Over the past decade, terahertz electromagnetic waves with sub-millimeter wavelength (30 µm to 3 mm) have attracted much attention due to the wide range of applications in medical and industrial fields. Magnetic thin film heterostructures (spintronic emitters) consisting of ferromagnet and nonmagnetic metal layers have recently emerged as broadband THz sources that may have advantages over conventional sources such as photoconductive antennas (PCA) and nonlinear crystals. Here, we demonstrate how to use spintronic emitters patterned into microstructures of different geometries and dimensions to modify the characteristic electromagnetic spectrum of the emitted THz waves. Furthermore, we theoretically explore the possibility of combining emergent spintronic emitters with conventional PCA as hybrid emitters for THz pulse shaping and controlling the handedness of the polarization of THz waves. This new method takes advantage of the broad bandwidth of spintronic emitters and high-intensity THz emission at the low frequency of PCAs. These modelings are confirmed by preliminary experiments. Our results are beneficial to the production of functional THz devices with tunable parameters.
The capability of magnons to hybridize and strongly couple with diverse excitations offers a promising avenue for realizing and controlling emergent properties that hold significant potential for applications in devices, circuits, and information processing. In this talk, we present recent theoretical developments in magnon-based hybrid systems, focusing on the combination of magnon excitation in an antiferromagnet with other excitations, namely plasmons in a topological insulator, phonons in a 2D AFM. We explore several directions to advance magnon hybrid systems, including strong coupling between a surface plasmon and magnon polariton in a TI/AFM bilayer and a giant spin Nernst effect induced by magnon phonon coupling in 2D AFMs. These examples highlight the potential of magnon-based hybrid systems for advancing device and information processing technologies and the importance of both understanding and controlling material properties and interactions to realize such technologies.
The bright emission from thick flakes makes gallium selenide a fantastic material for understanding the relationship between local strain and optical response. Here, we investigate complex strain distributions by transferring gallium selenide flakes onto nanostructures patterned in close proximity, enabling the study of a variety of strain distributions, such as uniaxial, biaxial, and triaxial strain within a single flake. Our findings reveal that finite strain distributions and resulting bandgap shifts occur in regions of gallium selenide suspended between closely-spaced nanostructures, in good agreement with strain distributions simulated using finite element analysis. This research paves the way for designer strain distributions and tailorable nanophotonic behavior in two-dimensional materials.
Strain engineering of the two-dimensional semiconductor gallium selenide has recently revealed exciting nanophotonic effects such as localized bandgap tuning, exciton funneling, and the creation of site-specific single photon emitters. We investigate the reversible local strain engineering of suspended gallium selenide flakes by using a novel micromechanical spring with nanoscale probes for inducing symmetry-controlled localized strain. By performing strain engineering measurements on suspended gallium selenide flakes as opposed to using patterned substrates, unintended strain originating from the surrounding environment is avoided. Our results show that gallium selenide undergoes a reversible bandgap redshift of >6 meV. The presented research establishes a new platform for streamlining the quantitative understanding of material properties as a function of complex local strain in two-dimensional materials for quantum photonics applications.
We theoretically study the thermal Hall and spin Nernst effect induced by the interaction between magnonic and phononic resonances at THz frequency in FePS3, a two-dimensional antiferromagnet (2D AFM) material. We find that a strong coupling between the magnetic excitation (magnon) and elastic excitation (phonon) in FePS3 combined with time-reversal-symmetry-breaking results in a finite Berry curvature concentrating within the anti-crossing point formed between the two distinct excitation bands. More interestingly, a very large spin Berry curvature emerges even in the absence of an external magnetic field due to phonon-mediated magnon-magnon interactions that cause a small energy gap between two magnon states. This results in topological transverse transport of quasi particles and spin momenta when a temperature gradient is applied to the quasi two-dimensional magnon phonon system in FePS3. We investigate the dependence of the thermal Hall and spin Nernst conductivity on the external magnetic field and temperature and find a very large spin Nernst conductivity at zero magnetic field. This results suggests possible experiments to explore the topological transport of a magnon-polaron system at THz frequency in a realistic 2D AFM material.
Self-assembled InAs Quantum Dots (QDs) are often called “artificial atoms" and have long been of interest as components of quantum photonic and spintronic devices. Although there has been substantial progress in demonstrating optical control of both single spins confined to a single QD and entanglement between two separated QDs, the path toward scalable quantum photonic devices based on spins remains challenging. Quantum Dot Molecules, which consist of two closely-spaced InAs QDs, have unique properties that can be engineered with the solid state analog of molecular engineering in which the composition, size, and location of both the QDs and the intervening barrier are controlled during growth. Moreover, applied electric, magnetic, and optical fields can be used to modulate, in situ, both the spin and optical properties of the molecular states. We describe how the unique photonic properties of engineered Quantum Dot Molecules can be leveraged to overcome long-standing challenges to the creation of scalable quantum devices that manipulate single spins via photonics.
Rising efforts concerning the reduction of CO2 emission promote the use of fiber reinforced plastics, e.g. in automotive
or aircraft engineering due to their low mass compared to classical materials. Although fiber reinforced plastics have
critical properties such as low mass and high stiffness compared to classical materials, they also may suffer
unpredictable failures due to hidden structural damage. Thus structural health monitoring is vital for the development of
modern lightweight structures.
Our concept of material integrated sensor technology is based on a combination of a piezoelectric foil with a quantum
dot polymer composite. By application of a mechanical (over-) load, electrical charges are generated and injected into
the nanocrystals causing PL quenching, which is detectable as local optical contrast. A very efficient charge injection is
crucial for sensitive load detection, because of limited amount of generated charges and transport losses.
Consequently we have investigated the charge injection and charge storage properties of various types of quantum dots,
in particular core shell types CdSe/ZnS and InP/ZnS, embedded in semi-conducting poly(9-vinylcarbazole) (PVK). PL
quenching was realized by application of external voltages smaller than 20 V. Initial results indicated a longer charge
storage time in InP/ZnS quantum dots, which we attribute to a difference in band level alignment between valence band
levels of respective quantum dots and PVK.
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