arXiv subjects

Tomohiro Yoshida

Publications and source records attributed to Tomohiro Yoshida.

17 recordsLinked to original sources

arXiv2025

SO emission in the dynamically perturbed protoplanetary disks around CQ Tau and MWC 758

We report the serendipitous detection of the SO $J_N=6_5-5_4$ (219.949 GHz) rotational transition in archival Atacama Large Millimeter/submillimeter Array (ALMA) observations of the spiral hosting protoplanetary disks around CQ Tau (with $\approx4.9σ$ significance) and MWC 758 (with $\approx3.4σ$ significance). In the former, the SO emission comes in the shape of a ring, arises from the edge of the continuum cavity, and is qualitatively consistent, at the currently available spectral resolution, with being in Keplerian rotation. In the latter, instead, while arising primarily from inside the continuum cavity, the SO emission also extends to the continuum ring(s), and its morphology and kinematics are less clear. We put these sources in the context of the other protoplanetary disks where SO detections have been previously reported in the literature and discuss the possible origins of SO in terms of (thermal) desorption or formation in the gas phase. We argue that these processes might be fostered by dynamical perturbations caused by unseen embedded massive companions, shadows, or late-time infall, thus suggesting a possible link between perturbed dynamics and SO emission in (these) protoplanetary disks. If confirmed, our interpretation would imply that chemical evolution timescales could be significantly shorter in these systems than is commonly assumed, indicating that dynamical perturbations might influence the composition of newborn (proto-)planets by altering the volatile makeup of their formation environment.

astro-ph.EP↗

arXiv2025

Dust characterization of protoplanetary disks: a guide to multi-wavelength analyses and accurate dust mass measurements

Multi-wavelength dust continuum observations of protoplanetary disks are essential for accurately measuring two key ingredients of planets formation theories: the dust mass and grain size. Unfortunately, they are also extremely time-expensive. We aim to investigate the most economic way of performing this analysis. We benchmark the dust characterization analysis on multi-wavelength observations of two disk models. We test three different combinations of bands (in the 0.45 mm $\to$ 7.46 mm range) to see how optically thick and thin observations aid the reconstruction of the dust properties for different morphologies and in three different dust mass regimes. We also test different spatial resolutions. Dust properties are robustly measured in a multi-band analysis if optically thin observations are included. For typical disks, this requires wavelengths longer than 3 mm. High-resolution (< 0.03"-0.05") is fundamental to resolve the changes in dust content of substructures. However, lower-resolution results still provide an accurate measurement of the total dust mass and of the level of grain growth of rings. Additionally, we propose a new approach that successfully combines lower and higher resolution observations in the multi-wavelength analysis without losing spatial information. We also test individually enhancing the resolution of each radial intensity profile with Frank but we note the presence of artifacts. Finally, we discuss on the total dust mass that we derive from the SED analyses and compare it with the traditional method of deriving dust masses from millimeter fluxes. Accurate dust mass measurements from the SED analysis can be derived by including optically thin tracers. On the other hand, single-wavelength flux-based masses are always underestimated by even more than one order of magnitude.

astro-ph.EP↗

arXiv2022

Infrared-Shielding of Plasmonic Random Metasurface Constructed by Cesium-Doped Tungsten Bronze

The heat-shielding properties of random metasurface, composed of spherical or spheroidal nanoparticles with random displacements and/or random deformation, were theoretically investigated using the finite difference time domain method. The effective coverage was defined using the total area of nanoparticles in the metasurface, and the robustness of the near-infrared light reflection against randomness was investigated. When the effective coverage was high, the near-infrared light reflection was reduced by at least 20% in both nanoparticle arrangement and shape randomness compared to the hexagonal close-packed perfect metasurface. In contrast, when effective coverage was low, the randomness of the nanoparticle arrangement had almost no effect on the near-infrared light reflection. Furthermore, the near-infrared light reflection performance was improved by the randomness of the nanoparticle shape.

physics.optics↗

arXiv2020

Multi-epoch SMA observations of the L1448C(N) protostellar SiO jet

L1448C(N) is a young protostar in Perseus, driving an outflow and an extremely high-velocity (EHV) molecular jet. We present multi-epoch observations of SiO $J = 8-7$, CO $J = 3-2$ lines, and 345 GHz dust continuum toward L1448C(N) in 2006, 2010, and 2017 with the Submillimeter Array. The knots traced by the SiO line show the averaged proper motion is $\sim0''.06~{\rm yr^{-1}}$ and $\sim0''.04~{\rm yr^{-1}}$ for the blue- and red-shifted jet, respectively. The corresponding transverse velocities are $\sim78~{\rm km s^{-1}}$ (blueshifted) and $\sim52~{\rm km s^{-1}}$ (redshifted). Together with the radial velocity, we found the inclination angle of the jets from the plane of the sky to be $\sim34$°$ $ for the blueshifted jet and $\sim46$°$ $ for the redfshifted jet. Given the new inclination angles, the mass-loss rate and mechanical power were refined to be $\sim1.8\times 10^{-6}~M_\odot$ and $\sim1.3~L_\odot$, respectively. In the epoch of 2017, a new knot is detected at the base of the redshifted jet. We found that the mass-loss rate of the new knot is three times higher than the averaged mass-loss rate of the redshifted jet. Besides, continuum flux has enhanced by $\sim37\%$ between 2010 and 2017. These imply that the variation of the mass-accretion rate by a factor of $\sim3$ has occurred in a short timescale of $\sim10-20$ yr. In addition, a knot in the downstream of the redshifted jet is found to be dimming over the three epochs.

astro-ph.SR↗

arXiv2020

Synergy of Binary Substitutions for Improving the Cycle Performance in LiNiO2 Revealed by Ab Initio Materials Informatics

We explore LiNiO2-based cathode materials with two-element substitutions by an ab initio simulation based materials informatics (AIMI) approach. According to our previous study, a higher cycle performance strongly correlates with less structural change during charge-discharge cycles; the latter can be used for evaluating the former. However, if we target the full substitution space, full simulations are infeasible even for all binary combinations. To circumvent such an exhaustive search, we rely on Bayesian optimization. Actually, by searching only 4% of all the combinations, our AIMI approach discovered two promising combinations, Cr-Mg and Cr-Re, whereas each atom itself never improved the performance. We conclude that the synergy never emerges from a common strategy restricted to combinations of "good" elements that individually improve the performance. In addition, we propose a guideline for the binary substitutions by elucidating the mechanism of crystal structure change.

cond-mat.mtrl-sci↗

arXiv2019

First-Principles Study of Structural Transition in LiNiO2 and High Throughput Screening for Long Life Battery

Herein, we performed ab initio screening to identify the best doping of LiNiO2 to achieve improved cycle performance in lithium ion batteries. The interlayer interaction that dominates the c-axis contraction and overall performance was captured well by density functional theory using van der Waals exchange-correlation functionals. The screening indicated that Nb-doping is promising for improving cycle performance. To extract qualitative reasonings, we performed data analysis in a materials informatics manner to obtain a reasonable regression to reproduce the obtained results. LASSO analysis implied that the charge density between the layers in the discharged state is the dominant factor influencing cycle performance.

cond-mat.mtrl-sci↗

arXiv2016

Generic Weyl phase in the vortex state of quasi-two-dimensional chiral superconductors

We study the collective behavior of Majorana modes in the vortex state of chiral $p$-wave superconductors. Away from the isolated vortex limit, the zero-energy Majorana states communicate with each other on a vortex lattice, and form a coherent band structure with non-trivial topological character. We revealed that the topological nature of Majorana bands changes sensitively via quantum phase transitions in the two-dimensional (2D) systems, as sweeping magnetic field or Fermi energy. Through the dimensional reduction, we showed the existence of generic superconducting Weyl phase in a low magnetic field region of quasi-2D-chiral superconductors.

cond-mat.supr-con↗

arXiv2016

Topological D+p-wave superconductivity in Rashba systems

We show two-dimensional "strong" topological superconductivity in d-wave superconductors (SCs). Although the topological invariant of the bulk wave function cannot be defined in d_{x^2-y^2}-wave and d_{xy}-wave SCs because of nodal excitations, the bulk energy spectrum of d-wave SCs on a substrate is fully gapped in a magnetic field. Then the superconducting state is specified by a nontrivial Chern number, and hence topologically nontrivial properties are robust against disorders and interactions. We discuss high-temperature topological superconductivity in cuprate SCs recently fabricated on a substrate. Furthermore, we show that the three-dimensional noncentrosymmetric d-wave SC is a Weyl SC hosting topologically protected Weyl nodes. Noncentrosymmetric heavy-fermion SCs, such as CeRhSi_3 and CeIrSi_3, are candidates for Weyl SCs.

cond-mat.supr-con↗

arXiv2016

Excitation spectra and wave functions of quasiparticle bound states in bilayer Rashba superconductors

We study the excitation spectra and the wave functions of quasiparticle bound states at a vortex and an edge in bilayer Rashba superconductors under a magnetic field. In particular, we focus on the quasiparticle states at the zero energy in the pair-density wave state in a topologically non-trivial phase. We numerically demonstrate that the quasiparticle wave functions with zero energy are localized at both the edge and the vortex core if the magnetic field exceed the critical value.

cond-mat.supr-con↗

arXiv2016

Robust zero-energy bound states around a pair-density-wave vortex core in locally noncentrosymmetric superconductors

We numerically investigate the electronic structures around a vortex core in a bilayer superconducting system, with s-wave pairing, Rashba spin-orbit coupling and Zeeman magnetic field, with use of the quasiclassical Green's function method. The Bardeen-Cooper-Schrieffer (BCS) phase and the so-called pair-density wave (PDW) phase appear in the temperature-magnetic-field phase diagram in a bulk uniform system [Phys. Rev. B 86, 134514 (2012)]. In the low magnetic field perpendicular to the layers, the zero-energy vortex bound states in the BCS phase are split by the Zeeman magnetic field. On the other hand, the PDW state appears in the high magnetic field, and sign of the order parameter is opposite between the layers. We find that the vortex core suddenly shrinks and the zero-energy bound states appear by increasing the magnetic field through the BCS-PDW transition. We discuss the origin of the change in vortex core structure between the BCS and PDW states by clarifying the relation between the vortex bound states and the bulk energy spectra. In the high magnetic field region, the PDW state and vortex bound states are protected by the spin-orbit coupling. These characteristic behaviors in the PDW state can be observed by scanning tunneling microscopy/spectroscopy.

cond-mat.supr-con↗

arXiv2015

Odd-parity superconductivity by competing spin-orbit coupling and orbital effect in artificial heterostructures

We show that odd-parity superconductivity occurs in multilayer Rashba systems without requiring spin-triplet Cooper pairs. A pairing interaction in the spin-singlet channel stabilizes the odd-parity pair-density-wave (PDW) state in the magnetic field parallel to the two-dimensional conducting plane. It is shown that the layer-dependent Rashba spin-orbit coupling and the orbital effect play essential roles for the PDW state in binary and tricolor heterostructures. We demonstrate that the odd-parity PDW state is a symmetry-protected topological superconducting state characterized by the one-dimensional winding number in the symmetry class BDI. The superconductivity in the artificial heavy-fermion superlattice CeCoIn_5/YbCoIn_5 and bilayer interface SrTiO_3/LaAlO_3 is discussed.

cond-mat.supr-con↗

arXiv2015

Topological Crystalline Superconductivity in Locally Non-centrosymmetric Multilayer Superconductors

Topological crystalline superconductivity in the locally non-centrosymmetric multilayer superconductors (SCs) is proposed. We study the odd-parity pair-density wave (PDW) state induced by the spin-singlet pairing interaction through the spin-orbit coupling. It is shown that the PDW state is a topological crystalline SC protected by a mirror symmetry, although it is topologically trivial according to the classification based on the standard topological periodic table. The topological property of the mirror subsectors is intuitively explained by adiabatically changing the BdG Hamiltonian. A subsector of the bilayer PDW state reduces to the two-dimensional non-centrosymmetric SC, while a subsector of trilayer PDW state is topologically equivalent to the spinless p-wave SC. Chiral Majorana edge modes in trilayers can be realized without Cooper pairs in the spin-triplet channel and chemical potential tuning.

cond-mat.supr-con↗

arXiv2014

Vortex Core Structure in Multilayered Rashba Superconductors

We numerically study the electronic structure of a single vortex in two dimensional superconducting bilayer systems within the range of the mean-field theory. The lack of local inversion symmetry in the system is taken into account through the layer dependent Rashba spin-orbit coupling. The spatial profiles of the pair potential and the local quasiparticle density of states are calculated in the clean spin-singlet superconductor on the basis of the quasiclassical theory. In particular, we discuss the characteristic core structure in the pair-density wave state, which is spatially modulated exotic superconducting phase in a high magnetic field.

cond-mat.supr-con↗

arXiv2013

Parity-Mixed Superconductivity in Locally Non-centrosymmetric System

We study the parity-mixed superconductivity in locally non-centrosymmetric systems. In multilayer systems an inhomogeneous Rashba spin-orbit coupling is induced by the local violation of inversion symmetry. Our previous study revealed that a pair-density wave (PDW) phase, with a sign-modulated order parameter, is stabilized in the spin-singlet multilayer superconductors owing to the spin-orbit coupling. In this letter, we show that the uniform spin-triplet superconductivity emerges through parity mixing in the PDW phase, taking into account a weak interaction in the spin-triplet channel, which was neglected in our previous study. The spin-triplet superconducting phase is nonunitary owing to field-induced parity mixing. The critical magnetic field is markedly increased by the emergence of spin-triplet superconductivity. We calculate the density of states and analyze the signature specific to this phase.

cond-mat.supr-con↗

arXiv2013

Complex-Stripe Phases Induced by Staggered Rashba Spin-Orbit Coupling

We study superconducting phases in a quasi-two-dimensional multilayer system without local inversion symmetry. Broken local inversion symmetry induces layer-dependent Rashba-type spin-orbit couplings. We find that a complex-stripe phase, which is the intermediate phase between the Fulde-Ferrell (FF) phase and Larkin-Ovchinnikov (LO) phase, is realized in the magnetic field applied parallel to the layers. A crossover from the FF phase to the LO phase appears by tuning temperature and magnetic field. We show the local density of states that characterizes the complex-stripe phase. As a possible realization of the complex-stripe phase, we discuss the artificial superlattices of CeCoIn_5.

cond-mat.supr-con↗

arXiv2012

Pair-density wave states through spin-orbit coupling in multilayer superconductors

Spin singlet superconductors with quasi-two dimensional multilayer structure are studied in high magnetic fields. Specifically we concentrate on bi- and tri-layer systems whose layers by symmetry are subject Rashba-type spin-orbit coupling. The combination of magnetic field and spin-orbit coupling leads to a first order phase transition between different states of layer-dependent superconducting order parameters upon rising the magnetic field. In this context we distinguish the low-field Bardeen-Cooper-Schrieffer state where all layers have order parameters of the same sign and the high-field pair-density wave state where the layer-dependent order parameters change the sign at the center layer. We also show that progressive paramagnetic limiting effects yield additional features in the H-T phase diagram. As possible realizations of such unusual superconducting phases we consider artificial superlattices of CeCoIn_5, as well as some multilayer high-T_c cuprates.

cond-mat.supr-con↗

arXiv2011

Rotating Fulde-Ferrell-Larkin-Ovchinnikov state in cold Fermi gases

We study an effect of rotation on the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state of two component Fermi superfluid gases in a toroidal trap. We investigate a stability of the FFLO states in the quasi-one-dimensional regime on the basis of the Bogoliubov-de Gennes equation. We find that two novel FFLO phases, i.e., the half quantum vortex state and the intermediate state of Fulde-Ferrell (FF) state and Larkin-Ovchinnikov (LO) state, are stabilized by the rotation. The phase diagram for the FF state, LO state, intermediate state, and half quantum vortex state is shown in both T-P plane and T-h plane. We demonstrate characteristic features of these states, such as the order parameter, flux quantization, and local polarization. Several related works are discussed, and the advantages of cold Fermi gases are indicated.

cond-mat.quant-gas↗