****NON-TECHNICAL ABSTRACT**** This Faculty Early Career Award funds a project that will probe quantum dynamics in semiconductor nanostructures with designed geometry. These dynamic processes ultimately determine the limits of operational speed and the efficiency of electronic devices that interact with light (optoelectronic devices). Taking the opportunity offered by the newly developed nanostructures, one expects to discover novel phenomena arising from collective electron excitation and light emission in nanostructures. Harnessing quantum properties of semiconductor nanostructures may also enable new capabilities in the emerging field of quantum information science. The education component of this project will explore a wide range of methods to integrate research and education in both undergraduate and graduate levels. Effective pedagogical methods in introductory physics courses for non-science majors will be practiced by teaching with technology. A graduate-level course, "ultrafast optics and spectroscopy", will be developed. This course includes both lectures and training in presentation and scientific writing skills. In response to the congressionally requested report, "Rising above the Gathering Strom: Energizing and Employing America for a Brighter Economic Future", future and current high school teachers will be involved in the education and research activities via the platform of the UTeach program at the University of Texas-Austin. This award is supported by the Division of Materials Research and the Division of Physics.
This Faculty Early Career Award funds a project that will probe quantum dynamics in semiconductor nanostructures with designed geometry. In semiconductor nanostructures, structural, electronic and optical properties are closely related. Following optical excitation, excitons (or bound electron-hole pairs) are formed. Exciton dynamics ultimately determine the limits of operational speed and the efficiency of optoelectronic devices. A central question is how quantum dynamics are determined by a combination of physical dimensions, the arrangement of building blocks, and Coulomb interactions. To answer this question, this project will probe exciton dynamics in nanostructures with designed geometry using comprehensive optical spectroscopy tools. The proposed research is significant in that it advances quantum engineering in nanostructures to a new level of sophistication. Taking the opportunity offered by the newly developed nanostructures, one expects to discover novel quantum phenomena arising from collective electron excitation and photon emission in nanostructures. The education component of this proposal will explore a wide range of methods to integrate research and education in both undergraduate and graduate levels. Future and current high school teachers will be involved in the education and research activities via the platform of the UTeach program at the University of Texas-Austin. This award is supported by the Division of Materials Research and the Division of Physics.
Our research focuses on investigating quantum dynamics in advanced nanostructures using optical spectroscopy. These nanostructures have promising applications in conventional optoelectronic devices as well as novel quantum information processing device. Our main research accomplishments include: (i) Development of an advanced coherent nonlinear optical spectroscopy method, called optical two-dimensional Fourier transform spectroscopy (2DFTS). Optical 2DFTS is introduced to address limitations of traditional coherent spectroscopy method. First, congested 1D spectra are often impossible to interpret due to severe overlap between resonances. By spreading the spectra into two dimensions, overlapped spectra are unraveled much like opening a window blind. Second, the phenomenon of coherent transfer can be used to identify couplings and energy/charge transfer without ambiguity using cross peaks in a 2D spectrum. Finally, excited states relax and dephase via many possible quantum mechanical pathways, all of which contribute to the signal in conventional spectroscopy measurements. Using the new technique, one can separate quantum mechanical pathways and gain detailed information about relaxation and dephasing dynamics by detecting the amplitude and phase (not just the intensity) of the signal field. Using this spectroscopy method, we investigated the problem of exciton coherent coupling in disordered quantum wells. The presence or absence of coherent coupling among excitons significantly influence energy transfer, photon emission statistics, and even quantum-logic operations in semiconductor heterostructures such as quantum wells, quantum wires, and quantum dots. This problem is also relevant for a broader range of materials including natural/artificial photosynthetic systems and conjugated polymers. We have investigated coherent coupling among exciton resonances in disordered quantum wells. We articulate how strong coherent coupling occurs between certain types of excitons but is missing between other types of excitons using a powerful spectroscopy tools known as the electronic two-dimensional Fourier transform spectroscopy. In simple terms, the distinctive nature of excitons results in different spatial overlap and different coupling strength. If time permits, we will also present our most recent results on monolayer transition metal dichalcogenides. (ii) Development of an integrated atomic force microscope and confocal microscope. We use atomic force microscope (AFM) to assembly plasmonic nanostructures and then characterize their properties using single particle spectroscopy. AFM based assembly method combines the advantages of top-down and bottom-up fabrication techniques. The individual components are synthesized using solution based self-assembly methods. Therefore, the components are easy/cheap to produce, small in size, of high crystalline quality, and give us flexibility in selecting materials. Yet, the assembly process relies on a scanning probe which provides the degree of control typically only achievable using the top-down approach. We have assembled and investigated a number of interesting plasmonic nanostructures including a hybrid molecule consisted of a single quantum dot and a single nanoparticle, a four-particle metamolecule exhibiting overlapped magnetic and electric dipole resonances in the visible frequency range, and a plasmonic nano-protractor capable of determining relative orientation between two dissimilar nanoparticles. (iii) We have studied a number of other topics including second harmonic generation in tetragonal crystals, dynamics of semiconductor quantum dot molecules, and coupling between quantum dot and nanowires, all of which are within the scope of the quantum dynamics of designed nanostructures as originally proposed. (iv) The PI has developed a graduate level-course called "ultrafast optics". The course was offered twice during the last five years. The PI extended the instructional method to offer the course to several students at UT-El Paso, a minority serving institute. (v) The PI has taught an innovative introductory physics course specifically for designed for elementary education majors.
