10 February 2017

Fancy fridge for frigid physics

MagLab physicists Ju-Hyun Park (left) and Hongwoo Baek install the portable dilution refrigerator. MagLab physicists Ju-Hyun Park (left) and Hongwoo Baek install the portable dilution refrigerator. Stephen Bilenky

The National MagLab is known for its world-record magnets, like the 45-tesla hybrid magnet — the strongest on the planet.

But for some physics experiments, there’s another critical ingredient to good results: extremely cold temperatures. And thanks to a fancy cooling machine called the portable dilution refrigerator (dil fridge, or PDF, for short), the National MagLab is able to offer a potent combination of experimental conditions unique in the world.

This month, the PDF is set up in one of our magnets, allowing scientists to observe what happens to materials when they are under magnetic fields as high as 35 teslas and at temperatures just above absolute zero (-459 degrees Fahrenheit or -273 degrees Celsius).

Leveraging the cooling power of liquid helium, the PDF removes thermal energy from the materials the researchers are studying. “This allows scientists to see the physical properties of materials, such as quantized energy states and quantum phase transitions,” said MagLab physicist Hongwoo Baek, who is in charge of the apparatus.

“If you add magnetic fields,” Baek continued, “you will also see magnetic properties, such as magnetic phase transitions, and other detailed electronic features that are not normally shown at zero field, that can be utilized in future electronics and applications.”

The National MagLab is the only place scientists can throw that one-two punch of very high fields and very low temperatures.

“Many institutes have 20-millikelvin dilution refrigerators, and some have 35-tesla magnets,” said Baek, “but none of them can provide the experimental platform with 20 millikelvin and 35- to 45-tesla magnet together.”

The MagLab system offers another big bonus: it can rotate samples within the magnetic field without generating much heat, allowing the sample to align to the magnetic field and stay nice and cold.

Over the next few weeks, research groups from Rice University, Princeton University, Northwestern University, the University of Cambridge and the MagLab will conduct experiments in this unique setup, studying phenomena ranging from the fractional quantum Hall states to exotic magnetic phase transitions of various materials.

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Text by Kristen Coyne. Photo by Stephen Bilenky.

Last modified on 10 February 2017