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Ultra-long carrier lifetime in neutral graphene-hBN van der Waals heterostructures under mid-infrared illumination
摘要： Graphene/hBN heterostructures are promising active materials for devices in the THz domain, such as emitters and photodetectors based on interband transitions. Their performance requires long carrier lifetimes. However, carrier recombination processes in graphene possess sub-picosecond characteristic times for large non-equilibrium carrier densities at high energy. An additional channel has been recently demonstrated in graphene/hBN heterostructures by emission of hBN hyperbolic phonon polaritons (HPhP) with picosecond decay time. Here, we report on carrier lifetimes in graphene/hBN Zener-Klein transistors of ~30 ps for photoexcited carriers at low density and energy, using mid-infrared photoconductivity measurements. We further demonstrate the switching of carrier lifetime from ~30 ps (attributed to interband Auger) down to a few picoseconds upon ignition of HPhP relaxation at finite bias and/or with infrared excitation power. Our study opens interesting perspectives to exploit graphene/hBN heterostructures for THz lasing and highly sensitive THz photodetection as well as for phonon polariton optics.
关键词： photodetectors,mid-infrared,phonon polaritons,van der Waals heterostructures,THz,Graphene,carrier lifetime,hBN
更新于2025-09-23 15:19:57
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Thermostimulated THz Radiation Emission of GaAs at Surface Plasmon-Phonon Polariton Frequencies
摘要： The THz radiation reflection, absorption and emission spectra of conductive n-GaAs/air surface are considered. The influence of thermostimulated surface plasmon-phonon (SPP) polariton oscillations on THz radiation reflection, absorption and emission of high conductivity GaAs polished plates with electron density n = 7·1017 cm–3 and 4·1018 cm–3 and thickness of 350 μm is studied experimentally. The frequencies of thermostimulated transverse and longitudinal optical phonons and SPP oscillations, which characterize a heated lattice state, were determined. It is found that the heated highly doped interface layer (GaAs/air) emits the THz radiation at selected frequencies of SPP oscillations in the (7 – 8) THz and (10 – 15) THz ranges. It is shown that thermal heating of the GaAs/air interface enhances the absorption of the incident THz radiation. The huge decrease of the incident radiation reflectivity at the SPP frequencies with an increase of GaAs temperature is observed experimentally.
关键词： surface plasmon-phonon polaritons,black-body radiation,GaAs,thermostimulated THz radiation emission
更新于2025-09-19 17:15:36
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Surface Polariton‐Like s‐Polarized Waveguide Modes in Switchable Dielectric Thin Films on Polar Crystals
摘要： Surface phonon polaritons (SPhPs) and surface plasmon polaritons (SPPs), evanescent modes supported by media with negative permittivity, are a fundamental building block of nanophotonics. These modes are unmatched in terms of field enhancement and spatial confinement, and dynamical all-optical control can be achieved, e.g., by employing phase-change materials. However, the excitation of surface polaritons in planar structures is intrinsically limited to p-polarization. On the contrary, waveguide modes in high-permittivity films can couple to both p- and s-polarized light, and in thin films, their confinement can become comparable to surface polaritons. Here, it is demonstrated that the s-polarized waveguide mode in a thin Ge3Sb2Te6 (GST) film features a similar dispersion, confinement, and electric field enhancement as the SPhP mode of the silicon carbide (SiC) substrate, while even expanding the allowed frequency range. Moreover, it is experimentally shown that switching the GST film grants nonvolatile control over the SPhP and the waveguide mode dispersions. An analytical model is provided for the description of the GST/SiC waveguide mode and it is shown that the concept is applicable to the broad variety of polar crystals throughout the infrared spectral range. As such, complementarily to the polarization-limited surface polaritons, the s-polarized waveguide mode constitutes a promising additional building block for nanophotonic applications.
关键词： waveguide modes,infrared spectral range,phase-change materials,surface plasmon polaritons,silicon carbide,nanophotonics,Ge3Sb2Te6,surface phonon polaritons,s-polarized light
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Soliton Self-Compression and Spectral Broadening of 1 μm Femtosecond Pulses in Single-Domain KTiOPO <sub/>4</sub>
摘要： Efficient, diode-pumped high energy femtosecond laser systems around 1 μm based on Yb-gain media are readily commercially available. However, owing to the gain bandwidth limitations, the pulses generated in such lasers are substantially longer than the ones generated in Ti:Sapphire systems. A simple, energy-scalable pulse self-compression scheme for the pulses around 1 μm thus would be of great interest for many applications, including time-resolved pump-probe spectroscopy, high-harmonics generation, etc. The self-phase modulation during nonlinear propagation in filaments in gasses is often employed for pulse self-compression [1,2]. Such schemes typically require rather bulky setups and careful control of group velocity dispersion. Some years ago it has been shown theoretically that Raman-active molecules in gaseous form could be used for mid-infrared pulse compression [3]. Here we exploit highly-efficient interaction of optical pulses with phonon-polaritons in KTiOPO4 (KTP) [4] for self-compression of fs pulses at 1 μm. The experimental setup consists of a 1030 nm femtosecond pump laser. The pulses were loosely focused by a f=150 mm lens to a beam waist with 1/e2 radius of 160 μm in a 10 mm-long, 5mm-thick single-domain KTP sample. The pulses were polarized along the c-axis of the crystal. The dependence of the pulse output spectrum as a function of the beam focus position in the crystal is shown in Fig.1 (a), where 300 fs full width at half maximum (FWHM) input pulses from a fiber-based system were employed. The broadest spectrum was obtained with the focal plane being located close to the entrance of the crystal. We employed time-resolved digital holography [5] to verify the coupling of the optical pulse with phonon-polariton wave during propagation through the crystal. Characterization experiments with 173 fs FWHM pulses derived from a commercial solid-state laser system were conducted using a custom-built d-scan setup [6]. The setup included chirped mirrors covering the spectral region of Fig.1 (a).
关键词： Femtosecond Pulses,KTiOPO4,Spectral Broadening,Soliton Self-Compression,Phonon-polaritons
更新于2025-09-11 14:15:04
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Cavity quantum-electrodynamical polaritonically enhanced electron-phonon coupling and its influence on superconductivity
摘要： So far, laser control of solids has been mainly discussed in the context of strong classical nonlinear light-matter coupling in a pump-probe framework. Here, we propose a quantum-electrodynamical setting to address the coupling of a low-dimensional quantum material to quantized electromagnetic fields in quantum cavities. Using a prototypical model system describing FeSe/SrTiO3 with electron-phonon long-range forward scattering, we study how the formation of phonon polaritons at the two-dimensional interface of the material modifies effective couplings and superconducting properties in a Migdal-Eliashberg simulation. We find that through highly polarizable dipolar phonons, large cavity-enhanced electron-phonon couplings are possible, but superconductivity is not enhanced for the forward-scattering pairing mechanism due to the interplay between coupling enhancement and mode softening. Our results demonstrate that quantum cavities enable the engineering of fundamental couplings in solids, paving the way for unprecedented control of material properties.
关键词： phonon polaritons,electron-phonon coupling,superconductivity,cavity quantum electrodynamics,quantum materials
更新于2025-09-10 09:29:36
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Oriented Asymmetric Wave Propagation and Refraction Bending in Hyperbolic Media
摘要： Crystal quartz is a well-known anisotropic medium with optically active phonons in the THz region where hyperbolic phonon-polaritons can be excited. Here, we use this material to illustrate how the behavior of bulk and surface hyperbolic polaritons can be drastically modified by changing the orientation of the crystal’s anisotropy axis with respect to its surface. We demonstrate, both theoretically and experimentally, phenomena associated with the orientation of hyperbolic media. We show the consequences of changes in the crystal’s orientation in various ways, such as the modification of the effective reststrahl regions and associated surface phonon polariton dispersion. Of particular significance, however, is the transmission behavior of radiation passing through a rotated hyperbolic crystal. Here, even a small rotation of the optical axes with respect to the crystal surface can lead to a very large degree of asymmetry in the transmitted intensity. In addition, the refracting angle (which in a hyperbolic medium may correspond to negative refraction and slab lensing behavior) itself becomes asymmetric, so that a slab lens with a laterally displaced image becomes possible. We discuss some of the possible consequences of these types of effects.
关键词： Surface Polaritons,Hyperbolic Media,Attenuated Total Reflection,Negative Refraction,Phonon-Polaritons
更新于2025-09-09 09:28:46