Crackling noise is the intermittent, scale-invariant response of materials systems to external forces. The Earth's crust crackles through earthquakes when sheared by continental drift; paper crackles when crumpled; iron crackles (Barkhausen noise) when magnetized; nanowires crackle when bent; bones crackle before they fracture. The broad range of event sizes in each of these systems reflects emergent scale invariance, which we understand using scaling methods underpinned by renormalization-group theory. The field of crackling noise is maturing scientifically, where identification and quantification of universal scaling functions and corrections to scaling are playing a central role in future applications. With support from the Division of Materials Research, the investigators in the US/Italian Materials World Network project will develop and hone methods to find effective, powerful multivariable scaling functions to describe the effects of long-range fields on crackling noise in magnets and glassy metals, to understand crossovers between different types of emergent scale invariance, and to test basic assumptions in the field about the relation of continuous evolution models and lattice models. In each project, they propose to systematically analyze analytic, singular, and subdominant corrections to the theory, rigorously assess statistical and systematic errors, and extend the realm of applicability of these powerful theories.
NON-TECHNICAL SUMMARY: Many systems, when squeezed, stretched, or twisted, emit crackling noise. The earth's crust crackles through earthquakes as the continents drift apart; bones crackle before they break, paper crackles when crumpled. While a nuisance in many practical applications, this noise can also be useful in testing and predicting failure in materials. The noise also becomes more severe the smaller the system, and can be dominant for some nanoscale systems (forming wires on integrated circuits in modern electronics, for example). Crackling noise happens when a slow force produces a series of sharp events with an enormous range of sizes. In the past two decades, the investigators have explained why crackling noise arises, using tools from statistical mechanics. In this joint international project, they will lead a team of graduate students and post-docs from the US and Italy to turn this explanation into a quantitative tool for predicting and controlling crackling noise. This interdisciplinary project will expose theoretical physics students both to state-of-the art tools in statistical mechanics and to practical materials problems in engineering fracture, nanotechnology and microelectronics.
