# Achieving Balance of Valley Occupancy in Narrow AlAs Quantum Wells

## TL;DR

This study investigates the terahertz photoconductivity of narrow AlAs quantum wells, revealing valley transitions and simultaneous occupation of different valleys, which could enable valleytronic applications.

## Contribution

It demonstrates the valley transition behavior in narrow AlAs quantum wells and shows simultaneous valley occupation at specific widths, advancing valleytronics research.

## Key findings

- Valley transition observed in AlAs QWs of 4-15 nm width.
- Simultaneous occupation of $X_{x-y}$ and $X_z$ valleys at 6 nm width.
- Photoresponse dominated by collective magnetoplasmon excitations.

## Abstract

Terahertz photoconductivity of $100~\mu$m and $20~\mu$m Hall bars fabricated from narrow AlAs quantum wells (QWs) of different widths is investigated in this paper. The photoresponse is dominated by collective magnetoplasmon excitations within the body of the Hall structure. We observed a radical change of magnetoplasma spectrum measured precisely for AlAs QWs of width ranging from $4$~nm up to $15$~nm. We have shown that the observed behavior is a vivid manifestation of valley transition taking place in the two-dimensional electron system. Remarkably, we show that photoresponse for AlAs QWs of width $6$~nm features two resonances, indicating simultaneous occupation of strongly anisotropic $X_{x-y}$ valleys and isotropic $X_z$ valley in the QW plane. Our results pave the way to realizing valley-selective layered heterostructures, with potential application in valleytronics.