[{"content":"Affiliation School of General and Management Studies, Suwa University of Science\nOffice Room 23E, Building 2\nContact Email: kobayashi_shingo (at) rs.sus.ac.jp Please replace “(at)” with “@” to avoid spam.\n","permalink":"https://kobayashi-physics.github.io/en/contact/","summary":"\u003ch2 id=\"affiliation\"\u003eAffiliation\u003c/h2\u003e\n\u003cp\u003eSchool of General and Management Studies, \u003cbr\u003e\nSuwa University of Science\u003c/p\u003e\n\u003ch2 id=\"office\"\u003eOffice\u003c/h2\u003e\n\u003cp\u003eRoom 23E, Building 2\u003c/p\u003e\n\u003ch2 id=\"contact\"\u003eContact\u003c/h2\u003e\n\u003cp\u003eEmail: kobayashi_shingo (at) rs.sus.ac.jp  \u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ePlease replace “(at)” with “@” to avoid spam.\u003c/em\u003e\u003c/p\u003e\n\u003c!--\r\nQuantum Matter Theory Research Group  \r\nRIKEN Center for Emergent Matter Science (CEMS)\r\n\r\n## Office\r\n\r\nMain Research Building, 3rd Floor, Room 329\r\n\r\n## Contact\r\n\r\nEmail: shingo.kobayashi (at) riken.jp  \u003cbr\u003e\r\n\r\n*Please replace “(at)” with “@” to avoid spam.*\r\n--\u003e","title":"Contact"},{"content":"\rI am a theoretical condensed-matter physicist working on quantum materials, including superconductors and topological materials. My research focuses in particular on topological superconductivity and the topological classification of superconducting and electronic states.\nGoogle Scholar ORCiD researchmap Education April 2006 – March 2008 Bachelor of Science, Physics Adviser : Prof. Takafumi Kita Department of Physics, Hokkaido University, Japan\nApril 2008 – March 2010 Master\u0026rsquo;s Degree, Physics Adviser : Prof. Masahito Ueda Department of Physics, Tokyo Institute of Technology, Japan\nApril 2010 – March 2013 Ph.D., Physics Thesis title: “Theoretical Study on Topological Phenomena in Ultracold Atomic Gases” Adviser : Prof. Masahito Ueda Department of Physics, University of Tokyo, Japan\nResearch Experience April 2013 – March 2016 Postdoctoral Researcher, JSPS Research Fellow for Young Scientists (PD) Tanaka and Sato Group, Department of Applied Physics, Nagoya University, Japan\nApril 2016 – July 2019 YLC Assistant Professor, Institute for Advanced Research, Nagoya University, Japan\nAugust 2019 – March 2026 Research Scientist, RIKEN Center for Emergent Matter Science (CEMS), Japan\nSeptember 2024 – March 2026 Part-time Lecturer, Tokyo City University, Japan\nApril 2025 – March 2026 Part-time Lecturer, Tokyo Denki University, Japan\nMarch 2026 – Present Associate Professor, School of General and Management Studies, Suwa University of Science, Japan\n","permalink":"https://kobayashi-physics.github.io/en/profile/","summary":"\u003cp align=\"left\"\u003e\r\n  \u003cimg src=\"https://www2.riken.jp/lab-www/cond-mat-theory/kobayashi/ja/images/profile-DJ.jpeg\" width=\"350\"\u003e\r\n\u003c/p\u003e\r\n\u003cp\u003eI am a theoretical condensed-matter physicist working on quantum materials, including superconductors and topological materials. My research focuses in particular on topological superconductivity and the topological classification of superconducting and electronic states.\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003e\u003ca href=\"https://scholar.google.com/citations?user=tQaznegAAAAJ\u0026amp;hl=en\"\u003eGoogle Scholar\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"https://orcid.org/0000-0003-3213-2385\"\u003eORCiD\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"https://researchmap.jp/raccoon-dog1985\"\u003eresearchmap\u003c/a\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003chr\u003e\n\u003ch2 id=\"education\"\u003eEducation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003eApril 2006 – March 2008  \u003cbr\u003e\nBachelor of Science, Physics \u003cbr\u003e\nAdviser : Prof. Takafumi Kita \u003cbr\u003e\nDepartment of Physics, Hokkaido University, Japan\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eApril 2008 – March 2010 \u003cbr\u003e\nMaster\u0026rsquo;s Degree, Physics \u003cbr\u003e\nAdviser : Prof. Masahito Ueda \u003cbr\u003e\nDepartment of Physics, Tokyo Institute of Technology, Japan\u003c/p\u003e","title":"Curriculum Vitae"},{"content":"Articles Majorana-assisted nonlocal spin correlation in quasi-one-dimensional Kitaev spin liquids Yuki Yamazaki, Shingo Kobayashi, and Akira Furusaki, Physical Review B 114, 105141 (2026).\nHinge modes of three-dimensional Euler insulators Yutaro Tanaka and Shingo Kobayashi, Physical Review B 114, 045120 (2026).\nExceptionally large winding number of a finite-size topological superconductor Satoshi Ikegaya, Shingo Kobayashi, and Yasuhiro Asano, Physical Review B 113, 054519 (2026).\nEuler band topology in superfluids and superconductors Shingo Kobayashi, Manabu Sato, and Akira Furusaki, Physical Review B 113, L060501 (2026).\nThree-dimensional spinless Euler insulators with rotational symmetry Manabu Sato, Shingo Kobayashi, Motoaki Hirayama, and Akira Furusaki, Physical Review B 112, 195108 (2025). Editors’ Suggestion\nHigher-order topological phases for time-reversal-symmetry breaking superconductivity in UTe2 Yuki Yamazaki and Shingo Kobayashi, Physical Review B 112, 174507 (2025).\nOscillating-charged Andreev bound states and their appearance in UTe2 Satoshi Ando*, Shingo Kobayashi*, Andreas P. Schnyder, Yasuhiro Asano, and Satoshi Ikegaya*, Physical Review B 112, 094506 (2025). *These authors contributed equally to this work.\nThermoelectric effect in a superconductor with Bogoliubov Fermi surfaces Tomoya Sano, Takumi Sato, Akihiro Sasaki, Satoshi Ikegaya, Shingo Kobayashi, and Yasuhiro Asano, Physical Review B 111, 174503 (2025). Ideal spin-orbit-free Dirac semimetal and diverse topological transitions in Pr8CoGa3 Family Manabu Sato, Juba Bouaziz, Shuntaro Sumita, Shingo Kobayashi, Ikuma Tateishi, Stefan Blugel, Akira Furusaki, and Motoaki Hirayama, Communications Materials 5, 253 (2024). Majorana multipole response with magnetic point group symmetry Yuki Yamazaki and Shingo Kobayashi, Physical Review B 110, 134518 (2024). Editors’ Suggestion RIKEN Research Highlights\nDiscontinuous transition to superconducting phase Takumi Sato, Shingo Kobayashi, and Yasuhiro Asano, Physical Review B 110, 144503 (2024).\nRepresentation-protected topology of spin-singlet s-wave superconductors Shingo Kobayashi and Akira Furusaki, Physical Review B 110, L100508 (2024). RIKEN Research Highlights\nSurface density of states and tunneling spectroscopy of a spin-3/2 superconductor with Bogoliubov Fermi Surfaces Ryoi Ohashi, Shingo Kobayashi, Shotaro Kanazawa, Yukio Tanaka, and Yuki Kawaguchi, Physical Review B 110, 104515 (2024).\nElectromagnetic response of spinful Majorana fermions Shingo Kobayashi and Masatoshi Sato, Progress of Theoretical and Experimental Physics 2024, 08C106 (2024).\nCrystal symmetry protected gapless vortex line phases in superconducting Dirac semimetals Shingo Kobayashi, Shuntaro Sumita, Motoaki Hirayama, and Akira Furusaki, Physical Review B 107, 214518 (2023).\nSpin Susceptibility of a J = 3/2 Superconductor Dakyeong Kim, Takumi Sato, Shingo Kobayashi, and Yasuhiro Asano, Journal of the Physical Society of Japan 92, 054703 (2023). JPSJ Papers of Editors\u0026rsquo; Choice\nNuclear spin relaxation rate of nonunitary Dirac and Weyl superconductors Koki Maeno, Yuki Kawaguchi, Yasuhiro Asano, and Shingo Kobayashi, Physical Review B 107, 064511 (2023).\nBogoliubov Fermi surfaces from pairing of emergent j = 3/2 fermions on the pyrochlore lattice Shingo Kobayashi, Ankita Bhattacharya, Carsten Timm, and P. M. R. Brydon, Physical Review B 105, 134507 (2022).\nFragile topological insulators protected by rotation symmetry without spin-orbit coupling Shingo Kobayashi and Akira Furusaki, Physical Review B 104, 195114 (2021). Erratum: Physical Review B, 105, 039903(E) (2022).\nPossible topological phases in quantum anomalous Hall insulator/unconventional superconductor hybrid systems Ryoi Ohashi, Shingo Kobayashi, and Yukio Tanaka, Physical Review B 104, 134518 (2021).\nQuasiparticle on Bogoliubov Fermi surface and odd-frequency Cooper pair Dakyeong Kim, Shingo Kobayashi and Yasuhiro Asano, Journal of Physical Society Japan [Letters] 90, 104708 (2021).\nElectric multipoles of double Majorana Kramers pairs Yuki Yamazaki, Shingo Kobayashi, and Ai Yamakage, Journal of Physical Society Japan [Letters] 90, 073701 (2021).\nMajorana multipole response: General theory and application to wallpaper groups Shingo Kobayashi, Yuki Yamazaki, Ai Yamakage, and Masatoshi Sato, Physical Review B 103, 224504 (2021).\nJosephson effect of superconductors with J = 3/2 electrons Dakyeong Kim, Shingo Kobayashi, and Yasuhiro Asano, Physical Review B 103, 184516 (2021).\nMagnetic response of Majorana Kramers pairs with an order-two symmetry Yuki Yamazaki, Shingo Kobayashi, and Ai Yamakage, Physical Review B 103, 094508 (2021).\nDouble Majorana vortex zero modes in superconducting topological crystalline insulators with surface rotation anomaly Shingo Kobayashi and Akira Furusaki, Physical Review B 102, 180505(R) (2020). RIKEN Research Highlights\nNodal Andreev spectra in multi-Majorana three-terminal Josephson junctions Keimei Sakurai, Maria Teresa Mercaldo, Shingo Kobayashi, Ai Yamakage, Satoshi Ikegaya, Tetsuro Habe, Panagiotis Kotetes, Mario Cuoco, and Yasuhiro Asano, Physical Review B 101, 174506 (2020).\nMagnetic response of Majorana Kramers pairs protected by Z2 invariants Yuki Yamazaki, Shingo Kobayashi, and Ai Yamakage, Journal of Physical Society Japan [Letters] 89, 043703 (2020). JPSJ Papers of Editors\u0026rsquo; Choice JPSJ注目論文\nGeneralized Berry phase for a bosonic Bogoliubov system with exceptional points Terumichi Ohashi, Shingo Kobayashi, and Yuki Kawaguchi, Physical Review A 101, 013625 (2020).\nMajorana multipole response of Topological Superconductors Shingo Kobayashi, Ai Yamakage, Yukio Tanaka, Masatoshi Sato, Physical Review Letters 123, 097002 (2019).\nTopological crystalline materials of J = 3/2 electrons: Antiperovskites, Dirac points, and high winding topological superconductivity Takuto Kawakami, Tetsuya Okamura, Shingo Kobayashi, and Masatoshi Sato, Physical Review X 8, 041026 (2018).\nSymmetry-protected line nodes and Majorana flat bands in nodal crystalline superconductors Shingo Kobayashi, Shuntaro Sumita, Youichi Yanase, and Masatoshi Sato, Physical Review B 97, 180504(R) (2018).\nSymmetry conditions of a nodal superconductor for generating robust flat-band Andreev bound states at its dirty surface Satoshi Ikegaya, Shingo Kobayashi, and Yasuhiro Asano, Physical Review B 97, 174501 (2018).\nCrossing-line-node semimetals: General Theory and application to rare-earth trihydrides Shingo Kobayashi, Youichi Yamakawa, Ai Yamakage, Takumi Inohara, Yoshihiko Okamoto, and Yukio Tanaka, Physical Review B 95, 245208 (2017).\nAnisotropic magnetic responses of topological crystalline superconductors Yuansen Xiong, Ai Yamakage, Shingo Kobayashi, Masatoshi Sato, and Yukio Tanaka, Crystals 7, 58 (2017).\nTheory of surface Andreev bound states and tunneling spectroscopy in three-dimensional chiral superconductors Shun Tamura, Shingo Kobayashi, Lu Bo, and Yukio Tanaka, Physical Review B 95, 104511 (2017).\nTopologically stable gapless phases in nonsymmorphic superconductors Shingo Kobayashi, Youichi Yanase, and Masatoshi Sato, Physical Review B 94, 134512 (2016).\nSuperconductivity in the antiperovskite Dirac-metal oxide Sr3-xSnO Mohamed Oudah, Atsutoshi Ikeda, Jan Niklas Hausmann, Shingo Yonezawa, Toshiyuki Fukumoto, Shingo Kobayashi, Masatoshi Sato, and Yoshiteru Maeno, Nature Communications 7, 13617 (2016).\nSuperconductivity in doped Dirac semimetals Tatsuki Hashimoto, Shingo Kobayashi, Yukio Tanaka, and Masatoshi Sato, Physical Review B 94, 014510 (2016).\nFragile surface zero-energy flat bands in three-dimensional chiral superconductors Shingo Kobayashi, Yukio Tanaka, and Masatoshi Sato, Physical Review B 92, 214514 (2015).\nTopological superconductivity in Dirac semimetals Shingo Kobayashi and Masatoshi Sato, Physical Review Letters 115, 187001 (2015).\nTheory of tunneling conductance of anomalous Rashba metal/superconductor junctions Toshiyuki Fukumoto, Katsuhisa Taguchi, Shingo Kobayashi, and Yukio Tanaka, Physical Review B 92, 144514 (2015).\nTopological Blount\u0026rsquo;s theorem of odd parity superconductors Shingo Kobayashi, Ken Shiozaki, Yukio Tanaka, and Masatoshi Sato, Physical Review B 90, 024516 (2014).\nTopological influence and back-action between topological excitations Shingo Kobayashi, Nicolas Tarantino, and Masahito Ueda, Physical Review A 89, 033603 (2014).\nGauge-spin-space rotation-invariant vortices in spin-orbit-coupled Bose-Einstein condensates Zhi-Fang Xu, Shingo Kobayashi, and Masahito Ueda, Physical Review A 88, 013621 (2013).\nTopological classification of vortex-core structures of spin-1 Bose-Einstein condensates Shingo Kobayashi, Yuki Kawaguchi, Muneto Nitta, and Masahito Ueda, Physical Review A 86, 023612 (2012).\nAbe homotopy classification of topological excitations under the topological influence of vortices Shingo Kobayashi, Michikazu Kobayashi, Yuki Kawaguchi, Muneto Nitta, and Masahito Ueda, Nuclear Physics B 856, 577-606 (2012).\nProceedings Theoretical band structure of the superconducting antiperovskite oxide Sr3-xSnO Atsutoshi Ikeda, Toshiyuki Fukumoto, Mohamed Oudah, Jan Niklas Hausmann, Shingo Yonezawa, Shingo Kobayashi, Masatoshi Sato, Cedric Tassel, Fumitaka Takeiri, Hiroshi Takatsu, Hiroshi Kageyama, and Yoshiteru Maeno, Physica B: Condensed Matter 536, 752-756 (2018). International Conference on Strongly Correlated Electron Systems 2017 (Prague, Czech Republic)\nProjected Symmetry breaking in Dipole-Locked 3He-B Hiromitsu Takeuchi and Shingo Kobayashi, Journal of Low Temperature Physics 183, 78-84 (2016). 27th International Conference on Low Temperature Physics (Buenos Aires, Argentina) Articles in Japanese Journals 2重マヨラナクラマース対が形成する電磁多極子の理論 ―動的歪みとの結合による表面スピン流生成 山崎勇樹, 小林伸吾, 山影相, 日本物理学会誌 80, 10, 584-588 (2025).\n物質中のマヨラナ粒子の磁気異方性―映進対称性と四極子型の磁気応答― 山崎勇樹, 小林伸吾, 山影相, 固体物理 56, 1, 49-58 (2021).\n超伝導ギャップ構造の現代的分類理論 角田峻太郎, 小林伸吾, 固体物理 55, 10, 463-478 (2020).\nArXiv preprint Pressure-induced superconductivity in a bilayer metal Tomoya Sano, Satoshi Ikegaya, Shingo Kobayashi, and Yasuhiro Asano, arXiv:2610.27664\nNonuniform superconducting states caused by odd-frequency Cooper pairs Takumi Sato, Satoru Hayami, Shingo Kobayashi, and Yasuhiro Asano, arXiv:2503.01673\nAwards JPSJ Papers of Editors\u0026rsquo; Choice. 受賞論文「Spin Susceptibility of a J = 3/2 Superconductor」, 日本物理学会, 2023/4 第9回RIKEN CEMS Award, トポロジカル超伝導体のマヨラナ粒子に関する理論的研究, 理化学研究所創発物性科学研究センター, 2022/4 第13回理研桜舞賞（研究奨励賞）, トポロジカル超伝導体のマヨラナ粒子に関する理論的研究, 理化学研究所, 2022/3 第14回日本物理学会若手奨励賞（領域４）, マヨラナフラットバンドを有するトポロジカル超伝導体の理論研究, 日本物理学会, 2020/3 JPSJ Papers of Editors\u0026rsquo; Choice, 受賞論文「Magnetic Response of Majorana Kramers Pairs Protected by Z2 Invariants」, 日本物理学会, 2020/5 Research Grants 2025年度 - 2028年度　科研費　基盤研究C 研究課題「多自由度を持つs波超伝導におけるトポロジカル相とその量子現象」 研究代表者, 研究経費 4160千円\n2024年度 - 2027年度　科研費　基盤研究B 研究課題「非保存量子系における新奇量子相とその制御」 研究分担者（研究代表者 川口由紀）, 研究経費 17420千円\n2022年度 - 2024年度　科研費　基盤研究C 研究課題「多自由度を有する超伝導におけるギャップレス相の研究」 研究代表者, 研究経費 2730千円\n2019年度 - 2022年度　科研費　基盤研究B 研究課題「原子気体ボース・アインシュタイン凝縮体におけるトポロジカル量子現象」 研究分担者 （研究代表者：川口由紀）, 研究経費 15210千円\n2019年度 - 2021年度　科研費　若手研究 研究課題「異方的超伝導体におけるトポロジカル量子現象の研究」 研究代表者, 研究経費 4160千円\n2017年度 - 2019年度　科研費　基盤研究B 研究課題「対称性と相関によって生じる多彩な量子秩序相の研究」 研究分担者（研究代表者：佐藤昌利）, 研究経費 19110千円\n2016年度 - 2020年度　科学技術振興機構　「科学技術人材育成のコンソーシアムの構築事業」連携型博士研究人材総合育成システム　若手研究者スタートアップ研究費 研究課題「凝縮系におけるトポロジカル量子現象の理論的研究」 研究代表者, 研究経費 10000千円\n2016年度 - 2017年度　科研費　研究活動スタート支援 研究課題「トポロジカル半金属における新奇トポロジカル量子現象の理論的研究」\n研究代表者, 研究経費 2660千円\n2013年度 - 2015年度　科研費　特別研究員(PD)　研究費 研究課題「相互作用するフェルミ粒子系におけるトポロジカル不変量を用いた分類とその応用」\n研究代表者, 研究経費 3300千円\n2010年度 - 2012年度　科研費　特別研究員(DC1)　研究費 研究課題「新しいホモトピーを用いたトポロジカル励起の分類」 研究代表者, 研究経費 2100千円 ","permalink":"https://kobayashi-physics.github.io/en/publications/","summary":"\u003ch2 id=\"articles\"\u003eArticles\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cstrong\u003e\u003ca href=\"https://journals.aps.org/prb/abstract/10.1103/glbs-j4hl\"\u003eMajorana-assisted nonlocal spin correlation in quasi-one-dimensional Kitaev spin liquids\u003c/a\u003e\u003c/strong\u003e \u003cbr\u003e\nYuki Yamazaki, Shingo Kobayashi, and Akira Furusaki, \u003cbr\u003e\n\u003cem\u003ePhysical Review B\u003c/em\u003e \u003cstrong\u003e114\u003c/strong\u003e, 105141 (2026).\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cstrong\u003e\u003ca href=\"https://journals.aps.org/prb/abstract/10.1103/pnkp-6tzk\"\u003eHinge modes of three-dimensional Euler insulators\u003c/a\u003e\u003c/strong\u003e \u003cbr\u003e\nYutaro Tanaka and Shingo Kobayashi, \u003cbr\u003e\n\u003cem\u003ePhysical Review B\u003c/em\u003e \u003cstrong\u003e114\u003c/strong\u003e, 045120 (2026).\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cstrong\u003e\u003ca href=\"https://journals.aps.org/prb/abstract/10.1103/rf8j-lf4s\"\u003eExceptionally large winding number of a finite-size topological superconductor\u003c/a\u003e\u003c/strong\u003e \u003cbr\u003e\nSatoshi Ikegaya, Shingo Kobayashi, and Yasuhiro Asano, \u003cbr\u003e\n\u003cem\u003ePhysical Review B\u003c/em\u003e \u003cstrong\u003e113\u003c/strong\u003e, 054519 (2026).\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cstrong\u003e\u003ca href=\"https://journals.aps.org/prb/abstract/10.1103/nxxl-wxwm\"\u003eEuler band topology in superfluids and superconductors\u003c/a\u003e\u003c/strong\u003e \u003cbr\u003e\nShingo Kobayashi, Manabu Sato, and Akira Furusaki, \u003cbr\u003e\n\u003cem\u003ePhysical Review B\u003c/em\u003e \u003cstrong\u003e113\u003c/strong\u003e, L060501 (2026).\u003c/p\u003e","title":"Publications"},{"content":"Real-Band Topology in Superconductors and Superfluids In systems with space-time inversion symmetries, a distinct type of topological structure known as real-band topology can emerge. Unlike conventional complex-band topology, real-band topology is defined for real Bloch wave functions, and it is characterized by topological invariants such as the Euler class and the Stiefel-Whitney classes. This framework has recently attracted growing interest in the study of twisted bilayer graphene, topological insulators, semimetals, and metamaterials.\nOur research explores how real-band topology arises in superconductors and superfluids. We first demonstrated that, under appropriate space–time symmetries, the Bogoliubov-de Gennes Hamiltonian of a superconductor can also host real-band topology. We then derived general relations connecting these real-band topological invariants to other known topological invariants. Using these results, we showed that the B phase of superfluid helium-3 in a magnetic field is characterized by a nontrivial Euler class and therefore realizes a topological superfluid protected by real-band topology.\nThe B phase of superfluid helium-3 is already known to be a topological superfluid in the presence of time-reversal symmetry. However, once a magnetic field is applied, this conventional topological invariant is no longer defined. Despite this, several studies have reported robust topological phenomena even in the presence of a magnetic field, leading to a long-standing puzzle. Our work resolves this issue by showing that these phenomena originate from Euler-class topology, which survives even when time-reversal symmetry is broken. Moreover, our theory predicts additional topological responses unique to the Euler class, pointing toward new directions for future experiments and materials exploration.\nEuler band topology in superfluids and superconductors Shingo Kobayashi, Manabu Sato, and Akira Furusaki, Physical Review B 113, L060501 (2026). Higher-Order Topological Phases in Spin-Triplet Superconductivity in UTe2 The uranium compound UTe2 has recently attracted broad interest as a promising candidate for spin-triplet superconductivity. Experimental observations such as its extremely large upper critical field, nearly unchanged spin susceptibility below the superconducting transition, and characteristic tunneling spectra all support this possibility. However, a key unresolved question remains: if UTe2 is indeed a spin-triplet superconductor, what kind of topology does it host? This question is highly nontrivial because UTe2 is a multiband system with a complex crystal structure, in sharp contrast to the well-known spin-triplet superfluid helium-3.\nIn this work, we address this question using a recently developed topological-classification framework for higher-order topological phases. This approach not only determines the topological invariants of a given superconducting state, but also predicts the dimensionality and distribution of the resulting boundary states. We systematically applied this method to all chiral pairing states compatible with the crystal symmetry of UTe2.\nOur classification reveals a striking result: except for the trivial spin-singlet pairing state, every symmetry-allowed chiral pairing state in UTe2 realizes a higher-order topological phase. Depending on the pairing symmetry, the system may host third-order topology with Majorana corner states, second-order topology with Majorana hinge states, or even hybrid phases in which corner and hinge states coexist.\nThese findings suggest that UTe2 provides a fertile platform for realizing and exploring higher-order topological superconductivity in real materials. The predicted boundary states offer experimentally accessible signatures that may help determine the true pairing symmetry of UTe2 and deepen our understanding of spin-triplet superconductivity.\nHigher-order topological phases for time-reversal-symmetry breaking superconductivity in UTe2 Yuki Yamazaki and Shingo Kobayashi, Physical Review B 112, 174507 (2025). Representation Protected Topology in Spin-Singlet s-Wave Superconductors Topological superconductors are superconductors that possess nontrivial topological invariants. A hallmark of these systems is the emergence of exotic quasiparticles, known as Majorana quasiparticles, at their boundaries. Because Majorana quasiparticles obey unique quantum statistics, they are considered promising building blocks for topological quantum computation. Early theoretical work predicted that spin-triplet p-wave superconductors naturally host such topological superconducting phases, and this idea has served as a guiding principle in the search for candidate materials. However, spin-triplet p-wave superconductivity is extremely rare in nature, whereas most known superconductors are conventional spin-singlet s-wave superconductors.\nIn this work, we theoretically demonstrate that topological superconductivity can also emerge in spin-singlet s wave superconductors, in a way that parallels spin triplet systems. The key ingredient is the orbital degree of freedom of electrons, for example p- and d-orbitals, which plays a role analogous to spin when constrained by crystal symmetries. As a result, the orbital structure of the electronic wave functions can give rise to robust topological phases even when the superconducting pairing itself is of the conventional spin-singlet s-wave type.\nWe further establish a general method to compute the relevant topological invariants in such multiorbital systems. Using this framework, we predict that orbital-driven topological superconducting phases may appear in real materials, including iron-based superconductors, which are among the most intensively studied s-wave multiorbital systems.\nThese results broaden the landscape of topological superconductivity by showing that unconventional pairing symmetry is not a strict requirement. Instead, orbital structure and symmetry can work together to realize representation protected topology, opening new avenues for discovering topological superconductors in widely studied material families.\nRepresentation-protected topology of spin-singlet s-wave superconductors Shingo Kobayashi and Akira Furusaki, Physical Review B 110, L100508 (2024). Classification of Majorana Multipole Responses under Magnetic Point-Group Symmetry At the surface of a time reversal symmetric topological superconductor, quasiparticles known as Majorana Kramers pairs necessarily appear. These pairs exhibit highly anisotropic responses to magnetic fields. Earlier theoretical work has shown that such anisotropy gives rise to a rich variety of magnetic responses, collectively referred to as Majorana multipole responses, which are strongly constrained by the crystal symmetry of the superconducting state. Moreover, these responses are closely linked to the Cooper pair symmetry.\nHowever, when time reversal symmetry is broken, Majorana Kramers pairs no longer exist and the usual Majorana multipole response disappears. In multiband superconductors, on the other hand, internal degrees of freedom can cause several Majorana quasiparticles to remain degenerate even without time reversal symmetry. In this case, the magnetic crystal symmetry protects their degeneracy. Motivated by this observation, we extend the theory of Majorana multipole responses to topological superconductors in which time reversal symmetry is broken.\nWithin this framework, we identify the general symmetry conditions under which Majorana quasiparticles remain degenerate under magnetic point group symmetries, and we show that such degenerate Majorana quasiparticles can exhibit both magnetic and electric multipole responses. We then apply our theory to model systems of two candidate materials: the ferromagnetic superconductor UCoGe and the chiral p-wave superconductor candidate UTe2. In both cases, numerical calculations demonstrate the emergence of a magnetic quadrupole response of the Majorana quasiparticles. This quadrupole response is a characteristic topological phenomenon that appears only when time reversal symmetry is broken.\nThese results provide a unified way to classify and predict multipole responses of Majorana quasiparticles in superconductors with magnetic crystal symmetry. They also suggest new experimental probes for identifying pairing symmetry and topological character in unconventional superconductors.\nMajorana multipole response with magnetic point group symmetry Yuki Yamazaki and Shingo Kobayashi, Physical Review B 110, 134518 (2024). Editors’ Suggestion RIKEN Research Highlights Geometric Phases and Surface States in Sublattice Superconductors In topological superconductors, nontrivial integer valued topological invariants guarantee the appearance of Majorana quasiparticles at the surface. This raises a natural question: what happens when a superconductor instead hosts a nontrivial geometric phase, which takes continuous real values rather than integers? Does the surface still exhibit anomalous behavior?\nIn this work, we show that the answer is yes. Focusing on superconductors that possess a sublattice degree of freedom, we demonstrate that a nontrivial geometric phase can generate a new type of surface state that is distinct from both Majorana quasiparticles and conventional Andreev bound states. The key feature of this state is that the BCS charge, meaning the difference between electron and hole components of the Bogoliubov quasiparticle wave function, oscillates spatially along the surface. For this reason, we refer to it as an oscillating charge Andreev bound state (OCABS).\nOCABS appear only when both the sublattice structure and a finite geometric phase are present. Remarkably, these states carry either purely electron like or purely hole like spectral weight at the surface, in sharp contrast to ordinary Andreev states that mix electrons and holes. As a direct consequence, Andreev reflection is suppressed, leading to striking signatures such as a vanishing tunneling conductance at the corresponding energies.\nOur results reveal that geometric phases, usually discussed in the context of band theory, can fundamentally modify superconducting surface physics when internal sublattice structure is present. This opens a pathway to discovering and controlling new classes of surface states beyond the familiar Majorana paradigm, with clear experimental consequences for tunneling spectroscopy and related probes.\nOscillating-charged Andreev bound states and their appearance in UTe2 Satoshi Ando*, Shingo Kobayashi*, Andreas P. Schnyder, Yasuhiro Asano, and Satoshi Ikegaya*, Physical Review B 112, 094506 (2025). *These authors contributed equally to this work. ","permalink":"https://kobayashi-physics.github.io/en/research/","summary":"\u003ch2 id=\"real-band-topology-in-superconductors-and-superfluids\"\u003eReal-Band Topology in Superconductors and Superfluids\u003c/h2\u003e\n\u003cp\u003eIn systems with space-time inversion symmetries, a distinct type of topological structure known as real-band topology can emerge. Unlike conventional complex-band topology, real-band topology is defined for real Bloch wave functions, and it is characterized by topological invariants such as the Euler class and the Stiefel-Whitney classes. This framework has recently attracted growing interest in the study of twisted bilayer graphene, topological insulators, semimetals, and metamaterials.\u003c/p\u003e","title":"Research Overview"},{"content":"2026年 Euler band topology in superfluids and superconductors Shingo Kobayashi, Majorana workshop 2026, Okochi Hall, RIKEN, Wako Japan, 2026/10/15\n磁場または圧力下におけるリエントラント超伝導 佐野智哉, 田畑滉太, 池谷聡, 小林伸吾, 浅野泰寛, 日本物理学会第81回年次大会, 東京大学駒場キャンパス, 2026/9/17\nスピン1重項超伝導における実バンドトポロジー 小林伸吾, 佐藤真武, 古崎昭, 日本物理学会2026年春季大会, オンライン, 2026/3/25\nEuler band topology in superfluids and superconductors Shingo Kobayashi, Manabu Sato, Akira Furusaki, DPG Spring Meeting 2026, Dresden Germany, 2026/3/9\n2025年 副格子自由度を持つ超伝導体の表面状態と輸送現象 佐野智哉, 佐々木章宏, 池谷聡, 小林伸吾, 浅野泰寛, 日本物理学会第80回年次大会, 広島大学, 2025/9/18\n擬一次元キタエフハニカム模型における非局所スピン相関 山崎勇樹, 小林伸吾, 古崎昭, 日本物理学会第80回年次大会, 広島大学, 2025/9/16\n回転対称性を持つ3次元スピンレスオイラー絶縁体 佐藤真武，小林伸吾，平山元昭，古崎昭, 日本物理学会第80回年次大会, 広島大学, 2025/9/16\nトポロジカル超伝導におけるオイラーバンドトポロジー 小林伸吾，佐藤真武，古崎昭, 日本物理学会第80回年次大会, 広島大学, 2025/9/16\nHigher-order topological phases for time-reversal-symmetry-breaking superconductivity in UTe2 Shingo Kobayashi and Yuki Yamazaki, 30th International Conference on Low Temperature Physics, Bilbao Spain, 2025/8/9\nHigher-order topological phases for time-reversal-symmetry-breaking superconductivity in UTe2 Shingo Kobayashi and Yuki Yamazaki, CEMS Symposium on Emergent Quantum Materials 2025, Tokyo Japan, 2025/5/20\nキタエフハニカム模型における有限サイズ効果のトポロジー 山崎勇樹, 小林伸吾, 古崎昭, 日本物理学会2025年春季大会, オンライン, 2025/3/20\nボゴリューボフ・フェルミ面を持つd波超伝導体の熱電効果 佐野智哉, 佐藤匠, 佐々木章宏, 池谷聡, 小林伸吾, 浅野泰寛, 日本物理学会2025年春季大会, オンライン, 2025/3/18\n2024年 ScAuSiにおけるスピンレストポロジカル絶縁相 佐藤真武, 小林伸吾, 角田峻太郎, 立石幾真, 古崎昭, 平山元昭, 日本物理学会2024年春季大会, オンライン, 2024/3/20\n多バンド超伝導体における有限重心運動量秩序 佐藤匠, 速水賢, 小林伸吾, 浅野泰寛, 日本物理学会第79回年次大会, 北海道大学, 2024/9/19\nボゴリューボフ・フェルミ面を持つ超伝導体の熱電効果 佐野智哉, 佐藤匠, 池谷聡, 小林伸吾, 浅野泰寛, 日本物理学会第79回年次大会, 北海道大学, 2024/9/19\n磁気点群により保護されたマヨラナ準粒子の多極子応答 小林伸吾，山崎勇樹, 日本物理学会第79回年次大会, 北海道大学, 2024/9/18\nフルギャップなカイラル超伝導相と表面マヨラナ準粒子の多極子応答 山崎勇樹, 小林伸吾, 日本物理学会第79回年次大会, 北海道大学, 2024/9/18\nWilson loopバンドの局所的特徴付けと表面状態との関係 佐藤真武, 小林伸吾, 立石幾真, 角田峻太郎, 古崎昭, 平山元昭, 日本物理学会第79回年次大会, 北海道大学, 2024/9/17\n振動電荷アンドレーエフ束縛状態 池谷聡, 安藤叡史, 小林伸吾, 浅野泰寛, 日本物理学会2024年春季大会, オンライン, 2024/3/21\nスピン1重項超伝導における表現に保護されたトポロジー 小林伸吾, 古崎昭, 日本物理学会2024年春季大会, オンライン, 2024/3/21\nキタエフスピン液体におけるマヨラナエッジ状態の磁気ラマン散乱 山崎勇樹, 小林伸吾, 古崎昭, 日本物理学会2024年春季大会, オンライン, 2024/3/20\nCrystal-symmetry-protected gapless vortex-line phases in superconducting Dirac semimetals Shingo Kobayashi, Shuntaro Sumita, Motoaki Hirayama, Akira Furusaki, APS March Meeting 2024, Minneapolis MN, 2024/3/4\nElectric response of Majorana Fermions in topological crystalline superconductors Yuki Yamazaki, Shingo Kobayashi, and Ai Yamakage, APS March Meeting 2024, Minneapolis MN, 2024/3/4\nRepresentation protected topology of spin-singlet superconductors Shingo Kobayashi and Akira Furusaki, CEMS Symposium on Emergent Quantum Materials 2024, Tokyo Japan, 2024/2/21\nMagnetic and electric response of Majorana fermions in time-reversal-symmetry-broken topological superconductors Yuki Yamazaki and Shingo Kobayashi, CEMS Symposium on Emergent Quantum Materials 2024, Tokyo Japan, 2024/2/21\n","permalink":"https://kobayashi-physics.github.io/en/talks/","summary":"\u003ch2 id=\"2026年\"\u003e2026年\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cstrong\u003eEuler band topology in superfluids and superconductors\u003c/strong\u003e \u003cbr\u003e\nShingo Kobayashi, \u003cbr\u003e\nMajorana workshop 2026, Okochi Hall, RIKEN, Wako Japan, 2026/10/15\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cstrong\u003e磁場または圧力下におけるリエントラント超伝導\u003c/strong\u003e  \u003cbr\u003e\n佐野智哉, 田畑滉太, 池谷聡, 小林伸吾, 浅野泰寛, \u003cbr\u003e\n日本物理学会第81回年次大会, 東京大学駒場キャンパス, 2026/9/17\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cstrong\u003eスピン1重項超伝導における実バンドトポロジー\u003c/strong\u003e \u003cbr\u003e\n小林伸吾, 佐藤真武, 古崎昭, \u003cbr\u003e\n日本物理学会2026年春季大会, オンライン, 2026/3/25\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cstrong\u003eEuler band topology in superfluids and superconductors\u003c/strong\u003e \u003cbr\u003e\nShingo Kobayashi, Manabu Sato, Akira Furusaki, \u003cbr\u003e\nDPG Spring Meeting 2026, Dresden Germany, 2026/3/9\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003ch2 id=\"2025年\"\u003e2025年\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cstrong\u003e副格子自由度を持つ超伝導体の表面状態と輸送現象\u003c/strong\u003e \u003cbr\u003e\n佐野智哉, 佐々木章宏, 池谷聡, 小林伸吾, 浅野泰寛, \u003cbr\u003e\n日本物理学会第80回年次大会, 広島大学, 2025/9/18\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cstrong\u003e擬一次元キタエフハニカム模型における非局所スピン相関\u003c/strong\u003e \u003cbr\u003e\n山崎勇樹, 小林伸吾, 古崎昭, \u003cbr\u003e\n日本物理学会第80回年次大会, 広島大学, 2025/9/16\u003c/p\u003e","title":"Talks"},{"content":"Courses 2026 - Present Vector Calculus, Suwa University of Science, second-year undergraduate students 2026 - Present Physics A,B,C; Fundamentals of Physics, Suwa University of Science, first-year undergraduate students 2025 - 2026 Physics A, Tokyo Denki University, first-year undergraduate students 2024 - 2026 Fundamentals of Electromagnetism, Tokyo City University, first-year undergraduate students 2017 - 2019 Applied Physics Tutorial V (Condensed Matter Physics), Nagoya University, third-year undergraduate students 2016 - 2017 Applied Physics Tutorial III (Electromagnetism), Nagoya University, second-year undergraduate students Outreach Activities October 2025 Exhibition Guide, RIKEN Wako Campus Open Day August 2024 Lecturer, Laboratory Tour for High School Students in Shizuoka Prefecture October 2018 Moderator, Public Lecture organized by the Institute for Advanced Research, Nagoya University August 2013 Lecturer, Career Exploration Program for Junior High School Students in Kanagawa Prefecture ","permalink":"https://kobayashi-physics.github.io/en/teaching/","summary":"\u003ch2 id=\"courses\"\u003eCourses\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003e2026 - Present  Vector Calculus, Suwa University of Science, second-year undergraduate students\u003c/li\u003e\n\u003cli\u003e2026 - Present  Physics A,B,C; Fundamentals of Physics, Suwa University of Science, first-year undergraduate students\u003c/li\u003e\n\u003cli\u003e2025 - 2026  Physics A, Tokyo Denki University, first-year undergraduate students\u003c/li\u003e\n\u003cli\u003e2024 - 2026  Fundamentals of Electromagnetism, Tokyo City University, first-year undergraduate students\u003c/li\u003e\n\u003cli\u003e2017 - 2019  Applied Physics Tutorial V (Condensed Matter Physics), Nagoya University, third-year undergraduate students\u003c/li\u003e\n\u003cli\u003e2016 - 2017  Applied Physics Tutorial III (Electromagnetism), Nagoya University, second-year undergraduate students\u003c/li\u003e\n\u003c/ul\u003e\n\u003ch2 id=\"outreach-activities\"\u003eOutreach Activities\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eOctober 2025 Exhibition Guide, RIKEN Wako Campus Open Day\u003c/li\u003e\n\u003cli\u003eAugust 2024 Lecturer, Laboratory Tour for High School Students in Shizuoka Prefecture\u003c/li\u003e\n\u003cli\u003eOctober 2018 Moderator, Public Lecture organized by the Institute for Advanced Research, Nagoya University\u003c/li\u003e\n\u003cli\u003eAugust 2013 Lecturer, Career Exploration Program for Junior High School Students in Kanagawa Prefecture\u003c/li\u003e\n\u003c/ul\u003e","title":"Teaching"}]