CAREER: Theories of Gapless Quantum Matter Beyond Quasiparticles

NONTECHNICAL SUMMARY

This CAREER award supports an integrated research, outreach, and education program in theoretical condensed matter physics. At sufficiently low temperature some materials can exhibit superconductivity, a state of matter where electrons self-organize into a cooperative state which can conduct electricity without dissipation. The search for superconductivity at high temperatures is driven by the potential of superconductors to transform the future of quantum technologies and human society, with applications in energy storage and transmission, medical diagnostics, and quantum computing.

However, the microscopic reasons for superconductivity at high temperature remain mysterious. The research will be focused on a class of unconventional metals, which are the “parent” states for high temperature superconductors. Unlike simple metals such as copper, whose properties can be effectively understood by considering the electrons one at a time, these unconventional metals are best described as a collective quantum fluid where the electrons are strongly entangled over long distances with one another.

This research will develop the required technical framework to describe these entangled electronic liquids. This will pave the way for identifying the key microscopic mechanisms responsible for the origin of superconductivity at high temperatures.

The PI and his group will develop new theoretical methods building on recent theoretical developments across different subfields. The PI will develop exact theoretical methods that have a predictive power that can be tested against experiments on real materials in the laboratory. The resulting outcome will impact the fundamental understanding of the collective quantum mechanical properties of trillions of entangled electrons, and potentially help guide the future search for new materials displaying exotic properties. The methods and results will be disseminated to the wider community.

In parallel, the PI will initiate and participate in a variety of educational and outreach activities. Although quantum physics has impact on the development of new technologies that become part of everyone’s daily lives, it has a reputation for being inaccessible. The PI will start a new podcast series, which will host informal discussions with a diverse lineup of well-known researchers, to get students and the general public excited about the physics of quantum materials.

The PI will also organize workshops for high school science teachers to co-develop engaging lesson plans. The PI will mentor undergraduate and graduate students in original research, and write pedagogical articles aimed at training them in the new scientific developments aligned with the research activities.

TECHNICAL SUMMARY

This CAREER award supports an integrated research, outreach, and education program in theoretical condensed matter physics. The goal of the research will be to address some of the key facets of the long-standing mystery of high-temperature superconductivity. Specifically, the focus will be on the unusual gapless metallic phases out of which superconductivity emerges in quantum materials.

Experiments suggest that the quantum motion of electrons is frustrated and entangled over long distances in strongly correlated metals, and the microscopic degrees of freedom, namely electrons and phonons, are strongly intertwined with each other. This research activity will develop novel, non-perturbative theoretical approaches to solve the problem of electronic liquids entangled with other collective degrees of freedom, to expose universal aspects of gapless quantum many-body systems.

The PI will formulate new approaches for studying interacting gapless phases that do not rely on the existence of well-defined, electron-like (“quasiparticle”) excitations. To address their non-trivial dynamics, the PI will develop novel theoretical techniques that are based on technical advances in the study of frustrated magnets, thermalization in chaotic quantum many-body systems, and numerically exact algorithms that do not suffer from the fermion “sign problem”.

The PI will build on the following conjectures: (i) interacting frustrated liquids offer a non-trivial starting point for including the effects of quantum fluctuations and describing previously unexplored gapless phases; and (ii) the conventional theory for electrical transport in metals can break down over a wide range of intermediate temperatures for sufficiently “chaotic” models with generic interactions. The PI will also exploit recent breakthroughs in the highly controllable moiré systems, focusing on the problem of narrow electronic bands coupled to low-energy phonons using numerically exact methods.

Analyzing these questions will offer an important conceptual framework for tying together a vast amount of existing experimental data on high-temperature superconductors, and help direct the search for new materials displaying similar phenomena.

The PI’s educational and outreach activities are integrated synergistically with the research. The PI will start a new podcast series with a diverse lineup of well-known researchers to increase awareness about the excitement in the field amongst the general public and students. The PI will mentor undergraduate and graduate students in original research, and write pedagogical articles aimed at training them at the new scientific developments aligned with the research activities.

Leveraging existing infrastructure available at Cornell University through the STEM teacher program, the PI will organize a series of workshops for high school science teachers to co-develop engaging lesson plans.

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.