When superconductivity disappears in a quantum tube

By replacing the electrons with ultra-cold atoms, a group of physicists has created a perfectly clean material, unveiling new states of matter at the quantum level.

In a one-dimensional periodic potential, represented here by a Toblerone bar, there is no flow of electrons (represented by Gummy bears) when two of them occupy a hollow space. The research made it possible to observe similar behaviour with ultra-cold lithium-6 atoms. (ETH Zurich)
In a one-dimensional periodic potential, represented here by a Toblerone bar, there is no flow of electrons (represented by Gummy bears) when two of them occupy a hollow space. The research made it possible to observe similar behaviour with ultra-cold lithium-6 atoms. (ETH Zurich)

A material is a metal or an insulator relies upon a progression of microscopic details, for example, the quality of the connections between electrons; the nearness of impurities or obstacles; or the number of measurements through which the charge transporters can engender. This high level of complexity implies that anticipating the electronic properties of a given material is a hard errand.

Regardless of whether we know superbly how to demonstrate the direction of a molecule in a vacuum, we battle to do a similar thing in a material (a precious stone for instance), where the electrons flow between the cores of emphatically charged iotas. The last produce an intermittent potential, much like a progression of pinnacles that influence the movement of the electrons, along these lines complicating predictions as follows:

Will the material be a metal? An insulator? Or a semiconductor? However, it will all depend on two parameters: the strength of the interaction between the electrons and the strength of the periodic potential.

To figure out the answer of these questions, physicists from the University of Geneva (UNIGE), ETH Zurich and EPFL conducted an experiment where they replaced the electrons with ultra-cold neutral lithium atoms that they had circulated in a one-dimensional quantum tube. By using a very clean artificial material, they could control the interaction and the periodic potential.

Instead of circulating electrons whose long-range interactions make predictions more difficult, the scientists used ultra-cold neutral lithium-6 atoms, which they stored using a laser in two borderless tanks, veritable ‘bowls of light’.

Next, they connected some atomic reservoirs in which a second laser was employed to simulate the ‘peaks’ of the periodic potential. The scientists could gauge the conductivity of the tube while differing the important parameters, including the length and stature of the occasional potential together with the connections between the particles going through it.

The researchers featured a bizarre state of matter, anticipated by the hypothesis yet which nobody had possessed the capacity to see until at that point: a band insulator that is kept up paying little respect to the quality of the appealing connection between the particles. The instinctive conclusion was that the more prominent the fascination between the particles, the more probable it was that the material would be a conductor or superconductor.

Giamarchi explained, “The core of this experiment is the coldest place in the universe. The temperature there only reaches 70 billionths of a degree above absolute zero, which is much lower than in an interstellar vacuum.”

“It’s true, in a three-dimensional world but in the low-dimensional quantum world, it’s an urban legend. When you manage to confine the material in a one-dimensional quantum tube with a periodic potential, it remains insulating, even if there is an infinite attraction.”

“We can see this system as a kind of simulator that will define the ingredients to be used to devise a material that does not yet exist, and that could meet the requirements for future electronic systems – in quantum computers, for example.”

This work, published in PRX, opens the way to the search for new materials with atypical properties.