Understanding low-temperature bulk transport in samarium hexaboride without relying on in-gap bulk states

Abstract

We present a new model to explain the difference between the transport and spectroscopy gaps in samarium hexaboride (SmB${}_6$), which has been a mystery for some time. We propose that SmB${}_6$ can be modeled as an intrinsic semiconductor with a depletion length that diverges at cryogenic temperatures. In this model, we find a self-consistent solution to Poisson's equation in the bulk, with boundary conditions based on Fermi energy pinning due to surface charges. The solution yields band bending in the bulk; this explains the difference between the two gaps because spectroscopic methods measure the gap near the surface, while transport measures the average over the bulk. We also connect the model to transport parameters, including the Hall coefficient and thermopower, using semiclassical transport theory. The divergence of the depletion length additionally explains the 10-12 K feature in data for these parameters, demonstrating a crossover from bulk dominated transport above this temperature to surface-dominated transport below this temperature. We find good agreement between our model and a collection of transport data from 4-40 K. This model can also be generalized to materials with similar band structure.

12 pages, 8 figures

References in corpus (7)

• Topological Insulators with Inversion Symmetry
• Correlated Topological Insulators with Mixed Valence
• Direct observation of the spin texture in strongly correlated SmB6 as evidence of the topological Kondo insulator
• Hybridization, Inter-Ion Correlation, and Surface States in the Kondo Insulator SmB6
• Kondo Breakdown in Topological Kondo Insulators
• Heavy surface state in a possible topological Kondo insulator: Magneto-thermoelectric transport on the (011)-plane of SmB${}_6$
• Coexistence of light and heavy surface states in a topological multi-band Kondo insulator

Cited by in corpus (6)

• Properties of the donor impurity band in mixed valence insulators
• Reduction of the low-temperature bulk gap in samarium hexaboride under high magnetic fields
• Bulk transport paths through defects in floating zone and Al flux grown SmB${}_6$
• Extraordinary Bulk Insulating Behavior in the Strongly Correlated Materials FeSi and FeSb${}_2$
• Realizing a topological diode effect on the surface of a topological Kondo insulator
• Persistence of correlation-driven surface states in SmB6 under pressure