Transport gap in SmB₆ protected against disorder

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Chemistry

Background:

• Samarium hexaboride (SmB6) exhibits complex electronic properties, including a topological insulating state.
• Understanding the interplay between bulk and surface conduction is crucial for SmB6 applications.
• Disorder, induced by off-stoichiometric growth, can significantly alter material properties.

Purpose of the Study:

• To investigate the bulk resistivity of SmB6 under conditions where surface conduction becomes dominant.
• To determine if SmB6 maintains its insulating properties despite significant structural disorder.
• To characterize the intrinsic electrical behavior of SmB6 bulk.

Main Methods:

• The inverted resistance method was employed to measure bulk resistivity.
• Samples were grown under large off-stoichiometric conditions to introduce defects like samarium vacancies and boron interstitials.
• Resistivity measurements were conducted over a range to observe the transition from surface-dominated to bulk-dominated regimes.

Main Results:

• Bulk resistivity of SmB6 was extended to a regime where surface conduction is significant.
• Despite substantial disorder, the bulk resistivity exhibited a clear intrinsic thermally activated behavior.
• The resistivity changed over 7-10 orders of magnitude, confirming insulating characteristics.

Conclusions:

• Samarium hexaboride behaves as an ideal insulator, largely immune to disorder.
• The intrinsic bulk properties of SmB6 are robust even under challenging growth conditions.
• These findings highlight SmB6's potential for applications requiring stable insulating behavior.