# Giant Berry‐phase‐Driven X‐Ray Beam Translations in Strain‐Engineered Semiconductor Crystals

## TL;DR

This paper shows how X-ray beams can be translated by manipulating crystal deformations in semiconductors, using the Berry-phase effect for potential X-ray optics applications.

## Contribution

A novel method is introduced to control X-ray beam translations via strain-engineered semiconductor crystals using hydrogenation.

## Key findings

- Beam translations exceeding 100 µm are observed in selectively hydrogenated GaAsN epilayers.
- The translations are linked to specific deformation regions through a theoretical model comparison.
- The Berry-phase effect is harnessed to control X-ray propagation in engineered crystal structures.

## Abstract

The manipulation of light through its interactions with artificially structured media is a cornerstone of photonics. The rescaling of this concept to the X‐ray realm—which will enable us to control X‐ray light with the same precision routinely available in the visible/IR range—has so far been hindered by the inherent difficulty of realizing photonic structures with the sub‐nanometric resolution dictated by X‐ray wavelengths. A promising approach to this challenge is based on the so‐called Berry‐phase effect, the large beam translations undergone by X‐ray photons propagating in a deformed crystal, due to the simultaneous presence of Berry curvatures in real and reciprocal space. In this work, the controlled crystal distortions required to rein in this effect are obtained by pairing the lattice expansion observed upon H irradiation of GaAsN with a spatially selective hydrogenation technique. The macroscopic beam translations measured here are striking manifestations of the Berry curvatures associated with the sub‐nanometric lattice distortions induced by H incorporation. Through the comparison with a dedicated theoretical model, the individual translation branches observed in X‐ray transmission can be traced back to specific deformation features present within the samples, establishing a predictive framework for the control of X‐ray propagation in the fabricated structures.

Due to the Berry‐phase effect, X‐rays propagating in deformed crystals undergo large translations, interesting for X‐ray optics applications. Here, the lattice expansion observed upon H irradiation of dilute‐nitride semiconductors is exploited to engineer the deformation landscape of selectively hydrogenated GaAsN epilayers. Beam translations >100 µm are subsequently observed and linked to specific deformation regions through the comparison with a dedicated model.