Lateral Size and Thickness Dependence in Ferroelectric Nanostructures Formed by Localized Domain Switching

Ferroelectric nanostructures can be formed by local switching of domains using techniques such as piezo-force microscopy (PFM). Understanding lateral size effects is important to determine the minimum feature size for writing ferroelectric nanostructures. To understand these lateral size effects, we use the time-dependent-Ginzburg-Landau equations to simulate localized switching of domains for a PFM type and parallel-plate capacitor configurations. Our investigations indicate that fringing electric fields lead to switching via 90 deg domain wedge nucleation for thicker films while at smaller thicknesses, the polarization switches directly by 180 deg rotations. The voltage required to switch the domain increases by decreasing the lateral size and at very small lateral sizes the coercive voltage becomes so large that it becomes virtually impossible to switch the domain. In all cases, the width of the switched region extends beyond the electrodes, due to fringing.Comment: 21 pages, 11 figure

Field-tuned quantum tunneling in a supramolecule dimer [Mn4]2[Mn_4]_2

Field-tuned quantum tunneling in two single-molecule magnets coupled antiferromagnetically and formed a supramolecule dimer is studied. We obtain step-like magnetization curves by means of the numerically exact solution of the time-dependent Schr\H{o}dinger equation. The steps in magnetization curves show the phenomenon of quantum resonant tunneling quantitatively. The effects of the sweeping rate of applied field is discussed. These results obtained from quantum dynamical evolution well agree with the recent experiment[W.Wernsdorfer et al. Nature 416(2002)406].Comment: 11 pages, 4 figures, 2 tables. Submited to Phys. Rev.

Vacuum structure of Toroidal Carbon Nanotubes

Low energy excitations in carbon nanotubes can be described by an effective field theory of two components spinor. It is pointed out that the chiral anomaly in 1+1 dimensions should be observed in a metallic toroidal carbon nanotube on a planar geometry with varying magnetic field. We propose an experimental setup for studying this quantum effect. We also analyze the vacuum structure of the metallic toroidal carbon nanotube including the Coulomb interactions and discuss some effects of external charges on the vacuum.Comment: 10 pages, 11 figure

Temperature dependent dielectric and Raman spectra and microwave dielectric properties of gehlenite‐typed Ca2Al2SiO7 ceramics

Gehlenite‐typed Ca2Al2SiO7 ceramics were prepared by the conventional solid‐state reaction. Two anomalies were found in the plot of dielectric constant vs. temperature, which was associated to space charge polarization. Pure phase crystal structure and no phase transition were observed in the temperature dependent XRD patterns and Raman spectra from room temperature to 900°C. There was relevant relation between Q× f and τƒ with the stretching vibrations of Ca‐O bond and O‐Ca‐O bending in CaO8 polyhedron. Excellent microwave dielectric properties (εr = 8.86, Q × f = 22,457GHz, and τf = −51.06 ppm/°C) were obtained for Ca2Al2SiO7 sintered at 1440°C in air, which had the potential application to use in microwave and millimeter‐wave devices such as capacitors and substrates

Quantum phase transitions from topology in momentum space

Many quantum condensed matter systems are strongly correlated and strongly interacting fermionic systems, which cannot be treated perturbatively. However, physics which emerges in the low-energy corner does not depend on the complicated details of the system and is relatively simple. It is determined by the nodes in the fermionic spectrum, which are protected by topology in momentum space (in some cases, in combination with the vacuum symmetry). Close to the nodes the behavior of the system becomes universal; and the universality classes are determined by the toplogical invariants in momentum space. When one changes the parameters of the system, the transitions are expected to occur between the vacua with the same symmetry but which belong to different universality classes. Different types of quantum phase transitions governed by topology in momentum space are discussed in this Chapter. They involve Fermi surfaces, Fermi points, Fermi lines, and also the topological transitions between the fully gapped states. The consideration based on the momentum space topology of the Green's function is general and is applicable to the vacua of relativistic quantum fields. This is illustrated by the possible quantum phase transition governed by topology of nodes in the spectrum of elementary particles of Standard Model.Comment: 45 pages, 17 figures, 83 references, Chapter for the book "Quantum Simulations via Analogues: From Phase Transitions to Black Holes", to appear in Springer lecture notes in physics (LNP

A CsI(Tl) Scintillating Crystal Detector for the Studies of Low Energy Neutrino Interactions

Scintillating crystal detector may offer some potential advantages in the low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed near the core of Nuclear Power Station II in Taiwan is being constructed for the studies of electron-neutrino scatterings and other keV-MeV range neutrino interactions. The motivations of this detector approach, the physics to be addressed, the basic experimental design, and the characteristic performance of prototype modules are described. The expected background channels and their experimental handles are discussed.Comment: 34 pages, 11 figures, submitted to Nucl. Instrum. Method

Symmetry and topology in antiferromagnetic spintronics

Antiferromagnetic spintronics focuses on investigating and using antiferromagnets as active elements in spintronics structures. Last decade advances in relativistic spintronics led to the discovery of the staggered, current-induced field in antiferromagnets. The corresponding N\'{e}el spin-orbit torque allowed for efficient electrical switching of antiferromagnetic moments and, in combination with electrical readout, for the demonstration of experimental antiferromagnetic memory devices. In parallel, the anomalous Hall effect was predicted and subsequently observed in antiferromagnets. A new field of spintronics based on antiferromagnets has emerged. We will focus here on the introduction into the most significant discoveries which shaped the field together with a more recent spin-off focusing on combining antiferromagnetic spintronics with topological effects, such as antiferromagnetic topological semimetals and insulators, and the interplay of antiferromagnetism, topology, and superconductivity in heterostructures.Comment: Book chapte

Regimen-specific rates of chemotherapy-related amenorrhea in breast cancer survivors

Young women who have not begun or completed their desired childbearing at the time of diagnosis with breast cancer often wish to understand and minimize their risk of chemotherapy-related amenorrhea (CRA). However, the incidence of CRA after regimens that do not include either an anthracycline or a cyclophosphamide is poorly studied. For patients with human epidermal growth factor receptor 2-positive disease, anthracycline- and cyclophosphamide-sparing regimens (eg, carboplatin/taxane) are common (in combination with human epidermal growth factor receptor 2-directed therapy). In this study, accrued in collaboration with Army of Women, menstrual data were analyzed for 151 breast cancer survivors (median age = 41 years at diagnosis, and median time between last chemotherapy and survey = 62.5 months). Last menstrual period was before the last chemotherapy dose in 51% of the 86 participants who received anthracycline/cyclophosphamide/taxane, in 42% of the 43 who received only taxane/cyclophosphamide, and in 13% of the 15 who received carboplatin/taxane. This study suggests that carboplatin/taxane causes less CRA than cyclophosphamide-based regimens

Violations of the equivalence principle in a dilaton-runaway scenario

We explore a version of the cosmological dilaton-fixing and decoupling mechanism in which the dilaton-dependence of the low-energy effective action is extremized for infinitely large values of the bare string coupling $g_s^2 = e^{\phi}$. We study the efficiency with which the dilaton $\phi$ runs away towards its ``fixed point'' at infinity during a primordial inflationary stage, and thereby approximately decouples from matter. The residual dilaton couplings are found to be related to the amplitude of the density fluctuations generated during inflation. For the simplest inflationary potential, $V (\chi) = {1/2} m_{\chi}^2 (\phi) \chi^2$, the residual dilaton couplings are shown to predict violations of the universality of gravitational acceleration near the $\Delta a / a \sim 10^{-12}$ level. This suggests that a modest improvement in the precision of equivalence principle tests might be able to detect the effect of such a runaway dilaton. Under some assumptions about the coupling of the dilaton to dark matter and/or dark energy, the expected time-variation of natural ``constants'' (in particular of the fine-structure constant) might also be large enough to be within reach of improved experimental or observational data.Comment: 32 pages, 1 figure, minor change