S. Aswartham

Specific heat and upper critical fields in KFe2As2 single crystals

We report low-temperature specific heat measurements for high-quality single crystalline KFe2As2 (T_c about 3.5 K). The investigated zero-field specific heat data yields an unusually large nominal Sommerfeld coefficient gamma_n of 94(3) mJ/mol K^2 which is however significantly affected by extrinsic contributions as evidenced by a sizable residual linear specific heat and various theoretical considerations including also an analysis of Kadowaki-Woods relations. Then KFe2As2 should be classified as a weak to intermediately strong coupling superconductor with a total electron-boson coupling constant lambda_tot near 1 (including a calculated weak electron-phonon coupling constant of lambda_el-ph =0.17. From specific heat and ac susceptibility studies in external magnetic fields the magnetic phase diagram has been constructed. We confirm the high anisotropy of the upper critical fields B_c2(T) ranging from a factor of 5 near T_c to a slightly reduced value approaching T=0 for fields B || ab

Strong electron pairing at the iron 3d(xz) (yz) orbitals in hole-doped BaFe2As2 superconductors revealed by angle-resolved photoemission spectroscopy

and || c and show that their ratio Gamma slightly exceeds the mass anisotropy of 4.35 derived from our full-relativistic LDA-band structure calculations. Its slight reduction when approaching T=0 is not a consequence of Pauli-limiting as in less perfect samples but point likely to a multiband effect. We also report irreversibility field data obtained from ac susceptibility measurements. The double-maximum in the T-dependence of its imaginary part for fields B || c indicates a peak-effect in the T-dependence of critical currents.

Lattice-tuned magnetism of Ru 4 + ( 4 d 4 ) ions in single crystals of the layered honeycomb ruthenates Li 2 RuO 3 and Na 2 RuO 3

D.V.Evtushinsky,1 V.B. Zabolotnyy,1 T.K.Kim,1, 2 A.A.Kordyuk,1, 3 A.N. Yaresko,4 J.Maletz,1 S.Aswartham,1 S.Wurmehl,1 A.V. Boris,4 D.L. Sun,4 C.T. Lin,4 B. Shen,5 H.H.Wen,6 A.Varykhalov,7 R.Follath,7 B.Büchner,1 and S.V.Borisenko1 Institute for Solid State Research, IFW Dresden, P.O.Box 270116, D-01171 Dresden, Germany Diamond Light Source Ltd., Didcot, Oxfordshire, OX11 0DE, United Kingdom Institute of Metal Physics of National Academy of Sciences of Ukraine, 03142 Kyiv, Ukraine Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China BESSY GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany

Electronic band structure and momentum dependence of the superconducting gap in Ca1−xNaxFe2As2 from angle-resolved photoemission spectroscopy

We synthesize and study single crystals of the layered honeycomb lattice Mott insulators Na2RuO3 and Li2RuO3 with magnetic Ru4+(4d4) ions. The newly found Na2RuO3 features a nearly ideal honeycomb lattice and orders antiferromagnetically at 30 K. Single-crystals of Li2RuO3 adopt a honeycomb lattice with either C2/m or more distorted P21/m below 300 K, depending on detailed synthesis conditions. We find that Li2RuO3 in both structures hosts a well-defined magnetic state, in contrast to the singlet ground state found in polycrystalline Li2RuO3. A phase diagram generated based on our results uncovers a new, direct correlation between the magnetic ground state and basal-plane distortions in the honeycomb ruthenates.

Local magnetic anisotropy in BaFe2As2: A polarized inelastic neutron scattering study

Iron-based high-temperature superconductors form an in-creasingly growing subject for investigation. Unlike othertypes of high-temperature superconductors, iron-based com-pounds can be synthesized in the form of various crystals, ex-hibiting a large variety of electronic band structures, magneticproperties, superconducting order parameters, and electronicproperties in general.

Critical current and vortex dynamics in single crystals of Ca ( Fe 1 − x Co x ) 2 As 2

The anisotropy of the magnetic excitations in BaFe

Evidence of d-wave superconductivity in K1-xNaxFe2As2 (x=0,0.1) single crystals from low-temperature specific-heat measurements

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Intrinsic pinning and the critical current scaling of clean epitaxial Fe(Se,Te) thin films

As

Hole doping in BaFe2As2: The case of Ba1-xNaxFe2As2 single crystals

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Flux dynamics and avalanches in the 122 pnictide superconductor Ba0.65Na0.35Fe2As2.

was studied by polarized inelastic neutron scattering which allows one to separate the components of the magnetic response. Despite the in-plane orientation of the static ordered moment we find the in-plane polarized magnons to exhibit a larger gap than the out-of-plane polarized ones indicating very strong single-ion anisotropy within the layers. It costs more energy to rotate a spin within the orthorhombic {\it a-b} plane than rotating it perpendicular to the FeAs layers.