Non-Abelian tensor Berry connections in multi-band topological systems

TL;DR

This paper introduces non-Abelian tensor Berry connections in multi-band topological systems, providing a unified framework to characterize complex topological phases and revealing new topological invariants and models.

Contribution

It develops a novel formalism of non-Abelian tensor Berry connections from momentum-space Higgs fields, generalizing existing gauge theories in topological matter.

Findings

Derivation of topological invariants from Higgs field winding numbers

Construction of higher-dimensional Berry-Zak phases

Identification of models with space-time inversion and chiral symmetries

Abstract

Here, we introduce and apply non-Abelian tensor Berry connections to topological phases in multi-band systems. These gauge connections behave as non-Abelian antisymmetric tensor gauge fields in momentum space and naturally generalize Abelian tensor Berry connections and ordinary non-Abelian (vector) Berry connections. We build these novel gauge fields from momentum-space Higgs fields, which emerge from the degenerate band structure of degenerate-band models. Firstly, we show that the conventional topological invariants of two-dimensional topological insulators and three-dimensional Dirac semimetals can be derived from the winding number associated to the Higgs field. Secondly, through the non-Abelian tensor Berry connections we construct higher-dimensional Berry-Zak phases and show their role in the topological characterization of several gapped and gapless systems, ranging from two-dimensional Euler insulators to four-dimensional Dirac semimetals. Importantly, through our new theoretical formalism, we identify and characterize a novel class of models that support space-time inversion and chiral symmetries. Our work provides an unifying framework for different multi-band topological systems and sheds new light on the emergence of non-Abelian gauge fields in condensed matter physics, with direct implications on the search for novel topological phases in solid-state and synthetic systems.