Observation of Negative Terahertz Photoconductivity in Large Area Type-II Dirac Semimetal PtTe2

Abstract

As a newly emergent type-II Dirac semimetal, Platinum Telluride (PtTe 2 ) stands out from other 2D noble-transition-metal dichalcogenides for the unique structure and novel physical properties, such as high carrier mobility, strong electron-phonon coupling and tunable bandgap, which make the PtTe 2 a good candidate for applications in optoelectronics, valleytronics and far infrared detectors. Although the transport properties of PtTe 2 have been studied extensively, the dynamics of the nonequilibrium carriers remain nearly uninvestigated. Herein we employ optical pump-terahertz (THz) probe spectroscopy (OPTP) to systematically study the 2 photocarrier dynamics of PtTe 2 thin films with varying pump fluence, temperature, and film thickness. Upon photoexcitation the THz photoconductivity (PC) of 5 nm PtTe 2 film shows abrupt increase initially, while the THz PC changes into negative value in a subpicosecond time scale, followed by a prolonged recovery process that lasted hundreds of picoseconds (ps). This unusual THz PC response observed in the 5 nm PtTe 2 film was found to be absent in a 2 nm PtTe 2 film. We assign the unexpected negative THz PC as the small polaron formation due to the strong electron-E g -mode phonon coupling, which is further substantiated by pump fluence-and temperature-dependent measurements as well as the Raman spectroscopy. Moreover, our investigations give a subpicosecond time scale of sequential carrier cooling and polaron formation. The present study provides deep insights into the underlying dynamics evolution mechanisms of photocarrier in type-II Dirac semimetal upon photoexcitation, which is fundamental importance for designing PtTe 2 -based optoelectronic devices.

Wafer‐scale patterned growth of type‐II Dirac semimetal platinum ditelluride for sensitive room‐temperature terahertz photodetection

“…In the meanwhile, type‐II DSM PtTe 2 allows a novel undamped surface plasmon resonance mode in THz region since the presence of electron and hole pockets near the Fermi surface 43 . And, the PtTe 2 also exhibits the transient THz transmission caused by the carriers cooling and the formation of small polaron, which makes PtTe 2 with enhanced absorption and fast response capability for THz band 44 . These unique energy band structure and topologically protected nontrivial electronic properties of PtTe 2 endow it with unique superiority for THz bands detection 40,45 …”

“…43 And, the PtTe 2 also exhibits the transient THz transmission caused by the carriers cooling and the formation of small polaron, which makes PtTe 2 with enhanced absorption and fast response capability for THz band. 44 These unique energy band structure and topologically protected nontrivial electronic properties of PtTe 2 endow it with unique superiority for THz bands detection. 40,45 However, the present PtTe 2 THz PDs mainly rely on mechanically exfoliated nanosheets and chemical vapor deposition (CVD) grown nanoflakes, 40,45 which are of high quality and suitable for fundamental research, but the resulting small size and uncontrollable thickness prevent its large-scale THz applications in industry.…”

Optically Controlling Broadband Terahertz Modulator Based on Layer-Dependent PtSe2 Nanofilms

“…One needs to find the material with high carrier mobility, short carrier relaxation time, and significant surface conductivity for the modulator [26,27]. As novel transition metal dichalcogenide (TMDCs) materials, PtSe 2 and its parental compounds such as PtTe 2 , PdTe 2 , and NiTe 2 have been widely studied by researchers for their unique energy band structure and novel physical properties [28][29][30][31]. However, PtSe 2 stands out due to its unique properties of having high carrier mobility, an adjustable band gap of 0-1.2 eV, and fast response characteristics [32][33][34].…”

Dynamic switching between bound states in the continuum (BIC) and quasi-BIC based on a Dirac semimetal terahertz metasurface

“…Thus, a material referred to as “3D graphene”, a Dirac semimetal, has attracted significant research attention. 26–28 Dirac semimetals exhibit excellent electromagnetic properties in the THz band and have been applied to tunable metamaterial absorbers, 29,30 plasmon-induced transparency, 31,32 asymmetric transmission, 33,34 polarization converters, 35,36 and dynamic BIC metasurfaces. 37,38 Thus, Dirac semimetals can serve as a basis for the realization of dynamically tunable BIC metasurfaces in the THz band.…”