Researchers from the Photonics Initiative at the Advanced Science Research Center at The Graduate Center, CUNY (CUNY ASRC), and Georgia Tech have provided a major breakthrough. They presented with the first demonstration of topological order based on time modulations, which is a major advancement as far as Physics and Engineering are concerned.
Researchers can now propagate sound waves along the boundaries of topological metamaterials without worrying about them going backward or being thwarted by material defects.
How Will This Discovery Help Us?
The new results, published in Science Advances, will pave the way for cheaper, lightweight devices that use less battery power and can operate in harsh environments. The paper was co-authored by Andrea Alù, founding director of the CUNY ASRC Photonics Initiative and Professor of Physics at The Graduate Center, CUNY, and postdoctoral research associate Xiang Ni. They were joined by Georgia Tech’s Amir Ardabi and Michael Leamy.
The study of properties of an object that are not affected by continuous deformations is known as topology. Electrical currents will flow along the boundaries of a topological insulator, and this flow is resistant to interruption by the object’s imperfections. Following similar concepts, recent advances in the field of metamaterials have expanded these features to regulate the transmission of sound and light.
If you are writing a paper on it, you should be familiar with Wave Theory, and the Physics behind Sound Waves. If you need Physics homework help, you can seek professional assistance online.
Previous research from Alù’s and Alexander Khanikaev’s labs at City College of New York used geometrical asymmetries to establish topological order in 3D-printed acoustic metamaterials. Sound waves were seen to be limited to traveling around the object’s edges and around sharp corners in these objects, but there was a major downside.
These waves weren’t fully constrained; they could move forward or backward while maintaining the same properties. This effect restricted the overall solidity of this approach to topological order for sound. Certain forms of disorder or imperfections would, in fact, represent sound propagating along the object’s boundaries backward.
A terminology was used in the previous section, known as geometrical asymmetry. For that, you have to understand geometric symmetry. Symmetry is characterized in geometry as a balanced and proportionate similarity between two halves of an object. It implies that one half is the mirror image of the other. The line of symmetry is an imaginary line or axis around which you can fold a figure to obtain symmetrical halves.
There are four types of symmetry
- Translation Symmetry
- Rotational Symmetry
- Reflection Symmetry
- Glide Symmetry
Essentially, geometric asymmetry deals with objects that do not exhibit these properties. If the object is split into two halves, there can be no mirror images.
Overcoming the Shortcoming
This latest experiment overcomes this barrier by demonstrating that topological order can be induced using time-reversal symmetry breaking rather than geometrical asymmetries. In topological insulators, the absence of time-reversal symmetry is critical for the occurrence of topologically protected surface states.
Sound propagation becomes completely unidirectional and highly resistant to disorder and imperfections using this tool. As per Alù, the result is a breakthrough for topological physics, as the scientists were able to demonstrate topological order arising from time variations. This is distinct from and more beneficial than the broad body of work on topological acoustics based on geometrical asymmetries.
He mentioned that previous methods necessitated the existence of a backward channel through which sound could be reflected. This resulted in a limitation of their topological protection. The researchers were able to suppress backward propagation and provide good topological security using time modulations.
What Did the Researchers Use?
The researchers created a system with a honeycomb lattice of circular piezoelectric resonators arranged in repeating hexagons and bonded to a thin polylactic acid disc. They then linked this to external circuits, which produced a time-modulated signal that disrupted the time-reversal symmetry.
Their architecture also allows for programmability. As a result, they can direct waves along with a number of reconfigurable paths with little loss. This finding could support sonar, ultrasound imaging, and electronic systems that use surface acoustic wave technology, according to Alù.
As per the authors, Topological Order has been attracting increased attention for classical wave phenomena. It started right after the discovery of the Quantum Hall Effect (QHE) in condensed matter physics. Mechanical topological insulators (TIs), in particular, are simple to fabricate and exhibit interfacial wave transport with minimal dissipation, allowing for efficient and reliable signal transport.
Quantum Hall Effect
In order to understand what has been written so far, one needs to comprehend Quantum Hall Effect. In two-dimensional electron systems subjected to low temperatures and intense magnetic fields, the quantum Hall effect is observed. It is a quantized variant of the Hall effect in which the Hall resistance Rxy exhibits steps that take on quantized values at a certain stage.
Rxy= (VH)/IC= h/ (e2v)
Here, VHis the Hall voltage and IC is the channel current. And, h is the Planck’s constant and e is the elementary charge, and v is the divisor.
The QHE seen in the 2D electron gas (2DEG) developed in semiconductor GaAs/AlGaAs heterojunctions has been used to describe the ‘ohm’ in metrology, the field of standards, and defining SI units. Graphene also exhibits its own kind of QHE, which has sparked interest in it as a possible calibration norm.
Hopefully, you have some insight into the research carried out by Andrea Alù, Xiang Ni, Amir Ardabi, and Michael Leamy. If you go through the journal, you will get further insight into the subject matter.
About Author: Jacob Ryan is a former Physics professor at a reputed university in Canada. Though he has retired from teaching, he still shares important updates and offers his perspective on the matter. Currently, he is associated with MyAssignmenthelp.com, where he supervises the academic papers written by the experts.