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Author: Lee, B. × Has files: Yes ×

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    Tuning the interplay between nematicity and spin fluctuations in Na1-x Li x FeAs superconductors
    (London : Nature Publishing Group, 2018) Baek, S.-H.; Bhoi, D.; Nam, W.; Lee, B.; Efremov, D.V.; Büchner, B.; Kim, K.H.
    Strong interplay of spin and charge/orbital degrees of freedom is the fundamental characteristic of the iron-based superconductors (FeSCs), which leads to the emergence of a nematic state as a rule in the vicinity of the antiferromagnetic state. Despite intense debate for many years, however, whether nematicity is driven by spin or orbital fluctuations remains unsettled. Here, by use of transport, magnetization, and 75As nuclear magnetic resonance (NMR) measurements, we show a striking transformation of the relationship between nematicity and spin fluctuations (SFs) in Na1-x Li x FeAs; For x ≤ 0.02, the nematic transition promotes SFs. In contrast, for x ≥ 0.03, the system undergoes a non-magnetic phase transition at a temperature T 0 into a distinct nematic state that suppresses SFs. Such a drastic change of the spin fluctuation spectrum associated with nematicity by small doping is highly unusual, and provides insights into the origin and nature of nematicity in FeSCs.
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    A Search for QPOs in the Blazar OJ287: Preliminary Results from the 2015/2016 Observing Campaign
    (Basel : MDPI, 2016) Zola, S.; Valtonen, M.; Bhatta, G.; Goyal, A.; Debski, B.; Baran, A.; Krzesinski, J.; Siwak, M.; Ciprini, S.; Gopakumar, A.; Jermak, H.; Nilsson, K.; Reichart, D.; Matsumoto, K.; Sadakane, K.; Gazeas, K.; Kidger, M.; Piirola, V.; Alicavus, F.; Baliyan, K.; Berdyugin, A.; Boyd, D.; Campas Torrent, M.; Campos, F.; Carrillo Gómez, J.; Caton, D.; Chavushyan, V.; Dalessio, J.; Dimitrov, D.; Drozdz, M.; Er, H.; Erdem, A.; Escartin Pérez, A.; Fallah Ramazani, V.; Filippenko, A.; Garcia, F.; Gómez Pinilla, F.; Gopinathan, M.; Haislip, J.; Harmanen, J.; Hudec, R.; Hurst, G.; Ivarsen, K.; Jelinek, M.; Joshi, A.; Kagitani, M.; Kaur, N.; Keel, W.; LaCluyze, A.; Lee, B.; Lindfors, E.; Lozano de Haro, J.; Moore, J.; Mugrauer, M.; Naves Nogues, R.; Neely, A.; Nelson, R.; Ogloza, W.; Okano, S.; Pandey, J.; Perri, M.; Pihajoki, P.; Poyner, G.; Provencal, J.; Pursimo, T.; Raj, A.; Reinthal, R.; Sadegi, S.; Sakanoi, T.; Sameer, null; Salto González, J.-L.; Schweyer, T.; Soldán Alfaro, F.; Karaman, N.; Sonbas, E.; Steele, I.; Stocke, J.; Strobl, J.; Takalo, L.; Tomov, T.; Tremosa Espasa, L.; Valdes, J.; Valero Pérez, J.; Verrecchia, F.; Webb, J.; Yoneda, M.; Zejmo, M.; Zheng, W.; Telting, J.; Saario, J.; Reynolds, T.; Kvammen, A.; Gafton, E.; Karjalainen, R.; Blay, P.
    We analyse the light curve in the R band of the blazar OJ287, gathered during the 2015/2016 observing season. We did a search for quasi-periodic oscillations (QPOs) using several methods over a wide range of timescales. No statistically significant periods were found in the high-frequency domain both in the ground-based data and in Kepler observations. In the longer-period domain, the Lomb–Scargle periodogram revealed several peaks above the 99% significance level. The longest one—about 95 days—corresponds to the innermost stable circular orbit (ISCO) period of the more massive black hole. The 43-day period could be an alias, or it can be attributed to accretion in the form of a two-armed spiral wave.