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To reliably transmit information, cells exploit nonequilibrium drives to reduce errors. Kinetic proofreading is a classic mechanism that sharpens ligand discrimination by T lymphocytes, yet it remains unclear whether adaptive immunity relies on kinetic proofreading alone to achieve high fidelity. Here, we propose an alternative: an enhanced form of mechanical proofreading (MPR), in which adaptive force generation during dynamic cell-cell contact enables faithful selection of high-affinity B lymphocytes. Using a coarse-grained model validated by experiments, we show that adaptive MPR, characterized by mechanical feedback between force exertion and contact formation, supports robust discrimination of receptor quality regardless of ligand quantity. While MPR generally balances tradeoffs between speed and fidelity, a negative scaling of contact duration with ligand abundance reveals the presence of feedback. By modulating interactions among distinct ligands that share mechanical load at membrane contacts, adaptive MPR may help mitigate autoimmunity or enhance multivalent vaccines. Overall, this work generalizes proofreading to include cellular designs that operate across scales to reconcile competing functional demands at the systems level. 

The growing interest in the growth and study of thin films of low-dimensional metallic delafossites, with the general formula ABO2, is driven by their potential to exhibit electronic and magnetic characteristics that are not accessible in bulk systems. The layered structure of these compounds introduces unique surface states as well as electronic and structural reconstructions, making the investigation of their surface behavior pivotal to understanding their intrinsic electronic structure. In this work, we study the surface phenomena of epitaxially grown PtCoO2, PdCoO2, and PdCrO2 films, utilizing a combination of molecular-beam epitaxy and angle-resolved photoemission spectroscopy. Through precise control of surface termination and treatment, we discover a pronounced 3×3 surface reconstruction in PtCoO2 films and PdCoO2 films, alongside a 2 × 2 surface reconstruction observed in PdCrO2 films. These reconstructions have not been reported in prior studies of delafossites. Furthermore, our computational investigations demonstrate the BO2 surface’s relative stability compared to the A-terminated surface and the significant reduction in surface energy facilitated by the reconstruction of the A-terminated surface. These experimental and theoretical insights illuminate the complex surface dynamics in metallic delafossites, paving the way for future explorations of their distinctive properties in low-dimensional studies. 

Utilizing the powerful combination of molecular-beam epitaxy (MBE) and angle-resolved photoemission spectroscopy (ARPES), we produce and study the effect of different terminating layers on the electronic structure of the metallic delafossite PdCoO 2 . Attempts to introduce unpaired electrons and synthesize new antiferromagnetic metals akin to the isostructural compound PdCrO 2 have been made by replacing cobalt with iron in PdCoO 2 films grown by MBE. Using ARPES, we observe similar bulk bands in these PdCoO 2 films with Pd-, CoO 2 -, and FeO 2 -termination. Nevertheless, Pd- and CoO 2 -terminated films show a reduced intensity of surface states. Additionally, we are able to epitaxially stabilize PdFe x Co 1− x O 2 films that show an anomaly in the derivative of the electrical resistance with respect to temperature at 20 K, but do not display pronounced magnetic order.