Journals
2016 EN
Yu. G. Naidyuk · G. Fuchs · D. A. Chareev
+1 more
Rise in superconducting critical temperature Tc more than two times(exceeding 20 K) is discov- ered in point-contacts created betweeniron-chalcogenide FeSe single crystal and Cu. The possible reasons of such Tcincrease in point-contacts are discussed. The most probable cause for this maybe the interfacial carriers doping and/or interfacial enhanced electron-phononinteraction.
American Physical Society
Journals
2016 EN
M. AbdelHafiez · Y. J. Pu · Jérémy Brisbois
+7 more
A comprehensive study of the doping dependence of the phase diagram of FeSe-based superconductors is still required due to the lack of a clean and systematic means of doping control. Here, we report on the magneto-optical imaging, thermodynamic and transport properties, as well as in situ angle-resolved photoemission spectroscopy (ARPES) studies of impurity scattering in stoichiometric FeSe single crystals. Co doping at the Fe site is found to decrease the superconducting transition temperature $({T}_{c})$. The upper critical field and specific heat all indicate a possible multiband superconductivity with strong coupling in the Co-doped system. A remarkable feature in FeSe is that its temperature dependent resistivity exhibits a wide hump at high temperatures, a signature of a crossover from a semiconductinglike behavior to metallic behavior. A structural tetragonal-to-orthorhombic phase transition $({T}_{s})$ (a consequence of the electronic nematicity) is suppressed by either physical or chemical pressures. Due to the reconstruction of the Fermi surface at ${T}_{s}$, specific heat anomalies at ${T}_{s}$ present $\mathrm{\ensuremath{\Delta}}{C}_{p}/{T}_{s}\ensuremath{\approx}{\ensuremath{\gamma}}_{n}$, being ${\ensuremath{\gamma}}_{n}$ the Sommerfield coefficient at low temperature. This reflect an additional electronic instability in the ${\mathrm{FeSe}}_{1\ensuremath{-}x}{\mathrm{S}}_{x}$ system. ARPES data between 180 and 282 K indicates the existence of a chemical potential shift with increasing thermal excitations, resulting in a change of the Fermi-surface topology and exhibiting a semimetal behavior. We found that the temperature-induced Lifshitz transition is much higher than the temperature for the nematic order.
American Physical Society
Journals
2016 EN
D. I. Badrtdinov · O. S. Volkova · A. A. Tsirlin
+3 more
We study electronic and magnetic properties of the quasi-one-dimensionalspin-1/2 magnet Ba3Cu3Sc4O12 with a distinct orthogonal connectivity of CuO4plaquettes. An effective low-energy model taking into account spin-orbitcoupling was constructed by means of first-principles calculations. On thisbasis a complete microscopic magnetic model of Ba3Cu3Sc4O12, includingsymmetric and antisymmetric anisotropic exchange interactions, is derived. Theanisotropic exchanges are obtained from a distinct first-principles numericalscheme combining, on one hand, the local density approximation taking intoaccount spin-orbit coupling, and, on the other hand, projection procedure alongwith the microscopic theory by Toru Moriya. The resulting tensors of thesymmetric anisotropy favor collinear magnetic order along the structural chainswith the leading ferromagnetic coupling J1 = -9.88 meV. The interchaininteractions J8 = 0.21 meV and J5 = 0.093 meV are antiferromagnetic. QuantumMonte Carlo simulations demonstrated that the proposed model reproduces theexperimental Neel temperature, magnetization and magnetic susceptibility data.The modeling of neutron diffraction data reveals an important role of thecovalent Cu-O bonding in Ba3Cu3Sc4O12.
American Physical Society
Journals
2016 EN
J. Werner · C. Koo · R. Klingeler
+5 more
The magnetic phase diagram and low-energy magnon excitations of structurallyand magnetically chiral MnSb2O6 are reported. The specific heat and the staticmagnetization are investigated in magnetic fields up to 9 and 30 T,respectively, while the dynamicmagnetic properties are probed by X-band as wellas tunable high-frequency electron spin-resonance spectroscopy. Below TN = 11.5K, we observe antiferromagnetic resonance modes which imply small but finiteplanar anisotropy showing up in a zero-field splitting of 20 GHz. The data arewell described by means of an easy-plane two-sublattice model with theanisotropy field BA = 0.02 T. The exchange field BE = 13 T is obtained from thesaturation field derived from the pulsed-field magnetization. A crucial role ofthe small anisotropy for the spin structure is reflected by competingantiferromagnetic phases appearing, at T = 2 K, in small magnetic fields at BC1$\approx$ 0.5 T and BC2 = 0.9 T. We discuss the results in terms of spinreorientation and of small magnetic fields favoring helical spin structure overthe cycloidal ground state which, at B = 0, is stabilized by the planaranisotropy. Above TN, short-range magnetic correlations up to >=60 K andmagnetic entropy changes well above TN reflect the frustrated triangulararrangement of Mn2+ ions in MnSb2O6.
American Physical Society
Journals
2016 EN
V. V. Rylkov · S. N. Nikolaev · K. Yu. Chernoglazov
+9 more
We present results of experimental studies of structural, magneto-transportand magnetic properties of CoFe-B-Al-O films deposited onto a glass ceramicsubstrate by the ion-beam sputtering of the target composed of Co40Fe40B20 andAl2O3 plates. The system consists on the strained crystalline CoFe metallicnanogranules with the size 2-5 nm which are embedded into the B-Al-O oxideinsulating matrix. Our investigations are focused on the anomalous Hall effect(AHE) resistivity Rh and longitudinal resistivity R at T=5-200 K on themetallic side of metal-insulator transition in samples with the metal contentx=49-56 at.%, that nominally corresponds to (Co40Fe40B20)x(Al2O3)100-x in theformula approximation. The conductivity at T > 15 K follows the lnT behaviorthat matches a strong tunnel coupling between nanogranules. It is shown thatthe scaling power-laws between AHE resistivity and longitudinal resistivitystrongly differ, if temperature T or metal content x are variable parameters:Rh(T)~R(T)^0.4-0.5 obtained from the temperature variation of R and Rh at fixedx, while Rh(x)/x~R(x)^0.24, obtained from measurements at the fixed lowtemperature region (10-40 K) for samples with different x. We qualitativelydescribe our experimental data in the frame of phenomenological model of twosources of AHE e.m.f. arising from metallic nanogranules and insulatingtunneling regions, respectively, at that the tunneling AHE (TAHE) source isstrongly shunted due to generation of local circular Hall currents. We considerour experimental results as the first experimental proof of the TAHEmanifestation.
American Physical Society
Journals
2016 EN
A. A. Sinchenko · P. D. Grigoriev · A. P. Orlov
+5 more
The cuprates and iron-based high-temperature superconductors share manycommon features: layered strongly anisotropic crystal structure, strongelectronic correlations, interplay between different types of electronicordering, the intrinsic spatial inhomogeneity due to doping. The understandingof complex interplay between these factors is crucial for a directed search ofnew high-temperature superconductors. Here we show the appearance ofinhomogeneous gossamer superconductivity in bulk FeSe compound at ambientpressure and at temperature 5 times higher than its zero-resistance $T_c$. Thisdiscovery helps to understand numerous remarkable superconducting properties ofFeSe. We also find and prove a general property: if inhomogeneoussuperconductivity in a anisotropic conductor first appears in the form ofisolated superconducting islands, it reduces electric resistivityanisotropically with maximal effect along the least conducting axis. This givesa simple and very general tool to detect inhomogeneous superconductivity inanisotropic compounds, which is critically important to study the onset ofhigh-temperature superconductivity.
American Physical Society
Journals
2016 EN
V. Gnezdilov · Yu. Pashkevich · V. Kurnosov
+6 more
We performed Raman studies and a dielectric characterization of thepseudo-kagome Cu3Bi(SeO3)2O2X (X = Cl, Br). These compounds share competingnearest-neighbour ferromagnetic exchange and frustrating next-nearest-neighbourantiferromagnetic exchange as well as highly noncollinear magnetic groundstate. However, at low temperature they differ with respect to the existence ofinversion symmetry. For both compounds there exists a pronounced interplay ofpolar phonon modes with quantum magnetic fluctuations. A novel Raman modeappears for temperatures below the Neel temperature with a Fano lineshape andan enormous intensity that exceeds most of the phonon lines. We discuss apossible contribution of longitudinal magnons to this signal. In contrast, onemagnon scattering based on linear transvers magnons is excluded based on asymmetry analysis of spin wave representations and Raman tensor calculations.There exists evidence that in these pseudo-kagome compounds magnetic quantumfluctuations carry an electric dipole moment. Our data as well as a comparisonwith previous far-infrared spectra allow us to conclude that Cu3Bi(SeO3)2O2Clchanges its symmetry most likely from Pmmn to P21mn with a second orderstructural phase transition at T*=120 K and becomes multiferroic.Cu3Bi(SeO3)2O2Br represents an interesting counter part as it does not showthis instability and stays inversion symmetric down to lowest temperatures,investigated.
American Physical Society
Journals
2016 EN
STAR Collaboration · L. Adamczyk · J. K. Adkins
+332 more
Elliptic flow (v_2) values for identified particles at midrapidity in Au + Aucollisions measured by the STAR experiment in the Beam Energy Scan at theRelativistic Heavy Ion Collider at sqrt{s_{NN}}= 7.7--62.4 GeV are presentedfor three centrality classes. The centrality dependence and the data atsqrt{s_{NN}}= 14.5 GeV are new. Except at the lowest beam energies we observe asimilar relative v_2 baryon-meson splitting for all centrality classes which isin agreement within 15% with the number-of-constituent quark scaling. Thelarger v_2 for most particles relative to antiparticles, already observed forminimum bias collisions, shows a clear centrality dependence, with the largestdifference for the most central collisions. Also, the results are compared withA Multiphase Transport Model and fit with a Blast Wave model.
American Physical Society
Journals
2016 EN
STAR Collaboration · L. Adamczyk · J. K. Adkins
+328 more
We report on the measurement of $\rm{J}/\psi$ production in the dielectronchannel at mid-rapidity (|y|$ from the measured $\rm{J}/\psi$ invariant cross section inp+p and d+Au collisions are evaluated and compared to similar measurements atother collision energies. The nuclear modification factor for $\rm{J}/\psi$ isextracted as a function of $p_{T}$ and collision centrality in d+Au andcompared to model calculations using the modified nuclear Parton DistributionFunction and a final-state $\rm{J}/\psi$ nuclear absorption cross section.
American Physical Society
Journals
2016 EN
STAR Collaboration · B. Abelev · L. Adamczyk
+333 more
We present measurements of the near-side of triggered di-hadron correlationsusing neutral strange baryons ($\Lambda$, $\bar{\Lambda}$) and mesons ($K^0_S$)at intermediate transverse momentum (3 $<$ $p_T$ $<$ 6 GeV/$c$) to look forpossible flavor and baryon/meson dependence. This study is performed in $d$+Au,Cu+Cu and Au+Au collisions at $\sqrt{s_{{NN}}}$ = 200 GeV measured by the STARexperiment at RHIC. The near-side di-hadron correlation contains twostructures, a peak which is narrow in azimuth and pseudorapidity consistentwith correlations due to jet fragmentation, and a correlation in azimuth whichis broad in pseudorapidity. The particle composition of the jet-likecorrelation is determined using identified associated particles. The dependenceof the conditional yield of the jet-like correlation on the trigger particlemomentum, associated particle momentum, and centrality for correlations withunidentified trigger particles are presented. The neutral strange particlecomposition in jet-like correlations with unidentified charged particletriggers is not well described by PYTHIA. However, the yield of unidentifiedparticles in jet-like correlations with neutral strange particle triggers isdescribed reasonably well by the same model.
American Physical Society