Hongxiang Chen

Coexistence of magnetism and superconductivity in a new Fe-containing cuprate superconductor (Fe0.5Cu0.5)SrBaYCu2O7+δ

In this paper, we demonstrate the coexistence of ferromagnetism and superconductivity in a new cuprate superconductor (Fe0.5Cu0.5)SrBaYCu2O7+delta synthesized under high pressure. This compound has a 1212-type structure, with tetragonal symmetry, lattice parameters a = 3.844(3), c = 11.53(2) Angstrom and S.G. = P4/mmm. This ferromagnetic superconductor displays a magnetic transition temperature T-M = 150 K and a superconducting transition temperature T-C = 77 K. The occurrence of ferromagnetism in this superconductor can be explained by Dzyaloshinsky-Moriya (D-M)-type superexchange interaction

Anisotropic magneto-transport and magnetic properties of low-temperature phase of TaTe2

TaTe2 is a quasi-2D charge density wave (CDW) compound with distorted-1T type structure exhibiting double-zigzag chains. Here we report the Fermi surface topology of low temperature phase of TaTe2 (LT-TaTe2) by anisotropic magneto-transport and magnetic measurements on high-quality single crystals. An anomalous large linear magnetoresistance up to 140% at 3 K in 9 T was observed, suggesting the existence of a small Fermi pocket in Dirac cone state in quantum transport models. Meanwhile, strong magnetic anisotropy was observed for B (001) and B//(001). Angle-dependent magnetoresistance and de Hass-van Alphen oscillations suggest the anisotropy of the normal Fermi surface and the small Fermi pocket in Dirac cone state.

Impurity screening and stability of Fermi arcs against Coulomb and magnetic scattering in a Weyl monopnictide

We present a quasiparticle interference study of clean and Mn surface-doped TaAs, a prototypical Weyl semimetal, to test the screening properties as well as the stability of Fermi arcs against Coulomb and magnetic scattering. Contrary to topological insulators, the impurities are effectively screened in Weyl semimetals. The adatoms significantly enhance the strength of the signal such that theoretical predictions on the potential impact of Fermi arcs can be unambiguously scrutinized. Our analysis reveals the existence of three extremely short, previously unknown scattering vectors. Comparison with theory traces them back to scattering events between large parallel segments of spin-split trivial states, strongly limiting their coherence. In sharp contrast to previous work [R. Batabyal et al., Sci. Adv. 2, e1600709 (2016)], where similar but weaker subtle modulations were interpreted as evidence of quasiparticle interference originating from Femi arcs, we can safely exclude this being the case. Overall, our results indicate that intra- as well as inter-Fermi arc scattering are strongly suppressed and may explain why-in spite of their complex multiband structure-transport measurements show signatures of topological states in Weyl monopnictides.

Quantum linear magnetoresistance in NbTe 2

Abstract NbTe2 is a quasi-2D layered semimetal with charge density wave ground state showing a distorted-1T structure at room temperature. Here we report the anisotropic magneto-transport properties of NbTe2. An anomalous linear magnetoresistance up to 30% at 3 K in 9 T was observed, which can be well explained by a quantum linear magnetoresistance model. Our results reveal that a large quasi-2D Fermi surface and small Fermi pockets with linearly dispersive bands coexist in NbTe2. The comparison with the isostructural TaTe2 provides more information about the band structure evolution with charge density wave transitions in NbTe2 and TaTe2.

A self-powered sensitive ultraviolet photodetector based on epitaxial graphene on silicon carbide*

A self-powered graphene-based photodetector with high performance is particularly useful for device miniaturization and to save energy. Here, we report a graphene/silicon carbide (SiC)-based self-powered ultraviolet photodetector that exhibits a current responsivity of 7.4 mA/W with a response frequency of over a megahertz under 325-nm laser irradiation. The built-in photovoltage of the photodetector is about four orders of magnitude higher than previously reported results for similar devices. These favorable properties are ascribed to the ingenious device design using the combined advantages of graphene and SiC, two terminal electrodes, and asymmetric light irradiation on one of the electrodes. Importantly, the photon energy is larger than the band gap of SiC. This self-powered photodetector is compatible with modern semiconductor technology and shows potential for applications in ultraviolet imaging and graphene-based integrated circuits.