Phonon-induced near-field resonances in multiferroic BiFeO3 thin films at infrared and THz wavelengths

Wehmeier, Lukas; Nörenberg, Tobias; Oliveira, Thales V. A. G. de; Klopf, J. Michael; Yang, So Young; Martin, Lane W.; Ramesh, R.; Eng, Lukas M.; Kehr, Susanne C.

doi:10.1063/1.5133116

Cited by 27 publications

(22 citation statements)

References 55 publications

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“…Free Electron Lasers (FEL) offer the advantage of broad continuous tunability combined with an extremely narrow spectral bandwidth (~ 0.5 -2.5 % FWHM). The higher spectral brightness of the FEL compensates for the reduced detection sensitivity at THz frequencies 37,38 .…”

Section: Methodsmentioning

confidence: 99%

Nanoscale‐Confined Terahertz Polaritons in a van der Waals Crystal

et al. 2020

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Electromagnetic field confinement is crucial for nanophotonic technologies, since it allows for enhancing light–matter interactions, thus enabling light manipulation in deep sub‐wavelength scales. In the terahertz (THz) spectral range, radiation confinement is conventionally achieved with specially designed metallic structures—such as antennas or nanoslits—with large footprints due to the rather long wavelengths of THz radiation. In this context, phonon polaritons—light coupled to lattice vibrations—in van der Waals (vdW) crystals have emerged as a promising solution for controlling light beyond the diffraction limit, as they feature extreme field confinements and low optical losses. However, experimental demonstration of nanoscale‐confined phonon polaritons at THz frequencies has so far remained elusive. Here, it is provided by employing scattering‐type scanning near‐field optical microscopy combined with a free‐electron laser to reveal a range of low‐loss polaritonic excitations at frequencies from 8 to 12 THz in the vdW semiconductor α‐MoO3. In this study, THz polaritons are visualized with: i) in‐plane hyperbolic dispersion, ii) extreme nanoscale field confinement (below λo ⁄75), and iii) long polariton lifetimes, with a lower limit of >2 ps.

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Section: Methodsmentioning

confidence: 99%

Nanoscale‐Confined Terahertz Polaritons in a van der Waals Crystal

et al. 2020

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“…THz-SNOMs are being successfully applied to an expanding list of materials and interesting problems. For example, THz-SNOM methods have provided insights into nanoscale studies of electronic phase separation in the vicinity of the insulator-to-metal transition in VO 2 23 , 28 29 , the plasmonic response of graphene 26 – 31 , free carrier distributions in nanodevices 32 , 33 , and phonon resonances in multiferroic materials 34 .…”

Section: Introductionmentioning

confidence: 99%

Terahertz response of monolayer and few-layer WTe2 at the nanoscale

et al. 2021

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Tungsten ditelluride (WTe2) is an atomically layered transition metal dichalcogenide whose physical properties change systematically from monolayer to bilayer and few-layer versions. In this report, we use apertureless scattering-type near-field optical microscopy operating at Terahertz (THz) frequencies and cryogenic temperatures to study the distinct THz range electromagnetic responses of mono-, bi- and trilayer WTe2 in the same multi-terraced micro-crystal. THz nano-images of monolayer terraces uncovered weakly insulating behavior that is consistent with transport measurements. The near-field signal on bilayer regions shows moderate metallicity with negligible temperature dependence. Subdiffractional THz imaging data together with theoretical calculations involving thermally activated carriers favor the semimetal scenario with $$\Delta \approx -10\,{{{\rm{meV}}}}$$ Δ ≈ − 10 meV over the semiconductor scenario for bilayer WTe2. Also, we observed clear metallic behavior of the near-field signal on trilayer regions. Our data are consistent with the existence of surface plasmon polaritons in the THz range confined to trilayer terraces in our specimens. Finally, data for microcrystals up to 12 layers thick reveal how the response of a few-layer WTe2 asymptotically approaches the bulk limit.

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“…The schematic of the THz s-SNOM setup is shown in Figure 1 A. This THz near-field imaging system operates in the self-homodyne scheme ( Wehmeier et al., 2020 ; de Oliveira et al., 2020 ) with a bilateral symmetric light path and no asymmetric Michelson interferometer is used in order to minimize the loss of the THz energy as the beam splitter will cause at least three-quarters of the energy loss. The electrically pumped THz QCL is placed in a cryostat at the temperature of 10 K and emits a 4.2 THz (red) beam.…”

Section: Resultsmentioning

confidence: 99%