Comment on "Terahertz time-domain spectroscopy of transient metallic and superconducting states" (arXiv:1506.06758)

We comment on the model proposed by Orenstein and Dodge in arXiv:1506.06758v1, which describes time-domain terahertz measurements of transiently generated, high-electron-mobility (or superconducting) phases of solids. The authors' main conclusion is that time-domain terahertz spectroscopy does not measure a response function that is mathematically identical to the transient optical conductivity. We show that although this is correct, the difference between the measured response function and the microscopic optical conductivity is small for realistic experimental parameters. We also show that for the experiments reported by our group on light-induced superconducting-like phases in cuprates and in organic conductors, the time-domain terahertz yields a very good estimate for the optical conductivity.Comment: 3 pages, 1 figure, comment on arXiv:1506.0675

Pressure tuning of light-induced superconductivity in K3C60

Optical excitation at terahertz frequencies has emerged as an effective means to manipulate complex solids dynamically. In the molecular solid K3C60, coherent excitation of intramolecular vibrations was shown to transform the high temperature metal into a non-equilibrium state with the optical conductivity of a superconductor. Here we tune this effect with hydrostatic pressure, and we find it to disappear around 0.3 GPa. Reduction with pressure underscores the similarity with the equilibrium superconducting phase of K3C60, in which a larger electronic bandwidth is detrimental for pairing. Crucially, our observation excludes alternative interpretations based on a high-mobility metallic phase. The pressure dependence also suggests that transient, incipient superconductivity occurs far above the 150 K hypothesised previously, and rather extends all the way to room temperature.Comment: 33 pages, 17 figures, 2 table

Superconducting fluctuations observed far above T_c in the isotropic superconductor K₃C₆₀

Alkali-doped fullerides are strongly correlated organic superconductors that exhibit high transition temperatures, exceptionally large critical magnetic fields and a number of other unusual properties. The proximity to a Mott insulating phase is thought to be a crucial ingredient of the underlying physics, and may also affect precursors of superconductivity in the normal state above T$_\text{c}$. We report on the observation of a sizeable magneto-thermoelectric (Nernst) effect in the normal state of K$_3$C$_{60}$, which displays the characteristics of superconducting fluctuations. The anomalous Nernst effect emerges from an ordinary quasiparticle background below a temperature of 80K, far above T$_\text{c}$ = 20K. At the lowest fields and close to T$_\text{c}$, the scaling of the effect is captured by a model based on Gaussian fluctuations. The temperature up to which we observe fluctuations is exceptionally high for a three-dimensional isotropic system, where fluctuation effects are usually suppressed

An ancient pointed maize rich in phlobaphenes: the "Nero Spinoso" from Valcamonica (Brescia, Italy)

The variety of the species Zea mays called \u201cNero Spinoso\u201d is a traditional crop in the Middle Valle Camonica (Northern Italy) although its cultivation was almost completely abandoned during the second half of the twentieth century due to the introduction of commercial hybrids and to a reduction in the consumption of polenta, for centuries a staple food of the rural population. This work characterized this ancient pigmented maize. A preliminary spectrophotometric analysis revealed the presence of flavonols, phenolic acids and in particular phlobaphenes, probably responsible for ear coloration. Phlobaphenes are reddish insoluble substances synthesized in maize through the flavonoids pathway by the polymerization of flavan-4-ols. In maize this pigment is due to the presence of the pericarp1 gene (p1), a transcription factor belonging to the MYB gene family driving the accumulation of the pigment in the pericarp layer. Genetic and molecular analysis confirmed the presence of the P1 gene in this landrace and histological analysis confirmed that the pigment is accumulated in the pericarp. In the meantime HPLC analyses also showed the presence of a large amount of carotenoids and, probably thanks to the high amount of pigments, this maize variety showed very high antioxidant ability. Given the chronic disease prevention properties of antioxidant molecules, this variety could be of great interest also from a nutritional point of view. Characterization will allow an accurate description of this landrace with the aim of studying and preserving maize biodiversity in Europe and in particular in Italy. We have collaborated with the municipalities of Esine and Piancogno in the application process needed to register this ancient cultivar on the National Register of conservation varieties with the aim of valorizing this ancient landrace. The "Nero Spinoso" maize was recorded in the National Register in January 2016

"war to the knife" against thromboinflammation to protect endothelial function of COVID-19 patients

In this viewpoint, we summarize the relevance of thromboinflammation in COVID-19 and discuss potential mechanisms of endothelial injury as a key point for the development of lung and distant organ dysfunction, with a focus on direct viral infection and cytokine-mediated injury. Entanglement between inflammation and coagulation and resistance to heparin provide a rationale to consider other therapeutic approaches in order to preserve endothelial function and limit microthrombosis, especially in severe forms. These strategies include nebulized heparin, N-acetylcysteine, plasma exchange and/or fresh frozen plasma, plasma derivatives to increase the level of endogenous anticoagulants (tissue factor pathway inhibitor, activated protein C, thrombomodulin, antithrombin), dipyridamole, complement blockers, different types of stem cells, and extracellular vesicles. An integrated therapy including these drugs has the potential to improve outcomes in COVID-19

An optically stimulated superconducting-like phase in K3C60 far above equilibrium Tc

The control of non-equilibrium phenomena in complex solids is an important research frontier, encompassing new effects like light induced superconductivity. Here, we show that coherent optical excitation of molecular vibrations in the organic conductor K3C60 can induce a non-equilibrium state with the optical properties of a superconductor. A transient gap in the real part of the optical conductivity and a low-frequency divergence of the imaginary part are measured for base temperatures far above equilibrium Tc=20 K. These findings underscore the role of coherent light fields in inducing emergent order.Comment: 40 pages, 23 figure

An effective magnetic field from optically driven phonons

Light fields at terahertz and mid-infrared frequencies allow for the direct excitation of collective modes in condensed matter, which can be driven to large amplitudes. For example, excitation of the crystal lattice has been shown to stimulate insulator–metal transitions, melt magnetic order or enhance superconductivity. Here, we generalize these ideas and explore the simultaneous excitation of more than one lattice mode, which are driven with controlled relative phases. This nonlinear mode mixing drives rotations as well as displacements of the crystal-field atoms, mimicking the application of a magnetic field and resulting in the excitation of spin precession in the rare-earth orthoferrite ErFeO3. Coherent control of lattice rotations may become applicable to other interesting problems in materials research—for example, as a way to affect the topology of electronic phases

Nutritional and phenotypical characterization of two South African maize (Zea mays L) varieties sampled in the Qwa-Qwa region

Zea mays L represents one of the main source of energy in the diet in many African countries, especially in the sub-Saharan regions. White maize varieties, characterized by the lack of carotenoids, are usually widely preferred in Africa for human consumption, and this contributes to the occurrence of Vitamin A deficiency; yellow varieties, often derived from commercial hybrids, are usually destined for animal feeding. In this study we characterized from the phenotypical and nutritional points of view one white and one yellow South African landrace maize cultivar obtained directly from the farmers in the rural region of Qwa-Qwa (Free State Province). Calorific value, oil, protein, starch, minerals, flavonoids and carotenoids content were determined, together with free and phytic phosphorus (P). Both of the varieties showed lower protein and Fe content in comparison to the ones used as control, and the yellow one also had a low content of Zn. The white variety was characterized by a higher free P content but also by a very low level of carotenoids. Our data show that there are no nutritional reasons to prefer the white variety for human consumption, with the exception of the large size of the seeds, which make them particularly adapted for milling; hence the nutritional value of these varieties, and in particular of the white one, should be improved (pro-tein, Fe and carotenoids), contributing in this way to tackle the problem of malnutrition in South African rural areas