A new horizon for optoelectronic devices

Researchers at the Technion Institute of Technology in Israel have developed a coherent and controllable optical laser based on a single atomic layer. This finding is enabled by spin-dependent coherent interactions between a single atomic layer and a horizontally confined photon spin lattice, the latter of which supports high-quality spin-valley states through Rashba-type photonic spin splitting of a continuum-linked state.

Posted in nature materials Also featured in the journal’s Research Brief, the achievement paves the way for the study of spin-dependent coherent phenomena in both classical and quantum systems, opening new avenues in fundamental research and optoelectronic devices that exploit electron and photon spin.

Can we raise the spin degradation of light sources in the absence of magnetic fields at room temperature? According to Dr. Rong, “Spin photonic light sources combine optical modes with electronic transitions, thus providing a way to study spin information exchange between electrons and photons and to develop advanced optoelectronic devices.”

“To create these sources, the prerequisite is to raise the spin decay between the two opposing spin states in either their optical or electronic parts. This is usually achieved by applying magnetic fields under the influence of Faraday or Zeeman, although these methods generally require strong magnetism” there Another promising method takes advantage of artificial magnetic fields for optical spin-splitting states in momentum space, supported by the geometric phase mechanism.”

“Unfortunately, previous observations of spin-splitting states relied heavily on propagation modes with low quality factors, which impose undesirable constraints on the spatial and temporal coherence of sources. This approach is also hampered by the spin-controllable properties of bulk laser gain by material unavailability or difficulty. Accessible for active control of sources, especially in the absence of magnetic fields at room temperature.”

To achieve high-quality spin-splitting states, the researchers constructed photonic spin networks with different symmetry properties, which include a reflective asymmetric core and a reflective asymmetric cladding integrated with WS.₂ Monolayer to create horizontally confined spin-valley states. The asymmetric and reflexive core network used by the researchers has two important properties.

1. A controllable spin-dependent reciprocal lattice vector due to the space-varying geometries of anisotropic heterogeneous nanopores. This vector splits the spin-degenerate band into two spin-polarized branches in momentum space, and is referred to as the photonic Rashba effect.
2. A pair of correlated (quasi) states with high Q symmetry in the continuum, that is, the optical spin valley states ± K (Brillouin zone angles), at the band edges of the spin-splitting branches. Moreover, the two states form a coherent superposition state of equal amplitude.

Professor Coren noted that “we used WS₂ Monolayer as Gain Material Because the direct bandgap transition metal chalcogenide possesses unique valley pseudopins, which have been extensively investigated as an alternative information carrier at Valleytronics. Specifically, ±K’ valley excitons (which radiate as spin-polarized in-plane dipole emitters) can be selectively excited by spin-polarized light according to the valley paradoxical selection rule, thus enabling active control of spin-optical light sources without magnetic fields.”

In monolayer compact spin-valley microcavities, the ±K’-valley excitons are coupled to the ±K-spin-valley states due to polarization matching, and room-temperature optical excitation lasers are achieved through strong optical feedback. Meanwhile, the ±K’ valley excitons (initially without phase correlation) are triggered by the laser mechanism to find the minimum loss state of the system, which causes it to re-establish phase-locked correlation according to the opposite geometrical phases ±K of the spin valley states.

Valley coherence driven by the laser mechanism removes the need for cooled temperatures to suppress time-lapse scattering. Moreover, the minimum loss state of the monolayer Rashba laser can be regulated until it is satisfied (broken) via linear (circular) pump polarization, providing a way to control laser intensity and spatial coherence.

“The unveiled Rashba photonic spin-valley effect provides a general mechanism for the construction of surface-emitting photonic light sources. The demonstrated valley coherence in the monolayer compact spin-valley cavity is a step towards realizing entanglement of valley excitons ± K’ for the quantum. Information via Qubits”, explains Professor Hassanan.

“For a long time, our group has been developing spin optics to harness photonic spin as an effective tool for controlling the behavior of electromagnetic waves. In 2018, we were drawn into the canyon in two-dimensional materials and thus initiated a long-term project to study the active control of optical light sources at the atomic scale. In the absence of magnetic fields we initially tackled the challenge of capturing the coherent geometric phase from individual valley excitons using nonlocal Berry phase defect mode.”

However, the fundamental coherent addition of multiple valley excitons to the realized monolayer Rashba light sources remained unsolved, due to the lack of a strong synchronization mechanism between the excitons. This problem inspired us to think about high-quality Rashba optical modes. Through new physical methods, we have achieved Rashba lasers. monolayer described here.”

This achievement paves the way for the study of spin-dependent coherent phenomena in both classical and quantum systems, opening new avenues in fundamental research and optoelectronic devices that exploit electron and photon spin.

The study was conducted within the research group of Prof. Erez Hashman, Head of the Laboratory of Atomic Photonics, in collaboration with Prof. Elad Koren, Head of the Laboratory of Nanoelectronic Materials and Devices in the Department of Materials Science and Engineering, and Prof. Ariel Ismach at Tel Aviv University.

The two groups are at the Technion in collaboration with the Helen Deller Quantum Center and the Russell Perry Institute for Nanotechnology (RBNI). The research was conducted and led by Dr. Qixiu Rong, who collaborated with Dr. Xiaoyang Duan, Dr. Bo Wang, Dr. Vladimir Kleiner, Dr. Asil Cohen, and Dr. Pranab K. Mohapatra, Dr. Avinash Bachcha, Dr. Subrajit Mukherjee, Dror Reichenberg, Chih Li Liu, and Vlady Gorovoy.

Manufacturing was carried out at the MNF&PU at the Technion.