Layer‐controlled nonlinear terahertz valleytronics in two‐dimensional semimetal and semiconductor PtSe₂

Abstract

Platinum diselenide () is a promising two‐dimensional (2D) material for the terahertz (THz) range as, unlike other transition metal dichalcogenides (TMDs), its bandgap can be uniquely tuned from a semiconductor in the near‐infrared to a semimetal with the number of atomic layers. This gives the material unique THz photonic properties that can be layer‐engineered. Here, we demonstrate that a controlled THz nonlinearity—tuned from monolayer to bulk —can be realized in wafer size polycrystalline through the generation of ultrafast photocurrents and the engineering of the bandstructure valleys. This is combined with the layer interaction with the substrate for a broken material centrosymmetry, permitting a second order nonlinearity. Further, we show layer dependent circular dichroism, where the sign of the ultrafast currents and hence the phase of the emitted THz pulse can be controlled through the excitation of different bandstructure valleys. In particular, we show that a semimetal has a strong dichroism that is absent in the monolayer and few layer semiconducting limit. The microscopic origins of this TMD bandstructure engineering are highlighted through detailed DFT simulations, and shows the circular dichroism can be controlled when becomes a semimetal and when the K‐valleys can be excited. As well as showing that is a promising material for THz generation through layer controlled optical nonlinearities, this work opens up a new class of circular dichroism materials beyond the monolayer limit that has been the case of traditional TMDs, and impacting a range of domains from THz valleytronics, THz spintronics to harmonic generation.image

Atomic‐Layer Controlled Transition from Inverse Rashba–Edelstein Effect to Inverse Spin Hall Effect in 2D PtSe2 Probed by THz Spintronic Emission

“…The THz E‐field is seven times less for PtSe 2 than for Pt. Considering that the absorption length at the pump laser wavelength (λ = 800 nm) of Pt (respectively PtSe 2 ) is 10 nm [ 51 ] (respectively 5 nm, [ 52,53 ] ) we can deduce θ SHE (Pt)/θ SHE (PtSe 2 ) ≈ 3.5. By spin pumping (see Figure , Supporting Information), we find θ SHE (Pt)/θ SHE (PtSe 2 ) ≈ 9.…”

Defect-induced helicity dependent terahertz emission in Dirac semimetal PtTe2 thin films

“…In this regard, polarized terahertz (THz) emission spectroscopy based on ultrafast femtosecond lasers is a powerful optical tool for generating and detecting ultrafast spin photocurrents 24 , 25 . Very recently, THz emission has been observed in centrosymmetric Dirac semimetal PtSe 2 films due to the photon drag effect 26 , 27 and a second nonlinearity from a structural asymmetry 28 . Remarkably, Luo et al 5 observed the light-induced transient phase transition and hence giant photocurrent (i.e., THz emission) in bulk Dirac semimetal ZrTe 5 .…”