Evidence of directional structural superlubricity and L\'evy flights in a van der Waals heterostructure

TL;DR

This paper demonstrates directional structural superlubricity in a van der Waals heterostructure, revealing spontaneous island hopping and L{é}vy flight dynamics, a phenomenon largely unobserved in condensed matter.

Contribution

It provides the first evidence of directional superlubricity in a 2D heterostructure and uncovers L{é}vy flight behavior in condensed matter systems.

Findings

Directional superlubricity observed in $$-bismuthene/graphite heterostructure

Spontaneous island hopping over hundreds of nanometres at room temperature

Heavy-tailed distribution of hopping lengths and sticking times indicating L{é}vy flights

Abstract

Structural superlubricity is a special frictionless contact in which two crystals are in incommensurate arrangement such that relative in-plane translation is associated with vanishing energy barrier crossing. So far, it has been realized in multilayer graphene and other van der Waals two-dimensional crystals with hexagonal or triangular crystalline symmetries, leading to isotropic frictionless contacts. Directional structural superlubricity, to date unrealized in two-dimensional systems, is possible when the reciprocal lattices of the two crystals coincide in one direction only. Here, we evidence directional structural superlubricity a $\alpha$-bismuthene/graphite van der Waals system, manifested by spontaneous hopping of the islands over hundreds of nanometres at room temperature, resolved by low-energy electron microscopy and supported by registry simulations. Statistical analysis of individual and collective $\alpha$-bismuthene islands populations reveal a heavy-tailed distribution of the hopping lengths and sticking times indicative of L{\'e}vy flight dynamics, largely unobserved in condensed-matter systems.