Numerical Study of Photo-Induced Dynamics in Double-Exchange Model

Photo-induced spin and charge dynamics in double-exchange model are numerically studied. The Lanczos method and the density-matrix renormalization-group method are applied to one-dimensional finite-size clusters. By photon irradiation in a charge ordered (CO) insulator associated with antiferromagnetic (AFM) correlation, both the CO and AFM correlations collapse rapidly, and appearances of new peaks inside of an insulating gap are observed in the optical spectra and the one-particle excitation spectra. Time evolutions of the spin correlation and the in-gap state are correlated with each other, and are governed by the transfer integral of conduction electrons. Results are interpreted by the charge kink/anti-kink picture and their effective motions which depend on the localized spin correlation. Pump-photon density dependence of spin and charge dynamics are also studied. Roles of spin degree of freedom are remarkable in a case of weak photon density. Implications of the numerical results for the pump-probe experiments in perovskite manganites are discussed.Comment: 16 pages, 16 figure

Photoinduced magnetic bound state in itinerant correlated electron system with spin-state degree of freedom

Photo-excited state in correlated electron system with spin-state degree of freedom is studied. We start from the two-orbital extended Hubbard model where energy difference between the two orbitals is introduced. Photo-excited metastable state is examined based on the effective model Hamiltonian derived by the two-orbital Hubbard model. Spin-state change is induced by photo-irradiation in the low-spin band insulator near the phase boundary. High-spin state is stabilized by creating a ferromagnetic bound state with photo-doped hole carriers. An optical absorption occurs between the bonding and antibonding orbitals inside of the bound state. Time-evolution for photo-excited states is simulated in the time-dependent mean-field scheme. Pair-annihilations of the photo-doped electron and hole generate the high-spin state in a low-spin band insulator. We propose that this process is directly observed by the time-resolved photoemission experiments.Comment: 15 pages, 16 figure

Absence of sign problem in two-dimensional N=(2,2) super Yang-Mills on lattice

We show that N=(2,2) SU(N) super Yang-Mills theory on lattice does not have sign problem in the continuum limit, that is, under the phase-quenched simulation phase of the determinant localizes to 1 and hence the phase-quench approximation becomes exact. Among several formulations, we study models by Cohen-Kaplan-Katz-Unsal (CKKU) and by Sugino. We confirm that the sign problem is absent in both models and that they converge to the identical continuum limit without fine tuning. We provide a simple explanation why previous works by other authors, which claim an existence of the sign problem, do not capture the continuum physics.Comment: 27 pages, 24 figures; v2: comments and references added; v3: figures on U(1) mass independence and references added, to appear in JHE

Orbital effects in manganites

In this paper I give a short review of some properties of the colossal magnetoresistance manganites, connected with the orbital degrees of freedom. Ions Mn{3+}, present in most of these compounds, have double orbital degeneracy and are strong Jahn-Teller ions, causing structural distortions and orbital ordering. Mechanisms leading to such ordering are shortly discussed, and the role of orbital degrees of freedom in different parts of the phase diagram of manganites is described. Special attention is paid to the properties of low-doped systems (doping 0.1 - 0.25), to overdoped systems (x > 0.5), and to the possibility of a novel type of orbital ordering in optimally doped ferromagnetic metallic manganites.Comment: 28 pages, 7 figures, to be published in J. Mod. Phys.

Source mechanism of the magnitude 7.2 Grand Banks earthquake of November 1929: Double couple or submarine landslide?

We have examined P, S, and surface waves derived from seismograms that we collected for the 1929 Grand Banks, Canada, earthquake. This event is noteworthy for the sediment slide and turbidity current that broke the trans-Atlantic cables and for its destructive tsunami. Both the surface-wave magnitude, M_S, and the body-wave magnitude, m_B, calculated from these seismograms are 7.2. Fault mechanisms previously suggested for this event include a NW-SE-striking strike-slip mechanism and an approximately E-W-striking thrust mechanism. In addition, because of the presence of an extensive area of slump and turbidity current, there exists the possibility that sediment slumping could also be a primary causative factor of this event. We tested these fault models and a horizontal single-force (oriented N5°W) model representing a sediment slide against our data. Among these models, only the single-force model is consistent with the P-, S-, and surface-wave data. Our data, however, do not preclude fault models which were not tested. From the spectral data of Love waves at a 50-sec period, we estimated the magnitude of the single force to be about 1.4 × 10^(20) dynes. From this value, we estimated the total volume of sedimentary slumping to be about 5.5 × 10^(11) m^3, which is approximately 5 times larger than a recent estimate of volume from in situ measurements. The difference in estimates of overall volume is likely due to a combination of the inherent difficulty in estimating accurately the displaced sediments from in situ measurements, and of inadequacy of the seismic model; or perhaps because not only the slump but also a tectonic earthquake could have been the cause of this event and contributed significantly to the waveforms studied

Formulation of Supersymmetry on a Lattice as a Representation of a Deformed Superalgebra

The lattice superalgebra of the link approach is shown to satisfy a Hopf algebraic supersymmetry where the difference operator is introduced as a momentum operator. The breakdown of the Leibniz rule for the lattice difference operator is accommodated as a coproduct operation of (quasi)triangular Hopf algebra and the associated field theory is consistently defined as a braided quantum field theory. Algebraic formulation of path integral is perturbatively defined and Ward-Takahashi identity can be derived on the lattice. The claimed inconsistency of the link approach leading to the ordering ambiguity for a product of fields is solved by introducing an almost trivial braiding structure corresponding to the triangular structure of the Hopf algebraic superalgebra. This could be seen as a generalization of spin and statistics relation on the lattice. From the consistency of this braiding structure of fields a grading nature for the momentum operator is required.Comment: 45 page

Dynamical coupling and separation of multiple degrees of freedom in a photoexcited double-exchange system

We present a theory of ultrafast photo-induced dynamics in a spin-charge coupled system, motivated by pump-probe experiments in perovskite manganites. A microscopic picture for multiple dynamics in spin and charge degrees is focused on. Real-time simulations are carried out by two complimentary methods. Our calculation demonstrates that electron motion governs a short-time scale where charge and spin dynamics are combined strongly, while, in a long-time scale controlled by spin relaxation, charge sector does not follow remarkable change in spin sector. Present results are in contrast to a conventional double-exchange picture in equilibrium states.Comment: 5 pages, 4 figures, to be published in Phys. Rev. Let

The chiral and flavour projection of Dirac-Kahler fermions in the geometric discretization

It is shown that an exact chiral symmetry can be described for Dirac-Kahler fermions using the two complexes of the geometric discretization. This principle is extended to describe exact flavour projection and it is shown that this necessitates the introduction of a new operator and two new structures of complex. To describe simultaneous chiral and flavour projection, eight complexes are needed in all and it is shown that projection leaves a single flavour of chiral field on each.Comment: v2: 17 pages, Latex. 5 images eps. Added references, reformatted and clarification of some point

Surface-wave constraints on the August 1, 1975, Oroville earthquake

Observations of Love and Rayleigh waves on WWSSN and Canadian Network seismograms have been used to place constraints upon the source parameters of the August 1, 1975, Oroville earthquake. The 20-sec surface-wave magnitude is 5.6. The surface-wave radiation pattern is consistent with the fault geometry determined by the body-wave study of Langston and Butler (1976). The seismic moment of this event was determined to be 1.9 × 10^(25) dyne-cm by both time-domain and long-period (T ≥ 50 sec) spectral amplitude determinations. This moment value is significantly greater than that determined by short-period studies. This difference, together with the low seismic efficiency of this earthquake, indicates that the character of the source is intrinsically different at long periods from those aspects which dominate the shorter-period spectrum

The July 27, 1976 Tangshan, China earthquake—A complex sequence of intraplate events

The Tangshan earthquake (M_s = 7.7), of July 27, 1976 and its principal aftershock (M_s = 7.2), which occurred 15 hr following the main event, resulted in the loss of life of over 650,000 persons in northeast China. This is the second greatest earthquake disaster in recorded history, following the 1556 Shensi Province, Chinese earthquake in which at least 830,000 persons lost their lives. Detailed analyses of the teleseismic surface waves and body waves are made for the Tangshan event. The major conclusions are: (1) The Tangshan earthquake sequence is a complex one, including strike-slip, thrust, and normal-fault events. (2) The main shock, as determined from surface waves, occurred on a near vertical right-lateral strike-slip fault, striking N40°E. (3) A seismic moment of 1.8 × 10^(27) dyne-cm is obtained. From the extent of the aftershock zone and relative location of the main shock epicenter, symmetric (1:1) bilateral faulting with a total length of 140 km may be inferred. If a fault width of 15 km is assumed, the average offset is estimated to be 2.7 meters with an average stress drop of about 30 bars. (4) The main shock was initiated by an event with a relatively slow onset and a seismic moment of 4 × 10^(26) dyne-cm. The preferred fault-plane solution, determined from surface-wave analyses, indicates a strike 220°, dip 80°, and rake −175°. (5) Two thrust events follow the strike-slip event by 11 and 19 sec, respectively. They are located south to southwest of the initial event and have a total moment of 8 × 10^(25) dyne-cm. This sequence is followed by several more events. (6) The principal aftershock was a normal-fault double event with the fault planes unconstrained by the P-wave first motions. Surface waves provide additional constraints to the mechanism to yield an oblique slip solution with strike N120°E, dip 45°SW, and rake −30°. A total moment of 8 × 10^(26) dyne-cm is obtained. (7) The triggering of lesser thrust and normal faults by a large strike-slip event in the Tangshan sequence has important consequences in the assessment of earthquake hazard in other complex strike-slip systems like the San Andreas