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Title: Anomalous three-dimensional bulk ac conduction within the Kondo gap of SmB 6 single crystals

The Kondo insulator SmB 6 has long been known to display anomalous transport behavior at low temperatures, T < 5 K. In this temperatures range, a plateau is observed in the dc resistivity, contrary to the exponential divergence expected for a gapped system. Some recent theoretical calculations suggest that SmB 6 may be the first topological Kondo insulator (TKI) and propose that the residual conductivity is due to topological surface states which reside within the Kondo gap. Since the TKI prediction many experiments have claimed to observe high mobility surface states within a perfectly insulating hybridization gap. We investigate the low energy optical conductivity within the hybridization gap of single crystals of SmB 6 via time domain terahertz spectroscopy. Samples grown by both optical floating zone and aluminum flux methods are investigated to probe for differences originating from sample growth techniques. We find that both samples display significant three-dimensional bulk conduction originating within the Kondo gap. Although SmB 6 may be a bulk dc insulator, it shows significant bulk ac conduction that is many orders of magnitude larger than any known impurity band conduction. The nature of these in-gap states and their coupling with the low energy spin excitons ofmore » SmB 6 is discussed. In addition, the well-defined conduction path geometry of our optical experiments allows us to show that any surface states, which lie below our detection threshold if present, must have a sheet resistance of R / square ≥ 1000 Ω .« less
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [3] ;  [1]
  1. Johns Hopkins Univ., Baltimore, MD (United States). Inst. for Quantum Matter
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of California, Irvine, CA (United States). Dept. of Physics and Astronomy
  3. Johns Hopkins Univ., Baltimore, MD (United States). Inst. for Quantum Matter, Dept. of Chemistry
  4. Univ. of California, Irvine, CA (United States). Dept. of Physics and Astronomy
Publication Date:
OSTI Identifier:
1392878
Report Number(s):
LA-UR-17-23576
Journal ID: ISSN 2469-9950; PRBMDO; TRN: US1702709
Grant/Contract Number:
AC52-06NA25396; FG02-08Er46544; DMR 08-01253; FG02-08ER46544
Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 94; Journal Issue: 16; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Material Science