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

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

Estimation of fire-induced carbon emissions from Equatorial Asia in 2015 using in situ aircraft and ship observations

Inverse analysis was used to estimate fire carbon emissions in Equatorial Asia induced by the big El Niño event in 2015. This inverse analysis is unique because it extensively used high-precision atmospheric mole fraction data of carbon dioxide (CO2) from the commercial aircraft observation project CONTRAIL. Through comparisons with independent shipboard observations, especially carbon monoxide (CO) data, the validity of the estimated fire-induced carbon emissions was demonstrated. The best estimate, which used both aircraft and shipboard CO2 observations, indicated 273 Tg C for fire emissions from September–October 2015. This 2-month period accounts for 75 % of the annual total fire emissions and 45 % of the annual total net carbon flux within the region, indicating that fire emissions are a dominant driving force of interannual variations of carbon fluxes in Equatorial Asia. Several sensitivity experiments demonstrated that aircraft observations could measure fire signals, though they showed a certain degree of sensitivity to prior fire-emission data. The inversions coherently estimated smaller fire emissions than the prior data, partially because of the small contribution of peatland fires indicated by enhancement ratios of CO and CO2 observed by the ship. In future warmer climate conditions, Equatorial Asia may experience more severe droughts, which risks releasing a large amount of carbon into the atmosphere. Therefore, the continuation of aircraft and shipboard observations is fruitful for reliable monitoring of carbon fluxes in Equatorial Asia.</p

Photoinduced charge and spin dynamics in strongly correlated electron systems

Motivated by photoinduced phase transition in manganese oxides, charge and spin dynamics induced by photoirradiation are examined. We calculate the transient optical absorption spectra of the extended double-exchange model by the density matrix renormalization group (DMRG) method. A charge-ordered insulating (COI) state becomes metallic just after photoirradiation, and the system tends to recover the initial COI state. The recovery is accompanied with remarkable suppression of an antiferromagnetic correlation in the COI state. The DMRG results are consistent with recent pump-probe spectroscopy data.Comment: 5 pages, 4 figure

A 4D-Var inversion system based on the icosahedral grid model (NICAM-TM 4D-Var v1.0) – Part 2: Optimization scheme and identical twin experiment of atmospheric CO₂ inversion

A four-dimensional variational method (4D-Var) is a popular technique for source/sink inversions of atmospheric constituents, but it is not without problems. Using an icosahedral grid transport model and the 4D-Var method, a new atmospheric greenhouse gas (GHG) inversion system has been developed. The system combines offline forward and adjoint models with a quasi-Newton optimization scheme. The new approach is then used to conduct identical twin experiments to investigate optimal system settings for an atmospheric CO2 inversion problem, and to demonstrate the validity of the new inversion system. In this paper, the inversion problem is simplified by assuming the prior flux errors to be reasonably well known and by designing the prior error correlations with a simple function as a first step. It is found that a system of forward and adjoint models with smaller model errors but with nonlinearity has comparable optimization performance to that of another system that conserves linearity with an exact adjoint relationship. Furthermore, the effectiveness of the prior error correlations is demonstrated, as the global error is reduced by about 15 % by adding prior error correlations that are simply designed when 65 weekly flask sampling observations at ground-based stations are used. With the optimal setting, the new inversion system successfully reproduces the spatiotemporal variations of the surface fluxes, from regional (such as biomass burning) to global scales. The optimization algorithm introduced in the new system does not require decomposition of a matrix that establishes the correlation among the prior flux errors. This enables us to design the prior error covariance matrix more freely

Generation of maximum spin entanglement induced by cavity field in quantum-dot systems

Equivalent-neighbor interactions of the conduction-band electron spins of quantum dots in the model of Imamoglu et al. [Phys. Rev. Lett. 83, 4204 (1999)] are analyzed. Analytical solution and its Schmidt decomposition are found and applied to evaluate how much the initially excited dots can be entangled to the remaining dots if all of them are initially disentangled. It is demonstrated that the perfect maximally entangled states (MES) can only be generated in the systems of up to 6 dots with a single dot initially excited. It is also shown that highly entangled states, approximating the MES with a good accuracy, can still be generated in systems of odd number of dots with almost half of them being excited. A sudden decrease of entanglement is observed by increasing the total number of dots in a system with a fixed number of excitations.Comment: 6 pages, 7 figures, to appear in Phys. Rev.

Estimating Asian terrestrial carbon fluxes from CONTRAIL aircraft and surface CO2 observations for the period 2006 to 2010

Current estimates of the terrestrial carbon fluxes in Asia show large uncertainties particularly in the boreal and mid-latitudes and in China. In this paper, we present an updated carbon flux estimate for Asia ("Asia" refers to lands as far west as the Urals and is divided into boreal Eurasia, temperate Eurasia and tropical Asia based on TransCom regions) by introducing aircraft CO2 measurements from the CONTRAIL (Comprehensive Observation Network for Trace gases by Airline) program into an inversion modeling system based on the CarbonTracker framework. We estimated the averaged annual total Asian terrestrial land CO2 sink was about -1.56 Pg C yr-1 over the period 2006–2010, which offsets about one-third of the fossil fuel emission from Asia (+4.15 Pg C yr-1). The uncertainty of the terrestrial uptake estimate was derived from a set of sensitivity tests and ranged from -1.07 to -1.80 Pg C yr-1, comparable to the formal Gaussian error of ±1.18 Pg C yr-1 (1-sigma). The largest sink was found in forests, predominantly in coniferous forests (-0.64 ± 0.70 Pg C yr-1) and mixed forests (-0.14 ± 0.27 Pg C yr-1); and the second and third large carbon sinks were found in grass/shrub lands and croplands, accounting for -0.44 ± 0.48 Pg C yr-1 and -0.20 ± 0.48 Pg C yr-1, respectively. The carbon fluxes per ecosystem type have large a priori Gaussian uncertainties, and the reduction of uncertainty based on assimilation of sparse observations over Asia is modest (8.7–25.5%) for most individual ecosystems. The ecosystem flux adjustments follow the detailed a priori spatial patterns by design, which further increases the reliance on the a priori biosphere exchange model. The peak-to-peak amplitude of inter-annual variability (IAV) was 0.57 Pg C yr-1 ranging from -1.71 Pg C yr-1 to -2.28 Pg C yr-1. The IAV analysis reveals that the Asian CO2 sink was sensitive to climate variations, with the lowest uptake in 2010 concurrent with a summer flood and autumn drought and the largest CO2 sink in 2009 owing to favorable temperature and plentiful precipitation conditions. We also found the inclusion of the CONTRAIL data in the inversion modeling system reduced the uncertainty by 11% over the whole Asian region, with a large reduction in the southeast of boreal Eurasia, southeast of temperate Eurasia and most tropical Asian areas

Seasonal characteristics of trace gas transport into the extratropical upper troposphere and lower stratosphere

To investigate the seasonal characteristics of trace gas distributions in the extratropical upper troposphere and lower stratosphere (ExUTLS) as well as stratosphere–troposphere exchange processes, origin fractions of air masses originating in the stratosphere, tropical troposphere, midlatitude lower troposphere (LT), and high-latitude LT in the ExUTLS are estimated using 10-year backward trajectories calculated with European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim data as the meteorological input. Time series of trace gases obtained from ground-based and airborne observations are incorporated into the trajectories, thus reconstructing spatiotemporal distributions of trace gases in the ExUTLS. The reconstructed tracer distributions are analyzed with the origin fractions and the stratospheric age of air (AoA) estimated using the backward trajectories. The reconstructed distributions of SF6 and CO2 in the ExUTLS are linearly correlated with those of AoA because of their chemically passive behavior and quasi-stable increasing trends in the troposphere. Distributions of CH4, N2O, and CO are controlled primarily by chemical decay along the transport path from the source region via the stratosphere and subsequent mixing of such stratospheric air masses with tropospheric air masses in the ExUTLS.</p