Speaker
Description
Janus monolayers of transition metal dichalcogenides (TMDs) constitute a highly interesting group of modern $2$D materials, due to the in-built symmetry breaking and its non-trivial consequences [1]. Among various TMDs, the structures forming charge density waves (CDWs) at low temperatures offer highly complex physics.
In the paper, we report a computational, density functional theory-based study of the properties of a Janus TaSSe TMD monolayer in its $1$T polymorph [2]. The study involves both normal and CDW state with $\sqrt{13}\times\sqrt{13}$ reconstruction, as the parent monolayer compounds (TaS$_2$ and TaSe$_2$) are known to develop such ordering. We provide an extensive comparison of the predicted structural and electronic properties of our Janus system to those of its parent compounds.
For the normal state, we predict the emergence of an electric dipole moment due to the symmetry breaking, with pronounced sensitivity to the perpendicular electric field applied to the structure. The presence of the temperature-dependent imaginary phonon modes marks the instability which is characteristic of the CDW-forming systems.
For the CDW state, a peculiar feature of the electronic structure is the presence of a pair of weakly dispersive bands at the Fermi level. Their splitting stems from the symmetry breaking in Janus structure, yielding the presence of spin-orbit coupling (SOC) characterized by the contribution of both linear and cubic terms [3]. We discuss the possibility of controlling the SOC with the external electric field. Moreover, we address computationally the problem of magnetism in CDW state of our system.
In the field of modern spintronics, heterostructures of CDW-forming TMD with graphene exhibit the unique functionalities [4]. Therefore, we supplement our study with a discussion of the electronic properties of heterostructures composed of monolayer TaSSe and monolayer graphene.
The results suggest the novel interesting platform for studies of CDW-related phenomena.
Acknowledgements
We acknowledge Polish high-performance computing infrastructure PLGrid for providing computer facilities and support within computational grant no. PLG/2024/017470.
References
[1] A.-Y. Lu et al., “Janus monolayers of transition metal dichalcogenides,” Nature Nanotechnology, vol. 12, no. 8. Springer Science and Business Media LLC, pp. 744–749, May 15, 2017. https://doi.org/10.1038/nnano.2017.100
[2] K. Szałowski, “Janus Monolayer of 1T-TaSSe: A Computational Study,” Materials, vol. 17, no. 18. MDPI AG, p. 4591, Sep. 19, 2024. https://doi.org/10.3390/ma17184591
[3] C. Cheng et al., “Nonlinear Rashba spin splitting in transition metal dichalcogenide monolayers,” Nanoscale, vol. 8, no. 41. Royal Society of Chemistry (RSC), pp. 17854–17860, 2016. https://doi.org/10.1039/c6nr04235j
[4] K. Szałowski et al., “Spin–orbit and exchange proximity couplings in graphene/1T-TaS2 heterostructure triggered by a charge density wave,” 2D Materials, vol. 10, no. 2. IOP Publishing, p. 025013, Feb. 23, 2023. https://doi.org/10.1088/2053-1583/acbb19
