اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدIr d-band Derived Superconductivity in the Lanthanum-Iridium System LaIr3
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The electronic properties of the heavy metal superconductor LaIr3 are reported. The estimated superconducting parameters obtained from physical properties measurements indicate that LaIr3 is a BCS-type superconductor. Electronic band structure calculations show that Ir d- states dominate the Fermi level. A comparison of electronic band structures of LaIr3 and LaRh3 shows that the Ir-compound has a strong spin-orbit-coupling effect, which creates a complex Fermi surface.
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We have studied the superconducting properties of LaIr$_3$ with a rhombohedral structure using magnetization, heat capacity, and muon-spin rotation/relaxation ($mu$SR) measurements. The zero-field cooled and field cooled susceptibility measurements e
xhibit a superconducting transition below $T_{mathrm{C}}$ = 2.5 K. Magnetization measurements indicate bulk type-II superconductivity with upper critical field $mu_0H_{mathrm{c2}}(0)$ = 3.84 T. Two successive transitions are observed in heat capacity data, one at $T_{mathrm{C}}$ = 2.5 K and a second at 1.2 K below $T_{mathrm{C}}$ whose origin remain unclear. The heat capacity jump reveals $Delta C$/$gamma T_{mathrm{C}} sim$ 1.0 which is lower than 1.43 expected for BCS weak coupling limit. Transverse field-$mu$SR measurements reveal a fully gapped $s-$wave superconductivity with 2$Delta(0)/k_{mathrm{B}}T_{mathrm{C}}$ = 3.31, which is small compared to BCS value 3.56, suggesting weak coupling superconductivity. Moreover the study of the temperature dependence of the magnetic penetration depth estimated using the transverse field-$mu$SR measurements gives a zero temperature value of the magnetic penetration depth $lambda_{mathrm{L}}(0)$ = 386(3) nm, superconducting carrier density $n_{mathrm{s}}$ = 2.9(1) $times$10$^{27}$ carriers $m^{-3}$ and the carriers effective-mass enhancement $m^{*}$ = 1.53(1) $m_{mathrm{e}}$. Our zero-field-$mu$SR measurements do not reveal the spontaneous appearance of an internal magnetic field below the transition temperature, which indicates that time-reversal symmetry is preserved in the superconducting state of LaIr$_3$.
Polycrystalline sample of superconducting ThIr$_{3}$ was obtained by arc-melting Th and Ir metals. Powder x-ray diffraction revealed that the compound crystalizes in a rhombohedral crystal structure (R-3m, s.g. no. 166) with the lattice parameters: a
= 5.3394(1) $r{A}$ and c = 26.4228(8) $r{A}$. Normal and superconducting states were studied by magnetic susceptibility, electrical resistivity and heat capacity measurements. The results showed that ThIr$_{3}$ is a type II superconductor (Ginzburg-Landau parameter $kappa$ = 38) with the critical temperature T$_{c}$ = 4.41 K. The heat capacity data yielded the Sommerfeld coefficient $gamma$ = 17.6 mJ mol$^{-1}$ K$^{-2}$ and the Debye temperature $Theta_{D}$ = 169 K. The ratio $Delta$C / ($gamma$ T$_{c}$) = 1.6, where $Delta$C stands for the specific heat jump at T$_{c}$, and the electron-phonon coupling constant $lambda_{e-p}$ = 0.74 suggest that ThIr$_{3}$ is a moderate-strength superconductor. The experimental studies were supplemented by band structure calculations, which indicated that the superconductivity in ThIr$_{3}$ is governed mainly by 5d states of iridium. The significantly smaller band-structure value of Sommerfeld coefficient as well as the experimentally observed quadratic temperature dependence of resistivity and enhanced magnetic susceptibility suggest presence of electronic interactions in the system, which compete with superconductivity.
Here we report the synthesis and discovery of superconductivity in a novel ternary iridium-arsenide compound BaIr2As2. The polycrystalline BaIr2As2 sample was synthesized by a high temperature and high pressure method. Crystal structural analysis ind
icates that BaIr2As2 crystallizes in the ThCr2Si2-type layered tetragonal structure with space group I4/mmm (No. 139), and the lattice parameters were refined to be a = 4.052(9) {AA} and c = 12.787(8) {AA}. By the electrical resistivity and magnetic susceptibility measurements we found type-II superconductivity in the new BaIr2As2 compound with a Tc (critical temperature) of 2.45 K, and an upper critical field u0Hc2(0) about 0.2 T. Low temperature specific heat measurements gave a Debye temperature about 202 K and a distinct specific jump with delta Ce/{gamma}Tc = 1.36, which is close to the value of BCS weak coupling limit and confirms the bulk superconductivity in this new BaIr2As2 compound.
The effects of lithium absorption on the crystal structure and electronic properties of IrSi3, a binary silicide with a noncentrosymmetric crystal structure, were studied. X-ray and neutron diffraction experiments revealed that hexagonal IrSi3 (space
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Polyhydrides offer intriguing perspectives as high-temperature superconductors. Here we report the high-pressure synthesis of a series of lanthanum-yttrium ternary hydrides: cubic hexahydride $(La,Y)H_{6}$ with a critical temperature $T_{C}$ = 237 +/
- 5 K and decahydrides $(La,Y)H_{10}$ with a maximum $T_{C}$ ~${253 K}$ and an extrapolated upper critical magnetic field $B_{C2(0)}$ up to ${135 T}$ at 183 GPa. This is one of the first examples of ternary high-$T_{C}$ superconducting hydrides. Our experiments show that a part of the atoms in the structures of recently discovered ${Im3m}$-$YH_{6}$ and ${Fm3m}$-$LaH_{10}$ can be replaced with lanthanum (~70 %) and yttrium (~25 %), respectively, with a formation of unique ternary superhydrides containing incorporated $La@H_{24}$ and $Y@H_{32}$ which are specific for ${Im3m}$-$LaH_{6}$ and ${Fm3m}$-$YH_{10}$. Ternary La-Y hydrides were obtained at pressures of 170-196 GPa via the laser heating of $P6_{3}$${/mmc}$ lanthanum-yttrium alloys in the ammonia borane medium at temperatures above 2000 K. A novel tetragonal $(La,Y)H_{4}$ was discovered as an impurity phase in synthesized cubic $(La,Y)H_{6}$. The current-voltage measurements show that the critical current density $J_{C}$ in $(La,Y)H_{10}$ may exceed $2500 A/mm^{2}$ at 4.2 K, which is comparable with that for commercial superconducting wires such as ${NbTi}$, $Nb_{3}$${Sn}$. Hydrides that are unstable in a pure form may nevertheless be stabilized at relatively low pressures in solid solutions with superhydrides having the same structure.
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