Loading effect of aluminum hydroxide onto the mechanical. Recently, we have reported a transport j c as high as 1. Calculated conductivity of al2o3 is similar to those measured for metallic fluid h, n, o, rb, and cs. They offer transition temperatures as high as 55 k as well as essentially isotropic, and extremely large, upper, superconducting critical fields, in excess of 40 t at 20 k. The institute of physics iop is a leading scientific society promoting physics and bringing physicists together for the benefit of all. Despite different materials, pressures and temperatures, and compression techniques, both experimental and theoretical, conductivities of all these poor metals reach a common end state typical of strongscattering disordered materials. In contrast to the cuprates, the bafe2as2 system appears to. Superconductivity at 38k in the iron arsenide ba1xkxfe2as2. The discovery of the hight c iron pnictide superconductor lafeaso 1x f x 1 stimulated the search for related superconductors, and various febased systems have been found. Evidence for signchanging gaps between hole pockets in heavily holedoped ba,kfe 2as 2. Superconductivity at 22 k in codoped bafe 2 as 2 crystals athena s. Generic sglass fiber, s2 glass and sglass have the same composition. The magnetic field in flux vortices destroys superconductivity inside them, but the regions between flux vortices retain the superconducting state.
Superconducting gap symmetry in bafe 2as 2 based superconductors 1. Created june 6, 2011, updated february 19, 2017 headquarters 100 bureau drive gaithersburg, md 20899. Superconductivity in ybdoped bafe2as2 sciencedirect. Superconductivity induced by ni doping in bafe2as2 single.
This result indicates that small uniaxial stress along caxis strongly suppresses the structuralantiferromagnetic ordering and stabilizes superconductivity at much lower pressure. A model platform for unconventional superconductivity. Sundar materials science division, indira gandhi centre for atomic research kalpakkam 603102, tamilnadu, india abstract the evolution of pressure induced superconductivity in single crystal as well as. Meets maximum leakage of 100 microampsft at 75 kv for 3 minutes. A new generation of superconductors is needed with high transition temperatures but that are relatively isotropic.
Band structure and electrical conductivity in semiconductors. Under pressure, the transition temperatures in bafe2as2, are found to be a strong function of hydrostaticity of the pressure cell. Thermal conductivity was calculated based on equation 3. Extraordinary magnetic behaviors, resistivity properties, and lattice parameters of the main sample bafe2as2 and bafe2. We report the discovery of superconductivity in ybdoped bafe 2 as 2. Thermal conductivity, k 3 where t is the sample thickness m, q is the sample conductivity value w, a is the tested surface area of.
Materials and mechanisms of superconductivity 2012, jul 2012, washington dc, united states. A highpressure method was used to systematically dope an antiferromagnetically metallic compound, bafe2as2, with pt, and the doped compounds were studied using xray diffraction, energy. Electronic structure of the bafe2as2 family of iron. A material with a high level of electrical conductivity, for instance, would easily accommodate the movement of an electric charge. A reassessment of the strain model of superconductivity. The recent discovery of superconductivity with relatively high transition temperature tc in the layered ironbased quaternary oxypnictides lao1. Superconductivity up to 29 k in srfe2as2 and bafe2as2 at. The electrical conductivity of al2o3 under shockcompression.
This chart gives the thermal conductivity of gases as a function of temperature. Superconductivity induced by doping platinum in bafe2as2 by xiyu zhu, fei han, gang mu, jun tang, jing ju, katsumi tanigaki and haihu wen get pdf 863 kb. Superconductivity occurs before the structural distortion of the parent compound bafe 2 as 2 x0 is completely suppressed by doping see phase diagram. Possible unconventional superconductivity in substituted bafe 2 as. A comparative study on thermal conductivity of al2o3water.
Superconductivity in undoped bafe2as2 by tetrahedral. Since the discovery of hightemperature superconductivity hts in ironbased compounds, a variety of systems with different spacer layers have been fabricated. The discovery of hight c superconductivity in ironbased compounds, however, drastically alters this concept, as the origin of its superconductivity is closely related to magnetism of iron. Although much attention has been focused on understanding the interplay between magnetism. These results suggest the importance of distortion of feas4 tetrahedra, in stabilizing the. A systematic characterization of codoped bafe 2 as 2 ba122 thin films has been carried out. Normalstate and superconducting properties of codoped. However, progress has slowed in achieving highperformance 11 tapes by the pit method 23. Magnetic properties of bafe2as2 from spinspiral calculations. In the 1111 phase family, superconductivity is mostly induced by electron doping, i. Both of these systems manifest substantial t c values when the structuralantiferromagnetic phase transitions are suf. Here, we experimentally demonstrate a systematic approach. At this additional transition ordered magnetic moments reorient from in. Decoupling of the superconducting and magneticstructural.
A cartoon of magnetic flux vortices penetrating through a sample is shown in fig. Both the magnetic and structural transitions are gradually. Bafe2as2 has a rich and flexible materials chemistry that makes it an ideal model. We report the discovery of superconductivity at high pressure in srfe2as2 and.
Strain induced superconductivity in the parent compound. We find that substitution of ru for fe is isoelectronic, i. The ternary iron arsenide bafe2as2 becomes superconducting by hole doping, which was achieved by partial substitution of the barium site with potassium. While bafe2as2 remains metallic at all temperatures, we observe a depletion in the far infrared energy interval of the optical conductivity below tsdw, ascribed to the formation of a. Outline iron pnictides hightc superconductivity from itinerant or localized electrons. The pt doped system showed a domelike superconductivity region in the thermal phase diagram 0. Spin excitation anisotropy in the paramagnetic tetragonal. Bafe 2 as 2 is structurally simple, available as highquality large crystals, can be both hole and electron doped, and is amenable to firstprinciples electronic structure calculations. B, condensed matter 8110 january 2010 with 40 reads. Materials database thermal properties thermtest inc. Thermal conductivity of gases chart engineers edge.
For 11type, the frequency dependence of the complex conductivity can be understood as that of bcstype superconductor near the superconducting gap energy, and we estimated the superconducting gap energy to be 0. Hightemperature superconductivity in iron pnictides occurs when electrons and. Bafe2as2 is the parent compound of a family of unconventional superconductors with critical temperatures approaching 40 k. The tiny difference of hydrostaticity between the cubic anvil apparatus and modified bridgman anvil cell induces a drastic effect on the phase diagram of bafe2as2. The notation p 0 indicates the low pressure limiting value is given. The discovery of high t c superconductivity in ironbased compounds, however, drastically alters this concept, as the origin of its superconductivity is closely related to magnetism of iron. Based on firstprinciple flapwgga calculations, we have investigated the electronic structure of the newly discovered oxygenfree 38k superconductor ba 1. Noncrystalline systems eg glass have much lower conductivity. Two textile brands temperature40of to 212of 40oc to 100oc nonconductive nonconductive. The superconducting transition temperature for the crystals was determined by dc magnetic susceptibility measurements with a commercial squid magnetometer.
Pressure dependence of the bafe2as2 fermi surface within the. Andersen the discovery of superconductivity in fdoped lafeaso 1. At ambient pressure it undergoes a phase transition from a metallic tetragonal phase to an orthorhombic antifer. The bulk superconductivity in codoped bafe 2 as 2 below t c 22 k is demonstrated by resistivity, magnetic susceptibility, and specific heat data. This is the first example of superconductivity induced by electron doping in this family of materials. Feastype tetrahedral ly coordinated layers are the key structural ingredient in all iron based superconducting materials known to date. Kamihara y, watanabe t, hirano m, hosono h 2008 ironbased layered superconductor lao1xfx feas x 0. Electron irradiation of co, ni, and pdoped bafe2as2 type. Structural and superconductivity properties of bafe 2. Two samples were available, one grown on caf 2 substrate and the other on mgo with an fe buffer layer. The reason that e 2 is only visible in the cut perpendicular to the x direction is likely due to a combination of its orbital. Jan 11, 2016 the electrical conductivity of our bi 2 te 3 single crystal nr was also increased to 0. It has a worldwide membership of around 50 000 comprising physicists from all sectors, as well as those with an interest in physics.
Neutrondiffraction measurements of magnetic order and a. The terahertz and infrared spectra of the complex dynamic conductivity, as well as the temperature dependences of the density of a superconducting condensate and the electronic specific heat of superconducting bafe 1. Pressureinduced superconductivity in bafe2as2 single crystal. By performing synchrotron xray powder diffraction measurements with diamond anvil cells up to 26. Hightemperature superconductivity in doped bafe2as2. Electronic structure of the bafe2as2 family of ironpnictide.
The discovery of superconductivity in the lafeaso ref. Medium pressure hydraulic applications where shock hazards exist and non conductivity is required. Role of magnetism in superconductivity of bafe2as2 physical. The superconducting transition temperatures are up to 27 k in. The density of states, magnetic properties, nearfermi band compositions, together with the sommerfeld coefficients. Yanina fasano, et al electron irradiation of co, ni, and pdoped bafe2as2 type ironbased superconductors. Highresolution measurements of the thermal expansion of. It states that an applied electric field will continually accelerate superconducting charges and that superconducting charges will move at constant velocity in the absence of an electric field. Superconductor science and technology paper related content.
Superconductivity at 23 k in pt doped bafe2as2 single crystals. Unless otherwise noted, the values refer to a pressure of 100 kpa 1 bar or to the saturation vapor pressure if that is less than 100 kpa. Layered materials are known to exhibit highly anpansions over some temperature ranges. Pressure dependence of the bafe2as2 fermi surface within.
The bulk materials have been prepared by the solidstate reaction method and sealed into a quartz tube. In the study on their superconducting mechanism, the spins, orbitals, lattices, and their couplings, have been pointed out to have possible roles in realizing the hight c superconductivity, because they are multi. Similar to the cuprates, superconductivity in these systems appear in proximity to magnetically ordered phases and strong magnetic fluctuations persist in paramagnetic superconductors. Doping dependence of spin excitations and its correlations. However, the correlation between thermal conductivity and bulk. Improving superconductivity in bafe 2 as 2 based crystals by cobalt clustering and electronic uniformity. Superconductivity in the socalled 111 phase compound lifeas with a similar structure has also been reported. Neutron scattering is an ideal probe to study spinspin correlations and hence the interplay between magnetism and superconductivity. Neutrondiffraction measurements of magnetic order and a structural transition in the parent bafe2as2 compound of feasbased hightemperature superconductors q. Nanofluids, thermal conductivity enhancement, al 2 o 3 cuo hybrid nanofluids 1. In addition, they may well provide insight into exotic superconductivity that extends beyond. Bafe 2 as 2 is the parent compound of a family of unconventional superconductors with critical temperatures approaching 40 k. Of course, this measurement has diverse practical applications, from using.
Request pdf superconductivity in undoped bafe2as2 by tetrahedral geometry design febased superconductors exhibit a diverse interplay between charge, orbital, and magnetic ordering14. Generally speaking, conductivity is the rate at which matter or energy can pass through a given material. Hall data indicate that the dominant carriers are electrons, as expected from simple chemical reasoning. Neutron scattering studies of some nafeas and bafe2as2.
Bafe2as2 122 is a parent of fesc that transitions from the tetragonal i4mmm nonmagnetic state into the orthorhombic fmmm sdw striped. Bafe2as2 is structurally simple, available as highquality large crystals, can be both hole and electron doped, and is amenable to firstprinciples electronic structure calculations. Here we report the interplay of magnetic and structural transitions in a parent compound of ironbased. What controls the phase diagram and superconductivity in. As shown in figure 1c, under an applied pressure of 5. The experimental thermal conductivity values were compared with the theoretical thermal conductivity values. Pressuredecoupled magnetic and structural transitions of.
Observation of the node lifting by disorder in bafe 2as,p 2 2. Thermal conductivity tensor of single crystalline codoped. Thermal conductivity tensor has been measured using single crystalline codoped bafe 2 as 2 down to 0. Magnetic properties of bafe2as2 from spinspiral calculations a. For ba 1x k x fe 2 as 2 the specific heat capacity jump at t c measured over the whole extent of. The possible existence of a signchanging gap symmetry in bafe2as2derived superconductors sc has been an exciting topic of research in. Sci china mater crystal structure and phase diagrams of ironbased superconductors xigang luo xianhui chen mater. Pressure induced superconductivity in bafe 2as 2 single crystal awadhesh mani, nilotpal ghosh, s. Bafe2as2 is the parent compound of a family of unconventional superconductors with critical. In contrast to the cuprates, the febased system appears to tolerate considerable disorder in. Superconductivity at 22 k in codoped bafe2as2 crystals. More interestingly, there are no measured, significant changes in the shape of the. We present a systematic investigation of the antiferromagnetic ordering and structural distortion for the series of bafe1. Thermal properties of copper thermal conductivity of copper.
These studies point out that the thermal conductivity of bricks is mainly related to their bulk density, so that increasing the thermal insulating properties implies the production of materials with a higher porosity jungk et al. Thermal and electrical conduction of singlecrystal bi 2 te 3. Magnetic ordering and structural distortion in rudoped. Various silanes and starch oil are used as binders.
Like in cuprates, hightemperature superconductivity is implemented by. Variations in atomic geometry affect electron hopping between fe atoms5,6 and the fermi surface topology, influencing magnetic frustration and the pairing mechanism through changes of orbital overlap and occupancies711. Super conductivity can be induced by partially replacing ba by k in bafe 2as 2 to form holedoped ba 1. Article open caxis pressureinduced antiferromagnetic order in optimally pdoped bafe 2as 0. Pdf a brief overview of changes in the superconducting transition temperature under pressure and evolution of specific heat capacity jump at tc for. The recently discovered feasbased superconductors are a new, promising set of materials for technological and basic research. In the past few years, the pnictides have been found as a new class of unconventional superconductors 3,7,8,9,10,11,12. Febased superconductors exhibit a diverse interplay between charge, orbital, and magnetic ordering14.
Neutron and xray diffraction measurements demonstrate that, unlike for the electrondoped compounds, the structural and magnetic transitions remain coincident in temperature. A brief overview of changes in the superconducting transition temperature under pressure and evolution of specific heat capacity jump at t c for two related families of ironbased superconductors, ba 1x k x fe 2 as 2 0. We observe peak anomalies both in the thermal conductivity and the thermal hall conductivity in the superconducting state as an indication of enhancement of the quasiparticle meanfree path. The discovery of superconductivity with a transition temperature, tc, up to 65 k in singlelayer fese bulk tc8 k films grown on srtio3 substrates has attracted special attention to febased. Sglass is no longer made by agy, but used to have a reactive epoxy size.
Possible unconventional superconductivity in substituted. The goal was to investigate films magnetic and superconducting properties, their reciprocal interplay, and the role played by the fe buffer layer in modifying them. Pdf superconductivity induced by doping platinum in bafe2as2. The crystal structure of all samples exhibited the thcr2si2type crystal structure. Bafe 2 as 2 has a rich and flexible materials chemistry that makes it an ideal model. Structural evolution with pressure is used to understand this behavior. Superconductivity induced by doping platinum in bafe2as2. We use high resolution angleresolved photoemission to study the electronic structure of the iron based hightemperature superconductors bafe1xrux2as2 as a function of ru concentration. A small increase of t c is observed, as expected for nearly opd samples 3. Pressure induced superconductivity in bafe2as2feplcm. A special feature of the arsenide superconductors is that application of external pressure and iso. Superconductivity at 23 k in pt doped bafe2as2 single crystals s r saha 1,tdrye, k kirshenbaum1,npbutch, p y zavalij2 and johnpierre paglione1 1 center for nanophysics and advanced materials, department of physics, university of maryland, college park, md 20742, usa 2 department of chemistry and biochemistry, university of maryland, college. Thermal properties of aluminum liquid thermal conductivity of aluminum. Superconductivity can be induced with the application of pressure but it disappears eventually upon heavy compression in the ironbased parent compound bafe2as2.
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