Spontaneous emission modulation in biaxial hyperbolic van der Waals material

Abstract

As a natural van der Waals crystal, α-MoO3 has excellent in-plane hyperbolic properties and essential nanophotonics applications. However, its tunable properties are generally neglected. Here, we achieve effective modulation of spontaneous emission (SE) from a single-layer flat plate by changing the crystal directions. Numerical results and theoretical analysis show that α-MoO3 exhibits good tunability when the crystal directions of α-MoO3 are different in y– z or x– y planes. A modulation factor of more than three orders of magnitude is obtained at 634 cm−1. This phenomenon is caused by the excitation of hyperbolic phonon polaritons in α-MoO3 at specific bands. However, when the crystal directions of α-MoO3 are different in the x– z plane, the SE of the material exhibits strong angle independence. Additionally, for the semi-infinite α-MoO3 flat structure, we determine the distribution of the modulation factor of SE using the wavenumber and rotation angle. Finally, we extend the calculation results from semi-infinite media to finite thickness films. We obtain the general evolution law of the peak angle of the modulation factor with thickness, increasing the modulation factor to approximately 2000, which exceeds the maximum modulation factor observed in previous works by 48 times. We believe this work could guide the SE modulation of anisotropic materials and benefit the field of micro-/nano-lasers and quantum computing.

Optical properties and polaritons of low symmetry 2D materials

“…Previous studies revealed that highly confined plasmon and PhPs in 2D materials, such as graphene and h-BN, can be explored to enhance the IR absorption of molecules [307][308][309][310] . [305] . (b) Spontaneous emission enhancement of air/ graphene/α-MoO 3 /Si heterostructure with different doping levels of graphene.…”

“…The discovery of natural hyperbolic polaritons on 2D surfaces provided a new platform to study the SE enhancement, since they avoid complicated nanofabrication and host even higher optical DOSs and stronger field confinement. Liu et al studied the modulation of SE in biaxial hyperbolic vdWs α-MoO3 flat plates [305] . They calculated the Purcell factor of the quantum emitter at different rotation angles and varying wavenumbers, by which the distribution of the modulation factor was extracted.…”

“…(a) (left) Schematic of α-MoO3 slab. (a) (right) Evaluation of the modulation factor of α-MoO3 as a function of rotation along different axes [305] . (b) Spontaneous emission enhancement of air/graphene/α-MoO3/Si heterostructure with different doping levels of graphene.…”

Coupling polaritons in near-field radiative heat transfer between multilayer graphene/vacuum/α-MoO3/vacuum heterostructures

“…Both two-dimensional (2D) materials and hyperbolic materials have attracted considerable attention for enhancing and manipulating the NFRHT in recent studies, including graphene, [41][42][43][44][45][46][47][48] hBN, [49][50][51][52][53] black phosphorus [54][55][56][57] and a-MoO 3 . [58][59][60][61][62][63][64] Generally speaking, 2D materials and hyperbolic materials can be stacked to form multilayer heterostructures, which support complicated lightmatter interactions and provide significant potential to enhance the NFRHT. Take the case of multilayer graphene/a-MoO 3 heterostructures, graphene-supported surface plasmon polaritons (SPPs) could be coupled to HPPs supported by a-MoO 3 to form the hybrid polaritons, such as surface plasmon-phonon polaritons, 43 which strongly enhance the NFRHT outside the angular frequency region of the Reststrahlen band of a-MoO 3 .…”

A polarization-dependent perfect absorber with high Q-factors enabled by Tamm phonon polaritons in hyperbolic materials

“…Hyperbolic materials (HMs) offer significant benefits in the development of polarization-dependent optical devices. [35][36][37] Recently, an emerging two-dimensional van der Waals (vdW) material, denoted as a-phase molybdenum trioxide (a-MoO 3 ), has garnered substantial attention due to its exceptional characteristics of high anisotropy and inherent capability to support hyperbolic polaritons. [38][39][40][41][42][43][44] As an excellent natural biaxial hyperbolic material, a-MoO 3 has three distinct reststrahlen bands (RBs) aligned with different crystal axes, enabling effortless achievement of in-plane anisotropy.…”