New field of atomic-scale spin optical laser optoelectronic devices

Technion researchers report a spin-optical single-layer ultra-thin laser that integrates a single layer of tungsten disulfide WS2 into a heterostructured microcavity that supports a high-Q photonic spin valley resonance. The relevant results were published in Nature Materials under the title of ".

In this paper, we report a spin optical monolayer laser that integrates monolayer WS2 into a heterostructured microcavity that supports high Q photon spin valley resonance. Inspired by the generation of valley pseudospins in monolayers, the spin valley pattern is generated by the Rashba spin splitting of bound photons in the continuum, and the opposite spin polarization ±K valley is generated by the spin-orbit interaction of photons arising from the reversal symmetry breaking.

Rashba single-layer laser has inherent spin polarization, high spatiotemporal coherence, inherent symmetry and robustness. WS2 single-layer laser can achieve valley coherence at any pump polarization at room temperature. The researchers' single-layer integrated spin valley microcavity opens the way for further exploration of classical and non-classical coherent spin optical sources of electron and photon spin. It opens up new horizons for basic research and optoelectronic devices using electron and photon spin.

Figure 1: The spin valley optical microcavity is formed by connecting an antisymmetric (yellow nuclear region) and an antisymmetric (cyan cladding region) photonic spin lattice. By means of Rashba spin splitting of bound photons in the continuum, this heterostructure can selectively constrain the spin valley of emergent photons in high Q resonances in the core laterally. Thus, coherent and controllable spin-polarized lasers (red and blue beams) are achieved from valley excitons of the merged WS2 monolayer (purple region).

Spin optical sources combine photon modes and electron transitions, thus providing a way to study the exchange of spin information between electrons and photons and to develop advanced optoelectronic devices.

Figure 2: Spin Valley Rashba single-layer laser diagram.

There is a pair of highly Q-symmetric (quasi) bound states at the edge of the spin-splitting branch, namely ±K(Brillouin region) photon spin valley. Moreover, the two states form a coherent superposition of equal amplitude.

Professor Koren noted: "We used the WS2 monolides as the gain material because this direct band-gap transition metal disulfide has a unique valley pseudospin and has been extensively studied as an alternative information carrier for valley electrons.

Specifically, their ±K 'valley excitons (which radiate as in-plane spin-polarized dipole emitters) can be selectively excited by spin-polarized light according to valley contrast selection rules, enabling active control of spin-polarized light sources without magnetic fields."

Figure 3: Schematic diagram of spin valley generation using photon Rashba effect.

In a single-layer integrated spin valley microcavity, the ±K 'valley excitons are coupled to ±K spin valley states due to polarization matching, and spin exciton laser is realized at room temperature by strong light feedback. At the same time, driven by the laser mechanism, the ±K 'valley excitons (which initially had no phase correlation) find the minimum loss state of the system and re-establish the locking correlation according to the geometric phase opposite the ±K spin valley state.

Figure 4: Spin Valley Rashba single layer laser characteristics.

This laser-driven valley coherence eliminates the need for low temperature suppression of intervalley scattering. In addition, the minimum loss state of the Rashba single-layer laser can be adjusted to a satisfied (broken) state by linear (circular) pumping polarization, which provides a way to control the laser intensity and spatial coherence.

Links to relevant papers:

Kexiu Rong et al, Spin-valley Rashba monolayer laser, Nature Materials (2023). DOI: 10.1038/s41563-023-01603-3
https://phys.org/news/2023-09-atomic-scale-spin-optical-laser-horizon-optoelectronic.html

Source: Sohu-Yangtze River Delta Laser Alliance