We present a systematic study of both the temperature and frequency dependence of the optical response in TaAs, a material that has recently been realized to host the Weyl semimetal state. Our study reveals that the optical conductivity of TaAs features a narrow Drude response alongside a conspicuous linear dependence on frequency. The weight of the Drude peak decreases upon cooling, following a T 2 temperature dependence, in good agreement with theoretical predictions. Two linear components with distinct slopes dominate the low-temperature optical conductivity. A comparison between our experimental results and theoretical calculations suggests that the linear conductivity below ∼230cm −1 arises purely from interband transitions near the Weyl points, providing rich information about the Weyl semimetal state in TaAs.

An investigation on the formation of ␣ Љ martensite and its influence on Young's modulus and mechanical properties of forged Ti-29Nb-13Ta-4.6Zr (wt pct) alloy is reported in this article. For icewater-quenched specimens after solution treatment at 1023, 1123, and 1223 K in the single ␤ -phase field for 1.8, 3.6, 14.4, and 28.8 ks, X-ray diffraction and internal friction measurements showed that the volume fraction of the ␣ Љ martensite changes with both solution temperature and time. This effect has been attributed mainly to the influence of grain size of the ␤ -parent phase on the stability of the ␤ phase and, consequently, on the martensitic start (M S ) temperature. A critical grain size of 40 m was identified for the ␤ phase, below which the martensitic transformation is largely suppressed because of low M S temperature. With the ␤ grain size increasing above this critical value, the volume fraction of the ␣ Љ martensite increases significantly at first and then decreases gradually with further grain growth. The ␣ Љ martensite was shown to possess good ductility and, compared to the ␤ phase, lower strength and hardness but nearly identical Young's modulus in the studied alloy.

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We investigate polarization-dependent ultrafast photocurrents in the Weyl semimetal TaAs using terahertz (THz) emission spectroscopy. Our results reveal that highly directional, transient photocurrents are generated along the non-centrosymmetric c-axis regardless of incident light polarization, while helicity-dependent photocurrents are excited within the ab-plane. This is consistent with earlier static photocurrent experiments, and demonstrates on the basis of both the physical constraints imposed by symmetry and the temporal dynamics intrinsic to current generation and decay that optically induced photocurrents in TaAs are inherent to the underlying crystal symmetry of the transition metal monopnictide family of Weyl semimetals.In this letter, we demonstrate the generation of both helicity-dependent and helicity-independent ultra-arXiv:1811.02723v2 [cond-mat.str-el]

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