Yujia Long

Observation of the Chiral-Anomaly-Induced Negative Magnetoresistance in 3D Weyl Semimetal TaAs

Xiaochun Huang, Lingxiao Zhao, Yujia Long, Peipei Wang, Dong Chen, Zhanhai Yang, Hui Liang, Mianqi Xue, Hongming Weng, Zhong Fang, Xi Dai, and Genfu Chen Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China Collaborative Innovation Center of Quantum Matter, Beijing 100084, China (Received 14 May 2015; published 24 August 2015)

Atom-Thin SnS2–xSex with Adjustable Compositions by Direct Liquid Exfoliation from Single Crystals

Two-dimensional (2D) chalcogenide materials are fundamentally and technologically fascinating for their suitable band gap energy and carrier type relevant to their adjustable composition, structure, and dimensionality. Here, we demonstrate the exfoliation of single-crystal SnS2-xSex (SSS) with S/Se vacancies into an atom-thin layer by simple sonication in ethanol without additive. The introduction of vacancies at the S/Se site, the conflicting atomic radius of sulfur in selenium layers, and easy incorporation with an ethanol molecule lead to high ion accessibility; therefore, atom-thin SSS flakes can be effectively prepared by exfoliating the single crystal via sonication. The in situ pyrolysis of such materials can further adjust their compositions, representing tunable activation energy, band gap, and also tunable response to analytes of such materials. As the most basic and crucial step of the 2D material field, the successful synthesis of an uncontaminated and atom-thin sample will further push ahead the large-scale applications of 2D materials, including, but not limited to, electronics, sensing, catalysis, and energy storage fields.

Direct Pen Writing of High-Tc, Flexible Magnesium Diboride Superconducting Arrays.

High-Tc , flexible MgB2 -nanowire-based superconducting arrays are fabricated via a direct pen writing method on both copper foils and poly(dimethylsiloxane) (PDMS) substrates. Such superconducting arrays constitute a new approach for fabricating superconducting devices. The realization of a PDMS-based device demonstrates the potential for expanding this material into other high-Tc superconductor systems, which may lead to novel ways of driving the development of real-life applications.

Pressure-induced topological phase transitions and strongly anisotropic magnetoresistance in bulk black phosphorus

Chun-Hong Li, Yu-Jia Long, Ling-Xiao Zhao, Lei Shan, Zhi-An Ren, Jian-Zhou Zhao, Hong-Ming Weng, Xi Dai, Zhong Fang, Gen-Fu Chen, Cong Ren 1 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190, China 2 Physics Department, Yunnan University, Kunming 671000, China 3 Co-Innovation Center for New Energetic Materials, Southwest University of Science and Technology, Mianyang, Sicuan 621010, China and 4 Collaborative Innovation Center of Advanced Microstructures, Beijing 100190, China

Anomalous Magneto-Transport Behavior in Transition Metal Pentatelluride HfTe5

There is a long-standing confusion concerning the physical origin of the anomalous resistivity peak in transition metal pentatelluride HfTe5. Several mechanisms, such as the formation of charge density wave or polaron, have been proposed, but so far no conclusive evidence has been presented. In this work, we investigate the unusual temperature dependence of magneto-transport properties in HfTe5. It is found that a three-dimensional topological Dirac semimetal state emerges only at around Tp (at which the resistivity shows a pronounced peak), as manifested by a large negative magnetoresistance. This accidental Dirac semimetal state mediates the topological quantum phase transition between the two distinct weak and strong topological insulator phases in HfTe5. Our work not only provides the first evidence of a temperature-induced critical topological phase transition in HfTe5 but also gives a reasonable explanation on the long-lasting question.

Superconductivity in Pd-intercalated charge-density-wave rare earth poly-tellurides RETe n

The interplay between magnetism and superconductivity is one of the dominant themes in the study of unconventional superconductors, such as high-Tc cuprates, iron pnictides and heavy fermions. In such systems, the same d- or f-electrons tend to form magnetically ordered states and participate in building up a high density of states at the Fermi level, which is responsible for the superconductivity. Charge-density-wave (CDW) is another fascinating collective quantum phenomenon in some low dimensional materials, like the prototypical transition-metal poly-chalcogenides, in which CDW instability is frequently found to accompany with superconducting transition at low temperatures. Remarkably, similar to the antiferromagnetic superconductors, superconductivity can also be achieved upon suppression of CDW order via chemical doping or applied pressure in 1T-TiSe2. However, in these CDW superconductors, the two ground states are believed to occur in different parts of Fermi surface (FS) sheets, derived mainly from chalcogen p-states and transition metal d-states, respectively. The origin of superconductivity and its interplay with CDW instability has not yet been unambiguously determined. Here we report on the discovery of bulk superconductivity in Pd-intercalated CDW RETen (RE=rare earth; n=2.5, 3) compounds, which belong to a large family of rare-earth poly-chalcogenides with CDW instability usually developing in the planar square nets of tellurium at remarkably high transition temperature and the electronic properties are also dominated by chalcogen p-orbitals. Our study demonstrates that the intercalation of palladium leads to the suppression of the CDW order and the emergence of the superconductivity. Our finding could provide an ideal model system for comprehensive studies of the interplay between CDW and superconductivity.

Single Crystal Growth and Physical Property Characterization of Non-centrosymmetric Superconductor PbTaSe2 *

We report on the single crystal growth and superconducting properties of PbTaSe2 with the non-centrosymmetric crystal structure. By using the chemical vapor transport technique, centimeter-size single crystals are successfully obtained. The measurement of temperature dependence of electrical resistivity ρ(T) in both normal and superconducting states indicates a quasi-two-dimensional electronic state in contrast to that of polycrystalline samples. Specific heat C(T) measurement reveals a bulk superconductivity with Tc 3.75 K and a specific heat jump ratio of 1.42. All these results are in agreement with a moderately electron–phonon coupled, type-II Bardeen–Cooper–Schrieffer superconductor.

Direct imaging of incommensurate wave pockets in the charge-density-wave state of LaTe2

We herein report the study of the atomic structure for a fully incommensurate CDW in LaTe2 using Cs-corrected scanning transmission electron microscopy (STEM). It is directly revealed for the first time that the atomic displacements adopt an incommensurate wave-pocket structure along each Te chain. This pocket structure has a long periodicity determined by the CDW incommensurability. We can use the sinusoidal waves as the first-order approximation to characterize the atomic motions within the pocket pattern, which can yield atomic displacements in good agreement with the theoretical model commonly used for studying CDW. These facts demonstrate that the incommensurate pocket patterns should be an essential structural nature in the CDW states and play a critical role for developing the mechanism of the CDW transitions.

Superconductivity in Pd-Intercalated Ternary Rare-Earth Polychalcogenide NdSeTe2*

We synthesize a set of Pd-doped polycrystalline samples PdxNdSeTe2 and measure their physical properties. Compared with pure NdSeTe2, the charge density wave (CDW) order is continuously suppressed with the Pd-intercalation. Bulk superconductivity first appears at x = 0.06 with Tc nearly 2.5K, coexisting with a CDW transition at 176K. Further Pd-doping enhances Tc, until it reaches the maximum value 2.84K at x=0.1, meanwhile the CDW transition vanishes. The upper critical field for the optimal doping sample Pd0.1NdSeTe2 is determined from the R-H measurement, which is estimated to be 0.6 T. These results provide another kind of ideal compound for studying the interplay between CDW and superconductivity systematically.