Dipolar excitonic quantum wires at atomically sharp lateral interfaces

One-dimensional (1D) quantum systems are a cornerstone of many-body physics. However, their realization in solids has traditionally relied on top-down methods, which are limited by structural disorder and coarse confinement. Here, we demonstrate a fundamentally distinct route: the emergence of 1D quantum matter at the atomically sharp interface between monolayer semiconductors. Using lateral $MoSe_2-WSe_2$ heterostructures, we identify interfacial excitonic quasiparticles that are bound to the crystal junction. Photoluminescence spectroscopy resolves these excitons into a ladder of discrete states, establishing nanoscopic 1D confinement at length scales of 3 nm. These excitons possess exceptional large permanent in-plane electric dipole moments exceeding e x 2 nm, and exhibit micron-scale, highly anisotropic diffusion confined to the interface. Crucially, the lateral geometry enables dynamic, in-situ reconfiguration of the exciton’s internal structure. By introducing electrostatic doping, we demonstrate a collapse of the dipole moment and a 20-fold reduction in radiative lifetime. This structural tunability establishes lateral interfaces as a uniquely powerful platform for the ‘bottom-up’ engineering of 1D quantum matter. By enabling the dynamic tuning of wavefunctions within a single atomic monolayer, this work opens a scalable route toward 1D excitonic circuits and strongly correlated 1D bosonic phases.

💡 Research Summary

In this work the authors demonstrate a fundamentally new route to one‑dimensional (1D) quantum matter by exploiting the atomically sharp lateral interface between monolayer transition‑metal dichalcogenides (TMDs) MoSe₂ and WSe₂. Chemical‑vapor‑deposited (CVD) lateral heterostructures (LHS) provide a seamless stitching of the two monolayers within a single atomic plane, yielding a crystallographically defined 1D boundary only a few lattice constants wide but extending over tens of micrometers. High‑angle annular dark‑field scanning transmission electron microscopy (HAADF‑STEM) confirms the interface’s atomic sharpness.

Optical spectroscopy reveals a new photoluminescence (PL) resonance at 1.53 eV that appears exclusively at the junction and lies ~100 meV below the MoSe₂ neutral exciton. This feature, absent in the bulk regions, is identified as an interfacial dipolar exciton (X_LI) in which the electron resides in MoSe₂ and the hole in WSe₂, bound by Coulomb attraction across the type‑II band offset. Spatially resolved PL maps show that X_LI emission is confined to the 1D line, persisting uniformly along its ~20 µm length.

Time‑correlated single‑photon counting yields a radiative lifetime of τ ≈ 14.6 ns, three orders of magnitude longer than intralayer excitons, reflecting the reduced electron–hole overlap inherent to charge‑transfer states. Steady‑state diffusion imaging under continuous‑wave excitation uncovers a highly anisotropic “cigar‑shaped” emission profile: the transverse width remains diffraction‑limited while the longitudinal spread reaches a diffusion length L_D ≈ 0.72 µm. From the measured lifetime the authors extract a 1D diffusion coefficient D_y ≈ 0.4 cm² s⁻¹ and an exciton mobility μ ≈ 1.2 × 10³ cm² V⁻¹ s⁻¹ at 4 K, indicating exceptionally clean transport along the interface.

When the excitation power is reduced, the broad X_LI line resolves into a ladder of narrow peaks (Γ ≈ 1–3 meV). The peak energies follow a linear progression E_n = E₀ + ℏω_x n with ℏω_x ≈ 7.2 meV, evidencing quantized center‑of‑mass (COM) motion in an effective harmonic confinement. Using the exciton effective mass (m_X ≈ 1.3 m₀) the transverse confinement length is estimated as ℓ_x ≈ 2.8 nm, comparable to the dipole length.

Applying an in‑plane electric field via split top gates produces a linear Stark shift of each COM state, allowing direct extraction of the permanent dipole length d_e‑h. The lowest state exhibits d_e‑h ≈ 2.2 nm, decreasing to ≈ 1.6 nm for higher states, confirming an exceptionally large in‑plane dipole moment. The systematic reduction of d_e‑h with increasing quantum number reflects the strong coupling between COM and relative motion in the “strong‑confinement” regime, where the internal wavefunction reshapes under the external potential.

Electrostatic doping through a back gate tunes the exciton’s properties dramatically. Increasing electron density induces a blue shift of ~70 meV and reduces the radiative lifetime from 15 ns at charge neutrality to ~0.8 ns at high n‑doping—a more than 20‑fold change. This collapse of the dipole moment and acceleration of recombination arise because added carriers screen the band offset, allowing the electron and hole to occupy the same layer.

Overall, the study establishes that atomically sharp lateral TMD interfaces act as intrinsic 1D quantum wires hosting dipolar excitons with (i) sub‑3 nm transverse confinement, (ii) permanent in‑plane dipoles exceeding 2 nm, (iii) micron‑scale, highly anisotropic diffusion, and (iv) electrical tunability of both dipole strength and radiative lifetime. By providing a bottom‑up, disorder‑free platform for engineering 1D quantum matter, these findings open pathways toward scalable excitonic circuitry, exploration of strongly correlated 1D bosonic phases (e.g., Luttinger liquids, Tonks‑Girardeau gases), and novel optoelectronic devices that exploit the unique combination of confinement, dipolar interactions, and dynamic control.