Papers - TAKAYOSHI Shintaro
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Many-Body Effects on High-Harmonic Generation in Hubbard Ladders Reviewed International coauthorship
Yuta Murakami, Thomas Hansen, Shintaro Takayoshi, Lars Bojer Madsen, Philipp Werner
Physical Review Letters 134 ( 9 ) 096504 2025.3
Publisher：American Physical Society (APS)
DOI： 10.1103/physrevlett.134.096504
Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.134.096504/fulltext
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Phase transitions and spin dynamics of the quasi-one dimensional Ising-like antiferromagnet BaCo2V2O8 in a longitudinal magnetic field Reviewed International coauthorship
Shintaro Takayoshi, Quentin Faure, Virginie Simonet, Béatrice Grenier, Sylvain Petit, Jacques Ollivier, Pascal Lejay, Thierry Giamarchi
Physical Review Research 5 ( 2 ) 023205 2023.6
Authorship：Lead author, Corresponding author Publisher：American Physical Society (APS)
DOI： 10.1103/physrevresearch.5.023205
Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevResearch.5.023205/fulltext
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Spin, Charge, and η-Spin Separation in One-Dimensional Photodoped Mott Insulators Reviewed International coauthorship
Yuta Murakami, Shintaro Takayoshi, Tatsuya Kaneko, Andreas M. Läuchli, Philipp Werner
Physical Review Letters 130 ( 10 ) 106501 2023.3
Publisher：American Physical Society (APS)
DOI： 10.1103/PhysRevLett.130.106501
Other Link： https://link.aps.org/article/10.1103/PhysRevLett.130.106501
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Mott memristors based on field-induced carrier avalanche multiplication Reviewed International coauthorship
Francesco Peronaci, Sara Ameli, Shintaro Takayoshi, Alexandra S. Landsman, Takashi Oka
Physical Review B 107 ( 7 ) 075154 2023.2
Publisher：American Physical Society (APS)
DOI： 10.1103/PhysRevB.107.075154
Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.107.075154/fulltext
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Dynamical conductivity of disordered quantum chains Reviewed International coauthorship
Shintaro Takayoshi, Thierry Giamarchi
The European Physical Journal D 76 ( 11 ) 213 2022.11
Authorship：Lead author Publisher：Springer Science and Business Media LLC
Abstract
We study the transport properties of a one-dimensional quantum system with disorder. We numerically compute the frequency dependence of the conductivity of a fermionic chain with nearest-neighbor interaction and a random chemical potential by using the Chebyshev matrix product state (CheMPS) method. As a benchmark, we investigate the noninteracting case first. Comparison with exact diagonalization and analytical solutions demonstrates that the results of CheMPS are reliable over a wide range of frequencies. We then calculate the dynamical conductivity spectra of the interacting system for various values of the interaction and disorder strengths. In the high-frequency regime, the conductivity decays as a power law, with an interaction-dependent exponent. This behavior is qualitatively consistent with the bosonized field theory predictions, although the numerical evaluation of the exponent shows deviations from the analytically expected values. We also compute the characteristic pinning frequency at which a peak in the conductivity appears. We confirm that it is directly related to the inverse of the localization length, even in the interacting case. We demonstrate that the localization length follows a power law of the disorder strength with an exponent dependent on the interaction, and find good quantitative agreement with the field theory predictions. In the low-frequency regime, we find a behavior consistent with the one of the noninteracting system $$\omega ^{2}(\ln \omega )^{2}$$ independently of the interaction. We discuss the consequences of our finding for experiments in cold atomic gases.
Graphical abstractDOI： 10.1140/epjd/s10053-022-00524-1
Other Link： https://link.springer.com/article/10.1140/epjd/s10053-022-00524-1/fulltext.html
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Second-order magnetic responses in quantum magnets: Magnetization under ac magnetic fields Reviewed International coauthorship
Tatsuya Kaneko, Yuta Murakami, Shintaro Takayoshi, Andrew J. Millis
Physical Review B 105 ( 19 ) 195126 2022.5
Publisher：American Physical Society (APS)
We investigate second-order magnetic responses of quantum magnets against ac magnetic fields. We focus on the case where the z component of the spin is conserved in the unperturbed Hamiltonian and the driving field is applied in the xy plane. We find that linearly polarized driving fields induce a second-harmonic response, while circularly polarized fields generate only a zero-frequency response, leading to a magnetization with a direction determined by the helicity. Employing an unbiased numerical method, we demonstrate the nonlinear magnetic effect driven by the circularly polarized field in the XXZ model and show that the magnitude of the magnetization can be predicted by the dynamical spin structure factor in the linear response regime.
DOI： 10.1103/physrevb.105.195126
Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.105.195126/fulltext
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Exploring nonequilibrium phases of photo-doped Mott insulators with generalized Gibbs ensembles Reviewed International coauthorship
Yuta Murakami, Shintaro Takayoshi, Tatsuya Kaneko, Zhiyuan Sun, Denis Golež, Andrew J. Millis, Philipp Werner
Communications Physics 5 ( 1 ) 23 2022.1
Publisher：Springer Science and Business Media LLC
Many experiments show that strong excitations of correlated quantum materials can cause non-thermal phases without equilibrium analogues. Understanding the origin and properties of these nonequilibrium states has been challenging due to the limitations of theoretical methods for nonequilibrium strongly correlated systems. In this work, we introduce a generalized Gibbs ensemble description that enables a systematic analysis of the long-time behavior of photo-doped states in Mott insulators based on equilibrium methods. We demonstrate the power of the method by mapping out the nonequilibrium phase diagram of the one-dimensional extended Hubbard model, which features η-pairing and charge density wave phases in a wide photo-doping range. We furthermore clarify that the peculiar kinematics of photo-doped carriers, and the interaction between them, play an essential role in the formation of these non-thermal phases. Our results establish a new path for the systematic analysis of nonequilibrium strongly correlated systems.
DOI： 10.1038/s42005-021-00799-7
Other Link： https://www.nature.com/articles/s42005-021-00799-7
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Solitonic excitations in the Ising anisotropic chain BaCo2V2O8 under large transverse magnetic field Reviewed International coauthorship
Quentin Faure, Shintaro Takayoshi, Béatrice Grenier, Sylvain Petit, Stéphane Raymond, Martin Boehm, Pascal Lejay, Thierry Giamarchi, and Virginie Simonet
Physical Review Research 3 ( 4 ) 043227 2021.12
Publisher：American Physical Society (APS)
DOI： https://doi.org/10.1103/PhysRevResearch.3.043227
Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevResearch.3.043227/fulltext
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Nonadiabatic nonlinear optics and quantum geometry - Application to the twisted Schwinger effect Reviewed International coauthorship
Shintaro Takayoshi, Jianda Wu, Takashi Oka
SciPost Physics 11 ( 4 ) 075 2021.10
Authorship：Lead author Publisher：SCIPOST FOUNDATION
We study the tunneling mechanism of nonlinear optical processes in solids induced by strong coherent laser fields. The theory is based on an extension of the Landau-Zener model with nonadiabatic geometric effects. In addition to the rectification effect known previously, we find two effects, namely perfect tunneling and counterdiabaticity at fast sweep speed. We apply this theory to the twisted Schwinger effect, i.e., nonadiabatic pair production of particles by rotating electric fields, and find a nonperturbative generation mechanism of the opto-valley polarization and photo-current in Dirac and Weyl fermions.
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Scanning Tunneling Microscopy as a Single Majorana Detector of Kitaev's Chiral Spin Liquid Reviewed
Masafumi Udagawa, Shintaro Takayoshi, Takashi Oka
Physical Review Letters 126 ( 12 ) 127201 2021.3
Joint Work
Publisher：AMER PHYSICAL SOC
We propose a local detection scheme for the Majorana zero mode (MZM) carried by a vison in Kitaev's chiral spin liquid (CSL) using scanning tunneling microscopy (STM). The STM introduces a single Majorana into the system through hole-charge injection and the Majorana interacts with the MZM to form a stable composite object. We derive the exact analytical expression of single-hole Green's function in the Mott insulating limit of Kitaev's model, and show that the differential conductance has split peaks, as a consequence of resonant tunneling through the vison-hole composite. The peak splitting turns out comparable to the Majorana gap in CSL, well within the reach of experimental observation.
DOI： 10.1103/PhysRevLett.126.127201
Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.126.127201/fulltext
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Diagrammatic study of optical excitations in correlated systems Reviewed International coauthorship
Olivier Simard, Shintaro Takayoshi, Philipp Werner
Physical Review B 103 ( 10 ) 104415 2021.3
Joint Work
Publisher：AMER PHYSICAL SOC
The optical conductivity contains relevant information on the properties of correlated electron systems. In infinite dimensions, where dynamical mean field theory becomes exact, vertex corrections can be neglected and the conductivity computed from particle-hole bubbles. An interesting question concerns the nature and effect of the most relevant vertex corrections in finite-dimensional systems. A recent numerical study showed that the dominant vertex correction near an ordering instability with wave vector pi comes from a vertical ladder, analogous to the Maki-Thompson diagram. Since the random phase approximation version of this ladder diagram, dubbed pi-ton, can be easily evaluated, this suggests a simple procedure for incorporating antiferro-magnetic or charge density wave fluctuations into dynamical mean field estimates of the optical conductivity and related susceptibilities. We implement this procedure for the half-filled Hubbard model, considering the pi-ton, a double-ladder extension of the pi-ton and Aslamazov-Larkin-type diagrams, and reveal the spectral signatures of these vertex corrections.
DOI： 10.1103/PhysRevB.103.104415
Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.103.104415/fulltext
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High-harmonic generation in one-dimensional Mott insulators Reviewed International coauthorship
Yuta Murakami, Shintaro Takayoshi, Akihisa Koga, Philipp Werner
Physical Review B 103 ( 3 ) 035110 2021.1
Joint Work
Publisher：AMER PHYSICAL SOC
We study high-harmonic generation (HHG) in the one-dimensional Hubbard model in order to understand its relation to elementary excitations as well as the similarities and differences to semiconductors. The simulations are based on the infinite time-evolving block decimation (iTEBD) method and exact diagonalization. We clarify that the HHG originates from the doublon-holon recombination, and the scaling of the cutoff frequency is consistent with a linear dependence on the external field. We demonstrate that the subcycle features of the HHG can be reasonably described by a phenomenological three step model for a doublon-holon pair. We argue that the HHG in the one-dimensional Mott insulator is closely related to the dispersion of the doublon-holon pair with respect to its relative momentum, which is not necessarily captured by the single-particle spectrum due to the many-body nature of the elementary excitations. For the comparison to semiconductors, we introduce effective models obtained from the Schrieffer-Wolff transformation, i.e., a strong-coupling expansion, which allows us to disentangle the different processes involved in the Hubbard model: intraband dynamics of doublons and holons, interband dipole excitations, and spin exchanges. These demonstrate the formal similarity of the Mott system to the semiconductor models in the dipole gauge, and reveal that the spin dynamics, which does not directly affect the charge dynamics, can reduce the HHG intensity. We also show that the long-range component of the intraband dipole moment has a substantial effect on the HHG intensity, while the correlated hopping terms for the doublons and holons essentially determine the shape of the HHG spectrum. A new numerical method to evaluate single-particle spectra within the iTEBD method is also introduced.
DOI： 10.1103/PhysRevB.103.035110
Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.103.035110/fulltext
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Optomagnonic Barnett effect Reviewed
Kouki Nakata, Shintaro Takayoshi
Physical Review B 102 ( 9 ) 094417 2020.9
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Ultrafast nonequilibrium evolution of excitonic modes in semiconductors Reviewed International coauthorship
Yuta Murakami, Michael Schueler, Shintaro Takayoshi, Philipp Werner
Physical Review B 101 ( 3 ) 035203 2020.1
Joint Work
Publisher：AMER PHYSICAL SOC
We study the time evolution of excitonic states after photoexcitation in the one-dimensional spinless extended Falicov-Kimball model. Several numerical methods are employed and benchmarked against each other: time-dependent mean-field simulations, the second-Born approximation (2BA) within the Kadanoff-Baym formalism, the generalized Kadanoff-Baym ansatz (GKBA) implemented with the 2BA, and the infinite time-evolving block decimation (iTEBD) method. It is found that the GKBA gives the best agreement with iTEBD and captures the relevant physics. Excitations to the particle-hole continuum and resonant excitations of the equilibrium exciton result in a qualitatively different dynamics. In the former case, the exciton binding energy remains positive and the frequency of the corresponding coherent oscillations is smaller than the band gap. On the other hand, resonant excitations trigger a collective mode whose frequency is larger than the band gap. We discuss the origin of these different behaviors by evaluating the nonequilibrium susceptibility using the nonthermal distribution and a random phase approximation. The peculiar mode with frequency larger than the band gap is associated with a partial population inversion with a sharp energy cutoff. We also discuss the effects of the cooling by a phonon bath. We demonstrate the real-time development of coherence in the polarization, which indicates excitonic condensation out of equilibrium.
DOI： 10.1103/PhysRevB.101.035203
Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.101.035203/fulltext
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Laser control of magnonic topological phases in antiferromagnets Reviewed International coauthorship
Kouki Nakata, Se Kwon Kim, Shintaro Takayoshi
Physical Review B 100 ( 1 ) 014421 2019.7
Joint Work
Authorship：Last author Publisher：AMER PHYSICAL SOC
We study the laser control of magnon topological phases induced by the Aharonov-Casher effect in insulating antiferromagnets (AFs). Since the laser electric field can be considered as a time-periodic perturbation, we apply the Floquet theory and perform the inverse frequency expansion by focusing on the high frequency region. Using the obtained effective Floquet Hamiltonian, we study nonequilibrium magnon dynamics away from the adiabatic limit and its effect on topological phenomena. We show that a linearly polarized laser can generate helical edge magnon states and induce the magnonic spin Nernst effect, whereas a circularly polarized laser can generate chiral edge magnon states and induce the magnonic thermal Hall effect. In particular, in the latter, we find that the direction of the magnon chiral edge modes and the resulting thermal Hall effect can be controlled by the chirality of the circularly polarized laser through the change from the left-circular to the right-circular polarization. Our results thus provide a handle to control and design magnon topological properties in the insulating AF.
DOI： 10.1103/PhysRevB.100.014421
Other Link： https://link.aps.org/article/10.1103/PhysRevB.100.014421
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Tomonaga-Luttinger Liquid Spin Dynamics in the Quasi-One-Dimensional Ising-Like Antiferromagnet BaCo2V2O8 Reviewed International coauthorship
Quentin Faure, Shintaro Takayoshi, Virginie Simonet, Beatrice Grenier, Martin Mansson, Jonathan S. White, Gregory S. Tucker, Christian Ruegg, Pascal Lejay, Thierry Giamarchi, Sylvain Petit
Physical Review Letters 123 ( 2 ) 027204 2019.7
Joint Work
Authorship：Corresponding author Publisher：AMER PHYSICAL SOC
Combining inelastic neutron scattering and numerical simulations, we study the quasi-one-dimensional Ising anisotropic quantum antiferromagnet BaCo2V2O8 in a longitudinal magnetic field. This material shows a quantum phase transition from a Neel ordered phase at zero field to a longitudinal incommensurate spin density wave at a critical magnetic field of 3.8 T. Concomitantly, the excitation gap almost closes and a fundamental reconfiguration of the spin dynamics occurs. These experimental results are well described by the universal Tomonaga-Luttinger liquid theory developed for interacting spinless fermions in one dimension. We especially observe the rise of mainly longitudinal excitations, a hallmark of the unconventional low-field regime in Ising-like quantum antiferromagnetic chains.
DOI： 10.1103/PhysRevLett.123.027204
Other Link： https://link.aps.org/article/10.1103/PhysRevLett.123.027204
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High-harmonic generation in quantum spin systems Reviewed International coauthorship
Shintaro Takayoshi, Yuta Murakami, Philipp Werner
Physical Review B 99 ( 18 ) 184303 2019.5
Joint Work
Authorship：Lead author Publisher：AMER PHYSICAL SOC
We theoretically study the high-harmonic generation (HHG) in one-dimensional spin systems. While in electronic systems the driving by ac electric fields produces radiation from the dynamics of excited charges, we consider here the situation where spin systems excited by a magnetic field pulse generate radiation via a time-dependent magnetization. Specifically, we study the magnetic dipole radiation in two types of ferromagnetic spin chain models, the Ising model with static longitudinal field and the XXZ model, and reveal the structure of the spin HHG and its relation to spin excitations. For weak laser amplitude, a peak structure appears which can be explained by time-dependent perturbation theory. With increasing amplitude, plateaus with well-defined cutoff energies emerge. In the Ising model with longitudinal field, the thresholds of the multiple plateaus in the radiation spectra can be explained by the annihilation of multiple magnons. In the XXZ model, which retains the Z(2) symmetry, the laser magnetic field can induce a phase transition of the ground state when it exceeds a critical value, which results in a drastic change of the spin excitation character. As a consequence, the first cutoff energy in the HHG spectrum changes from a single-magnon to a two-magnon energy at this transition. Our results demonstrate the possibility of generating high-harmonic radiation from magnetically ordered materials and the usefulness of high-harmonic signals for extracting information on the spin excitation spectrum.
DOI： 10.1103/PhysRevB.99.184303
Other Link： https://link.aps.org/article/10.1103/PhysRevB.99.184303
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Topological transition between competing orders in quantum spin chains Reviewed
Shintaro Takayoshi, Shunsuke C. Furuya, Thierry Giamarchi
Physical Review B 98 ( 18 ) 2018.11
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Topological quantum phase transition in the Ising-like antiferromagnetic spin chain BaCo2V2O8 Reviewed International coauthorship
Quentin Faure, Shintaro Takayoshi, Sylvain Petit, Virginie Simonet, Stephane Raymond, Louis-Pierre Regnault, Martin Boehm, Jonathan S. White, Martin Mansson, Christian Rueegg, Pascal Lejay, Benjamin Canals, Thomas Lorenz, Shunsuke C. Furuya, Thierry Giamarchi, Beatrice Grenier
Nature Physics 14 ( 7 ) 716 - 722 2018.5
Joint Work
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Field theory of symmetry-protected valence bond solid states in (2+1) dimensions Reviewed International coauthorship
Shintaro Takayoshi, Pierre Pujol, Akihiro Tanaka
Physical Review B 94 ( 23 ) 235159 2016.12
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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.