Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSuperconducting energy gap in $rm Ba_{1-x}K_xBiO_3$: Temperature dependence
68
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The superconducting energy gap of $rm Ba_{1-x}K_xBiO_3$ has been measured by tunneling. Despite the fact that the sample was macroscopically single phase with very sharp superconducting transition $T_c$ at 32~$K$, some of the measured tunnel junctions made by point contacts between silver tip and single crystal of $rm Ba_{1-x}K_xBiO_3$ had lower transition at 20~$K$. Local variation of the potassium concentration as well as oxygen deficiency in $rm Ba_{1-x}K_xBiO_3$ at the place where the point contact is made can account for the change of $T_c$. The conductance curves of the tunnel junctions reveal the BCS behavior with a small broadening of the superconducting-gap structure. A value of the energy gap scales with $T_c$. The reduced gap amounts to $2Delta/kT_c = 4div 4.3$ indicating a medium coupling strength. Temperature dependence of the energy gap follows the BCS prediction.
rate research
Read More
The conductance curves of point-contact tunnel junctions between Ag and $rm Ba_{1-x}K_xBiO_3$ ($xsimeq 0.4$) reveal a BCS behavior with low leakage current at zero voltage and some broadening of the superconducting-gap structure. In the energy range above the superconducting energy gap, the structure in the voltage dependence of the second derivative $d^2V/dI^2$ of the voltage with respect to the current of the tunnel junction has been investigated in detail in magnetic fields up to $10 T$. While part of this structure is rapidly changing in a magnetic field, three reproducible peaks in $d^2V/dI^2(V)$ remain stable up to the transition temperature from the superconducting to the normal state with only additional broadening in the applied magnetic field. An analysis of this structure in terms of strong-coupling effects yields the spectral function $alpha^2F$ for the electron-phonon interaction. The obtained spectral weight in the energy region 20-70~$meV$ points to the importance of the oxygen optical modes in the electron-phonon coupling for the superconductivity of $rm Ba_{1-x}K_xBiO_3$.
Resolving the microscopic pairing mechanism and its experimental identification in unconventional superconductors is among the most vexing problems of contemporary condensed matter physics. We show that Raman spectroscopy provides an avenue for this quest by probing the structure of the pairing interaction at play in an unconventional superconductor. As we study the spectra of the prototypical Fe-based superconductor ${rm Ba_{1-x}K_xFe_2As_2}$ for $0.22le x le 0.70$ in all symmetry channels, Raman spectroscopy allows us to distill the leading $s$-wave state. In addition, the spectra collected in the $B_{1g}$ symmetry channel reveal the existence of two collective modes which are indicative of the presence of two competing, yet sub-dominant, pairing tendencies of $d_{x^2-y^2}$ symmetry type. A comprehensive functional Renormalization Group (fRG) and random-phase approximation (RPA) study on this compound confirms the presence of the two sub-leading channels, and consistently matches the experimental doping dependence of the related modes. The synopsis of experimental evidence and theoretical modelling supports a spin-fluctuation mediated superconducting pairing mechanism.
The precise momentum dependence of the superconducting gap in the iron-arsenide superconductor with Tc = 32K (BKFA) was determined from angle-resolved photoemission spectroscopy (ARPES) via fitting the distribution of the quasiparticle density to a model. The model incorporates finite lifetime and experimental resolution effects, as well as accounts for peculiarities of BKFA electronic structure. We have found that the value of the superconducting gap is practically the same for the inner Gamma-barrel, X-pocket, and blade-pocket, and equals 9 meV, while the gap on the outer Gamma-barrel is estimated to be less than 4 meV, resulting in 2Delta/kT_c=6.8 for the large gap, and 2Delta/kT_c<3 for the small gap. A large (77 pm 3%) non-superconducting component in the photoemission signal is observed below T_c. Details of gap extraction from ARPES data are discussed in Appendix.
We report on isofield magnetization curves obtained as a function of temperature in two single crystals of $Ba_{1-x}K_xFe_2As_2$ with superconducting transition temperature $T_c$=28K and 32.7 K. Results obtained for fields above 20 kOe show a well defined rounding effect on the reversible region extending 1-3 K above $T_c(H)$ masking the transition. This rounding appears to be due to three-dimensional critical fluctuations, as the higher field curves obey a well know scaling law for this type of critical fluctuations. We also analysed the asymptotic behavior of $sqrt M$vs.T curves in the reversible region which probes the shape of the gap near $T_c(H)$. Results of the analysis suggests that phase fluctuations are important in $Ba_{1-x}K_xFe_2As_2$ which is consistent with nodes in the gap.
Temperature and fluence dependence of the 1.55-eV optical transient reflectivity in BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ was measured and analysed in the low and high excitation density limit. The effective magnitude of the superconducting gap of $sim 5$ meV obtained from the low-fluence-data bottleneck model fit is consistent with the ARPES results for the $gamma$-hole Fermi surface. The superconducting-state nonthermal optical destruction energy was determined from the fluence dependent data. The in-plane optical destruction energy scales well with T$_{mathrm{c}}^{2}$ and is found to be similar in a number of different layered superconductors.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
