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December 04, 2012

Dirac electrons found in unique material

In a discovery that helps clear a new path toward quantum computers, University of Michigan physicists have found elusive Dirac electrons in a superconducting material.

Quantum computers use atoms themselves to perform processing and memory tasks. They promise dramatic increases in computing power because of their ability to carry out scores of calculations at once. They could factor numbers dramatically faster than conventional computers, and would be game-changers for computer security.

The combination of properties the researchers identified in a shiny, black material called copper-doped bismuth selenide adds the material to an elite class that could serve as the silicon of the quantum era. Copper-doped bismuth selenide is a superconducting material.

Superconductors can—at cold enough temperatures—conduct electricity indefinitely from one kickstart of energy. They have no electrical resistance. Dirac electrons, named after the English physicist whose equation describes their behavior, are particles with such high energy that they straddle the realms of classical and quantum physics.

Physical Review Letters - Quantum Oscillations in the Topological Superconductor Candidate Cu0.25Bi2Se3



Quantum oscillations are generally studied to resolve the electronic structure of topological insulators. In Cu0.25Bi2Se3, the prime candidate of topological superconductors, quantum oscillations are still not observed in magnetotransport measurement. However, using torque magnetometry, quantum oscillations (the de Haas–van Alphen effect) were observed in Cu0.25Bi2Se3. The doping of Cu in Bi2Se3 increases the carrier density and the effective mass without increasing the scattering rate or decreasing the mean free path. In addition, the Fermi velocity remains the same in Cu0.25Bi2Se3 as that in Bi2Se3. Our results imply that the insertion of Cu does not change the band structure and that conduction electrons in Cu doped Bi2Se3 sit in the linear Dirac-like band.


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