The Atomic-Scale Spin-Optical Laser: Pioneering the Future of Optoelectronic Devices

The spin-valley optical microcavity is constructed by combining an inversion-asymmetric (yellow core region) and an inversion-symmetric (cyan cladding region) photonic spin lattice. Due to the photonic Rashba-type spin splitting of the bound state in the continuum, this heterostructure enables the selective lateral confinement of the photonic spin-valley state that emerges inside the core for high-Q resonances. As a result, coherent and controlled spin-polarized lasing (red and blue panels) is obtained from valley excitons in the monolayer of WS2 composite (purple area). Credit: Scholardesigner co, LTD

Scientists at the Technion – Israel Institute of Technology have revealed a coherent laser and controlled spin-optical laser based on a single array of atoms. This achievement is made possible by the spin-dependent coherent coupling between the single-atom layer and the confined photonic spin lattice, the latter supporting high-.Q spin-valley states through photonic Rashba-type spin splitting of the bound state in the continuum.

Published in a prestigious journal Natural Things and presented in the journal Research Insights, the achievement paves the way for the study of coherent phenomena that depend on spinomena in both the classical and quantum regimes. It opens new horizons in basic research and optoelectronic devices that exploit both electrons and photon rotates.

Research and Collaboration Group

The study was carried out in the research group of Professor Erez Hasman, head of the Atomic-Scale Photonics Laboratory, in collaboration with Professor Elad Koren, head of the Laboratory of Nanoscale Electronic Materials and Devices in the Department of Science and Engineering, and Professor. Ariel Ismach at Tel Aviv University. Two Technion teams are collaborating with the Helen Diller Quantum Center and the Russell Berrie Nanotechnology Institute. Dr. Kexiu Rong conducted and led the research, and collaborated with Dr. Xiaoyang Duan, Dr. Bo Wang, Dr. Vladimir Kleiner, Dr. Assael Cohen, Dr. Pranab K. Mohapatra, Dr. Avinash Patsha, Dr. Subhrajit Mukherjee, Dror Reichenberg, Chieh-li Liu, and Vladi Gorovoy.

The Spin Degeneracy Challenge

Can we raise the spin decay of light sources in the absence of magnetism at room temperature? According to Dr. Rong, “Spin-optical light sources combine photonic and electronic conversion methods and thus provide a way to study the exchange of spin information between electrons and photons and develop advanced optoelectronic devices. To build these sources, the need is to raise the degeneracy of spin between two oppositely rotating states in either their photo or electronic states.

This is usually achieved by using a magnetic field under the Faraday or Zeeman effect, although these methods generally require strong magnetic fields and cannot produce small sources. Another promising approach takes advantage of photonic spin-split state magnetization in a dynamic space, supported by a geometric phase structure.

Unfortunately, previous observations of spin-split states rely heavily on low-resolution scattering methods, which impose unnecessary limits on the spatial and temporal interactions of the sources. This method is also limited by the spin-controllable properties of many laser gain materials that are not available or important to achieve effective source control, especially in the absence of magnetism at room temperature.

Achieving High-Q Spin-Split States

To reach the top-Q For spin-split states, researchers have built photonic spin lattices with different symmetry properties, including an inversion-asymmetry core and an inversion-symmetry cladding combined with WS.₂ monolayer to form lateral confined spin-valley states. The critical inversion-asymmetry lattice used by researchers has two important properties. (1) Spin-dependent controllable lattice vector due to different geometric phases from inhomogeneous-anisotropic nanoholes.

This vector splits the spin-degenerate band into two spin branches in the momentum field, called the photonic Rashba effect. (2) Senior pair-Q symmetry-enabled (quasi-) bound states in the continuum, i.e., ±K (corners of the Brillouin zone) photonic spin-valley states, at the band edges of the splitting branches. Moreover, the two states form a parallel superposition mode with equal amplitudes.

Professor Koren noted, “We used WS₂ monolayer as a gain material because this direct-bandgap dichalcogenide transition metal has unique valley pseudospins, which have been widely investigated as an alternative information carrier in valleytronics. In particular, their ±K’ valley excitons (distributed as in-plane spin-polarized dipole emitters) can be selectively selected for spin-polarized light according to the anti-valley selection principle, thus allowing efficient control of spin-optical light sources without magnetism. in the fields.”

In monolayer-integrated spin-valley microcavities, ±K’valley excitons couple to ±K spin-valley states due to polarization pairing, and spin-optical excitonic lasing is achieved at room temperature using strong optical feedback. Meanwhile, the ±K’ Valley excitons (initially out of phase alignment) are driven by the locking mechanism to obtain the lowest system loss, which leads them to re-establish a phase-locked configuration in opposite geometric phases. ±K spin-valley states.

This lasing-mechanism-driven valley configuration eliminates the need for cryogenic heat to suppress intervalley scattering. Moreover, the minimum laser loss of the Rashba monolayer laser can be controlled to be satisfied (broken) by linear (circular) pump polarization, which provides a way to control the lasing intensity and spatial coherence.

Implications and future directions

“Rashba’s photonic spin valley unfolding provides a general way to construct spin-emitting light sources from a surface. The alignment of the reflected valley in a monolayer-integrated spin-valley microcavity makes a step toward achieving the coupling between ±K’ valley excitons for quantum information by using qubits,” explains Professor Hasman.

“For a long time, our group has been working to develop spin optics to use photonic spin as an effective tool to control the behavior of electromagnetic waves. In 2018, we were attracted by valley pseudospins in one-dimensional materials, and therefore started a long-term project to study the effective control of sources of atomic-scale spin-optical light in the absence of magnetism.

We first tackled the challenge of picking up the geometric phase from each valley of excitons using a non-local Berry-defect mode.

However, the fundamental coupling of multi-valley excitons of monolayer Rashba light sources remained unsolved, due to the lack of a strong mechanism of synchronization between excitons.

This question prompted us to think about high-Q Photonic modes Rashba. Following innovations in new physical methods, we have achieved the Rashba monolayer laser described here. “

Reference: “Spin-valley Rashba monolayer laser” by Kexiu Rong, Xiaoyang Duan, Bo Wang, Dror Reichenberg, Assael Cohen, Chieh-li Liu, Pranab K. Mohapatra, Avinash Patsha, Vladi Gorovoy, Subhrajit Mukherjee, Vladimir Kleiner, Ariel Ismach, Elad Koren and Erez Hasman, 6 July 2023, Natural Things.
DOI: 10.1038/s41563-023-01603-3