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.
Find out more ...
Text by Kristen Coyne. Photo by Stephen Bilenky.
In a well-run library, an authoritative "Sssshhhh!!" will quiet things down in a jiffy.
At the MagLab, we value our quiet time, too — especially in the Millikelvin Facility, home to some of our most sensitive equipment and experiments. But we need more than a pursed-lipped librarian: We need a building designed from top to bottom to shield its magnets from the noise of external electromagnetic (EM) radiation.
And we're about to get it. We recently broke ground on an extension to the existing Millikelvin Facility, currently home to three superconducting magnets that scientists use for experiments at ultra-low temperatures.
The 1,640-square-foot addition will house two new superconducting magnets, including the much-anticipated 32 tesla all-superconducting magnet. Designed and built at the MagLab, the 32 T will shatter existing records for field strength in superconducting magnets when it comes online later this year.
The design of the $1.2-million Millikelvin addition reflects the many lessons learned from two decades operating the existing facility, said MagLab Facility Director John Kynoch. The walls of the windowless structure will include a layer of copper, effectively creating an EM radiation-blocking Faraday cage. The magnets will be positioned safely below ground, surrounded by concrete reinforced with non-magnetic rebar. The extension's high-quality electrical grounds will be separate from the main building.
Even the LED lighting and air conditioning are designed to minimize noise, air currents and temperature fluctuations that could disturb finicky experiments, said Tim Murphy, who oversees Millikelvin as director of the DC Field Facility.
"If your building temperature swings wildly," said Murphy, "you can see that in your data."
Years in the planning, the addition is designed not just to house magnets, but to do science.
"We're treating the building as part of the instrument," said Murphy, "not just some place you put the instrument."
The new building is slated for completion in the spring of 2017.
Text by Kristen Coyne. Photo by Stephen Bilenky.
Two researchers play with nanostructures in a fun, fertile physics playground: the space between two things.
A faraday cage is an important tool for some scientists at the MagLab. But they don't work with it — they work inside it.
A new record for a trapped field in a superconductor could herald the arrival of materials in a broad range of fields.
Where thermal agitation ends, the Kelvin temperature scale begins.
MagLab scientist Tim Murphy will talk about extremely cold temperatures and why physicists into quantum mechanics really dig them.
Tim Murphy has been named the new director of the DC Field Facility at the MagLab.
A superconducting ground state has been observed at T < 3.8 K in copper-doped Bi2Se3 single crystals. Topological superconductivity is predicted in this material, assuming the superconducting electrons follow the linear energy-momentum dispersion (Dirac-like) seen in graphene and other materials of current interest. However, this presumption had not yet been confirmed by quantum oscillation measurements.