Vortex State of Tl2_2Ba2_2CuO6+δ_{6+\delta} via 205^{205}Tl NMR at 2 Tesla

We report a $^{205}$Tl NMR study of vortex state for an aligned polycrystalline sample of an overdoped high-$T_c$ superconductor Tl$_2$Ba$_2$CuO$_{6+\delta}$ ($T_{c}\sim$85 K) with magnetic field 2 T along the c axis. We observed an imperfect vortex lattice, so-called Bragg glass at $T$=5 K, coexistence of vortex solid with liquid between 10 and 60 K, and vortex melting between 65 and 85 K. No evidence for local antiferromagnetic ordering at vortex cores was found for our sample.Comment: 4 pages with 5 figure

Phase diagram of heavy fermion systems

The Meccano of heavy fermion systems is shown on different cases going from anomalous monochalcogenides to cerium intermetallic compounds with special focus on the ideal case of the CeRu2Si2 series. Discussion is made in the frame of the interplay between valence, electronic structure (Fermi surface), and magnetism. The nice tools given by the temperature, the pressure, and the magnetic field allow to explore different ground states as well as the slow downhill ''race'' before reaching a Fermi liquid finish line at very low temperature. Experimentally, the Gr"uneisen parameter i.e. the ratio of the thermal expansion by the specific heat is a coloured magic number; its temperature, pressure, and magnetic field dependence is a deep disclosure of competing hierarchies and the conversion of this adaptive matter to external responses.Comment: submitted ICM200

KIC 4150611: a rare multi-eclipsing quintuple with a hybrid pulsator

We present the results of our analysis of KIC 4150611 (HD 181469) - an interesting, bright quintuple system that includes a hybrid $\delta$ Sct/$\gamma$ Dor pulsator. Four periods of eclipses - 94.2, 8.65, 1.52 and 1.43 d - have been observed by the Kepler satellite, and three point sources (A, B, and C) are seen in high angular resolution images. From spectroscopic observations made with the HIDES spectrograph attached to the 1.88-m telescope of the Okayama Astrophysical Observatory (OAO), for the first time we calculated radial velocities (RVs) of the component B - a pair of G-type stars - and combined them with Kepler photometry in order to obtain absolute physical parameters of this pair. We also managed to directly measure RVs of the pulsator, also for the first time. Additionally, we modelled the light curves of the 1.52 and 1.43-day pairs, and measured their eclipse timing variations (ETVs). We also performed relative astrometry and photometry of three sources seen on the images taken with the NIRC2 camera of the Keck II telescope. Finally, we compared our results with theoretical isochrones. The brightest component Aa is the hybrid pulsator, transited every 94.2 days by a pair of K/M-type stars (Ab1+Ab2), which themselves form a 1.52-day eclipsing binary. The components Ba and Bb are late G-type stars, forming another eclipsing pair with a 8.65 day period. Their masses and radii are $M_{Ba}=0.894\pm0.010$ M$_\odot$, $R_{Ba}=0.802\pm0.044$ R$_\odot$ for the primary, and $M_{Bb}=0.888\pm0.010$ M$_\odot$, $R_{Bb}=0.856\pm0.038$ R$_\odot$ for the secondary. The remaining period of 1.43 days is possibly related to a faint third star C, which itself is most likely a background object. The system's properties are well-represented by a 35 Myr isochrone. There are also hints of additional bodies in the system.Comment: 14 pages, 15 figures, 7 tables, to appear in A&A, abstract modified in order to fit the arXiv limi

A Substellar Companion to the Intermediate-Mass Giant 11 Com

We report the detection of a substellar companion orbiting the intermediate-mass giant star 11 Com (G8 III). Precise Doppler measurements of the star from Xinglong station and Okayama Astrophysical Observatory (OAO) revealed Keplerian velocity variations with an orbital period of 326.03 +/- 0.32 days, a semiamplitude of 302.8 +/- 2.6 m/s, and an eccentricity of 0.231 +/- 0.005. Adopting a stellar mass of 2.7 +/- 0.3 M_solar, the minimum mass of the companion is 19.4 +/- 1.5 M_Jup, well above the deuterium burning limit, and the semimajor axis is 1.29 +/- 0.05 AU. This is the first result from the joint planet search program between China and Japan aiming at revealing statistics of substellar companions around intermediate-mass giants. 11 Com b emerged from 300 targets of the planet search program at OAO. The current detection rate of a brown dwarf candidate seems to be comparable to that around solar-type stars within orbital separations of $\sim$3 AU.Comment: 19 pages, 4 figures, accepted by Ap

Itinerant metamagnetism of CeRu2Si2 : bringing out the dead. Comparison with the new Sr3Ru2O7 case

Focus is given on the macroscopic and microscopic experimental works realized during a decade on the clear case of itinerant metamagnetism in the heavy fermion paramagnetic compound CeRu2Si2 . Emphasis is made on the feedback between the band structure, the exchange coupling and the lattice instability. Sweeps in magnetic field, pressure and temperature feel the pseudogap of this strongly correlated electronic system as well as its equivalent CeRu2Ge2 at a fictitious negative pressure. Some mysteries persist as the complete observation of the FS above the metamagnetic field HM and the detection of the dynamical ferromagnetic fluctuation near HM. The novelty of the bilayer ruthenate Sr3Ru2O7 is discussed by comparison. Despite differences in spin and electronic dimensionality many common trends emerge.Comment: 14 pages, 9 figure

A Hierarchically-Organized Phase Diagram near a Quantum Critical Point in URu2Si2

A comprehensive transport study, as a function of both temperature and magnetic field in continuous magnetic fields up to 45 T reveals that URu2Si2 possesses all the essential hallmarks of quantum criticality at temperatures above 5.5 K and fields around 38 T, but then collapses into multiple low temperature phases in a hierarchically-organized phase diagram as the temperature is reduced. Although certain generic features of the phase diagram are very similar to those in the cuprates and heavy fermion superconductors, the existence of multiple ordered hysteretic phases near the field-tuned quantum critical point is presently unique to URu2Si2. This finding suggests the existence of many competing order parameters separated by small energy difference in URu2Si2.Comment: 6 pages, twocolum texts, 3 coloured figure included, submitted to PR