In the lab at the Los Alamos Center for Integrated Nanotechnology, Michael Pettes and graduate research associate Micah Vallin used a custom confocal Raman spectroscopy to examine the vibrational signatures of two-dimensional magnetic materials at low temperatures. Image credit: Los Alamos National Laboratory
New research into the topological phase of matter may spur advances in innovative quantum devices. As described in a new paper published in the journal Nature Communications, a team of researchers, including scientists at Los Alamos National Laboratory, used a novel strain engineering approach to transform the material hafnium pentatelluride (HfTe5) into a strong topological insulator phase, increasing its volume resistance while decreasing its surface resistance, which is key to unlocking its quantum potential.
"I'm thrilled that our team was able to demonstrate that the elusive and highly sought-after topological surface state can be the primary conductive pathway," said Michael Pettes, a scientist at the Center's Center for Integrated Nanotechnology (CINT) in the lab.
"This is promising for the development of quantum optoelectronic devices, dark matter detectors, and topology protection devices such as quantum computers. The method we demonstrate is compatible with experiments with other quantum materials.
Strain engineering methods produce results
At the University of California, Irvine, members of the research team planted HfTe5 crystals and applied a strain engineering approach — applying mechanical force to the material at a low temperature of 1.5 Kelvin, or about minus 457 degrees Fahrenheit.
At Pettes' CINT laboratory in Los Alamos, samples are spectroscopically analyzed to image them at the submicron level. The CINT researchers then conducted angle-resolved optical emission spectroscopy at the University of Tennessee, helping to elucidate the effects of strain engineering.
- Pettes and Vallin work in CINT's lab. Image credit: Los Alamos National Laboratory
- Close-up view of confocal Raman spectroscopy using a 532 nm laser (see green) to probe the vibrating structure of van der Waals material contained in a 3.8 Kelvin high vacuum cryostat. Image credit: Los Alamos National Laboratory
The research team realized that strain engineering had changed the behavior of HfTe5, transforming it from a weak topological insulator to a strong topological insulator. That is, the bulk resistivity of the material, or the resistance to allow current to pass through, increases by more than three orders of magnitude.
The material also sees its topological surface state predominate in electron transport. These features can make HfTe5 ideal for quantum devices. These promising results also bode well for the extension of strain engineering methods to the study of topological phase transitions in van der Waals materials and heterostructures, which are characterized by strong in-plane bonds and weak out-of-plane bonds between atoms or molecules, just like the pages in a book.
When studied at high magnetic fields, the newly discovered topological properties may help reveal phenomena related to singular physics, such as quantum anomalies, unexplained symmetry breaks in physics. New experiments being conducted at the Pulsed Field Facility of the Los Alamos National High Magnetic Field Laboratory Subject HfTe5 strain under ultra-high magnetic fields of up to 65 Tesla.
More information: Jinyu Liu et al., Controllable strain-driven topological phase transitions and dominant surface state transfer in HfTe5, Nature Communications (2024). DOI： 10.1038/s41467-023-44547-7
期刊信息：Nature Communications