Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session M42: New Developments in Disordered Quantum MaterialsInvited

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Sponsoring Units: DCMP Chair: Srinivas Raghu, Stanford University Room: Ballroom B 
Wednesday, March 6, 2024 8:00AM  8:36AM 
M42.00001: From disorder to order and back again Invited Speaker: Jose A Hoyos One surprising phenomenon in frustrated magnets is the orderbydisorder mechanism: thermal and/or quantum fluctuations lift a macroscopic accidental degeneracy of the classical ground state of frustrated magnets. The resulting magnetically orderedby(thermal/quantum)disorder state often breaks a realspace symmetry of the crystal lattice. In this talk, we use symmetry arguments and Monte Carlo simulations to investigate the effects of impurities (vacancies, chemical doping, etc.). Because inhomogeneities generically break realspace symmetries, it couples to the orderparameter as a conjugate field. As a consequence, inhomogeneities are responsible for nonperturbative effects that destabilize an orderedbydisorder state at sufficiently low dimensions. As an example, we apply our theory to the J1J2 Heisenberg model on a square lattice and to the easyplane pyrochlores. 
Wednesday, March 6, 2024 8:36AM  9:12AM 
M42.00002: Interplay of disorder and superconductivity at quantum critical points Invited Speaker: Pavel Nosov We study the superconducting instability of a twodimensional disordered Fermi liquid weakly coupled to the soft fluctuations associated with proximity to an Isingferromagnetic quantum critical point. We derive interactioninduced corrections to the Usadel equation governing the superconducting gap function, and show that diffusion and localization effects drastically modify the interplay between fermionic incoherence and strong pairing interactions. In particular, we obtain the phase diagram, and demonstrate that (i) there is an intermediate range of disorder strength where superconductivity is enhanced, eventually followed by a tendency towards the superconductorinsulator transition at stronger disorder; and (ii) diffusive particleparticle modes (socalled "Cooperons") acquire anomalous dynamical scaling z=4, indicating strong nonFermi liquid behavior. 
Wednesday, March 6, 2024 9:12AM  9:48AM 
M42.00003: Anomalous successes and a surprising failure: The Dirac equation and topological materials Invited Speaker: Matthew S Foster The Dirac equation was formulated nearly a century ago, with the goal of combining quantum mechanics and special relativity. The elegance and simplicity of its construction infused the entire project of quantum physics, through the idea that a minimal combination of relativistic and quantum principles should define the basic building blocks of physical theories. This philosophy produced the mosttested, successful theories of physics, such as quantum electrodynamics (QED). In condensed matter physics, the Dirac equation has become a source of fascination in more recent times. Versions of the Dirac equation describe chiral edge states of quantum Hall droplets, "ultrarelativistic" carriers in graphene, Weyl semimetals, and moire materials, and surface states of 3D topological phases. 
Wednesday, March 6, 2024 9:48AM  10:24AM 
M42.00004: Electronic nematicity in disordered crystals: the impact of random strain Invited Speaker: Rafael M Fernandes Besides superconductivity, magnetism, and charge order, electronic interactions can also promote unusual types of electronic order analogous to liquidcrystalline phases. Indeed, electronic nematicity has been observed in a diverse set of systems, from unconventional superconductors to doped topological insulators to twisted moiré devices. In all cases, the presence of the underlying lattice (or superlattice) significantly influences the critical properties associated with the nematic phase by restricting the allowed directions of the nematic director, mediating longrange nematic interactions, and introducing random strain. The latter is ubiquitously generated in crystals by several sources, such as chemical substitution, vacancies, interstitials, and dislocations. In this talk, I will explore different aspects of the impact of random strain on electronic nematicity. First, I will discuss how surface defects can trigger a modulated nematic phase, which is the analogue of the smectic phase in liquid crystals. Then, I will show that important qualitative effects are not captured by descriptions based solely on the randomfield Ising model, such as the longrange correlated nature of the random strain and the disorderinduced correlations with phases intertwined with nematicity. I will propose and explore the properties of different types of models that incorporate these effects, such as a random Baxterfield model and a transversefield Ising model with correlated random longitudinal and transverse fields. I will conclude by arguing that the interplay between random strain and electronic nematicity leads to a unique landscape of phenomena with no counterparts in clean systems, which could explain puzzling experimental data in different materials. 
Wednesday, March 6, 2024 10:24AM  11:00AM 
M42.00005: Nonequilibrium transport and thermalization in strongly disordered 2D electron systems Invited Speaker: Dragana Popovic Understanding the dynamics of isolated disordered systems and its dependence on the range of interactions has been attracting a lot of research attention in recent years, but many questions remain open, especially in two spatial dimensions. At the same time, experiments have been limited mostly to those on synthetic quantum matter, such as ultracold atoms in optical lattices and superconducting qubits. However, observing the absence of thermalization and signatures of manybody localization (MBL) in real, solidstate materials has been a challenge. 
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