Crystal growth, characterization and electronic band structure of TiSeS

Layered semimetallic van der Waals materials TiSe2 has attracted a lot of attention because of interplay of a charge density wave (CDW) state and superconductivity. Its sister compound TiS2, being isovalent to TiSe2 and having the same crystal structure, shows a semiconducting behavior. The natural rises what happens at the transition point in TiSe2-xSx, which is expected for x close to 1. Here we report the growth and characterization of TiSeS single crystals and the study of the electronic structure using density functional theory (DFT) and angle-resolved photoemission (ARPES). We show that TiSeS single crystals have the same morphology as TiSe2. Transport measurements reveal a metallic state, no evidence of CDW was found. DFT calculations suggest that the electronic band structure in TiSeS is similar to that of TiSe2, but the electron and hole pockets in TiSeS are much smaller. The ARPES results are in good agreement with the calculations.Comment: 22 pages, 9 figure

Charge Density Wave Induced Peak Dip Hump Structure and the Multiband Superconductivity in a Kagome Superconductor CsV3Sb5

The entanglement of charge density wave CDW , superconductivity, and topologically nontrivial electronic structure has recently been discovered in the kagome metal AV3Sb5 A K, Rb, Cs family. With high resolution angle resolved photoemission spectroscopy, we study the electronic properties of CDW and superconductivity in CsV3Sb5. The spectra around K is found to exhibit a peak dip hump structure associated with two separate branches of dispersion, demonstrating the isotropic CDW gap opening below EF. The peak dip hump line shape is contributed by linearly dispersive Dirac bands in the lower branch and a dispersionless flat band close to EF in the upper branch. The electronic instability via Fermi surface nesting could play a role in determining these CDW related features. The superconducting gap of amp; 8764;0.4 amp; 8201; amp; 8201;meV is observed on both the electron band around amp; 915; and the flat band around K, implying the multiband superconductivity. The finite density of states at EF in the CDW phase is most likely in favor of the emergence of multiband superconductivity, particularly the enhanced density of states associated with the flat band. Our results not only shed light on the controversial origin of the CDW, but also offer insights into the relationship between CDW and superconductivit

Fermi surface tomography

Fermi surfaces are essential for predicting, characterizing and controlling the properties of crystalline metals and semiconductors. Angle-resolved photoemission spectroscopy (ARPES) is the only technique directly probing the Fermi surface by measuring the Fermi momenta (k(F)) from energy- and angular distribution of photoelectrons dislodged by monochromatic light. Existing apparatus is able to determine a number of k(F) -vectors simultaneously, but direct high-resolution 3D Fermi surface mapping remains problematic. As a result, no such datasets exist, strongly limiting our knowledge about the Fermi surfaces. Here we show that using a simpler instrumentation it is possible to perform 3D-mapping within a very short time interval and with very high resolution. We present the first detailed experimental 3D Fermi surface as well as other experimental results featuring advantages of our technique. In combination with various light sources our methodology and instrumentation offer new opportunities for high-resolution ARPES in the physical and life sciences

Isolated fourfold fermion in BiTeI

We use angle resolved photoemission spectroscopy to revisit the electronic structure of BiTeI, previously identified as a polar semiconductor with giant bulk Rashba splitting. We propose an alternative description, which is based on the experimentally determined crystal structure and agrees well with resistivity, quantum oscillations,and optical measurements. BiTeI emerges as a topological 3D Dirac semimetal hosting only two, well isolated from each other and rest of the band structure, Dirac points. Properly doped bulk material or the controlled synthesis of iodine terminated surface of the pristine material promise to become a canonical condensed matter system whose physical properties are completely defined by the behavior of fourfold fermion

Evidence of superconducting Fermi arcs

An essential ingredient for the production of Majorana fermions for use in quantum computing is topological superconductivity1,2. As bulk topological superconductors remain elusive, the most promising approaches exploit proximity induced superconductivity3, making systems fragile and difficult to realize4,5,6,7. Due to their intrinsic topology8, Weyl semimetals are also potential candidates1,2, but have always been connected with bulk superconductivity, leaving the possibility of intrinsic superconductivity of their topological surface states, the Fermi arcs, practically without attention, even from the theory side. Here, by means of angle resolved photoemission spectroscopy and ab initio calculations, we identify topological Fermi arcs on two opposing surfaces of the non centrosymmetric Weyl material trigonal PtBi2 ref. amp; 8201;9 . We show these states become superconducting at temperatures around 10 amp; 8201;K. Remarkably, the corresponding coherence peaks appear as the strongest and sharpest excitations ever detected by photoemission from solids. Our findings indicate that superconductivity in PtBi2 can occur exclusively at the surface, rendering it a possible platform to host Majorana modes in intrinsically topological superconductor normal metal superconductor Josephson junction