Scientists model the formation of multivalleys in semiconductor microcavities

April 25, 2017, Institute for Basic Science
Plot of polaritons' energy dispersion vs momentum in a semiconductor microcavity, seen from above (left) and the side (right). Minimal energy locations, called valleys, are shown with white crosses. Credit: Institute for Basic Science

Everything we experience is made of light and matter. And the interaction between the two can bring about fascinating effects. For example, it can result in the formation of special quasiparticles, called polaritons, which are a combination of light and matter. A team at the Center for Theoretical Physics of Complex Systems, within the Institute for Basic Science (IBS), modeled the behavior of polaritons in microcavities, nanostructures made of a semiconductor material sandwiched between special mirrors (Bragg mirrors). Published in Scientific Reports, this research brings new ideas to the emerging valleytronics field.

Emerging from the coupling of (photons) and matter (bound state of electrons and holes known as excitons), polaritons have characteristics of each. They are formed when a light beam of a certain frequency bounces back and forth inside microcavities, causing the rapid interconversion between light and matter and resulting in polaritons with a short lifetime. "You can imagine these quasiparticles as waves that you make in water, they move together harmoniously, but they do not last very long. The short lifetime of polaritons in this system is due to the properties of the photons," explains Mr Meng Sun, first author of the study.

Researchers are studying polaritons in microcavities to understand how their characteristics could be exploited to outperform the present semiconductor technologies. Modern optoelectronics read, process, and store information by controlling the flow of particles, but looking for new more efficient alternatives, other parameters, like the so-called 'valleys' could be considered. Valleys can be visualized by plotting the energy of the polaritons to their momentum. Valleytronics aims to control the properties of the valleys in some materials, like (TMDCs), indium gallium aluminum arsenide (InGaAlAs), and graphene.

Scientists model the formation of multivalleys in semiconductor microcavities
Model of valleys with different polarizations. The model uses vectors (arrows) and colors (from yellow to blue) to show opposite polarizations on different valleys (white crosses). The opposite polarizations (arrow direction) can be, in principle, excited selectively by a polarized laser. Credit: Institute for Basic Science

Being able to manipulate their features would lead to tunable valleys with two clearly different states, corresponding for example to 1 bit and 0 bit, like on-off states in computing and digital communications. A way to distinguish valleys with the same energy level is to obtain valleys with different polarization, so that electrons (or polaritons) would preferentially occupy one valley over the others. IBS scientists have generated a theoretical model for valley polarization that could be useful for valleytronics.

Although polaritons are formed by the coupling of photons and excitons, the research team modeled the two components independently. "Modeling potential profiles of photons and excitons separately is the key to find where they overlap, and then determine the minimal energy positions where valleys occur," points out Sun.

A crucial feature of this system is that polaritons can inherit some properties, like polarization. Valleys with different polarization form spontaneously when the splitting of the transverse (i.e. perpendicular) electronic and magnetic modes of the is taken into consideration (TE-TM splitting).

Since this theoretical model predicts that valleys with opposite polarization can be distinguished and tuned, in principle, different could be selectively excited by a polarized laser light, leading to a possible application in valleytronics.

Explore further: Carbon nanotubes couple light and matter

More information: M. Sun et al. Multivalley engineering in semiconductor microcavities, Scientific Reports (2017). DOI: 10.1038/srep45243

Related Stories

Carbon nanotubes couple light and matter

November 15, 2016

With their research on nanomaterials for optoelectronics, scientists from Heidelberg University and the University of St Andrews (Scotland) have succeeded for the first time to demonstrate a strong interaction of light and ...

New way to cool micro-electronic devices

May 18, 2015

(Phys.org)—A team of researchers working at the University of Grenoble has developed a new way to cool solids at the micro level. In their paper published in Physical Review Letters, the team describes how they used laser ...

The power of light-matter coupling

February 5, 2015

A theoretical study shows that strong ties between light and organic matter at the nanoscale open the door to modifying these coupled systems' optical, electronic or chemical properties.

Spiral laser beam creates quantum whirlpool

November 17, 2014

(Phys.org) —Physicists at Australian National University have engineered a spiral laser beam and used it to create a whirlpool of hybrid light-matter particles called polaritons.

Recommended for you

ATLAS experiment observes light scattering off light

March 20, 2019

Light-by-light scattering is a very rare phenomenon in which two photons interact, producing another pair of photons. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of ...

How heavy elements come about in the universe

March 19, 2019

Heavy elements are produced during stellar explosion or on the surfaces of neutron stars through the capture of hydrogen nuclei (protons). This occurs at extremely high temperatures, but at relatively low energies. An international ...

Trembling aspen leaves could save future Mars rovers

March 18, 2019

Researchers at the University of Warwick have been inspired by the unique movement of trembling aspen leaves, to devise an energy harvesting mechanism that could power weather sensors in hostile environments and could even ...

Quantum sensing method measures minuscule magnetic fields

March 15, 2019

A new way of measuring atomic-scale magnetic fields with great precision, not only up and down but sideways as well, has been developed by researchers at MIT. The new tool could be useful in applications as diverse as mapping ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.