Absorption (logic)

About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.

Paramagnetic Meissner effect in high-temperature superconductors

Abstract: We have studied the low-field Meissner effect of polycrystalline Bi high-temperature superconductors using a special superconducting-quantum-interference-device magnetometer. In certain samples a surprising feature was observed: Instead of the usual diamagnetic moment a paramagnetic moment develops in the field cooling mode below ${\mathit{T}}_{\mathit{c}}$ for fields H1 Oe. The data are consistent with orbital paramagnetic moments due to spontaneous currents. Such currents may originate in so-called \ensuremath{\pi} contacts in the weak-link network of polycrystalline material. In some of these samples also an anomaly in the low-field microwave absorption was observed, which is obviously correlated with the existence of spontaneous currents.

Observation and absolute frequency measurements of the 1S0-3P0 optical clock transition in neutral ytterbium.

Abstract: We report the direct excitation of the highly forbidden $(6{s}^{2})^{1}S_{0}\ensuremath{\leftrightarrow}(6s6p)^{3}P_{0}$ optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at $\ensuremath{\sim}70\text{ }\text{ }\ensuremath{\mu}\mathrm{K}$ in a magneto-optical trap. The measured frequency in $^{171}\mathrm{Yb}$ ($\mathrm{F}=1/2$) is $518\text{ }295\text{ }836\text{ }591.6\ifmmode\pm\else\textpm\fi{}4.4\text{ }\text{ }\mathrm{kHz}$. The measured frequency in $^{173}\mathrm{Yb}$ ($\mathrm{F}=5/2$) is $518\text{ }294\text{ }576\text{ }847.6\ifmmode\pm\else\textpm\fi{}4.4\text{ }\text{ }\mathrm{kHz}$. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a ${10}^{6}$-fold reduction in uncertainty. The natural linewidth of these $J=0$ to $J=0$ transitions is calculated to be $\ensuremath{\sim}10\text{ }\text{ }\mathrm{mHz}$, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.

Soft-x-ray-absorption studies of the electronic-structure changes through the VO2 phase transition.

Abstract: We present the O 1s and V 2p absorption edges of ${\mathrm{VO}}_{2}$ at room temperature and at T=120 \ifmmode^\circ\else\textdegree\fi{}C, i.e., below and above the metal-insulator transition temperature ${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}67 \ifmmode^\circ\else\textdegree\fi{}C. The O 1s spectra show a clear splitting of 1 eV in the unoccupied ${\mathit{d}}_{\mathrm{?}}$ band below ${\mathit{T}}_{\mathit{c}}$. Because the V 2p absorption edges are dominated by the V 2p-3d interaction in the final state, these spectra show minor changes that cannot be easily correlated with the changes in the unoccupied density of states.

X-ray absorption study of the O 2p hole concentration dependence on O stoichiometry in YBa2Cu3Ox.

Abstract: A detailed x-ray absorption study of the oxygen $K$ edge of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$ is presented. A preedge peak is observed for all samples with $x\ensuremath{\ge}6.4$ which we argue to be due to holes in the $\mathrm{O} 2p$ band. By comparison to ${\mathrm{Li}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x}\mathrm{O}$ the $x$ dependence of the number $\mathrm{O} 2p$ holes in $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$ is determined.

Comprehensive analysis of intermolecular charge-transfer excited states in C 60 and C 70 films

Abstract: We have investigated intermolecular charge transfer (CT) excited states and demonstrated their contribution to the excitation-relaxation and photocarrier generation mechanisms for both ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ polycrystalline films. This has been done (1) experimentally, using UV-visible absorption (Abs) and electroabsorption (EA), luminescence and its modulation by external electric-field and steady-state photoconductivity; (2) semiempirically, analyzing the Abs and EA spectra in order to determine the CT state energies and to estimate the variation of the average polarizability tensor and the dipole moment; and (3) theoretically, by performing calculations of polarization energies and electrostatic stabilization energies. The most significant CT states have been identified at approximately 2.43 and 3.50 eV for ${\mathrm{C}}_{60}$ films and at 2.26 and 3.60 eV for ${\mathrm{C}}_{70}$ films (data from the semiempirical analysis). Their properties have been discussed in terms of crystallographic and electronic structure, with special emphasis on their mixing with Frenkel states.