Phase diagrams, critical and multicritical behavior of hard-core Bose-Hubbard models

We determine the zero-temperature phase diagram of the hard-core Bose-Hubbard model on a square lattice by mean-field theory supplemented by a linear spin-wave analysis. Due to the interplay between nearest and next-nearest neighbor interaction and cubic anisotropy several supersolid phases with checkerboard, stripe domain or intermediate symmetry are stabilized. The phase diagrams show three different topologies depending on the relative strength of nearest and next-nearest neighbor interaction. We also find a rich variety of new quantum critical behavior and multicritical points and discuss the corresponding effective actions and universality classes.Comment: 19 pages, ReVTeX, 18 figures included, submitted to PR

Quantum-Phase Transitions of Interacting Bosons and the Supersolid Phase

We investigate the properties of strongly interacting bosons in two dimensions at zero temperature using mean-field theory, a variational Ansatz for the ground state wave function, and Monte Carlo methods. With on-site and short-range interactions a rich phase diagram is obtained. Apart from the homogeneous superfluid and Mott-insulating phases, inhomogeneous charge-density wave phases appear, that are stabilized by the finite-range interaction. Furthermore, our analysis demonstrates the existence of a supersolid phase, in which both long-range order (related to the charge-density wave) and off-diagonal long-range order coexist. We also obtain the critical exponents for the various phase transitions.Comment: RevTex, 20 pages, 10 PostScript figures include

Superfluids and Supersolids on Frustrated 2D Lattices

We study the ground state of hard-core bosons with nearest-neighbor hopping and nearest-neighbor interactions on the triangular and Kagom\'e lattices by mapping to a system of spins ($S={1\over2}$), which we analyze using spin-wave theory. We find that the both lattices display superfluid and supersolid (a coexistence of superfluid and solid) order as the parameters and filling are varied. Quantum fluctuations seem large enough in the Kagom\'e system to raise the interesting possibility of a disordered ground state.Comment: Latex format, 24 figures available by email upon request. Submitted to Physical Review

Solid 4He and the Supersolid Phase: from Theoretical Speculation to the Discovery of a New State of Matter? A Review of the Past and Present Status of Research

The possibility of a supersolid state of matter, i.e., a crystalline solid exhibiting superfluid properties, first appeared in theoretical studies about forty years ago. After a long period of little interest due to the lack of experimental evidence, it has attracted strong experimental and theoretical attention in the last few years since Kim and Chan (Penn State, USA) reported evidence for nonclassical rotational inertia effects, a typical signature of superfluidity, in samples of solid 4He. Since this "first observation", other experimental groups have observed such effects in the response to the rotation of samples of crystalline helium, and it has become clear that the response of the solid is extremely sensitive to growth conditions, annealing processes, and 3He impurities. A peak in the specific heat in the same range of temperatures has been reported as well as anomalies in the elastic behaviour of solid 4He with a strong resemblance to the phenomena revealed by torsional oscillator experiments. Very recently, the observation of unusual mass transport in hcp solid 4He has also been reported, suggesting superflow. From the theoretical point of view, powerful simulation methods have been used to study solid 4He, but the interpretation of the data is still rather difficult; dealing with the question of supersolidity means that one has to face not only the problem of the coexistence of quantum coherence phenomena and crystalline order, exploring the realm of spontaneous symmetry breaking and quantum field theory, but also the problem of the role of disorder, i.e., how defects, such as vacancies, impurities, dislocations, and grain boundaries, participate in the phase transition mechanism.Comment: Published on J. Phys. Soc. Jpn., Vol.77, No.11, p.11101

Optimal Analysis for the Enhancement in the Thermal Variables Measurement by Smart and Modular Solid State Sensors

The proposed research aims to analyze and optimize the measurement of thermal physical variables during the operation of a hydrogen combustion engine. The optimal measurement of the flow, temperature, pressure, and volume is given over the hydrogen, which is the main fuel of the studied combustion motor. Hence, the success of the measurement is based on the polynomial analysis of the combustion motor operation, which needs nonlinear algorithms to get the optimal correlation of the measured physical variables as well as a high robustness and short response time during the transduction of the measured physical variable, which is achieved as a consequence of the anodic aluminum oxide (AAO) amorphous nanostructures properties that are modular solid state integration of the designed smart sensor. The short response time and high robustness is a good advantage for the designed smart sensor since it gives more time to execute sophisticated algorithms in order to get the optimal physical variables measurement. In fact, the proposed smart sensor keeps the possibility to be modular and solid state for the interaction with the hydrogen fuel as well as recognizing the presence of other molecules mixed in the fluid, which can alarm the user who is able to recognize whether it is joined oxygen or carbon residues. Therefore, the proposed research work toward a good compromise to care for the environment condition based on a cleaner combustion motor operation

Reactive and Regulative Temperament in Youths: Psychometric Evaluation of the Early Adolescent Temperament Questionnaire-Revised

The present study examined the psychometric properties of the self-report version of the Early Adolescent Temperament Questionnaire-Revised (EATQ-R), which is a scale for measuring reactive and regulative temperament traits, in a large sample of children and adolescents (N = 1,055). The results indicated that the internal consistency was acceptable for most EATQ-R temperament scales. Further, principal components analysis of the instrument yielded a structure with nine components, which generally reflected the temperament scales of the EATQ-R. The test–retest stability of the scale was moderate to good, whereas the parent–child agreement was rather low. Finally, the scale correlated in a theoretically meaningful way with children’s self-reports of personality and psychopathology. It can be concluded that the EATQ-R is a useful scale for measuring aspects of reactive and regulative temperament in children and adolescents, although there is certainly room for improving the instrument