Public defence, Photonics and Nanotechnology, M.Sc. Fedor Nigmatulin

The title of the thesis: Emergent Phenomena in Two-Dimensional Magnetic and Excitonic Materials

Thesis defender: Fedor Nigmatulin
Opponent: Prof. Stephan Roche, Institut Català de Nanociència i Nanotecnologia (ICN2), Spain
Custos: Prof. Zhipei Sun, Aalto University School of Electrical Engineering

Two-dimensional (2D) materials, represented by atomically thin layers, have been the focus of intense recent research due to their strong potential for applications and fundamental physics. These prospects are driven by the exceptional features of 2D materials, including spatial confinement, accessible tunability, and integrability into heterostructures, which give rise to a broad spectrum of emergent phenomena. However, the transition from proof-of-concept demonstrations of emergent phenomena in 2D materials to real applications, such as spintronic and polaritonic devices, faces significant challenges. These include detecting subtle 2D noncollinear magnetism and achieving long-distance energy transfer between quantum emitters. These pivotal challenges for spintronics and polaritonics are addressed in this thesis.

First, this thesis demonstrates that electrical measurements provide a promising strategy for probing elusive 2D spin-spiral magnetization. In particular, it is shown that electrical current in topological edge channels can be leveraged to extract signatures of spin-spiral magnetic order. Furthermore, a machine learning algorithm was applied to complex electrical transport data modulated by electrostatic gating and external magnetic field, successfully reconstructing arbitrary 2D spin-spiral textures realized in moiré materials while remaining robust to impurities and noise.

Second, it is shown that polaritons, hybrid states consisting of a mixture of matter and light, can mediate energy transfer between excitons (bound electron-hole pairs) in 2D materials inside an optical cavity. Using experimental data as inputs to quantum simulations of exciton population dynamics, efficient energy transfer at room temperature is demonstrated over an unprecedented microscale distance, exceeding the range of conventional energy transfer by a hundredfold.

The findings of this thesis advance the study of emergent phenomena in 2D materials with a focus on future experimental realizations. This work opens new avenues for probing and understanding 2D noncollinear magnetic materials, including thriving frustrated, multiferroic, and moiré systems. Moreover, it addresses the challenge of long-distance energy transfer between excitons in 2D materials, laying a foundation for prospective applications.

Key words: two-dimensional materials

Thesis available for public display 7 days prior to the defence at Aaltodoc. 

Contact: 
email: fedor.nigmatulin@aalto.fi