Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTemperature-dependent $s_pm leftrightarrow s_{++}$ transitions in the multiband model for Fe-based superconductors with impurities
148
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We study the dependence of the superconducting gaps on both the disorder and the temperature within the two-band model for iron-based materials. In the clean limit, the system is in the $s_pm$ state with the sign-changing gaps. Scattering by nonmagnetic impurities leads to the change of sign of the smaller gap thus resulting in a transition from the $s_{pm}$ to the $s_{++}$ state with the sign-preserving gaps. We show here that the transition is temperature-dependent, thus, there is a line of $s_pm to s_{++}$ transition in the temperature-disorder phase diagram. There exists a narrow range of impurity scattering rates, where the disorder-induced $s_pm to s_{++}$ transition occurs at low temperatures, but then the low-temperature $s_{++}$ state transforms back to the $s_pm$ state at higher temperatures. With increasing impurity scattering rate, temperature of such $s_{++} to s_{pm}$ transition shifts to the critical temperature $T_c$ and only the $s_{++}$ state is left for higher amount of disorder.
rate research
Read More
Irradiation of superconductors with different particles is one of many ways to investigate effects of disorder. Here we study the disorder-induced transition between $s_pm$ and $s_{++}$ states in two-band model for Fe-based superconductors with nonmagnetic impurities. Specifically, the important question of whether the superconducting gaps during the transition change smoothly or steeply? We show that the behavior can be of either type and is controlled by the ratio of intra- and interband impurity scattering and a parameter $sigma$ that represents a scattering strength and changes from zero (Born approximation) to one (unitary limit). For the pure interband scattering potential and $sigma lesssim 0.11$, the $s_pm to s_{++}$ transition is accompanied by the steep behavior of gaps, while for larger values of $sigma$, gaps change smoothly. The steep behavior of the gaps occurs at low temperatures, $T < 0.1 T_{c0}$, otherwise it is smooth. The critical temperature $T_c$ is always a smooth function of the scattering rate in spite of the steep changes in the behavior of the gaps.
Disorder - impurities and defects violating an ideal order - is always present in solids. It can result in interesting and sometimes unexpected effects in multiband superconductors. Especially if the superconductivity is unconventional thus having other than the usual s-wave symmetry. This paper uses the examples of iron-based pnictides and chalcogenides to examine how both nonmagnetic and magnetic impurities affect superconducting states with $s_pm$ and $s_{++}$ order parameters. We show that disorder causes the transitions between $s_pm$ and $s_{++}$ states and examine observable effects these transitions can produce.
The $s_pm$ and $s_{++}$ models for the superconducting state are subject of intense studies regarding Fe-based superconductors. Depending on the parameters, disorder may leave intact or suppress $T_c$ in these models. Here we study the special case of disorder with equal values of intra- and interband impurity potentials in the two-band $s_pm$ and $s_{++}$ models. We show that this case can be considered as an isolated point and $T_c$ there has maximal damping for a wide range of parameters.
We report theoretical and experimental studies of the effect of Zn-impurity in Fe-based superconductors. Zn-impurity is expected to severely suppress sign reversed s$_pm$ wave pairing. The experimentally observed suppression of T$_c$ under Zn-doping strongly depends on the materials and the charge carrier contents, which suggests competition of $s_{++}$ and $s_{pm}$ pairings in Fe-base superconductors. We study a model incorporating both $s_{++}$ and $s_{pm}$ pairing couplings by using Bogoliubov de-Gennes equation, and show that the Zn-impurity strongly suppresses $s_{pm}$ pairing and may induce a transition from $s_{pm}$ to $s_{++}$-wave. Our theory is consistent with various experiments on the impurity effect. We present new experimental data on the Zn-doping SmFe$_{1-x}$Zn$_x$AsO$_{0.9}$F$_{0.1}$ of T$_c=$ 50K, in further support of our proposal.
The determination of the most appropriate starting point for the theoretical description of Fe-based materials hosting high temperature superconductivity remains among the most important unsolved problem in this relatively new field. Most of the work to date has focused on the pnictides, with LaFeAsO, BaFe2As2 and LiFeAs being representative parent compounds of three families known as 1111, 122 and 111, respectively. This Topic Review examines recent progress in this area, with particular emphasis on the implication of experimental data which have provided evidence for the presence of electron itinerancy and the detection of local spin moments. In light of the results presented, the necessity of a theoretical framework contemplating the presence and the interplay between itinerant electrons and large spin moments is discussed. It is argued that the physics at the heart of the macroscopic properties of pnictides Fe-based high temperature superconductors appears to be far more complex and interesting than initially predicted.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
