Quantitative Nanoinfrared Spectroscopy of Anisotropic van der Waals Materials

Ruta, Francesco L.; Sternbach, Aaron; Dieng, Adji B.; McLeod, Alexander; Basov, D. N.

doi:10.1021/acs.nanolett.0c02671

Cited by 22 publications

(11 citation statements)

References 47 publications

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“…Here, we use  = 3.8. 35 The final term in eq. ( 2) is the potential drop developed across TOS and graphene as a result of charge transfer, which can be determined from Poisson's equation.…”

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confidence: 99%

High carrier mobility in graphene doped using a monolayer of tungsten oxyselenide

et al. 2021

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Highly doped graphene holds promise for next-generation electronic and photonic devices.However, chemical doping cannot be precisely controlled, and introduces external disorder that significantly diminishes the carrier mobility and therefore the graphene conductivity. Here, we show that monolayer tungsten oxyselenide (TOS) created by oxidation of WSe2 acts as an efficient and low-disorder hole-dopant for graphene. When the TOS is directly in contact with graphene, the induced hole density is 3 × 10 13 cm -2 , and the room-temperature mobility is 2,000 cm 2 /V•s, far exceeding that of chemically-doped graphene. Inserting WSe2 layers between the TOS and graphene tunes the induced hole density as well as reduces charge disorder such that the mobility exceeds 20,000 cm 2 /V•s and reaches the limit set by acoustic phonon scattering, resulting in sheet resistance below 50 /□. An electrostatic model based on work-function mismatch accurately describes the tuning of the carrier density with WSe2 interlayer thickness. These films show unparalleled performance as transparent conductors at telecommunication wavelengths, as shown by measurements of transmittance in thin films and insertion loss in photonic ring resonators. This work opens up new avenues in optoelectronics incorporating two-dimensional heterostructures including infrared transparent conductors, electro-phase modulators, and various junction devices.

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confidence: 99%

High carrier mobility in graphene doped using a monolayer of tungsten oxyselenide

et al. 2021

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“…Polarized light microscopy is an established approach to characterize the local orientation of structural domains in anisotropic crystalline matter. , This approach is, however, diffraction-limited, preventing the characterization of nanotextured domain patterns. SNOM can overcome the diffraction limit, but the nano-optical signal is a complicated combination of the optical responses along different crystal axes. , Since the SNOM signal effectively averages optical responses from all directions, the optical contrast between structural domains is usually slight as differences in the nano-optical signal for different crystal orientations tend to be minor . However, the optical contrast between structural domains can be strongly enhanced by phonons in anisotropic samples, , which are sensitive to the local structural orientation.…”

Section: Results and Discussionmentioning

confidence: 99%

Nanotextured Dynamics of a Light-Induced Phase Transition in VO₂

et al. 2021

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We investigate transient nanotextured heterogeneity in vanadium dioxide (VO 2 ) thin films during a light-induced insulator-to-metal transition (IMT). Timeresolved scanning near-field optical microscopy (Tr-SNOM) is used to study VO 2 across a wide parameter space of infrared frequencies, picosecond time scales, and elevated steady-state temperatures with nanoscale spatial resolution. Room temperature, steady-state, phonon enhanced nano-optical contrast reveals preexisting "hidden" disorder. The observed contrast is associated with inequivalent twin domain structures. Upon thermal or optical initiation of the IMT, coexisting metallic and insulating regions are observed. Correlations between the transient and steady-state nano-optical textures reveal that heterogeneous nucleation is partially anchored to twin domain interfaces and grain boundaries. Ultrafast nanoscopic dynamics enable quantification of the growth rate and bound the nucleation rate. Finally, we deterministically anchor photoinduced nucleation to predefined nanoscopic regions by locally enhancing the electric field of pump radiation using nanoantennas and monitor the on-demand emergent metallicity in space and time.

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“…In analyzing the diamond-shaped case, we again use the parametrization (70) in terms of θ . With the piecewise approximation for the Fermi velocity, the angular integrations over θ in Eq.…”

Section: Reference Geometry: Diamond-shaped Configurationmentioning

confidence: 99%

“…The reduced symmetry of the electronic dispersion may also be accompanied by a variation of the momentum-relaxation rates along different spatial coordinates. The ensuing anisotropic conductivity tensor generates a sizable anisotropy in the electrodynamic properties of novel materials, as observed in quasi-2D layered systems like delafossites [44,[60][61][62][63][64][65] and van der Waals compounds [66][67][68][69][70][71]. Notice that, if the local (q = 0) conductivity tensor is not rotational-invariant, the electrodynamic anisotropy manifests itself already in the local limit.…”

Section: Introductionmentioning

confidence: 99%

Kinetic theory of the non-local electrodynamic response in anisotropic metals: skin effect in 2D systems

Valentinis¹,

Baker²,

Bonn³

et al. 2022

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The electrodynamic response of ultra-pure materials at low temperatures becomes spatially non-local. This non-locality gives rise to phenomena such as hydrodynamic flow in transport and the anomalous skin effect in optics. In systems characterized by an anisotropic electronic dispersion, the non-local dynamics becomes dependent on the relative orientation of the sample with respect to the applied field, in ways that go beyond the usual, homogeneous response. Such orientational dependence should manifest itself not only in transport experiments, as recently observed, but also in optical spectroscopy. In this paper we develop a kinetic theory for the distribution function and the transverse conductivity of two-and three-dimensional Fermi systems with anisotropic electronic dispersion. By expanding the collision integral into the eigenbasis of a collision operator, we include momentum-relaxing scattering as well as momentum-conserving collisions. We examine the isotropic 2D case as a reference, as well as anisotropic hexagonal and square Fermi-surface shapes. We apply our theory to the quantitative calculation of the skin depth and the surface impedance, in all regimes of skin effect. We find qualitative differences between the frequency dependence of the impedance in isotropic and anisotropic systems. In the latter case, we study the orientational dependence of skin effect, thus providing guidance for the experimental study of non-local optical effects.

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Quantitative Nanoinfrared Spectroscopy of Anisotropic van der Waals Materials

Cited by 22 publications

References 47 publications

High carrier mobility in graphene doped using a monolayer of tungsten oxyselenide

High carrier mobility in graphene doped using a monolayer of tungsten oxyselenide

Nanotextured Dynamics of a Light-Induced Phase Transition in VO₂

Kinetic theory of the non-local electrodynamic response in anisotropic metals: skin effect in 2D systems

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Quantitative Nanoinfrared Spectroscopy of Anisotropic van der Waals Materials

Cited by 22 publications

References 47 publications

High carrier mobility in graphene doped using a monolayer of tungsten oxyselenide

High carrier mobility in graphene doped using a monolayer of tungsten oxyselenide

Nanotextured Dynamics of a Light-Induced Phase Transition in VO2

Kinetic theory of the non-local electrodynamic response in anisotropic metals: skin effect in 2D systems

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Nanotextured Dynamics of a Light-Induced Phase Transition in VO₂