Flat band excitons in a three-dimensional supertwisted spiral transition metal dichalcogenide

TL;DR

This paper reports the discovery of flat-band excitons in 3D supertwisted WS2, revealing unique optical phenomena and electronic properties that extend moire physics from 2D to three dimensions, with implications for quantum optoelectronics.

Contribution

It introduces the first observation of flat-band excitons in 3D supertwisted TMDs, combining experimental photoluminescence with advanced electronic structure calculations.

Findings

Observation of flat-band excitons in 3D supertwisted WS2

Detection of novel direct and indirect exciton emissions

Coexistence of 2D and 3D flatband gaps

Abstract

A new frontier in van der Waals twistronics is the development of three-dimensional (3D) supertwisted materials, where each successive atomic layer rotates by the same angle. While two-dimensional (2D) moire systems have been extensively studied, the unique phenomena arising from 3D twistronics remain largely unexplored. In this work, we report the discovery of flat-band excitons in 3D supertwisted WS2, revealed by systematic photoluminescence (PL) experiments and electronic structure calculations. These excitons retain key features of 2D moire transition metal dichalcogenides (TMDs)-such as layer confinement, moire-driven localization, and strong Coulomb interactions-while also offering advantages in scalability and enhanced optical responses in three dimensions. Beyond the PL signatures reminiscent of 2D A excitons, we observe novel direct and indirect exciton emission uniquely tied to the supertwist geometry. Using generalized Bloch band theory and local density of states calculations that incorporate screw rotational symmetry, we uncovered the coexistence of 2D and 3D flatband gaps. These flat-band excitons serve as sensitive probes of the electronic properties of 3D supertwisted semiconductors and open new pathways for applications in quantum optoelectronics.