# Effect of Negative permittivity?

• indio007
In summary, the conversation discusses the concept of a negative ε value in quantum theory and its potential impact on probability densities. It is explained that a negative permittivity is possible and can arise near a resonance where the polarization is out of phase with the driving field. This can be understood in the context of a classical driven harmonic oscillator.
indio007
Does anyone know how quantum theory accounts for a ε value that is negative?
Wouldn't this change probability densities?

indio007 said:
Does anyone know how quantum theory accounts for a ε value that is negative?
Wouldn't this change probability densities?

You can have a negative permittivity, no problem. For example, an implicit equation for the dispersion of surface plasmons is given by setting the (frequency and wavelength dependent) permittivity to -1.

Usually a negative permittivity arises just above a resonance where the polarization is 180 degree out of phase with the driving field. This can already be understood in the case of a classical driven harmonic oscillator.

## 1. What is negative permittivity and how does it affect materials?

Negative permittivity is a property of materials that describes how they respond to an electric field. It is defined as the ratio of the electric flux density to the electric field strength in a material. When a material has a negative permittivity, it means that the material can store energy in the form of an electric field, and this energy can be released later. This can affect the behavior and properties of the material, such as its ability to conduct electricity or its optical properties.

## 2. How is negative permittivity measured?

Negative permittivity is typically measured using a device called a capacitance meter. The meter applies an electric field to the material and measures the resulting electric flux density. The ratio of the two values gives the negative permittivity of the material.

## 3. What are some examples of materials with negative permittivity?

Some common materials with negative permittivity include metals, semiconductors, and certain types of crystals. These materials often have unique electrical and optical properties, such as the ability to block or reflect certain wavelengths of light, which make them useful for various applications in technology and science.

## 4. How does negative permittivity play a role in electromagnetic waves?

Negative permittivity is a crucial factor in the behavior of electromagnetic waves. In materials with negative permittivity, the speed of light is slower than in a vacuum, and the wavelength of the wave is shortened. This phenomenon is known as negative refraction and has important implications for the design of materials for lenses and other optical devices.

## 5. Can negative permittivity be manipulated or controlled?

Yes, negative permittivity can be manipulated and controlled through the use of metamaterials. These are artificially engineered materials with unique properties that can be designed to have negative permittivity. They are currently being studied and developed for various applications, including advanced optics, telecommunications, and sensing technologies.

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