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We explore the symmetry-breaking in cuprate high temperature superconductors (HTS) as a function of energy (117–2330 meV), doping, and temperature (30–300 K). We measure the Faraday rotation angle $\theta_{\mathrm{F}}$ of transmitted radiation through thin YBa 2 Cu 3 O 7-x (YBCO) films as the sample is rotated. We observe twofold rotational symmetry in $\theta_\mathrm{{F}}$ , which is associated with linear dichroism (LD) that can be generally associated with symmetry breaking. The LD signal shows a peak in the few hundred meV range and is strongest in under-doped films.

We measure as a function of sample orientation, doping, temperature, and energy, the Faraday rotation of linearly polarized THz light by high temperature cuprate superconductors. We observe a linear dichroism signal which increases with decreasing frequency and may exhibit resonances in the THz (1–6 meV) range. Preliminary results also show strong temperature dependence to the Faraday rotation signal.

By measuring the polarization changes in THz, infrared, and visible radiation over an extended energy range (3-2330 meV), we observe symmetry-breaking in cuprate high temperature superconductors over wide energy, doping, and temperature ranges. We measure the polarization rotation and ellipticity of transmitted radiation though thin films as the sample is rotated. We observe a two-fold rotational symmetry in the Faraday angle, which is associated with linear dichroism (LD) and occurs when electromagnetic radiation polarized along one direction is absorbed more strongly than radiation polarized in the perpendicular direction. Such polarization anisotropies can be generally associated with symmetry breakings. We measure the amplitude of the LD signal and study its temperature, energy, and doping dependence. The LD signal shows a resonant behavior with a peak in the few hundred meV range, which is coincident with the mid-infrared optical feature that has been associated with the formation of the pseudogap state. The strongest LD signal is found in under-doped films, although it is also observed in optimally- and over-doped samples. The LD signal is consistent with nematic charge ordering as well as novel magnetoelectric effects., Comment: 10 pages, 4 figures

We explore the electronic and magnetic properties of superconducting iron pnictide films by probing their infrared Hall conductivity as a function of probe energy (0.1-1.3 eV), temperature (10-300 K) and magnetic field (B = 0-7 T). We find hysteretic behavior in the complex infrared Faraday angle, $\theta_{F}$, at lowB over the entire temperature range. At higher $B, \theta_{\mathrm{F}}$ is linear in B and we observe a peak in the high B -field slope near 50 K, which may be related to the superconducting phase of the films.

Quantum light sources in solid-state systems are of major interest as a basic ingredient for integrated quantum photonic technologies. The ability to tailor quantum emitters via site-selective defect engineering is essential for realizing scalable architectures. However, a major difficulty is that defects need to be controllably positioned within the material. Here, we overcome this challenge by controllably irradiating monolayer MoS2 using a sub-nm focused helium ion beam to deterministically create defects. Subsequent encapsulation of the ion exposed MoS2 flake with high-quality hBN reveals spectrally narrow emission lines that produce photons in the visible spectral range. Based on ab-initio calculations we interpret these emission lines as stemming from the recombination of highly localized electron–hole complexes at defect states generated by the local helium ion exposure. Our approach to deterministically write optically active defect states in a single transition metal dichalcogenide layer provides a platform for realizing exotic many-body systems, including coupled single-photon sources and interacting exciton lattices that may allow the exploration of Hubbard physics. Light emitters can be induced in transition metal dichalcogenides by defect engineering, but challenges remain in their controlled spatial positioning. Here, the authors irradiate monolayer MoS2 with a sub-nm focused helium ion beam to deterministically create defects, and obtain spectrally narrow emission lines that produce photons in the visible spectral range

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

We report the observation of the generation and routing of single plasmons generated by localized excitons in a WSe

We report the observation of the generation and routing of single plasmons generated by localized excitons in a WSe$_2$ monolayer flake exfoliated onto lithographically defined Au-plasmonic waveguides. Statistical analysis of the position of different quantum emitters shows that they are $(3.3 \pm 0.7)\times$ more likely to form close to the edges of the plasmonic waveguides. By characterizing individual emitters we confirm their single-photon character via the observation of antibunching of the signal ($g^{(2)}(0) = 0.42$) and demonstrate that specific emitters couple to the modes of the proximal plasmonic waveguide. Time-resolved measurements performed on emitters close to, and far away from the plasmonic nanostructures indicate that Purcell factors up to $15 \pm 3$ occur, depending on the precise location of the quantum emitter relative to the tightly confined plasmonic mode. Measurement of the point spread function of five quantum emitters relative to the waveguide with

We have carried out mid-infrared magneto-optical studies of Ga1−x Mn x As films grown using two different techniques: low temperature molecular beam epitaxy (LT-MBE) and a combination of ion-implantation and pulsed laser melting (II-PLM). The second method is a high temperature growth technique which minimizes the formation of Mn interstitials. Both samples exhibit a ferromagnetic response with similar Curie temperatures (T C). The samples show qualitatively similar behavior in below bandgap Faraday and Kerr measurements, which probe the valence band structure of the materials. This suggests that the same mid-infrared transitions are dominating the magneto-optical response of both samples.

We use terahertz time domain spectroscopy to examine finite size effects on the optical phonon modes in SrTiO3 thin films. In temperature-dependent measurements we find a near absence of mode softening in the TO1 phonon frequency. Furthermore we see an increase in the soft mode frequency with reduced thickness. Both of these results correlate well with the reduced dielectric response observed for nanoscale ferroelectric systems.

Infrared ( $20--120$ and $900--1100{\mathrm{cm}}^{\ensuremath{-}1}$) Faraday rotation and circular dichroism are measured in high- ${T}_{c}$ superconductors using sensitive polarization modulation techniques. Optimally doped ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ thin films are studied at temperatures in the range ( $15lTl300\phantom{\rule{0ex}{0ex}}\mathrm{K}$) and magnetic fields up to 8 T. At $1000{\mathrm{cm}}^{\ensuremath{-}1}$ the Hall conductivity ${\ensuremath{\sigma}}_{\mathrm{xy}}$ varies strongly with temperature in contrast to the longitudinal conductivity ${\ensuremath{\sigma}}_{\mathrm{xx}}$ which is nearly independent of temperature. The Hall scattering rate ${\ensuremath{\gamma}}_{\mathrm{H}}$ has a ${T}^{2}$ temperature dependence but, unlike a Fermi liquid, depends only weakly on frequency. The experiment puts severe constraints on theories of transport in the normal state of high- ${T}_{c}$ superconductors.

We measure the Hall angle, θ H , in YBCO films in the far- and mid-infrared to determine the temperature and frequency dependence of the Hall scattering. Using novel modulation techniques we measure both the Faraday rotation and ellipticity induced by these films in high magnetic fields to deduce the complex conductivity tensor. We observe a strong temperature dependence of the mid-infrared Hall conductivity in sharp contrast to the weak dependence of the longitudinal conductivity. By fitting the frequency dependent normal state Hall angle to a Lorentzian θ H (ω) = ω H /(γ H − iω) we find the Hall frequency, ω H , is nearly independent of temperature. The Hall scattering rate, γ H , is consistent with γ H ≈ T 2 up to 200 K and is remarkably independent of IR frequency suggesting non-Fermi liquid behavior.

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

Monolayer two-dimensional transition metal dichalcogenides (TMDCs) such as MoS2 with broken inversion symmetry possesses two degenerate yet inequivalent valleys that can be selectively excited by circularly polarized light. This unique property renders interesting valley physics. The ability to manipulate valley degrees of freedom with light or external field makes them attractive for optoelectronic and spintronic applications. There is great demand for large area monolayer (ML) TMDCs for certain measurements and device applications. Recent reports on large area ML TDMCs focus on chemical vapor deposition growth. In this work, we report a facile approach to grow largescale continuous ML MoS2 nearly free of overgrowth and voids, by sulfurizing evaporated molybdenum trioxide ultrathin films. Photo conductivity scales with device sizes up to 4.5 mm, suggesting excellent film uniformity. The growth mechanism is found to be vaporization, diffusion, sulfurization and lateral growth, all at local micrometer scale. Our approach provides a new pathway for large-area ML TMDC growth and lithography-free device fabrication.

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 report a new broad band technique for rapidly measuring the complex Faraday and Kerr rotations in materials such as topological insulators and graphene, combining the distinct advantages of THz time domain spectroscopy and polarization modulation techniques. The performance of the system is demonstrated using GaAs two dimensional electron gas in a magnetic field.

We report the THz response of thin films of the topological insulator Bi2Se3. At low frequencies, transport is essentially thickness independent showing the dominant contribution of the surface electrons. Despite their extended exposure to ambient conditions, these surfaces exhibit robust properties including narrow, almost thickness-independent Drude peaks, and an unprecedentedly large polarization rotation of linearly polarized light reflected in an applied magnetic field. This Kerr rotation can be as large as 65° and can be explained by a cyclotron resonance effect of the surface states.

We report on Faraday rotation measurements in the THz regime of a two dimensional electron gas in the magnetic field region of cyclotron resonance. Clear steps at several filling factors in the Faraday rotation as a function of carrier density are interpreted as THz ac quantum Hall plateaus. Unlike the dc case, the steps are not quantized but they do depend on filling factor.

The origin of the Hall effect in many itinerant ferromagnets is still not resolved with an anomalous contribution from the sample magnetization that can exhibit extrinsic or intrinsic behavior. We report the midinfrared (MIR) measurements of the complex Hall $({\ensuremath{\theta}}_{H})$, Faraday $({\ensuremath{\theta}}_{F})$, and Kerr $({\ensuremath{\theta}}_{K})$ angles, as well as the Hall conductivity $({\ensuremath{\sigma}}_{xy})$ in a ${\text{SrRuO}}_{3}$ film in the 115--1400 meV energy range. The magnetic field, temperature, and frequency dependence of the Hall effect is explored. The MIR magneto-optical response shows very strong frequency dependence including sign changes. Below 200 meV, the MIR ${\ensuremath{\theta}}_{H}(T)$ changes sign between 120 and 150 K, as is observed in dc Hall measurements. Above 200 meV, the temperature dependence of ${\ensuremath{\theta}}_{H}$ is similar to that of the dc magnetization and the measurements are in good agreement with predictions from a band calculation for the intrinsic anomalous Hall effect (AHE). The temperature and frequency dependence of the measured Hall effect suggests that whereas the behavior above 200 meV is consistent with an intrinsic AHE, the extrinsic AHE may play an important role in the lower-energy response.

It was recently shown that oligolamellar vesicles of 3:1 mixtures of dioleoylphosphatidylethanolamine (DOPE) and the photopolymerizable lipid 1,2-bis[10-(2',4'-hexadienoyloxy)decanoyl]-sn-glycero-3-phosphocho line (SorbPC) are destabilized by polymerization of the SorbPC [Lamparski, H., Liman, U., Frankel, D.A., Barry, J.A., Ramaswami, V., Brown, M.F., & O'Brien, D.F. (1992) Biochemistry 31, 685-694]. The current work describes the polymorphic phase behavior of these mixtures in extended bilayers, as studied by 31P NMR spectroscopy and X-ray diffraction. In the NMR experiments, samples with varying degrees of polymerization were slowly raised in temperature, with spectra acquired every 2.5-10 degrees C. In the unpolymerized mixiture, and in those photopolymerized samples where the monomeric SorbPC was decreased by 33% and 51%, an isotropic signal grew progressively until no signal from the lamellar liquid-crystalline (L alpha) phase remained. In the highly polymerized sample with a 90% loss of monomeric SorbPC, less than 20% of the lipids underwent this transition. In none of the samples was an inverted hexagonal phase (HII) observed, under conditions of slow heating to almost 100 degrees C. The X-ray diffraction studies indicated that samples which exhibit the isotropic NMR signal corresponded to a structure exhibiting no well-defined crystalline order, which upon thermal cycling became an inverted cubic phase belonging to either the Pn3m or Pn3 space groups. The temperature of the transition to the cubic precursor decreased as the extent of polymerization increased, demonstrating that photopolymerization of these lipid bilayers can significantly alter the composition and thermotropic phase behavior of the mixture.

We employ Faraday and Kerr effect spectroscopy in the infrared range to investigate the electronic structure of ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ near the Fermi energy. The band structure of this archetypical dilute-moment ferromagnetic semiconductor has been a matter of controversy, fueled partly by previous measurements of the unpolarized infrared absorption and their phenomenological impurity-band interpretation. Unlike the unpolarized absorption, the infrared magneto-optical effects we study are intimately related to ferromagnetism, and their interpretation is much more microscopically constrained in terms of the orbital character of the relevant band states. We show that the conventional theory of the disordered valence band with an antiferromatnetic exchange term accounts semiquantitatively for the overall characteristics of the measured infrared magneto-optical spectra.

We employ Faraday and Kerr effect spectroscopy in the infrared range to investigate the electronic structure of Ga_{1-x}Mn_{x}As near the Fermi energy. The band structure of this archetypical dilute-moment ferromagnetic semiconductor has been a matter of controversy, fueled partly by previous measurements of the unpolarized infrared absorption and their phenomenological impurity-band interpretation. Unlike the unpolarized absorption, the infrared magneto-optical effects we study are intimately related to ferromagnetism, and their interpretation is much more microscopically constrained in terms of the orbital character of the relevant band states. We show that the conventional theory of the disordered valence band with an antiferromatnetic exchange term accounts semiquantitatively for the overall characteristics of the measured infrared magneto-optical spectra.

The electron-doped cuprate ${\mathrm{Pr}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ is investigated using infrared magneto-optical measurements. The optical Hall conductivity ${\ensuremath{\sigma}}_{xy}(\ensuremath{\omega})$ shows a strong doping, frequency, and temperature dependence consistent with the presence of a temperature- and doping-dependent coherent backscattering amplitude which doubles the electronic unit cell and produces a spin density wave state. At low temperatures, the data suggest that the coherent backscattering vanishes at a quantum critical point inside the superconducting dome and is associated with the commensurate antiferromagnetic order observed by other workers. Using a spectral weight analysis, we have further investigated the Fermi-liquid-like behavior of the overdoped sample. The observed Hall-conductance spectral weight is about ten times less than that predicted by band theory, raising the fundamental question of the effect of Mott and antiferromagnetic correlations on the Hall conductance of strongly correlated materials.

A series of 12 epitaxial films was grown across the entire range of the solid solution ${\mathrm{Ca}}_{x}{\mathrm{Sr}}_{1\ensuremath{-}x}\mathrm{Ru}{\mathrm{O}}_{3}$ in order to systematically examine the behavior of the anomalous Hall effect in this system. While all samples in this series are known from bulk studies to behave as Curie-Weiss paramagnets at high temperatures, samples with less than 70% Ca also order ferromagnetically with a maximal Curie temperature $({T}_{C})$ of $\ensuremath{\sim}160\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for pure $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$. Temperature $(T)$ and magnetic field $(H)$ dependent transport measurements were used in tandem with mean field simulations of sample magnetization $(M)$ to track the composition and temperature dependence of the ordinary $({R}_{o})$ and anomalous $({R}_{s})$ parts of the Hall resistivity $({\ensuremath{\rho}}_{H})$ in this system using the standard relation ${\ensuremath{\rho}}_{H}={R}_{o}B+{R}_{s}4\ensuremath{\pi}M$. In the high-temperature Curie-Weiss paramagnetic regime, the only temperature dependence of the Hall resistivity comes from the anomalous portion, allowing the ordinary and anomalous contributions to ${\ensuremath{\rho}}_{H}$ to be estimated via Curie-Weiss type fits. ${R}_{s}$ was observed to be positive and nearly $T$ independent at high temperatures $(g200\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and smoothly increased with increasing Ca content in this regime. In all ferromagnetic samples, ${R}_{s}$ decreased significantly on cooling below ${T}_{C}$ in response to magnetic ordering, actually changing sign for samples with $\ensuremath{\leqslant}20%$ Ca. This behavior is consistent with a two-component behavior of ${R}_{s}$, with the two different regimes (above ${T}_{C}$ and below ${T}_{C}$) resulting from substantial changes in the band structure of this itinerant ferromagnet on crossing ${T}_{C}$. The symmetric behavior of the anomalous Hall effect around the $\text{ferromagnetic}\ensuremath{\rightarrow}\text{paramagnetic}$ quantum phase transition is perhaps an indicator of hidden magnetic order in $\mathrm{Ca}\mathrm{Ru}{\mathrm{O}}_{3}$.

We present measurement and analysis techniques that allow the complete complex magneto-conductivity tensor to be determined from mid-infrared (11-1.6 micron; 100-800 meV) measurements of the complex Faraday (theta_F) and Kerr (theta_K) angles. Since this approach involves measurement of the geometry (orientation axis and ellipticity of the polarization) of transmitted and reflected light, no absolute transmittance or reflectance measurements are required. Thick film transmission and reflection equations are used to convert the complex theta_F and theta_K into the complex longitudinal conductivity sigma_xx and the complex transverse (Hall) conductivity sigma_xy. theta_F and theta_K are measured in a Ga_(1-x)Mn_xAs and SrRuO_3 films. The resulting sigma_xx is compared to the values obtained from conventional transmittance and reflectance measurements, as well as the results from Kramers-Kronig analysis of reflectance measurements on similar films., Comment: LaTeX file 25 pages, 7 figures

Far infrared dielectric response is used to characterize the collective mode density of states for cytochrome c as a function of oxidation state and hydration using terahertz time domain spectroscopy. A strong absorbance and refractive index increase was observed with the oxidation. A simple phenomenological fitting using a continuous distribution of oscillators reproduces the frequency dependence of the complex dielectric response as well as demonstrates quantitative agreement with a uniform increase in either mode density or polarizability with oxidation in the $5--80\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ frequency range. Hydration dependence measurements find that a difference in the equilibrium water content for ferri and ferro cytochrome c is not sufficient to account for the large change in terahertz response. The large dielectric increase at terahertz frequencies with oxidation suggests either a significant global softening of the potential and/or a significant increase in polarizability with oxidation.

We demonstrate the use of terahertz time domain spectroscopy for determination of ligand binding for biomolecules. Vibrational modes associated with tertiary structure conformational motions lay in the THz frequency range. We examine the THz dielectric response for hen egg white lysozyme (HEWL): free and bound with tri-N-acetyl-D-glucosamine. Transmission measurements on thin films show that there is a small change in the real part of the refractive index as a function of binding and a sizable decrease in the absorbance. A phenomenological model is used to determine the source of the absorbance change. A change in the vibrational mode density of states and net dipole moment changes will necessarily happen for all biomolecule-ligand binding, thus THz dielectric measurements may provide an universally applicable method to determine probe-target binding for biosensor applications.

We use terahertz (THz) spectroscopy as a biomaterials characterization tool. Previously we have shown a strong contrast between the THz dielectric response for wild type (WT) and D96N mutant of bacteriorhodopsin. In those studies we observed a large increase in the THz absorbance of WT with excitation to thermally captured photo-intermediates whereas no such increase in absorbance was observed for the mutant D96N. These results suggest that the THz response is sensitive to structural changes and relative flexibility of biomolecules. However the photo-intermediate populations of the WT and D96N samples were not equivalent in those measurements. While the WT samples had relaxed (bR), M and P state intermediates present, the D96N samples had only bR and M states. Here we present terahertz absorbance measurements of D96N as a function of M and P state populations at room temperature. The THz response is constant for intermediate states populations up to 23% M state and up to 30% P state. These results verify that there is a fundamental difference in the conformational dynamics as measured by THz dielectric response for a single residue mutation.

By monitoring changes in excitonic photoluminescence (PL) that are induced by terahertz (THz) radiation, we observe resonant THz absorption by magnetoexcitons in ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum wells. Changes in the PL spectrum are explored as a function of temperature and magnetic field, providing insight into the mechanisms which allow THz absorption to modulate PL. The strongest PL-quenching occurs at the heavy hole $1\stackrel{\ensuremath{\rightarrow}}{s}{2p}^{+}$ resonance where heavy hole excitons are photothermally converted into light hole excitons.

A sensitive mid-infrared (MIR, 900-1100 cm-1, 112-136 meV) photo-elastic polarization modulation technique is used to measure simultaneously Faraday rotation and circular dichroism in thin metal films. These two quantities determine the complex AC Hall conductivity. This novel technique is applied to study Au and Cu thin films at temperatures down to 20 K and magnetic fields up to 8 T. The Hall frequency is consistent with band theory predictions. We report the first measurement of the MIR Hall scattering rate, which is significantly lower than that derived from Drude analysis of zero magnetic field MIR transmission measurements. This difference is qualitatively explained in terms of the anisotropy of the Fermi surface in Au and Cu., Comment: 14 pages of text, 5 figures

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.

It was recently shown that oligolamellar vesicles of 3:1 mixtures of dioleoylphosphatidylethanolamine (DOPE) and the photopolymerizable lipid 1,2-bis[10-(2',4'-hexadienoyloxy)decanoyl]-sn-glycero-3-phosphocho line (SorbPC) are destabilized by polymerization of the SorbPC [Lamparski, H., Liman, U., Frankel, D.A., Barry, J.A., Ramaswami, V., Brown, M.F.,O'Brien, D.F. (1992) Biochemistry 31, 685-694]. The current work describes the polymorphic phase behavior of these mixtures in extended bilayers, as studied by 31P NMR spectroscopy and X-ray diffraction. In the NMR experiments, samples with varying degrees of polymerization were slowly raised in temperature, with spectra acquired every 2.5-10 degrees C. In the unpolymerized mixiture, and in those photopolymerized samples where the monomeric SorbPC was decreased by 33% and 51%, an isotropic signal grew progressively until no signal from the lamellar liquid-crystalline (L alpha) phase remained. In the highly polymerized sample with a 90% loss of monomeric SorbPC, less than 20% of the lipids underwent this transition. In none of the samples was an inverted hexagonal phase (HII) observed, under conditions of slow heating to almost 100 degrees C. The X-ray diffraction studies indicated that samples which exhibit the isotropic NMR signal corresponded to a structure exhibiting no well-defined crystalline order, which upon thermal cycling became an inverted cubic phase belonging to either the Pn3m or Pn3 space groups. The temperature of the transition to the cubic precursor decreased as the extent of polymerization increased, demonstrating that photopolymerization of these lipid bilayers can significantly alter the composition and thermotropic phase behavior of the mixture.

We measure the Hall angle, θH, in YBCO films in the far- and mid-infrared to determine the temperature T and frequency ω dependence of the Hall scattering. Using novel polarization modulation techniques we measure both the Faraday rotation and ellipticity induced by these films in high magnetic fields to deduce the complex conductivity tensor. We observe a strong temperature dependence of the Hall conductivity in sharp contrast to the weak dependence of the longitudinal conductivity. By fitting the frequency-dependent normal state Hall angle to a Lorentzian θH(ω)=ωH/(γH−iω) we find the Hall frequency, ωH, is nearly independent of temperature. The Hall scattering rate, γH, is consistent with γH≈T2 and is remarkably independent of IR frequency suggesting non-Fermi liquid behavior.