Nav: Home

'Tantalizing' clues about why a mysterious material switches from conductor to insulator

May 18, 2020

Tantalum disulfide is a mysterious material. According to textbook theory, it should be a conducting metal, but in the real world it acts like an insulator. Using a scanning tunneling microscope, researchers from the RIKEN Center for Emergent Matter Science have taken a high-resolution look at the structure of the material, revealing why it demonstrates this unintuitive behavior. It has long been known that crystalline materials should be good conductors when they have an odd number of electrons in each repeating cell of the structure, but may be poor conductors when the number is even. However, sometimes this formula does not work, with one case being "Mottness," a property based on the work of Sir Nevill Mott. According to that theory, when there is strong repulsion between electrons in the structure, it leads the electrons to become "localized"--paralyzed in other words--and being unable to move around freely to create an electric current. What makes the situation complicated is that there are also situations where electrons in different layers of a 3-D structure can interact, pairing up to create a bilayer structure with an even number of electrons. It has been previously suggested that this "pairing" of electrons would restore the textbook understanding of the insulator, making it unnecessary to invoke "Mottness" as an explanation.

For the current study, published in Nature Communications, the research group decided to look at tantalum disulfide, a material with 13 electrons in each repeating structure, which should therefore be a conductor. However, it is not, and there has been controversy over whether this property is caused by its "Mottness" or by a pairing structure.

To perform the research, the researchers created crystals of tantalum disulfide and then cleaved the crystals in a vacuum to reveal ultra-clean surfaces which they then examined, at a temperature close to absolute zero--with a method known as scanning tunneling microscopy--a method involving a tiny and extremely sensitive metal tip that can sense where electrons are in a material, and their degree of conducting behavior, by using the quantum tunneling effect. Their results showed that there was indeed a stacking of layers which effectively arranged them into pairs. Sometimes the crystals cleaved between the pairs of layers, and sometimes through a pair, breaking it. They performed spectroscopy on both the paired and unpaired layers and found that even the unpaired ones are insulating, leaving Mottness as the only explanation.

According to Christopher Butler, the first author of the study, "The exact nature of the insulating state and of the phase transitions in tantalum disulfide have been long-standing mysteries, and it was very exciting to find that Mottness is a key player, aside from the pairing of the layers. This is because theorists suspect that a Mott state could set the stage for an interesting phase of matter known as a quantum spin liquid."

Tetsuo Hanaguri, who led the research team, said, "The question of what makes this material move between insulating to conducting phases has long been a puzzle for physicists, and I am very satisfied we have been able to put a new piece into the puzzle. Future work may help us to find new interesting and useful phenomena emerging from Mottness, such as high-temperature superconductivity."
-end-


RIKEN

Related Electrons Articles:

Plasma electrons can be used to produce metallic films
Computers, mobile phones and all other electronic devices contain thousands of transistors, linked together by thin films of metal.
Flatter graphene, faster electrons
Scientists from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel developed a technique to flatten corrugations in graphene layers.
Researchers develop one-way street for electrons
The work has shown that these electron ratchets create geometric diodes that operate at room temperature and may unlock unprecedented abilities in the illusive terahertz regime.
Photons and electrons one on one
The dynamics of electrons changes ever so slightly on each interaction with a photon.
Using light to put a twist on electrons
Method with polarized light can create and measure nonsymmetrical states in a layered material.
What if we could teach photons to behave like electrons?
The researchers tricked photons - which are intrinsically non-magnetic - into behaving like charged electrons.
Electrons in rapid motion
Researchers observe quantum interferences in real-time using a new extreme ultra-violet light spectroscopy technique.
Taming electrons with bacteria parts
In a new study, scientists at the MSU-DOE Plant Research Laboratory report a new synthetic system that could guide electron transfer over long distances.
Hot electrons harvested without tricks
Semiconductors convert energy from photons into an electron current. However, some photons carry too much energy for the material to absorb.
Cooling nanotube resonators with electrons
In a study in Nature Physics, ICFO researchers report on a technique that uses electron transport to cool a nanomechanical resonator near the quantum regime.
More Electrons News and Electrons Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Making Amends
What makes a true apology? What does it mean to make amends for past mistakes? This hour, TED speakers explore how repairing the wrongs of the past is the first step toward healing for the future. Guests include historian and preservationist Brent Leggs, law professor Martha Minow, librarian Dawn Wacek, and playwright V (formerly Eve Ensler).
Now Playing: Science for the People

#566 Is Your Gut Leaking?
This week we're busting the human gut wide open with Dr. Alessio Fasano from the Center for Celiac Research and Treatment at Massachusetts General Hospital. Join host Anika Hazra for our discussion separating fact from fiction on the controversial topic of leaky gut syndrome. We cover everything from what causes a leaky gut to interpreting the results of a gut microbiome test! Related links: Center for Celiac Research and Treatment website and their YouTube channel
Now Playing: Radiolab

The Flag and the Fury
How do you actually make change in the world? For 126 years, Mississippi has had the Confederate battle flag on their state flag, and they were the last state in the nation where that emblem remained "officially" flying.  A few days ago, that flag came down. A few days before that, it coming down would have seemed impossible. We dive into the story behind this de-flagging: a journey involving a clash of histories, designs, families, and even cheerleading. This show is a collaboration with OSM Audio. Kiese Laymon's memoir Heavy is here. And the Hospitality Flag webpage is here.