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Orbital tomography for highly symmetric adsorbate systems¹
by B. Stadtmüller, M. Willenbockel, E. M. Reinisch, T. Ules, F. C. Bocquet, S. Soubatch, P. Puschnig, G. Koller, M. G. Ramsey, F. S. Tautz

Orbital tomography is a new and very powerful tool to analyze the angular distribution of a photoemission spectroscopy experiment. It was successfully used for organic adsorbate systems to identify (and consequently deconvolute) the contributions of specific molecular orbitals to the photoemission data. The technique was so far limited to surfaces with low symmetry like fcc(110) oriented surfaces, owing to the small number of rotational domains that occur on such surfaces. In this letter we overcome this limitation and present an orbital tomography study of a 3,4,9,10-perylene-tetra-carboxylic-dianhydride (PTCDA) monolayer film adsorbed on Ag(111). Although this system exhibits twelve differently oriented molecules, the angular resolved photoemission data still allow a meaningful analysis of the different local density of states and reveal different electronic structures for symmetrically inequivalent molecules. We also discuss the precision of the orbital tomography technique in terms of counting statistics and linear regression fitting algorithm. Our results demonstrate that orbital tomography is not limited to low-symmetry surfaces, a finding which makes a broad field of complex adsorbate systems accessible to this powerful technique.

Sub-Doppler laser cooling of fermionic 40K atoms in three-dimensional gray optical molasses²
by D. Rio Fernandes, F. Sievers, N. Kretzschmar, S. Wu, C. Salomon and F. Chevy

We demonstrate sub-Doppler cooling of ⁴⁰K on the D₁ atomic transition. Using a gray-molasses scheme, we efficiently cool a compressed cloud of 6.5 x 10⁸ atoms from ∼ 4 mK to 20 µK in 8 ms. After transfer to a quadrupole magnetic trap, we measure a phase space density of ∼ 10^-5. This technique offers a promising route for fast evaporation of fermionic ⁴⁰K.

Double mid-latitude dynamical reconnection at the magnetopause: An efficient mechanism allowing solar wind to enter the Earth’s magnetosphere³
by M. Faganello, F. Califano, F. Pegoraro and T. Andreussi

Three-dimensional simulations of the Kelvin-Helmholtz (KH) instability in a magnetic configuration reproducing typical conditions at the flank Earth’s magnetosphere during northward periods show the system’s ability to generate favorable conditions for magnetic reconnection to occur at mid-latitude. Once these conditions are established, magnetic reconnection proceeds spontaneously in both hemispheres generating field lines that close on Earth but are connected to the solar wind at low latitude, allowing direct entrance of solar wind plasma into the magnetosphere. These results are consistent with recent observations of KH vortices showing the signature of reconnection events occurring well outside the equatorial plane (Bavassano M. B. et al., Ann. Geophys., 28 (2010) 893).

Evidence for nodeless superconducting gap in NaFe1−xCoxAs from low-temperature thermal conductivity measurements⁴
by S. Y. Zhou, X. C. Hong, X. Qiu, B. Y. Pan, Z. Zhang, X. L. Li, W. N. Dong, A. F. Wang, X. G. Luo, X. H. Chen and S. Y. Li

The thermal conductivity of optimally doped NaFe_0.972Co_0.028As (Tc ∼ 20 K) and overdoped NaFe_0.925Co_0.075As (Tc ∼ 11 K) single crystals were measured down to 50 mK. No residual linear term κ₀/T is found in zero magnetic field for both compounds. Applying a field H = 3 T (≈H_c2/12) does not noticeably increase κ₀/T in NaFe_1.972Co_0.028As. The κ₀/T of overdoped NaFe_1.925Co_0.075As shows a field dependence similar to the optimally doped BaFe_1.85Co_0.15As₂. All these results suggest nodeless superconducting gaps in NaFe_1-xCo_xAs from the optimal doping to the overdoped regime, with low anisotropy or ratio between the magnitudes of different gaps.

1. B. Stadtmüller, M. Willenbockel, E. M. Reinisch, T. Ules, F. C. Bocquet, S. Soubatch, P. Puschnig, G. Koller, M. G. Ramsey, F. S. Tautz. 2012. Orbital tomography for highly symmetric adsorbate systems. EPL, 100, 260008. DOI: 10.1209/0295-5075/100/26008 [↩]
2. D. Rio Fernandes, F. Sievers, N. Kretzschmar, S. Wu, C. Salomon and F. Chevy. 2012. Sub-Doppler laser cooling of fermionic 40K atoms in three-dimensional gray optical molasses. EPL, 100, 63001. DOI: 10.1209/0295-5075/100/63001 [↩]
3. M. Faganello, F. Califano, F. Pegoraro and T. Andreussi. 2012.Double mid-latitude dynamical reconnection at the magnetopause: An efficient mechanism allowing solar wind to enter the Earth’s magnetosphere. EPL, 100, 63001. DOI: 10.1209/0295-5075/100/69001 [↩]
4. S. Y. Zhou, X. C. Hong, X. Qiu, B. Y. Pan, Z. Zhang, X. L. Li, W. N. Dong, A. F. Wang, X. G. Luo, X. H. Chen and S. Y. Li. 2013.Evidence for nodeless superconducting gap in NaFe1−xCoxAs from low-temperature thermal conductivity measurements. EPL, 101, 17007. DOI: 10.1209/0295-5075/101/17007 [↩]

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