Speaker

Title

Kristian Berland

Recent developments in van der Waals density functional theory and its future

Abstract : Density functional theory is the workhorse method for gaining atom-level understanding in material science, condensed matter physics, and chemistry. Lack of London dispersion forces was once a hallmark deficiency of DFT, but much progress has been made with methods such as the van der Waals density functional (vdW-DF). In this talk, I will discuss recent and potential future developments of the method and argue why its electronic-density based description has inherent advantages compared to an atom-based description. I hope my talk can stimulate to a discussion on what would be the best way to bridge the mesoscopic description employed in modelling Casimir forces, where dielectric screening effect are essential and retardation can be important, with microscopic descriptions, which hinges on a detailed knowledge of the atomic structure.

Michael Bordag

On the entropy of a spherical plasma shell

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Mathias Boström

A habitat for life

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Iver Brevik

Repulsive Casimir Forces

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Inés Cavero-Pelaéz

Renormalization group flow and C-functions

Manuel Donaire

Casimir Momentum of Chiral Molecules and Nucleons in Magnetic Fields

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Johannes Fiedler

Orientational dependent van der Waals forces and their application to spectroscopy

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Johan Høye

Correlation energy of the uniform quantized electron gas

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Roland Kjellander

Nonlocal Electrostatics in Electrolytes: Consequences for Screened Electrostatic Interactions

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Eduardo Lima

Colloid science and van der Waals interactions: applications in biology, cosmetics and petroleum science

Abstract : The talk will start with a brief introduction about colloid science and the importance of van der Waals interactions in this field. Then, some physical fundamentals involved in the modeling of colloidal systems will be discussed. Finally examples of applications will be given. These examples will cover several different themes including ion partitioning in animal cells, ecology, protein adsorption, stability of cosmetic emulsions and foams, and asphaltene coagulation.

Bing S.-Lu

Van der Waals interaction between anisotropic topological insulator slabs

Abstract : Van der Waals (vdW) interactions are prevalent in Nature and account for diverse natural phenomena, such as the flocculation of colloids and the adhesion of geckos to walls. Between similar dielectric materials such interactions are typically attractive and give rise to the problem of stiction and non-contact friction in micro and nano electro-mechanical systems, thus it is of potential importance to find possibilities of overcoming such stiction and friction. In the seminar we consider the vdW interaction between topological insulators, which are materials that are characterized by "axion electrodynamics", for which an electric field can give rise to magnetic polarization and a magnetic field can also give rise to electric polarization. For the case of dielectrically anisotropic topological insulators, we examine how such electrodynamics can give rise to the possibility of repulsive vdW forces and a reduction of frictional torque.

Reference: B. S-. Lu, Phys. Rev. B 97, 045427 (2018)

Kimball Milton

Quantum Electromagnetic Stress Tensor in an Inhomogeneous Medium

Abstract : Continuing a program of examining the behavior of the vacuum expectation value of the stress tensor in a background which varies only in a single direction, we here study the electromagnetic stress tensor in a medium with permittivity depending on a single spatial coordinate, specifically, a planar dielectric half-space facing a vacuum region. There are divergences occurring that are regulated by temporal and spatial point-splitting, which have a universal character for both transverse electric and transverse magnetic modes. The nature of the divergences depends on the model of dispersion adopted. And there are singularities occurring at the edge between the dielectric and vacuum regions, which also have a universal character, depending on the structure of the discontinuities in the material properties there. Remarks are offered concerning renormalization of such models, and the significance of the stress tensor. The ambiguity in separating “bulk” and “scattering” parts of the stress tensor is discussed.

Sergei Odintsov

Unifying inflation with dark energy in higher-derivative gravity

Abstract : We study inflation in several models of higher derivative gravity. R2 inflation and its generalizations are discussed. Inflation in quantum R2 gravity is presented. Finally, the unification of inflation with dark energy in higher-derivative gravity is presented.

Prachi Parashar

On the Casimir energy and torque for biaxially anisotropic materials using a perturbative approach

Abstract : We present a systematic decomposition of Casimir energies, suitable for perturbative analysis, that ensures the separation of the divergent contributions to the single-body energies. We use this decomposition to calculate the torque between two planar biaxial materials, which is used in our recently published paper “Distance-Dependent Sign Reversal in the Casimir-Lifshitz Torque,” P. Thiyam, P. Parashar, K. V. Shajesh, O. I. Malyi, M. Boström, K. A. Milton, I. Brevik, and C. Persson, Phys. Rev. Lett. 120, 131601 (2018).

Drew Parsons

Ion specific effects at low concentration: interplay between surface charge and nonelectrostatic physisorption

Irina Pirozhenko

Dispersion forces between fields confined to half spaces

Abstract : We consider the Casimir effect for a scalar field interacting with another scalar field that is confined to two half spaces. This model is aimed to mimic the interaction of the photon field with matter in two slabs. We use Dirichlet boundary conditions on the interfaces for the fields in the half spaces and calculate their one-loop contribution to the wave equation for the other field. We perform the ultraviolet renormalization and develop a convenient formalism for the calculation of the vacuum energy in this configuration.

17.

Aram Saharian

The Casimir effect for current densities in braneworlds with compact dimensions

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18.

K. V. Shajesh

Casimir energies for fractal configurations

Abstract : We show that it is possible to evaluate the Casimir interaction energy of self-similar configurations of $\delta$-function plates using the idea of self-similarity alone. Using scaling arguments and the property of self-similarity we derive the Casimir energies of Sierpinski triangles and Sierpinski rectangles. The Hausdorff-Besicovitch dimension (fractal dimension) of the Casimir energy is introduced and the Berry-Weyl conjecture is discussed for these geometries.

19.

Raul Esquivel Sirvent

General formalism of Casimir forces under external magnetic fields

Abstract : Tuning or controlling the Casimir force is a problem widely study, and several proposals have been made. Metamaterials, phase-change materials, doped semiconductors are some examples. Previously, the use of external magnetic fields was used to reduce the Casimir force.

We present a general description of the role of magnetoplasmons in the Casimir effect and show how the direction of the magnetic field influences the Casimir effect. Depending on the direction of the applied magnetic field, mode conversion of the reflection coefficients is present, and this will change the value of the force.

Given the large magnetic fields needed to see this effect, we explore the use of pseudo-magnetic fields in 2D materials, like graphene under stress.

20.

Priyadarshini Thiyam

Sign-reversal of Casimir-Lifshitz torque over distance for anisotropically polarizable dielectric materials

Abstract : Using the perturbative formalism of deriving retarded Casimir-Lifshitz torque between two biaxial planar slabs (as presented in Talk by Prachi Parashar), we find a sign-reversal effect of the torque with respect to distance owing to specific properties in the in-planar anisotropic polarizabilities of the dielectric slabs. The biaxial material under consideration is the black bulk phosphorus and its 2D counterpart phosphorene. The modeling of the anisotropic frequency-dependent dielectric tensors with density functional theory (DFT) will be briefly addressed.

Lecturer

Topic / Title / Subtitles

Kristian Berland

Friday: Electronic and optical properties in density functional theory and beyond

Saturday: van der Waals density functional theory

(a) Dispersion forces in density functional theory

(b) Applications

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Iver Brevik

On 5D cosmology: (1) Bulk viscosity on single brane; (2) Casimir-related stabilization of a two-brane system

Abstract : (1) The presence of a bulk viscosity for the cosmic fluid on a single Randall-Sundrum brane is considered, assuming the spatial curvature to be zero. The 5D Friedmann equation is derived, together with the energy conservation equation, and the governing equations are solved in special cases. Assuming the bulk viscosity to be proportional to the Hubble parameter, it is pointed out that even if the fluid starts from the quintessence region initially, the presence of a sufficiently large bulk viscosity will drive it into the phantom region and thereafter inevitably into the Big Rip.

(2) A two-brane Randall-Sundrum model is considered, in which there are massive fermions assumed to be present in the AdS 5 bulk. The thermodynamic energy is calculated in the case where the temperature is very low, and is shown to possess a minimum, making it possible to stabilize the brane system without fine-tuning.

Emilio Elizalde

Zeta Functions, the Casimir Effect, and Cosmology

Abstract : A summary of relevant properties of the Riemann zeta function and of different zeta functions corresponding to pseudodifferential operators will be given, mainly in connection with the zeta-function regularization method. After that, important applications of zeta function regularization in quantum field theory, mainly in the calculation of quantum vacuum fluctuations, and in cosmology will be discussed, together with some associated problems.

Johan Høye

Statistical mechanical approach to induced Casimir forces

Abstract : We shortly review and sketch how Casimir forces can be evaluated from the statistical mechanical theory for dielectric fluids. By that the properties of the quantized electromagnetic field are eliminated to be replaced by dipole-dipole interactions between particles (molecules). In this way Casimir forces can be interpreted in different, but equivalent ways, since the physical picture appears quite differently, and methods developed for classical statistical mechanics can utilized. First we here sketch how the electromagnetic field can be removed from the problem to be replaced by dipolar interactions. Then basic theory for polar fluids is considered where general densities can be dealt with on basis of γ-ordering. This is extended to polarizable fluids where the dipole moments are assumed to perform thermal fluctuations in harmonic potentials. On basis of the Feynman path integral it was found that this use of classical statistical mechanics at thermal equilibrium could be extended to quantization of the oscillators with further extension to time dependent interactions like the radiating dipole-dipole interaction. At the end we shortly show how the Casimir free energy between a pair of polarizable particles is obtained from their dipole interaction. Also the corresponding evaluation of the Casimir force between half-planes is briefly indicated.

Roland Kjellander

(a) Electrostatics and dispersion interactions in bulk electrolytes

(b) Surface interactions in electrolyte systems

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Eduardo Lima

Modeling specific ion effects and colloidal interactions: from Poisson-Boltzmann to Density Functional Theory

(a) Fundamentals of classical Poisson-Boltzmann and classical Density Functional Theory

Abstract : In the part (a) of the lecture the physicochemical and statistical mechanics fundamentals of classical Poisson-Boltzmann (PB) and classical Density Functional Theory (DFT) will be discussed: Boltzmann distributions and chemical potential equality; the Poisson Equation; DLVO theory; Hamaker interactions; The Hohenberg-Kohn Theorem; different contributions for the excess Helmholtz energy functionals; the minimization of the Grand Potential, and numerical approaches for solving the resulting equations.

(b) Modifications and Improvements

In the part (b) we will discuss modifications and improvements proposed in both PB and DFT. It will be discussed the inclusion of van der Waals interactions between ions and surfaces and of potentials of mean force coming from molecular simulation, and also the use of different geometries in both theories. The inclusion of ion size correlations and electrostatic correlations in PB will also be addressed. Finally, different approaches to account for electrostatic correlations in DFT will be discussed.

Kimball Milton

Fundamentals of Casimir Physics: Calculating Casimir energies and forces using Schwinger’s effective action and Green’s functions

(a) Formalism: Effective electromagnetic action and variational principle, Symbolic reformulation, TGTG formula,

Local description, Finite temperature

(b) Application: Force on a dielectric body, Planar geometries, Lifshitz formula

Abstract : In these lectures, we give an overview of the effective action (or source theory) approach to Casimir physics spearheaded by Julian Schwinger in the 1970s. Modern developments are sketched, as are applications to parallel dielectrics.

Sergei Odintsov

Introduction to modified gravity: dark energy and cosmological applications

Abstract : We give general overview of several classes of modified gravities including F(R) and F(G) gravity. The corresponding cosmological dynamics is studied. Dark energy universe is described. Number of different cosmological applications are described. Various generalizations to other modified gravities is given.

George Palasantzas

Experimental overview and future directions in the Casimir Physics

(a) Complex materials and optical properties towards Casimir-Lifshitz forces

(b) Geometry, morphology towards Casimir actuation and surface adhesion

Abstract : Understanding the vacuum state of a system is a challenge of fundamental physics and associated important technologies. If confined within boundaries, quantum vacuum fluctuations manifest themselves by the generation of Casimir forces. However, boundaries between interacting bodies possess in many cases nanoscale surface roughness, which is both difficult to avoid and control. When two bodies are separated by a small distance (less than 100 nm) then nanoscale roughness starts to play an important role on the Casimir interaction between the bodies and their adhesion upon contact. Control of this short-distance interaction is crucial for micro and nanoelectromechanical devices, microfluidics, and bonding technologies. The Casimir forces for flat bodies can be described by the Lifshitz theory that takes into account the actual measured, but complex, optical properties of the interacting materials. However, for rough surfaces the problem is more complicated by the nonadditivity of the dispersion forces taking into account variation of optical properties due to variation of material fabrication.

In my two school oriented talks I will review the current state of the problems in relation to future directions and still remaining open problems. Attention will be given to metallic systems, phase change materials, and poor conductors (promising for operation in severe environments) with respect to adhesion/bonding/robotic technologies and actuation dynamics micro/nano electromechanical devices. In addition, several problems will be discussed and solved with the students to increase experimental understanding.

Drew Parsons

Impact of Casimir effects on surface adsorption and surface forces

Synopsis :

• experimental measurement of surface forces

  • surface force apparatus (SFA)

  • atomic force microscopy (AFM)

  • turbidometry

• the colloid chemist’s view of van der Waals forces: DLVO theory

  • electrostatic

  • entropic

  • van der Waals (Hamaker)

• the physicists view of surface force measurements

  • proximity force approximation and the Derjaguin approximation

  • free energy and disjoining pressure

• specific ion effects

  • ion size

  • ionic dispersion forces

• surface charge and ion specificity

  • capacitance

  • charge regulation

• quantum chemistry

  • polarisability and ion size

  • turbomole, molpro, Gaussian, ADF

• Poisson-Boltzmann computations

  • weak formulation and FEniCS

• turbidometry and the second virial coefficient

11.

Aram Saharian

The Casimir effect in gravitational fields

(a) The topological and boundary-induced Casimir densities in de Sitter spacetime
(b) The Casimir effect on anti-de Sitter bulk with applications in braneworlds

12.

Raul Esquivel Sirvent

(a) Dielectric function of Au, Theory, Experiment and Validity

Abstract : In this talk, we discuss the use of the dielectric function in Casimir force calculations the advantages and disadvantages of the use of Matsubara frequencies. First, we discuss the importance of the dielectric function in Casimir force calculations and show that the well known dielectric data for Au by Palik may not be correct in a broad frequency range since it does not satisfy Kramers-Kronig relations, and discuss alternatives for the dielectric function of Au.

(b) Plasmonic and polaritonic materials in the Casimir force. Real frequency representation

In the second part, we analyze the advantages of calculating the Casimir force in the real frequency space where the contribution of the evanescent and propagating modes. In particular, we show the behavior of the force between plasmonic and polaritonic materials and how the coupling of plasmonic and polaritonic modes can be used to change the force. Recent advances in Casimir force in 2D materials will also be discussed.

Speaker

Title

Patrícia Abrantes

Repulsive van der Waals interaction between an atom and a nanoring

Abstract : In this work, we investigate the non-retarded dispersive force exerted on a polarizable quantum particle by a perfectly conducting ring, which has a non-trivial topology. We employ a very convenient method developed by Eberlein and Zietal that essentially transforms the quantum problem of calculating dispersion forces between an atom and a perfectly conducting surface of arbitrary shape into a (presumably simpler) problem of electrostatics. After brie#y introducing this method, we apply it to compute the non-retarded dispersive force between a polarizable quantum particle and a conducting ring, modeled appropriately by a toroid. For simplicity, we consider the particle in the symmetry axis of the toroid. We solve the problem analytically and show that depending on the relations between the various distance scales of the problem (the two radii of the toroid and the distance from the atom to its center), the force exerted on the quantum particle is repulsive.

Victoria Esteso

Casimir force and levitation phenomena in plane-parallel systems made of dielectric materials

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Benjamin Spreng

Numerics for the Casimir interaction for spherical geometries in the plane-wave basis
Abstract : We present a numerical method for computing the Casimir energy within the scattering approach based on plane waves. For plane waves the scattering matrices are integral operators. By employing a Nyström discretization, the scattering formula can be evaluated numerically. A suitable choice of quadrature rules allows to exploit the azimuthal symmetry of the problem leading to a fast numerical scheme. Although the method is applicable to arbitrary materials, we present results for perfectly conducting objects in the sphere-plane and sphere-sphere geometry.

César Romaniega Sancho

Schr\"odinger operators with $\delta$-$\delta'$ potentials and their application to Quantum Field Theory

Abstract : The spectrum of Schr\"odinger operators with spherical potentials of the type $a\delta(r-r_0)+b\delta'(r-r_0)$ is

characterised in arbitrary dimension $d \geq 2$. In particular, we completely solve the scattering problem. This enables us to promote the previous system to an effective scalar massless quantum field theory, computing the Casimir interaction energy between several spherically symmetric bodies using the \textit{TGTG} formula. We specially focus on the Casimir energy between near-Dirichlet spheres $S^{d-1}$.

Daniel Reiche

Spatial dispersion in Atom-surface interactions

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Frieder Lindel

Casimir Force and Torque for Nonreciprocal Media and Applications to Photonic Topological Insulators

Abstract : The Casimir force was originally proposed as an attractive force between two perfectly conducting plates due to a reduced virtual photon pressure in the space between the plates. In macroscopic quantum electrodynamics (QED) the Casimir force was further generalised to bodies of arbitrary shape and material by realising that its existence stems from fluctuating charge carries within the materials.

We derive an even more general expression of the Casimir force within this framework of macroscopic QED for the case of bodies which break the Lorentz reciprocity condition and thus violate time reversal symmetry. We apply our result to a certain photonic topological insulator media, namely magnetised plasma with a static bias magnetic field to find that the Casimir force can be tuned by controlling the bias field. We further show that for certain configurations there exists a tunable Casimir torque which shows unique features due to uni-directional surface plasmons provided by the topological structure of the material.

Helge Dobbertin

Van der Waals interaction at finite temperature

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Luís Pires

Probing colloidal interactions with optical tweezers

Abstract : Using an optical tweezer, our objective is to characterize the screening effect on the Casimir force and corrections to the PFA. In our system, we measured forces in the femntonewton scale between dielectric spheres in water with different saline concentrations. We have already published results for the double layer interaction in our system (Ether Jr, Pires, LB, Umrath, S., Martinez, D., Ayala, Y., Pontes, B., NB (2015) Probing the Casimir force with optical tweezers EPL (Europhysics Letters), 112 (4), 44001.). In this talk will be presented our last results.

Marty Oelschläger

Manipulating Dispersion Forces with Superlattice Nano-structures

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Severin Bang

Calculating Interatomic Coulombic Decay Rates from Atomic Data: A case study

Abstract : Interatomic Coulombic decay is an ultra-fast decay process by which energy can be transported between molecules. There are two main aproaches to the calculation of the ICD rate, namely ab initio quantum chemistry simulations, or in terms of atomic transitions with their associated photon emission and absorption. In this talk, I will discuss the intricacies of the process by which ICD rates can be calculated from atomic line data. The whole ICD process begins with a donor species being in a excited state, followed by a relaxation and the corresponding photon emission, which in turn ionises an acceptor species. The ultimate aim of this work is to critically evaluate the ability of currently available spectral line data to give reliable predictions for ICD. Using data from the NIST spectral line database, we will show an example calculation for a neon-argon cluster. We will also point out cases where the data necessary for such investigations is incomplete. For some transitions, no dipole moments are available, and the photoionization cross-section data is very sparse. Finally, we compare our asymptotic ICD rates with those from ab initio approaches, noting that the latter experience difficulties when taking the large-separation limit of initially composite systems.

Vinicius Henning

Derjaguin approximation and specular reflection application of semiclassical Mie scattering to the Casimir effect

Abstract : The electromagnetic Casimir interaction between two spheres is studied within the scattering approach using the plane-wave basis. It is demonstrated that the proximity force approximation (PFA) corresponds to the specular-reection limit of Mie scattering. Using the leading-order semiclassical WKB approximation for the direct reection term in the Debye expansion for the scattering amplitudes, we prove that PFA provides the correct leading-order divergence for arbitrary materials and temperatures in the sphere-sphere and the plane-sphere geometry. Our derivation implies that only a small section around the points of closest approach between the interacting spherical surfaces contributes in the PFA regime. The corresponding characteristic length scale is estimated from the width of the Gaussian integrand obtained within the saddle-point approximation. At low temperatures, the area relevant for the thermal corrections is much larger than the area contributing to the zero-temperature result.

Yang Li

Casimir Force on Bodies Immersed in Inhomogeneous Media

Wijnand Broer

Casimir Force and Torque between  Multilayer Anisotropic Topological Insulators 

Abstract : It is well established that the Casimir force between 3D topological insulators (TI) can become repulsive if they are covered with a thin magnetic layer. If the TIs are embedded in a multilayer structure, where each layer consist of a TI slab covered by a  normal insulator (NI) slab, the Casimir repulsion will be enhanced compared to the case of a single interface.  Here, we investigate the the Casimir torque and force between two such coplanar TI-NI multilayer slabs separated by a vacuum gap. The optical axes of the anisotropic TI slabs are each perpendicular to the normal direction to the slab-gap interface, and also generally differently oriented from each other.  If the angle between the optical axes is nonzero, the dielectric contrast in the azimuthal direction will give rise to a Casimir torque. The possibility of the force and the torque to change sign could prove useful in building an oscillator based on vacuum forces.