Preprint
Emergent topological magnetism in Hund's excitonic insulator
R. Okuma, K. Yamagami, Y. Fujisawa, C. H. Hsu, Y. Obata, N. Tomoda, M. Dronova, K. Kuroda, H. Ishikawa, K. Kawaguchi, K. Aido, K. Kindo, Y. H. Chan, H. Lin, Y. Ihara, T. Kondo, Y. Okada
Imaging emergent exotic quasiparticle state in a frustrated transition metal oxide
Y. Fujisawa, A. Krishnadas, C. H. Hsu, T. Takeda, S. Liu, M. P. Almanza, Y. Obata, D. van Dinter, K. Yamagami, G. Chang, M. Kobayashi, C. Y. Kuo, Y. Okada
Visualizing magnetic field-induced rotational electronic symmetry breaking in a spinel oxide superconductor
Y. Fujisawa, A. Krishnadas, C. H. Hsu, B. Smith, M. P. Almanza, Y. Obata, D. van Dinter, G. Chang, Y. Nagai, T. Machida, Y. Okada
Publication
2025
Realization of significantly unbalanced electron filling between chains and planes at the surface of Ca-doped YBCO films
A. Krishnadas, Y. Fujisawa, M. Pardo-Almanza, Y. Obata, K. Yamagami, Y. Okada
Long-range magnetic perturbations at Bi2Te3/Cr2Te3 interfaces induced by chemical diffusion and proximity effects
Markel Pardo-Almanza, Yuita Fujisawa, Takatsugu Onishi, Chia Hsiu Hsu, Alec P. LaGrow, Yoshinori Okada
Phys. Rev. Mat. 9, 034203 (2025)
Observation of two-level critical-state in the van-der-Waals superconductor Pt(Bi1−xSex)2
Y. Samukawa, M. Maeda, N. Jiang, R. Nakamura, M. Watanabe, K. Takaki, Y. Moriyasu, T. Ikushima, T. Kida, M. Hagiwara, T. Nakamura, Y. Okada, K. Kudo, and Y. Niimi
Phys. Rev. B 111, 064506 (2025)
2024
Imaging Josephson Vortices on Curved Junctions
Y. Fujisawa, A. Krishnadas, B. Smith, M. Pardo-Almanza, H. Hiyane, Y. Nagai, T. Machida, Y. Okada
Phys. Rev. B 110, 224501 (2024)
Revealing Pronounced Electron-Hole Fermi Pockets in the Charge Density Wave Semimetal LaTe3
T. Nakamura, Y. Fujisawa, B. R. M. Smith, N. Tomoda, T. J. Hasiweder, Y. Okada
Phys. Rev. B 110 235415 (2024)
Uncovering hidden Fermi surface instabilities through visualizing unconventional quasi-particle interference in CeTe3
B. R. M. Smith, Y. Fujisawa, P. Wu, T. Nakamura, N. Tomoda, S. Kuniyoshi, D. Ueta, R. Kobayashi, R. Okuma, K. Arai, K. Kuroda,
C-H. Hsu, G. Chang, C-Y. Huang, H. Lin, Z. Y. Wang, T. Kondo, Y. Okada
Phys. Rev. Mat. 8 104004 (2024)
Electronic, magnetic, and topological properties of ferromagnetic 2D perovskite-type oxides
Susaiammal Arokiasamy, Gennevieve M Macam, Sreeparvathy P C, Rovi Angelo B Villaos, Zhi-Quan Huang, Chia-Hsiu Hsu, Yoshinori Okada, Hsin Lin and Feng-Chuan Chuang*
Dimensionality-driven power-law gap in the bilayer TaTe2 grown by molecular-beam epitaxy
Bruno. Kenichi Saika,S. Yoshida,M. P. Almanza, N. Mitsuishi, M. Sakano, Y. Fujisawa, Y. Wang, Y. Iwasa, H. Matsuoka, H. Takahashi,S. Ishiwata, Y. Okada, M. Nakano and K. Ishizaka
APL Materials 12, 071105 (2024)
Nontrivial Topology in Monolayer MA2Z4 (M = Ti, Zr, or Hf; A = Si or Ge; and Z = N, P, As, Sb, or Bi)
Ina Marie R. Verzola, R. A. B. Villaos, Z. Q. Huang, C. H. Hsu, Y. Okada, H. Lin, and F. C. Chuang
J. Phys. Chem. C 128, 6829 (2024)
Magnetotransport properties in van-der-Waals RTe3 (R = La, Ce, Tb)
T. Higashihara, R. Asama, R. Nakamura, M. Watanabe, N. Tomoda,
T. J. Hasiweder, Y. Fujisawa, Y. Okada, T. Iwasaki, K. Watanabe, T. Taniguchi, N. Jiang, and Y. Niimi
Physical Rev. B 109, 134404 (2024)
2023
Widely tunable Berry curvature in the Magnetic Semimetal Cr1+dTe2
Y. Fujisawa, M. Pardo-Almanza, C. H. Hsu, A. Mohamed, K. Yamagami, A. Krishnadas, F. C. Chuang, K. H. Khoo, J. Zang, A. Soumyanarayanan, Y. Okada
Enhancement of spin–flop-induced magnetic hysteresis in van der Waals magnet (Fe1-xCox)5GeTe2
T Ohta, K. Kurokawa, N. Jiang, K. Yamagami, Y. Okada, and Y. Niimi
Appl. Phys. Lett. 122, 152402 (2023)
Visualization of robust two-dimensional bulk states with suppressed surface state on epitaxial PdCoO2 thin films with bipolar surfaces
T. Kawamoto, A. Krishnadas, C. H. Hsu, M. Pardo-Almanza,
Y. Fujisawa, G. Chang, T. Harada, Y. Okada
Phys. Rev. Materials 7, 024001 (2023)
2022
Controlling inversion disorder in a stoichiometric spinel magnet
Margarita G. Dronova, Feng Ye, Scott E. Cooper, Anjana Krishnadas, Christina M. Hoffmann, Yuita Fujisawa,
Yoshinori Okada, Daniel I. Khomskii, Yejun Feng
PNAS 119, e2208748119 (2022)
Large antiferromagnetic fluctuation enhancement of the thermopower at a critical doping in magnetic semimetal Cr1+dTe2
M. Atwa, Y. Fujisawa, T. Onishi, M. Pardo-Almanza, M. Couillard, K. Harada, T. Takeuch, Y. Okada
Phys. Rev. B 106, 155112 (2022)
Anomalous Magnetic Moment Direction under Magnetic Anisotropy Originated from Crystalline Electric Field
in van der Waals Compounds CeTe3 and CeTe2Se
D. Ueta, R. Kobayashi, H. Sawada, Y. Iwata, S. Yano, S. Kuniyoshi, Y. Fujisawa, T. Masuda, Y. Okada, and S. Itoh
J. Phys. Soc. Jpn. 91, 094706 (2022)
Metallic delafossite thin films for unique device applications
T. Harada and Y. Okada
APL Materials 10, 070902 (2022)
Enhanced d–p hybridization intertwined with anomalous ground state formation in van der Waals-coupled magnetic metal Fe5GeTe2
K. Yamagami, Y. Fujisawa, M. Pardo-Almanza, B. R. M. Smith, K. Sumida, Y. Takeda, and Y. Okada
Phys. Rev. B 106, 045137 (2022)
Observation of near EF Fermi-arc van Hove singularity with prominent coupling to phonon in a van der Waals coupled Weyl semimetal
Z. Wang, C. Y. Huang, C. H. Hsu, H. Namiki, T. R. Chang, F. C. Chuang, H. Lin, T. Sasagawa, V. Madhavan, and Y. Okada
Phys. Rev. B 105, 075110 (2022)
2021
Magnetic frustration in a van der Waals metal CeSiI
R. Okuma, C. Ritter, G. J. Nilsen, Y. Okada
Phys. Rev. Materials (L) 5, L121401 (2021)
Visualizing superconductivity in an inversion-symmetry- broken doped Weyl semimetal
Z. Wang, J. Olivares, H. Namiki, V. Pareek, K. Dani, T. Sasagawa, V. Madhavan and Y. Okada
Phys. Rev. B 104, 115102 (2021)
Itinerant ferromagnetism mediated by giant spin polarization of metallic ligand band in van der Waals magnet Fe5GeTe2
K. Yamagami, Y. Fujisawa, B. Driesen, C. H. Hsu, K. Kawaguchi, H. Tanaka, T. Kondo, Y. Zhang, H. Wadati, K. Araki, T. Takeda, Y. Takeda, T. Muro, F. C. Chuang, Y. Niimi, K. Kuroda, M. Kobayashi, Y. Okada
Phys. Rev. B (L) 103, L060403 (2021)
Single Molecular Adsorption of Terbium(III) Bis-phthalocyaninato (TbPc2) Governed by Two Surface Reconstructions of Perovskite Type SrVO3 Epitaxial Ultrathin Film
Hirofumi Oka, Keiichi Katoh, Yoshinori Okada, Daichi Oka, Taro Hitosugi, Masahiro Yamashita, and Tomoteru Fukumura
Butterfly-shaped magnetoresistance in van der Waals ferromagnet Fe5GeTe2
T. Ohta, M. Tokuda, S. Iwakiri, K. Sakai, B. Driesen, Y. Okada, K. Kobayashi, and Y. Niimi
AIP Advances 11, 025014 (2021)
Shubnikov-de-Haas oscillation and possible modification of effective mass in CeTe3 thin films
M. Watanabe, R. Nakamura, S. Lee, T. Asano, T. Ibe, M. Tokuda, H. Taniguchi, D. Ueta, Y. Okada, K. Kobayashi, and Y. Niimi
AIP Advances 11, 015005 (2021)
2020
Tailoring Magnetism in Self-intercalated Cr1+δTe2 Epitaxial Films
Y. Fujisawa, M. Pardo-Almanza, J. Garland, K. Yamagami, X. Zhu, X. Chen, K. Araki, T. Takeda, M. Kobayashi, Y. Takeda, C. H. Hsu, F. C. Chuang, R. Laskowski, K. H. Khoo, A. Soumyanarayanan, and Y. Okada
Phys. Rev. Materialls 4, 114001 (2020)
Fermionic Order by Disorder in a van der Waals Antiferromagnet
R. Okuma, D. Ueta, S. Kuniyoshi, Y. Fujisawa, B. Smith, C. H. Hsu, Y. Inagaki, W. Si, T. Kawae, H. Lin, F. C. Chuang, T. Masuda, R. Kobayashi, Y. Okada
Scientific Reports 10, 15311 (2020)
Quantum oscillations with magnetic hysteresis observed in CeTe3 thin films
M. Watanabe, S. Lee, T. Asano, T. Ibe, M. Tokuda, H. Taniguchi, D. Ueta, Y. Okada, K. Kobayashi, and Y. Niimi
Appl. Phys. Lett. 117, 072403 (2020)
Enhancement of coercive field in atomically-thin quenched Fe5GeTe2
T. Ohta, K. Sakai, H. Taniguchi, B. Driesen, Y. Okada, K. Kobayashi and Y. Niimi
Appl. Phys. Express 13, 043005 (2020)
Three-dimensional electronic structure in ferromagnetic Fe3Sn2 with breathing kagome bilayers
H. Tanaka, Y. Fujisawa, K. Kuroda, R. Noguchi, S. Sakuragi, C. Bareille, B. Smith, C. Cacho, S. W. Jung, T. Muro, Y. Okada, and T. Kondo
Phys. Rev. B 101, 161114(R) (2020)
Top-down Approach using Supercritical Carbon Dioxide Ball Milling for Producing Sub-10 nm scaled Bi2Te3 Powders
M. Atwa, T. Nakagawa, A. Yonamine, D. C. Lloyd, M. Schreiber, K. Miyazaki, T. Takeuchi and Y. Okada
Applied Physics Express 13 067002 (2020)
Width-induced metal-insulator transition in SrVO3 lateral nanowires spontaneously formed on the ultrathin film
H. Oka, Y. Okada, K. Kaminaga, D. Oka, T. Hitosugi, and T. Fukumura
Applied Physics Letters 117, 051603(2020)
before coming to OIST
Two distinct surface terminations of SrVO3 (001) ultrathin films as an influential factor on metallicity
H. Oka, Y. Okada, T. Hitosugi, and T. Fukumura
Appl. Phys. Lett. 113, 171601 (2018)
Disorder induced power-law gaps in an Insulator-Metal Mott transition
Z. Wang, Y. Okada, J. O’ Neal, W. Zhou, D. Walkup, C. Dhital, T. Hogan, P. Clancy, Y. J. Kim, Y. F. Hu, L. Santos, S. D. Wilson, N, Trivedi and V. Madhavan
PNAS 115, 11198 (2018)
Anisotropic Band Splitting in Monolayer NbSe2: Implications for Superconductivity and Charge Density Wave
Y. Nakata, K. Sugawara, S. Ichinokura, Y. Okada, T. Hitosugi, T. Koretsune, K. Ueno, S. Hasegawa, T. Takahashi, and T. Sato,
npj 2D Materials and Applicationsvolume 2, 12 (2018)
Atomic-scale visualization of oxide thin-film surfaces
K. Iwaya, T. Ohsawa, R. Shimizu, Y. Okada, and T. Hitosugi
Sci Technol Adv Mater. 19(1): 282–290 (2018).
Scanning tunneling spectroscopy of superconductivity on surfaces of LiTi2O4(111) thin films
Y. Okada, Y. Ando, R. Shimizu, E. Minamitani, S. Shiraki, S. Watanabe, and T. Hitosugi
Nature Communications 8, 15975 (2017)
Quasiparticle interference on cubic perovskite oxide surfaces
Y. Okada, T. R. Chang, G. Chang, R. Shimizu, H. T. Jeng, S. Shiraki, A. Bansil, H. Lin, T. Hitosugi
Phys. Rev. Lett. 119, 086801 (2017
Monolayer 1T-NbSe2 as a Mott insulator
Y. Nakata, K. Sugawara, R. Shimizu, Y. Okada, P. Han, T. Hitosugi, K. Ueno, T. Sato, and T. Takahashi
NPG Asia Materials 8, e321 (2016)
Nanoscale determination of the mass enhancement factor in the lightly doped bulk insulator lead selenide
I. Zeljkovic, K. L. Scipioni, D. Walkup, Y. Okada, Wenwen Zhou, R. Sankar, G. Chang,Y. J. Wang, H. Lin, A. Bansil, F. Chou, Z. Wang and V. Madhavan
Nature Communication 6, 6559-6563 (2015)
Dirac mass generation from crystal symmetry breaking on the surfaces of topological crystalline insulators
I. Zeljkovic★, Y. Okada★, C. Y. Huang, R. Sankar, D. Walkup, W. Zhou, M. Serbyn, F. Chou, W. F. Tsai, H. Lin, A. Bansil, L. Fu, M. Z. Hasan, V. Madhavan
Nature Materials 14, 318–324 (2015)
Mapping the unconventional orbital texture in topological crystalline insulators
I. Zeljkovic★, Y. Okada★, C. Y. Huang, R. Sankar, D. Walkup, W. Zhou, M. Serbyn, F. Chou, W. F. Tsai, H. Lin, A. Bansil, L. Fu, M. Z. Hasan, V. Madhavan
Nature Physics 10, 572-577 (2014)
Electronic phase separation in the doped spin-orbit driven Mott phase of Sr3(Ir1-xRux)2O7
C. Dhital, T. Hogan, W. Zhou, X. Chen, Z. Ren, M. Pokharel, Y. Okada, M. Heine, W Tian, Z. Yamani, C. Opeil, J. S. Helton, J. W. Lynn, Z. Wang, V. Madhavan, S. D. Wilson
Nature Communications 5, 3377 (2014)
Observation of Dirac node formation and mass acquisition in a topological crystalline insulator
Y. Okada, M. Serbyn, H. Lin, D. Walkup, W. Zhou, C. Dhital, M. Neupane, S. Xu, Y. J. Wang, R. Sankar, F. Chou, A. Bansil, Z. Hasan, S. D. Wilson, L. Fu and Vidya Madhavan
Science 341, 1496-1499 (2013)
Topological insulators: Plasmons at the surface
Yoshinori Okada, Vidya Madhavan
Nature Nanotechnologies 8, 541-542 (2013)
Topological dangling bonds with large spin splitting on the surfaces of Bi2Se3
Hsin Lin, T. Das, Y. Okada, M. C. Boyer, W. D. Wise, M. Tomasik, B. Zhen, E. Hudson, W. Zhou, V. Madhavan, C. Y. Ren, H. Ikuta, and A. Bansil1
Nano Letters, 13, 1915–1919 (2013)
Imaging the evolution of metallic states in a spin-orbit interaction driven correlated iridate
Y. Okada, D. Walkup, H. Lin, C. Dhital, T. R. Chang, S. Khadka, W. Zhou, H. T. Jeng, A. Bansil, Z. Wang, S. Wilson, V. Madhavan
Nature Materials 12, 707-713 (2013)
Ripple modulated electronic structure of a 3D topological insulator
Y. Okada, W. Zhou, D. Walkup, C. Dhital, S. D. Wilson, V. Madhavan
Nature Communications 3, 1158 (6 pages) (2012)
Visualizing Landau levels of Dirac electrons in a one dimensional potential
Y. Okada, Wenwen Zhou, Chetan. Dhital, D. Walkup, Ying Ran, Z. Wang, Stephen D. Wilson, V. Madhavan
Phys. Rev. Lett. 109, 166407 (2012)
Direct Observation of Broken Time-Reversal Symmetry on the Surface of a Magnetically Doped Topological Insulator
Y. Okada, C. Dhital, W. Zhou, E. D. Huemiller, H. Lin, S. Basak, A. Bansil, Y. -B. Huang, H. Ding, Z. Wang, S. D. Wilson, and V. Madhavan
Phys. Rev. Lett. 106, 206805-206808 (2011)
Three energy- and temperature-scales corresponding to competing pseudogap state, incoherent-, and coherent-superconductivity in high-Tc cuprates
Y. Okada, T. Kawaguchi, M. Ohkawa, K. Ishizaka, T. Takeuchi, S. Shin, and H. Ikuta
Phys. Rev. B 83, 104502-104507 (2011).
Enhancement of superconducting fluctuation under the coexistence of a competing pseudogap state in Bi2Sr2-xRxCuOy
Y. Okada, Y. Kuzuya, T. Kawaguchi, and H. Ikuta
Phys. Rev. B 81, 214520-214524 (2010).
Origin of the anomalously strong influence of out-of-plane disorder on high-Tc superconductivity
Y. Okada, T. Takeuchi, T. Baba, S. Shin, and H. Ikuta