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T Morimoto, T Miyamoto, H Yamakawa, T Terashige, T Ono, N Kida, H Okamoto
A rapid polarization control in paraelectric materials is important for an ultrafast optical switching useful in the future optical communication. In this study, we applied terahertz-pump second-harmonic-generation-probe and optical-reflectivity-probe spectroscopies to the paraelectric neutral phase of an organic molecular dielectric, tetrathiafulvalene-p-chloranil and revealed that a terahertz pulse with the electric-field amplitude of ∼400  kV/cm produces in the subpicosecond time scale a large macroscopic polarization whose magnitude reaches ∼20% of that in the ferroelectric ionic phase...
March 10, 2017: Physical Review Letters
Sarwat A Baig, Jessica L Boland, Djamshid A Damry, Hark Hoe Tan, Chennupati Jagadish, Hannah J Joyce, Michael B Johnston
Progress in the terahertz (THz) region of the electromagnetic spectrum is undergoing major advances, with advanced THz sources and detectors being developed at a rapid pace. Yet, ultrafast THz communication is still to be realised, owing to the lack of practical and effective THz modulators. Here, we present a novel ultrafast active THz polarization modulator based on GaAs semiconductor nanowires arranged in a wire-grid configuration. We utilise an optical pump--terahertz probe spectroscopy system and vary the polarization of the optical pump beam to demonstrate ultrafast THz modulation with a switching time of less than 5\,ps and a modulation depth of -8dB...
March 23, 2017: Nano Letters
Jeremy M Moix, James E Parker, Ibtissam Echchgadda
The dynamics of the low-frequency vibrational modes of microtubules play a key role in many theoretical models regarding their biological function. We analyze these dynamics through large scale, classical molecular dynamics simulations of a microtubule composed of 42 tubulin heterodimers to provide insights into the qualitative nature of the vibrational energy absorption and dissipation mechanisms. The computed microtubule absorption spectra and vibrational density of states in the terahertz regime are presented, along with an analysis of the vibrational dephasing rates of the tubulin monomer center of mass dynamics, which are shown to be overdamped...
March 20, 2017: Journal of Physical Chemistry. B
Masae Takahashi, Nubuyuki Okamura, Xinyi Fan, Hitoshi Shirakawa, Hiroaki Minamide
We have investigated the terahertz-spectral property of nicotinamide focusing on the temperature dependence in the range of 14 to 300 K. We observed that almost all peaks in the terahertz spectrum of the nicotinamide crystal showed a remarkable shift with temperature, whereas the lowest-frequency peak at 34.8 cm-1 showed a negligible shift with temperature. By analyzing the terahertz spectrum with the dispersion-corrected density-functional-theory calculations, we found that the difference in the temperature dependence of the peak shift is well understood in terms of the presence/absence of stretching vibration of the intermolecular hydrogen bond in the mode and the change of cell parameters...
March 20, 2017: Journal of Physical Chemistry. A
Daniel Jänsch, Ivan Ivanov, Yulian Zagranyarski, Ivana Duznovic, Martin Baumgarten, Dimitry Turchinovich, Chen Li, Mischa Bonn, Klaus Müllen
Soluble ultra-narrow armchair graphene nanoribbons (AGNRs) with length of ≈20 nm and completely fused cores exceeding 5 nm in length, pronounced near-infrared (NIR) absorption up to 1400 nm, and a low band gap (≈0.9 eV) are synthesized from 3,9(3,10)-dibromoperylene and 3,4,9,10-tetrabromoperylene. Since the monomers are obtained from perylene carboxyanhydrides, a remarkable link between dye and graphene chemistry is established. The two-step protocol for the AGNR synthesis by aryl-aryl coupling and subsequent cyclodehydrogenation is compared with a direct Yamamoto polymerization...
March 20, 2017: Chemistry: a European Journal
Uta Meyer, Géraldine Haack, Christoph Groth, Xavier Waintal
The oscillatory interlayer exchange interaction between two magnetic layers separated by a metallic spacer is one of the few coherent quantum phenomena that persists at room temperature. Here, we show that this interaction can be controlled dynamically by illuminating the sample (e.g., a spin valve) with radiation in the 10-100 THz range. We predict that the exchange interaction can be changed from ferromagnetic to antiferromagnetic (and vice versa) by tuning the amplitude and/or the frequency of the radiation...
March 3, 2017: Physical Review Letters
Michael T Ruggiero, J Axel Zeitler, Alessandro Erba
The intermolecular anharmonic potential of crystalline purine is probed by means of temperature-dependent terahertz time-domain spectroscopy, low-frequency Raman scattering, X-ray diffraction, and ab initio quasi-harmonic quantum-chemical simulations. As temperature increases, anharmonicity in the intermolecular interactions results in strongly anisotropic thermal expansion - with a negative thermal expansion along the b crystallographic axis - yielding corresponding bulk structural modifications. The observed thermally-induced shifts of most vibrational bands in the terahertz region of the spectra are shown to arise from volume-dependent thermal changes of the hydrogen-bond pattern along the a and b crystallographic axes...
March 17, 2017: Chemical Communications: Chem Comm
Keiichiro Shiraga, Aya Adachi, Masahito Nakamura, Takuro Tajima, Katsuhiro Ajito, Yuichi Ogawa
Modification of the water hydrogen bond network imposed by disaccharides is known to serve as a bioprotective agent in living organisms, though its comprehensive understanding is still yet to be reached. In this study, aiming to characterize the dynamical slowing down and destructuring effect of disaccharides, we performed broadband dielectric spectroscopy, ranging from 0.5 GHz to 12 THz, of sucrose and trehalose aqueous solutions. The destructuring effect was examined in two ways (the hydrogen bond fragmentation and disordering) and our result showed that both sucrose and trehalose exhibit an obvious destructuring effect with a similar strength, by fragmenting hydrogen bonds and distorting the tetrahedral-like structure of water...
March 14, 2017: Journal of Chemical Physics
Katherine A Niessen, Mengyang Xu, Alessandro Paciaroni, Andrea Orecchini, Edward H Snell, Andrea G Markelz
Nearly all protein functions require structural change, such as enzymes clamping onto substrates, and ion channels opening and closing. These motions are a target for possible new therapies; however, the control mechanisms are under debate. Calculations have indicated protein vibrations enable structural change. However, previous measurements found these vibrations only weakly depend on the functional state. By using the novel technique of anisotropic terahertz microscopy, we find that there is a dramatic change to the vibrational directionality with inhibitor binding to lysozyme, whereas the vibrational energy distribution, as measured by neutron inelastic scattering, is only slightly altered...
March 14, 2017: Biophysical Journal
Francisco J Rodriguez, Diana E Aznakayeva, Owen P Marshall, Vasyl G Kravets, Alexander N Grigorenko
The gate-tunable wide-band absorption of graphene makes it suitable for light modulation from terahertz to visible light. The realization of graphene-based modulators, however, faces challenges connected with graphene's low absorption and the high electric fields necessary to change graphene's optical conductivity. Here, a solid-state supercapacitor effect with the high-k dielectric hafnium oxide is demonstrated that allows modulation from the near-infrared to shorter wavelengths close to the visible spectrum with remarkably low voltages (≈3 V)...
March 15, 2017: Advanced Materials
J Lloyd-Hughes, Connor Mosley, Samuel Jones, Martin R Lees, Aiping Chen, Quanxi Jia, Eun Mi Choi, Judith L MacManus Driscoll
Colossal magnetoresistance (CMR) is demonstrated at terahertz (THz) frequencies by using terahertz time-domain magnetospectroscopy to examine nanocolumns and planar thin films of La0.7Sr0.3MnO3. At the metal-insulator transition the THz conductivity of the nanocolumn film was dramatically enhanced by the application of a magnetic field, creating a non-Drude conductivity that increased with frequency. The colossal magnetoresistance at 1.0THz is -99.9% at the Curie temperature (room temperature), far exceeding the dc magnetoresistance...
March 13, 2017: Nano Letters
Oleg Mitrofanov, Leonardo Viti, Enrico Dardanis, Maria Caterina Giordano, Daniele Ercolani, Antonio Politano, Lucia Sorba, Miriam S Vitiello
Near-field imaging with terahertz (THz) waves is emerging as a powerful technique for fundamental research in photonics and across physical and life sciences. Spatial resolution beyond the diffraction limit can be achieved by collecting THz waves from an object through a small aperture placed in the near-field. However, light transmission through a sub-wavelength size aperture is fundamentally limited by the wave nature of light. Here, we conceive a novel architecture that exploits inherently strong evanescent THz field arising within the aperture to mitigate the problem of vanishing transmission...
March 13, 2017: Scientific Reports
Paweł Bilski, Kacper Drużbicki, Jacek Jenczyk, Jadwiga Mielcarek, Jan Wąsicki
Molecular and vibrational dynamics of a widely used cholesterol-lowering agent, lovastatin, have been studied by combining nuclear magnetic resonance relaxation experiments ((1)H NMR) with inelastic neutron scattering (INS) and periodic density functional theory modeling (plane-wave DFT). According to a complementary experimental study, lovastatin shows no phase transitions down to cryogenic conditions, while a progressive, stepwise activation of several molecular motions is observed below room temperature...
March 23, 2017: Journal of Physical Chemistry. B
Carlo Vicario, Mostafa Shalaby, Christoph P Hauri
We report on the experimental observation of extreme laser spectral broadening and a change in optical transmission in gallium phosphite induced by 25  MV/cm terahertz (THz) single-cycle internal field. Such intense THz radiation leads to twofold transient modifications of the optical properties in the electro-optical crystal. First, the electric field provokes extensive cross-phase modulation via the χ^{(2)} and χ^{(3)} nonlinearities on a copropagating 50 fs near infrared laser pulse which turns into 500% spectral broadening...
February 24, 2017: Physical Review Letters
Mohammad Adabi, Johannes Lischner, Stephen M Hanham, Andrei P Mihai, Olena Shaforost, Rui Wang, Ling Hao, Peter K Petrov, Norbert Klein
Metallic gate electrodes are often employed to control the conductivity of graphene based field effect devices. The lack of transparency of such electrodes in many optical applications is a key limiting factor. We demonstrate a working concept of a double layer graphene field effect device that utilizes a thin film of sputtered aluminum nitride as dielectric gate material. For this system, we show that the graphene resistance can be modified by a voltage between the two graphene layers. We study how a second gate voltage applied to the silicon back gate modifies the measured microwave transport data at around 8...
March 9, 2017: Scientific Reports
Fang Wang, Dongbo Zhao, Hao Dong, Ling Jiang, Yunfei Liu, Shuhua Li
Terahertz (THz) spectra of DNA nucleobase crystals were experimentally studied by terahertz time domain spectroscopy (THz-TDS), Fourier transform infrared spectroscopy (FTIR), and computationally studied by the generalized energy-based fragmentation approach under periodic boundary conditions (denoted as PBC-GEBF). We analyzed the vibrational spectra of solid-state DNA nucleobases and assigned the corresponding vibrational modes to the main peaks in the experimental spectra with the PBC-GEBF results. The computational results were verified to be in good accordance with the experimental data...
February 21, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
W J Wan, H Li, T Zhou, J C Cao
Homogeneous broadband and electrically pumped semiconductor radiation sources emitting in the terahertz regime are highly desirable for various applications, including spectroscopy, chemical sensing, and gas identification. In the frequency range between 1 and 5 THz, unipolar quantum cascade lasers employing electron inter-subband transitions in multiple-quantum-well structures are the most powerful semiconductor light sources. However, these devices are normally characterized by either a narrow emission spectrum due to the narrow gain bandwidth of the inter-subband optical transitions or an inhomogeneous broad terahertz spectrum from lasers with heterogeneous stacks of active regions...
March 8, 2017: Scientific Reports
Jae Yeon Park, Hyuck Jae Choi, Hwayeong Cheon, Seong Whi Cho, Seungkoo Lee, Joo-Hiuk Son
Terahertz (THz) imaging was used to differentiate the metastatic states of frozen lymph nodes (LNs) by using spectroscopic integration technique (SIT). The metastatic states were classified into three groups: healthy LNs, completely metastatic LNs, and partially metastatic LNs, which were obtained from three mice without infection and six mice infected with murine melanoma cells for 30 days and 15 days, respectively. Under histological examination, the healthy LNs and completely metastatic LNs were found to have a homogeneous cellular structure but the partially metastatic LNs had interfaces of the melanoma and healthy tissue...
February 1, 2017: Biomedical Optics Express
Daniel Markl, Parry Wang, Cathy Ridgway, Anssi-Pekka Karttunen, Mousumi Chakraborty, Prince Bawuah, Pertti Pääkkönen, Patrick Gane, Jarkko Ketolainen, Kai Peiponen, J Axel Zeitler
Novel excipients are entering the market to enhance the bioavailability of drug particles by having a high porosity and thus providing a rapid liquid uptake and disintegration to accelerate subsequent drug dissolution. One example of such a novel excipient is functionalised calcium carbonate (FCC), which enables the manufacture of compacts with a bimodal pore size distribution consisting of larger inter-particle and fine intra-particle pores. Five sets of FCC tablets with a target porosity of 45% to 65% were prepared in 5% steps and characterised using terahertz time-domain spectroscopy (THz-TDS) and X- ray computed microtomography (XμCT)...
March 3, 2017: Journal of Pharmaceutical Sciences
Jean-Marie Poumirol, Peter Q Liu, Tetiana M Slipchenko, Alexey Y Nikitin, Luis Martin-Moreno, Jérôme Faist, Alexey B Kuzmenko
The magnetic circular dichroism and the Faraday rotation are the fundamental phenomena of great practical importance arising from the breaking of the time reversal symmetry by a magnetic field. In most materials, the strength and the sign of these effects can be only controlled by the field value and its orientation. Furthermore, the terahertz range is lacking materials having the ability to affect the polarization state of the light in a non-reciprocal manner. Here we demonstrate, using broadband terahertz magneto-electro-optical spectroscopy, that in graphene both the magnetic circular dichroism and the Faraday rotation can be modulated in intensity, tuned in frequency and, importantly, inverted using only electrostatic doping at a fixed magnetic field...
March 7, 2017: Nature Communications
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