NTNU Physicists Achieve Multilevel Photomemory via Vortex Light
A research group led by Professors Yen-Wen Lan and Ting-Hua Lu of the Department of Physics, in collaboration with PhD student Yeh-Ru Chen, master’s student Po-Wen Wang, and postdoctoral researcher Wen-Hao Chang, has published new findings in the October 2025 issue of Science Advances. The article, titled “Orbital angular momentum–driven multistate photomemory,” presents a method for achieving multilevel photomemory utilizing the orbital angular momentum (OAM) of light. This work marks a departure from the binary constraints of conventional optical memory and establishes the angular momentum of light as a viable and independent parameter for information storage and control.
Orbital Angular Momentum as a Degree of Freedom in Memory Devices
The development of information technologies continues to face limitations in storage capacity, energy consumption, and operational speed. Standard electronic and optical memory devices typically rely on binary encoding which restricts both scalability and efficiency.
Addressing these limitations, the NTNU team employed vortex light, characterized by its helical phase front and quantized OAM. This form of light produces a longitudinal electric-field distribution that can be used to modulate electronic states within optoelectronic materials.
Their experimental photomemory device was constructed using monolayer molybdenum disulfide (MoS₂) as the functional medium. When illuminated by OAM beams with varying topological charges, the light’s helical structure modified the density of trap states within the material. This effect enabled control over charge trapping and release, governed solely by the angular momentum of the incident light.
The team demonstrated that altering only the OAM value resulted in distinct, reproducible memory states. The device exhibited measurable variations in readout current corresponding to different topological charges. These results confirm the feasibility of encoding multiple memory states in a single device, thereby enhancing storage density and functional versatility beyond binary representation.
Mechanism and Implications for Future Technologies
Current–voltage and time-resolved analyses verified the stability and repeatability of the observed OAM-driven memory effect. The underlying mechanism is attributed to Poole–Frenkel barrier modulation, whereby the longitudinal electric field associated with OAM alters the energy landscape of electron traps. This enables controlled carrier transport, independent of light intensity or wavelength.
The findings underscore the potential for using spatial light structure as a functional control parameter in optoelectronic systems. The research introduces a new framework for memory design based on angular momentum, offering advantages in terms of contactless control and multistate encoding.
According to the authors, this approach lays a foundation for applications in photonic computing, artificial intelligence hardware, and reconfigurable neuromorphic memory systems. It also represents a broader contribution to the field of light–matter interaction, highlighting NTNU’s ongoing research strengths in optoelectronics and two-dimensional materials.
Prospects for Further Research
The team intends to expand this work by exploring the applicability of OAM-driven control in other two-dimensional materials and heterostructures. Future research will also address the integration of such mechanisms with existing semiconductor manufacturing processes. If successful, these developments may lead to the creation of optical memory devices characterized by high speed, low energy consumption, and compatibility with photonic integrated circuits that support next-generation data storage and optical computing technologies.
Thesis URL: https://www.science.org/doi/10.1126/sciadv.adx8795