Layered Materials Property from Semiconductor, Topological Insulator, to Weyl Semimetal Crystal Growth
Dr. Raman Sankar1*
1† Institute of Physics,, Academia Sinica,, Taipei 10617, Taiwan, Taiwan
2Center for Condensed Matter Science, National Taiwan University, Taipei, Taiwan, Taiwan
* presenting author:RAMAN SANKAR,

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The abstract is consisting of three important and intriguing materials. First involve, PbTaSe2 crystallizes in a layered structure and the crystal symmetry is non-centrosymmetric of space group P6m2. Superconductivity with Tc = 3.83±0.02 K has been characterized fully with electrical resistivity ρ(T), magnetic susceptibility χ(T), and heat capacity Cp(T) measurements using single crystal samples. The superconductivity is type-II with lower critical field Hc1 and upper critical field Hc2 of 65 and 450 Oe (H ⊥ to the ab- plane), 140 and 1500 Oe (H  to the ab-plane), respectively. These results indicate that the superconductivity of PbTaSe2 is anisotropic. the single crystal growth and superconducting properties of a misfit layered (SnS)1.15(TaS2) compound. The transport, magnetic and thermodynamic properties revealed the superconducting transition with a critical temperature at ~2.97 K. HRTEM image clearly shows the misfit phase with a regular stacking of SnS and TaS2 layers. From the Werthamer-Helfand-Hohenberg (WHH) formula and Ginzburg-Landau theory, the zero temperature limit of the upper critical field (Hc2(0) =0.42±0.02 T) and the coherence length (ξ = 28 nm) were calculated. The Sommerfeld coefficient γ = 11.70 ± 0.26 mJ mol-1 K-2, Debye temperature ΘD = 155 K, specific heat jump ∆Ce/γTc = 0.972 and the electron-phonon coupling constant λel-ph ~0.713) reveal a weak-coupling nature of (SnS)1.15(TaS2) misfit layered compound.

Second deals with, Large size ( ~2 cm) single crystals of layered MoTe2 in both 2H- and 1T‘-types were synthesized using TeBr4 as the source of Br2 transport agent in the chemical vapor transport (CVT) growth. The resistivity ρ(T), magnetic susceptibility χ(T), and heat capacity Cp(T) measurement results reveal a first order structural phase transition near ~240 K for 1T‘-MoTe2, which has been identified to be the orthorhombic Td-phase of MoTe2 as a candidate of Weyl semimetal. The STM study revealed the different local defect geometries found on the surface of 2H- and Td-types of MoTe6 unit in trigonal prismatic and distorted octahedral
Finally, following the room temperature agglomeration (RTA) treatment of the precursor, the single crystals of BiTeI obtained from three different growth methods, including vertical Bridgman, melt growth and chemical vapour transport (CVT), were compared. Crystals grown using the Bridgman method showed the highest residual-resistance ratio (RRR) and mobility, and the largest domain size among the three. Additionally, Mn-intercalated and -substituted BiTeI crystals have also been investigated.

Keywords: semiconductor, , topological insulator, , Weyl semimetal, magnetic