After growing successfully TaP single crystal, we measured its longitudinal resistivity (ρxx) and Hall resistivity (ρyx) at magnetic fields up to 9T in the temperature range of 2-300K. It was found that at 2K its magnetoresistivity (MR) reaches to 3.28×105 %, at 300K to 176% at 8T, and both do not appear saturation. We confirmed that TaP is indeed a low carrier concentration, hole-electron compensated semimetal, with a high mobility of hole µ h =3.71×105 cm 2 /V s, and found that a magnetic-field-induced metal-insulator transition occurs at room temperature. Remarkably, as a magnetic field (H ) is applied in parallel to the electric field (E ), the negative MR due to chiral anomaly is observed, and reaches to -3000% at 9T without any signature of saturation, too, which distinguishes with other Weyl semimetals (WSMs). The analysis on the Shubnikov-de Haas (SdH) oscillations superimposing on the MR reveals that a nontrivial Berry's phase with strong offset of 0.3958 realizes in TaP, which is the characteristic feature of the charge carriers enclosing a Weyl nodes. These results indicate that TaP is a promising candidate not only for revealing fundamental physics of the WSM state but also for some novel applications. [8] compound, in which fine-tuning the chemical composition is necessary for breaking inversion symmetry, a WSM has not realized experimentally in any of these compounds due to either no enough large magnetic domain or difficulty to tune the chemical composition within 5%. Very recently, the theoretical proposal [9,10] for a WSM in a class of stoichiometric materials, including TaAs, TaP, NbAs and NbP, which break crystalline inversion symmetry, has been soon confirmed by the experiments [11][12][13][14], except for TaP due to difficulty to grow large crystal. The exotic transport properties exhibiting in these materials ignite an extensive interesting in both the condensed matter physics and material science community, especial for their extremely large magnetoresistance (MR) and ultrahigh mobility of charge carriers.Materials with large MR have been used as magnetic sensors [16], in magnetic memory [17], and in hard drives [18] at room temperature. Large MR is an uncommon property, mostly of magnetic compounds, such as a giant magnetoresistance (GMR) [19] emerging in Fe/Cr thin-film, and colossal magnetoresistance (CMR) in the manganese based perovskites [20,21]. In contrast, ordinary MR, a relatively weak effect, is commonly found in non-magnetic compounds and elements [22]. Magnetic materials typically have negative MR. Positive MR is seen in metals, usually at the level of a few percent, and in some semiconductors, such as 200% at room temperature in Ag 2+δ (Te,Se) [30], comparable with those of materials showing CMR [24], and semimetals, such as high-purity bismuth, graphite [25], and 4.5×10 4 % in WTe 2 [26]. In the semimetals, very high MR is attributed to a balanced hole-electron "resonance" condition, as described in Ref. [26]. WSM provides another possibility to realize extremely large MR, ...
We have synthesized polycrystalline samples of Fe 1.11 (Te 1−x S x ) and single crystals of Fe 1+y (Te 0.88 S 0.12 ), and characterized their properties. Our results show that the solid solution of S in the Fe 1.11 Te tetragonal lattice is limited, ~10%. We observed superconductivity at ~8 K in both polycrystalline samples and single crystals. Magnetization measurements reveal that the volume fraction is small for this superconducting phase in both polycrystalline samples as-synthesized and single crystals as-grown. It is found that annealing in air enhances the superconducting fraction; the maximum fraction is almost 100% in the single crystals annealed in air at 300°C. We discuss the effect of annealing on superconductivity and transport properties at the normal state in the Fe 1+y (Te 1−x S x ) system in terms of decrease of the excess Fe. Fe-Based superconductors, Fe 1+y (Te 1−x S x ) single crystal, annealing effect PACS: 74.62.Bf, 74.90+nThe recent rapid development in Fe-based superconductors is remarkable. After the report of superconductivity at 26 K in LaFeAsO 1−x F x [1], materials with much higher superconducting transition temperatures up to 43-56 K were almost immediately discovered in LaFeAsO 1−x F x under high pressure [2], and in the Ce-, Sm-, Nd-, Th-or Sr-substituted isostructural systems [3][4][5][6][7][8][9]. Moreover, superconductivity has also been revealed in such oxygen-free systems as (Ba 1−x K x )Fe 2 As 2 [10-12] and Li 1−x FeAs [13][14][15]. One of the remarkable properties of these materials is that their undoped parent compounds show SDW-type antiferromagnetic (AFM) orders, which either follow, or are accompanied by structure transitions [16][17][18][19]. Charge carrier doping in these materials suppresses long-range AFM orders and induces superconductivity, suggesting that magnetic correlations play an essential role in mediating superconducting pairing.Another class of binary Fe-based superconductor α-FeSe with T c~8 K was discovered [20], and its T c can be enhanced to 27 K by applying hydrostatic pressure [21]. In order to determine if the superconductivity in FeSe is associated with magnetic correlations, we previously studied the evolution of superconductivity and the phase diagram of the ternary Fe(Se 1−x Te x ) 0.82 (0≤x≤1.0) system [22]. We found an enhanced superconducting phase with T c,max ~14 K in the 0.3
A feasible strategy for realizing the Majorana fermions is searching for a simple compound with both bulk superconductivity and Dirac surface states. In this paper, we perform calculations of electronic band structure, the Fermi surface, and the surface states, and measure the resistivity, magnetization, and specific heat of a TlSb compound with a CsCl-type structure. The band structure calculations show that TlSb is a Dirac semimetal when spin-orbit coupling is considered. TlSb is first determined to be a type-II superconductor with T c =4.38 K, H c1 (0) = 148 Oe, H c2 (0)=1.12 T, and κ GL = 10.6. We also confirm that TlSb is a moderately coupled s-wave superconductor. Although we cannot determine the band near the Fermi level E F that is responsible for superconductivity, its coexistence with topological surface states implies that the TlSb compound may be a simple material platform to realize the fault-tolerant quantum computations.
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