90 research outputs found
Superconductivity in the Honeycomb-Lattice Pnictide SrPtAs
We report superconductivity in the honeycomb-lattice pnictide SrPtAs with Tc
= 2.4 K. To our knowledge, SrPtAs is the first superconducting pnictide with a
honeycomb lattice structure. Our finding opens up new playground to develop
pnictide superconductors with honeycomb lattices, in addition to square
lattices known in iron-based superconductors.Comment: 2 pages, 3 figure
Copper Doping of BaNiAs: Giant Phonon Softening and Superconductivity Enhancement
The effects of copper doping on the structural and superconducting phase
transitions of Ba(NiCu)As were studied by examining
the resistivity, magnetic susceptibility, and specific heat. We found an abrupt
increase in the superconducting transition temperature from 0.6 K
in the triclinic phase with less copper ( 0.16) to 2.5-3.2 K in the
tetragonal phase with more copper ( 0.16). The specific-heat data
suggested that doping-induced phonon softening was responsible for the enhanced
superconductivity in the tetragonal phase. All of these observations exhibited
striking similarities to those observed in the phosphorus doping of
BaNi(AsP) [K. Kudo et al., Phys. Rev. Lett. 109,
097002 (2012).], which markedly contrast the behavior of phosphorus and copper
doping of the iron-based superconductor BaFeAs.Comment: 5 pages, 4 figure
Suppression of Structural Phase Transition in IrTe2 by Isovalent Rh Doping
We report that the isovalent Rh doping of IrTe2 suppresses the
structural/electronic phase transition and induces superconductivity at 2.6 K.
The doping level of Rh that is necessary for suppressing the transition is
three times higher than those of Pt and Pd. Ir1-xRhxTe2 might provide us with a
unique opportunity to study the origin of the structural/electronic phase
transition in IrTe2.Comment: 6 pages, 2 figure
Superconductivity in MgPtSi: An orthorhombic variant of MgB2
A ternary compound, MgPtSi, was synthesized by solid-state reaction. An
examination of the compound by powder X-ray diffraction revealed that it
crystallizes in the orthorhombic TiNiSi-type structure with the Pnma space
group. The structure comprises alternately stacked layers of Mg and PtSi
honeycomb network, which is reminiscent of MgB2, and the buckling of the
honeycomb network causes orthorhombic distortion. Electrical and magnetic
studies revealed that MgPtSi exhibited superconductivity with a transition
temperature of 2.5 K. However, its isostructural compounds, namely, MgRhSi and
MgIrSi, were not found to exhibit superconductivity.Comment: 6 pages, 7 figures, 1 tabl
Breakdown of Chemical Scaling for Pt-Doped CaFe2As2
We report a breakdown of the scaling of the antiferromagnetic transition
temperature T_N on chemical doping for Pt-doped CaFe2As2. The substitution of
Pt is ineffective in the reduction of antiferromagnetic ordering as well as in
inducing superconductivity in Ca(Fe1-xPtx)2As2. The Pt-doped CaFe2As2 that does
not exhibit superconductivity will, however, provide us an ideal opportunity to
elucidate the role of chemical doping in the occurrence of superconductivity in
iron-based materials.Comment: 7 pages, 2 figure
Enhancing high-temperature thermoelectric properties of PtAs2 by Rh doping
The effects of Rh doping on the thermoelectric properties of Pt1-xRhxAs2 (x =
0, 0.005, and 0.01) with pyrite structure were studied by conducting
measurements of electrical resistivity rho, Seebeck coefficient S, and thermal
conductivity kappa. The sample with x = 0.005 exhibited large S and low rho,
resulting in a maximum power factor (S^2/rho) of 65 muW/cmK^2 at 440 K. The
peculiarly shaped "corrugated flat band" predicted for PtSb2 might explain the
enhanced thermoelectric properties of doped PtAs2.Comment: 3 pages, 2 figure
Large Seebeck effect in the electron-doped FeAs driven by quasi one dimensional pudding-mold type band
We investigate the thermoelectric propeties of the electron-doped FeAs
both experimentally and theoretically. Electrons are doped by partially
substituting Se for As, which leads to a metallic behavior in the resistivity.
A Seebeck coefficient of about 200 V/K is reached at 300 K for 1%
doping, and about 120 V/K even at 5% doping. The origin of this large
Seebeck coefficient despite the metallic conductivity is analyzed from a band
structure point of view. The first-principles band calculation reveals the
presence of a pudding-mold type band just above the band gap, somewhat similar
to NaCoO, but with a quasi-one-dimensional nature. We calculate the
Seebeck coefficient using a tightbinding model that correctly reproduces this
band structure, and this gives results close to the experimental observations.
The origin of this peculiar band shape is also discussed.Comment: 6 pages, 6 figure
Composition-induced structural instability and strong-coupling superconductivity in Au1-xPdxTe2
The physical properties and structural evolution of the MX-type solid
solution AuPdTe are reported. The end member AuTe is a
normal metal with a monoclinic distorted CdI-type structure with preformed
Te-Te dimers. A monoclinic--trigonal structural phase transition at a finite
temperature occurs upon Pd substitution and is suppressed to zero temperature
near = 0.55, and a superconducting phase with a maximum = 4.65
K emerges. A clear indication of strong coupling superconductivity is observed
near the composition of the structural instability. The competitive
relationship between Te-Te dimers and superconductivity is proposed.Comment: 6 pages, 8 figure
Superconducting Transition Temperatures of up to 47 K from Simultaneous Rare-Earth Element and Antimony Doping of 112-Type CaFeAs2
The effects of simultaneous Sb doping on the superconductivity of 112-type
Ca1-xRExFeAs2 (RE = La, Ce, Pr, and Nd) were studied through measurements of
the magnetization and electrical resistivity. In Sb-free materials, the
superconducting transition temperature Tc of the La-doped sample was 35 K,
while those of the Pr- and Nd-doped samples were ~10 K; no superconductivity
was observed in the Ce-doped sample. Sb doping increased the Tc of all RE-doped
samples: Tc increased to 47, 43, 43, and 43 K for RE = La, Ce, Pr, and Nd,
respectively. We also found that the enhanced superconductivity results from
the increase in the lattice parameter b, which increases the As-Fe-As bond
angle to be closer to the ideal tetrahedron value. These observations provide
insight for further increasing the Tc of the 112 phase.Comment: 4 pages, 4 figure
Pressure-Induced Superconductivity in Mineral Calaverite AuTe2
The pressure dependences of resistivity and ac susceptibility have been
measured in the mineral calaverite AuTe. Resistivity clearly shows a
first-order phase transition into a high-pressure phase, consistent with the
results of a previous structural analysis. We found zero resistivity and a
diamagnetic shielding signal at low temperatures in the high-pressure phase,
which clearly indicates the appearance of superconductivity. Our experimental
results suggest that bulk superconductivity appears only in the high-pressure
phase. For AuTe, the highest superconducting transition temperature under
pressure is = 2.3 K at 2.34 GPa; it was = 4.0 K for
Pt-doped (AuPt)Te. The difference in between
the two systems is discussed on the basis of the results obtained using the
band calculations and McMillan's formula.Comment: 5 pages, 6 figure
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