arXiv subjects

E. T. Kokkinakis

Publications and source records attributed to E. T. Kokkinakis.

4 recordsLinked to original sources

arXiv2025

Non-Hermitian off-diagonal disordered optical lattices

Within the framework of non-Hermitian photonics, we investigate the spectral and dynamical properties of one- and two-dimensional non-Hermitian off-diagonal disordered optical lattices, where randomness is applied to the couplings rather than to the on-site potential terms. We analyze eigenvalue distributions and the localization properties of the eigenmodes, comparing them with those of the corresponding Hermitian lattices. Furthermore, we study their transport behavior under single-channel excitation and identify unconventional phenomena such as jumps between distant lattice regions in systems with a purely real spectrum, as well as complex spectrum-induced Anderson jumps, reported here for the first time in two dimensions. Our results establish a reference framework for non-Hermitian off-diagonal disorder and open new directions for future studies of localization phenomena.

cond-mat.dis-nn↗

arXiv2025

Evolving disorder in non-Hermitian lattices

The impact of disorder on wave transport has been extensively studied in Hermitian systems, where static randomness gives rise to Anderson localization. In non-Hermitian lattices, static disorder can lead to peculiar transport features, including jumpy wave evolution. By contrast, much less is known about how transport is modified when the on-site disorder evolves during propagation. Here we address this problem by investigating two pertinent non-Hermitian lattice models with disorder altered at regular intervals, characterized by a finite disorder period. In lattices with symmetric couplings and complex on-site disorder, short disorder periods suppress localization and give rise to diffusion-like spreading, while longer periods allow the emergence of jumps. In Hatano-Nelson lattices with real on-site disorder, the non-Hermitian skin effect asymptotically dominates regardless of the disorder strength, while the disorder period reshapes the drift velocity and modulates its competition with Anderson localization. These results establish evolving disorder as a novel way of tuning non-Hermitian transport.

cond-mat.dis-nn↗

arXiv2025

Non-Hermitian impurity problem

The problem of a single Hermitian impurity has long served as a cornerstone in condensed matter physics, offering fundamental insights into the mechanisms of Anderson localization. Yet, despite the increased interest in the spectral and localization properties of non-Hermitian lattices with defects, the non-Hermitian extension of the single impurity problem remains largely unexplored. In this work, we investigate the role of a single complex impurity in one-, two-, and three-dimensional infinite tight-binding lattices. Our study reveals a series of counterintuitive phenomena, including regions where localization vanishes and re-emerges as the impurity strength varies. Next, we study the corresponding finite-sized lattices, which are highly relevant to experimental realizations in readily accessible photonic platforms, revealing a variety of exotic features, such as scale-free localized states, exceptional points, and peculiar cross-shaped localized eigenstates, whose profiles deviate from the conventional exponential localization. This work paves the way for future studies on transport phenomena in non-Hermitian disordered lattices.

cond-mat.dis-nn↗

arXiv2024

Anderson localization versus hopping asymmetry in a disordered lattice

In the framework of non-Hermitian photonics, we investigate the interplay between disorder and non-Hermiticity in a one-dimensional Hatano-Nelson lattice. While Anderson localization dictates the wave's evolution in conservative random systems, the introduction of non-Hermiticity tends to force the beam to unidirectionally propagate towards one edge of the potential due to the existence of skin modes. As we show, the antagonism between these effects results in qualitatively distinct phases of wave diffraction, including counter-intuitive characteristics regarding the relationship between the strength of disorder and the wavepacket's velocity.

cond-mat.dis-nn↗