# Flat band and Planckian metal

## TL;DR

This paper explores an extended SYK model that demonstrates flat bands and their role in the linear resistivity observed in strange metals, linking microscopic theory with phenomenological ideas.

## Contribution

It provides a microscopic derivation of flat bands in an interacting model, supporting the idea that flat bands cause linear resistivity in strange metals.

## Key findings

- Identification of flat bands in an extended SYK model.
- Support for flat bands causing linear temperature dependence of resistivity.
- Connection between microscopic flat band formation and phenomenological models.

## Abstract

We discuss the recent extension of the Sachdev-Ye-Kitaev (SYK) microscopic model by Patel and Sachdev in arXiv:1906.03265, which demonstrates the characteristic features of the Khodel-Shaginyan fermion condensate -- the existence of the finite region of momenta, where the energy of electrons is exactly zero (the flat band). The microscopic derivation of the flat band in this interacting model supports the original idea of Khodel and Shaginyan based on the phenomenological approach. It also suggests that it is the flat band, which is responsible for the linear dependence of resistivity on temperature in "strange metals".