THz emission from Co/Pt bilayers with varied roughness, crystal structure, and interface intermixing

Ultrafast demagnetization of Co/Pt heterostructures induced by a femtosecond 800-nm laser pulse launches a spin current from Co to Pt and subsequent conversion of the spin current to a charge current in the Pt layer due to the inverse spin-Hall effect. At the same time, due to the spin-dependent photogalvanic effect, a circularly polarized femtosecond laser pulse also generates a photocurrent at the Co/Pt interface. Both ultrashort photocurrent pulses are effectively detected in a contactless way by measuring the THz radiation they emit. Here we aim to understand how the properties of the Co/Pt interface affect the photocurrents in the bilayers. By varying the interfacial roughness, crystal structure, and interfacial intermixing, as well as having an explicit focus on the cases when THz emissions from these two photocurrents reveal opposite trends, we identify which interface properties play a crucial role for the photocurrents. In particular, we show that by reducing the roughness, the THz emission due to the spin-dependent photogalvanic effect reduces to zero while the strength of the THz emission from the photocurrent associated with the inverse spin-Hall effect increases by a factor of 2. On the other hand, while intermixing strongly enhances the THz emission from the inverse spin-Hall effect by a factor of 4.2, THz emission related to the spin-dependent photogalvanic effect reveals the opposite trend. These findings indicate that microstructural properties of the Co-Pt interface play a decisive role in the generation of photocurrents

Sub-wavelength focusing of mid-IR light using metal/diamond/metal campanile probe for ultra-broadband SPM

Developing methods for efficient nanoscale probing of light-matter interaction, especially in the Mid-IR and THz spectral range, is essential for studying fundamental physical phenomena as well as chemical properties at micrometer to nanometer length scales. A highly efficient nanoscale focusing of visible and near-IR radiation light was reported recently using Au-SiO2-Au tapered gap campanile plasmon waveguide with an 830 nm wavelength that couples free space light into the nanoscale domain, enabling probing of materials in the visible and near-IR spectral range [1]. We expand this capability to the highly important mid-IR and THz range providing valuable information on local nanoscale chemistry and physical processes of materials and devices using a campanile shaped diamond tetragonal pyramid [2]. Our finite difference time domain (FDTD) simulation reveals that nanoscale focusing of mid-IR light is possible within the range of geometries and metal coatings including Au, Al and Cu. Here we report linked modeling and experimental results showing the confining efficiency of diamond pyramid in the mid-IR range (8-10 µm). Furthermore, we will demonstrate the integration of Au/diamond/Au light concentrator into a scanning probe microscope for performing sub-wavelength spectroscopy of various materials in both reflection and transmission geometries

Insulin Resistance and Markers of Inflammation in HIV-infected Ugandan Children in the CHAPAS-3 Trial

BACKGROUND: Few studies have investigated metabolic complications in HIV-infected African children and their relation with inflammation. METHODS:: We compared baseline and changes in insulin resistance (HOMA-IR) and in markers of inflammation over 48 weeks, in a subset of antiretroviral therapy (ART) naïve Ugandan children from the CHAPAS-3 trial randomized to zidovudine (AZT), stavudine (D4T) or abacavir (ABC) based regimens. Non-parametric methods were used to explore between and within group differences and multivariable analyses to assess associations of HOMA-IR. RESULTS:: 118 children were enrolled; median age (IQR) was 2.8 years (1.7-4.3). Baseline median HOMA-IR (IQR) was 0.49 (0.38, 1.07) and similar between the arms. At week 48, median relative changes in HOMA-IR were 14% (-29%, 97%) in the AZT arm, -1% (-30%, 69%) in the D4T arm, and 6% (-34%, 124%) in the ABC arm (p≤0.03 for all arms compared to baseline, but p=0.90 for between-group differences). Several inflammation markers significantly decreased in all study arms; sCD14 increased on ABC and did not change in the other two arms. In multivariate analysis, only changes in sCD163 were positively associated with HOMA-IR changes. CONCLUSIONS:: In ART naïve Ugandan children, HOMA-IR changed significantly after 48 weeks of ART and correlated with monocyte activation

Micromagnetic simulation of THz signals in antiferromagnetic FeRh by sub-picosecond thermal pulses

The generation of electrical field signals in the terahertz frequency (THz) range has gained increasing attention in recent years. The use of antiferromagnets (AFM) has been proposed as a possible alternative to generate high frequency signals using spin transfer torque (STT) induced damping compensation. In this work, we simulated a potential mechanism for laser-induced THz signals in the AFM phase of FeRh/Pt bilayer films using micromagnetic model. The FeRh film is modeled as two Fe-sublattices coupled via intra-lattice exchange field, and subjected to a sub-picosecond thermal pulse. A partial canting between the magnetizations of two Fe-sublattices, is observed within the first picosecond after the excitation. This short lived state relaxes abruptly into the initial AFM phase, injecting a spin current into the Pt layer via spin pumping, which will eventually be converted into charge current oscillating at THz frequency