Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAnisotropic resistivity of Na$_{1-delta}$Fe$_{1-x}$Co$_x$As
134
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Temperature-dependent resistivity is studied in single crystals of iron-arsenide superconductor Na$_{1-delta}$Fe$_{1-x}$Co$_x$As for electrical current directions along, $rho_a (T)$, and transverse, $rho_c (T)$, to the Fe-As layers. Doping with Co increases stability of this compound to reaction with the environment and suppresses numerous features in both $rho_a(T)$ and $rho_c(T)$ compared to the stoichiometric NaFeAs. Evolution of $rho_a (T)$ with $x$ follows a universal trend observed in other pnictide superconductors, exhibiting a $T$-linear temperature dependence close to the optimal doping and development of $T^2$ dependence upon further doping. $rho_c (T)$ in parent compound shows a non - monotonic behavior with a crossover from non-metallic resistivity increase on cooling from room temperature down to $sim$ 80 K to a metallic decrease below this temperature. Both $rho_a (T)$ and $rho_c (T)$ show several correlated crossover - like features at $T>$ 80 K. Despite a general trend towards more metallic behavior of inter - plane resistivity in Co-doped samples, the temperature of the crossover from insulating to metallic behavior (80 K) does not change much with doping.
rate research
Read More
Single crystals of Na$_{1-delta}$Fe$_{1-x}$T$_x$As with T = Co, Rh have been grown using a self-flux technique. The crystals were thoroughly characterized by powder X-ray diffraction, magnetic susceptibility and electronic transport with particular focus on the Rh-doped samples. Measurements of the specific heat and ARPES were conducted exemplarily for the optimally doped compositions. The spin-density wave transition (SDW) observed for samples with low Rh concentration ($0,leq,x,leq,0.013$) is fully suppressed in the optimally doped sample. The superconducting transition temperature ($T_c$) is enhanced from $10$~K in Na$_{1-delta}$FeAs to $21$~K in the optimally doped sample ($x$ = 0.019) of the Na$_{1-delta}$Fe$_{1-x}$Rh$_x$As series and decreases for the overdoped compounds, revealing a typical shape for the superconducting part of the electronic phase diagram. Remarkably, the phase diagram is almost identical to that of Co-doped Na$_{1-delta}$FeAs, suggesting a generic phase diagram for both dopants.
We measured the in-plane resistivity anisotropy in the underdoped Ca$_{1-x}$Na$_x$Fe$_2$As$_2$ single crystals. The anisotropy (indicated by $rho_{rm b} - rho_{rm a}$) appears below a temperature well above magnetic transition temperature $T_{rm N}$, being positive ($rho_{rm b} - rho_{rm a} > 0$) as $xleq$ 0.14. With increasing the doping level to $x$ = 0.19, an intersection between $rho_{rm b}$ and $rho_{rm a}$ is observed upon cooling, with $rho_{rm b} - rho_{rm a} < 0$ at low-temperature deep inside a magnetically ordered state, while $rho_{rm b} - rho_{rm a}> 0$ at high temperature. Subsequently, further increase of hole concentration leads to a negative anisotropy $rho_{rm b} - rho_{rm a} < 0$ in the whole temperature range. These results manifest that the anisotropic behavior of resistivity in the magnetically ordered state depends strongly on the competition of the contributions from different mechanisms, and the competition between the two contributions results in a complicated evolution of the anisotropy of in-plane resistivity with doping level.
We investigate the optical conductivity as a function of temperature with light polarized along the in-plane orthorhombic $a$- and $b$-axes of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ for $x$=0 and 2.5$%$ under uniaxial pressure. The charge dynamics at low frequencies on these detwinned, single domain compounds tracks the anisotropic $dc$ transport properties across their structural and magnetic phase transitions. Our findings allow us to estimate the dichroism, which extends to relatively high frequencies. These results are consistent with a scenario in which orbital order plays a significant role in the tetragonal-to-orthorhombic structural transition.
We report inelastic x-ray scattering measurements of the in-plane polarized transverse acoustic phonon mode propagating along $qparallel$[100] in various hole-doped compounds belonging to the 122 family of iron-based superconductors. The slope of the dispersion of this phonon mode is proportional to the square root of the shear modulus $C_{66}$ in the $q rightarrow 0$ limit and, hence, sensitive to the tetragonal-to-orthorhombic structural phase transition occurring in these compounds. In contrast to a recent report for Ba(Fe$_{0.94}$Co$_{0.06}$)$_2$As$_2$ [F. Weber et al., Phys. Rev. B 98, 014516 (2018)], we find qualitative agreement between values of $C_{66}$ deduced from our experiments and those derived from measurements of the Youngs modulus in Ba$_{1-x}$(K,Na)$_x$Fe$_2$As$_2$ at optimal doping. These results provide an upper limit of about 50 {AA} for the nematic correlation length for the optimally hole-doped compounds. Furthermore, we also studied compounds at lower doping levels exhibiting the orthorhombic magnetic phase, where $C_{66}$ is not accessible by volume probes, as well as the C4 tetragonal magnetic phase.investigated
Measurements of the current-voltage characteristics were performed on Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals with doping level $0.044 leq x leq 0.1$. An unconventional increase in the flux-flow resistivity $rho_{rm ff}$ with decreasing magnetic field was observed across this doping range. Such an abnormal field dependence of flux-flow resistivity is in contrast with the linear field dependence of $rho_{rm ff}$ in conventional type-II superconductors, but is similar to the behavior recently observed in the heavy-fermion superconductor CeCoIn$_5$. A significantly enhanced $rho_{rm ff}$ was found for the x=0.06 single crystals, implying a strong single-particle energy dissipation around the vortex cores. At different temperatures and fields and for a given doping concentration, the normalized $rho_{rm ff}$ scales with normalized field and temperature. The doping level dependence of these parameters strongly suggests that the abnormal upturn flux-flow resisitivity is likely related to the enhancement of spin fluctuations around the vortex cores of the optimally doped samples.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
