# Enhanced interaction effects in the vicinity of the topological transition

## TL;DR

This paper investigates how electron interactions near a topological transition significantly affect quasiparticle properties, spectrum renormalization, and electron density oscillations, leading to observable effects on conductivity.

## Contribution

It provides a detailed analysis of interaction effects on electrons near a topological transition, highlighting spectrum renormalization and anisotropic Friedel oscillations.

## Key findings

- Electrons near the transition have short inelastic lifetimes.
- Interactions cause strong spectrum renormalization near the transition.
- Friedel oscillations become anisotropic and influence conductivity.

## Abstract

A metal near the topological transition can be loosely viewed as consisting of two groups of electrons. First group are "bulk" electrons occupying most of the Brillouin zone. Second group are electrons with wave vectors close to the topological transition point. Kinetic energy, $\tilde{E}_F$, of electrons of the first group is much bigger than kinetic energy, $E_F$, of electrons of the second group. With electrons of the second group being slow, the interaction effects are more pronounced for these electrons. We perform a calculation illustrating that electrons of the second group are responsible for inelastic lifetime making it anomalously short, so that the concept of quasiparticles applies to these electrons only marginally. We also demonstrate that interactions renormalize the spectrum of electrons in the vicinity of topological transition, the parameters of renormalized spectrum being strongly dependent on the proximity to the transition. Another many-body effect that evolves dramatically as the Fermi level is swept through the transition is the Friedel oscillations of the electron density created by electrons of the second group around an impurity. These oscillations are strongly anisotropic with a period depending on the direction. Scattering of electrons off these oscillations give rise to a temperature-dependent ballistic correction to the conductivity.