Non-perturbative methods for metallic quantum criticality and beyond
Final Report Abstract
Optical spectra obtained by shining light on quantum materials can convey detailed information about the underlying ground states and excitation landscapes. For strongly correlated materials, this information may be "hidden" in the spectra, and it is a theoretical challenge to extract it from experimental data. In this project, me and my collaborators have undertaken this challenge for various interesting metallic states and new experimental platforms, applying a mix of perturbative and non-perturbative methods. In the first part of the project, we have analyzed spectra of impurities embedded in metals. When the impurities are heavy and have vanishing kinetic energy, the spectra feature power law singularities. This standard result is usually obtained by studying impurities and metal electrons which have plane-wave-like character. We have extended this result to a situation where the wave functions deviate from the plane wave form, uncovering a modification of the power law that reflects the "quantum geometry" of the wave functions. In the second part of the project, we studied particle-hole bound states (excitons) in doped twodimensional semiconductors. The spectra of excitons are well-understood and can serve as a reference to gain indirect information about low-energy degrees of freedom which cannot be detected directly. We provided theoretical modeling for pump-probe experiments, where the lowenergy degrees of freedom are excited with a THz pump field, and the change in the excitonic spectra is recorded in a time- and spatially resolved manner. This paves the way for further exploration of exotic quantum materials employing excitonic spectra. In the third part, we studied spectra of microwave photons in superconducting resonators. These can be used to e.g., detect unconventional superconductivity in small samples deposited on the resonator, since the temperature dependence of the photon frequency is determined by the low-energy excitations in the superconductor. We have provided a potential explanation for unexpected behavior observed in a recent experiment where microwave photons were used to probe induced superconductivity in ferromagnetic superconductor. Finally, we studied the dynamics of ultracold bose gases, modeling oscillations between atomic and molecular condensate fractions in a recent experiment. We have uncovered a new resonant damping mechanism in these systems, which for instance precludes a strong driving of the oscillations.
Publications
-
Bose-enhanced relaxation of driven atom-molecule condensates. Physical Review A, 109(4).
Pimenov, Dimitri & Mueller, Erich J.
-
Polaron spectra and edge singularities for correlated flat bands. Physical Review B, 109(19).
Pimenov, Dimitri
