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In a honeycomb-lattice spin-orbit assisted Mott insulator {\alpha}-RuCl3, an ultrafast magnetization is induced by circularly polarized excitation below the Mott gap. Photo-carriers play an important role, which are generated by turning down the synergy of the on-site Coulomb interaction and the spin-orbit interaction realizing the insulator state. An ultrafast 6- fs measurement of photo-carrier dynamics and a quantum mechanical analysis clarify the mechanism, according to which the magnetization emerges from a coherent charge motion between different t2g orbitals (dyz-dxz-dxy) of Ru3+ ions. This ultrafast magnetization is weakened in the antiferromagnetic (AF) phase, which is opposite to the general tendency that the inverse Faraday effect is larger in AF compounds than in paramagnetic ones. This temperature dependence indicates that the interorbital charge motion is affected by pseudo-spin rotational symmetry breaking in the AF phase.

Charge acceleration during an intense light field application to solids attracts much attention as elementary processes in high-harmonic generation and photoelectron emission [1-7]. For manipulating such attosecond dynamics of charge, carrier-envelope-phase (CEP:relative phase between carrier oscillation of light field and its envelope function) control has been employed in insulators, nanometal and graphene [8-10]. In superconducting materials, collective control of charge motion is expected because of its strongly coherent nature of quasi-particles. Here, in a layered organic superconductor, second harmonic generation (SHG) is observed by using a single-cycle 6 femtosecond near infrared pulse, which is in contrast to the common belief that even harmonics are forbidden in the centrosymmetric system. The SHG shows a CEP sensitive nature and an enhancement near the superconducting temperature. The result and its quantum many-body analysis indicate that a polarized current is induced by non-dissipative acceleration of charge, which is amplified by superconducting fluctuations. This will lead to petahertz functions of superconductors and of strongly correlated systems., Comment: Anotherversion hase been accepted in Nature communications

We present the result of a multi-longitude campaign on the photometric study of the dwarf nova ASASSN-18fk during its superoutburst in 2018. It was observed with 18 telescopes at 15 sites during ~70 nights within a three-month interval. Observations covered the main outburst, six rebrightenings and 50-d decline to a near-quiescent state. We identify ASASSN-18fk as WZ Sge-type dwarf nova with multiple rebrightenings and show the evolution of the 0.06-d superhump period over all stages of the superoutburst. A strong 22-min brightness modulation that superimposed on superhumps is found during rebrightenings and decline. Some evidence of this modulation in a form of a sideband signal is detected during the very onset of the outburst. We interpret the 22-min modulation as a spin period of the white dwarf and suggest that ASASSN-18fk is a good candidate for a superhumping intermediate polar., Comment: 12 pages, 8 figures

Intense light-field application to solids produces enormous/ultrafast non-linear phenomena such as high-harmonic generations 1, 2 and attosecond charge dynamics 3, 4. They are distinct from conventional photonics. However, main targets have been limited to insulators and semiconductors, although theoretical approaches have been made also for correlated metals and superconductors 5. Here, in a layered organic superconductor, a non-linear charge oscillation driven by a nearly single-cycle strong electric field of >10 megavolts /cm is observed as a stimulated emission. The charge oscillation is different from a linear response and ascribed to a polar charge oscillation with a period of 6 fs. This non-linear polar charge oscillation is enhanced by critical fluctuations near a superconducting transition temperature and a critical end point of first order Mott transitions. Its observation on an ultrafast timescale of 10 fs clarifies that the Coulomb repulsion plays an essential role in superconductivity of organic superconductors., Comment: 5 Figs. for main text, 3 Figs for supplementary information

Polarization selectivity of light-field-induced charge localization was investigated in an organic metal alpha-(BEDT-TTF)2I3 with a triangular lattice. Dependences of transient reflectivity spectra on polarizations of the 7-fs pump and probe lights indicate that a short-range charge order (CO) is efficiently induced from the metallic phase for the pump polarization perpendicular to the 1010-type CO axis. Numerical solution of a time-dependent Schrodinger equation clarified that the 1010-CO is induced by field-induced re-distribution of charges cooperating with competing inter-site Coulomb repulsions in the triangular lattice., Comment: accepted Phys. Rev. B (rapid commun.)

The strong light-field effect of (TMTTF)2AsF6 was investigated utilizing 1.5-cycle, 7-fs infrared pulses. The ultarfast (20 fs) and large (40%) response of the plasma-like reflectivity edge (0.7 eV) was analyzed by the changes in omega_p=sqrt(ne2/(epsilon_0*epsilon(infty)*m)} (n: number of charges in the 1/4 filled-band, m: mass of charge, epsilon(infty): dielectric constants for high-frequency and vacuum, e: elementary charge). The 3% reduction in omega_p is attributed to the 6% increase in m. Furthermore, 20 fs oscillation of omega_p in the time domain indicates that the plasma-like edge is affected by the charge gap (0.2 eV) nature. Theoretical calculations suggest that the Coulomb repulsion plays an important role in the increase in m., Comment: Phys. Rev. B accepted (26, March, 2016)

We have observed the characteristic temperature dependence of the intermolecular phonon spectrum in the organic dimer Mott insulator kappa-(ET)2Cu2(CN)3 exhibiting a dielectric anomaly at 30 K. The anomalous spectral narrowing of the 55 cm-1 phonon peak at 30 K was analyzed in terms of motional narrowing within the framework of a stationary Gaussian process, i. e., the phonon frequency is modulated by the ultrafast charge fluctuation. The spectral narrowing occurs because the time constant of the correlation time tau_c and the amplitude of the frequency modulation delta satisfy the relation tau_c

The terahertz (THz) response in 10-100 cm^-1 was investigated in an organic dimer-Mott (DM) insulator kappa-(ET)_2Cu_2(CN)_3 that exhibits a relaxor-like dielectric anomaly. 30 cm^-1 band in the optical conductivity was attributable to collective excitation of the intra-dimer electric dipoles which are formed by an electron correlation. We succeeded in observing photoinduced enhancement of this 30 cm^-1 band, reflecting the growth of the electric dipole cluster in the DM phase. Such optical responses in kappa-(ET)_2Cu_2(CN)_3 reflect instability near the boundary between the DM-ferroelectric charge ordered phases., Comment: 15 pages, 4 figures, Accepted Phys. Rev. Lett. Jan. 16, 2013

We investigate the possibility of the identification of TeV physics models including WIMP dark matter at the International Linear Collider. Many TeV physics models contain a WIMP dark matter (chi^0) and charged new particle (chi^{pm}) which interacts with the WIMP dark matter via the vertex chi^{pm} chi^0 W^{mp}. Through Monte Carlo simulations, we study the process, e^+e^- to chi^+ chi^- to chi^0 chi^0 W^+ W^-, because the signal contains the fruitful information of the model. We show that, in particular, the distribution of the chi^{pm} production angle is the powerful probe in the TeV physics model search., Comment: 6 pages, 1 figure, Proceeding of LCWS/ILC2010

Identification of beyond-standard-models including WIMP dark matter is studied in four particle final state with a W boson pair and a WIMP pair at the International Linear Collider. Models with different spin structures give distinguishable production angle distributions. After the mass determination in each model, the production angle is reconstructed using the four momentum of W bosons with a back-to-back constraint. Three models of Inert Higgs, Supersymmetry and Little Higgs are considered. Discrimination power at 200 fb and 40 fb signal cross section with 500 fb-1 luminosity at sqrt(s) = 500 GeV is obtained., Comment: 8 pages, 4 figures, Proceedings of LCWS10, correct typos in metadata

This report presents the results of studies that investigate the physics reach at a Super $B$ factory, an asymmetric-energy $e^+e^-$ collider with a design luminosity of $8 \times 10^{35}$ cm$^{-2}$s$^{-1}$, which is around 50 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented.

Effect of growth orientation on charge- and orbital-ordering (CO-OO) phenomena has been studied for Pr0.5Ca0.5MnO3 epitaxial thin films fabricated on (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (LSAT) substrates by means of resistivity, synchrotron x-ray diffraction, and polarized optical microscopy measurements. CO-OO transition is observed around 220 K for a film grown on an LSAT (011) substrate ((011)-film), similarly to a bulk sample, while a film grown on a (001) plane of LSAT ((001)-film) shows much higher transition temperature around 300 K. The domain size of OO is approximately 3 times as large in the (011)-film as in the (001)-film. These results demonstrate that various properties of CO-OO phenomena can be controlled with the growth orientation via the epitaxial strain from the substrate., Comment: 4 pages, 4 figures

For the study of ferromagnetic materials which are compatible with group-IV semiconductor spintronics, we demonstrate control of the ferromagnetic properties of Heusler-alloys Fe_3-xMn_xSi epitaxially grown on Ge(111) by tuning the Mn composition x. Interestingly, we obtain L2_1-ordered structures even for nonstoichiometric atomic compositions. The Curie temperature of the epilayers with x ~ 0.6 exceeds 300 K. Theoretical calculations indicate that the electronic structures of the nonstoichiometric Fe_3-xMn_xSi alloys become half-metallic for 0.75 < x < 1.5. We discuss the possibility of room-temperature ferromagnetic Fe_3-xMn_xSi/Ge epilayers with high spin polarization., Comment: 5 pages, 4 figures

Spin polarization of the tunnel conductivity has been studied for Fe/GaAs junctions with Schottky barriers. It is shown that band matching of resonant interface states within the Schottky barrier defines the sign of spin polarization of electrons transported through the barrier. The results account very well for experimental results including the tunneling of photo-excited electrons, and suggest that the spin polarization (from -100% to 100%) is dependent on the Schottky barrier height. They also suggest that the sign of the spin polarization can be controlled with a bias voltage., Comment: 5 pages, 4 figures

Effects of impurity scattering on tunneling conductance in dirty normal-metal/insulator/superconductor junctions are studied based on the Kubo formula and the recursive Green function method. The zero-bias conductance peak (ZBCP) is a consequence of the unconventional pairing symmetry in superconductors. The impurity scattering in normal metals suppresses the amplitude of the ZBCP. The degree of the suppression agrees well with results of the quasiclassical Green function theory. When superconductors have $d$+is-wave pairing symmetry, the time-reversal symmetry is broken in superconductors and the ZBCP splits into two peaks. The random impurity scattering reduces the height of the two splitting peaks. The position of the splitting peaks, however, almost remains unchanged even in the presence of the strong impurity scattering. Thus the two splitting peaks never merge into a single ZBCP., Comment: 12 pages, 5 figures, using jpsj2.cls and overcite.sty

We make a theoretical study of the quantum oscillations of the tunneling magnetoresistance (TMR) as a function of the spacer layer thickness. Such oscillations were recently observed in tunneling junctions with a nonmagnetic metallic spacer at the barrier-electrode interface. It is shown that momentum selection due to the insulating barrier and conduction via quantum well states in the spacer, mediated by diffusive scattering caused by disorder, are essential features required to explain the observed period of oscillation in the TMR ratio and its asymptotic value for thick nonmagnetic spacer., Comment: 4 pages, 5 figures, two column, REVTex4 style

We study the relation between tunnel magnetoresistance (TMR) and interfacial electronic states modified by magnetic impurities introduced at the interface of the ferromagnetic tunnel junctions, by making use of the periodic Anderson model and the linear response theory. It is indicated that the TMR ratio is strongly reduced depending on the position of the $d$-levels of impurities, based on reduction in the spin-dependent $s$-electron tunneling in the majority spin state. The results are compared with experimental results for Cr-dusted ferromagnetic tunnel junctions, and also with results for metallic multilayers for which similar reduction in giant magnetoresistance has been reported., Comment: 5 pages, 4 figures, 2 column revtex4 format, ICMFS 2002 (Kyoto)

The magnetic field responses of the zero-bias conductance peak (ZBCP) in tunneling spectra of high $T_{C}$ cuprate junctions are studied theoretically. Our calculation is based on the lattice Green's function method and takes the realistic electronic structure of the high $T_{C}$ cuprate into account. In marked contrast to previous works, it is shown that the critical magnetic field strength $H_{C}$ exists for the splittings of the ZBCP's to be discernible. $H_{C}$ is almost proportional to the product of the magnitude of pair potential, transmissivity of the junction, and the inverse of the Fermi velocity parallel to the interface (1/$v_{Fy}$). The calculated $H_{C}$'s for the hole-doped superconductors are higher than those for electron-doped ones because of relatively large magnitude of pair potential and the small magnitude of $v_{Fy}$ originating from peculiar shape of the Fermi surface., Comment: 5 pages, 6 figures, using jpsj2.cls

We discovered a new deeply eclipsing SU UMa-type dwarf nova, IY UMa, which experienced a superoutburst in 2000 January. Our monitoring revealed two distinct outbursts, which suggest a superoutburst interval of ~800 d, or its half, and an outburst amplitude of 5.4 mag. From time-series photometry during the superoutburst, we determined a superhump and orbital period of 0.07588 d and 0.0739132 d, respectively., Comment: 5 pages, 3 figures, accepted by PASJ letter