Spin Fluctuation Induced Linear Magnetoresistance in Ultrathin Superconducting FeSe Films

The discovery of high-temperature superconductivity in FeSe/STO has trigged great research interest to reveal a range of exotic physical phenomena in this novel material. Here we present a temperature dependent magnetotransport measurement for ultrathin FeSe/STO films with different thickness and protection layers. Remarkably, a surprising linear magnetoresistance (LMR) is observed around the superconducting transition temperatures but absent otherwise. The experimental LMR can be reproduced by magnetotransport calculations based on a model of magnetic field dependent disorder induced by spin fluctuation. Thus, the observed LMR in coexistence with superconductivity provides the first magnetotransport signature for spin fluctuation around the superconducting transition region in ultrathin FeSe/STO films

Suppression of Superconductivity by Twin Boundaries in FeSe

Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate twin boundaries in stoichiometric FeSe films grown by molecular beam epitaxy. Twin boundaries can be unambiguously identified by imaging the 90{\deg} change in the orientation of local electronic dimers from Fe site impurities on either side. Twin boundaries run at approximately 45{\deg} to the Fe-Fe bond directions, and noticeably suppress the superconducting gap, in contrast with the recent experimental and theoretical findings in other iron pnictides. Furthermore, vortices appear to accumulate on twin boundaries, consistent with the degraded superconductivity there. The variation in superconductivity is likely caused by the increased Se height in the vicinity of twin boundaries, providing the first local evidence for the importance of this height to the mechanism of superconductivity.Comment: 6 pages, 7 figure

A tetra­silver(I)ditungsten(VI) cluster with sulfide and bis­(diphenyl­phosphino)methane ligands

The asymmetric unit of the title complex, [Ag4W2S8(C25H22P2)3]·2C3H7NO, tris­[μ2-bis­(diphenyl­phosphino)meth­ane]-3:6κ2 P:P′;4:5κ2 P:P′;5:6κ2 P:P′-μ5-sulfido-2:3:4:5:6κ5 S-μ3-sulfido-1:3:4κ3 S-tetra-μ2-sulfido-1:3κ2 S;1:4κ2 S;2:5κ2 S;2:6κ2 S-disulfido-1κS,2κS-tetra­silver(I)ditungsten(VI) N,N-dimethyl­formamide disolvate, contains two [WS4]2− anions, four silver cations, three bidentate–bridging bis­(diphenyl­phosphino)methane (dppm) ligands and two N,N-dimethyl­formamide (DMF) solvent mol­ecules. The coordination geometry of each Ag atom is distorted tetra­hedral. Two Ag ions are coordinated by μ2-S and μ5-S atoms, and by two P atoms from two dppm ligands, while the other two Ag atoms are coordinated by μ2-S, μ3-S and μ5-S atoms, and by one P atom from a dppm ligand

Ripple: A Distributed Medium Access Protocol for Multi-hop Wireless Mesh Networks

Abstract-Wireless mesh network, a new wireless broadband access technology, is currently attracting significant attention. This work proposes a distributed medium access protocol, named Ripple, for wireless mesh networks (WMNs) under tree topology. In contrast to existing random-access approaches, Ripple uses a controlled-access approach to protect nodes from unintentional packet collisions and maximize the spatial reuse. The performance of Ripple under an error-free channel was investigated and the accuracy of the analysis was verified by simulation. Simulation results also indicated that Ripple achieved throughput, stability, and QoS enhancement than that of 802.11 DCF under a highly loaded situation in both chain and tree topologies

Imaging the Electron-Boson Coupling in Superconducting FeSe Films Using a Scanning Tunneling Microscope

Scanning tunneling spectroscopy has been used to reveal signatures of a bosonic mode in the local quasiparticle density of states of superconducting FeSe films. The mode appears below Tc as a “dip-hump” feature at energy Ω∼4.7kBTc beyond the superconducting gap Δ. Spectra on strained regions of the FeSe films reveal simultaneous decreases in Δ and Ω. This contrasts with all previous reports on other high-Tc superconductors, where Δ locally anticorrelates with Ω. A local strong coupling model is found to reconcile the discrepancy well, and to provide a unified picture of the electron-boson coupling in unconventional superconductors.Physic