Ultrafast Enhancement of Ferromagnetism via Photoexcited Holes in GaMnAs

We report on the observation of ultrafast photo-enhanced ferromagnetism in GaMnAs. It is manifested as a transient magnetization increase on a 100-ps time scale, after an initial sub-ps demagnetization. The dynamic magnetization enhancement exhibits a maximum below the Curie temperature Tc and dominates the demagnetization component when approaching Tc. We attribute the observed ultrafast collective ordering to the p-d exchange interaction between photoexcited holes and Mn spins, leading to a correlation-induced peak around 20K and a transient increase in Tc.Comment: 4 page

Inter nos: Between us

In the Anthropocene, the human epoch, humans have become increasingly disconnected from their natural environment. People have forgotten that they are a part of nature’s ecosystems and depend on them for their survival. The very act of breathing depends entirely on plants producing oxygen. Darrin Qualman suggests that nature’s cyclical processes of production, in which everything is transformed and recycled so that nothing is wasted, have been replaced with linear ones that rely largely on fossil fuels, which has led to oceans full of plastics and other objects that take centuries to decompose (2019, 6-10). This shift to linear systems of production has encouraged the human race to see themselves as separate and above non-human life. Inter nos: Between us explores interconnectivity and the spaces between industry and ecology in the Anthropocene through transdisciplinary knowledge and interactivity. The juxtaposition of plants living within the oil drums speaks to the traditional binary framework in which ecology and industry are opposed as well as the tangled and complicated history between them. The delicate patterns cut into the oil drums reference the parallels between the structural binaries supporting the oppression of women and those supporting the exploitation of nature. Bio-sonification acts as reminder of our connection to non-human life around us by transforming the invisible life force of the plant, which is influenced by its environment, into something that can be experienced audibly, creating a relationship between human and plant life. This relationship encourages the viewer to consider their influence on their immediate environment and their responsibility to care for and maintain it in the Anthropocene

Strong Electronic Correlation Effects in Coherent Multidimensional Nonlinear Optical Spectroscopy

We discuss a many−body theory of the coherent ultrafast nonlinear optical response of systems with a strongly correlated electronic ground state that responds unadiabatically to photoexcitation. We introduce a truncation of quantum kinetic density matrix equations of motion that does not rely on an expansion in terms of the interactions and thus applies to strongly correlated systems. For this we expand in terms of the optical field, separate out contributions to the time−evolved many−body state due to correlated and uncorrelated multiple optical transitions, and use “Hubbard operator” density matrices to describe the exact dynamics of the individual contributions within a subspace of strongly coupled states, including “pure dephasing”. Our purpose is to develop a quantum mechanical tool capable of exploring how, by coherently photoexciting selected modes, one can trigger nonlinear dynamics of strongly coupled degrees of freedom. Such dynamics could lead to photoinduced phase transitions. We apply our theory to the nonlinear response of a two−dimensional electron gas (2DEG) in a magnetic field. We coherently photoexcite the two lowest Landau level (LL) excitations using three time−delayed optical pulses. We identify some striking temporal and spectral features due to dynamical coupling of the two LLs facilitated by inter−Landau−level magnetoplasmon and magnetoroton excitations and compare to three−pulse four−wave−mixing (FWM) experiments. We show that these features depend sensitively on the dynamics of four−particle correlations between an electron−hole pair and a magnetoplasmon/magnetoroton, reminiscent of exciton−exciton correlations in undoped semiconductors. Our results shed light into unexplored coherent dynamics and relaxation of the quantum Hall system (QHS) and can provide new insight into non−equilibrium co−operative phenomena in strongly correlated systems

Anionic Complexes of Nickel(II)

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PENINGKATAN HASIL BELAJAR MENULIS PANTUN PADA SISWA KELAS IV SDN 037 SABANG BANDUNG MELALUI MODEL THINK TALK WRITE (TTW)

Problems in making rhymes sometimes occur in several public elementary schools in Bandung in the academic year 2019/2020. Based on observations and interviews with teachers conducted by researchers in fourth-grade students SDN 037 Negeri Sabang found that there is a low motivation to learn students seen from the inactivity of students asking questions when given the opportunity to ask questions by the teacher; Researchers set problem-solving with the TTW learning model to solve problems in the learning process of writing rhymes for fourth-grade students of SDN 037 Sabang. The purpose of this research is by choosing the TTW model because the TTW model helps students to understand the subject matter through direct learning using the TTW model so that students are able to carry out the stages of thinking and noting the unknowns correctly, discussing in groups, and writing rhymes. The research method used in this research is a descriptive qualitative method. The results of this study in the form of the application of the Think Talk Write (TTW) learning model helped students in fourth-grade students in SDN 037 Sabang Bandung in completing their poetry writing assignments and helped students in fourth-grade students in SDN 037 Sabang Bandung in thinking (think) and communicating with friends (talk ), teachers, and even with themselves in producing work in the form of poetry writing skills (write)

The Implementation of HOTS-based ESCOTING (Relay Writing and Collaborative Writing) Model in Writing Fable at a Primary School

Language skills are the most important part of language learning at primary schools that need to be taken seriously. If not, then this results in low writing skills of students in expressing ideas in writing. So, students' thinking skills or what so-called Higher Order Thinking Skills (HOTS) are essential to be developed by teachers through learning. This study aims to determine the implementation of the HOTS-based ESCOTING model in writing skills of fables at primary school level. The method used was a pre-experimental research design with a single treatment design (one-shot case study). The sample used in this study was 23 second-grade students of a primary school in Bandung. The results showed that there was a significant increase in student learning outcomes in writing skills. From these results it can be concluded that the implementation of the HOTS-based ESCOTING model can be used as a solution by the teacher to develop students' writing skills, especially in writing fables for the second-grade students

High-temperature terahertz optical diode effect without magnetic order in polar FeZnMo3_3O8_8

We present a terahertz spectroscopic study of polar ferrimagnet FeZnMo$_3$O$_8$. Our main finding is a giant high-temperature optical diode effect, or nonreciprocal directional dichroism, where the transmitted light intensity in one direction is over 100 times lower than intensity transmitted in the opposite direction. The effect takes place in the paramagnetic phase with no long-range magnetic order in the crystal, which contrasts sharply with all existing reports of the terahertz optical diode effect in other magnetoelectric materials, where the long-range magnetic ordering is a necessary prerequisite. In \fzmo, the effect occurs resonantly with a strong magnetic dipole active transition centered at 1.27 THz and assigned as electron spin resonance between the eigenstates of the single-ion anisotropy Hamiltonian. We propose that the optical diode effect in paramagnetic FeZnMo$_3$O$_8$ is driven by signle-ion terms in magnetoelectric free energy

Observation of inter-Landau-level quantum coherence in semiconductor quantum wells

Using three-pulse four-wave-mixing femtosecond spectroscopy, we excite a non-radiative coherence between the discrete Landau levels of an undoped quantum well and study its dynamics. We observe quantum beats that reflect the time evolution of the coherence between the two lowest Landau level magnetoexcitons. We interpret our observations using a many-body theory and find that the inter Landau level coherence decays with a new time constant, substantially longer than the corresponding interband magnetoexciton dephasing times. Our results indicate a new intraband excitation dynamics that cannot be described in terms of uncorrelated interband excitations.Comment: 5 pages, 5 figures, to appear in Phys. Rev. B Rapid Communication