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Author

Hirofumi Namatame

Other affiliations: Hiroshima University
Bio: Hirofumi Namatame is an academic researcher from Synchrotron Radiation Center. The author has contributed to research in topics: Angle-resolved photoemission spectroscopy & Photoemission spectroscopy. The author has an hindex of 43, co-authored 360 publications receiving 7182 citations. Previous affiliations of Hirofumi Namatame include Hiroshima University.


Papers
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Journal ArticleDOI
TL;DR: The finding of a huge spin-orbit interaction effect in a polar semiconductor composed of heavy elements, BiTeI, where the bulk carriers are ruled by large Rashba-likespin splitting is described, confirming that the spin splitting is indeed derived from bulk atomic configurations.
Abstract: A very large Rashba-type spin splitting, which is a consequence of spin–orbit interaction, has been observed in the heavy-element semiconductor BiTeI. The results show the possibility, in principle, of using the material in spintronics devices in which the electron spin is controlled by electric currents.

693 citations

Journal ArticleDOI
04 Dec 2003-Nature
TL;DR: In this article, angle-integrated photoemission measurements of carbon nanotubes (SWNTs) are reported, revealing an oscillation in the pi-electron density of states owing to one-dimensional van Hove singularities.
Abstract: The electronic transport properties of conventional three-dimensional metals are successfully described by Fermi-liquid theory. But when the dimensionality of such a system is reduced to one, the Fermi-liquid state becomes unstable to Coulomb interactions, and the conduction electrons should instead behave according to Tomonaga-Luttinger-liquid (TLL) theory. Such a state reveals itself through interaction-dependent anomalous exponents in the correlation functions, density of states and momentum distribution of the electrons. Metallic single-walled carbon nanotubes (SWNTs) are considered to be ideal one-dimensional systems for realizing TLL states. Indeed, the results of transport measurements on metal-SWNT and SWNT-SWNT junctions have been attributed to the effects of tunnelling into or between TLLs, although there remains some ambiguity in these interpretations. Direct observations of the electronic states in SWNTs are therefore needed to resolve these uncertainties. Here we report angle-integrated photoemission measurements of SWNTs. Our results reveal an oscillation in the pi-electron density of states owing to one-dimensional van Hove singularities, confirming the one-dimensional nature of the valence band. The spectral function and intensities at the Fermi level both exhibit power-law behaviour (with almost identical exponents) in good agreement with theoretical predictions for the TLL state in SWNTs.

396 citations

Journal ArticleDOI
TL;DR: It is demonstrated that the Fermi energy of naturally electron-doped Bi2Se3 can be tuned by 1% Mg doping in order to realize the quantum topological transport.
Abstract: A hexagonal deformation of the Fermi surface of ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ has been for the first time observed by angle-resolved photoemission spectroscopy. This is in contrast to the general belief that ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ possesses an ideal Dirac cone. The hexagonal shape is found to disappear near the Dirac node, which would protect the surface state electrons from backscattering. It is also demonstrated that the Fermi energy of naturally electron-doped ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ can be tuned by 1% Mg doping in order to realize the quantum topological transport.

239 citations

Journal ArticleDOI
TL;DR: It is demonstrated that a metallic surface-state band with a dominant Pb 6p character exhibits a large Rashba spin splitting of 200 meV and an effective mass of 0.028 me at the Fermi level, which provides a material basis for the novel field of spin transport/accumulation on semiconductor surfaces.
Abstract: Semiconductor spintronics applications require materials that can exhibit large spin-splitting while preserving a large number of carriers. Yaji and co-workers show this is possible at room temperature using a germanium surface covered with a lead monolayer.

205 citations

Journal ArticleDOI
TL;DR: The underlying mechanism of the martensitic phase transition (MPT) in a new class of ferromagnetic shape memory alloys, Ni2Mn1+xSn1-x, is revealed by the combination of bulk-sensitive hard-x-ray photoelectron spectroscopy and a first-principles density-functional calculation.
Abstract: We have revealed the underlying mechanism of the martensitic phase transition (MPT) in a new class of ferromagnetic shape memory alloys, Ni2Mn1+xSn1-x, by the combination of bulk-sensitive hard-x-ray photoelectron spectroscopy and a first-principles density-functional calculation. The Ni 3d e{g} state in the cubic phase systematically shifts towards the Fermi energy with an increase in the number of Mn atoms substituted in the Sn sites. An abrupt decrease of the intensity of the Ni 3d e{g} states upon MPT for x=0.36-0.42 has been observed in the vicinity of the Fermi level. The energy shift of the Ni 3d minority-spin e{g} state in the cubic phase originates from hybridization with the antiferromagnetically coupled Mn in the Sn site. Below the MPT temperature, the Ni 3d state splits into two levels located below and above the Fermi energy in order to achieve an energetically stable state.

188 citations


Cited by
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28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Proceedings Article
14 Jul 1996
TL;DR: The striking signature of Bose condensation was the sudden appearance of a bimodal velocity distribution below the critical temperature of ~2µK.
Abstract: Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

3,530 citations

Journal ArticleDOI
TL;DR: Weyl and Dirac semimetals as discussed by the authors are three-dimensional phases of matter with gapless electronic excitations that are protected by topology and symmetry, and they have generated much recent interest.
Abstract: Weyl and Dirac semimetals are three-dimensional phases of matter with gapless electronic excitations that are protected by topology and symmetry. As three-dimensional analogs of graphene, they have generated much recent interest. Deep connections exist with particle physics models of relativistic chiral fermions, and, despite their gaplessness, to solid-state topological and Chern insulators. Their characteristic electronic properties lead to protected surface states and novel responses to applied electric and magnetic fields. The theoretical foundations of these phases, their proposed realizations in solid-state systems, and recent experiments on candidate materials as well as their relation to other states of matter are reviewed.

3,407 citations

Journal ArticleDOI
24 Apr 2008-Nature
TL;DR: In this article, the authors used incident-photon-energy-modulated angle-resolved photoemission spectroscopy (IPEM-ARPES) to locate the Kramers points at the sample's boundary and provide a comprehensive mapping of the Dirac insulator's gapless surface electron bands.
Abstract: When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic fields. Bulk Bi(1-x)Sb(x) single crystals are predicted to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher-dimensional analogues of the edge states that characterize a quantum spin Hall insulator. In addition to its interesting boundary states, the bulk of Bi(1-x)Sb(x) is predicted to exhibit three-dimensional Dirac particles, another topic of heightened current interest following the new findings in two-dimensional graphene and charge quantum Hall fractionalization observed in pure bismuth. However, despite numerous transport and magnetic measurements on the Bi(1-x)Sb(x) family since the 1960s, no direct evidence of either topological Hall states or bulk Dirac particles has been found. Here, using incident-photon-energy-modulated angle-resolved photoemission spectroscopy (IPEM-ARPES), we report the direct observation of massive Dirac particles in the bulk of Bi(0.9)Sb(0.1), locate the Kramers points at the sample's boundary and provide a comprehensive mapping of the Dirac insulator's gapless surface electron bands. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the 'topological metal'. They also suggest that this material has potential application in developing next-generation quantum computing devices that may incorporate 'light-like' bulk carriers and spin-textured surface currents.

2,739 citations