Papers - TAKAYOSHI Shintaro
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Laser-Driven Multiferroics and Ultrafast Spin Current Generation Reviewed
Masahiro Sato, Shintaro Takayoshi, Takashi Oka
Physical Review Letters 117 ( 14 ) 147202 2016.9
Joint Work
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Magnetism and superconductivity in ferromagnetic heavy-fermion system UCoGe under in-plane magnetic fields
Yasuhiro Tada, Shintaro Takayoshi, Satoshi Fujimoto
PHYSICAL REVIEW B 93 ( 17 ) 2016.5
Joint Work
Publisher：AMER PHYSICAL SOC
We study the ferromagnetic superconductor UCoGe at ambient pressure under ab-plane magnetic fields H, which are perpendicular to the ferromagnetic easy axis. It is shown that, by taking into account the Dyaloshinskii-Moriya interaction arising from the zigzag chain crystal structure of UCoGe, we can qualitatively explain the experimentally observed in-plane anisotropy for critical magnetic fields of the paramagnetic transition. Because of this strong dependence on the magnetic field direction, upper critical fields of superconductivity, which is mediated by ferromagnetic spin fluctuations, also become strongly anisotropic. The experimental observation of S-shaped H-c2 parallel to b axis is qualitatively explained as a result of enhancement of the spin fluctuations due to decreased Curie temperature by the b-axis magnetic field. We also show that the S-shaped H-c2 is accompanied by a rotation of the d vector, which would be a key to understand the experiments not only at ambient pressure but also under pressure.
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Symmetry-protected topological order in magnetization plateau states of quantum spin chains
Shintaro Takayoshi, Keisuke Totsuka, Akihiro Tanaka
PHYSICAL REVIEW B 91 ( 15 ) 2015.4
Joint Work
Publisher：AMER PHYSICAL SOC
A symmetry-protected topologically ordered phase is a short-range entangled state, for which some imposed symmetry prohibits the adiabatic deformation into a trivial state which lacks entanglement. In this paper we argue that magnetization plateau states of one-dimensional antiferromagnets which satisfy the conditions S - m is an element of odd integer, where S is the spin quantum number and m the magnetization per site, can be identified as symmetry-protected topological states if an inversion symmetry about the link center is present. This assertion is reached by mapping the antiferromagnet into a nonlinear sigma model type effective field theory containing a novel Berry phase term (a total derivative term) with a coefficient proportional to the quantity S - m, and then analyzing the topological structure of the ground state wave functional which is inherited from the latter term. A boson-vortex duality transformation is employed to examine the topological stability of the ground state in the absence/presence of a perturbation violating link-center inversion symmetry. Our prediction based on field theories is verified by means of a numerical study of the entanglement spectra of actual spin chains, which we find to exhibit twofold degeneracies when the aforementioned condition is met. We complete this study with a rigorous analysis using matrix product states.
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A short guide to topological terms in the effective theories of condensed matter
Akihiro Tanaka, Shintaro Takayoshi
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 16 ( 1 ) 014404 - 014404 2015.2
Joint Work
Publisher：IOP PUBLISHING LTD
This article is meant as a gentle introduction to the topological terms that often play a decisive role in effective theories describing topological quantum effects in condensed matter systems. We first take up several prominent examples, mainly from the area of quantum magnetism and superfluids/superconductors. We then briefly discuss how these ideas are now finding incarnations in the studies of symmetry-protected topological phases, which are in a sense a generalization of the concept of topological insulators to a wider range of materials, including magnets and cold atoms.
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Laser-induced magnetization curve
Shintaro Takayoshi, Masahiro Sato, Takashi Oka
PHYSICAL REVIEW B 90 ( 21 ) 2014.12
Joint Work
Publisher：AMER PHYSICAL SOC
We propose an all optical ultrafast method to highly magnetize general quantum magnets using a circularly polarized terahertz laser. The key idea is to utilize a circularly polarized laser and its chirping. Through this method, one can obtain magnetization curves of a broad class of quantum magnets as a function of time even without any static magnetic field. We numerically demonstrate the laser-induced magnetization process in realistic quantum spin models and find a condition for the realization. The onset of magnetization can be described by a many-body version of Landau-Zener mechanism. In a particular model, we show that a plateau state with topological properties can be realized dynamically.
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Magnetization and phase transition induced by circularly polarized laser in quantum magnets
Shintaro Takayoshi, Hideo Aoki, Takashi Oka
PHYSICAL REVIEW B 90 ( 8 ) 2014.8
Joint Work
Publisher：AMER PHYSICAL SOC
We theoretically predict a nonequilibrium phase transition in quantum spin systems induced by a laser, which provides a purely quantum-mechanical way of coherently controlling magnetization. Namely, when a circularly polarized laser is applied to a spin system, the magnetic component of a laser is shown to induce a magnetization normal to the plane of polarization, leading to an ultrafast phase transition. We first demonstrate this phenomenon numerically for an S = 1 antiferromagnetic Heisenberg spin chain, where a new state emerges with magnetization perpendicular to the polarization plane of the laser in place of the topologically ordered Haldane state. We then elucidate its physical mechanism by mapping the system to an effective static model. The theory also indicates that the phenomenon should occur in general quantum spin systems with a magnetic anisotropy. The required laser frequency is in the terahertz range, with the required intensity being within a prospective experimental feasibility.
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Phase diagram and pair Tomonaga-Luttinger liquid in a Bose-Hubbard model with flat bands
Shintaro Takayoshi, Hosho Katsura, Noriaki Watanabe, Hideo Aoki
PHYSICAL REVIEW A 88 ( 6 ) 2013.12
Joint Work
Publisher：AMER PHYSICAL SOC
To explore superfluidity in flat-band systems, we consider a Bose-Hubbard model on a cross-linked ladder with p flux, which has a flat band with a gap between the other band for noninteracting particles, where we study the effect of the on-site repulsion nonperturbatively. For low densities, we find exact degenerate ground states, each of which is a Wigner solid with nonoverlapping Wannier states on the flat band. At higher densities, the many-body system, when projected onto the lower flat band, can be mapped to a spin-chain model. This mapping enables us to reveal the existence of a Tomonaga-Luttinger liquid comprising pairs of bosons. Interestingly, the high- and low-density regions have an overlap, where the two phases coexist.
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Mass ratio of elementary excitations in frustrated antiferromagnetic chains with dimerization
Shintaro Takayoshi, Masaki Oshikawa
PHYSICAL REVIEW B 86 ( 14 ) 2012.10
Joint Work
Publisher：AMER PHYSICAL SOC
Excitation spectra of S = 1/2 and 1 frustrated Heisenberg antiferromagnetic chains with bond alternation (explicit dimerization) are studied using a combination of analytical and numerical methods. The system undergoes a dimerization transition at a critical bond alternation parameter delta = delta(c), where delta(c) = 0 for the S = 1/2 chain. The SU(2)-symmetric sine-Gordon theory is known to be an effective field theory of the system except at the transition point. The sine-Gordon theory has a SU(2)-triplet and a SU(2)-singlet of elementary excitation, and the mass ratio r of the singlet to the triplet is root 3. However, our numerical calculation with the infinite time-evolving block decimation method shows that r depends on the frustration (next-nearest-neighbor coupling) and is generally different from root 3. This can be understood as an effect of marginal perturbation to the sine-Gordon theory. In fact, at the critical frustration separating the second-order and first-order dimerization transitions, the marginal operator vanishes and r = root 3 holds. We derive the mass ratio r analytically using form-factor perturbation theory combined with a renormalization-group analysis. Our formula agrees well with the numerical results, confirming the theoretical picture. The present theory also implies that, even in the presence of a marginally irrelevant operator, the mass ratio approaches root 3 in the very vicinity of the second-order dimerization critical point delta similar to delta(c). However, such a region is extremely small and would be difficult to observe numerically.
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Spin-chain description of fractional quantum Hall states in the Jain series
Zheng-Yuan Wang, Shintaro Takayoshi, Masaaki Nakamura
PHYSICAL REVIEW B 86 ( 15 ) 2012.10
Joint Work
Publisher：AMER PHYSICAL SOC
We discuss the relationship between fractional quantum Hall (FQH) states at filling factor nu = p/(2mp + 1) and quantum spin chains. This series corresponds to the Jain series nu = p/(2mp + 1) with m = 1 where the composite fermion picture is realized. We show that the FQH states with toroidal boundary conditions beyond the thin-torus limit can be mapped to effective quantum spin S = 1 chains with p spins in each unit cell. We calculate energy gaps and the correlation functions for both the FQH systems and the corresponding effective spin chains, using exact diagonalization and the infinite time-evolving block decimation (iTEBD) algorithm. We confirm that the mass gaps of these effective spin chains are decreased as p is increased which is similar to S = p integer Heisenberg chains. These results shed new light on a link between the hierarchy of FQH states and the Haldane conjecture for quantum spin chains.
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Single-ion anisotropy in Haldane chains and the form factor of the O(3) nonlinear sigma model
Shunsuke C. Furuya, Takafumi Suzuki, Shintaro Takayoshi, Yoshitaka Maeda, Masaki Oshikawa
PHYSICAL REVIEW B 84 ( 18 ) 2011.11
Joint Work
Publisher：AMER PHYSICAL SOC
We consider spin-1 Haldane chains with single-ion anisotropy, which exists in known Haldane chain materials. We develop a perturbation theory in terms of anisotropy, where the magnon-magnon interaction is important even in the low-temperature limit. The exact two-particle form factor in the O(3) nonlinear sigma model leads to quantitative predictions on several dynamical properties, including the dynamical structure factor and electron-spin-resonance frequency shift. These agree very well with numerical results, and with experimental data on the Haldane chain material Ni(C5H14N2)(2)N-3(PF6).
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Coefficients of bosonized dimer operators in spin-1/2 XXZ chains and their applications
Shintaro Takayoshi, Masahiro Sato
PHYSICAL REVIEW B 82 ( 21 ) 2010.12
Joint Work
Publisher：AMER PHYSICAL SOC
Comparing numerically evaluated excitation gaps of dimerized spin-1/2 XXZ chains with the gap formula for the low-energy effective sine-Gordon theory, we determine coefficients d(xy) and d(z) of bosonized dimerization operators in spin-1/2 XXZ chains, which are defined as (-1)(j)((SjSj+1x)-S-x + (SjSj+1y)-S-y) = d(xy) sin[root 4 pi phi(x)]+ ... and (-1)(SjSj+1z)-S-j-S-z = d(z) sin[root 4 pi phi(x)]+ ... . We also calculate the coefficients of both spin and dimer operators for the spin-1/2 Heisenberg antiferromagnetic chain with a nearest-neighbor coupling J and a next-nearest-neighbor coupling J(2)=0.2411J. As applications of these coefficients, we present ground-state phase diagrams of dimerized spin chains in a magnetic field and antiferromagnetic spin ladders with a four-spin interaction. The optical conductivity and electric polarization of one-dimensional Mott insulators with Peierls instability are also evaluated quantitatively.
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Spontaneous population imbalance in two-component Bose and Fermi gases
Shintaro Takayoshi, Masahiro Sato, Shunsuke Furukawa
PHYSICAL REVIEW A 81 ( 5 ) 2010.5
Joint Work
Publisher：AMER PHYSICAL SOC
We study two-component (or pseudo-spin-1/2) Bose or Fermi gases in one dimension, in which particles are convertible between the components. Through bosonization and numerical analyses of a simple lattice model, we demonstrate that, in such gases, a strong intercomponent repulsion induces spontaneous population imbalance between the components, namely, the ferromagnetism of the pseudo spins. The imbalanced phase contains gapless charge excitations characterized as a Tomonaga-Luttinger liquid and gapped spin excitations. We uncover a crucial effect of the intercomponent particle hopping on the transition to the imbalanced phase. In the absence of this hopping, the transition is of first order. At the transition point, the energy spectrum reveals certain degeneracy indicative of an emergent SU(2) symmetry. With an infinitesimal intercomponent hopping, the transition becomes of Ising type. We determine the phase diagram of the model accurately and test the reliability of the weak-coupling bosonization formalism.
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Density Variation of the Frustrated Ferromagnetism in 2D Solid 3He
D. Sato, S. Takayoshi, K. Obata, T. Matsui, Hiroshi Fukuyama
Journal of Low Temperature Physics 158 ( 3-4 ) 544 - 549 2010.2
Joint Work
Publisher：Springer Science and Business Media LLC
DOI： 10.1007/s10909-009-9993-9
Other Link： http://link.springer.com/article/10.1007/s10909-009-9993-9/fulltext.html
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S. Takayoshi, Hiroshi Fukuyama
Journal of Low Temperature Physics 158 ( 3-4 ) 672 - 677 2010.2
Joint Work
Publisher：Springer Science and Business Media LLC
We described details of a method to estimate with good accuracy the mosaic
angle distributions of microcrystallites (platelets) in exfoliated graphite
like Grafoil which is commonly used as an adsorption substrate for helium thin
films. The method is based on analysis of resonance field shifts in
continuous-wave (CW) NMR spectra of $^{3}$He ferromagnetic monolayers making
use of the large nuclear polarization of the adsorbate itself. The mosaic angle
distribution of a Grafoil substrate analyzed in this way can be well fitted to
a gaussian form with a $27.5\pm2.5$ deg spread. This distribution is quite
different from the previous estimation based on neutron scattering data which
showed an unrealistically large isotropic powder-like component.DOI： 10.1007/s10909-009-9995-7
Other Link： http://link.springer.com/article/10.1007/s10909-009-9995-7/fulltext.html
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D. Sato, D. Tsuji, S. Takayoshi, K. Obata, T. Matsui, Hiroshi Fukuyama
Journal of Low Temperature Physics 158 ( 1-2 ) 201 - 206 2010.1
Joint Work
Publisher：Springer Science and Business Media LLC
We made heat-capacity measurements of two dimensional (2D) $^3$He adsorbed on
graphite preplated with monolayer $^4$He in a wide temperature range (0.1 $\leq
T \leq$ 80 mK) at densities higher than that for the 4/7 phase (= 6.8
nm$^{-2}$). In the density range of 6.8 $\leq \rho \leq$ 8.1 nm$^{-2}$, the 4/7
phase is stable against additional $^3$He atoms up to 20% and they are promoted
into the third layer. We found evidence that such promoted atoms form a
self-bound 2D Fermi liquid with an approximate density of 1 nm$^{-2}$ from the
measured density dependence of the $\gamma$-coefficient of heat capacity. We
also show evidence for the first-order transition between the commensurate 4/7
phase and the ferromagnetic incommensurate phase in the second layer in the
density range of 8.1 $\leq \rho \leq$ 9.5 nm$^{-2}$.DOI： 10.1007/s10909-009-0013-x
Other Link： http://link.springer.com/article/10.1007/s10909-009-0013-x/fulltext.html
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The boiling suppression of liquid nitrogen
S. Takayoshi, W. Kokuyama, H. Fukuyama
CRYOGENICS 49 ( 5 ) 221 - 223 2009.5
Joint Work
Publisher：ELSEVIER SCI LTD
When He gas is injected from room temperature into boiling liquid N(2), boiling is suppressed, leaving liquid surface flat like a mirror. Although the qualitative explanation for this phenomenon is known [Minkoff GJ, Scherber FI, Stober AK. Suppression of bubbling in boiling refrigerants. Nature 1957;180(4599):1413-4], it has not been studied quantitatively and comprehensively yet. In this report, we made careful simultaneous measurements of temperature and weight variation of the liquid. The results clearly indicate that the boiling suppression is caused by cooling of the liquid with "internal evaporation" of N(2) into the He bubbles. (C) 2009 Elsevier Ltd. All rights reserved.
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Spin-Echo Measurements for an Anomalous Quantum Phase of 2D Helium-3
S. Takayoshi, K. Obata, D. Sato, T. Matsui, Hiroshi Fukuyama
25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 3 150 ( 3 ) 032104 - 032104 2009
Joint Work
Publisher：IOP PUBLISHING LTD
Previous heat-capacity measurements of our group had shown the possible existence of an anomalous quantum phase containing the zero-point vacancies (ZPVs) in 2D (3)He. The system is monolayer (3)He adsorbed on graphite preplated with monolayer 4 He at densities (rho) just below the 4/7 commensurate phase (0.8 <= rho/rho(4/7) <= 1). We carried out pulsed-NMR measurements in order to examine the microscopic and dynamical nature of this phase. The measured decay of spin echo signals shows the non-exponential behaviour. The decay curve can be fitted with the double exponential function, but the relative intensity of the component with a longer time constant is small (5 %) and does not depend on density and temperature, which contradicts to the macroscopic fluid and 4/7 phase coexistence model. This slowdown is likely due to the mosaic angle spread of Grafoil substrate and the anisotropic spin-spin relaxation time T(2) in 2D systems with respect to the magnetic field direction. The inverse T(2) value deduced from the major echo signal with a shorter time constant, which obeys the single exponential function, decreases linearly with decreasing density from n = 1, supporting the ZPV model.