8 research outputs found
Femtosecond phononic coupling to both spins and charges in a room-temperature antiferromagnetic semiconductor
No full textSpintronics is postulated on the possibility to employ the magnetic degree of freedom of electrons for computation and couple it to charges. In this view the combination of the high frequency of spin manipulations offered
by antiferromagnets, with the wide tunability of the electronic properties peculiar of semiconductors, provides
a promising and intriguing platform. Here we explore this scenario in α-MnTe, which is a semiconductor
antiferromagnetically ordered at room temperature. Relying on a Raman mechanism and femtosecond laser
pulses, we drive degenerate modes of coherent optical phonons, which modulate the chemical bonds involved
in the superexchange interaction. The spectrally resolved measurements of the transient reflectivity reveal a
coherent modulation of the band gap at the frequency of 5.3 THz. The detection of the rotation of the polarization,
typically associated with magneto-optical effects, shows coherent and incoherent contributions. Modeling how
the ionic motion induced by the phonons affects the exchange interaction in the material, we calculate the
photoinduced THz spin dynamics: the results predict both a coherent and incoherent response, the latter of which
is consistent with the experimental observation. Our work demonstrates that the same phonon modes modulate
both the charge and magnetic degree of freedom, suggesting the resonant pumping of phonons as a viable way
to link spin and charge dynamics even in nonlinear regimes
Wide spectral range ultrafast pump–probe magneto-optical spectrometer at low temperature, high-magnetic and electric fields
No full textExchange-mediated magnetic blue-shift of the band-gap energy in the antiferromagnetic semiconductor MnTe
No full textIn magnetic semiconductors the optical spectrum and, in particular, the absorption edge representing the band-gap are strongly affected by the onset of the magnetic order. This contribution to the band-gap energy has hitherto been described theoretically in terms of a Heisenberg Hamiltonian, in which a delocalized conduction carrier is coupled to the localized magnetic moments by the exchange interaction. Such models, however, do not take into account the strong correlations displayed in a wide variety of magnetic semiconductors, which are responsible for the formation of the local moments. In particular, the itinerant carrier itself contributes to the spin moment. Here, we overcome this simplification in a combined experimental and theoretical study of the antiferromagnetic semiconductor α-MnTe. First, we present a spectroscopic optical investigation as a function of temperature, from which we extract the magnetic contribution to the blue-shift of the band-gap. Second, we formulate a minimal model based on a Hubbard–Kondo Hamiltonian. In this model, the itinerant charge is one of the electrons forming the localized magnetic moment, which properly captures correlation effects in the material. Our theory reproduces the experimental findings with excellent quantitative agreement, demonstrating that the magnetic contribution to the band-gap energy of α-MnTe is mediated solely by the exchange interaction. These results describe an intrinsic property of the material, independent of the thickness, substrate and capping layer of the specimen. One of the key findings of the model is that the basic effect, namely a blue-shift of the band-gap due to the establishment of the magnetic order, is a general phenomenon in charge-transfer insulators. The identification of the relevant magnetic interaction discloses the possibility to exploit the effect here discussed to induce a novel regime of coherent spin dynamics, in which spin oscillations on a characteristic time-scale of 100 fs are triggered and are intrinsically coupled to charges
Temperature dependence of the picosecond spin Seebeck effect
No full textWe performed temperature-dependent optical pump–THz emission measurements in Y₃Fe₅O₁₂ (YIG)|Pt from 5 K to room temperature in the presence of an externally applied magnetic field. We study the temperature dependence of the spin Seebeck effect and observe a continuous increase as temperature is decreased, opposite to what is observed in electrical measurements, where the spin Seebeck effect is suppressed as 0 K is approached. By quantitatively analyzing the different contributions, we isolate the temperature dependence of the spin-mixing conductance and observe features that are correlated with the bands of magnon spectrum in YIG
Expanding forest research with terrestrial LiDAR technology
No full textAbstract The three-dimensional arrangement of plant components, both within and among individual trees, is fundamental for characterizing forest ecosystems. This structure not only influences but also responds to environmental changes, playing a key role in regulating light regimes, forest productivity, as well as physiological and biophysical processes. Over the past few decades, terrestrial laser scanning (TLS, or terrestrial LiDAR) has provided a unique perspective of this 3D structure, offering new insights into ecological processes and forest disturbances, as well as enhancing structural assessments in forest and carbon inventories. Here, we examine recent advancements in TLS and its applications in forest science. We also explore how increasing computational power, alongside the rise of artificial intelligence, is empowering researchers to tackle more complex questions, paving the way for breakthroughs in understanding forest ecosystem dynamics in a changing world
Femtosecond phononic coupling to both spins and charges in a room temperature antiferromagnetic semiconductor
No full textSpintronics is postulated on the possibility to employ the magnetic degree of freedom of electrons for computation and couple it to charges. In this view, the combination of the high-frequency of spin manipulations offered by antiferromagnets, with the wide tunability of the electronic properties peculiar of semiconductors provides a promising and intriguing platform. Here we explore this scenario in -MnTe, which is a semiconductor antiferromagnetically ordered at room temperature. Relying on a Raman mechanism and femtosecond laser pulses, we drive degenerate modes of coherent optical phonons, which modulate the chemical bonds involved in the super-exchange interaction. The spectrally-resolved measurements of the transient reflectivity reveal a coherent modulation of the band-gap at the frequency of 5.3 THz. The detection of the rotation of the polarisation, typically associated with magneto-optical effects, shows coherent and incoherent contributions. Modelling how the ionic motion induced by the phonons affects the exchange interaction in the material, we calculate the photoinduced THz spin dynamics: the results predict both a coherent and incoherent response, the latter of which is consistent with the experimental observation. Our work demonstrates that the same phonon modes modulate both the charge and magnetic degree of freedom, suggesting the resonant pumping of phonons as a viable way to link spin and charge dynamics even in nonlinear regimes
Compiling analysis-ready ice data across cryosphere disciplines
No full textIce is omnipresent in our Solar System: on Earth, on different planetary bodies, and on moons in the outer Solar System. In the past, terrestrial and extraterrestrial cryosphere science mostly developed as independent research fields whereas synergies may shed light on both fields. In fact, close cooperation across different cryosphere research communities is a necessary prerequisite for designing future planetary exploration missions. An in-depth knowledge of similarities and differences between ice regimes on Earth and beyond paves the way for a mission preparation that optimally orchestrates terrestrial analogue field test, lab experiments, and simulation-based extrapolation to hypothesized ice regimes at the target body.
The authors of this contribution constitute the International Space Science Institute (ISSI) team Bridging the gap: from terrestrial to icy moons cryospheres, which started in 2023 and brings together scientists of different focus in terrestrial and extra-terrestrial cryosphere research. The overall goal of our project is to make knowledge hidden in the vast amounts of existing data from different research groups accessible by consolidating it into a comprehensive meta-data enriched compilation of ice properties including uncertainty margins if available. This extends to relevant physical regimes and different scales on both Earth, and icy moons including data from field campaign measurements, laboratory experiments, and planetary missions. A particular focus of our work will be to increase the analysis readiness of the data for subsequent data-driven or simulation-based analysis. This approach will provide us with the unique opportunity to transfer and extrapolate the information from the Earth to the outer Solar System bodies.
Here, we will introduce the project and its rationale, describe our approach to selecting and compiling the data, as well as how we will make them accessible, and present first results
TRIPLE -Technologies for Rapid Ice Penetration and Subglacial Lake Exploration: Whitepaper by the TRIPLE Project within the German Space Agency Explorer Initiative at DLR
No full textTRIPLE (Technologies for Rapid Ice Penetration and subglacial Lake Exploration) is a project line initiated by the German Space Agency at DLR (Deutsches Zentrum für Luft- und Raumfahrt - engl. German Aerospace Center) focused on developing, demonstrating and providing an autonomous exploration system for subglacial lakes and ocean environments. The project aims to contribute to future missions searching for extraterrestrial life in the ice-covered ocean worlds of the outer Solar System by demonstrating an integrated system aiming for conducting contamination-free and robust explorations of subglacial lakes, including sample return.
TRIPLE consists of three core components: a melting probe for penetrating the ice, an autonomous underwater vehicle for exploring the water reservoir, and an astrobiological laboratory for in-situ analysis of the collected samples. The operational capability of the technologies will be validated in a test campaign in Antarctica’s Dome C region, which serves as an analogous terrestrial scenario for simulating extraterrestrial environments.
In this whitepaper, we present a comprehensive overview of the project line, highlighting its key objectives and the strategies devised to achieve them. Released as the second issue following the initial publication on May 29, 2020, this document serves as an expanded update to its predecessor
