Collective quantum state at the atomic limit

TL;DR

This study visualizes collective quantum states at atomic scales in monolayer WSe2, revealing persistent Luttinger-liquid behavior and new quantum dot phenomena from confined collective modes, advancing quantum materials engineering.

Contribution

It demonstrates atomic-scale confinement of collective quantum states and their distinct coupling behaviors, expanding understanding of many-body quantum phenomena at the atomic limit.

Findings

Quantized collective modes observed in nanometer segments.

Persistent spin-charge separation at atomic confinement scales.

Ordered chains show unique coupling responses of many-body modes.

Abstract

Collective quantum states are often associated with extended systems, where spatially extensive degrees of freedom enable emergent many-body behavior; whether such strongly correlated states survive at atomic dimensions remains a fundamental question. Tomonaga-Luttinger liquids provide a paradigmatic example of one-dimensional collective quantum matter characterized by spin-charge separation. Using low-temperature scanning tunneling microscopy and spectroscopy, we directly visualize quantized collective modes in atomically confined mirror twin boundary segments of monolayer WSe2. Distinct standing-wave branches associated with fractionalized spin and charge excitations persist in segments as short as one nanometer, establishing the atomic-scale confinement limit of Luttinger-liquid behavior. These ultrashort segments form a new class of many-body quantum dots whose discrete spectra arise from confined collective bosonic modes rather than single-particle electron states. When assembled into ordered chains, inter-dot coupling reshapes electron-like fundamental states while collective spin/charge excitations remain largely intact, revealing distinct coupling responses of emergent many-body modes. Our results demonstrate that collective quantum matter can persist and exhibit fundamentally distinct coupling behavior at atomic length scales, establishing a novel platform for engineering strongly correlated quantum phases from atomically confined building blocks.