Lectures, Workshops, Conferences (Archiv)

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Abstract: Chemistry is all about understanding and controlling the properties of matter -- Where are the electrons? How do particular arrangements of atoms and bonds result in the zoo of behaviors known in matter? What new properties can be created by arranging atoms in unnatural configurations? Today, there are about 50 million known chemical compounds. Where and how will the next billion be discovered, and what new properties will they have [1]? In this talk, I will highlight the progress being made to address these questions, with a particular emphasis on the confluence of quantum materials, quantum information science, and data science. Examples will include our forays into closed loop coupling of human experiment and AI/ML prediction for superconductor discovery [2,3], the creation of approaches for the systematic design of complex materials [4], and the importance of advancing old and new materials synthesis methods [5,6]. As time permits, I will highlight how these methods come together to enable discovery of new chemistry, and new physics, and provide my perspective on the future of materials design, synthesis, and discovery. 1. https://dx.doi.org/10.1021/acs.accounts.8b00382 2. https://doi.org/10.1038/s41524-023-01131-3 3. https://openreview.net/forum?id=SfEsK3O2KT 4. https://doi.org/10.1021/jacs.4c08941 5. https://doi.org/10.1021/acs.chemmater.3c03077 6. https://doi.org/10.1038/s41535-022-00527-6 [mehr]

How can we make new materials and better understand how their underlying structures form? The direct observation of crystal growth and transitions remains supremely challenging, but gaining insight into these fundamental processes is central to our quest of creating materials in a rational and targeted way, connecting structure to functionality. We build self-assembly models, study how they react to perturbations on the particle and system levels, and investigate their impact on crystal growth and transformation pathways. We use simple coarse-grained models to gain systematic insights into the phenomena that lead to the crystallization of complex crystal structures, partial disorder, or magic-size assemblies, allowing us to derive the essential principles that govern the formation of materials' structures. Our goal is to use these insights to find ways to tailor crystallization pathways and to create new functional materials. Our work promises to establish new pathways to materials design through simulations, which explicitly incorporate and explore phase transformation kinetics. [mehr]

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Abstract: We investigate the lattice relaxation effect on moir´e band structures in twisted bilayer MoTe2 with two approaches: (a) large-scale plane-wave basis first principle calculation down to 2.88 deg, (b) transfer learning structure relaxation + local-basis first principles calculation down to 1.1 deg. Two types of van der Waals corrections have been examined: the D2 method of Grimme and the density-dependent energy correction. We note the density-dependent energy correction yields a continuous evolution of bandwidth with twist angles. Including second harmonic of intralayer potential/interlayer tunneling and the strain induced gauge field, we develop a more complete continuum model with a single set of parameters for a wide range of twist angles, and perform many-body simulations at v=-1,-2/3, -1/3. We further identify a series of C=1 Chern bands around 2 from Wilson loop and edges state calculation, which serves as the foundation point for even-denominator non-Abelian states. [mehr]

Abstract: Non-collinear chiral antiferromagnet (AFM) Mn₃Sn is an attractive material since this AFM exhibits a Néel temperature of 420 K and a non-negligible magneto-optical Kerr effect (MOKE) due to magnetic-octupole order and topological Weyl nature. Despite extensive research on ultrafast magnetization dynamics in ferromagnets and ferrimagnets, investigations into such chiral AFMs are still in their very early stages. In particular, magnetic damping significantly influences both the energy efficiency and operational speed of the device aiming to utilize the electronic spin degree of freedom, thus further understanding is demanded. Here we investigate, for the first time, time-resolved magneto-optical Kerr effect for Mn₃Sn films with a perpendicular magnetic anisotropy to gain insight into the physics of octupole dynamics. The films were prepared using magnetron sputtering technique. The film stacking structure is single crystalline MgO (110) sub./W(2) /Ta(3) /Mn₃Sn(30) /MgO_(1.3) /Ru(1) (thickness is in nm). The time-resolved MOKE (TR-MOKE) was measured using an all-optical pump-probe technique. The out-of-plane magnetic-octupole dynamics is induced by the pump laser pulse and is detected via MOKE for a probe laser pulse. We observed an ultrafast change of Kerr rotation angle at the zero delay, which is attributed to ultrafast collapse of magnetic octupole order. We also observed the damped-oscillation which would be attributed to GHz-frequency magnetic octupole order dynamics. [mehr]

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