Developing Teaching Adaptability in Pre-service Teachers using Practice-Based Teacher Education

The purpose of this study was to examine how pre-service teachers (PSTs) develop their teaching adaptive competence through teaching rehearsal and repeated teaching, which is one of the focused teacher education strategies in practice-based teacher education (PBTE). This study was conducted in an introductory teaching methods course of a physical education teacher education (PETE) program. A total of 22 PSTs participated in the study. Fourteen were male, and eight were female. The PSTs had varied coaching experiences ranging from little to no coaching in limited recreational sports settings, and none had teaching or coaching experience in the school setting. A total of 150 lesson plans (three different lesson plans per PST that were revised across five weeks) and 85 teaching videos (five peer-teaching sessions) were collected and analyzed to examine PSTs’ adaptive competence in the lesson plans and enacted teachings. First, PSTs’ lesson plans were analyzed by the total number of adaptations, the number of adaptations to each Core Practice, and the number of types of adaptations. Second, PSTs’ teaching videos were explored by the number of adaptations (add and miss), and errors. Last, it was examined whether there are relationships between PSTs’ teaching adaptations demonstrated in lesson plans and errors in enacted teaching. The results showed that PSTs created a wide-ranged number of adaptations to lesson plan one to three (lesson plan one [Median=38.50, range 6-101]; two [Median=49.00, range 14-184]; three [Median=38.00, range 18-97]). The PSTs made the most adaptations to Core Practice two (providing clear instruction) followed by one (establishing rules and routine) and five (building positive relationships with students); minimum adaptations were made to Core Practices three (breaking down the content into smaller elements) and four (checking students’ understanding). Also, the majority of teaching adaptations made by PSTs were type two (refine) adaptations, and a minimal number of teaching adaptations were made for types one (modify) and three (apply). Relative to teaching, the results showed that PSTs were able to make teaching adaptations (add and miss) in enacted teaching that was not on their lesson plans, and PSTs showed fewer errors in enacted teaching as they progressed from week one to five. Last, Spearman’s rho analysis showed that there were no relationships between PSTs’ adaptations to their lesson plans and errors in enacted teaching. Preservice teachers developed their teaching adaptive competence in lesson plans and enacted teaching through teaching rehearsals and repeated teaching in authentic settings with the use of teaching scenarios, quality supervisors’ feedback, and structured reflection. In conclusion, PBTE is an effective framework for promoting PSTs’ teaching adaptive competence in lesson planning and enacted teaching

Using electron irradiation to probe iron - based superconductors

High energy electron irradiation is an efficient way to create vacancy-interstitial Frenkel pairs in crystal lattice, thereby inducing controlled non-magnetic point - like scattering centers. In combination with London penetration depth and resistivity measurements, the irradiation was particularly useful as a phase - sensitive probe of the superconducting order parameter in iron - based superconductors lending strongest support to sign - changing $s_{\pm}$ pairing. Here we review the key results on the effect of electron irradiation in iron-based superconductors

Energy Gap Evolution Across the Superconductivity Dome in Single Crystals of (Ba1−x_{1-x}Kx_x)Fe2_2As2_2

The mechanism of unconventional superconductivity in iron-based superconductors (IBSs) is one of the most intriguing questions in current materials research. Among non-oxide IBSs, (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ has been intensively studied because of its high superconducting transition temperature and fascinating evolution of the superconducting gap structure from being fully isotropic at optimal doping ($x\approx$0.4) to becoming nodal at $x >$0.8. Although this marked evolution was identified in several independent experiments, there are no details of the gap evolution to date because of the lack of high-quality single crystals covering the entire K-doping range of the superconducting dome. We conducted a systematic study of the London penetration depth, $\lambda (T)$, across the full phase diagram for different concentrations of point-like defects introduced by 2.5 MeV electron irradiation. Fitting the low-temperature variation with the power law, $\Delta \lambda \sim T^{n}$, we find that the exponent $n$ is the highest and $T_c$ suppression rate with disorder is the smallest at optimal doping, and they evolve with doping being away from optimal, which is consistent with increasing gap anisotropy, including an abrupt change around $x\simeq 0.8$, indicating the onset of nodal behavior. Our analysis using a self-consistent $t$-matrix approach suggests the ubiquitous and robust nature of s$_{\pm}$ pairing in IBSs and argues against a previously suggested transition to a $d-$wave state near $x=1$ in this system

Intermediate scattering potential strength in electron-irradiated YBa2Cu3O7−δ\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-\delta} from London penetration depth measurements

Temperature-dependent London penetration depth, $\lambda(T)$, of a high quality optimally-doped $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-\delta}$ single crystal was measured using tunnel-diode resonator. Controlled artificial disorder was induced at low-temperature of 20~K by 2.5 MeV electron irradiation at accumulating large doses of $3.8\times10^{19}$ and $5.3\times10^{19}$ electrons per $\textrm{cm}^{2}$. The irradiation caused significant suppression of the superconductor's critical temperature, $T_{c}$, from 94.6 K to 90.0 K, and then to 78.7 K, respectively. The low-temperature behavior of $\lambda\left(T\right)$ evolves from a $T-$linear in pristine state to a $T^{2}-$behavior after the irradiation, expected for a line-nodal $d-$wave superconductor. However, the original theory that explained such behavior had assumed a unitary limit of the scattering potential, whereas usually in normal metals and semiconductors, Born scattering is sufficient to describe the experiment. To estimate the scattering potential strength, we calculated the normalized superfluid density, $\rho_{s}\left(t=T/T_{c}\right)=\lambda^{2}\left(0\right)/\lambda^{2}\left(t\right)$, varying the amount and the strength of non-magnetic scattering using a self-consistent $t-$matrix theory. Fitting the obtained curves to a power-law, $\rho_{s}=1-Rt^{n}$, and to a polynomial, $\rho_{s}=1-At-Bt^{2}$, and comparing the coefficients $n$ in one set, and $A$ and $B$ in another with the experimental values, we estimate the phase shift to be around 70$^{\circ}$ and 65$^{\circ}$, respectively. We correlate this result with the evolution of the density of states with non-magnetic disorder

Ion-selective scattering studied by the variable-energy electron irradiation of Ba0.2_{0.2}K0.8_{0.8}Fe2_2As2_2 superconductor

Low-temperature variable-energy electron irradiation was used to induce non-magnetic disorder in a single crystal of hole-doped iron-based superconductor, Ba$_{1-x}$K$_x$Fe$_2$As$_2$, $x=$0.80. To avoid systematic errors, the beam energy was adjusted non-consequently for five values between 1.0 and 2.5 MeV, whence sample resistance was measured in-situ at 22 K. For all energies, the resistivity raises linearly with the irradiation fluence suggesting the creation of uncorrelated dilute point-like disorder (confirmed by simulations). The rate of the resistivity increase peaks at energies below 1.5 MeV. Comparison with calculated partial cross-sections points to the predominant creation of defects in the iron sublattice. Simultaneously, superconducting $T_c$, measured separately between the irradiation runs, is monotonically suppressed as expected since it depends on the total scattering rate, hence total cross-section, which is a monotonically increasing function of energy. Our work confirms experimentally an often-made assumption of the dominant role of the iron sub-lattice in iron-based superconductors

Effect of controlled point-like disorder induced by 2.5 MeV electron irradiation on nematic resistivity anisotropy of hole-doped (Ba,K)Fe2_2As2_2

In-plane anisotropy of electrical resistivity was studied in samples of the hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ in the composition range $0.21 \leq x \leq 0.26$ where anisotropy changes sign. Low-temperature ($\sim$20~K) irradiation with relativistic 2.5 MeV electrons was used to control the level of disorder and residual resistivity of the samples. Modification of the stress-detwinning technique enabled measurements of the same samples before and after irradiation, leading to conclusion of anisotropic character of predominantly inelastic scattering processes. Our main finding is that the resistivity anisotropy is of the same sign irrespective of residual resistivity, and remains the same in the orthorhombic $C_2$ phase above the re-entrant tetragonal transition. Unusual $T$-linear dependence of the anisotropy $\Delta \rho \equiv \rho_a(T)-\rho_b(T)$ is found in pristine samples with $x=$0.213 and $x=$0.219, without similar signatures in either $\rho_a(T)$ or $\rho_b(T)$. We show that this feature can be reproduced by a phenomenological model of R.~M.~Fernandes {\it et al.} Phys. Rev. Lett. {\bf 107},217002 (2011). We speculate that onset of fluctuations of nematic order on approaching the instability towards the re-entrant tetragonal phase contributes to this unusual dependence