We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on trigonal tellurium consisting of helical chains in the crystal. Through the band-structure mapping in the three-dimensional Brillouin zone, we found a definitive evidence for the band splitting originating from the chiral nature of crystal. A direct comparison of the band dispersion between the ARPES results and the first-principles band-structure calculations suggests the presence of Weyl nodes and tiny spin-polarized hole pockets around the H point. The present result opens a pathway toward studying the interplay among crystal symmetry, band structure, and exotic physical properties in chiral crystals. PACS numbers: 74.25.Jb, 74.70.Xa, Chirality, the asymmetry of an object upon its mirroring, is ubiquitous in nature. In the standard model of particle physics, quantum vacuum state is regarded to be chiral and the characteristic of elementary particles (quarks and leptons) is essentially different between lefthanded and right-handed counterparts. Chirality also emerges as chiral molecules, ions, and crystals, playing an important role in a wide variety of subjects such as chemistry, biology, and solid-state physics [1,2]. Chiral crystals are recently attracting a great deal of attention, since they are known to be useful for advanced applications such as polarization optics [3][4][5], multiferroics [6,7], and spintronics [8][9][10]. Also, they are predicted to host peculiar optical and transport properties, essentially owing to the spin splitting of electronic energy bands originating from the space-inversion-symmetry (SIS) breaking of the crystal [11][12][13][14][15]. The chiral crystals belong to the non-symmorphic space group, and are characterized by the screw symmetry (translational plus rotational symmetry), which is currently discussed to be one of key ingredients for the realization of novel topological semimetals [13,16,17].Amongst various chiral crystals, trigonal tellurium (Te) is recently attracting particular attention due to its simple crystal structure suitable for the band engineering [13,16,[18][19][20][21][22][23][24][25]. As shown in Figs. 1(a) and 1(b), trigonal Te consists of three atoms in a unit cell with infinite helical chains arranged in a hexagonal array, which spiral around axes parallel to c ([001] axis). Depending on the right-handed or left-handed screw axis, the space group is P3 1 21 or P3 2 21 (D 4 3 or D 6 3 ) [note that the right-handed case is displayed in Figs. 1(a) and 1(b)], in which the SIS is broken. Trigonal Te is a semiconductor with a band gap of 0.32 eV [18,19] in which the valence-band (VB) maxima and conduction-band (CB) minima are located at around the H point of the bulk Brillouin zone (BZ) [13,16,20,22], and it shows intriguing physical properties such as high efficiency thermoelectricity [24], circular photon drag effect [14], and current-induced spin polarization [11,12]. Under pressure, it undergoes complex structural changes and semiconductor to metal transition [21]. Ab in...

Wear volume, surface area and coefficient of friction of UHMWPE cup crosslinked with gamma radiation of 0, 50, 75, 100, 125, 150 and 200 Mrad sliding against an alumina ball were measured using a sphere-on-flat reciprocating type tribology testing machine. The effects of gamma radiation were scarcely observed in coefficient of friction. The coefficient of friction under lubricated (distilled water) and non-lubricated testing conditions was 0.08 to 0.12 and 0.20 to 0.25, respectively. The wear volume of UHMWPE with radiation of 50 Mrad, 75 to 150 Mrad, and 200 Mrad was 70 to 80%, 18 to 25%, and 12 to 15%, respectively, in comparison to non-irradiated specimens. Elongation and tensile strength of UHMWPE with radiation of 100 Mrad decreased to 6%, and 50% of that without radiation, respectively. The hardness increased with increase of the radiation dose. From several kinds of tribological findings, mechanical strength tests, and studies of long-term clinical findings, it is concluded that approximately 200 Mrad is the optimum dose of gamma radiation for clinical use in total hip prostheses.

The discovery of high-temperature (Tc) superconductivity in monolayer FeSe on SrTiO3 raised a fundamental question whether high Tc is commonly realized in monolayer iron-based superconductors. Tetragonal FeS is a key material to resolve this issue because bulk FeS is a superconductor with Tc comparable to that of isostructural FeSe. However, difficulty in synthesizing tetragonal monolayer FeS due to its metastable nature has hindered further investigations. Here we report elucidation of band structure of monolayer FeS on SrTiO3, enabled by a unique combination of in-situ topotactic reaction and molecular-beam epitaxy. Our angle-resolved photoemission spectroscopy on FeS and FeSe revealed marked similarities in the electronic structure, such as heavy electron doping and interfacial electron-phonon coupling, both of which have been regarded as possible sources of high Tc in FeSe. However, surprisingly, high-Tc superconductivity is absent in monolayer FeS. This is linked to the weak superconducting pairing in electron-doped multilayer FeS in which the interfacial effects are absent. Our results strongly suggest that the cross-interface electron-phonon coupling enhances Tc only when it cooperates with the pairing interaction inherent to the superconducting layer. This finding provides a key insight to explore new heterointerface high-Tc superconductors.

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