Temperature-driven massless Kane fermions in HgCdTe crystals.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Topological Materials

Background:

• Bulk gapless HgCdTe exhibits pseudo-relativistic three-dimensional particles known as massless Kane fermions.
• These unique electronic states cannot be described by conventional relativistic particles.
• The band structure of HgCdTe is tunable via cadmium content or temperature, leading to topological phase transitions.

Purpose of the Study:

• To investigate the continuous evolution of the HgCdTe band structure across the topological phase transition.
• To explore the behavior of Kane fermions during this transition using far-infrared magneto-spectroscopy.

Main Methods:

• Far-infrared magneto-spectroscopy was employed to study bulk HgCdTe.
• Temperature was tuned across the semimetal-to-semiconductor topological phase transition point.
• Band structure evolution and electronic state properties were analyzed.

Main Results:

• The rest mass of Kane fermions was observed to change sign at the critical temperature of the topological phase transition.
• The velocity of the Kane fermions remained constant across a wide range of temperatures and Cd concentrations.
• A universal velocity value of (1.07±0.05) × 10(6) m/s was determined for these pseudo-relativistic particles.

Conclusions:

• The study demonstrates a striking universality in the pseudo-relativistic description of Kane fermions in HgCdTe.
• The sign change of the rest mass at the topological phase transition highlights unique quantum phenomena in this material.
• The constant and universal velocity underscores the robustness of the pseudo-relativistic nature of these electronic states.