By Suchitra Sebastian
Imagine a world where ultra-fast levitating trains zip between destinations, where wind energy from the North Sea and solar energy from the Sahara power the electric grid in New York, where carbon-free electric aircraft crisscross the skies and handheld MRIs deliver bedside scans. Astonishing materials known as superconductors can deliver these and more revolutionary breakthroughs powered by quantum effects.
As electricity flows through normal metals, electrons bump into each other and the crystal structure walls they flow through, losing greater amounts of energy the further they travel. But in some remarkable materials known as superconductors, when cooled below a characteristic superconducting temperature, electrons pair up and coalesce into a massive quantum wave, now flowing in coherent motion, without losing any energy at all.
Such exotic behaviour is far from a mere construct. Superconducting magnets, where superconducting current flows without loss through a solenoid to create a magnetic field, are ubiquitous in everyday life, forming the scanning enclosure in MRI machines, and the enormous 27km-long particle accelerator ring at the Large Hadron Collider near Geneva. Lengths of superconducting electricity transmission cables are already used in electricity grids around the world, such as in Essen, Germany.
High voltage, high efficiency
In a world of possibilities, superconductors will be a ubiquitous element of alternative energy transmission. Our present alternating-current (AC) transmission cables lose too much energy and are too unstable to carry electricity over distances approaching several hundreds of metres, from offshore and deserts where alternative energy is created, to urban areas where it is most used; this is where high-voltage direct current (DC) and lossless superconducting electrical transmission cables can have the biggest impact.
In addition to finding ways of engineering better electrical transmission cables out of superconductors that currently operate at the highest known temperatures (which are still incredibly low) – the copper oxide family of superconductors – we need to find families of new superconductors with even higher superconducting temperatures.
Finding new superconductors by design has proved a challenge, given that we still don’t understand the quantum physics behind how the currently best-known copper oxide family of superconductors work. The need of the hour is both to understand the quantum physics underlying the copper oxide family of superconductors, and to find diverse ways of creating new superconductors by design.
Our approach to creating new superconductors by design is to start with materials that are on the verge of being superconducting – of which there are several – often with properties of magnetism, almost insulating character, and a stretched (low-dimensional) crystal structure, and then to subject them to high pressures. We press tiny crystals of selected materials between the tips of diamond anvils, reaching pressures higher than the tip of a stiletto heel, approaching those at the bottom of the ocean.
By applying pressure to selected non-superconducting materials, we find that a transformation occurs, turning them into new superconducting materials, almost by quantum alchemy. This approach has already yielded superconducting temperatures above 200 degree Kelvin (around -73°C), and is expected to yield new and exciting superconducting families of materials.
Going forward, we are looking to create many more diverse families of superconductors by design, ultimately resulting even in room temperature superconductors. This will set us firmly en route to a transformed energy outlook for the world.
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