Superconductors are super resilient to magnetic fields

Date:
September 10, 2020
Source:
University of Tsukuba
Summary:
A professor provides a new theoretical mechanism that explains
the ability of superconductive materials to bounce back from
being exposed to a magnetic field. This work may lead to energy
systems that operate without resistive losses. It is also useful
for building qubits for quantum computers.



FULL STORY ==========================================================================
A researcher at the University of Tsukuba has offered a new explanation
for how superconductors exposed to a magnetic field can recover --
without loss of energy -- to their previous state after the field is
removed. This work may lead to a new theory of superconductivity and a
more eco-friendly electrical distribution system.


========================================================================== Superconductors are a class of materials with the amazing property
of being able to conduct electricity with zero resistance. In fact,
an electrical current can circle around a loop of superconducting wire indefinitely. The catch is that these materials must be kept very cold,
and even so, a strong magnetic field can cause a superconductor to revert
back to normal.

It was once assumed that the superconducting-to-normal transition caused
by a magnetic field could not be reversed easily, since the energy would
be dissipated by the usual process of Joule heating. This mechanism,
by which the resistance in normal wires converts electrical energy into
heat, is what allows us to use an electric stovetop or space heater.

"Joule heating is usually considered negatively, because it wastes
energy and can even cause overloaded wires to melt," explains Professor Hiroyasu Koizumi of the Division of Quantum Condensed Matter Physics, the Center for Computational Sciences at the University of Tsukuba. "However,
it has been known for a long time from experiments that, if you remove
the magnetic field, a current-carrying superconductor can, in fact, be
returned to its previous state without loss of energy," Now, Professor
Koizumi has proposed a new explanation for this phenomenon. In the superconducting state, elections pair up and move in sync, but the true
cause of this synchronized motion is the presence of so-called "Berry connection," characterized by the topological quantum number. It is an
integer and if it is nonzero, current flows. Thus, this supercurrent
can be switched off abruptly by changing this number to zero without
Joule heating.

The founder of modern electromagnetic theory, James Clerk Maxwell, once postulated a similar molecular vortex model that imagined space being
filled with the rotation of currents in tiny circles. Since everything
was spinning the same way, it reminded Maxwell of "idle wheels," which
were gears used in machines for this purpose.

"The surprising thing is that a model from the early days of
electromagnetism, like Maxwell's idle wheels, can help us resolve
questions arising today," Professor Koizumi says. "This research may help
lead to a future in which energy can be delivered from power plants to
homes with perfect efficiency."

========================================================================== Story Source: Materials provided by University_of_Tsukuba. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Hiroyasu Koizumi. Reversible superconducting-normal phase transition
in a
magnetic field and the existence of topologically protected
loop currents that appear and disappear without Joule
heating. EPL (Europhysics Letters), 2020; 131 (3): 37001 DOI:
10.1209/0295-5075/131/37001 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200910100615.htm

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