Image illustrating sound frequency with light

A new mechanism has been discovered that controls the flow of sound

The effect of the magnetic field on electrons has a wide influence. It can lead to many unique phenomena in materials. For many applications, it would be useful if the same were achieved for vibrations and sound waves. Scientists have long wanted to see if a similar effect of a magnetic field on electrons could be achieved on sound that does not have a charge.

In a new study, scientists from AMOLF used a network of light-controlled vibrational nanostrings to control the flow of sound. They were able to make sound waves move in a specific, irreversible direction and attenuate or amplify the waves in a controlled manner for the first time. This leads to the effect of the laser on the sound.

Surprisingly, scientists have come up with new mechanisms called “geometric phases”. This mechanism allowed them to control and transmit sound in systems that were thought impossible.

Group leader Ewald Verhagen said, “This opens the way to new types of (descriptive) materials with properties that we don’t yet know from existing materials.”

The magnetic field of sound

Since there is no charge to mechanical vibrations, they do not respond to magnetic fields. But it is sensitive to the pressure of light radiation.

The scientists then used laser light to affect the nanomechanical resonators.

Verhagen said, “We have now shown that if we create a network of multivibrational nanostrings, we can perceive a range of unconventional vibration patterns by illuminating strings with laser light. For example, we have been able to make sound particles (phonons) move in one direction in the same way that they move in one direction. Electrons in the quantum Hall effect.”

Scientists also realized that radiation pressure could also be used to control sound amplification and attenuation.

Verhagen said, “Such amplification or attenuation is impossible for electrons in a magnetic field.”

The scientists are the first to conduct experiments in which propelling light amplifies sound waves while also confirming that they are subjected to a magnetic field-like effect.

Verhagen said, We discovered that amplification and time-reversal symmetry breaking lead to a host of new and unexpected physical effects. First of all, the laser light determines the direction in which the sound is amplified. In the other direction, the sound is blocked. This is caused by a geometric phase: a quantity that indicates how much the sound wave is transformed as it passes through the nanostring network, which in this case is caused by radiation pressure. “

“Our experiment allowed us to fully control and modify that geometric stage. In addition, we used the radiation pressure of the laser light to amplify the sound. This sound can oscillate automatically, like a light in a laser. We discovered that the geometric stage we apply determines whether or not that will happen. And with what power to amplify.”

We discovered that new engineering phases can be achieved in systems where this was not possible. In all of these phases affect the amplification, direction and pitch of sound waves.

Geometrical phases are important in many branches of physics, as they describe the behavior of different systems and materials. When combined with magnetic fields, they can result in a topological insulator of electrons, but which properties a “sound” variable can have based on the discovered principles is something we still need to learn. However, we know this won’t be the same as anything we know.”

“We can further investigate the effects by attaching more nanochains in sonic ‘supermaterials’ that we control with light. But the effects we observed should apply to a range of waves without charge, including light, microwaves, and cold atoms. , etc. We expect that through the new mechanisms that we have discovered, it will be possible to produce new (descriptive) materials with properties that we do not yet know from existing materials.”

“Such materials and systems have unusual properties that may have useful applications. It is still too early to give a complete overview of the possibilities. However, we can already identify some potential trends. For example, a unidirectional amplifier for waves could have Useful applications in quantum communications. We can also make sensors much more sensitive by breaking the time-reversal symmetry.”

Journal reference:

  1. Javier del Pino, Jesse J. Slim, Ewald Verhagen, Non-hermetic chiral acoustics through mechanically induced stress, Nature, 2 June (2022). DOI: 10.1038 / s41586-022-04609-0

2022-06-02 08:08:54

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