Giant photon momentum locked THz emission in a centrosymmetric Dirac semimetal

Abstract

Strong second-order optical nonlinearities often require broken material centrosymmetry, thereby limiting the type and quality of materials used for nonlinear optical devices. Here, we report a giant and highly tunable terahertz (THz) emission from thin polycrystalline films of the centrosymmetric Dirac semimetal PtSe 2 . Our PtSe 2 THz emission is turned on at oblique incidence and locked to the photon momentum of the incident pump beam. Notably, we find an emitted THz efficiency that is giant: It is two orders of magnitude larger than the standard THz-generating nonlinear crystal ZnTe and has values approaching that of the noncentrosymmetric topological material TaAs. Further, PtSe 2 THz emission displays THz sign and amplitude that is controlled by the incident pump polarization and helicity state even as optical absorption is only weakly polarization dependent and helicity independent. Our work demonstrates how photon drag can activate pronounced optical nonlinearities that are available even in centrosymmetric Dirac materials.

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

“…Note that the THz emission efficiency of our PtTe 2 films is three order magnitude larger than that of the standard ZnTe (Supplementary Fig. 13 and Supplementary Table 1 ), and it is comparable to those of topological semimetals 13 , 27 . The linear pump-fluence dependence of THz emission indicates that the emitted THz signals are dominated by a second-order nonlinear effect (Supplementary Fig.…”

“…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 .…”

Highly Efficient Spintronic Terahertz Emitter Utilizing a Large Spin Hall Conductivity of Type-II Dirac Semimetal PtTe2

“…51 These nonlinear optical effects are the primary cause of THz emission in single-layer (only NM layer) systems. 29,52 Because PtTe 2 has a centrosymmetric structure, it does not result in any THz emission under normal laser incidence, which is also evident in Figure 2b. Therefore, the polarization angle-dependent results shown in panels b and c of Figure 3 confirm that the entire THz emission from the PtTe 2 /Co-STE can be attributed to the SCC phenomena.…”

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

“…Prior investigations of the nonlinear properties of have been restricted to as a saturable absorber with no demonstrations on the layer dependent nonlinearities 28 . Very recent studies have investigated THz photocurrents in but were limited to a single thickness of 2.4 nm 29 or 50 nm, 30 limiting the understanding of the effect of the bandstructure. Further, these studies have assumed an entirely centrosymmetric nature and neglected the effect of the substrate.…”