无法停止的磁致电阻

Mazhar Ali, a fifth-year graduate student in the laboratory of Bob Cava, the Russell Wellman Moore Professor of Chemistry at Princeton University, has spent his academic career discovering new superconductors, materials coveted¹ for their ability to let electrons flow without resistance. While testing his latest candidate, the semimetal tungsten ditelluride (WTe2), he noticed a peculiar² result. Ali applied³ a magnetic field to a sample of WTe2, one way to kill superconductivity if present, and saw that its resistance doubled. Intrigued⁴, Ali worked with Jun Xiong, a student in the laboratory of Nai Phuan Ong, the Eugene Higgins Professor of Physics at Princeton, to re-measure the material's magnetoresistance, which is the change in resistance as a material is exposed to stronger magnetic fields.

 

"He noticed the magnetoresistance kept going up and up and up -- that never happens." said Cava. The researchers then exposed WTe2 to a 60-tesla magnetic field, close to the strongest magnetic field humans can create, and observed a magnetoresistance of 13 million percent. The material's magnetoresistance displayed unlimited⁵ growth, making it the only known material without a saturation⁶ point. The results were published on September 14 in the journal Nature.

 

Electronic information storage is dependent on the use of magnetic fields to switch between distinct resistivity values that correlate to either a one or a zero. The larger the magnetoresistance, the smaller the magnetic field needed to change from one state to another, Ali said. Today's devices use layered materials with so-called "giant magnetoresistance," with changes in resistance of 20,000 to 30,000 percent when a magnetic field is applied. "Colossal⁷ magnetoresistance" is close to 100,000 percent, so for a magnetoresistance percentage in the millions, the researchers hoped to coin a new term.

 

Their original choice was "ludicrous" magnetoresistance, which was inspired by "ludicrous speed," the fictional⁸ form of fast-travel used in the comedy "Spaceballs." They even included an acknowledgement to director Mel Brooks⁹. After other lab members vetoed "ludicrous," the researchers considered "titanic¹⁰" before Nature editors ultimately steered¹¹ them towards the term "large magnetoresistance."

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