Explore Projects Non-Hermitian systems

When the edge takes everything.

In an ordinary crystal, electron waves spread through the whole material. Make the hopping one-sided and every single state crowds against one wall. This is the non-Hermitian skin effect. We study what happens when it meets disorder and topology.

StatusTwo preprints, one manuscript in development
MethodsExact diagonalization, transfer matrices, analytics
BySouvik Ghosh, with Sayak Roy and co-authors

The effect

Tilt the hopping. Watch the bulk empty.

A chain of 48 sites between two walls. Drag the slider to make hopping to the right easier than hopping to the left.

This is the simplest textbook model of the effect (the Hatano–Nelson chain), solved exactly and drawn live. It is not a result of ours. Our papers start where this picture stops.

LeftwardRightward

Hopping to the right: 1.30
Hopping to the left: 0.70
Weight within six sites of the wall: 96 %

Gold bars: where the particle sits, averaged over all 48 states. White line: one state on its own. Illustration of the standard model, not a simulation of a real device.

Our work

What happens when two kinds of trapping compete.

The skin effect pushes every state to a wall. Quasiperiodic disorder pins each state where it stands. Put both into a dimerized chain and they fight.

Preprint · 2026

A fifth regime, where disorder frees the states.

We map the full phase diagram and identify five regimes. In one of them, not reported before, a moderate amount of quasiperiodic disorder breaks up the pile at the wall and partly delocalizes the states again, before stronger disorder pins them all.

Read the preprint

Same preprint

A formula for the boundary.

An analytical expression for where localization sets in, which agrees with the numerical calculation. The disorder also unwinds the loops of the complex spectrum, and the skin effect drives the entanglement almost to zero.

Preprint · 2025 · with Sayak Roy

The same chain, pushed four ways.

Topology, quasiperiodic disorder, non-Hermiticity and a periodic drive in one computational study: edge states destroyed by strong modulation, phases sorted by unsupervised machine learning, and a driven chain made topological.

Read the preprint

In development

Can the skin effect charge a battery?

A working manuscript asks whether the pile-up at the wall is a resource for a quantum battery, and how the answer depends on the charging protocol.

The record

Read it for yourself.

Preprint · 2026Competing skin effect and quasiperiodic localization in the non-Hermitian SSH chainSouvik GhosharXiv:2603.20330
Preprint · 2025Exploring Topological and Localization Phenomena in SSH Chains under Generalized AAH ModulationSouvik Ghosh & Sayak RoyarXiv:2506.10195
Working manuscriptNon-Hermitian Skin Effect as a Quantum Battery Resource: Passive Ergotropy and Protocol-Dependent Charging in the SSH ChainSouvik Ghosh, Sayak Roy, Saurabh Mishra & Nituparna DasIn development

Preprints are posted on arXiv ahead of peer review.

Souvik Ghosh Need a simulation like this? VV Research Desk

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