The ability to combine continuously tunable narrow-band terahertz (THz) generation that can access both the far-infrared and mid-infrared regimes with nanometer-scale spatial resolution is highly promising for identifying underlying light-matter interactions and realizing selective control of rotational or vibrational resonances in nanoparticles or molecules. Here, we report selective difference frequency generation with over 100 THz bandwidth via femtosecond optical pulse shaping. The THz emission is generated at nanoscale junctions at the interface of LaAlO3/SrTiO3 (LAO/STO) that is defined by conductive atomic force microscope lithography, with the potential to perform THz spectroscopy on individual nanoparticles or molecules. Numerical simulation of the time-domain signal facilitates the identification of components that contribute to the THz generation. This ultra-wide-bandwidth tunable nanoscale coherent THz source transforms the LAO/STO interface into a promising platform for integrated lab-on-chip optoelectronic devices with various functionalities.
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The recently published paper in journal of ACS NANO on Ultrafast Microscopy of Spin-Momentum Locked Surface Plasmon Polaritons is an essential research for designing optical elements to control spin-polarized SPP (surface plasmon polaritons) fields on the nano femto scale. Hrvoje Petek and his colleagues have shown two-photon photoemission electron microscopy images formed by coupling and propagation of longitudinal and transverse components of SPP fields of light. Further, they have also shown the spin-momentum locked SPP wave packets launched with circularly polarized excitation propagate at the same phase and group velocities as for the linearly polarized excitation using time-resolved experiments.Continue reading
Michael Widom and his colleagues showed what happens at the grain boundaries of one particular alloy of the metals nickel and bismuth that makes it brittle in their paper published in Science. Using advanced electron microscopes, Widom’s collaborators at Lehigh University scrutinized these microscopic grain boundaries at an atomic level. In a "very heroic experimental program" they discovered that when grains met, the bismuth and nickel atoms realigned into lattices to form layered superstructures at the grain boundaries. These superstructures had previously been thought to exist only rarely in some alloys. Finding it at many different boundaries led the team to conclude that these superstructures are probably much more common than many people had thought. Continue reading
Owing to high surface to volume ratios and chemical potential, nanoparticles possess unique optical, electrical, and thermal properties, which constitute the basis of novel applications in sensing, catalysis, nanoelectronics, bio-tagging etc. Despite the great advances in the synthesis, the total structure determination of nanoclusters still remains to be a major challenge. Recently Hyung J. Kim and their colleagues have reported the synthesis and crystal structure of a nanocluster composed of 23 silver atoms capped by 8 phosphine and 18 phenylethanethiolate ligands in the journal of Nature Communications.Continue reading
In the recently published paper in Scientific Reports, Sara A. Majetich and their colleagues have demonstrated the engineering of spin canting across a Magnetic nanoparticles (MNP) via the Dzyaloshinskii-Moriya interaction (DMI). In this paper, they have shown that strong DMI can lead to magnetic frustration within the shell and cause canting of the net particle moment. These results have illuminated how core/shell nanoparticle systems can be engineered for spin canting across the whole of the particle, rather than solely at the surface.
In the recently accepted paper in Physical Review Letter, Hrvoje Petek and his colleagues investigate the coherent electron transfer from an interface state that forms upon chemisorption of Ag nanoclusters onto graphite to a σ symmetry interlayer band of graphite. Interfacial charge transfer is a fundamental process in heterogeneous and plasmonically enhanced catalysis. The charge transfer, however, is thought to be restrained by an interfacial potential barrier, such as a Schottky barrier at a metal-semiconductor interface. With optical excitation, the interfacial charge transfer can also be efficiently completed by coherent dipole coupling between the donor and acceptor bands. In this study Petek and his colleagues advance the time-resolved multidimensional multiphoton photoemission spectroscopy technique to not only pump the donor band and probe the acceptor band, but also directly image the coherent polarization dynamics between them. They discover a direct resonant ... Continue reading
Geoff Hutchison is the 2018 Tina and David Bellet Excellence Awardee. The award recognizes his effectiveness and his innovations in teaching. Among many innovations Hutchinson developed Avagadro molecular editor; with that software, he designed projects hat allow Physical Chemistry students to perform quantum mechanical calculations to visualize results/concepts. Continue reading
On the morning of July 9, the National Science Foundation announced a $10 million dollar grant to the Pittsburgh Supercomputing Center (PSC) to fund a new piece of cutting-edge hardware for the local research institutions. Known as Bridges-2, the machine, currently under construction by Hewlett Packard Enterprise, will specialize in artificial intelligence and machine learning and is scheduled to launch in the summer of 2020.
If only! This headline might be a near-future reality soon enough though as a collaborative effort between UPitt professor Hrvoje Petek and a team at the University of Tsukuba has made progress towards affordable consumer quantum computers. Studying a novel process for creating coherent lattice waves inside silicon crystals using ultrashort laser pulses (shown in image), they were able to show that coherent vibrational signals could be maintained inside the samples. This research may lead to quantum computers based on existing silicon devices that can rapidly perform tasks out of the reach of even the fastest supercomputers now available.
The need to bring different educational methods to different academic subjects has long been clear to Chandralekha Singh, a physics and astronomy professor at UPitt and director of dB-SERC — the Discipline-Based Science Education Research Center. She has been conducting research on discipline-based education for more than two decades. She continues to amass evidence that gearing educational methods to specific types of students in specific subjects can result in measurable gains in knowledge and in attitude, which can be just as important. On average, the GPAs of engineering majors in introduction physics courses, who are study subjects for Singh's students, did not change over four years
“I don’t believe it is the students’ fault,” she says, if they do not improve their GPAs across their college careers. “We as faculty in the University should think of it as our responsibility to help these students.” That’s the impetus behind dB-SERC and the motivation for its course transformation awards. Since db-SERC’s founding in 2013, it has funded as many as 10 awards annually — up to $10,000 — to natural sciences faculty members in the Dietrich School of Arts and Sciences.
The dB-SERC course transformation awardees meet weekly and present talks about their ideas and progress. “Participating in those, my first year at Pitt, I met a lot of the other science faculty,” Whittinghill recalls. “It helped me feel a part of a community at Pitt.” The weekly gatherings help faculty improve their approaches to course changes and conceive of new directions, based on others’ experience and thoughts, Singh says: “A lot of times when people are doing some innovative teaching and learning, things may not work as people expected. You may need to keep refining things to make them really adaptable to your students, to your own style.”
