Unconventional Charge Transport in Kondo insulator YbB12

Published July 18, 2022

Sketch of the two fluids in YbB12 showing their densities of states

Three complementary measurements in intense magnetic fields shed light on a very unusual material that behaves like a metal, but does not conduct electricity!

What did scientists discover?

Insulators are characterized by poor electrical conductivity and conversely metals are characterized by good electrical conductivity. In both of these cases, the material properties are determined by the quantum mechanical behavior of the electrons. With YbB₁₂ quantum mechanics throws a wrench into scientists' understanding by pushing the electrons to form two teams: one that behaves like electrons in a metal, yet can carry no electrical charge and another team that carries electrical charge, but does not behave like electrons in a metal should.

Why is this important?

YbB₁₂is a Kondo insulator, a material that has very poor electrical conductivity at low temperatures. However, the resistance and magnetization of YbB12 oscillate in magnetic fields, behavior usually seen only in metals with very good electrical conductivity. Careful measurements of the resistance and magnetization, compared with measurements of a quantity called the Hall effect, show that the electrons in YbB₁₂ reorganize into two cohabiting fluids.

One fluid behaves in many ways like the electrons in conventional metals; however, this fluid – bizarrely - cannot conduct electrical charge! The other fluid carries electrical charge but acts in a very exotic manner previously seen in materials such as high-temperature superconductors. The properties of YbB₁₂ are due to collisions ("scattering") among particles from the two fluids, allowing them to interact and influence each others' behavior. Searches are underway for other materials that host this new phase of matter.

Who did the research?

Z. Xiang^1,2, K.-W. Chen¹, L. Chen¹, T. Asaba^1,3, Y. Sato³, N. Zhang², D. Zhang¹, Y. Kasahara³, F. Iga⁴, W. Coniglio⁵, Y. Matsuda³, J. Singleton⁶, Lu Li¹

¹University of Michigan, ²University of Science and Technology of China, ³Kyoto University, ⁴Ibaraki University, ⁵MagLab FSU, ⁶MagLab LANL

Why did they need the MagLab?

The MagLab has unique magnets that provide the 45–73T magnetic fields essential for the research. MagLab staff worked hard to reduce the electrical noise and mechanical vibrations in the specialized equipment, a crucial ingredient for success with sensitive experiments of this kind.