Fine structure of alpha decay in odd nuclei

Using an alpha decay level scheme, an explanation for the fine structure in odd nuclei is evidenced by taking into account the radial and rotational couplings between the unpaired nucleon and the core of the decaying system. It is stated that the experimental behavior of the alpha decay fine structure phenomenon is directed by the dynamical characteristics of the system.Comment: 8 pages, 3 figures, REVTex, submitted to Physical Review

Raman light scattering study and microstructural analysis of epitaxial films of the electron-doped superconductor La_{2-x}Ce_{x}CuO_{4}

We present a detailed temperature-dependent Raman light scattering study of optical phonons in molecular-beam-epitaxy-grown films of the electron-doped superconductor La_{2-x}Ce_{x}CuO_{4} close to optimal doping (x ~ 0.08, T_c = 29 K and x ~ 0.1, T_c = 27 K). The main focus of this work is a detailed characterization and microstructural analysis of the films. Based on micro-Raman spectroscopy in combination with x-ray diffraction, energy-dispersive x-ray analysis, and scanning electron microscopy, some of the observed phonon modes can be attributed to micron-sized inclusions of Cu_{2}O. In the slightly underdoped film (x ~ 0.08), both the Cu_{2}O modes and others that can be assigned to the La_{2-x}Ce_{x}CuO_{4} matrix show pronounced softening and narrowing upon cooling below T ~ T_c. Based on control measurements on commercial Cu_{2}O powders and on a comparison to prior Raman scattering studies of other high-temperature superconductors, we speculate that proximity effects at La_{2-x}Ce_{x}CuO_{4}/Cu_{2}O interfaces may be responsible for these anomalies. Experiments on the slightly overdoped La_{2-x}Ce_{x}CuO_{4} film (x ~ 0.1) did not reveal comparable phonon anomalies.Comment: 7 pages, 8 figure

Superconductivity and Pseudogap in Quasi-Two-Dimensional Metals around the Antiferromagnetic Quantum Critical Point

Spin fluctuations (SF) and SF-mediated superconductivity (SC) in quasi-two-dimensional metals around the antiferrromagnetic (AF) quantum critical point (QCP) are investigated by using the self-consistent renormalization theory for SF and the strong coupling theory for SC. We introduce a parameter y0 as a measure for the distance from the AFQCP which is approximately proportional to (x-xc), x being the electron (e) or hole (h) doping concentration to the half-filled band and xc being the value at the AFQCP. We present phase diagrams in the T-y0 plane including contour maps of the AF correlation length and AF and SC transition temperatures TN and Tc, respectively. The Tc curve is dome-shaped with a maximum at around the AFQCP. The calculated one-electron spectral density shows a pseudogap in the high-density-of-states region near (pi,0) below around a certain temperature T* and gives a contour map at the Fermi energy reminiscent of the Fermi arc. These results are discussed in comparison with e- and h-doped high-Tc cuprates.Comment: 5 pages, 3 figure

Anomalous electronic structure and pseudogap effects in Nd_1.85Ce_0.15CuO_4

We report a high-resolution angle-resolved photoemission spectroscopic (ARPES) study of the electron-doped (n-type) cuprate superconductor Nd_1.85Ce_0.15CuO_4. We observe regions along the Fermi surface where the near-E_F intensity is suppressed and the spectral features are broad in a manner reminiscent of the high-energy ``pseudogap'' in the underdoped p-type (hole doped) cuprates. However, instead of occurring near the (pi, 0) region, as in the p-type materials, this pseudogap falls near the intersection of the underlying Fermi surface with the antiferromagnetic Brillouin zone boundary.Comment: 5 pages, 3 figures, RevTex, submitted Phys. Rev. Lett. December 21, 200

Evidence for Different Freeze-Out Radii of High- and Low-Energy Pions Emitted in Au+Au Collisions at 1 GeV/nucleon

Double differential production cross sections of negative and positive pions and the number of participating protons have been measured in central Au+Au collisions at 1 GeV per nucleon incident energy. At low pion energies the pi^- yield is strongly enhanced over the pi^+ yield. The energy dependence of the pi^-/pi^+ ratio is assigned to the Coulomb interaction of the charged pions with the protons in the reaction zone. The deduced Coulomb potential increases with increasing pion c.m. energy. This behavior indicates different freeze-out radii for different pion energies in the c.m.~frame.Comment: IKDA is the Institute for Nuclear Physics in Darmstadt/German

Evidence for a Soft Nuclear Equation-of-State from Kaon Production in Heavy Ion Collisions

The production of pions and kaons has been measured in Au+Au collisions at beam energies from 0.6 to 1.5 AGeV with the Kaon Spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is enhanced in Au+Au collisions by factors up to 6 relative to C+C reactions whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.Comment: 14 pages, 2 figures, accepted for publication in Phys. Rev. Let

Strength of Correlations in electron and hole doped cuprates

High temperature superconductivity was achieved by introducing holes in a parent compound consisting of copper oxide layers separated by spacer layers. It is possible to dope some of the parent compounds with electrons, and their physical properties are bearing some similarities but also significant differences from the hole doped counterparts. Here, we use a recently developed first principles method, to study the electron doped cuprates and elucidate the deep physical reasons why their behavior is so different than the hole doped materials. We find that electron doped compounds are Slater insulators, e.g. a material where the insulating behavior is the result of the presence of magnetic long range order. This is in sharp contrast with the hole doped materials, where the parent compound is a Mott charge transfer insulator, namely a material which is insulating due to the strong electronic correlations but not due to the magnetic order.Comment: submitted to Nature Physic

Production of Charged Pions, Kaons and Antikaons in Relativistic C+C and C+Au Collisions

Production cross sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating nucleon M(pi+)/A_part is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the Au target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating nucleon M(K+)/A_part are independent of the target size at 1 AGeV and at 1.8 AGeV. The K- multiplicity per participating nucleon M(K-)/A_part is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K mesons are neglected.Comment: 19 pages, 14 figures, accepted for publication in Eur. Phys. J.

Cortical miR-709 links glutamatergic signaling to NREM sleep EEG slow waves in an activity-dependent manner.

MicroRNAs (miRNAs) are key post-transcriptional regulators of gene expression that have been implicated in a plethora of neuronal processes. Nevertheless, their role in regulating brain activity in the context of sleep has so far received little attention. To test their involvement, we deleted mature miRNAs in post-mitotic neurons at two developmental ages, i.e., in early adulthood using conditional Dicer knockout (cKO) mice and in adult mice using an inducible conditional Dicer cKO (icKO) line. In both models, electroencephalographic (EEG) activity was affected and the response to sleep deprivation (SD) altered; while the rapid-eye-movement sleep (REMS) rebound was compromised in both, the increase in EEG delta (1 to 4 Hz) power during non-REMS (NREMS) was smaller in cKO mice and larger in icKO mice compared to controls. We subsequently investigated the effects of SD on the forebrain miRNA transcriptome and found that the expression of 48 miRNAs was affected, and in particular that of the activity-dependent miR-709. In vivo inhibition of miR-709 in the brain increased EEG power during NREMS in the slow-delta (0.75 to 1.75 Hz) range, particularly after periods of prolonged wakefulness. Transcriptome analysis of primary cortical neurons in vitro revealed that miR-709 regulates genes involved in glutamatergic neurotransmission. A subset of these genes was also affected in the cortices of sleep-deprived, miR-709-inhibited mice. Our data implicate miRNAs in the regulation of EEG activity and indicate that miR-709 links neuronal activity during wakefulness to brain synchrony during sleep through the regulation of glutamatergic signaling