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| The quantum material tantalum disulfide has paradoxical properties: it consists of layers, one of which becomes superconducting upon cooling while the other acts as an insulator. Under pressure, this interplay changes – and the material becomes superconducting at temperatures roughly three times higher. Image Credit: © Studio HübnerBraun |
Scientific Frontline: Extended "At a Glance" Summary: Quantum Materials Under Pressure
The Core Concept: Applying high pressure to the quantum material tantalum disulfide dramatically increases the temperature at which it achieves superconductivity and fundamentally alters the nature of its superconducting state.
Key Distinction/Mechanism: Unlike under standard atmospheric conditions where insulating atomic layers disrupt the process, immense pressure compresses the crystal layers of tantalum disulfide. This physical squeezing brings superconducting layers into closer contact, releases electrons from the insulating layer, and enables a robust, three-dimensional superconductivity with a sevenfold increase in participating electrons.
Major Frameworks/Components:
- Muon Spin Spectroscopy: The use of muons—heavy, unstable elementary particles—as highly sensitive microscopic probes to investigate the magnetic fields and superconducting properties within the material.
- Crystal Lattice Compression: The physical mechanism of squeezing the atomic layers of tantalum disulfide with pressures hundreds of times greater than a car tire to overcome insulating barriers.
- Altered Electron Pairing: The pressure-induced shift in how electrons pair up and move together through the material, resulting in a more robust superconducting state.
Branch of Science: Condensed Matter Physics, Quantum Physics, and Materials Science.
Future Application: The insights gained from these experiments will aid theoretical physicists in designing tailor-made quantum materials capable of high-temperature (and ideally room-temperature) superconductivity under standard atmospheric pressure.
Why It Matters: Unlocking the mechanisms behind pressure-induced superconductivity provides the foundational knowledge necessary to engineer advanced, zero-resistance materials. This is a critical prerequisite for developing next-generation, energy-efficient technologies and power grids.
Under high pressure, a quantum material can become superconducting at a significantly higher temperature than without pressure. Researchers at the Paul Scherrer Institute (PSI) have now investigated this using muons. Their study provides new insights into the emergence of unconventional superconductivity. This could contribute to the search for superconductors that function at temperatures suitable for practical applications: an important prerequisite for the development of energy-efficient technologies.
Superconductors have long been considered a promising technology for the energy systems of the future. They can conduct electricity without resistance, thus eliminating both conduction losses and waste heat. Up to now, however, superconductors have only been applied in special cases, as in the immensely powerful magnet coils of particle accelerators such as the Large Hadron Collider at CERN. This is because superconductors must be well-cooled, down to extremely low temperatures for some materials. In the future, novel materials with special quantum properties are expected to make superconductivity possible at higher, more easily achievable subzero temperatures. A research team led by Zurab Guguchia at PSI has now provided the first comprehensive characterization of such a quantum material. This should contribute to a detailed understanding of these processes and facilitate the search for technologically usable superconductors. The results are published in the journal Nature Communications.
“Currently, research is being conducted worldwide on novel, unconventional superconductors that exhibit robust superconductivity even at higher temperatures or in strong external magnetic fields,” Guguchia says. The physicist is a research group leader in the PSI Center for Neutron and Muon Sciences and works with his team on the materials of the future.
Layered Material with Surprising Properties
For their new experiments, Guguchia and his team chose a material with an impressive range of unusual quantum properties. Tantalum disulfide belongs to a class of materials made up of extremely thin layers. Although it does not exhibit high-temperature superconductivity, its interesting properties offer exciting opportunities for experimentation. “Its chemical formula sounds very simple: for every tantalum atom, there are two sulfur atoms,” says Guguchia. “But inside, it is an enormously complex material with almost paradoxical properties.”
If tantalum disulfide is produced in the right way, two alternating layers with different atomic arrangements are always formed. “This means that the electronic properties of these two layers behave in completely opposite ways,” the researcher explains. Both layers are metallic at high temperatures and can conduct electrons. As the material cools, something strange happens: one layer becomes an insulator, while the other becomes superconducting. The tantalum disulfide then only conducts current in the superconducting layer, in one plane, because the insulating layers do not allow electrons to pass through.
However, if the material is cooled to an extremely low temperature—to just over one degree above absolute zero—something unusual happens: “Suddenly, the entire material becomes superconducting, so the insulating layers also become conductive and take part in superconductivity,” Guguchia says. If the material is subjected to high pressure, the temperature at which this happens actually increases. The exact reason for this was previously unknown, as the interaction of electrons at the atomic level is not well understood.
Muons Provide Deep Insights into Materials
This is precisely where the PSI team’s experiments come in. The researchers have access to state-of-the-art experimental methods. One important technique is muon spin spectroscopy.
Muons are elementary particles—similar to electrons, but about two hundred times heavier and with a lifetime of only a few millionths of a second. Implanted in materials, muons react to the magnetic properties of their environment with extreme sensitivity. This allows researchers to probe what happens inside a material on a microscopic scale. PSI is particularly well-equipped for such experiments: with the Swiss Muon Source (SμS), it operates the world’s most powerful muon source.
“Since muons are exceptionally sensitive probes for magnetic and superconducting properties, we can gain unique insights into quantum materials here at PSI,” Guguchia says.
In addition to muon measurements, the team used other methods to investigate how electrons move within the material. This combination of techniques enabled a breakthrough in the understanding of tantalum disulfide.
What Happens When the Material Is Squeezed
The researchers conducted a series of experiments in which they subjected the material to varying levels of pressure and analyzed the behavior of electrons within the material at very low temperatures.
Two factors play a role here. At very high pressure—several hundred times higher than in a car tire—the crystal layers of tantalum disulfide are tightly squeezed together. This first leads to the superconducting layers coming into closer contact with each other, so that the separating, insulating atomic layer has a less disruptive effect. Second, some of the electrons in the insulating layer are released and can then also participate in superconductivity. Guguchia summarizes the measurements: “Due to these effects, high pressure causes tantalum disulfide to become superconducting in all three dimensions at temperatures approximately three times higher.” Furthermore, a sevenfold increase was observed in the number of electrons participating in superconductivity.
“So, pressure not only raises the temperature at which superconductivity can occur but also changes the very nature of the superconducting state,” the researcher explains. “It alters the way electrons pair up and move together through the material, resulting in a more robust form of superconductivity.”
Superconductivity Under More Practical Conditions
These precise results will be a valuable aid for theoretical physicists, enabling them to better describe such quantum materials in the future. This will bring the research closer to a long-term goal: tailor-made materials that are superconducting at high temperatures—ideally at room temperature—and under atmospheric pressure. The path to this goal still presents some challenges, but research is advancing. “By investigating important quantum materials, we want to uncover the fundamental mechanisms underlying superconductivity,” Guguchia says. “This will allow us to find ways to optimize the temperatures at which superconductivity occurs.”
In the future, researchers at PSI will be able to delve even deeper into the fascinating world of superconducting quantum materials. After an upgrade of the muon source within the framework of the IMPACT project in the coming years, muon beams hundreds of times more powerful will be available (IMPACT stands for Isotope and Muon Production using Advanced Cyclotron and Target technologies). PSI also leads the Swiss National Centre of Competence in Research (NCCR) Muoniverse. Building on PSI’s muon source, this project brings together muon research from leading institutions in Switzerland. “We are already looking forward to the new perspectives these two developments will offer,” Guguchia concludes. “Especially for work on superconducting quantum materials, this opens up unimagined experimental possibilities.”
Additional information: Dr. Zurab Guguchia is an experimental solid-state physicist specializing in muon spin rotation and magnetotransport under extreme conditions. He leads a research group focused on discovering and controlling competing quantum phases—superconductivity, magnetism, and charge ordering—using parameters such as pressure, tension, and strong magnetic fields. In 2026, he received the ICSM2026 International Career (Lifetime) Achievement Award on Superconductivity for his outstanding work on novel superconducting materials.
Published in journal: Nature Communications
Title: Competing quantum orders in \(6R\text{-TaS}_{\text{2}}\) revealed by pressure
Authors: V. Sazgari, J. N. Graham, S. S. Islam, A. Achari, P. Král, O. Gerguri, J. N. Tangermann, J. A. Krieger, H. Gopakumar, G. Simutis, M. Janoschek, M. Bartkowiak, J.-X. Yin, R. Khasanov, H. Luetkens, F. O. von Rohr, R. R. Nair, and Z. Guguchia
Source/Credit: Paul Scherrer Institute | Dirk Eidemüller
Edited by: Scientific Frontline
Reference Number: phy070726_01