Semiconductors reach the quantum world

Date:
December 22, 2021
Source:
Paul Scherrer Institute
Summary:
Quantum effects in superconductors could give semiconductor
technology a new twist. Researchers have identified a composite
material that could integrate quantum devices into semiconductor
technology, making electronic components significantly more
powerful.



FULL STORY ========================================================================== Quantum effects in superconductors could give semiconductor technology
a new twist. Researchers at the Paul Scherrer Institute PSI and Cornell University in New York State have identified a composite material that
could integrate quantum devices into semiconductor technology, making electronic components significantly more powerful. They publish their
findings today in the journal Science Advances.


==========================================================================
Our current electronic infrastructure is based primarily on
semiconductors.

This class of materials emerged around the middle of the 20th century and
has been improving ever since. Currently, the most important challenges
in semiconductor electronics include further improvements that would
increase the bandwidth of data transmission, energy efficiency and
information security.

Exploiting quantum effects is likely to be a breakthrough.

Quantum effects that can occur in superconducting materials are
particularly worthy of consideration. Superconductors are materials in
which the electrical resistance disappears when they are cooled below
a certain temperature. The fact that quantum effects in superconductors
can be utilised has already been demonstrated in first quantum computers.

To find possible successors for today's semiconductor electronics,
some researchers -- including a group at Cornell University -- are investigating so- called heterojunctions, i.e. structures made of two
different types of materials. More specifically, they are looking at
layered systems of superconducting and semiconducting materials. "It
has been known for some time that you have to select materials with
very similar crystal structures for this, so that there is no tension
in the crystal lattice at the contact surface," explains John Wright,
who produced the heterojunctions for the new study at Cornell University.

Two suitable materials in this respect are the superconductor niobium
nitride (NbN) and the semiconductor gallium nitride (GaN). The latter
already plays an important role in semiconductor electronics and is
therefore well researched.

Until now, however, it was unclear exactly how the electrons behave
at the contact interface of these two materials -- and whether it is
possible that the electrons from the semiconductor interfere with the superconductivity and thus obliterate the quantum effects.

"When I came across the research of the group at Cornell, I knew: here
at PSI we can find the answer to this fundamental question with our spectroscopic methods at the ADRESS beamline," explains Vladimir Strocov, researcher at the Synchrotron Light Source SLS at PSI.

This is how the two groups came to collaborate. In their experiments,
they eventually found that the electrons in both materials "keep to themselves." No unwanted interaction that could potentially spoil the
quantum effects takes place.

Synchrotron light reveals the electronic structures The PSI researchers
used a method well-established at the ADRESS beamline of the SLS: angle-resolved photoelectron spectroscopy using soft X-rays -- or SX-
ARPES for short. "With this method, we can visualise the collective motion
of the electrons in the material," explains Tianlun Yu, a postdoctoral researcher in Vladimir Strocov's team, who carried out the measurements
on the NbN/GaN heterostructure. Together with Wright, Yu is the first
author of the new publication.

The SX-ARPES method provides a kind of map whose spatial coordinates
show the energy of the electrons in one direction and something like
their velocity in the other; more precisely, their momentum. "In
this representation, the electronic states show up as bright bands in
the map," Yu explains. The crucial research result: at the material
boundary between the niobium nitride NbN and the gallium nitride GaN,
the respective "bands" are clearly separated from each other. This tells
the researchers that the electrons remain in their original material
and do not interact with the electrons in the neighbouring material.

"The most important conclusion for us is that the superconductivity
in the niobium nitride remains undisturbed, even if this is placed
atom by atom to match a layer of gallium nitride," says Vladimir
Strocov. "With this, we were able to provide another piece of
the puzzle that confirms: This layer system could actually lend
itself to a new form of semiconductor electronics that embeds
and exploits the quantum effects that happen in superconductors." ========================================================================== Story Source: Materials provided by Paul_Scherrer_Institute. Original
written by Laura Hennemann. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Tianlun Yu, John Wright, Guru Khalsa, Betu"l Pamuk, Celesta
S. Chang,
Yury Matveyev, Xiaoqiang Wang, Thorsten Schmitt, Donglai Feng,
David A.

Muller, Huili Grace Xing, Debdeep Jena, Vladimir
N. Strocov. Momentum- resolved electronic structure and band
offsets in an epitaxial NbN/GaN superconductor/semiconductor
heterojunction. Science Advances, 2021; 7 (52) DOI:
10.1126/sciadv.abi5833 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211222152958.htm

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