Historical research guide · 0629 · 2016
Materials perspective on Casimir and van der Waals interactions
L. M. Woods · D. A. R. Dalvit · A. Tkatchenko · P. Rodriguez-Lopez · A. W. Rodriguez · R. Podgornik
In one minute
Lilia Woods, Diego Dalvit, Alexandre Tkatchenko, Pablo Rodriguez-Lopez, Alejandro Rodriguez and Rudolf Podgornik survey the whole field of forces produced by electromagnetic fluctuations, and their first move is to insist on the unification: the van der Waals force that lets a gecko hang from glass and the Casimir force between two mirrors are one phenomenon, read at different distances. What has changed in the past decade is materials. Graphene absorbs 2.3 percent of the light that falls on it, a figure fixed by the fine-structure constant alone, and that universal response gives it a Casimir force unlike a metal’s, with thermal effects that arrive far sooner. Topological insulators, Chern insulators, chiral metamaterials and sculpted geometries can turn the force from attraction to repulsion. The review’s message to its community is that this force has become a design variable: choose the material and the boundary, and you choose the sign, the strength and the reach of the vacuum’s pull.
Connection
Chapter two rests on the vacuum being measurable, and this is the field’s standard reference for how those measurements are made and what sets their size. Chapter six needs the next step, which this review supplies: the Casimir force is now something engineers select materials to shape, which is exactly what a vacuum energy device has to do.
From the source
Van der Waals and Casimir interactions are the same phenomenon at different scales — both come from electromagnetic fluctuations, both are present between any two objects of finite size at any separation, and at thermodynamic equilibrium the dipole energy of the van der Waals picture is the field energy of the Casimir picture.Section I, Introduction and Figure 1
The force is already an engineering fact at the small scale: it becomes measurable below a micron, it produces the stiction and adhesion that plague micro- and nano-mechanical devices, and it has been used to actuate parts of small devices without contact.Section I, Introduction
Graphene absorbs about 2.3 percent of incident light, a value depending only on the fine-structure constant, and that universal two-dimensional conductivity makes its Casimir interaction differ from a metal’s in sign, magnitude and distance dependence, with thermal fluctuations dominating at far smaller separations.Section III, Dirac materials beyond atomic scale separations
Repulsion is reachable by choosing the boundary rather than by exotic matter: topological and Chern insulators with opposite signs of their topological parameter, chiral metamaterials, interleaved and structured geometries and objects with holes all give predicted or measured repulsive regimes, while a theorem forbids repulsion for any passive metal or dielectric metamaterial treated as an effective medium beyond its unit-cell scale.Section III.E; Sections IV and V
The first Casimir measurement involving graphene, on a graphene and silica system, agreed with theory that includes the Dirac spectrum; free-standing graphene, graphene stacks, and the temperature and asymptotic behaviour are named as the measurements still missing.Section VII, Experiments probing materials aspects
The open question the field states plainly is the low-frequency optical response of metals: thermal Casimir measurements have been read as favouring the Drude model in one experiment and the plasma model in others, and the isoelectronic technique, which removes the electrostatic patch corrections, is the proposed way to settle it.Section VIII, Future outlook
The way in
https://doi.org/10.1103/RevModPhys.88.045003How to cite it
L. M. Woods, D. A. R. Dalvit, A. Tkatchenko, P. Rodriguez-Lopez, A. W. Rodriguez, R. Podgornik (2016) Materials perspective on Casimir and van der Waals interactions doi:10.1103/RevModPhys.88.045003