Universal Scalings in 2D Anisotropic Dipolar Excitonic Systems

TL;DR

This paper establishes universal scaling laws for anisotropic dispersion in 2D dipolar excitonic systems, revealing unique spectroscopic signatures and confirming predictions through numerical simulations.

Contribution

It introduces the universal functional form of anisotropic dispersion in 2D dipolar excitonic systems and predicts distinctive spectroscopic behaviors.

Findings

Dispersion is linear parallel to dipoles, dispersionless perpendicular up to linear order.

Density of states scales as E^{0.5}.

Spectroscopic signatures include disorder and temperature-dependent linewidths, and angular peak splittings.

Abstract

Low-dimensional excitonic materials have inspired much interest owing to their novel physical and technological prospects. In particular, those with strong in-plane anisotropy are among the most intriguing but short of general analyses. We establish the universal functional form of the anisotropic dispersion in the small $k$ limit for 2D dipolar excitonic systems. While the energy is linearly dispersed in the direction parallel to the dipole in-plane, the perpendicular direction is dispersionless up to linear order, which can be explained by the quantum interference effect of the interaction among the constituents of 1D subsystems. The anisotropic dispersion results in a $E^{\sim0.5}$ scaling of the system density of states and predicts unique spectroscopic signatures including: (1) disorder-induced absorption linewidth, $W(\sigma)\sim\sigma^{2.8}$, with $\sigma$ the disorder strength, (2) temperature dependent absorption linewidth, $W(T)\sim T^{s+1.5}$, with $s$ the exponent of the environment spectral density, and (3) the out-of-plane angular $\theta$ dependence of the peak splittings in absorption spectra, $\Delta E(\theta)\propto\sin^2\theta$. These predictions are confirmed quantitatively with numerical simulations of molecular thin films and tubules.