97 research outputs found

    A New Method of the High Temperature Series Expansion

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    We formulate a new method of performing high-temperature series expansions for the spin-half Heisenberg model or, more generally, for SU(nn) Heisenberg model with arbitrary nn. The new method is a novel extension of the well-established finite cluster method. Our method emphasizes hidden combinatorial aspects of the high-temperature series expansion, and solves the long-standing problem of how to efficiently calculate correlation functions of operators acting at widely separated sites. Series coefficients are expressed in terms of cumulants, which are shown to have the property that all deviations from the lowest-order nonzero cumulant can be expressed in terms of a particular kind of moment expansion. These ``quasi-moments'' can be written in terms of corresponding ``quasi-cumulants'', which enable us to calculate higher-order terms in the high-temperature series expansion. We also present a new technique for obtaining the low-order contributions to specific heat from finite clusters.Comment: 20 pages, 30 figures, to appear in J. Stat. Phy

    Grand canonical Gutzwiller approximation for magnetic inhomogeneous systems

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    The Gutzwiller approximation (GA) for Gutzwiller-projected grand canonical wave functions with fugacity factors is investigated in detail. Our systems in general contain inhomogeneity and local magnetic moments. In deriving renormalization formulae, we also derive or estimate terms of higher powers of intersite contractions neglected in the conventional GA. We examine several different constraints, i.e., local/global spin-dependent/independent particle-number conservation. Out of the four, the local spin-dependent constraint seems the most promising at present. An improved GA derived from it agrees with the variational Monte Carlo method better than the conventional GA does. The corrections to the conventional GA can be interpreted as two-site correlation including the phase difference of configurations. Furthermore, projected quasi-particle excited states are orthogonal to each other within the GA. Using these states, spectral weights are calculated. We show that asymmetry between electron addition and removal spectra can appear by taking into account the higher powers of the intersite contractions in the case of the d-wave superconductors and the Fermi sea; the addition is smaller than the removal. However, the asymmetry is quite weak especially near the Fermi level. In contrast, projected s-wave superconductors can have the opposite asymmetry (addition larger than removal) especially near the Fermi level. In addition, formulae from the other three constraints are also derived, which may be useful depending on purposes.Comment: 18 pages. 8 figures added. Sec.II B, Sec.III F G H, Sec.IV G mainly revise

    High Temperature Expansion for the SU(n) Heisenberg Model in One Dimension

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    Thermodynamic properties of the SU(nn) Heisenberg model in one dimension is studied by means of high-temperature expansion for arbitrary nn. The specific heat up to O[(βJ)23]O[(\beta J)^{23}] and the correlation function up to O[(βJ)18]O[(\beta J)^{18}] are derived with βJ\beta J being the antiferromagnetic exchange in units of temperature. It is found for n>2n>2 that the specific heat shows a shoulder in the high-temperature side of a peak. The origin of this structure is clarified by deriving the temperature dependence of the correlation function. With decreasing temperature, the short-range correlation with two-site periodicity develops first, and then another correlation with nn-site periodicity at lower temperature. This behavior is in contrast to that of the inverse square interaction model, where the specific heat shows a single peak according to the exact solution. Our algorithm has an advantage that neither computational time nor memory depends on the multiplicity nn per site; the series coefficients are obtained as explicit functions of nn.Comment: 4 pages including 4 PS-figures, submitted to J. Phys. Soc. Jp

    The cluster glass state in the two-dimensional extended t-J model

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    The recent observation of an electronic cluster glass state composed of random domains with unidirectional modulation of charge density and/or spin density on Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} reinvigorates the debate of existence of competing interactions and their importance in high temperature superconductivity. By using a variational approach, here we show that the presence of the cluster glass state is actually an inherent nature of the model based on the antiferromagnetic interaction (J) only, i.e. the well known t-J model. There is no need yet to introduce a competing interaction to understand the existence of the cluster glass state. The long-range pairing correlation is not much influenced by the disorder in the glass state which also has nodes and linear density of states. In the antinodal region, the spectral weight is almost completely suppressed. The modulation also produces subgap structures inside the "coherent" peaks of the local density of states.Comment: 9 pages, 5 figures, submitted to PR

    On the evaluation of matrix elements in partially projected wave functions

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    We generalize the Gutzwiller approximation scheme to the calculation of nontrivial matrix elements between the ground state and excited states. In our scheme, the normalization of the Gutzwiller wave function relative to a partially projected wave function with a single non projected site (the reservoir site) plays a key role. For the Gutzwiller projected Fermi sea, we evaluate the relative normalization both analytically and by variational Monte-Carlo (VMC). We also report VMC results for projected superconducting states that show novel oscillations in the hole density near the reservoir site

    Mobilization and Drainage of the Pancreatic Bed as a Treatment for Severe Acute Pancreatitis

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    A new surgical procedure, mobilization and drainage of the pancreatic bed, was performed on two cases of severe acute pancreatitis in shock state, one edematous type and another necrotic type, and prompt improvement of shock state and excellent healing of pancreatitis were observed clinically. The authors have experimentally proved that shock in acute pancreatitis developed as the retroperitoneal tissues directly absorbed the pancreatic exudate. The advantage of this surgical procedure was also proved on experimental dogs whose severe hypotension was successfully treated. The authors believe that this procedure is a simple and reasonable surgical method for acute pancreatitis

    Nature and Happiness Levels: New SWB Domains for Rivers, a Lake, and Forests

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    By using a questionnaire survey, we measured nature-related happiness levels, which include specific domains that differ from the overall subjective well-being (SWB) in a Japanese watershed. We regarded nature-related happiness levels, specifically related to rivers, a lake, or forests, as meaningful indices because many people living separated from nature may be unaware of their relationship with nature. We found that nature-related happiness levels had convergent validity and distinct correlation patterns with the explanatory variables, and these patterns were different from those of the overall SWB. These findings support the case of measuring nature-related happiness levels and overall SWB. Nature-related happiness levels were positively correlated with leisure activities and contact with living things. The abundance of rivers in a district is negatively associated with river-related happiness. We speculated that this was due to unidentified disservices associated with the rivers. Lake-related happiness has stronger correlations with relaxation benefits than symbolism, local food culture, art/culture, or water sources. Considering these findings, policymakers should formulate policies based on nature-related happiness levels. Because nature-related happiness levels are not correlated with income level, such policies may contribute to residents’ well-being in an egalitarian manner
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