This CAREER award supports theoretical and computational research and education in a new type of phase transition found in two-dimensional materials. Phase transitions are commonly found around us; for example, in the boiling of water, or in the reverse process of condensing water vapor into rain. In some semiconducting materials, a remarkably similar phase transition may occur. When exposed to the energy a continuous laser beam, electrons in the material get excited from their normal quantum state into another. However, the excited electron in its new state feels an effective attraction to the "hole" it left behind, i.e. the place where it used to be. If enough electrons get pumped into the excited state, they - and their hole counterparts - can undergo a gas-to-liquid-type phase transition. This phase transition, although its constituents are electrons and holes, has characteristics similar to the one found in water. However, a significant difference is that this happens on ultrafast time-scales (nanoseconds), and it involves a driving laser. Importantly, because the constituents are manifestly quantum objects, a host of exciting and interesting properties arise.
The materials in question form two-dimensional sheets, which means they may be incorporated into flexible electronics. On top of this, there is now the possibility of switching their behavior within nanoseconds from being a straightforward semiconductor (which are typically transparent materials) to being an object that is metallic and reflecting. This has promising applications for solar-light harvesting and for bypassing Moore's law through photonics. The project involves substantial development of algorithms and software, which will be disseminated to the community as open-source code.
In addition to the research, this CAREER award will support the improvement of STEM education in the U.S. by partnering with the American Association of Physics Teachers (AAPT) to turn their successful "Bootstrap for Computational Modeling in Physics First" workshop into a distance-learning course. The workshop integrates computational modeling into 8th and 9th grade physics courses, and is typically attended in person. The development of a distance-learning version will enable reaching a much larger set of participants, in particular from rural areas which may not have ready access to long in-person workshops. Since computation is playing an increasingly larger role in the STEM workplace, earlier preparation and exposure will improve students' overall capabilities. This version of the workshop will initially be deployed in North Carolina, and will be further disseminated through AAPT across the country.
This CAREER award supports research and education in theoretical and computational investigations of ultrafast out-of-equilibrium phase transitions. The research team will study the transition into an electron-hole liquid (EHL) that occurs at room temperature upon high photoexcitation in transition-metal dichalcogenides. Due to the ultrafast nature of the phase transition, time-domain approaches are critical. This project will determine the conditions for creating and sustaining the EHL, its response to external stimuli and proximity-coupled emergent orders, its tunability, and its transport and transfer dynamics. This understanding will enable the use of the electron-hole liquid in novel devices, and, in particular, in applications for solar-light harvesting and for bypassing Moore's law through photonics.
The project exploits an opportunity for high-impact science through theoretical study and computational method development for nonequilibrium science. One essential aspect of the problem is that it must be tackled in the time domain, rather than resorting to the usual equilibrium analytic techniques. The PI will address this challenge through nonequilibrium many-body theory and through collaboration with the experimental community. The research team will consider the concept of a nonequilibrium phase transition without reliance on ergodicity by performing self-consistent calculations in the broken-symmetry states in the time domain. Through these approaches, the research team will re-evaluate how we think about nonequilibrium processes and phase transitions in quantum materials, and break the reliance on equilibrium concepts. The algorithms and software created throughout the project will be disseminated to the community as open-source code.
In addition to the research, this CAREER award will support the improvement of STEM education in the U.S. by partnering with the American Association of Physics Teachers (AAPT) to turn their successful "Bootstrap for Computational Modeling in Physics First" workshop into a distance-learning course. The workshop integrates computational modeling into 8th and 9th grade physics courses, and is typically attended in person. The development of a distance-learning version will enable reaching a much larger set of participants, in particular from rural areas which may not have ready access to long in-person workshops. Since computation is playing an increasingly larger role in the STEM workplace, earlier preparation and exposure will improve students' overall capabilities. This version of the workshop will initially be deployed in North Carolina, and will be further disseminated through AAPT across the country.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
