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Journal Articles

One-dimensional band structure in quasi-two-dimensional $$eta$$-Mo$$_4$$O$$_{11}$$ revealed by angle-resolved photoelectron spectroscopy and first-principles calculation

Sumida, Kazuki; Higaki, Sota*; Sato, Hitoshi*; Tsuru, Daichi*; Miyamoto, Koji*; Okuda, Taichi*; Kuroiwa, Yoshihiro*; Moriyoshi, Chikako*; Takase, Koichi*; Oguchi, Tamio*; et al.

Journal of the Physical Society of Japan, 92(8), p.084706_1 - 084706_6, 2023/08

Journal Articles

Exploring spin-polarization in Bi-based high-$$T_c$$ cuprates

Iwasawa, Hideaki*; Sumida, Kazuki; Ishida, Shigeyuki*; Le F$`e$vre, P.*; Bertran, F.*; Yoshida, Yoshiyuki*; Eisaki, Hiroshi*; Santander-Syro, A.*; Okuda, Taichi*

Scientific Reports (Internet), 13, p.13451_1 - 13451_7, 2023/08

Journal Articles

Ultrafast electron dynamics in a topological surface state observed in two-dimensional momentum space

Reimann, J.*; Sumida, Kazuki; Kakoki, Masaaki*; Kokh, K. A.*; Tereshchenko, O. E.*; Kimura, Akio*; G$"u$dde, J.*; H$"o$fer, U.*

Scientific Reports (Internet), 13, p.5796_1 - 5796_8, 2023/04

 Times Cited Count:0 Percentile:0(Multidisciplinary Sciences)

Journal Articles

Electronic structure and topological properties of Co-based Heusler alloys probed by photoelectron spectroscopy

Sumida, Kazuki; Sakuraba, Yuya*; Kimura, Akio*

Kotai Butsuri, 58(3), p.117 - 137, 2023/03

no abstracts in English

Journal Articles

Formation of monolayer V$$_5$$Se$$_8$$ from multilayer VSe$$_2$$ films via V- and Se-desorption

Sumida, Kazuki; Kusaka, Shotaro*; Takeda, Yukiharu; Kobayashi, Katsuyoshi*; Hirahara, Toru*

Physical Review B, 106(19), p.195421_1 - 195421_7, 2022/11

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

Journal Articles

Enhanced $$d$$-$$p$$ hybridization intertwined with anomalous ground state formation in the van der Waals itinerant magnet Fe$$_5$$GeTe$$_2$$

Yamagami, Kohei*; Fujisawa, Yuita*; Pardo-Almanza, M*; Smith, B. R. M.*; Sumida, Kazuki; Takeda, Yukiharu; Okada, Yoshinori*

Physical Review B, 106(4), p.045137_1 - 045137_8, 2022/07

 Times Cited Count:2 Percentile:37.1(Materials Science, Multidisciplinary)

Journal Articles

Fabrication of (Bi$$_2$$)$$_m$$(Bi$$_2$$Te$$_3$$)$$_n$$ superlattice films by Te desorption from a pristine Bi$$_2$$Te$$_3$$ film

Kusaka, Shotaro*; Sasaki, Taisuke*; Sumida, Kazuki; Ichinokura, Satoru*; Ideta, Shinichiro*; Tanaka, Kiyohisa*; Hono, Kazuhiro*; Hirahara, Toru*

Applied Physics Letters, 120(17), p.173102_1 - 173102_5, 2022/04

 Times Cited Count:2 Percentile:37.1(Physics, Applied)

Journal Articles

Short-range magnetic interaction in a monolayer 1$$T$$-VSe$$_2$$ film revealed by element-specific X-ray magnetic circular dichroism

Sumida, Kazuki; Takeda, Yukiharu; Kusaka, Shotaro*; Kobayashi, Katsuyoshi*; Hirahara, Toru*

Physical Review Materials (Internet), 6(1), p.014006_1 - 014006_8, 2022/01

 Times Cited Count:5 Percentile:68.76(Materials Science, Multidisciplinary)

We investigated the intrinsic magnetic properties of the two-dimensional ferromagnetic candidate monolayer 1$$T$$-VSe$$_2$$ films using X-ray magnetic circular dichroism (XMCD), an element-specific magnetic probe. By performing high-resolution measurements, we succeeded in detecting a clear XMCD signal from the atomically thin 1$$T$$-VSe$$_2$$ films under an external magnetic field. Through manipulation of the X-ray incidence angle, we were able to disentangle the in-plane and out-of-plane magnetic properties and found a strong magnetic anisotropy. Moreover, magnetic field- and temperature-dependent XMCD revealed that there is no long-range ferromagnetic ordering even at 6 K, but short-range ferromagnetic and antiferromagnetic interactions between neighboring vanadium ions exist. Such low-temperature magnetic behavior signifies that the monolayer 1$$T$$-VSe$$_2$$ is on the verge of ferromagnetism, and this fact accounts for the reported ferromagnetism in VSe$$_2$$-based heterostructures.

Journal Articles

Three-dimensional bulk Fermi surfaces and Weyl crossings of Co$$_2$$MnGa thin films underneath a protection layer

Kono, Takashi*; Kakoki, Masaaki*; Yoshikawa, Tomoki*; Wang, X.*; Sumida, Kazuki; Muro, Takayuki*; Goto, Kazuki*; Sakuraba, Yuya*; Umetsu, Rie*; Kimura, Akio*

Physical Review B, 104(19), p.195112_1 - 195112_8, 2021/11

 Times Cited Count:0 Percentile:18.63(Materials Science, Multidisciplinary)

Angle-resolved photoelectron spectroscopy utilizing soft X-ray synchrotron radiation was applied to Heusler-type Co$$_2$$MnGa thin films that have a 1-nm Al capping layer. The bulk Fermi surfaces and band structures varied along the out-of-plane momentum, stemming from the three-dimensional crystal structure, in the absence of any in situ surface treatment. In addition, there were characteristic intersecting bands (Weyl cones), with crossing points near the Fermi level, which were consistent with computed results. The Weyl cones are of bulk origin and are responsible for the high anomalous Nernst and the anomalous Hall coefficients. A close comparison of the experimental band structures in Co$$_2$$MnGe and Co$$_2$$MnGa indicated that the rigid band picture is valid in both alloys and that fine carrier tuning is possible by replacing Ga with Ge to improve the anomalous conductivity.

Journal Articles

Absence of ferromagnetism in MnBi$$_2$$Te$$_4$$/Bi$$_2$$Te$$_3$$ down to 6 K

Fukasawa, Takuro*; Kusaka, Shotaro*; Sumida, Kazuki; Hashizume, Mizuki*; Ichinokura, Satoru*; Takeda, Yukiharu; Ideta, Shinichiro*; Tanaka, Kiyohisa*; Shimizu, Ryota*; Hitosugi, Taro*; et al.

Physical Review B, 103(20), p.205405_1 - 205405_6, 2021/05

 Times Cited Count:7 Percentile:67.62(Materials Science, Multidisciplinary)

Journal Articles

Ultrafast surface Dirac fermion dynamics of Sb$$_2$$Te$$_3$$-based topological insulators

Sumida, Kazuki; Ishida, Yukiaki*; G$"u$dde, J.*; H$"o$fer, U.*; Shin, S.*; Kimura, Akio*

Progress in Surface Science, 96(2), p.100628_1 - 100628_15, 2021/05

 Times Cited Count:1 Percentile:2.31(Chemistry, Physical)

Journal Articles

Ultrafast carrier dynamics and light-induced functionalizations of topological insulators

Sumida, Kazuki; Ishida, Yukiaki*; Kimura, Akio*

Nihon Butsuri Gakkai-Shi, 75(12), p.756 - 760, 2020/12

Journal Articles

Spin-polarized Weyl cones and giant anomalous Nernst effect in ferromagnetic Heusler films

Sumida, Kazuki; Sakuraba, Yuya*; Masuda, Keisuke*; Kono, Takashi*; Kakoki, Masaaki*; Goto, Kazuki*; Zhou, W.*; Miyamoto, Koji*; Miura, Yoshio*; Okuda, Taichi*; et al.

Communications Materials (Internet), 1, p.89_1 - 89_9, 2020/11

Journal Articles

Fabrication of a novel magnetic topological heterostructure and temperature evolution of its massive Dirac cone

Hirahara, Toru*; Otrokov, M. M.*; Sasaki, Taisuke*; Sumida, Kazuki*; Tomohiro, Yuta*; Kusaka, Shotaro*; Okuyama, Yuma*; Ichinokura, Satoru*; Kobayashi, Masaki*; Takeda, Yukiharu; et al.

Nature Communications (Internet), 11, p.4821_1 - 4821_8, 2020/09

 Times Cited Count:35 Percentile:93.42(Multidisciplinary Sciences)

Journal Articles

Unveiling spin-dependent unoccupied electronic states of Co$$_{2}$$MnGe (Ga) film via Ge (Ga) $$L_{2,3}$$ absorption spectroscopy

Yoshikawa, Tomoki*; Antonov, V. N.*; Kono, Takashi*; Kakoki, Masaaki*; Sumida, Kazuki; Miyamoto, Koji*; Takeda, Yukiharu; Saito, Yuji; Goto, Kazuki*; Sakuraba, Yuya*; et al.

Physical Review B, 102(6), p.064428_1 - 064428_7, 2020/08

 Times Cited Count:1 Percentile:13.29(Materials Science, Multidisciplinary)

Journal Articles

Element-specific density of states of Co$$_{2}$$MnGe revealed by resonant photoelectron spectroscopy

Kono, Takashi*; Kakoki, Masaaki*; Yoshikawa, Tomoki*; Wang, X.*; Sumida, Kazuki*; Miyamoto, Koji*; Muro, Takayuki*; Takeda, Yukiharu; Saito, Yuji; Goto, Kazuki*; et al.

Physical Review B, 100(16), p.165120_1 - 165120_6, 2019/10

 Times Cited Count:4 Percentile:22.33(Materials Science, Multidisciplinary)

Journal Articles

Magnetic-impurity-induced modifications to ultrafast carrier dynamics in the ferromagnetic topological insulators Sb$$_{2-x}$$V$$_{x}$$Te$$_{3}$$

Sumida, Kazuki*; Kakoki, Masaaki*; Reimann, J.*; Nurmamat, M.*; Goto, Shinichi*; Takeda, Yukiharu; Saito, Yuji; Kokh, K. A.*; Tereshchenko, O. E.*; G$"u$dde, J.*; et al.

New Journal of Physics (Internet), 21(9), p.093006_1 - 093006_8, 2019/09

 Times Cited Count:10 Percentile:65.58(Physics, Multidisciplinary)

Journal Articles

Negative Te spin polarization responsible for ferromagnetic order in the doped topological insulator V$$_{0.04}$$(Sb$$_{1-x}$$Bi$$_{x}$$)$$_{1.96}$$Te$$_{3}$$

Ye, M.*; Xu, T.*; Li, G.*; Qiao, S.*; Takeda, Yukiharu; Saito, Yuji; Zhu, S.-Y.*; Nurmamat, M.*; Sumida, Kazuki*; Ishida, Yukiaki*; et al.

Physical Review B, 99(14), p.144413_1 - 144413_7, 2019/04

AA2018-0697.pdf:1.89MB

 Times Cited Count:12 Percentile:56.9(Materials Science, Multidisciplinary)

Journal Articles

Carrier-mediated ferromagnetism in the magnetic topological insulator Cr-doped (Sb,Bi)$$_{2}$$Te$$_{3}$$

Ye, M.*; Li, W.*; Zhu, S.-Y.*; Takeda, Yukiharu; Saito, Yuji; Wang, J.*; Pan, H.*; Nurmamat, M.*; Sumida, Kazuki*; Ji, F.*; et al.

Nature Communications (Internet), 6, p.8913_1 - 8913_7, 2015/11

AA2015-0647.pdf:0.64MB

 Times Cited Count:52 Percentile:90.05(Multidisciplinary Sciences)

Magnetically doped topological insulators are predicted to exhibit exotic phenomena including the quantized anomalous Hall effect and a dissipationless transport, which facilitate the development of low-power-consumption devices using electron spins. The realization of the quantized anomalous Hall effect is so far restricted to the Cr-doped (Sb,Bi)$$_{2}$$Te$$_{3}$$ system at extremely low temperature; however, the microscopic origin of its ferromagnetism is poorly understood. Here we present an element-resolved study for Cr-doped (Sb,Bi)$$_{2}$$Te$$_{3}$$ using X-ray magnetic circular dichroism to unambiguously show that the long-range magnetic order is mediated by the p-hole carriers of the host lattice, and the interaction between the Sb(Te) p and Cr d states is crucial.

Journal Articles

Spectroscopic evidence of band Jahn-Teller distortion upon martensitic phase transition in Heusler-type Ni-Fe(Co)-Ga ferromagnetic shape-memory alloy films

Sumida, Kazuki*; Shirai, Kaito*; Zhu, S.-Y.*; Taniguchi, Masaki*; Ye, M.*; Ueda, Shigenori*; Takeda, Yukiharu; Saito, Yuji; Aseguinolaza, I. R.*; Barandiar$'a$n, J. M.*; et al.

Physical Review B, 91(13), p.134417_1 - 134417_6, 2015/04

 Times Cited Count:6 Percentile:28.15(Materials Science, Multidisciplinary)

39 (Records 1-20 displayed on this page)