Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userStrong- to weak-coupling superconductivity in high-$T_c$ bismuthates: revisiting the phase diagram via $mu$SR
204
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Several decades after the discovery of superconductivity in bismuthates, the strength of their electron-phonon coupling and its evolution with doping remain puzzling. To clarify these issues, polycrystalline hole-doped Ba$_{1-x}$K$_{x}$BiO$_3$ ($0.1 le x le 0.6$) samples were systematically synthesized and their bulk- and microscopic superconducting properties were investigated by means of magnetic susceptibility and muon-spin rotation/relaxation ($mu$SR), respectively. The phase diagram of Ba$_{1-x}$K$_{x}$BiO$_3$ was reliably extended up to $x = 0.6$, which is still found to be a bulk superconductor. The lattice parameter $a$ increases linearly with K-content, implying a homogeneous chemical doping. The low-temperature superfluid density, measured via transverse-field (TF)-$mu$SR, indicates an isotropic fully-gapped superconducting state with zero-temperature gaps $Delta_0/k_mathrm{B}T_c$ = 2.15, 2.10, and 1.75, and magnetic penetration depths $lambda_0$ = 219, 184, and 279 nm for $x$ = 0.3, 0.4, and 0.6, respectively. A change in the superconducting gap, from a nearly ideal BCS value (1.76 $k_mathrm{B}$$T_c$ in the weak coupling case) in the overdoped $x$ = 0.6 region, to much higher values in the optimally-doped case, implies a gradual decrease in electron-phonon coupling with doping.
rate research
Read More
We present the numerical solution of the renormalization group (RG) equations derived in Ref. [1], for the problem of superconductivity in the presence of both electron-electron and electron-phonon coupling at zero temperature. We study the instability of a Fermi liquid to a superconductor and the RG flow of the couplings in presence of retardation effects and the crossover from weak to strong coupling. We show that our numerical results provide an ansatz for the analytic solution of the problem in the asymptotic limits of weak and strong coupling.
We propose that Resistivity Curvature Mapping (RCM) based on the in-plane resistivity data is a useful way to objectively draw an electronic phase diagrams of high-T_c cuprates, where various crossovers are important. In particular, the pseudogap crossover line can be conveniently determined by RCM. We show experimental phase diagrams obtained by RCM for Bi_{2}Sr_{2-z}La_{z}CuO_{6+delta}, La_{2-x}Sr_{x}CuO_{4}, and YBa_{2}Cu_{3}O_{y}, and demonstrate the universal nature of the pseudogap crossover. Intriguingly, the electronic crossover near optimum doping depicted by RCM appears to occur rather abruptly, suggesting that the quantum critical regime, if exists, must be very narrow.
We use neutron scattering to study the structural and magnetic phase transitions in the iron pnictides CeFeAsO1-xFx as the system is tuned from a semimetal to a high-transition-temperature (high-Tc) superconductor through Fluorine (F) doping x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a stripe like commensurate antiferromagnetic order with decreasing temperature. With increasing Fluorine doping, the structural phase transition decreases gradually while the antiferromagnetic order is suppressed before the appearance of superconductivity, resulting an electronic phase diagram remarkably similar to that of the high-Tc copper oxides. Comparison of the structural evolution of CeFeAsO1-xFx with other Fe-based superconductors reveals that the effective electronic band width decreases systematically for materials with higher Tc. The results suggest that electron correlation effects are important for the mechanism of high-Tc superconductivity in these Fe pnictides.
We have constructed a pressure$-$temperature ($P-T$) phase diagram of $P$-induced superconductivity in EuFe$_2$As$_2$ single crystals, via resistivity ($rho$) measurements up to 3.2 GPa. As hydrostatic pressure is applied, an antiferromagnetic (AF) transition attributed to the FeAs layers at $T_mathrm{0}$ shifts to lower temperatures, and the corresponding resistive anomaly becomes undetectable for $P$ $ge$ 2.5 GPa. This suggests that the critical pressure $P_mathrm{c}$ where $T_mathrm{0}$ becomes zero is about 2.5 GPa. We have found that the AF order of the Eu$^{2+}$ moments survives up to 3.2 GPa without significant changes in the AF ordering temperature $T_mathrm{N}$. The superconducting (SC) ground state with a sharp transition to zero resistivity at $T_mathrm{c}$ $sim$ 30 K, indicative of bulk superconductivity, emerges in a pressure range from $P_mathrm{c}$ $sim$ 2.5 GPa to $sim$ 3.0 GPa. At pressures close to but outside the SC phase, the $rho(T)$ curve shows a partial SC transition (i.e., zero resistivity is not attained) followed by a reentrant-like hump at approximately $T_mathrm{N}$ with decreasing temperature. When nonhydrostatic pressure with a uniaxial-like strain component is applied using a solid pressure medium, the partial superconductivity is continuously observed in a wide pressure range from 1.1 GPa to 3.2 GPa.
We employ the weak-coupling renormalization group approach to study unconventional superconducting phases emerging in the extended, repulsive Hubbard model on paradigmatic two-dimensional lattices. Repulsive interactions usually lead to higher-angular momentum Cooper pairing. By considering not only longer-ranged hoppings, but also non-local electron-electron interactions, we are able to find superconducting solutions for all irreducible representations on the square and hexagonal lattices, including extended regions of chiral topological superconductivity. For the square, triangular and honeycomb lattices, we provide detailed superconducting phase diagrams as well as the coupling strengths which quantify the corresponding critical temperatures depending on the bandstructure parameters, band filling, and interaction parameters. We discuss the sensitivity of the method with respect to the numerical resolution of the integration grid and the patching scheme. Eventually we show how to efficiently reach a high numerical accuracy.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
