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Register a new userSuperconductivity in Se-doped La2O2Bi2Pb2S6-xSex with a Bi2Pb2Ch4-type thick conducting layer
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Added by
Yoshikazu Mizuguchi
Publication date
2019
fields
Physics
and research's language is
English
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La2O2Bi2Pb2S6 is a layered Bi-based oxychalcogenide with a thick four-layer-type conducting layer. Although La2O2Bi2Pb2S6 is a structural analogue of La2O2Bi3AgS6, which is a superconductor, insulating behavior has been observed in La2O2Bi2Pb2S6 at low temperatures, and no superconductivity has been reported. Herein, we demonstrate superconductivity in La2O2Bi2Pb2S6-xSex via partial substitution of Se in the S sites. Owing to the Se doping, the normal state electrical resistivity of La2O2Bi2Pb2S6-xSex at low temperatures was dramatically suppressed, and superconductivity was observed at a transition temperature (Tc) of 1.15 K for x = 0.5. Tc increased with increasing Se concentration: Tc = 1.9 K for x = 1.0. The emergence of metallicity and superconductivity was explained via in-plane chemical pressure effects that can suppress local disorder and carrier localization, which are commonly observed in two-layer-type BiS2-based systems.
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We report the Se substitution effects on the crystal structure, superconducting properties, and valence states of self-doped BiCh2-based compound CeOBiS2-xSex. Polycrystalline CeOBiS2-xSex samples with x = 0-1.0 were synthesized. For x = 0.4 and 0.6, bulk superconducting transitions with a large shielding volume fraction were observed in magnetic susceptibility measurements; the highest transition temperature (Tc) was 3.0 K for x = 0.6. A superconductivity phase diagram of CeOBiS2-xSex was established based on Tc estimated from the electrical resistivity and magnetization measurements. The emergence of superconductivity in CeOBiS2-xSex was explained with two essential parameters of in-plane chemical pressure and carrier concentration, which systematically changed with increasing Se concentration.
We investigated the effects of Se substitution on the lattice constants and superconducting properties of CeO0.5F0.5Bi(S1-xSex)2. With increasing Se concentration, the a lattice constant increased, while the c lattice constant did not show any significant increase between x = 0.1 and x = 0.5. Bulk superconductivity was observed in samples with x = 0.2-0.4, and the superconducting transition temperature was the highest at x = 0.3. The obtained superconductivity phase diagram was compared to those of LaO0.5F0.5Bi(S1-xSex)2 and NdO0.5F0.5Bi(S1-xSex)2.
We have investigated Se substitution effect to superconductivity of an optimally-doped BiS2-based superconductor Eu0.5La0.5FBiS2. Eu0.5La0.5FBiS2-xSex samples with x = 0-1 were synthesized. With increasing x, in-plane chemical pressure is enhanced. For x = 0.6, 0.8, and 1, superconducting transitions with a large shielding volume fraction are observed in magnetic susceptibility measurements, and the highest Tc is 3.8 K for x = 0.8. From low-temperature electrical resistivity measurements, a zero-resistivity state is observed for all the samples, and the highest Tc is observed for x = 0.8. With increasing Se concentration, characteristics of electrical resistivity changes from semiconducting-like to metallic, suggesting that the emergence of bulk superconductivity is linked with the enhanced metallicity. A superconductivity phase diagram of the Eu0.5La0.5FBiS2-xSex superconductor is established. Temperature dependences of electrical resistivity show an anomalous two-step transition under high magnetic fields. Hence, the resistivity data are analyzed with assuming in-plane anisotropy of upper critical field.
Electron pairing in the vast majority of superconductors follows the Bardeen-Cooper-Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity is predicted in single layer graphene where the electrons pair with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing single layer graphene on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in single layer graphene. The realization of unconventional superconductivity in single layer graphene offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K.
Here we report the synthesis and superconductivity of a novel ternary compound LaPd2Bi2. Shiny plate-like single crystals of LaPd2Bi2 were first synthesized by high-temperature solution method with PdBi flux. X-ray diffraction analysis indicates that LaPd2Bi2 belongs to the primitive tetragonal CaBe2Ge2-type structure with the space group P4/nmm (No. 129), and the refined lattice parameters are a = 4.717(2) {AA}, c = 9.957(3) {AA}. Electrical resistivity and magnetic susceptibility measurements reveal that LaPd2Bi2 undergoes a superconducting transition at 2.83 K and exhibits the characteristics of type-II superconductivity. The discovery of superconductivity in LaPd2Bi2 with CaBe2Ge2-type structure may help to further understand the possible relationship between the occurrence of superconductivity and the crystal structures in 122-type materials.
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