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The Berreman effect, by which thin films of polar dielectric materials exhibit strong, narrow resonances near their longitudinal optic (LO) phonon frequency, results in strong material interactions...

Hexagonal boron nitride (hBN) is a wide, indirect bandgap semiconductor that holds great promise for optoelectronic devices in the ultraviolet and mid-infrared spectral regimes. The efficiency of o...

In this contribution we compare size-dependent optical properties of PbTe and SnTe nanocrystals (NCs). We demonstrate that the size dependence of the band edge absorption line and the photoluminescence (PL) of PbTe NCs can be quantitatively described by optical transitions between the lowest quantum confined states of conduction and valence bands. In contrast, the optical properties of SnTe NCs are strongly influenced by intrinsic gap states that arise from the inverted band structure that can be described by introducing a negative energy gap Eg < 0. In principle, these intrinsic gap states could be observed directly in PL and absorption of small size SnTe NCs, where the wave functions of these states are spread over the entire NC volume. In our samples, however, these transitions are not observed due to self-doping of SnTe NCs by holes created from negatively charged Sn vacancies. As a result, the absorption is blue-shifted due to filling of the gap states and confined valence band levels by holes (pheno...

Using a 2D metallic grating, we demonstrate the resonant enhancement of the external quantum efficiency of an nBn structure with a 0.5 $\mu \text{m}$ -thick-absorber. A total of two structures were studied with different barrier materials: ternary AlInSb and an InAs/AlInSb superlattice (SL). The device using an SL barrier had a diffusion-limited dark current of 6.7 $\mu \text{A}$ /cm2 at 150 K, which was four times lower than the ternary-barrier device. The surface plasmon polariton (SPP) resonance wavelength for devices with six different grating periods varied as predicted by simulations. The quantum efficiency (QE) was enhanced by up to 56% by coupling to the SPP mode. A peak external QE of 39% was achieved at $4~\mu \text{m}$ with a 1100 nm grating period.

The tunability of the longitudinal localized surface plasmon resonances (LSPRs) of metallic nanoarcs is demonstrated with key relationships identified between geometric parameters of the arcs and their resonances in the infrared. The wavelength of the LSPRs is tuned by the mid-arc length of the nanoarc. The ratio between the attenuation of the fundamental and second order LSPRs is governed by the nanoarc central angle. Beneficial for plasmonic enhancement of harmonic generation, these two resonances can be tuned independently to obtain octave intervals through the design of a non-uniform arc-width profile. Because the character of the fundamental LSPR mode in nanoarcs combines an electric and a magnetic dipole, plasmonic nanoarcs with tunable resonances can serve as versatile building blocks for chiroptical and nonlinear optical devices.

The mid-infrared spectra of many polar materials are dominated by highly reflective reststrahlen bands that occur between the transverse and longitudinal optical phonons. Within the reststrahlen bands, light can couple with optical phonons to support phonon-polariton modes. These modes enhance light-matter interactions through the concentration of light to nanoscale dimensions, and therefore, are particularly promising for mid-infrared nanophotonic applications. Here, we discuss our work on expanding the spectral range over which phonon-polaritons are supported by using new material systems, as well as active tuning of the modes via carrier photoinjection. In particular, we report on the confinement of hyperbolic phonon-polaritons in calcite, a ubiquitous polar material. We also report the use of the LO-phonon-plasmon-coupling (LOPC) effect to actively tune the Berreman mode of a GaN thin film.

We demonstrate a synthetic method to add a ZnS shell, with controlled thickness, to PbS nanocrystals using Zn oleate and thioacetamide as Zn and S precursors. The ZnS shell reaction is self-limiting and deposits approximately a monolayer of ZnS per shell reaction without causing the PbS nanocrystals to Ostwald ripen. The reaction is self-limiting because the sulfur precursor, thioacetamide, is less reactive toward the PbS/ZnS core/shell nanocrystal surface as compared to the Zn oleate precursor present in the reaction solution. To increase the ZnS shell thickness beyond a monolayer, subsequent ZnS shell reactions are modified by adding the thioacetamide 10 minutes before the Zn oleate. This gives the thioacetamide time to react at the PbS/ZnS core/shell nanocrystal surface before the Zn oleate is added. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) shows most ZnS shells lack crystalline order. However, select core/shell nanocrystals have epitaxial crystalline (zinc-b...

Surface phonon polaritons (SPhPs) are attractive alternatives to infrared plasmonics for subdiffractional confinement of infrared light. Localized SPhP resonances in semiconductor nanoresonators are narrow, but that linewidth and the limited extent of the Reststrahlen band limit spectral coverage. To address this limitation, we report active tuning of SPhP resonances in InP and 4H-SiC by photoinjecting free carriers into nanoresonators, taking advantage of the coupling between the carrier plasma and optic phonons to blueshift SPhP resonances. We demonstrate state-of-the-art tuning figures of merit upon continuous-wave excitation (in InP) or pulsed excitation (in 4H-SiC). Lifetime effects cause the tuning to saturate in InP, and carrier redistribution leads to rapid (

Naturally occurring materials with hyperbolic optical properties are attracting considerable interest due to their ability to confine light in small volumes and their resulting potential for applications in photonics. This paper uses a first-principles theoretical approach without adjustable parameters to investigate the hyperbolic optical properties of bulk calcite (CaCO3). This material exhibits natural hyperbolic behavior within its Reststrahlen bands at 1403–1552 and 864–887 cm−1. The calculated results are shown to be in good agreement with our reflectance data obtained from frequency- and polarization-dependent measurements. These results show that calcite is an attractive natural hyperbolic material; in addition, it has the advantage of low losses and is available commercially in a variety of crystal orientations.

Due to its 1 eV band gap and GaAs-matched lattice constant, GaInNAs has long been considered for use in four-junction multi-junction solar cells; but, material quality issues have impeded its use in highly efficient devices. Here, we present an analysis of GaInNAs samples partially hydrogenated via a UV-activated process in which nitrogen-related alloy fluctuations, impurities, and defects have been passivated; remarkably, removing completely the ‘s-shape’ dependence of the photoluminescence while keeping intact the effects of nitrogen substitution, i.e., the band gap of the alloy prior to passivation. Hydrogenation of the optical samples by a UV-activated process has resulted in GaInNAs photoluminescence dominated by the free-excitonic band gap transition, rather than radiative recombination processes from the shallow localized centers that result due to unavoidable alloy fluctuations. This behavior is unique since these centers dominate the low temperature photoluminescence even in the highest quality dilute nitrides. Density functional theory calculations show that the hydrogenation of the N and Ga atoms eliminates the defect levels from the band gap through the formation of H–N centers that act as donors; while at high concentration of hydrogen, Ga–H2–N complexes reside within the continuum. The formation of these hydrogen complexes, along with the incumbent change of the band structure, explains the reduction of emission from the localized centers upon hydrogenation.

Surface phonon polaritons (SPhPs), the surface-bound electromagnetic modes of a polar material resulting from the coupling of light with optic phonons, offer immense technological opportunities for nanophotonics in the infrared (IR) spectral region. However, once a particular material is chosen, the SPhP characteristics are fixed by the spectral positions of the optic phonon frequencies. Here, we provide a demonstration of how the frequency of these optic phonons can be altered by employing atomic-scale superlattices (SLs) of polar semiconductors using AlN/GaN SLs as an example. Using second harmonic generation (SHG) spectroscopy, we show that the optic phonon frequencies of the SLs exhibit a strong dependence on the layer thicknesses of the constituent materials. Furthermore, new vibrational modes emerge that are confined to the layers, while others are centered at the AlN/GaN interfaces. As the IR dielectric function is governed by the optic phonon behavior in polar materials, controlling the optic phonons provides a means to induce and potentially design a dielectric function distinct from the constituent materials and from the effective-medium approximation of the SL. We show that atomic-scale AlN/GaN SLs instead have multiple Reststrahlen bands featuring spectral regions that exhibit either normal or extreme hyperbolic dispersion with both positive and negative permittivities dispersing rapidly with frequency. Apart from the ability to engineer the SPhP properties, SL structures may also lead to multifunctional devices that combine the mechanical, electrical, thermal, or optoelectronic functionality of the constituent layers. We propose that this effort is another step toward realizing user-defined, actively tunable IR optics and sources.

We experimentally observe a significant improvements in polariton lifetime through isotopic enrichment of hexagonal boron nitride (hBN). Commensurate increases in the polariton propagation length are demonstrated via direct imaging of polaritonic standing waves by means of infrared nano-optics, with resolution greater than $\lambda/125$ observed in a preliminary hyperlens design. Our results provide the foundation for a materials-growth-directed approach aimed at realizing the loss control necessary for the development of next generation PhP-based nanophotonic devices.

We report a giant enhancement of the mid-infrared (MIR) magneto-optical complex Kerr angle (polarization change of reflected light) in a variety of materials grown on SiC. In epitaxially-grown multilayer graphene, the Kerr angle is enhanced by a factor of 68, which is in good agreement with Kerr signal modeling. Strong Kerr enhancement is also observed in Fe films grown on SiC and Al-doped bulk SiC. Our experiments and modelling indicate that the enhancement occurs at the high-energy edge of the SiC reststrahlen band where the real component of the complex refractive index n passes through unity. Furthermore, since the signal is greatly enhanced when n=1, the enhancement is predicted to exist over the entire visible/infrared (IR) spectrum for a free-standing film. We also predict similar giant enhancement in both Faraday (transmission) and Kerr rotation for thin films on a metamaterial substrate with refractive index n=-1. This work demonstrates that the substrate used in MOKE measurements must be carefully chosen when investigating magneto-optical materials with weak MOKE signals or when designing MOKE-based optoelectronic devices., 15 pages, 4 figures

Conventional optical components are limited to size-scales much larger than the wavelength of light, as changes to the amplitude, phase and polarization of the electromagnetic fields are accrued gradually along an optical path. However, advances in nanophotonics have produced ultrathin, so-called “flat” optical components that beget abrupt changes in these properties over distances significantly shorter than the free space wavelength. While high optical losses still plague many approaches, phonon polariton materials have demonstrated long lifetimes for localized modes in comparison to plasmon-polariton based nanophotonics. Our work predicts a further 14-fold increase in the optic phonon lifetime and we experimentally report a ~3-fold improvement through isotopic enrichment of hexagonal boron nitride (hBN). We establish commensurate increases in the phonon polariton propagation length via direct imaging of polaritonic standing waves by means of infrared nano-optics. Our results provide the foundation for a materials-growth-directed approach towards realizing the loss control necessary for the development of phonon polariton based nanophotonic devices.

Localized surface phonon-polariton (SPhP) resonances in polar semiconductor nanostructures can provide highly sub-diffractional electromagnetic fields. Furthermore, SPhP resonances offer enhanced resonant quality factors when compared to plasmon-polariton based systems. The various material platforms and nanostructure geometries achievable in polar semiconductors suggest they would be ideal platforms for tunable, long-wavelength photonics applications. Moreover, the constituent atomic basis defines the operating frequency regime for SPhP resonances; tunable from the mid-infrared to THz. Here, we investigate Raman active aspects of SPhP modes in GaN nanowire arrays that are grown via selective area molecular beam epitaxy. We detect strong Raman peaks within the Reststrahlen band of GaN that are not found in the bulk GaN Raman spectrum. These SPhP modes occur around 700 cm^-1 (~ 14.3 microns), offering a spectral region for device applications which is currently not accessible by plasmonic based systems or other SPhP enabled materials. Utilizing selective area epitaxy, we created GaN nanowire arrays with various diameters and pitches, from which the Raman spectra showed tuning of the apparent SPhP resonances. Infrared reflectance measurements were also performed with an FTIR microscope to further establish the physical properties of the resonances. Finally, computational studies of the structures’ reflectance were used to solidify our understanding of the geometry/SPhP-resonance-tuning relationship.

Phonon polaritons, hybrid light-matter quasiparticles resulting from strong coupling of the electromagnetic field with the lattice vibrations of polar crystals are a promising platform for mid-infrared photonics but for the moment there has been no proposal allowing for their electrical pumping. Electrical currents in fact mainly generate longitudinal optical phonons, while only transverse ones participate in the creation of phonon polaritons. We demonstrate how to exploit long-cell polytypes of silicon carbide to achieve strong coupling between transverse phonon polaritons and zone-folded longitudinal optical phonons. We develop a microscopic theory predicting the existence of the resulting hybrid longitudinal-transverse excitations. We then provide an experimental observation by tuning the resonance of a nanopillar array through the folded longitudinal optical mode, obtaining a clear spectral anti-crossing. The hybridisation of phonon polaritons with longitudinal phonons could represent an important step toward the development of phonon polariton-based electrically pumped mid-infrared emitters., Phonon polaritons are promising for mid-infrared photonics but only longitudinal optical phonons are directly accessed by electrical currents. Here, the authors predict and experimentally confirm hybrid longitudinal-transverse excitations. This could lead to phonon polariton-based electrically pumped mid-infrared emitters.

While plasmonics have a broad range of technological applications including infrared photovoltaics and photodetectors, plasmonic metals are subject to high optical losses in the long-wave infrared spectral regime. In order to reduce optical losses in the infrared, alternatives to plasmonic metals are being explored. One promising alternative employs polar dielectric materials, which exhibit a highly-reflective, optically-metallic spectral band (Reststrahlen band), bounded by the LO and TO optical phonons, and are capable of supporting plasmonic-like resonance in the infrared. In polar dielectrics, plasmonic-like resonances, known as surface phonon polariton (SPhP) resonances, arise from a coupling between incident light and collective oscillations of bound lattice charges, which are mediated by the optical phonons. In this study, we have examined the SPhP resonances of SiC nanopillars with constant height of 950 nm and width in the range of 200–400 nm, as a function of their aspect ratio (AR=Length/Width=0.5–16). As the nanopillar width is decreased, we have found that localized SPhP resonances redshift towards the zone folded LO (ZFLO) phonon that is normally not infrared active. However, as localized SPhP resonances are spectrally tuned through the ZFLO mode, we have found that the latter mode becomes infrared active. Furthermore, reflectance measurements have revealed strong coupling between the ZFLO and both the monopolar and dipolar localized SPhP resonances.

A response is provided to comments by Krell concerning the validity of the Hall–Petch relationship and the optical transmission in nanocrystalline ceramics discussed in a recent Acta Materialia paper.

An InGaAsP quantum well with a type-II band alignment is studied using continuous wave power and temperature dependent photoluminescence (PL) spectroscopy. The small energy separation between the ground state and first excited state results in significant thermal carrier redistribution and excited state occupation, particularly, with increasing excitation power and temperature. This state filling is evident as a high-energy shoulder in the PL spectra, the same energy region where in the simplest Planck-description the gradient is considered inversely proportional to carrier temperature. The outcome of an excited state occupation in broadening the high-energy PL tail is to perturb the temperature extracted using this analysis; therefore, the true temperature of carriers is not properly evaluated when significant state filling occurs. In addition, broadening of the PL due to phonons at higher temperatures also distorts (or falsely increases) the non-equilibrium “hot” carrier temperature and as such should be considered when using Planck's relation. The role of these two effects is considered and their mutual effect on the analysis of the extracted hot carrier temperature discussed. Copyright © 2017 John Wiley & Sons, Ltd.

We propose a novel methodology for III-V substrate cost reduction that does not rely on chemical-mechanical polishing (CMP) or low-throughput release layer etching. The details of this process are provided, and results of an economic model for GaAs and InP virtual substrates dictate 20x and 34x reductions to substrate cost, respectively. The impact of modeled assumptions are quantified in order to better understand the potential range of end-goal virtual substrate cost.

A significant improvement in the quality of dilute nitrides has recently led to the ability to reveal depletion widths in excess of 1 μm at 1 eV [1]. The real viability of dilute nitrides for PV has been recently demonstrated with the reporting of a record efficiency of 43.5% from a 4J MJSC including GaInNAs(Sb) [2]. Despite the progress made, these materials remain poorly understood and work continues to improve their lifetime and reproducibility. We have investigated the possibility of improving the functionality of GaInNAs using hydrogenation to selectively passivate mid-gap defects, while preserving the substitutional nitrogen. Temperature dependent photoluminescence measurements of the intrinsic region of a GaInNAs p-i-n solar cell show a classic “s-shape” associated with localization prior to hydrogenation. No sign of this “s-shape” is evident after hydrogenation, despite the retention of substitutional nitrogen as evidenced by the band absorption of 1 eV. The absence of an “s-shape” at low-temperature in hydrogenated GaInNAs is rather curious since, even in high quality nitrides this behavior is due to the emission of isoelectronic centers created via N-As substitution [3]. The potential origins of this behavior will be discussed. The promise of this process for GaInNAs solar cells was demonstrated by a three-fold improvement in the performance of a hydrogenated device with respect to an as-grown reference [4]. [1] “Wide-depletion width GaInNAs solar cells by thermal annealing,” I. R. Sellers, W-S. Tan, K. Smith, S. Hooper, S. Day and M. Kauer, Applied Physics Letters 99, 151111 (2011) [2] “43.5% efficient lattice matched solar cells,” M. Wiemer, V. Sabnis, and H. Yuen, Proc. SPIE 8108, 810804 (2011) [3]“Probing the nature of carrier localization in GaInNAs, epilayers using optical methods,” T. Ysai, B. Barman, T. Scarce, G. Lindberg, M. Fukuda, V. R. Whiteside, J. C. Keay, M. B. Johnson, I. R. Sellers, M. Al Khalfioui, M. Leroux, B. A. Weinstein and A. Petrou. Applied Physics Letters 103, 012104 (2013) [4] “Improved performance in GaInNAs solar cells by hydrogen passivation by hydrogen passivation,” M. Fukuda, V. R. Whiteside, J. C. Keay, A. Meleco, I. R. Sellers, K. Hossain, T. D. Golding, M. Leroux, and M. Al Khalfioui, Applied Physics Letters 106, 141904 (2015)

Plasmonics provides great promise for nanophotonic applications. However, the high optical losses inherent in metal-based plasmonic systems have limited progress. Thus, it is critical to identify alternative low-loss materials. One alternative is polar dielectrics that support surface phonon polariton (SPhP) modes, where the confinement of infrared light is aided by optical phonons. SiC nanopillar arrays support such modes, exhibiting a dipolar resonance transverse to the nanopillar axis and a monopolar resonance associated with the longitudinal axis dependent upon the SiC substrate. Both exhibit exceptionally narrow linewidths (7–24 cm−1), with quality factors of 40–135, which exceed the theoretical limit of plasmonic systems, with extreme subwavelength confinement of (λres3/Veff)1/3 = 50–200. These observations promise to reinvigorate research in SPhP phenomena and their use for nanophotonic applications. Another approach is the use of hyperbolic materials, which have been a focus of the nanophotonics community for their potential to realize sub-diffractional imaging and focusing of light, and novel optical properties, such as a negative index of refraction. The recent observation that hexagonal boron nitride (hBN) is a natural, high efficiency hyperbolic material has led to a surge in research within this field. Due to the low-loss nature, van der Waals bonding and extreme crystal anisotropy, the hyperbolic polaritons within hBN are not only promising for novel applications within the mid-infrared, but is also extremely well suited for fundamental investigations into their resonant behaviors. We have used scattering near-field optical microscopy (s-SNOM) to directly probe the local surface electromagnetic fields of three-dimensionally confined nanostructures of hBN, reporting the first experimental observation of frequency dependent internal angular reflection within a hyperbolic nanostructure, a phenomenon previously theoretically predicted.

It has been demonstrated that nanoresonators fabricated on the surface of polar dielectric materials, such as silicon carbide, are able to sustain plasmonic-like effects in the mid- to long- wave infrared spectral range with impressive figures of merit (Hillenbrand R, Taubner T, Keilmann F, Nature 418:159–162, 2002; Caldwell JD, Glembocki OJ, et al., Nano Lett 13:3690–3697, 2013; Wang T, Li P, et al., Nano Lett 13:5051–5055, 2013). Such phenomena is achieved by exploiting the TO and LO phonons to resonantly excite collective oscillations of bound lattice (Caldwell JD, Lindsay L, et al., Nanophotonics 4:2192–8614, 2015). The fact that these excitations are mediated by bound charges, rather than free charges - such as the case with plasmonic metals, results in extremely low optical losses and enhanced resonant phenomena. As such, polar dielectric nanoresonators may play a role in improving infrared nanophotonic technologies, such as waveguides, sources, near-field optics, solar cells, chemical sensors, biosensors, and photonic circuitry. However, fully realizing this potential, hinges on the ability to precisely control the near-field behavior of polar dielectric nanoresonators. In this work, we use a combination of optical measurements and finite element method simulations to investigate the far- and near-field resonant behavior of structurally-asymmetric, cuboidally-shaped, 4H-SiC nanoresonators with fixed height (\( h=950\ \mathrm{nm} \)), fixed length (\( l=400\ \mathrm{nm} \)), and varying width (\( w=400-6400\ \mathrm{nm} \)). Overall, we observe over 12 polarization-sensitive resonances that can be tuned across the Reststrahlen band of 4H-SiC (\( 796-964\ {\mathrm{cm}}^{-1} \)) (Ellis, C.T. et al. Scientific Reports 6:32959, 2016) by changing the nanopillar aspect ratio (\( AR=w/l=1-16 \)). Futhermore, we find that these resonances exhibit a wide range of near-field radiation patterns that vary from a simple transverse dipole mode that is preserved for all ARs to complex, high-order multipoles with modal profiles that evolve with aspect ratio.

Mechanical strengthening by grain refinement is a method whereby a material’s strength and hardness can be increased by decreasing the average crystallite grain size. The empirical Hall–Petch relationship mathematically describes grain boundary strengthening and provides guidance for a straightforward way to produce stronger materials. While the phenomenon has been widely explored in nanocrystalline metals, the difficulty associated with fabricating high-quality dense nanocrystalline ceramics has left unanswered the question of the validity and extent of the relationship in ceramics. Prior studies suggest the occurrence of an inverse Hall–Petch response in ceramics with grain sizes

Polar dielectrics have garnered much attention as an alternative to plasmonic metals in the mid- to long-wave infrared spectral regime due to their low optical losses. As such, nanoscale resonators composed of these materials demonstrate figures of merit beyond those achievable in plasmonic equivalents. However, until now, only low-order, phonon-mediated, localized polariton resonances, known as surface phonon polaritons (SPhPs), have been observed in polar dielectric optical resonators. In the present work, we investigate the excitation of 16 distinct high-order, multipolar, localized surface phonon polariton resonances that are optically excited in rectangular pillars etched into a semi-insulating silicon carbide substrate. By elongating a single pillar axis we are able to significantly modify the far- and near-field properties of localized SPhP resonances, opening the door to realizing narrow-band infrared sources with tailored radiation patterns. Such control of the near-field behavior of resonances can also impact surface enhanced infrared optical sensing, which is mediated by polarization selection rules, as well as the morphology and strength of resonator hot spots. Furthermore, through the careful choice of polar dielectric material, these results can also serve as the guiding principles for the generalized design of optical devices that operate from the mid- to far-infrared.

Strongly anisotropic media where principal components of the dielectric tensor have opposite signs are called hyperbolic. These materials permit highly directional, volume-confined propagation of slow-light modes at deeply sub-diffractional size scales, leading to unique nanophotonic phenomena. The realization of hyperbolic materials within the optical spectral range has been achieved primarily through the use of artificial structures typically composed of plasmonic metals and dielectric constituents. However, while proof-of-principle experiments have been performed, the high plasmonic losses and inhomogeneity of the structures limit most advances to the laboratory. Recently, hexagonal boron nitride (hBN) was identified as a natural hyperbolic material (NHM), offering a low-loss, homogeneous medium that can operate in the mid-infrared. We have exploited the NHM response of hBN within periodic arrays of conical nanoresonators to demonstrate ‘hyperbolic polaritons,’ deeply sub-diffractional guided waves that propagate through the volume rather than on the surface of a hyperbolic material. We have identified that the polaritons are manifested as a four series of resonances in two distinct spectral bands that have mutually exclusive dependencies upon incident light polarization, modal order, and aspect ratio. These observations represent the first foray into creating NHM building blocks for mid-infrared to terahertz nanophotonic and metamaterial devices. This talk will also discuss potential near-term applications stemming from these developments.

The remarkable electronic properties of graphene strongly depend on the thickness and geometry of graphene stacks. This wide range of electronic tunability is of fundamental interest and has many applications in newly proposed devices. Using the mid-infrared, magneto-optical Kerr effect, we detect and identify over 18 interband cyclotron resonances (CR) that are associated with ABA and ABC stacked multilayers as well as monolayers that coexist in graphene that is epitaxially grown on 4H-SiC. Moreover, the magnetic field and photon energy dependence of these features enable us to explore the band structure, electron-hole band asymmetries, and mechanisms that activate a CR response in the Kerr effect for various multilayers that coexist in a single sample. Surprisingly, we find that the magnitude of monolayer Kerr effect CRs is not temperature dependent. This unexpected result reveals new questions about the underlying physics that makes such an effect possible.

The midinfrared anomalous Hall effect (AHE) can provide critical new information for resolving the controversial origins of the dc AHE in Ca${}_{x}$Sr${}_{1\ensuremath{-}x}$RuO${}_{3}$. The complex Faraday and Kerr angles, as well as the complex Hall conductivity ${\ensuremath{\sigma}}_{xy}$, are measured in Ca${}_{x}$Sr${}_{1\ensuremath{-}x}$RuO${}_{3}$ films as a function of mid- and near-infrared energy $E$ from 0.1 eV to 1.4 eV, magnetic field $H$, temperature $T$, and Ca concentration $x$. For the ferromagnetic state from $x=0$ to 0.4, the $({d}_{xz},{d}_{yz})$-orbital tight-binding model is employed to investigate the quasiparticle role in the low energy response of the AHE ${\ensuremath{\sigma}}_{xy}(E)$ since the Berry curvature term becomes weak at low energies. The infrared Hall sign reversals with $T$ are observed only at $x=0$ and 0.13, which is narrower than the Ca concentration range in which the dc Hall sign reversal appears. The similarity of the infrared Hall angles between paramagnetic and ferromagnetic Ca${}_{x}$Sr${}_{1\ensuremath{-}x}$RuO${}_{3}$ compounds demonstrates the symmetric nature of the Hall response around the quantum phase transition at $x=0.7$.

Magnetic linear dichroism and birefringence in (Ga,Mn)As epitaxial layers is investigated by measuring the polarization plane rotation of reflected linearly polarized light when magnetization lies in the plane of the sample. We report on the spectral dependence of the rotation and ellipticity angles in a broad energy range of 0.12-2.7 eV for a series of optimized samples covering a wide range on Mn-dopings and Curie temperatures and find a clear blue shift of the dominant peak at energy exceeding the host material band gap. These results are discussed in the general context of the GaAs host band structure and also within the framework of the k.p and mean-field kinetic-exchange model of the (Ga,Mn)As band structure. We find a semi-quantitative agreement between experiment and theory and discuss the role of disorder-induced non-direct transitions on magneto-optical properties of (Ga,Mn)As., 18 pages

Office of Naval Research (ONR) (N00014-10-1-0942); Air Force Office of Scientific Research (AFOSR) (FA9550-14-1-0389); NRC/ASEE Postdoctoral Fellowship Naval Research Laboratory Nanoscience Institute (from ONR). Radiation patterns and the resonance wavelength of a plasmonic antenna are significantly influenced by its local environment, particularly its substrate. Here, we experimentally explore the role of dispersive substrates, such as aluminum-or gallium-doped zinc oxide in the near infrared and 4H-silicon carbide in the mid-infrared, upon Au plasmonic antennas, extending from dielectric to metal-like regimes, crossing through epsilon-near-zero (ENZ) conditions. We demonstrate that the vanishing index of refraction within this transition induces a "slowing down" of the rate of spectral shift for the antenna resonance frequency, resulting in an eventual "pinning" of the resonance near the ENZ frequency. This condition corresponds to a strong backward emission with near-constant phase. By comparing heavily doped semiconductors and undoped, polar dielectric substrates with ENZ conditions in the near- and mid-infrared, respectively, we also demonstrate the generality of the phenomenon using both surface plasmon and phonon polaritons, respectively. Furthermore, we also show that the redirected antenna radiation induces a Fano-like interference and an apparent stimulation of optic phonons within SiC. (C) 2016 Optical Society of America Office of Naval Research N00014-10-1-0942 United States Department of Defense Air Force Office of Scientific Research (AFOSR) FA9550-14-1-0389 NRC/ASEE Postdoctoral Fellowship Naval Research Laboratory Nanoscience Institute (ONR)

In this work we present mid-infrared (114 meV–224 meV) polarization-sensitive measurements on multilayer epitaxial graphene, which reveal graphene's rich and complex cyclotron resonant (CR) structure. By using Fourier transform Kerr spectroscopy we are able to separate and identify cyclotron resonances from graphene multilayers with various stacking orders and thicknesses. Moreover, from the identification of the layers present and their measured fundamental band parameters we are able to use these results to better understand previously unexplained CR features in far-infrared (0.1 meV – 87 meV) transmission measurements performed on the same sample.

Investigation of magnetic materials using the first-order magneto-optical Kerr effects (MOKE) is well established and is frequently used in the literature. On the other hand, the utilization of the second-order (or quadratic) magneto-optical (MO) effects for the material research is rather rare. This is due to the small magnitude of quadratic MO signals and the fact that the signals are even in magnetization (i.e., they do not change a sign when the magnetization orientation is flipped), which makes it difficult to separate second-order MO signals from various experimental artifacts. In 2005 a giant quadratic MO effect - magnetic linear dichroism (MLD) - was observed in the ferromagnetic semiconductor (Ga,Mn)As. This discovery not only provided a new experimental tool for the investigation of in-plane magnetization dynamics in (Ga,Mn)As using light at normal incidence, but it also motivated the development of experimental techniques for the measurement of second-order MO effects in general. In this paper we compare four different experimental techniques that can be used to measure MLD and to separate it from experimental artifacts. We show that the most reliable results are obtained when the harmonic dependence of MLD on a mutual orientation of magnetization and light polarization plane is used together with the in-situ rotation of the sample followed by the magnetic field-induced rotation of magnetization. Using this technique we measure the MLD spectra of (Ga,Mn)As in a broad spectral range from 0.1 eV to 2.7 eV and we observe that MLD has a comparable magnitude as polar MOKE signals in this material., Comment: 17 pages, 7 figures

We report the development of new terahertz techniques for rapidly measuring the complex Faraday angle in systems with broken time-reversal symmetry using the cyclotron resonance of a GaAs two-dimensional electron gas in a magnetic field as a system for demonstration of performance. We have made polarization modulation, high sensitivity (< 1 mrad) narrow band rotation measurements with a CW optically pumped molecular gas laser, and by combining the distinct advantages of terahertz (THz) time domain spectroscopy and polarization modulation techniques, we have demonstrated rapid broadband rotation measurements to < 5 mrad precision., 25 pages including 7 figures, introduces use of rotating polarizer with THz TDS for Complex Faraday Angle determination

We demonstrate up to 39% resonant enhancement of the quantum efficiency (QE) of a low dark current nBn midwave infrared photodetector with a 0.5 μm InAsSb absorber layer. The enhancement was achieved by using a 1D plasmonic grating to couple incident light into plasmon modes propagating in the plane of the device. The plasmonic grating is composed of stripes of deposited amorphous germanium overlaid with gold. Devices with and without gratings were processed side-by-side for comparison of their QEs and dark currents. The peak external QE for a grating device was 29% compared to 22% for a mirror device when the illumination was polarized perpendicularly to the grating lines. Additional experiments determined the grating coupling efficiency by measuring the reflectance of analogous gratings deposited on bare GaSb substrates.

A photoluminescence (PL) spectroscopy study of the bulk quaternary alloy InAlAsSb is presented. Samples were grown lattice-matched to InP by molecular beam epitaxy and two different growth temperatures of 450 °C and 325 °C were compared. Interpolated bandgap energies suggest that the development of this alloy would extend the range of available direct bandgaps attainable in materials lattice-matched to InP to energies as high as 1.81 eV. However, the peak energy of the observed PL emission is anomalously low for samples grown at both temperatures, with the 450 °C sample showing larger deviation from the expected bandgap. A fit of the integrated PL intensity (I) to an I∝Pk dependence, where P is the incident power density, yields characteristic coefficients k = 1.05 and 1.18 for the 450 °C and 325 °C samples, respectively. This indicates that the PL from both samples is dominated by excitonic recombination. A blue-shift in the peak emission energy as a function of P, along with an S-shaped temperature depe...

We measure the infrared (wavelength 11 - 0.8 microns; energy E = 0.1 - 1.5 eV) Faraday rotation and ellipticity in GaAs, BaF2, LaSrGaO4, LaSrAlO4, and ZnSe. Since these materials are commonly used as substrates and windows in infrared magneto-optical measurements, it is important to measure their Faraday signals for background subtraction. These measurement also provide a rigorous test of the accuracy and sensitivity of our unique magneto-polarimetry system. The light sources used in these measurements consist of gas and semiconductor lasers, which cover 0.1 - 1.3 eV, as well as a custom-modified prism monochromator with a Xe lamp, which allows continuous broadband measurements in the 0.28 - 1.5 eV energy range. The sensitivity of this broad-band system is approximately 10 micro-rad. Our measurements reveal that the Verdet coefficients of these materials are proportional to $1/\lambda^2$, which is expected when probing with radiation energies below the band gap. Reproducible ellipticity signals are also seen, which is unexpected since the radiation is well below the absorption edge of these materials, where no magnetic circular dichroism or magnetic linear birefringence should occur. We suggest that the Faraday ellipticity is produced by the static retardance (Rs) of the photoelastic modulator (PEM) and other optical elements such as windows, which convert the polarization rotation produced by the sample into ellipticity. This static retardance is experimentally determined by the ratio of the Faraday rotation and ellipticity signals, which are induced by either applying a magnetic field to a sample or mechanically rotating the polarization of light incident on the PEM and/or other optical components.

We use scanning near-field optical microscopy to study the response of hexagonal boron nitride nanocones at infrared frequencies, where this material behaves as a hyperbolic medium. The obtained images are dominated by a series of hot rings that occur on the sloped sidewalls of the nanocones. The ring positions depend on the incident laser frequency and the nanocone shape. Both dependences are consistent with directional propagation of hyperbolic phonon polariton rays that are launched at the edges and zigzag through the interior of the nanocones, sustaining multiple internal reflections off the sidewalls. Additionally, we observe a strong overall enhancement of the near-field signal at discrete resonance frequencies. These resonances attest to low dielectric losses that permit coherent standing waves of the sub-diffractional polaritons to form. We comment on potential applications of such shape-dependent resonances and the field concentration at the hot rings., Accepted for publication in Nano Letters