It was an effect so huge that it promised to increase the storage of computer hard-drives a thousand times over, but physicists are now clashing over whether it was just a mistake.

The effect, called ballistic magnetoresistance (BMR), would theoretically allow manufacturers to boost the data capacity of hard-drives — packing trillions of bits into a single square inch of disk surface.

The promise of BMR edged closer to reality last year, when Harsh Chopra and Susan Hua at the State University of New York at Buffalo revealed that they had observed a massive increase in resistance at the junction between two nickel wires (H. D. Chopra and S. Z. Hua Phys. Rev. B 66, 020403; 2002). Hard-drives depend on similar, less efficient effects for reading and storing data.

Now, a team led by William Egelhoff of the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, says it has results that cast doubt on Chopra and Hua’s findings.

BMR occurs when electrons aligned in one direction…

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