Tailoring higher-order van Hove singularities in non-Hermitian interface systems via Floquet engineering

TL;DR

This paper demonstrates how non-Hermitian interface systems driven by optical fields can be engineered to generate and control higher-order van Hove singularities, revealing new types of divergences in the density of states.

Contribution

It introduces a novel non-Hermitian interface platform for tailoring higher-order van Hove singularities using Floquet engineering and analyzes their unique properties.

Findings

Exceptional rings form on the Fermi line in NH systems.

Tuning NH parameters creates paired VHS with power-law divergences.

Different NH configurations lead to distinct DOS singularities.

Abstract

We propose a non-Hermitian (NH) interface system formed between two NH nodal line semimetals driven by optical fields as a platform for generation and tailoring of higher-order van Hove singularities (VHS). Through an analytical analysis of the density of states (DOS), we find VHS with logarithmic divergences in the Hermitian limit. Upon introducing NH terms, four exceptional rings on two sides of the Fermi line are formed. By tuning the NH parameters and the light amplitude, we find a situation when one exceptional ring crosses the Fermi line, where a saddle point appears and results in a paired VHS around the origin. In contrast, when an exceptional contour resides at the Fermi energy, the saddle points critically get destroyed and we obtain a single peak in the DOS, with power-law divergences. These higher-order divergences that appear in an NH system have a different origin than that of the higher-order VHS in Hermitian systems, where no saddle point merging is noted. Our results suggest NH interfaces to be promising avenues for exploring higher-order VHS.