Indication of band flattening at the Fermi level in a strongly correlated electron system

TL;DR

This study experimentally demonstrates that in a strongly correlated electron system, the effective mass at the Fermi level increases monotonically with interaction strength, indicating a precursor to spectrum flattening.

Contribution

It provides the first direct comparison between energy-averaged and Fermi-level effective masses in a high-quality quantum well system, revealing distinct behaviors related to electron interactions.

Findings

Fermi-level effective mass increases monotonically with interaction strength.

Energy-averaged mass saturates at low densities.

Evidence of spectrum flattening precursor in strongly correlated electrons.

Abstract

Using ultra-high quality SiGe/Si/SiGe quantum wells at millikelvin temperatures, we experimentally compare the energy-averaged effective mass, $m$, with that at the Fermi level, $m_F$, and verify that the behaviours of these measured values are qualitatively different. With decreasing electron density (or increasing interaction strength), the mass at the Fermi level monotonically increases in the entire range of electron densities, while the energy-averaged mass saturates at low densities. The qualitatively different behaviour reveals a precursor to the interaction-induced single-particle spectrum flattening at the Fermi level in this electron system.