Quantized vortices in pionic superfluid

The interplay between classical vorticity being the main undisputed source of polarization in heavy-ion collisions (HIC) and quantized vortices is considered. The vortex tubes emerging in the rotating pionic (super) fluid polarize the baryons in their cores and explain the emerging global polarization. The appearance of vortices in the region separating participants and spectators in non-central HIC is similar to that for sliding layers of liquid helium. From the other side, it is also the region where the classical vorticity was earlier found to be large forming the vortex sheets. The formation of tubes manifests a threshold at certain critical vorticity implying the vanishing polarization at lower energies. For central HIC the compact jet-like flows may lead to formation of vortex rings related to local polarization. The P-odd momentum correlations for their experimental investigation are suggested. The role of shear and viscosity in the emergence of polarization is discussed.

Formation of a Fast Charge Transfer Channel in Quasi-2D Perovskite Solar Cells through External Electric Field Modulation

Quasi-2D perovskites solar cells exhibit excellent environmental stability, but relatively low photovoltaic properties, compared with 3D perovskites solar cells. However, charge transport and extraction in quasi-2D perovskite solar cells are still limited by the inevitable quantum well effect, resulting in low power conversion efficiency (PCE). To date, most efforts concentrate on crystal orientation and favorable alignment during materials and films processing. In this paper, we demonstrated that the quasi-2D perovskite [(BA)2(MA)3Pb4I13 (n = 4)] solar cells show an optimized device performance through forming a fast charge transfer channel among 2D quantum wells through external electric field modulation, with appropriate modulation bias and time after the device has been fabricated. Essentially, ions will move directionally due to local polarization in quasi-2D perovskite solar cells under the action of electric field modulation. More importantly, the mobile ions function as a dopant to de-passivate the defects when releasing at grain boundaries, while decreasing built-in potential by applying forward modulation bias with proper modulation time. The capacitance-voltage characteristics indicate that electric field modulation can decrease the charge accumulation and improve the charge collection in quasi-2D perovskite solar cells. Photoluminescence (PL) studies confirm that the non-radiative recombination is reduced by electric field modulation, leading to enhanced charge transfer. Our work indicates that external electric field modulation is an effective method to form a fast charge transfer channel among 2D quantum wells, leading to enhanced charge transfer and charge collection through local polarization toward developing high–performance quasi-2D perovskite devices.

Microwave Atom Chip Design

We present a toolbox of microstrip building blocks for microwave atom chips geared towards trapped atom interferometry. Transverse trapping potentials based on the AC Zeeman (ACZ) effect can be formed from the combined microwave magnetic near fields of a pair or a triplet of parallel microstrip transmission lines. Axial confinement can be provided by a microwave lattice (standing wave) along the microstrip traces. Microwave fields provide additional parameters for dynamically adjusting ACZ potentials: detuning of the applied frequency to select atomic transitions and local polarization controlled by the relative phase in multiple microwave currents. Multiple ACZ traps and potentials, operating at different frequencies, can be targeted to different spin states simultaneously, thus enabling spin-specific manipulation of atoms and spin-dependent trapped atom interferometry.

Sharp Focusing of a Hybrid Vector Beam with a Polarization Singularity

The key result of this work is the use of the global characteristics of the polarization singularities of the entire beam as a whole, rather than the analysis of local polarization, Stokes and Poincare–Hopf indices. We extend Berry’s concept of the topological charge of scalar beams to hybrid vector beams. We discuss tightly focusing a new type of nth-order hybrid vector light field comprising n C-lines (circular polarization lines). Using a complex Stokes field, it is shown that the field polarization singularity index equals n/2 and does not preserve in the focal plane. The intensity and Stokes vector components in the focal plane are expressed analytically. It is theoretically and numerically demonstrated that at an even n, the intensity pattern at the focus is symmetrical, and instead of C-lines, there occur C-points around which axes of polarization ellipses are rotated. At n = 4, C-points characterized by singularity indices 1/2 and ‘lemon’-type topology are found at the focus. For an odd source field order n, the intensity pattern at the focus has no symmetry, and the field becomes purely vectorial (with no elliptical polarization) and has n V-points, around which linear polarization vectors are rotating.

Broadband decoupling of intensity and polarization with vectorial Fourier metasurfaces

Intensity and polarization are two fundamental components of light. Independent control of them is of tremendous interest in many applications. In this paper, we propose a general vectorial encryption method, which enables arbitrary far-field light distribution with the local polarization, including orientations and ellipticities, decoupling intensity from polarization across a broad bandwidth using geometric phase metasurfaces. By revamping the well-known iterative Fourier transform algorithm, we propose “à la carte” design of far-field intensity and polarization distribution with vectorial Fourier metasurfaces. A series of non-conventional vectorial field distribution, mimicking cylindrical vector beams in the sense that they share the same intensity profile but with different polarization distribution and a speckled phase distribution, is demonstrated. Vectorial Fourier optical metasurfaces may enable important applications in the area of complex light beam generation, secure optical data storage, steganography and optical communications.

Scanning probe microscopic study of P(VDF-TrFE) based ferroelectric nanocomposites

Ceramic and polymer based nanocomponents combine the properties of their constituents, e.g. flexibility, elasticity, polymer reprocessability, hardness typical of glass, wear resistance and high light refraction index. This helps improving many properties of the materials in comparison with the source components. Since recently researchers have been manifesting interest to the properties of complex composite compounds. This is primarily caused by the unique properties of their structures as compared with conventional materials having homogeneous composition. Secondly, this interest is caused by the fact that these compounds may prove to be much cheaper than homogeneous structures provided the physical properties of the composite in a preset range of parameters (temperature, applied field frequency etc.) are identical to those of the respective homogeneous materials. For example, polyvinyl idenfluoride (PVDF) type ferroelectric polymers and copolymers on its basis have found wide application for functional elements of various electromechanic devices in advanced electronics due to their relatively good piezoelectric and pyroelectric properties. The strong random polarization and the formation of polar non-centrosymmetric crystals provide for the high piezoelectric and pyroelectric activity in these crystals. Scanning probe microscopy has been used for study of ferroelectric nanocomposites having different compositions. The matrix specimen for study of local polarization switching at a nanoscale level was vinyl idenfluoride and trifluoroethylene P(VDF-TrFE) copolymer possessing sufficiently high crystallinity. The composite fillers were barium titanate BaTiO3 and deuterized triglycinsulfate DTGS ferroelectric powders and zirconate-titanate lead barium BPZT ceramic powder. We show these materials to show good promise for use in memory cells.