A Weyl semimetallic state with pairs of nondegenerate Dirac cones in three dimensions was recently predicted to occur in the antiferromagnetic state of the pyrochlore iridates. Here, we show that the THz optical conductivity and temperature dependence of the free carrier response in pyrochlore Eu2Ir2O7 match the predictions for a Weyl semimetal and suggest novel Dirac liquid behavior. The interband optical conductivity vanishes continuously at low frequencies signifying a semimetal. The metal-semimetal transition at TN = 110 K is manifested in the Drude spectral weight, which is independent of temperature in the metallic phase, and which decreases smoothly in the ordered phase. The temperature dependence of the free carrier weight below TN is in good agreement with theoretical predictions for a Dirac material. The data yield a Fermi velocity vF ≈ 4 • 10 7 cm/s, a logarithmic renormalization scale ΛL ≈ 600 K, and require a Fermi temperature of TF ≈ 100 K associated with residual unintentional doping to account for the low temperature optical response and dc resistivity.

Terahertz technology has recently emerged as a highly sought-after and versatile scientific tool in many fields, including medical imaging, security screening, and wireless communication. However, scientific progress has been hindered by the lack of sources and detectors in this frequency range, thereby known as the terahertz gap. Here, we show that carbon nanotube quantum dots coupled to antennas are extremely sensitive, broad-band, terahertz quantum detectors with spectral resolution. Their response is due to photon-assisted single-electron tunneling and it is substantially enhanced by a novel radiation-induced nonequilibrium cooling of the electrons, causing a sharp height increase of the Coulomb oscillation peaks.

Infrared ( 20-120 and 900-1100 cm(-1)) Faraday rotation and circular dichroism are measured in high- T(c) superconductors using sensitive polarization modulation techniques. Optimally doped YBa2Cu3O7 thin films are studied at temperatures in the range ( 15

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