Posted in | Materials Testing

Superconductivity Discovered In Quasicrystal

A new discovery has been made in the field of quasicrystals which reveals an instance of superconductivity. This means they are an extremely conductive material and it also opens the door to a new type of conductivity - fractal superconductivity.

The Department of Physics at the Graduate School of Science, Nagoya University, in Japan made the discovery of what it says is a first viewing of superconductivity in quasicrystals.

The atoms in quasicrystals are ordered over long distances but not in a periodically repeating arrangement. As such, the quasicrystal studied, Al-Zn-Mg, was found to show low electrical resistivity; key for superconductivity.

A quasicrystal is similar to the classical crystal, which is defined as a periodic arrangement of atoms with translational periodicity leading to an infinitely extended crystal structure by aligning building blocks. The difference is that quasicrystals have a long-range order but not one that is periodic. Another difference is that quasicrystals can feature a five-fold symmetry, meaning a non-crystallographic rotational symmetry.

Despite many previous studies, the electronic state of quasicrystals has largely remained a mystery. This new study has shown that the quasicrystal Al-Zn-Mg can exist in a state of superconductivity, meaning one with zero resistance. The results show not only that this is the first superconducting quasicrystal but also the first to exhibit the electronic long-range order.

The quasicrystals were studied using inductively coupled plasma spectroscopy and scanning electron microscopes. The alloy specimens themselves were crushed into fragments using an agate mortar and pestle, before being transferred onto a micro-grid mesh for the electron microscope observations. X-ray diffractions were also obtained as a measure of reactivity; obtained using a diffractometer.

The physical properties were also controlled. Four dilution refrigerators at the Nagoya and Tohoku Universities were used to control temperature. For electric resistivity four terminal dc or ac methods were used. For magnetic susceptibility a Squid magnetometer was employed. Finally, for the quasi-adiabatic heat-pulse the relaxation method was used.

The researchers say that the results show the formation of spatially extended pairs in the quasicrystal. This is apparently due to temperature dependences of the thermodynamic properties and the upper critical field within the weak-coupling framework of superconductivity. #

While superconductivity was discovered in the quasicrystal, the study did still find that there was a negative temperature coefficient of resistivity. That means that as the temperature increased the resistance did too, reducing the ability to transmit electricity. The peak anomaly which was discovered at low temperatures was the instance of superconductivity taking place.

The study found that bulk superconductivity in quasicrystals was evident from the shielding effect found upon cooling the sample under an external magnetic field. The results confirm that the system was a type-II superconductor, meaning the magnetic field penetrates the sample.

Another interesting result was that the critical eigenstates of quasicrystals would not have a dominant role in the superconductivity of that quasicrystal. However, due to the lack of specific findings for the specific weak-coupling, it would be difficult to find the fractal superconducting order parameter as a prediction.

The researchers look to future research from this finding, saying:“We hope that the present study stimulates a further work to reveal this new type of superconductivity.”

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