Successive phase transitions at finite temperatures of the supersolid in the three-dimensional extended Bose-Hubbard model

We study the finite temperature properties of the extended Bose-Hubbard model on a cubic lattice. This model exhibits the so-called supersolid state. To start with, we investigate ordering processes by quantum Monte Carlo simulations, and find successive superfluid and solid phase transitions. There, we find that the two order parameters compete with each other. We obtain the finite temperature phase diagram, which contains the superfluid, the solid, the supersolid and the disordered phase. We develop a mean-field theory to analyze the ordering processes and compare the result with that obtained by simulations, and discuss the mechanism of the competition of these two orders. We also study how the supersolid region shrinks as the on-site repulsion becomes strong.Comment: 6 pages, 6 figure

Resonant Control of Interaction Between Different Electronic States

We observe a magnetic Feshbach resonance in a collision between the ground and metastable states of two-electron atoms of ytterbium (Yb). We measure the on-site interaction of doubly-occupied sites of an atomic Mott insulator state in a three-dimensional optical lattice as a collisional frequency shift in a high-resolution laser spectroscopy. The observed spectra are well fitted by a simple theoretical formula, in which two particles with an s-wave contact interaction are confined in a harmonic trap. This analysis reveals a wide variation of the interaction with a resonance behavior around a magnetic field of about 1.1 Gauss for the energetically lowest magnetic sublevel of ${}^{170}$Yb, as well as around 360 mG for the energetically highest magnetic sublevel of ${}^{174}$Yb. The observed Feshbach resonance can only be induced by an anisotropic inter-atomic interaction. This novel scheme will open the door to a variety of study using two-electron atoms with tunable interaction.Comment: 5 pages, 5 figure

Fermi surface and antiferromagnetism in the Kondo lattice: an asymptotically exact solution in d>1 Dimensions

Interest in the heavy fermion metals has motivated us to examine the quantum phases and their Fermi surfaces within the Kondo lattice model. We demonstrate that the model is soluble asymptotically exactly in any dimension d>1, when the Kondo coupling is small compared with the RKKY interaction and in the presence of antiferromagnetic ordering. We show that the Kondo coupling is exactly marginal in the renormalization group sense, establishing the stability of an ordered phase with a small Fermi surface, AFs. Our results have implications for the global phase diagram of the heavy fermion metals, suggesting a Lifshitz transition inside the antiferromagnetic region and providing a new perspective for a Kondo-destroying antiferromagnetic quantum critical point.Comment: 4 pages, 4 figures; (v2) corrected typos and added reference/acknowledgment; (v3) version as published in Physical Review Letters (July, 2007

Magnetism and Fermi surface in heavy fermion metals

With a multitude of different phases and quantum critical points, heavy fermion materials should reign supreme as the prototype for competing order, a major contemporary theme in condensed matter physics. One key feature that differentiates the types of magnetic phases and critical points is the presence or absence of Kondo screening. This singlet formation is dramatically manifested in the Fermi surface, which may or may not include atomic f-orbital electron states. To provide a theoretical basis for the different types of magnetism, we have carried out asymptotically exact studies of the Kondo lattice model inside both the antiferromagnetic and ferromagnetic phases. A fundamental aspect of the approach is to map the magnetic Hamiltonian for the f-orbitals onto a quantum nonlinear sigma model (QNLsigmaM). The Kondo interaction results in an effective coupling between the QNLsigmaM fields and the conduction electrons. Renormalization group analyses show that the Fermi surface in the corresponding ordered states is small (not incorporating the f-orbitals) for both the ferromagnetic and antiferromagnetic cases. These results are of relevance to a number of materials, including YbRh2Si2 and CeRu2Ge2, where experimental measurements of magnetotransport and de Haas van Alphen effects have supplied evidence for small Fermi surface phases. The implications of our results for heavy fermion quantum critical points will also be discussed

Correlation between aerobic threshold and cardiopulmonary response to exercise onset in patients with myocardial infarction

Purpose: This study aimed to identify the correlation between aerobic threshold (AT) and cardiopulmonary response at the start of exercise in patients with myocardial infarction (MI). Subjects and Methods: Thirty-one male patients with MI underwent a sub-maximal cardiopulmonary exercise test with expiratory gas analysis to determine their peak oxygen uptake (V̇O₂) level, using Ramp protocol. Results: The patients demonstrated an extended time constant (TC) and decline in AT in this study. Extended TC suggested impaired cardiac function due to reduced left ventricular ejection fraction (LVEF), as well as an LVEF of 59.8% on average. However, there was no significant correlation between TC and AT. Pearson product-moment correlation coefficients were 0.56 between AT and area under the oxygen uptake curve (V̇O₂AUC), -0.22 between TC and V̇O₂AUC, and -0.23 between AT and TC. Conclusion: V̇O₂AUC is representative of oxygen utilization and is correlated with AT in patients with MI.首都大学東京学位論文 乙第192号 副論

Direct Measurement of Thermal Fluctuation of High-Q Pendulum

We achieved for the first time a direct measurement of the thermal fluctuation of a pendulum in an off-resonant region using a laser interferometric gravitational wave detector. These measurements have been well identified for over one decade by an agreement with a theoretical prediction, which was derived by a fluctuation-dissipation theorem. Thermal fluctuation is dominated by the contribution of resistances in coil-magnet actuator circuits. When we tuned these resistances, the noise spectrum also changed according to a theoretical prediction. The measured thermal noise level corresponds to a high quality factor on the order of 10^5 of the pendulum.Comment: 10 pages, 4 figure