Emergent Phenomena Induced by Spin-Orbit Coupling at Surfaces and Interfaces (1611.09521v1)

Abstract: Spin-orbit coupling (SOC) describes the relativistic interaction between the spin and momentum degrees of freedom of electrons, and is central to the rich phenomena observed in condensed matter systems. In recent years, new phases of matter have emerged from the interplay between SOC and low dimensionality, such as chiral spin textures and spin-polarized surface and interface states. These low-dimensional SOC-based realizations are typically robust and can be exploited at room temperature. Here we discuss SOC as a means of producing such fundamentally new physical phenomena in thin films and heterostructures. We put into context the technological promise of these material classes for developing spin-based device applications at room temperature.

• The paper demonstrates that spin-orbit coupling induces emergent states like Rashba and topological surface states with momentum-dependent spin polarization.
• It employs both experimental and theoretical analyses to quantify efficient spin-charge conversion in systems such as topological insulators and Rashba interfaces.
• The study highlights the role of SOC in facilitating Dzyaloshinskii-Moriya interactions, which stabilize chiral magnetic structures and support low-energy skyrmion-based memory applications.

Insights into Spin-Orbit Coupling Induced Phenomena at Surfaces and Interfaces

The paper discussed here provides a comprehensive analysis of how spin-orbit coupling (SOC) induces unique emergent phenomena at material surfaces and interfaces, focusing on their implications for condensed matter physics and device applications. SOC, a relativistic interaction, influences the band structure of materials, particularly in low-dimensional systems, giving rise to novel states and interactions. The paper elaborates on these effects and their potential technological applications at room temperature (RT).

Spin-orbit coupling (SOC) at material surfaces and interfaces results in a variety of phenomena that are robust and exploitable at room temperature. This behavior is highlighted by several key effects discussed in the paper:

1. Rashba and Topological States: The Rashba effect and the formation of topological surface states in certain insulators are prime examples of SOC-induced phenomena. These result in spin-split electronic states with momentum-dependent spin polarization. Rashba interfaces, on conventional metals like Au and Bi, and topological insulators (TIs), such as Bi$_2$Se$_3$, exhibit highly spin-polarized surface states. These states have prospective uses in energy-efficient spintronics due to their spin-momentum locking, which can significantly enhance spin-to-charge conversion efficiencies.
2. Spin-Charge Conversion: Technologies benefit from SOC by utilizing the Edelstein and inverse Edelstein effects for spin-charge conversion. These effects enable efficient interplay between charge and spin currents. Recent advancements have demonstrated significant conversion efficiencies in systems such as TIs and Rashba interfaces, providing an avenue for new spintronic devices.
3. Dzyaloshinskii-Moriya Interaction (DMI): In systems lacking inversion symmetry, SOC facilitates DMI, which stabilizes chiral magnetic structures such as skyrmions and domain walls. These structures are relevant for memory applications due to their stability and the potential for low-energy manipulation.
4. Magnetic Skyrmions: Skyrmions, stabilized by DMI in thin films and magnetic multilayers, offer a novel approach for data storage. The paper discusses their detection, manipulation, and potential device applications. Their small size, stability at room temperature, and solitonic properties make them compelling candidates for skyrmion-based memory architectures.
5. Materials Engineering: The synthesis of novel materials, although challenging, presents opportunities to harness SOC effects. The paper emphasizes the need for continued development of heterostructures and thin films with optimized SOC properties for real-world applications.

Implications and Future Prospects

The practical and theoretical implications of these SOC-induced phenomena are extensive. They pave the way for future developments in spintronic devices, offering avenues for low-energy data storage solutions and efficient logic devices. The interplay between SOC and material properties could lead to breakthroughs in non-volatile memory technologies and new quantum mater states tailored for opto-spintronics applications. The continued exploration of TIs' capabilities in converting charge-to-spin currents effectively positions these materials as candidates for future technology solutions, particularly in spin-Hall-effect applications.

Moreover, current research trends are guided towards achieving more efficient charge-spin interconversion in TIs, enhancing skyrmion stability in diverse environments, and developing interfaces with tailored SOC properties. These efforts are expected to further advance the field, introducing new paradigms in electronic and spintronic device architectures.

The detailed exploration of SOC at surfaces and interfaces emphasizes not only the fundamental scientific interest but also the considerable potential for innovation in materials science and device engineering. This paper lays the groundwork for an exciting future where SOC-driven phenomena may become integral to the technological advancements in the coming years.