Spin-Layer Locking Effects in Optical Orientation of Exciton Spin in Bilayer WSe2 (1311.7087v1)

Abstract: Coupling degrees of freedom of distinct nature plays a critical role in numerous physical phenomena. The recent emergence of layered materials provides a laboratory for studying the interplay between internal quantum degrees of freedom of electrons. Here, we report experimental signatures of new coupling phenomena connecting real spin with layer pseudospins in bilayer WSe2. In polarization-resolved photoluminescence measurements, we observe large spin orientation of neutral and charged excitons generated by both circularly and linearly polarized light, with a splitting of the trion spectrum into a doublet at large vertical electrical field. These observations can be explained by locking of spin and layer pseudospin in a given valley. Because up and down spin states are localized in opposite layers, spin relaxation is substantially suppressed, while the doublet emerges as a manifestation of electrically induced spin splitting resulting from the interlayer bias. The observed distinctive behavior of the trion doublet under circularly and linearly polarized light excitation further provides spectroscopic evidence of interlayer and intralayer trion species, a promising step toward optical manipulation in van der Waals heterostructures through the control of interlayer excitons.

• The paper demonstrates that spin-layer locking in bilayer WSe2 enables electrical manipulation of exciton spins using vertical electric fields.
• The researchers used polarization-resolved photoluminescence to distinguish between interlayer and intralayer trion states, evidencing reduced spin relaxation.
• The findings highlight the potential for controlled spin orientation in TMDCs to advance spintronic devices and coherent quantum systems.

Spin-Layer Locking Effects in Optical Orientation of Exciton Spin in Bilayer WSe$_2$

The paper presented in the paper investigates the coupling phenomena between different quantum degrees of freedom in bilayer transition metal dichalcogenides (TMDCs), specifically focusing on WSe$_2$. The researchers aim to explore how the spin and layer pseudospin are interconnected within bilayer WSe$_2$, utilizing polarization-resolved photoluminescence measurements. Through these experiments, critical observations concerning the spin orientation of neutral and charged excitons under both circularly and linearly polarized light were made. One of the primary results is the clear manifestation of a trion spectral doublet under strong vertical electrical fields, attributable to spin-layer locking.

Key Observations and Experimental Approaches

The authors employed polarization-resolved photoluminescence (PL) measurements to identify spin orientation features in neutral and charged excitons with photoluminescence measurements, revealing a substantial spin polarization. This was evidenced by the emergence of a trion spectrum doublet at higher vertical electrical fields. These phenomena are explained by the locking of real electron spin to layer pseudospin within specific valleys.

Under polarization-resolved PL, the researchers demonstrate that up and down spin states are localized in distinct layers of the bilayer structure, which efficiently suppresses spin relaxation. This locking leads to controlled electron spin states and opens up the possibility for optically manipulating electronic states in van der Waals heterostructures through interlayer excitons.

Spin-Layer Locking and Its Implications

The paper details how the spin-layer locking effect permits the electrical manipulation of spins through vertical electric fields, which effectively induce a spin Zeeman splitting. This discovery is remarkable because it indicates a substantial suppression of spin relaxation, a significant finding for potential applications in spintronics.

The experiments were conducted with careful attention to controlling the electronic environment of the WSe$_2$ layers, preventing unwanted doping and ensuring near-intrinsic conditions. The robust presentation of linear and circular polarization results under different gating conditions underscores the explicit manifestations of and differences between interlayer and intralayer trion states. This demonstrates the potential for spectrally distinguishing layer indices and controlling spin states in these materials.

Future Prospects and Applications

The implications of this research are profound for the development of novel spintronic devices. The tuning of spin states via electric fields in bilayer TMDCs could drive advancements in quantum logic applications where precise spin-valley-layer manipulation is needed. Additionally, the demonstration of interlayer excitonic states with preserved intervalley coherence provides a pathway toward robust, coherent quantum systems.

Moreover, the techniques and insights from this paper could be generalized to explore other similar layered materials, potentially revealing a broader spectrum of electronic and optical properties modifiable through engineered heterostructures.

This work opens new avenues in spintronics and quantum computation, suggesting that bilayer TMDCs, under the right conditions, are excellent candidates for controlling spin dynamics via electrical means. This novel paradigm of spin-layer coupling demonstrates both the richness and complexity inherent in two-dimensional materials and their potential for breakthrough technologies in quantum and optoelectronic applications. Future research may extend these methodologies to other variable conditions, further unfolding the potential of correlated quantum states in bilayer materials.