Photodetectors based on Weyl semimetal promise extreme performance in terms of highly sensitive, broadband and self-powered operation owing to its extraordinary material properties. Layered Type-II Weyl semimetal that break Lorentz invariance can be further integrated with other two-dimensional materials to form van der Waals heterostructures and realize multiple functionalities inheriting the advantages of other two-dimensional materials. Herein, we report the realization of a broadband self-powered photodetector based on Type-II Weyl semimetal T -MoTe . The prototype metal-MoTe -metal photodetector exhibits a responsivity of 0.40 mA W and specific directivity of 1.07 × 10 Jones with 43 μs response time at 532 nm. Broadband responses from 532 nm to 10.6 μm are experimentally tested with a potential detection range extendable to far-infrared and terahertz. Furthermore, we identify the response of the detector is polarization angle sensitive due to the anisotropic response of MoTe . The anisotropy is found to be wavelength dependent, and the degree of anisotropy increases as the excitation wavelength gets closer to the Weyl nodes. In addition, with power and temperature dependent photoresponse measurements, the photocurrent generation mechanisms are investigated. Our results suggest this emerging class of materials can be harnessed for broadband angle sensitive, self-powered photodetection with decent responsivities.
1T-TaS 2 undergoes successive phase transitions upon cooling and eventually enters an insulating state of mysterious origin. Some consider this state to be a band insulator with interlayer stacking order, yet others attribute it to Mott physics that support a quantum spin liquid state. Here, we determine the electronic and structural properties of 1T-TaS 2 using angle-resolved photoemission spectroscopy and X-Ray diffraction. At low temperatures, the 2π/2c-periodic band dispersion, along with half-integer-indexed diffraction peaks along the c axis, unambiguously indicates that the ground state of 1T-TaS 2 is a band insulator with interlayer dimerization. Upon heating, however, the system undergoes a transition into a Mott insulating state, which only exists in a narrow temperature window. Our results refute the idea of searching for quantum magnetism in 1T-TaS 2 only at low temperatures, and highlight the competition between on-site Coulomb repulsion and interlayer hopping as a crucial aspect for understanding the material's electronic properties.
We report on a spin-polarized inelastic neutron scattering study of spin waves in the antiferromagnetically ordered state of BaFe2As2. Three distinct excitation components are identified, with spins fluctuating along the c-axis, perpendicular to the ordering direction in the ab-plane, and parallel to the ordering direction. While the first two "transverse" components can be described by a linear spin-wave theory with magnetic anisotropy and inter-layer coupling, the third "longitudinal" component is generically incompatible with the local moment picture. It points towards a contribution of itinerant electrons to the magnetism already in the parent compound of this family of Fe-based superconductors.PACS numbers: 74.70. Xa, 75.30.Gw, 75.30.Ds Among very different classes of materials including the Fe-based superconductors (FeSC), the cuprates, and the heavy-Fermion compounds, a striking feature of unconventional superconductivity is that it commonly appears close to an antiferromagnetic (AF) phase [1]. Since magnetism may be a common thread for the pairing interaction in unconventional superconductors [2], it is important to determine the microscopic origin of the AF order. For the cuprates, it is well accepted that their Mott insulating parent compounds have localized moments, and the spin waves can be well described by a Heisenberg model [3][4][5]. In the case of iron pnictide families of FeSC, there is no consensus on the origin of the stripe-like AF order in the parent compounds [6-9]. On the one hand, these are semi-metals with hole-and electron-like Fermi pockets at the Brillouin zone center and zone corners, respectively ( Fig. 1a) [10][11][12][13], and the AF order ( Fig. 1b) may arise from nesting between the pockets [10], much like the spin-density-wave (SDW) order in chromium [14]. On the other hand, the bad-metal phenomenology of iron pnictides [15] suggests that these materials are near a Mott transition with magnetism arising from localized moments, much like in the cuprates [16][17][18].
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