Band structure and electrical conductivity in semiconductors. In contrast to the cuprates, the bafe2as2 system appears to. Role of magnetism in superconductivity of bafe2as2 physical. The institute of physics iop is a leading scientific society promoting physics and bringing physicists together for the benefit of all.
This result indicates that small uniaxial stress along caxis strongly suppresses the structuralantiferromagnetic ordering and stabilizes superconductivity at much lower pressure. Bafe2as2 122 is a parent of fesc that transitions from the tetragonal i4mmm nonmagnetic state into the orthorhombic fmmm sdw striped. In the 1111 phase family, superconductivity is mostly induced by electron doping, i. Pressure dependence of the bafe2as2 fermi surface within. 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. The superconducting transition temperatures are up to 27 k in. Jan 11, 2016 the electrical conductivity of our bi 2 te 3 single crystal nr was also increased to 0. Highresolution measurements of the thermal expansion of.
Materials and mechanisms of superconductivity 2012, jul 2012, washington dc, united states. Superconductivity up to 29 k in srfe2as2 and bafe2as2 at. Thermal conductivity of gases chart engineers edge. A new generation of superconductors is needed with high transition temperatures but that are relatively isotropic. Electronic structure of the bafe2as2 family of iron. By performing synchrotron xray powder diffraction measurements with diamond anvil cells up to 26. Superconductivity at 38k in the iron arsenide ba1xkxfe2as2.
The notation p 0 indicates the low pressure limiting value is given. Normalstate and superconducting properties of codoped. 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. We report the discovery of superconductivity in ybdoped bafe 2 as 2.
This is the first example of superconductivity induced by electron doping in this family of materials. Request pdf superconductivity in undoped bafe2as2 by tetrahedral geometry design febased superconductors exhibit a diverse interplay between charge, orbital, and magnetic ordering14. Similar to the cuprates, superconductivity in these systems appear in proximity to magnetically ordered phases and strong magnetic fluctuations persist in paramagnetic superconductors. A comparative study on thermal conductivity of al2o3water. 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. A reassessment of the strain model of superconductivity. The electrical conductivity of al2o3 under shockcompression. B, condensed matter 8110 january 2010 with 40 reads. We report the discovery of superconductivity at high pressure in srfe2as2 and. Neutron scattering studies of some nafeas and bafe2as2. The density of states, magnetic properties, nearfermi band compositions, together with the sommerfeld coefficients.
This chart gives the thermal conductivity of gases as a function of temperature. 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. The recent discovery of superconductivity with relatively high transition temperature tc in the layered ironbased quaternary oxypnictides lao1. 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. Superconductivity in ybdoped bafe2as2 sciencedirect.
Hightemperature superconductivity in doped bafe2as2. Noncrystalline systems eg glass have much lower conductivity. A systematic characterization of codoped bafe 2 as 2 ba122 thin films has been carried out. Doping dependence of spin excitations and its correlations. Superconductivity occurs before the structural distortion of the parent compound bafe 2 as 2 x0 is completely suppressed by doping see phase diagram. These results suggest the importance of distortion of feas4 tetrahedra, in stabilizing the. More interestingly, there are no measured, significant changes in the shape of the. Two textile brands temperature40of to 212of 40oc to 100oc nonconductive nonconductive. Pressure induced superconductivity in bafe2as2feplcm.
The discovery of superconductivity in the lafeaso ref. Magnetic properties of bafe2as2 from spinspiral calculations a. Strain induced superconductivity in the parent compound. Superconductivity at 22 k in codoped bafe2as2 crystals. A model platform for unconventional superconductivity. The ternary iron arsenide bafe2as2 becomes superconducting by hole doping, which was achieved by partial substitution of the barium site with potassium. Bafe 2 as 2 has a rich and flexible materials chemistry that makes it an ideal model. Andersen the discovery of superconductivity in fdoped lafeaso 1. Superconductivity at 23 k in pt doped bafe2as2 single crystals. Pressure induced superconductivity in bafe 2as 2 single crystal awadhesh mani, nilotpal ghosh, s. Hightemperature superconductivity in iron pnictides occurs when electrons and.
Like in cuprates, hightemperature superconductivity is implemented by. Article open caxis pressureinduced antiferromagnetic order in optimally pdoped bafe 2as 0. 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. 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. 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. At ambient pressure it undergoes a phase transition from a metallic tetragonal phase to an orthorhombic antifer. For ba 1x k x fe 2 as 2 the specific heat capacity jump at t c measured over the whole extent of. 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. Neutrondiffraction measurements of magnetic order and a. Possible unconventional superconductivity in substituted. 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. Neutron and xray diffraction measurements demonstrate that, unlike for the electrondoped compounds, the structural and magnetic transitions remain coincident in temperature. Structural and superconductivity properties of bafe 2. 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.
The superconducting transition temperature for the crystals was determined by dc magnetic susceptibility measurements with a commercial squid magnetometer. Thermal properties of copper thermal conductivity of copper. The bulk materials have been prepared by the solidstate reaction method and sealed into a quartz tube. A special feature of the arsenide superconductors is that application of external pressure and iso. Since the discovery of hightemperature superconductivity hts in ironbased compounds, a variety of systems with different spacer layers have been fabricated. Layered materials are known to exhibit highly anpansions over some temperature ranges. Outline iron pnictides hightc superconductivity from itinerant or localized electrons. Bafe2as2 is structurally simple, available as highquality large crystals, can be both hole and electron doped, and is amenable to firstprinciples electronic structure calculations. Thermal conductivity was calculated based on equation 3. 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. 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. Nanofluids, thermal conductivity enhancement, al 2 o 3 cuo hybrid nanofluids 1. Superconductor science and technology paper related content.
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. However, progress has slowed in achieving highperformance 11 tapes by the pit method 23. Materials database thermal properties thermtest inc. Structural feature controlling superconductivity in. Created june 6, 2011, updated february 19, 2017 headquarters 100 bureau drive gaithersburg, md 20899. Hall data indicate that the dominant carriers are electrons, as expected from simple chemical reasoning. Superconductivity in undoped bafe2as2 by tetrahedral. 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. Bafe2as2 has a rich and flexible materials chemistry that makes it an ideal model. 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. Thermal conductivity tensor of single crystalline codoped.
Meets maximum leakage of 100 microampsft at 75 kv for 3 minutes. The crystal structure of all samples exhibited the thcr2si2type crystal structure. Two samples were available, one grown on caf 2 substrate and the other on mgo with an fe buffer layer. Feastype tetrahedral ly coordinated layers are the key structural ingredient in all iron based superconducting materials known to date. Pressuredecoupled magnetic and structural transitions of. Decoupling of the superconducting and magneticstructural.
Extraordinary magnetic behaviors, resistivity properties, and lattice parameters of the main sample bafe2as2 and bafe2. Thermal properties of aluminum liquid thermal conductivity of aluminum. Superconductivity induced by ni doping in bafe2as2 single. The pt doped system showed a domelike superconductivity region in the thermal phase diagram 0. Both the magnetic and structural transitions are gradually. Superconductivity can be induced with the application of pressure but it disappears eventually upon heavy compression in the ironbased parent compound bafe2as2. As shown in figure 1c, under an applied pressure of 5. 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. Electron irradiation of co, ni, and pdoped bafe2as2 type. Magnetic properties of bafe2as2 from spinspiral calculations. 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.
Possible unconventional superconductivity in substituted bafe 2 as. Bafe2as2 is the parent compound of a family of unconventional superconductors with critical temperatures approaching 40 k. A material with a high level of electrical conductivity, for instance, would easily accommodate the movement of an electric charge. Yanina fasano, et al electron irradiation of co, ni, and pdoped bafe2as2 type ironbased superconductors. Neutrondiffraction measurements of magnetic order and a structural transition in the parent bafe2as2 compound of feasbased hightemperature superconductors q. Here we report the interplay of magnetic and structural transitions in a parent compound of ironbased. Sglass is no longer made by agy, but used to have a reactive epoxy size. The bulk superconductivity in codoped bafe 2 as 2 below t c 22 k is demonstrated by resistivity, magnetic susceptibility, and specific heat data. Calculated conductivity of al2o3 is similar to those measured for metallic fluid h, n, o, rb, and cs.
In contrast to the cuprates, the febased system appears to tolerate considerable disorder in. Pressureinduced superconductivity in bafe2as2 single crystal. Although much attention has been focused on understanding the interplay between magnetism. Here, we experimentally demonstrate a systematic approach. The recently discovered feasbased superconductors are a new, promising set of materials for technological and basic research. Magnetic ordering and structural distortion in rudoped. Thermal and electrical conduction of singlecrystal bi 2 te 3. What controls the phase diagram and superconductivity in. Observation of the node lifting by disorder in bafe 2as,p 2 2. Febased superconductors exhibit a diverse interplay between charge, orbital, and magnetic ordering14.
Loading effect of aluminum hydroxide onto the mechanical. 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. Pdf a brief overview of changes in the superconducting transition temperature under pressure and evolution of specific heat capacity jump at tc for. Based on firstprinciple flapwgga calculations, we have investigated the electronic structure of the newly discovered oxygenfree 38k superconductor ba 1. In the past few years, the pnictides have been found as a new class of unconventional superconductors 3,7,8,9,10,11,12.
Superconducting gap symmetry in bafe 2as 2 based superconductors 1. 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. Pressure dependence of the bafe2as2 fermi surface within the. Kamihara y, watanabe t, hirano m, hosono h 2008 ironbased layered superconductor lao1xfx feas x 0. Sci china mater crystal structure and phase diagrams of ironbased superconductors xigang luo xianhui chen mater. Super conductivity can be induced by partially replacing ba by k in bafe 2as 2 to form holedoped ba 1. It has a worldwide membership of around 50 000 comprising physicists from all sectors, as well as those with an interest in physics. 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. The magnetic field in flux vortices destroys superconductivity inside them, but the regions between flux vortices retain the superconducting state. We use high resolution angleresolved photoemission to study the electronic structure of the iron based hightemperature superconductors bafe1xrux2as2 as a function of ru concentration. Bafe 2 as 2 is the parent compound of a family of unconventional superconductors with critical temperatures approaching 40 k. We find that substitution of ru for fe is isoelectronic, i. Superconductivity induced by doping platinum in bafe2as2.
However, the correlation between thermal conductivity and bulk. 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. A cartoon of magnetic flux vortices penetrating through a sample is shown in fig. The experimental thermal conductivity values were compared with the theoretical thermal conductivity values. Bafe2as2 is the parent compound of a family of unconventional superconductors with critical. Cleaved surface of bafe2as2 is as terminated ba layer destroyed, some random ba atoms observed on surface no surface reconstruction some evidence of orbital order since only one dos of one type of as was detected bulk asfe and asba interlayer distances are 1.
Medium pressure hydraulic applications where shock hazards exist and non conductivity is required. Thermal conductivity tensor has been measured using single crystalline codoped bafe 2 as 2 down to 0. Generally speaking, conductivity is the rate at which matter or energy can pass through a given material. Superconductivity in the socalled 111 phase compound lifeas with a similar structure has also been reported. Structural evolution with pressure is used to understand this behavior. Electronic structure of the bafe2as2 family of ironpnictide. We present a systematic investigation of the antiferromagnetic ordering and structural distortion for the series of bafe1. 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. 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. Superconductivity and magnetism have been considered to be in competition with each other. Both of these systems manifest substantial t c values when the structuralantiferromagnetic phase transitions are suf. A reassessment of the strain model of superconductivity and a. A small increase of t c is observed, as expected for nearly opd samples 3.
Of course, this measurement has diverse practical applications, from using. Generic sglass fiber, s2 glass and sglass have the same composition. Various silanes and starch oil are used as binders. 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. Recently, we have reported a transport j c as high as 1. Spin excitation anisotropy in the paramagnetic tetragonal. Superconductivity at 22 k in codoped bafe 2 as 2 crystals athena s. In addition, they may well provide insight into exotic superconductivity that extends beyond. At this additional transition ordered magnetic moments reorient from in. Neutron scattering is an ideal probe to study spinspin correlations and hence the interplay between magnetism and superconductivity. Improving superconductivity in bafe 2 as 2 based crystals by cobalt clustering and electronic uniformity. Evidence for signchanging gaps between hole pockets in heavily holedoped ba,kfe 2as 2.
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