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Register a new userSuperconductivity in Se-doped new materials EuSr2Bi2S4F4 and Eu2SrBi2S4F4
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From our powder x ray diffraction pattern, electrical transport and magnetic studies we report the effect of isovalent Se substitution at S sites in the newly discovered systems EuSr2Bi2S4F4 and Eu2SrBi2S4F4. We have synthesized two new variants of 3244 type superconductor with Eu replaced by Sr which is reported elsewhere [Z. Haque et. al.]. We observe superconductivity at Tc 2.9 K (resistivity) and 2.3 K (susceptibility) in EuSr2Bi2S4-xSexF4 series for x = 2. In the other series Eu2SrBi2S4-xSexF4, two materials (x= 1.5; Tc = 2.6 K and x = 2; Tc = 2.75 K) exhibit superconductivity.
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Insight into why superconductivity in pristine and doped monolayer graphene seems strongly suppressed has been central for the recent years various creative approaches to realize superconductivity in graphene and graphene-like systems. We provide further insight by studying electron-phonon coupling and superconductivity in doped monolayer graphene and hexagonal boron nitride based on intrinsic phonon modes. Solving the graphene gap equation using a detailed model for the effective attraction based on electron tight binding and phonon force constant models, the various system parameters can be tuned at will. Consistent with results in the literature, we find slight gap modulations along the Fermi surface, and the high energy phonon modes are shown to be the most significant for the superconductivity instability. The Coulomb interaction plays a major role in suppressing superconductivity at realistic dopings. Motivated by the direct onset of a large density of states at the Fermi surface for small charge dopings in hexagonal boron nitride, we also calculate the dimensionless electron-phonon coupling strength there, but the comparatively large density of states cannot immediately be capitalized on, and the charge doping necessary to obtain significant electron-phonon coupling is similar to the value in graphene.
A hydrostatic pressure study was made on pure and Rh-doped specimens of the superconducting ferromagnetic compounds Ru1-xRhxSr2GdCu2O8 (x = 0-0.15) by means of measurement of electrical resistivity vs temperature, in pressures up to 2 GPa. Partial substitution of Rh for Ru decreases the magnetization of the material, lowers both the magnetic ordering temperature Tm, and the superconducting transition temperature Tc, and promotes granularity. The effect of pressure for all compositions is an increase in both the intra- and intergranular superconductivity transition temperatures, Tc and Tp respectively, as well as Tm. The rate of change of each transition temperature with pressure first drops for Rh concentrations near 5%, increasing latter for higher concentrations. While the rate of increase of Tc with pressure for all compositions is 2-3 times lower than in YBCO materials, the simultaneous increase of Tc and Tm with pressure could support the notion of competition between superconductivity and ferromagnetism in these materials. The effect of pressure on the weak-links was a significant improvement of inter-granular connectivity.
Unconventional superconductivity has been discovered in a variety of doped materials, including topological insulators, semimetals and twisted bilayers. A unifying property of these systems is strong orbital hybridization, which involves pairing of states with non-trivial Bloch wave functions. In contrast to naive expectation, many of these superconductors are relatively resilient to disorder. Here we study the effects of a generic disorder on superconductivity in doped 3D Dirac systems, which serve as a paradigmatic example for the dispersion near a band crossing point. We argue that due to strong orbital hybridization, interorbital scattering processes are naturally present and must be taken into account. We calculate the reduction of the critical temperature for a variety of pairing states and scattering channels using Abrikosov-Gorkov theory. In that way, the role of disorder is captured by a single parameter $Gamma$, the pair scattering rate. This procedure is very general and can be readily applied to different band structures and disorder configurations. Our results show that interorbital scattering has a significant effect on superconductivity, where the robustness of different pairing states highly depends on the relative strength of the different interorbital scattering channels. Our analysis also reveals a protection, analogous to the Andersons theorem, of the odd-parity pairing state with total angular momentum zero (the B-phase of superfluid $^3$He). This odd-pairty state is a singlet of partners under $mathcal{CT}$ symmetry (rather than $mathcal{T}$ symmetry in the standard Andersons theory), where $mathcal{C}$ and $mathcal{T}$ are chiral and time-reversal symmetries, respectively. As a result, it is protected against any disorder potential that respects $mathcal{CT}$ symmetry, which includes a family of time-reversal odd (magnetic) impurities.
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.
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.
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