Effect of order of transfer matrix exceptional points on transport at band edges

TL;DR

This paper investigates how the order of transfer matrix exceptional points at band edges influences conductance scaling in one-dimensional fermionic systems, revealing that universal subdiffusive behavior persists without dephasing but is affected by EP order when dephasing is present.

Contribution

It demonstrates that the universal $1/N^2$ conductance scaling at band edges is unaffected by EP order without dephasing, but EP order influences superballistic scaling under dephasing conditions.

Findings

Universal $1/N^2$ conductance scaling is unaffected by EP order without dephasing.

EP order affects phase coherence length and superballistic scaling regime with dephasing.

Higher order EPs can be realized with varying hopping parameters in the lattice model.

Abstract

Recently, it has been shown that, in one dimensional fermionic systems, close to band edges, the zero temperature conductance scales as $1/N^2$, where $N$ is the system length. This universal subdiffusive scaling of conductance at band edges has been tied to an exceptional point (EP) of the transfer matrix of the system that occur at every band edge. Further, in presence of bulk dephasing probes, this EP has been shown to lead to a counterintuitive superballistic scaling of conductance, where the conductance increases with $N$ over a finite but large regime of system lengths. In this work, we explore how these behaviors are affected by the order of the transfer matrix EP at the band edge. We consider a one-dimensional fermionic lattice chain with a finite range of hopping. Depending on the range of hopping and the hopping parameters, this system can feature band edges which correspond to arbitrarily higher order EPs of the associated transfer matrix. Using this system we establish in generality that, in absence of bulk dephasing, surprisingly, the universal $1/N^2$ scaling of conductance is completely unaffected by the order of the EP. This is despite the fact that existence of transfer matrix EP is crucial for such behavior. In presence of bulk dephasing, however, the phase coherence length, the extent of the superballisitic scaling regime and the exponent of superballistic scaling, all encode the order of the transfer matrix EP.