Multi-criticality and long-range effects in non-Hermitian topological models

TL;DR

This paper explores how non-Hermiticity and long-range interactions influence topological phases in a non-Hermitian SSH model, revealing new critical behaviors, higher winding numbers, and fractional invariants.

Contribution

It introduces a detailed analysis of the interplay between non-Hermiticity and long-range effects, including multi-criticality and fractional topological invariants, using momentum space and CRG methods.

Findings

Higher winding numbers with longer-range interactions

Existence of multi-critical points with distinct universality classes

Fractional topological invariants due to infinite-range effects

Abstract

Long-range effects induce some interesting behavior and considered as a gateway to understand the non-local behavior in the quantum systems. Especially, the long-range topological models became a platform for the realization of new quasi-particles, which are believed to be potential candidates for the topological qubits. In this work, we consider non-Hermitian Su-Schriffer-Heeger (SSH) model and discuss the interplay of non-Hermiticity and long-range effects. We use the approach of momentum space characterization, critical exponents and curvature renormalization group (CRG) method to understand the aspects of interplay. The longer-range (finite neighbors) effect produces higher winding numbers, where we observe a staircase of transitions among the even-even and odd-odd winding numbers which depends on the number of interacting neighbors. Here we also highlight the effect of multi-criticality in the system and show that they belong to a different universality class. The interplay of long-range (infinite neighbors) effect and non-Hermiticity produces fractional topological invariants, and we analyze them from the behavior of pseudo-spin vectors. We also determine the long-range and short-range limit of the model through universality class of critical exponents. Our work mainly showcases that how the study of criticality in topological system is interesting in exploring the interplay of non-Hermiticity and long-range effects.