# Unconventional quantum Hall effects in two-dimensional massive spin-1 fermion systems

## TL;DR

This paper explores unconventional quantum Hall effects in a 2D system with massive spin-1 fermions, revealing unique conductance behaviors and a novel sequence of Landau levels, supported by both continuous and dice model analyses.

## Contribution

It introduces a new quantum Hall effect phenomenon in 2D massive spin-1 fermion systems, showing how Landau levels evolve and lead to unusual conductance patterns.

## Key findings

- Hall conductance exhibits a zero crossing and revival as a staircase pattern.
- Sign reversal of Hall conductance occurs due to Van Hove singularity.
- Results are consistent between continuous and dice models.

## Abstract

Unconventional fermions with high degeneracies in three dimensions beyond Weyl and Dirac fermions have sparked tremendous interest in condensed matter physics. Here, we study quantum Hall effects (QHEs) in a two-dimensional (2D) unconventional fermion system with a pair of gapped spin-1 fermions. We find that the original unlimited number of zero energy Landau levels (LLs) in the gapless case develop into a series of bands, leading to a novel QHE phenomenon that the Hall conductance first decreases (or increases) to zero and then revives as an infinite ladder of fine staircase when the Fermi surface is moved toward zero energy, and it suddenly reverses with its sign being flipped due to a Van Hove singularity when the Fermi surface is moved across zero. We further investigate the peculiar QHEs in a dice model with a pair of spin-1 fermions, which agree well with the results of the continuous model.