研究者詳細 - 川口　由紀

We theoretically study spin and charge transport induced by a twisted light beam irradiated on a disordered surface of a doped three-dimensional topological insulator (TI). We find that various types of spin vortices are imprinted on the surface of the TI depending on the spin and orbital angular momentum of the incident light. The key mechanism for the appearance of the unconventional spin structure is the spin-momentum locking in the surface state of the TI. Besides, the diffusive transport of electrons under an inhomogeneous electric field causes a gradient of the charge density, which then induces nonlocal charge current and spin density as well as the spin current. We discuss the relation between these quantities within the linear response to the applied electric field using the Keldysh-Green's function method.

DOI： 10.1103/PhysRevB.93.195415

Web of Science

Spin Hall effect in a spinor dipolar Bose-Einstein condensate 査読有り

Toshiyuki Oshima, Yuki Kawaguchi

PHYSICAL REVIEW A 93 巻 ( 5 ) 2016年5月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

We theoretically show that the spin Hall effect arises in a Bose-Einstein condensate (BEC) of neutral atoms interacting via the magnetic dipole-dipole interactions (MDDIs). Since the MDDI couples the total spin angular momentum and the relative orbital angular momentum of two colliding atoms, it works as a spin-orbit coupling. Thus, when we prepare a BEC in a magnetic sublevel m=0, thermally and quantum-mechanically excited atoms in the m=1 and -1 states feel the Lorentz-like forces in the opposite directions. This is the origin for the emergence of the spin Hall effect. We define the mass-current and spin-current operators from the equations of continuity and calculate the spin Hall conductivity from the off-diagonal current-current correlation function within the Bogoliubov approximation. We find that the correction of the current operators due to the MDDI significantly contributes to the spin Hall conductivity. A possible experimental situation is also discussed.

DOI： 10.1103/PhysRevA.93.053605

Web of Science

Skyrmionic magnetization configurations at chiral magnet/ferromagnet heterostructures 査読有り

Yuki Kawaguchi, Yukio Tanaka, and Naoto Nagaosa

PHYSICAL REVIEW B 93 巻 ( 6 ) 2016年2月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

We consider magnetization configurations at chiral magnet (CM)/ferromagnet (FM) heterostructures. In the CM, magnetic skyrmions and spin helices emerge due to the Dzyaloshinskii-Moriya interaction, which then penetrate into the adjacent FM. However, because the nonuniform magnetization structures are energetically unfavorable in the FM, the penetrated magnetization structures are deformed, resulting in exotic three-dimensional configurations, such as skyrmion cones, sideways skyrmions, and twisted helices and skyrmions. We discuss the stability of possible magnetization configurations at the CM/FM and CM/FM/CM hybrid structures within the framework of the variational method, and find that various magnetization configurations appear in the ground state, some of which cause nontrivial emergent magnetic field.

DOI： 10.1103/PhysRevB.93.064416

Web of Science

Controlling and probing non-abelian emergent gauge potentials in spinor Bose-Fermi mixtures 査読有り

Nguyen Thanh Phuc, Gen Tatara, Yuki Kawaguchi, Masahito Ueda

NATURE COMMUNICATIONS 6 巻 2015年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

Gauge fields, typified by the electromagnetic field, often appear as emergent phenomena due to geometrical properties of a curved Hilbert subspace, and provide a key mechanism for understanding such exotic phenomena as the anomalous and topological Hall effects. Non-abelian gauge potentials serve as a source of non-singular magnetic monopoles. Here we show that unlike conventional solid materials, the non-abelianness of emergent gauge potentials in spinor Bose-Fermi atomic mixtures can be continuously varied by changing the relative particle-number densities of bosons and fermions. The non-abelian feature is captured by an explicit dependence of the measurable spin current density of fermions in the mixture on the variable coupling constant. Spinor mixtures also provide us with a method to coherently and spontaneously generate a pure spin current without relying on the spin Hall effect. Such a spin current is expected to have potential applications in the new generation of atomtronic devices.

DOI： 10.1038/ncomms9135

Web of Science

Coarsening dynamics driven by vortex-antivortex annihilation in ferromagnetic Bose-Einstein condensates 査読有り

Kazue Kudo, Yuki Kawaguchi

PHYSICAL REVIEW A 91 巻 ( 5 ) 2015年5月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

In ferromagnetic Bose-Einstein condensates (BECs), the quadratic Zeeman effect controls magnetic anisotropy, which affects magnetic domain pattern formation. While the longitudinal magnetization is dominant (similar to the Ising model) for a negative quadratic Zeeman energy, the transverse magnetization is dominant (similar to the XY model) for a positive one. When the quadratic Zeeman energy is positive, the coarsening dynamics is driven by vortex-antivortex annihilation in the same way as the XY model. However, due to a superfluid flow of atoms, there exist several combinations of vortex-antivortex pairs in ferromagnetic BECs, which makes the coarsening dynamics more complicated than that of the XY model. We propose a revised domain growth law, which is based on the growth law of the two-dimensional XY model, for a two-dimensional ferromagnetic BEC with a positive quadratic Zeeman energy.

DOI： 10.1103/PhysRevA.91.053609

Web of Science

Quantum Mass Acquisition in Spinor Bose-Einstein Condensates 査読有り

Nguyen Thanh Phuc, Yuki Kawaguchi, and Masahito Ueda

PHYSICAL REVIEW LETTERS 113 巻 ( 23 ) 2014年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

Quantum mass acquisition, in which a massless (quasi)particle becomes massive due to quantum corrections, is predicted to occur in several subfields of physics. However, its experimental observation remains elusive since the emergent energy gap is too small. We show that a spinor Bose-Einstein condensate is an excellent candidate for the observation of such a peculiar phenomenon as the energy gap turns out to be 2 orders of magnitude larger than the zero-point energy. This extraordinarily large energy gap is a consequence of the dynamical instability. The propagation velocity of the resultant massive excitation mode is found to be decreased by the quantum corrections as opposed to phonons.

DOI： 10.1103/PhysRevLett.113.230401

Web of Science

Goldstone-mode instability leading to fragmentation in a spinor Bose-Einstein condensate 査読有り

Yuki Kawaguchi

PHYSICAL REVIEW A 89 巻 ( 3 ) 2014年3月

担当区分：筆頭著者,　最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

We apply the number-conserving Bogoliubov theory to spinor Bose-Einstein condensates and show that the Goldstone magnon causes instability leading to fragmentation. Unlike the dynamical instability, where modes with complex eigenfrequencies grow exponentially, here the zero-energy mode exhibits algebraic growth. We also point out that a small fraction of thermally excited atoms enhances the fragmentation dynamics.

DOI： 10.1103/PhysRevA.89.033627

Web of Science

Fluctuation-induced and symmetry-prohibited metastabilities in spinor Bose-Einstein condensates 査読有り

Nguyen Thanh Phuc, Yuki Kawaguchi, Masahito Ueda

PHYSICAL REVIEW A 88 巻 ( 4 ) 2013年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

Spinor Bose-Einstein condensates provide a unique example in which the Bogoliubov theory fails to describe the metastability associated with first-order quantum phase transitions. This problem is resolved by developing the spinor Beliaev theory which takes account of quantum fluctuations of the condensate. It is these fluctuations that generate terms of higher than the fourth order in the order-parameter field which are needed for the first-order phase transitions. Besides the conventional first-order phase transitions which are accompanied by metastable states, we find a class of first-order phase transitions which are not accompanied by metastable states. The absence of metastability in these phase transitions holds to all orders of approximation since the metastability is prohibited by the symmetry of the Hamiltonian at the phase boundary. Finally, the possibility of macroscopic quantum tunneling from a metastable state to the ground state is discussed.

DOI： 10.1103/PhysRevA.88.043629

Web of Science

Kibble-Zurek mechanism in a trapped ferromagnetic Bose-Einstein condensate 査読有り

Hiroki Saito, Yuki Kawaguchi, Masahito Ueda

JOURNAL OF PHYSICS-CONDENSED MATTER 25 巻 ( 40 ) 2013年10月

Magnetic domain growth in a ferromagnetic Bose-Einstein condensate: Effects of current 査読有り

Kazue Kudo, Yuki Kawaguchi

PHYSICAL REVIEW A 88 巻 ( 1 ) 2013年7月

Beliaev theory of spinor Bose-Einstein condensates 査読有り

Nguyen Thanh Phuc, Yuki Kawaguchi, Masahito Ueda

ANNALS OF PHYSICS 328 巻頁： 158 - 219 2013年1月

Symmetry classification of spin-orbit-coupled spinor Bose-Einstein condensates 査読有り国際共著

Z. F. Xu, Y. Kawaguchi, L. You, M. Ueda

PHYSICAL REVIEW A 86 巻 ( 3 ) 2012年9月

Topological classification of vortex-core structures of spin-1 Bose-Einstein condensates 査読有り

Shingo Kobayashi, Yuki Kawaguchi, Muneto Nitta, Masahito Ueda

PHYSICAL REVIEW A 86 巻 ( 2 ) 2012年8月

Finite-temperature phase diagram of a spin-1 Bose gas 査読有り国際共著

Yuki Kawaguchi, Nguyen Thanh Phuc, P. Blair Blakie

PHYSICAL REVIEW A 85 巻 ( 5 ) 2012年5月

Abe homotopy classification of topological excitations under the topological influence of vortices 査読有り

Shingo Kobayashi, Michikazu Kobayashi, Yuki Kawaguchi, Muneto Nitta, Masahito Ueda

NUCLEAR PHYSICS B 856 巻 ( 2 ) 頁： 577 - 606 2012年3月

Symmetry classification of spinor Bose-Einstein condensates 査読有り

Yuki Kawaguchi, Masahito Ueda

PHYSICAL REVIEW A 84 巻 ( 5 ) 2011年11月

Effects of thermal and quantum fluctuations on the phase diagram of a spin-1 Rb-87 Bose-Einstein condensate 査読有り

Nguyen Thanh Phuc, Yuki Kawaguchi, Masahito Ueda

PHYSICAL REVIEW A 84 巻 ( 4 ) 2011年10月

Dissipative hydrodynamic equation of a ferromagnetic Bose-Einstein condensate: Analogy to magnetization dynamics in conducting ferromagnets 査読有り

Kazue Kudo, Yuki Kawaguchi

PHYSICAL REVIEW A 84 巻 ( 4 ) 2011年10月

内部自由度を持ったボース・アインシュタイン凝縮体 : スピノルBECにおけるトポロジカル励起(<シリーズ>超伝導・超流動研究の接点) 招待有り査読有り

川口由紀

物性研究 95 巻 ( 6 ) 頁： 543 - 582 2011年3月

Collision Dynamics of Non-Abelian Vortices in Spinor Bose-Einstein Condensates 査読有り

Kobayashi M., Kawaguchi Y., Nitta M., Ueda M.

JOURNAL OF LOW TEMPERATURE PHYSICS 162 巻 ( 3-4 ) 頁： 299 - 306 2011年2月

磁気双極子相互作用するボース・アインシュタイン凝縮体招待有り査読有り

斎藤弘樹, 川口由紀, 上田正仁

固体物理 46 巻 ( 1 ) 頁： 21 - 28 2011年1月

Hydrodynamic equation of a spinor dipolar Bose-Einstein condensate 査読有り

Kudo Kazue, Kawaguchi Yuki

PHYSICAL REVIEW A 82 巻 ( 5 ) 2010年11月

Spontaneous magnetic ordering in a ferromagnetic spinor dipolar Bose-Einstein condensate 査読有り

Kawaguchi Yuki, Saito Hiroki, Kudo Kazue, Ueda Masahito

PHYSICAL REVIEW A 82 巻 ( 4 ) 2010年10月

スピノル・ボース・アインシュタイン凝縮で実現する非可換量子渦と,その衝突ダイナミクス(最近の研究から) 招待有り査読有り

小林未知数, 川口由紀, 新田宗土, 上田正仁

日本物理學會誌 65 巻 ( 8 ) 頁： 625 - 628 2010年8月

記述言語：日本語掲載種別：研究論文（大学，研究機関等紀要）

近年,スピン自由度のあるボース・アインシュタイン凝縮体(スピノルBEC)が注目を浴びつつある.この系の特徴は,サイクリック相やノットなどの新奇な量子相やトポロジカル励起が期待できることである.非可換量子渦はその顕著な例である.スピンが2の原子からなるBECのサイクリック相で実現される非可換量子渦の非可換性は渦の衝突ダイナミクスにおいてユニークな効果を示すことが最近明らかになった.本稿ではこの研究成果について報告する.

Topological Excitations in Spinor Bose-Einstein Condensates 査読有り

Kawaguchi Yuki, Kobayashi Michikazu, Nitta Muneto, Ueda Masahito

PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT ( 186 ) 頁： 455 - 462 2010年

NEW PHYSICS IN DIPOLAR BOSE-EINSTEIN CONDENSATES

Kawaguchi Yuki, Saito Hiroki, Ueda Masahito

LASER SPECTROSCOPY 頁： 29 - 38 2010年

Spin-dependent inelastic collisions in spin-2 Bose-Einstein condensates 査読有り

Tojo Satoshi, Hayashi Taro, Tanabe Tatsuyoshi, Hirano Takuya, Kawaguchi Yuki, Saito Hiroki, Ueda Masahito

PHYSICAL REVIEW A 80 巻 ( 4 ) 2009年10月

Collision Dynamics and Rung Formation of non-Abelian Vortices 査読有り

Kobayashi Michikazu, Kawaguchi Yuki, Nitta Muneto, Ueda Masahito

PHYSICAL REVIEW LETTERS 103 巻 ( 11 ) 2009年9月

磁気双極子相互作用するボース・アインシュタイン凝縮体(最近の研究から) 招待有り査読有り

川口由紀, 斎藤弘樹, 上田正仁

日本物理學會誌 64 巻 ( 8 ) 頁： 623 - 627 2009年8月

担当区分：筆頭著者記述言語：日本語掲載種別：研究論文（大学，研究機関等紀要）

希薄な原子気体に働く磁気双極子相互作用は非常に微弱であるが,原子気体がひとたびボース・アインシュタイン凝縮すれば巨視的な現象を起こしうる.特にスピン内部自由度を持った凝縮体(スピノルBEC)では,スピンの空間構造(テクスチャ)の形成を通して超流動やスピン流を生じさせることがわかってきた.本稿では,スピノルBECの基本的な性質について解説した後に,双極子相互作用のもたらす凝縮体の新奇な性質を紹介する.

Ferrofluidity in a Two-Component Dipolar Bose-Einstein Condensate 査読有り

Saito Hiroki, Kawaguchi Yuki, Ueda Masahito

PHYSICAL REVIEW LETTERS 102 巻 ( 23 ) 2009年6月

Coherent collapses of dipolar Bose-Einstein condensates for different trap geometries 査読有り国際共著

Metz J., Lahaye T., Froehlich B., Griesmaier A., Pfau T., Saito H., Kawaguchi Y., Ueda M.

NEW JOURNAL OF PHYSICS 11 巻 2009年5月

KIBBLE-ZUREK MECHANISM IN MAGNETIZATION OF A SPINOR BOSE-EINSTEIN CONDENSATE 査読有り

Saito Hiroki, Kawaguchi Yuki, Ueda Masahito

PROCEEDINGS OF THE 9TH INTERNATIONAL SYMPOSIUM ON FOUNDATIONS OF QUANTUM MECHANICS IN THE LIGHT OF NEW TECHNOLOGY 頁： 33 - 36 2009年

d-wave collapse and explosion of a dipolar Bose-Einstein condensate 査読有り国際共著

Lahaye T., Metz J., Froehlich B., Koch T., Meister M., Griesmaier A., Pfau T., Saito H., Kawaguchi Y., Ueda M.

PHYSICAL REVIEW LETTERS 101 巻 ( 8 ) 2008年8月

Knots in a spinor Bose-Einstein condensate (vol 100, art no 180403, 2008) 査読有り

Kawaguchi Yuki, Nitta Muneto, Ueda Masahito

PHYSICAL REVIEW LETTERS 101 巻 ( 2 ) 2008年7月

Knots in a spinor Bose-Einstein condensate 査読有り

Kawaguchi Yuki, Nitta Muneto, Ueda Masahito

PHYSICAL REVIEW LETTERS 100 巻 ( 18 ) 2008年5月

Heteronuclear fermionic superfuids with spin degrees of freedom 査読有り国際共著

Dickerscheid D. B. M., Kawaguchi Y., Ueda M.

PHYSICAL REVIEW A 77 巻 ( 5 ) 2008年5月

Kibble-Zurek mechanism in a quenched ferromagnetic Bose-Einstein condensate 査読有り

Saito Hiroki, Kawaguchi Yuki, Ueda Masahito

PHYSICAL REVIEW A 76 巻 ( 4 ) 2007年10月

Symmetry breaking in scalar, spinor, and rotating Bose-Einstein condensates 査読有り

Saito Hiroki, Kawaguchi Yuki, Ueda Masahito

NUCLEAR PHYSICS A 790 巻頁： 737C - 471C 2007年6月

Can spinor dipolar effects be observed in Bose-Einstein condensates? 査読有り

Kawaguchi Yuki, Saito Hiroki, Ueda Masahito

PHYSICAL REVIEW LETTERS 98 巻 ( 11 ) 2007年3月

Topological defect formation in a quenched ferromagnetic Bose-Einstein condensates 査読有り

Saito Hiroki, Kawaguchi Yuki, Ueda Masahito

PHYSICAL REVIEW A 75 巻 ( 1 ) 2007年1月

Spontaneous circulation in ground-state spinor dipolar Bose-Einstein condensates 査読有り

Kawaguchi Yuki, Saito Hiroki, Ueda Masahito

PHYSICAL REVIEW LETTERS 97 巻 ( 13 ) 2006年9月

Einstein-de Haas effect in dipolar Bose-Einstein condensates 査読有り

Kawaguchi Y, Saito H, Ueda M

PHYSICAL REVIEW LETTERS 96 巻 ( 8 ) 2006年3月

Breaking of chiral symmetry and spontaneous rotation in a spinor Bose-Einstein condensate 査読有り

Saito H, Kawaguchi Y, Ueda M

PHYSICAL REVIEW LETTERS 96 巻 ( 6 ) 2006年2月

Symmetry breaking in Bose-Einstein condensates 査読有り

Ueda Masahito, Kawaguchi Yuki, Saito Hiroki, Kanamoto Rina, Nakajima Tatsuya

Atomic Physics 20 869 巻頁： 165 - 172 2006年

原子気体BECにおける量子渦の分裂招待有り査読有り

川口由紀

物性研究 83 巻 ( 6 ) 頁： 787 - 816 2005年3月

Topological phase imprinting in BEC in presence of gravitational field 査読有り

Kawaguchi Y, Nakahara M, Ohmi T

JOURNAL OF LOW TEMPERATURE PHYSICS 138 巻 ( 3-4 ) 頁： 699 - 704 2005年2月

Topological vortex formation in a Bose-Einstein condensate under gravitational field 査読有り

Kawaguchi Y, Nakahara M, Ohmi T

PHYSICAL REVIEW A 70 巻 ( 4 ) 2004年10月

Splitting instability of a multiply charged vortex in a Bose-Einstein condensate 査読有り

Kawaguchi Y, Ohmi T

PHYSICAL REVIEW A 70 巻 ( 4 ) 2004年10月

Stability of quadruply charged vortices in Bose-Einstein condensates 査読有り

Kawaguchi Y, Ohmi T

LASER PHYSICS 14 巻 ( 4 ) 頁： 575 - 580 2004年4月

Collective oscillations of vortex lattices in rotating Bose-Einstein condensates 査読有り国際共著

Mizushima T, Kawaguchi Y, Machida K, Ohmi T, Isoshima T, Salomaa MM

PHYSICAL REVIEW LETTERS 92 巻 ( 6 ) 2004年2月

Stability of magnetically trapped Bose-Einstein condensates 査読有り

Kawaguchi Y, Ohmi T

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 巻 ( 5 ) 頁： 1118-1122 2003年5月

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