Dark Matter Couture: Designer Targets and Tailored Detectors for Next-Generation Searches.

다국어 초록 (Multilingual Abstract)

Despite sustained efforts, direct detection of dark matter (DM) remains elusive. Propelled by cutting-edge advances in detector sensitivity and innovative proposals employing quantum materials, the search for DM has recently expanded to lower masses, encompassing well-motivated theories for light and ultralight candidates. However, detecting these low-mass candidates remains a formidable challenge, requiring target materials that exhibit measurable responses with just a few meV of energy deposition from dark matter scattering or absorption.State-of-the-art approaches for light DM detection face several challenges, including low-energy background discrimination, detection of single-phonons and single-magnons, and losses at the target-sensor interface. We address these challenges by proposing novel and complementary strategies from condensed matter physics: pressure-tunable targets and topological transition sensors.The first Chapter of this Dissertation provides a broad overview of DM and the effective field theory (EFT) we use to compute DM scattering rates from collective excitations in condensed matter systems. The second Chapter introduces relevant concepts from condensed matter theory, including the foundations of phonons and magnons within both classical and quantum formalisms. We detail several approaches for computing phonons and magnons from first-principles density functional theory (DFT), and close the Chapter by introducing topological insulators, a class of quantum materials central to most of the work we present.In the third Chapter, we explore how hydrostatic pressure---a well-established tool for tuning properties of condensed matter---presents a novel route for optimizing targets for light dark matter direct detection, specifically via phonons. Highly compressible solids are profoundly affected by pressure, and our results show that, in solid helium, the speed of sound and phonon frequencies are significantly enhanced by applying pressures up to 40 GPa. Our ab initio calculations illustrate how high pressure elevates helium from lacking single-phonon reach to rivaling leading candidates. Our findings establish pressure as an unexplored tuning knob for accessing lower dark matter mass regimes and suggest potential new avenues for background discrimination.In the fourth Chapter, we introduce topological transition sensors (TTSs), novel quantum sensors based on the bulk-boundary correspondence of topological insulators. Here, our DFT calculations show how phonons and magnons can transiently break bulk symmetries, gapping out topological surface states and driving a metal-insulator transition on the material's surface. We elucidate the unique advantages of TTSs for light DM detection and quantum sensing that complement conventional state-of-the-art cryogenic sensors. Further, we explore several readout schemes, and highlight the distinctive properties of TTSs, including directionality and quasiparticle selectivity.The fifth and sixth Chapters delve deeper into material realizations of TTSs in topological crystalline insulators (TCIs) for phonons and antiferromagnetic topological insulators (AFTIs) for magnons. We highlight the essential material properties for ideal TTS candidates, and thoroughly examine two material candidates, namely TCI Sr3PbO for phonons and AFTI VBi2Te2Se2 for magnons. These Chapters highlight many of the unique properties of TTSs that arise as a direct consequence of the interplay between the symmetries protecting the bulk topology and the quasiparticle-induced transient symmetry breaking. Further, we explore the inherent directionality of TTSs and illustrate the potential of doubly-topological materials for correlated multichannel sensing. Finally, in the seventh Chapter, we summarize our findings and explore future directions for tunable detectors and TTSs.