Antiferromagnetism and superfluidity of a dipolar Fermi gas in a 2D optical lattice

In a dipolar Fermi gas, the dipole-dipole interaction between fermions can be turned into a dipolar Ising interaction between pseduospins in the presence of an AC electric field. When trapped in a 2D optical lattice, such a dipolar Fermi gas has a very rich phase diagram at zero temperature, due to the competition between antiferromagnetism and superfluidity. At half filling, the antiferromagnetic state is the favored ground state. The superfluid state appears as the ground state at a smaller filling factor. In between there is a phase-separated region. The order parameter of the superfluid state can display different symmetries depending on the filling factor and interaction strength, including d-wave ($d$), extend s-wave ($xs$), or their linear combination ($xs+i\times d$). The implication for the current experiment is discussed.Comment: 11 pages, 3 figures, references update

Dark energy imprints on the kinematic Sunyaev-Zel'dovich signal

We investigate the imprint of dark energy on the kinetic Sunyaev-Zel'dovich (kSZ) angular power spectrum on scales of $\ell=1000$ to $10000$, and find that the kSZ signal is sensitive to the dark energy parameter. For example, varying the constant $w$ by 20\% around $w=-1$ results in a $\gtrsim10\%$ change on the kSZ spectrum; changing the dark energy dynamics parametrized by $w_a$ by $\pm0.5$, a 30\% change on the kSZ spectrum is expected. We discuss the observational aspects and develop a fitting formula for the kSZ power spectrum. Finally, we discuss how the precise modeling of the post-reionization signal would help the constraints on patchy reionization signal, which is crucial for measuring the duration of reionization.Comment: 12 pages, 9 figures, 2 table

Topological px+ipyp_{x}+ip_{y} Superfluid Phase of a Dipolar Fermi Gas in a 2D Optical Lattice

In a dipolar Fermi gas, the anisotropic interaction between electric dipoles can be turned into an effectively attractive interaction in the presence of a rotating electric field. We show that the topological $p_{x}+ip_{y}$ superfluid phase can be realized in a single-component dipolar Fermi gas trapped in a 2D square optical lattice with this attractive interaction at low temperatures. The $p_{x}+ip_{y}$ superfluid state has potential applications for topological quantum computing. We obtain the phase diagram of this system at zero temperature. In the weak-coupling limit, the p-wave superfluid phase is stable for all filling factors. As the interaction strength increases, it is stable close to filling factors $n=0$ or $n=1$, and phase separation takes place in between. When the interaction strength is above a threshold, the system is phase separated for any $0<n<1$. The transition temperature of the $p_{x}+ip_{y}$ superfluid state is estimated and the implication for experiments is discussed.Comment: 10 pages, 4 figure

Defect Chemistry and Ion Intercalation During the Growth and Solid-State Transformation of Metal Halide Nanocrystals

Abstract of the Dissertation Defect Chemistry and Ion Intercalation During the Growth and Solid-State Transformation of Metal Halide Nanocrystals Semiconductor metal halides as light-sensitive materials have applications in multiple areas, such as photographic film, antibacterial agents and photocatalysts. One focus of this dissertation is to achieve novel morphologies of ternary silver bromoiodide (AgBr1-xIx, 0 For the silver halide system, we demonstrate that the anion composition of AgBr1-xIx nanocrystals determines their shape through the introduction of twin defects as the nanocrystals are made more iodide-rich. AgBr1-xIx nanocrystals grow as single-phase, solid solutions with the rock salt crystal structure for anions compositions ranging from 0 ≤ x \u3c 0.38. With increasing iodide content the morphology of the nanocrystals evolves from cubic to truncated cubic to hexagonal prismatic. Structural characterization indicates the cubic nanocrystals are bound by {100} facets whereas the hexagonal platelet nanocrystals possess {111} facets as their top and bottom surface. Calculations based on first-principles density functional theory show that iodide substitution in AgBr stabilizes {111} surfaces and that twin defects parallel to these surfaces possess a low formation energy. Our experimental observations and calculations are consistent with a growth model in which the presence of multiple twin defects parallel to a {111} surface enhances lateral growth of the side facets and changes the nanocrystal shape. To study the reaction kinetics of solid-state conversion in the lead halide system, we use the change in fluorescence brightness to image the transformation of individual lead bromide (PbBr2) nanocrystals to methylammonium lead bromide (CH3NH3PbBr3) via intercalation of CH3NH3Br. Analyzing this reaction one nanocrystal at a time reveals information that is masked when the fluorescence intensity is averaged over many particles. Sharp rises in the intensity of single nanocrystals indicate they transform much faster than the time it takes for the ensemble average to transform. Furthermore, the intensity rises for individual nanocrystals are insensitive to the CH3NH3Br concentration. To explain these observations, we propose a phase transformation model in which the reconstructive transitions necessary to convert a PbBr2 nanocrystal into CH3NH3PbBr3 initially create a high energy barrier for ion intercalation. A critical point in the transformation occurs when the crystal adopts the perovskite phase, at which point the activation energy for further ion intercalation becomes progressively smaller. Monte Carlo simulations that incorporate this change in activation barrier into the likelihood of reaction events reproduce key experimental observations for the intensity trajectories of individual particles. The insights gained from this study may be used to further control the crystallization of CH3NH3PbBr3 and other solution-processed semiconductors. In this dissertation, we focus on two different systems, silver halide and lead halide perovskite. Even though the systems are different, we find that solid-state immiscibility between different halide compounds plays an important role in both reactions we are studying. In AgBr1-xIx, the structural immiscibility between rock salt AgBr and wurtzite AgI causes the formation of twin boundaries, which change the nanocrystal morphology. For the lead halide system, the sharp transition in fluorescence intensity observed in single nanocrystals is also due to structural immiscibility, which causes the sudden phase transition from PbBr2 to the perovskite phase. This structural immiscibility between different halide compounds plays a critical role for both metal halide systems

低遅延稠密無線ネットワークのためのエアタイム管理

京都大学新制・課程博士博士(情報学)甲第23327号情博第763号新制||情||130(附属図書館)京都大学大学院情報学研究科通信情報システム専攻(主査)教授 守倉 正博, 教授 原田 博司, 教授 大木 英司学位規則第4条第1項該当Doctor of InformaticsKyoto UniversityDGA

Cosmic Mach Number: A Sensitive Probe for the Growth of Structure

In this Letter, we investigate the potential power of the Cosmic Mach Number (CMN), which is the ratio between the mean velocity and the velocity dispersion of galaxies as a function of cosmic scales, to constrain cosmologies. We first measure the CMN from 5 catalogues of galaxy peculiar velocity surveys at low redshift (0.002<z<0.03), and use them to contrast cosmological models. Overall, current data is consistent with the WMAP7 LCDM model. We find that the CMN is highly sensitive to the growth of structure on scales 0.01<k<0.1 h/Mpc in Fourier space. Therefore, modified gravity models, and models with massive neutrinos, in which the structure growth generally deviates from that in the LCDM model in a scale-dependent way, can be well differentiated from the LCDM model using future CMN data.Comment: 7 pages, matches the version accepted to JCA