X-Ray-Diffraction Study of Charge-Density-Waves and Oxygen-Ordering in YBa2Cu3O6+x Superconductor

We report a temperature-dependent increase below 300 K of diffuse superlattice peaks corresponding to q_0 =(~2/5,0,0) in an under-doped YBa_2Cu_3O_6+x superconductor (x~0.63). These peaks reveal strong c-axis correlations involving the CuO_2 bilayers, show a non-uniform increase below \~220 K with a plateau for ~100-160 K, and appear to saturate in the superconducting phase. We interpret this unconventional T-dependence of the ``oxygen-ordering'' peaks as a manifestation of a charge density wave in the CuO_2 planes coupled to the oxygen-vacancy ordering.Comment: 4 pages, 4 figure

Atom Interferometers

Interference with atomic and molecular matter waves is a rich branch of atomic physics and quantum optics. It started with atom diffraction from crystal surfaces and the separated oscillatory fields technique used in atomic clocks. Atom interferometry is now reaching maturity as a powerful art with many applications in modern science. In this review we first describe the basic tools for coherent atom optics including diffraction by nanostructures and laser light, three-grating interferometers, and double wells on AtomChips. Then we review scientific advances in a broad range of fields that have resulted from the application of atom interferometers. These are grouped in three categories: (1) fundamental quantum science, (2) precision metrology and (3) atomic and molecular physics. Although some experiments with Bose Einstein condensates are included, the focus of the review is on linear matter wave optics, i.e. phenomena where each single atom interferes with itself.Comment: submitted to Reviews of Modern Physic

Resonant nonlinear magneto-optical effects in atoms

In this article, we review the history, current status, physical mechanisms, experimental methods, and applications of nonlinear magneto-optical effects in atomic vapors. We begin by describing the pioneering work of Macaluso and Corbino over a century ago on linear magneto-optical effects (in which the properties of the medium do not depend on the light power) in the vicinity of atomic resonances, and contrast these effects with various nonlinear magneto-optical phenomena that have been studied both theoretically and experimentally since the late 1960s. In recent years, the field of nonlinear magneto-optics has experienced a revival of interest that has led to a number of developments, including the observation of ultra-narrow (1-Hz) magneto-optical resonances, applications in sensitive magnetometry, nonlinear magneto-optical tomography, and the possibility of a search for parity- and time-reversal-invariance violation in atoms.Comment: 51 pages, 23 figures, to appear in Rev. Mod. Phys. in Oct. 2002, Figure added, typos corrected, text edited for clarit

Understanding Performance Limiting Interfacial Recombination in pin Perovskite Solar Cells

Funder: Alexander von Humboldt Foundation; Id: http://dx.doi.org/10.13039/100005156Abstract: Perovskite semiconductors are an attractive option to overcome the limitations of established silicon based photovoltaic (PV) technologies due to their exceptional opto‐electronic properties and their successful integration into multijunction cells. However, the performance of single‐ and multijunction cells is largely limited by significant nonradiative recombination at the perovskite/organic electron transport layer junctions. In this work, the cause of interfacial recombination at the perovskite/C60 interface is revealed via a combination of photoluminescence, photoelectron spectroscopy, and first‐principle numerical simulations. It is found that the most significant contribution to the total C60‐induced recombination loss occurs within the first monolayer of C60, rather than in the bulk of C60 or at the perovskite surface. The experiments show that the C60 molecules act as deep trap states when in direct contact with the perovskite. It is further demonstrated that by reducing the surface coverage of C60, the radiative efficiency of the bare perovskite layer can be retained. The findings of this work pave the way toward overcoming one of the most critical remaining performance losses in perovskite solar cells

Atominterferometrie in statischen elektrischen Feldern

Using a Borde atom-interferometer with a thermal atomic calcium beam, the shift of the interference structure in electric fields was studied. From the Stark shift of the intercombination line (4s4p "3P_1 - 4s"2 "1S_0) for the #pi# and the #sigma# transition the scalar and sensor polarizability of the 4s4p "3P_1 state were calculated. The measured Aharonov-Casher effect is by a factor of 10"3 smaller than the Stark effect and its measured value is close to the theoretically derived value. It is proposed to use the Borde atom interferometer for an optical frequency standard of high stability. (WEN)Available from TIB Hannover: RA 3254(48) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Structure and magnetism of Ho0.2Ca0.8MnO3

We studied polycrystalline Ho0.2Ca0.8MnO3 by neutron and X-ray diffraction. At room temperature Ho0.2Ca0.8MnO3 crystallizes in a distorted orthorhombic perovskite-like structure. At T-C = 160(1)K we observed a structural phase transition from space group Pnma to P2(1)/m. Below T-N = 146(I)K neutron diffractograms show sharp magnetic peaks which are due to a long-range antiferromagnetic order of the magnetic moments of the Mn-ions. We describe this magnetic order in a magnetic unit cell with lattice vectors: a(mag) = a(chem), b(mag) = b(chem), c(mag) = a(chem) + c(chem), magnetic spacegroup P(2a(mag))2(1)/m. The magnetic moments of the Mn-ions are alligned in (2a(mag) - c(mag))-direction. The size of the ordered moment is proportional to the monoclinic lattice distortion. (C) 2000 Elsevier Science B.V. All rights reserved