Researchers at the forefront of materials science have reported a novel approach to enhance spintronic devices by causing inversion symmetry breaking in a centrosymmetric transition metal dichalcogenide (TMDC) bilayer, known as PtTe2. This groundbreaking work reveals that thermal annealing can transform one layer of the PtTe2 sample into a transition metal monochalcogenide, PtTe, effectively creating a heterostructure that allows for a significant Rashba spin splitting.
The study, published in March 2025 in Nature Communications, indicates that the newly formed PtTe/PtTe2 heterostructure exhibits a remarkable Rashba coefficient of 1.8 eV ⋅ Å, a significant advancement for the development of efficient spintronic applications. Spintronics, a burgeoning field that exploits the intrinsic spin of electrons for novel device functionalities, requires materials that can generate large spin splittings in thin films.
Symmetry plays a critical role in dictating the physical properties of solid-state materials, with inversion symmetry being particularly influential in determining electronic states. Traditionally, many TMDCs, such as PtTe2 and PtSe2, are centrosymmetric, which limits their capacity for substantial spin splitting. However, in this latest research, scientists utilized thermal annealing, a process that involves heating the PtTe2 films in a controlled atmosphere, to selectively extract tellurium, effectively converting the structure into the desired PtTe form. This critical transformation forms the PtTe/PtTe2 heterostructure, which is characterized by its ability to break inversion symmetry.
Focusing on practical applications, the researchers began by growing high-quality bilayer PtTe2 thin films on bilayer graphene-terminated silicon carbide substrates using molecular beam epitaxy (MBE). The following thermal treatment at precisely controlled temperatures and durations resulted in the intended transformation into PtTe layers. The successful conversion was confirmed through various spectroscopic measurements, including Raman spectroscopy, which detected distinct vibrational modes indicative of the newly formed components within the heterostructure.
The study employed second harmonic generation (SHG) measurements to establish the breaking of inversion symmetry within the heterostructure, evidenced by the appearance of a six-fold rotational symmetry signal that contrasted starkly with the original bilayer PTTe2 structure's zero nonlinear susceptibility.
In addition to confirming the structural changes, angle-resolved photoemission spectroscopy (ARPES) was pivotal in visualizing the emergence of new electronic bands near the Fermi energy in the PtTe/PtTe2 sample. The pronounced spin splitting observed through spin-ARPES measurements further validated the expected spin polarization aligned along the y-direction, showcasing opposite polarizations for the splitting bands.
One of the standout achievements of this work is the identification of a giant Rashba effect, underscored by an impressive Rashba coefficient of αR = 1.8 ± 0.2 eV ⋅ Å, positioning this heterostructure favorably against other noted materials in the field. By comparing against existing two-dimensional Rashba systems, this discovery illustrates a substantial leap forward in material design for spintronics, particularly given the relatively modest thickness of the layers involved.
The authors note that their findings might have broader implications beyond the immediate study, suggesting that charge injections using doping could further enhance the Rashba splitting. For instance, doping with iridium could shift the giant Rashba states towards the Fermi level, an exciting prospect for future applications.
The potential to convert the PtTe/PtTe2 heterostructure back into PtTe2 through additional thermal treatments introduces the allure of reversible pathways to manipulate the electronic properties of these materials, offering exciting possibilities in device engineering and architecture.
In conclusion, this research provides a significant foothold in the ongoing quest to optimize spintronic materials, demonstrating a convenient method to induce large Rashba spin splitting in TMDCs through strategic manipulation of crystal symmetry. The ability to engineer these materials with high stability and remarkable spin properties might pave the way for the development of next-generation nanoscale spintronic devices, fundamentally altering the landscape of electronic technologies.
