nouvel effet quantique isolant topologique temperature ambiante couv

A new quantum state observed at room temperature could revolutionize electronics

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The search for new topological properties of matter is the new gold rush in modern physics. For the first time, physicists have observed new quantum effects in a topological insulator based on the element bismuth, at room temperature. This discovery opens up a new range of possibilities for the development of efficient and energy-efficient quantum technologies.

In recent years, the study of topological states of matter has attracted considerable attention among physicists and engineers and is currently the subject of great international interest and research. This field of study combines quantum physics with topology, a branch of theoretical mathematics that explores geometric properties that can be deformed, but not inherently change shape.

In other words, topology is the branch of mathematics that studies the properties of geometric objects preserved by continuous deformation without tearing or sticking, like a rubber band that can be stretched without breaking.

Mr. Zahid Hasan, professor of physics at Princeton University, lead author of the current study, underlines in a press release: New topological properties of matter have become one of the most sought-after treasures in modern physics, both from a fundamental physics perspective and finding potential applications in quantum engineering and next-generation nanotechnology. “.

In this context, spintronics arose. It is based on the use of a fundamental property of particles, known as spin, for information processing. Spin is a quantum property of particles closely linked to their rotational properties. It plays an essential role in the properties of matter.

Spintronics is analogous to electronics, the latter uses, instead of spin, the electric charge of an electron. Carrying information about the charge and spin of an electron potentially offers devices with a greater diversity of functionality.

Princeton researchers have discovered that a topological insulator-like material, made from the elements bismuth and bromine, exhibits quantum behaviors observed only under extreme experimental conditions of high pressure and temperatures near absolute zero. This discovery opens up a new range of possibilities for the development of efficient quantum technologies based on spintronics. His work is published in the magazine materials from nature.

A world first at room temperature

It should be noted that scientists have been using topological insulators to demonstrate quantum effects for more than a decade. It is a unique device that acts as an insulator by volume—the electrons inside the insulator are not free to move and therefore do not conduct electricity—but whose surface can nonetheless become a conductor.

The experiment described in this study is the first to observe them at room temperature. Generally, the induction and observation of quantum states in topological insulators requires temperatures close to absolute zero (around -273 degrees Celsius).

In fact, ambient or high temperatures create what physicists call “thermal noise,” defined as an increase in temperature such that atoms begin to vibrate violently. This action can disrupt delicate quantum systems, thus collapsing the quantum state.

In topological insulators, in particular, these higher temperatures create a situation where electrons at the insulator surface invade the insulator volume and cause the electrons to start conducting as well, which dilutes or breaks the special quantum effect.

Therefore, the solution is to subject these experiments to exceptionally cold temperatures, usually at or near absolute zero. At these temperatures, atomic and subatomic particles stop vibrating and are therefore easier to manipulate. However, creating and maintaining an ultra-cold environment is not practical for many reasons: cost, volume, high energy consumption.

A unique topological insulator

Hasan and his team have developed an innovative way to solve this problem. Building on their experience with topological materials, they made a new type of topological insulator based on bismuth bromide, an inorganic crystalline compound sometimes used for water treatment and chemical analysis.

Specifically, you should know that insulators, like semiconductors, have what are called insulation (or band) holes. They are essentially “barriers” between orbiting electrons, a kind of “no man’s land” where electrons cannot pass, the authors explain. These band gaps are extremely important as they provide the cornerstone for overcoming the limitation of obtaining a quantum state imposed by thermal noise.

However, they do if the width of the bandgap exceeds the width of the thermal noise. But too large a bandgap can potentially disrupt the coupling between the electron’s spin and orbit: that’s the interaction between an electron’s spin and its orbital motion around the nucleus. When this perturbation occurs, the topological quantum state collapses. Therefore, the trick to inducing and maintaining a quantum effect is to strike a balance between a wide bandgap and spin-orbit coupling effects.

The insulator that Hasan and his team studied has an isolation gap of more than 200 meV, large enough to overcome thermal noise, but small enough not to disturb the spin-orbit coupling effect and the inversion topology of the insulator. bandaged.

A revolutionary discovery for electronics.

Hassan says: In our experiments, we have found a balance between spin-orbit coupling effects and a large band gap. We found that there is a “sweet spot” where there can be relatively large spin-orbit coupling to create a topological spin and increase the bandgap without destroying it. It’s like a breakeven point for bismuth-based materials, which we’ve been studying for a long time. “.

To highlight this property, the researchers used a subatomic resolution scanning tunneling microscope, a unique device that uses a property known as “quantum tunneling.” Specifically, when the tip of a single atom in the microscope comes within 1 nm of the surface, the electrons at the tip are reluctant to stay on the tip and may transfer to the surface, illustrating tunneling. The microscope determines the electrical conductance between the tip and the surface, that is, the amount of current that passes through it. By scanning line after line, we get an electronic map of the surface and of every atom or molecule placed on it.

This is how the researchers observed a clear Hall edge state of quantum spin, which is one of the important properties that only exist in topological systems. This required additional new instrumentation to uniquely isolate the topological effect.

Nana Shumiya, postdoctoral research associate in electrical and computer engineering, one of the three co-lead authors of the study, explains: ” It’s great that we found them without giant pressure or ultra-high magnetic fields, which makes the materials more accessible for developing next-generation quantum technologies. “. She adds: ” I believe that our discovery will significantly advance the quantum frontier. “.

Now the researchers want to determine what other topological materials might work at room temperature and, more importantly, provide other scientists with the tools and new instrumentation methods to identify materials that work at room temperature and elevated temperatures.

Source: Nature Materials

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