Unfolding of the electronic structure through the induced representations of space groups: Application to Fe-based superconductors

TL;DR

This paper develops a generalized framework for bandstructure unfolding using induced representations of space groups, enhancing the interpretation of electronic structures and experiments in Fe-based superconductors.

Contribution

It introduces a unified method for bandstructure unfolding incorporating point group symmetries and applies it to Fe-based superconductors, clarifying the one-iron versus two-iron zone representations.

Findings

Unfolding can be understood as projection onto induced irreducible representations.

The framework includes point group operations and applies to any reciprocal space quantity.

Application to Fe-based superconductors shows the one-iron picture as an irreducible representation.

Abstract

We revisit the problem that relevant parts of bandstructures for a given cell choice can reflect exact or approximate higher symmetries of subsystems in the cell and can therefore be significantly simplified by an unfolding procedure that recovers the higher symmetry. We show that bandstructure unfolding can be understood as projection onto induced irreducible representations of a group obtained by extending the original group of translations with a number of additional symmetry operations. The resulting framework allows us to define a generalized unfolding procedure which includes the point group operations and can be applied to any quantity in the reciprocal space. The unfolding of the Brillouin zone follows naturally from the properties of the induced irreducible representations. In this context, we also introduce a procedure to derive tight-binding models of reduced dimensionality by making use of point group symmetries. Further, we show that careful consideration of unfolding has important consequences on the interpretation of angle resolved photoemission experiments. Finally, we apply the unfolding procedure to various representative examples of Fe-based superconductor compounds and show that the one iron picture arises as an irreducible representation of the glide mirror group and we comment on the consequences for the interpretation of one-iron versus two-iron Brillouin zone representations.