Probing Local Structure in Glass by the Application of Shear

TL;DR

This paper introduces the shear penetration depth as a new lengthscale to quantify structural connectivity in supercooled liquids, demonstrating its growth near the glass transition through simulations of NiZr2.

Contribution

The paper proposes a novel lengthscale, the shear penetration depth, and provides numerical evidence of its divergence approaching the glass transition.

Findings

Shear penetration depth increases dramatically near the glass transition.

Numerical simulations show divergence of the lengthscale at the transition.

Connects structural connectivity with the glass transition theory.

Abstract

The glass transition remains one of the great unsolved mysteries of contemporary condensed matter physics. When crystallization is bypassed by rapid cooling, a supercooled liquid, retaining amorphous particle arrangment, results. The physical phenomenology of supercooled liquids is as vast as it is interesting. Most significant, the viscosity of the supercooled liquid displays an incredible increase over a narrow temperature range. Eventually, the supercooled liquid ceases to flow, becomes a glass, and gains rigidity and solid-like behaviors. Understanding what underpins the monumental growth of viscosity, and how rigidity results without long range order is a long-sought goal. Many theories of the glassy slowdown require the growth of static lengthscale related to structure with lowering of the temperature. To that end, we have proposed a new, natural lengthscale- "the shear penetration depth". This lengthscale quantifies the structural connectivity of the supercooled liquid. The shear penetration depth is defined as the distance up to which a shear perturbation applied to the boundary propagates into the liquid. We provide numerical data, based on the simulations of $NiZr_2$, illustrating that this length scale exhibits dramatic growth and eventual divergence upon approach to the glass transition. We further discuss this in relation to percolating structural connectivity and a new theory of the glass transition.