Magneto-Quantum Oscillations Measured in Insulator Samarium Hexaboride

Published June 20, 2024

Residual specific heat vs inverse magnetic field (H−1) at T=0.58K and Φ=45°.

Topological materials are fascinating because they take the weirdness of quantum mechanics and turn it up a few notches to 11. The behavior of Samarium Hexaboride (SmB6) has puzzled scientists for five decades and now with the help of higher magnetic fields, more sensitive measurement techniques coupled to higher quality samples, scientists have been able to pull back the curtain on the source of the strange behavior in SmB6.

What did scientists discover?

Measuring specific heat, scientists observed a phenomenon called magneto-quantum oscillations in an insulator - Samarium hexaboride (SmB6). Magneto-quantum oscillations are a type of rhythmic change in a material’s properties that vary as the magnetic field changes. These new findings confirm and expand earlier torque magnetometry measurements which also showed similar oscillations. This data strongly suggests that in SmB6, it's not regular electrons causing the oscillations, but special particles called electrically-neutral quasiparticles that act like electrons.

Why is this important?

Until recently, all materials that exhibited quantum oscillations could be categorized as metals. Quantum oscillations occur as energy levels of electrons in atoms cross a dividing line between occupied and unoccupied with increases or decreases to magnetic field. In an insulator, electrons are “locked” in fully-occupied energy levels with no ability to move due to an applied magnetic field. Since SmB6 is an insulator, it should not exhibit quantum oscillations. However, it does under these unique conditions. Scientists believe the quantum mechanics of SmB6 may help produce these bizarre quasiparticles that carry no electric charge, but have magnetic properties like electrons. Materials with these properties may advance technology yielding more efficient thermoelectric materials, quantum computing and other unique electronic devices.

Who did the research?

P.G Barre¹, A. Rydh², J. Palmer-Fortune³, S.T. Hannahs⁴, A.P. Ramirez¹, and N.A. Fortune⁴

¹UCSC; ²Stockholm Univ.; ³Smith College; ⁴National MagLab

Why did they need the MagLab?

Observing SmB6 magneto-quantum oscillations required very high magnetic fields & low temperatures coupled to a quiet electromagnetic environment. The thermal energy changes in the SmB6 crystal are extremely small and the MagLab’s high magnetic fields were critical for the research team to observe the quantum oscillation amplitude growth.