Thin Layer In The Light

LMU scientists have investigated the optical properties of novel ultra-thin semiconductors and have developed a method for characterizing such materials quickly and efficiently.

They are novel semiconductors with astonishing optical properties: chemical compounds with elements from the group of transition metals can be prepared in such a way that two-dimensional crystals are formed from a single layer of atoms. A team of LMU physicists led by Alexander Högele has now investigated the properties of such semiconductor-layer of so-called transition metal dichalcogenides in cooperation with American scientists. On their findings, the researchers report in the journal Nature Nanotechnology .

The novel semiconductors have a particularly strong light-matter interaction and thus a great potential for various optoelectronic applications. In addition, electrons in the semiconductor can be excited with polarized light. "Circularly polarized light generates charge carriers that move cyclically either clockwise or counterclockwise. Their motion is thus quantized by the spin, which is described by the so-called Valley Index and detected as Valley polarization, "says Högele. According to the laws of quantum mechanics, the Valley Index can therefore be used in analogy to the quantized spin as a basic variable for applications that could reach the quantum computer.

However, the state-of-the-art research on the Valley Index is quite controversial: different values ​​for the Valley polarization of semiconductors have been observed in different studies around the world. In the example of the thin-film semiconductor, molybdenum disulfide, the scientists were able to elucidate the causes of such variances by means of a newly developed polarimetric method: "The response to polarized light strongly depends on crystal quality and can therefore vary considerably within one and the same crystal," says the physicist. "The relationship found by us between crystal quality and Valley-polarization may in future help, which are important for quantum technological applications sample parameters to determine quickly and efficiently."

In addition, the new method can be applied to other single-layer semiconductor and even to systems of several such materials. As a result, components based on these new atomically thin semiconductors, such as new LEDs, could be tested quickly and efficiently for their functionality in the future.