arXiv subjects

Makoto Yoshida

Publications and source records attributed to Makoto Yoshida.

At least 19 recordsLinked to original sources

arXiv2022

R&D works for Superconducting Magnet for Future Accelerator Applications in Japan

KEK cryogenics science center is developing superconducting magnet technology for future accelerator science. Three major technological categories are focused; 1) high precision 3D magnetic field technology based on the g-2/EDM magnet developments, 2) rad-hard superconducting magnet technology based on the COMET magnet developments, and 3) high magnetic field superconducting magnet technology for future colliders based on the LHC MQXA and HL-LHC D1 magnet developments. Extensive studies including Nb3Sn conductor and magnet developments for high field magnets and HTS for rad-hard superconducting magnets are ongoing with various collaboration programs such as the US-Japan research collaboration.

physics.acc-ph↗

arXiv2022

Superconducting detector magnets for high energy physics

Various superconducting detector solenoids for particle physics have been developed in the world. The key technology is the aluminum-stabilized superconducting conductor for almost all the detector magnets in particle physics experiments. With the progress of the conductor, the coil fabrication technology has progressed as well, such as the inner coil winding technique, indirect cooling, transparent vacuum vessel, quench protection scheme using pure aluminum strips and so on. The detector solenoids design study is in progress for future big projects in Japan and Europe, that is, ILC, FCC and CLIC, based on the technologies established over many years. The combination of good mechanical properties and keeping a high RRR is a key point for the development of Al-stabilized conductor. The present concern for the detector solenoid development is to have been gradually losing the key technologies and experiences, because large-scale detector magnets with Al-stabilized conductor has not been fabricated after the success of CMS and ATLAS-CS in LHC. Complementary efforts are needed to resume an equivalent level of expertise, to extend the effort on research and to develop these technologies and apply them to future detector magnet projects. Especially, further effort is necessary for the industrial technology of Al-stabilized superconductor production. The worldwide collaboration with relevant institutes and industries will be critically important to re-realize and validate the required performances. Some detector solenoids for mid-scale experiment wound with conventional copper-stabilized Nb-Ti conductor require precise control of magnetic field distribution. The development efforts are on-going in terms of the magnetic field design technology with high precision simulation, coil fabrication technology and control method of magnetic field distribution.

physics.ins-det↗

arXiv2021

Magnetic field-driven transition between valence bond solid and antiferromagnetic order in distorted triangular lattice

A molecular Mott insulator $κ$-(ET)$_2$B(CN)$_4$ [ET = bis(ethylenedithio)tetrathiafulvalene] with a distorted triangular lattice exhibits a quantum disordered state with gapped spin excitation in the ground state. $^{13}$C nuclear magnetic resonance, magnetization, and magnetic torque measurements reveal that magnetic field suppresses valence bond order and induces long-range magnetic order above a critical field $\sim 8$ T. The nuclear spin-lattice relaxation rate $1/T_1$ shows persistent evolution of antiferromagnetic correlation above the transition temperature, highlighting a quantum spin liquid state with fractional excitations. The field-induced transition as observed in the spin-Peierls phase suggests that the valence bond order transition is driven through renormalized one-dimensionality and spin-lattice coupling.

cond-mat.str-el↗

arXiv2020

Chaotic diffusion for particles moving in a time dependent potential well

The chaotic diffusion for particles moving in a time dependent potential well is described by using two different procedures: (i) via direct evolution of the mapping describing the dynamics and ; (ii) by the solution of the diffusion equation. The dynamic of the diffusing particles is made by the use of a two dimensional, nonlinear area preserving map for the variables energy and time. The phase space of the system is mixed containing both chaos, periodic regions and invariant spanning curves limiting the diffusion of the chaotic particles. The chaotic evolution for an ensemble of particles is treated as random particles motion and hence described by the diffusion equation. The boundary conditions impose that the particles can not cross the invariant spanning curves, serving as upper boundary for the diffusion, nor the lowest energy domain that is the energy the particles escape from the time moving potential well. The diffusion coefficient is determined via the equation of the mapping while the analytical solution of the diffusion equation gives the probability to find a given particle with a certain energy at a specific time. The momenta of the probability describe qualitatively the behavior of the average energy obtained by numerical simulation, which is investigated either as a function of the time as well as some of the control parameters of the problem.

cond-mat.stat-mech↗

arXiv2020

Application of the diffusion equation to prove scaling invariance on the transition from limited to unlimited diffusion

The scaling invariance for chaotic orbits near a transition from unlimited to limited diffusion in a dissipative standard mapping is explained via the analytical solution of the diffusion equation. It gives the probability of observing a particle with a specific action at a given time. We show the diffusion coefficient varies slowly with the time and is responsible to suppress the unlimited diffusion. The momenta of the probability are determined and the behavior of the average squared action is obtained. The limits of small and large time recover the results known in the literature from the phenomenological approach and, as a bonus, a scaling for intermediate time is obtained as dependent on the initial action. The formalism presented is robust enough and can be applied in a variety of other systems including time dependent billiards near a transition from limited to unlimited Fermi acceleration as we show at the end of the letter and in many other systems under the presence of dissipation as well as near a transition from integrability to non integrability.

nlin.CD↗

arXiv2019

Unusual change in the Dirac-cone energy band upon two-step magnetic transition in CeBi

We have performed angle-resolved photoemission spectroscopy (ARPES) on CeBi which undergoes a two-step antiferromagnetic (AF) transition with temperature. Soft-x-ray ARPES has revealed the inverted band structure at the X point of bulk Brillouin zone for CeBi (and also for LaBi) as opposed to LaSb with non-inverted band structure. Low-energy ARPES on CeBi has revealed the Dirac-cone band at the Gamma point in the paramagnetic phase associated with the bulk band inversion. On the other hand, a double Dirac-cone band appears on entering the first AF phase at T = 25 K, whereas a single Dirac-cone band recovers below the second AF transition at T = 14 K. The present result suggests an intricate interplay between antiferromagnetism and topological surface states in CeBi.

cond-mat.mes-hall↗

arXiv2019

Field-Induced Switching of Ferro-Quadrupole Order Parameter in PrTi2Al20

We report magnetic-field-induced first-order phase transitions in the ferro-quadrupole (FQ) ordered state of PrTi2Al20, in which non-Kramers Pr3+ ions with two 4f electrons have a non-magnetic Gamma3 doublet ground state in the cubic Td crystalline electric field. For magnetic fields along [111], 27Al-NMR and magnetization experiments reveal Qz \propto 3z2-r2 type FQ order below 2 K independent of field strength. Magnetic fields along [001] or [110], however, induce discontinuous switching of order parameters within the two dimensional space spanned by Qz and Qx \propto x2-y2 at small field values less than a few tesla. A symmetry-based theoretical analysis shows that the transitions can be caused by competition between the magnetic Zeeman interaction and anisotropy in the quadrupole-quadrupole interactions, if the latter dominates over the former in low fields and vice versa in high fields. Furthermore, striking violation of proportionality between NMR Knight shift and magnetic susceptibility is observed in the symmetry-broken FQ phases, indicating significant influence of FQ order on the hybridization between conduction and f electrons, which in turn mediates the RKKY-type quadrupole interaction causing the FQ order. This feedback effect may be a specific feature of quadrupole orders not commonly observed in magnetic phase transitions and play a key role for inducing the discontinuous transitions.

cond-mat.str-el↗

arXiv2019

Quantum critical behaviour and Lifshitz transition in intermediate valence $α$-YbAlB$_4$

Intermetallic compounds containing $f$-electron elements have been prototypical materials for investigating strong electron correlations and quantum criticality (QC). Their heavy fermion ground state evoked by the magnetic $f$-electrons is susceptible to the onset of quantum phases, such as magnetism or superconductivity, due to the enhanced effective mass ($m^{*}$) and a corresponding decrease of the Fermi temperature. However, the presence of $f$-electron valence fluctuations to a non-magnetic state is regarded an anathema to QC, as it usually generates a paramagnetic Fermi-liquid state with quasiparticles of moderate $m^{*}$. Such systems are typically isotropic, with a characteristic energy scale $T_0$ of the order of hundreds of kelvins that require large magnetic fields or pressures to promote a valence or magnetic instability. Here we show that the intermediate valence compound $α$-YbAlB$_4$ surprisingly exhibits both quantum critical behaviour and a Lifshitz transition under low magnetic field, which is attributed to the anisotropy of the hybridization between the conduction and localized $f$-electrons. These findings suggest a new route to bypass the large valence energy scale in developing the QC.

cond-mat.str-el↗

arXiv2017

Collinear Spin-density-wave Order and Anisotropic Spin Fluctuations in the Frustrated $J_1$--$J_2$ Chain Magnet NaCuMoO$_4$(OH)

The phase diagram of the quasi-one-dimensional magnet NaCuMoO$_4$(OH) is established through single-crystal NMR and heat-capacity measurements. The $^{23}$Na and $^1$H NMR experiments indicate a spiral and a collinear spin-density-wave (SDW) order below and above $B_c$ = 1.5-1.8 T, respectively. Moreover, in the paramagnetic state above the SDW transition temperature, the nuclear spin-lattice relaxation rate $1/T_1$ indicates anisotropic spin fluctuations that have gapped excitations in the transverse spectrum but gapless ones in the longitudinal spectrum. These static and dynamic properties are well described by a theoretical model assuming quasi-one-dimensional chains with competing ferromagnetic nearest-neighbor interactions $J_1$ and antiferromagnetic next-nearest-neighbor interactions $J_2$ ($J_1$-$J_2$ chains). Because of the excellent crystal quality and good one dimensionality, NaCuMoO$_4$(OH) is a promising compound to elucidate the unique physics of the frustrated $J_1$-$J_2$ chain.

cond-mat.str-el↗

arXiv2017

Dynamics of Bound Magnon Pairs in the Quasi-One-Dimensional Frustrated Magnet LiCuVO_4

We report on the dynamics of the spin-1/2 quasi-one-dimensional frustrated magnet LiCuVO$\mathrm{_4}$ measured by nuclear spin relaxation in high magnetic fields 10--34 T, in which the ground state has spin-density-wave order. The spin fluctuations in the paramagnetic phase exhibit striking anisotropy with respect to the magnetic field. The transverse excitation spectrum probed by $^{51}$V nuclei has an excitation gap, which increases with field. On the other hand, the gapless longitudinal fluctuations sensed by $^7$Li nuclei grow with lowering temperature, but tend to be suppressed with increasing field. Such anisotropic spin dynamics and its field dependence agree with the theoretical predictions and are ascribed to the formation of bound magnon pairs, a remarkable consequence of the frustration between ferromagnetic nearest neighbor and antiferromagnetic next-nearest-neighbor interactions.

cond-mat.str-el↗

arXiv2017

Shannon entropy analysis of the stretched exponential process : application to various shear induced multilamellar vesicles system

The stretched exponential function, $\exp[-(t/τ_{K})^β]$, describes various relaxation processes while it has been suggested that the power exponent, $β$ is derived from the non-uniformity of the process. In this paper, we attempted to estimate this non-uniformity by introducing Shannon entropy. Shannon entropy evaluates the average information contents of the distribution function, which reflects statistical homogeneity. We investigated the relaxation process of shear induced multilamellar system, which is described with the stretched exponential function. Three types of shear (constant, square, sine) at different frequencies are attempted in order to determine their effects on the relaxation process. We found that the Shannon entropy to which the first moment was introduced is maximized at $β~=~1$ : a single exponential. The Shannon entropy of sine shear experiments exhibited the frequency dependence. Thus it is interpreted that the increase of the intensity of shearing and the thermodynamic entropy are reflected on the Shannon entropy. We discussed the meaning of the maximum Shannon entropy in terms of various points of view, it was found that it corresponds to the diffusion process free from the restriction such as geometrical constraints. The constraints and the non-uniformity of process were successfully estimated by Shannon entropy. This study gives a new insight of entropy in general.

cond-mat.soft↗

arXiv2017

$J_1-J_2$ Square-Lattice Heisenberg Antiferromagnets with 4$d^1$ spins: AMoOPO$_4$Cl (A = K, Rb)

Magnetic properties of AMoOPO$_4$Cl (A = K, Rb) with Mo$^{5+}$ ions in the 4$d^1$ electronic configuration are investigated by magnetization, heat capacity and NMR measurements on single crystals, combined with powder neutron diffraction experiments. The magnetization measurements reveal that they are good model compounds for the spin-1/2 $J_1-J_2$ square lattice magnet with the first and second nearest-neighbor interactions. Magnetic transitions are observed at around 6 and 8 K in the K and Rb compounds, respectively. In contrast to the normal Néel-type antiferromagnetic order, the NMR and neutron diffraction experiments find a columnar antiferromagnetic order for each compound, which is stabilized by a dominant antiferromagnetic $J_2$. Both compounds realize the unusual case of two interpenetrating $J_2$ square lattices weakly coupled to each other by $J_1$.

cond-mat.str-el↗

arXiv2016

NMR Observation of Ferro-quadrupole Order in PrTi2Al20

We report the results of 27Al-NMR measurements on a single crystal of PrTi2Al20. This compound shows a phase transition near 2 K associated with the quadrupole degree of freedom of Pr ions, for which the ground state of the crystalline electric field is a nonmagnetic doublet. When a magnetic field is applied along the <111> direction, the NMR lines split upon entering the low-temperature phase, indicating the breaking of the three fold rotation symmetry due to the field-induced magnetic dipole perpendicular to the field. This provides microscopic evidence for a ferro order of the O20 quadrupole. Although a first-order transition is expected theoretically, the line splitting evolves continuously within the experimental resolution.

cond-mat.str-el↗

arXiv2016

Pressure-Tuned Exchange Coupling of a Quantum Spin Liquid in the Molecular Triangular Lattice $κ$-(ET)$_2$Ag$_2$(CN)$_3$

The effects of pressure on a quantum spin liquid are investigated in an organic Mott insulator $κ$-(ET)$_2$Ag$_2$(CN)$_3$ with a spin-1/2 triangular lattice. The application of negative chemical pressure to $κ$-(ET)$_2$Cu$_2$(CN)$_3$, which is a well-known sister Mott insulator, allows for extensive tuning of antiferromagnetic exchange coupling, with $J/k_{\rm B} = 175 - 310$ K, under hydrostatic pressure. Based on $^{13}$C nuclear magnetic resonance measurements under pressure, we uncover universal scaling in the static and dynamic spin susceptibilities down to low temperatures $\sim 0.1k_{\rm B}T/J$. The persistent fluctuations and residual specific heat coefficient are consistent with the presence of gapless low-lying excitations. Our results thus demonstrate fundamental finite-temperature properties of quantum spin liquid in a wide parameter range.

cond-mat.str-el↗

arXiv2014

Novel Phase Transitions in the Breathing Pyrochlore Lattice: 7Li-NMR on LiInCr4O8 and LiGaCr4O8

We report 7Li-NMR studies on LiInCr4O8 and LiGaCr4O8, in which Cr3+ ions with spin 3/2 form a breathing pyrochlore lattice, a network of tetrahedra with alternating sizes. In LiInCr4O8 with large alternation, the nuclear relaxation rate 1/T1 shows an activated temperature (T) dependence down to 18 K, indicating a singlet ground state with a spin gap. This behavior, however, is disrupted by an antiferromagnetic (AF) transition at 13 K, which is preceded by another, most likely structural, transition at 16 K. In contrast, LiGaCr4O8 with small alternation shows no spin gap but exhibits a first-order AF transition over a distributed T-range 13-20 K. Nevertheless, 1/T1 of the paramagnetic phase diverges toward 13 K, indicating proximity to a second-order transition. The results indicate that LiGaCr4O8 is located in the vicinity of a tricritical point in the phase diagram.

cond-mat.str-el↗

arXiv2013

Anisotropic spin fluctuations in the quasi one-dimensional frustrated magnet LiCuVO_4

We report results of NMR experiments on a single crystal of the quasi one-dimensional frustrated magnet LiCuVO_4. The NMR spectra of ^7Li and ^{51}V nuclei indicate a helical spin order in a magnetic field of 4 T with the helical spin plane perpendicular to the field and a spin-density-wave (SDW) order at 10 T with modulation in the magnitude of the moments aligned along the field, in agreement with earlier reports. The nuclear spin-lattice relaxation rate 1/T_1 at ^{51}V nuclei, which is selectively coupled to the transverse spin fluctuations perpendicular to the field, shows a pronounced peak near the helical ordering temperature in the field of 4 T applied along the a-axis. In the field of 10 T, however, such a peak is absent. Instead 1/T_1 at ^7Li nuclei probing longitudinal spin fluctuations shows divergent behavior towards the SDW ordering temperature. These results are qualitatively consistent with the theoretical description that the SDW correlation is due to bound magnon pairs, which produce an energy gap in the transverse spin excitation spectrum.

cond-mat.str-el↗

arXiv2012

Magnetic Order in the Spin-1/2 Kagome Antiferromagnet Vesignieite

We report results of magnetic susceptibility and 51V- and 63,65Cu-NMR measurements on a high-quality powder sample of vesignieite BaCu3V2O8(OH)2, a candidate for the spin-1/2 kagome antiferromagnet. We observed a twostep magnetic transition: the appearance of spatially inhomogeneous static moments below 13 K and a long-range order below 9 K. The NMR data indicate a Q = 0 magnetic structure at 1.4 K with the in-plane spin components of three sublattices oriented at nearly 120 degrees to each other and the magnitude of the ordered moments of at least 0.6 muB

cond-mat.str-el↗

arXiv2012

High-field Phase Diagram and Spin Structure of Volborthite Cu3V2O7(OH)2/2H2O

We report results of 51V NMR experiments on a high-quality powder sample of volborthite Cu3V2O7(OH)2/2H2O, a spin-1/2 Heisenberg antiferromagnet on a distorted kagome lattice. Following the previous experiments in magnetic fields $B$ below 12 T, the NMR measurements have been extended to higher fields up to 31 T. In addition to the two already known ordered phases (phases I and II), we found a new high-field phase (phase III) above 25 T, at which a second magnetization step has been observed. The transition from the paramagnetic phase to the antiferromagnetic phase III occurs at 26 K, which is much higher than the transition temperatures from the paramagnetic to the lower field phases I (B < 4.5 T) and II (4.5 < B < 25 T). At low temperatures, two types of the V sites are observed with different relaxation rates and line shapes in phase III as well as in phase II. Our results indicate that both phases II and III exhibit a heterogeneous spin state consisting of two spatially alternating Cu spin systems, one of which exhibits anomalous spin fluctuations contrasting with the other showing a conventional static order. The magnetization of the latter system exhibits a sudden increase upon entering into phase III, resulting in the second magnetization step at 26 T.We discuss the possible spin structure in phase III.

cond-mat.str-el↗