University of Minnesota
School of Physics & Astronomy

Research Spotlight

How to beat the Pauli Principle

Oriol Valls
Oriol Valls
Alex Schumann

Oriol T. Valls studies unusual properties of nanostructures consisting of layers of intercalated superconductor and ferromagnetic materials. Such structures are interesting for their applications in spintronics and because their physics are not completely understood. These structures exhibit what are called proximity effects: the superconductivity leaks into the magnetic layers and the magnetism into the superconducting ones.

Ordinary Cooper pairs (a pair of electrons bound together at low temperatures) in which the electrons have opposite spin are broken inside of ferromagnets. However they can be converted into triplet pairs with parallel spins. Professor Valls and his group proved that this can happen without violating the Pauli Exclusion Principle because the spin symmetric state occurs with a time delay. One member of the triplet pair has its spin correlated with that of the other but after a time delay. Recently, it has been shown experimentally that these triplet pairs exist and survive in a way that quantitatively agrees with the theory developed by the Valls’ group.

The group is also studying transport properties (their charge and spin) of these structures. They have found that in order to preserve the conservation laws, it is necessary to perform all calculations self-consistently, that is, with the superconducting proximity effects taken fully into account. Valls says that that previous calculations performed by other groups overlooked this important point.

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