Semi-Dirac Fermions in a Topological Metal

Published January 14, 2025

Left: Calculated band structure of ZrSiS near the semi-Dirac point (black sphere). Right: Comparison of the power-law behavior for the cyclotron energy versus magnetic field in various types of fermions in a log-log plot including this measurement.

In the zoo of emerging quasiparticles in condensed matter physics, semi-Dirac fermions stand out as being massive and massless depending on the directions of motion. Utilizing high-field magneto-infrared spectroscopy at the MagLab, a new study identifies semi-Dirac fermions at special crossings of nodal lines in ZrSiS. The experimental observation of two-thirds power law behavior of cyclotron energy with magnetic field provide direct evidence of these exotic, elusive quasiparticles.

What did scientists discover?

Scientists at the MagLab detected semi-Dirac fermions, a unique type of particle predicted 16 years ago, but never observed. These particles are massless in one direction and have mass in the perpendicular direction. Using high-field magneto-infrared spectroscopy, they found clear evidence of the fermions in zirconium silicon sulfide (ZrSiS) when exposed to strong magnetic fields and observed a distinct energy pattern that matches the predicted signature of semi-Dirac fermions (cyclotron energy scales with the two-thirds power of the magnetic field).

Why is this important?

These findings confirm the existence of novel quasiparticles hosted in bulk crystals and pave the way for exploring quantum geometry and electronic correlation effect in semi-Dirac fermions. Better understanding of semi-Dirac fermions could contribute to advances in quantum materials research, potentially enabling new technologies in electronics, sensors, and quantum computing.

Who did the research?

Yinming Shao^1,2, Seongphill Moon^3,4, A. N. Rudenko⁵, Jie Wang^6,7,8, Jonah Herzog-Arbeitman⁹, Mykhaylo Ozerov⁴, David Graf⁴, Zhiyuan Sun⁷, Raquel Queiroz¹, Seng Huat Lee², Yanglin Zhu², Zhiqiang Mao², M. I. Katsnelson⁵, B. Andrei Bernevig^9,10,11, Dmitry Smirnov⁴, Andrew J. Millis^1,12, and D.N. Basov¹

¹Columbia; ²PSU; ³FSU; ⁴National MagLab; ⁵Radboud; ⁶CMSA, Harvard; ⁷Harvard; ⁸Temple; ⁹Princeton; ¹⁰DIPS; ¹¹IKERBASQUE; ¹²Flatiron

Why did they need the MagLab?

The spectroscopic signature of the semi-Dirac fermions studied here reside in the far-infrared and requires high-field (> 8T) reflectance measurements in the Voigt geometry. The combination of FTIR and a 17.5T magnet were crucial for this discovery and only available at the MagLab.