Abstract
The honeycomb lattice iridates A2IrO3 (A=Na, Li) are spin-orbit assisted Mott insulators proximate to Kitaev's quantum spin liquid. The insulating state as well as the magnetic properties are believed to arise due to a delicate balance of several energy scales. We report on high-pressure electrical transport and X-ray-diffraction measurements on A2IrO3 (A=Na, Li) in an attempt to study their structural and electronic evolution with pressure. We found that while Li2IrO3 undergoes a structural phase transition into the dimerized state at a pressure of P ∼4 GPa, in Na2IrO3 the conservation of the original C2/m structure up to at least 58 GPa is observed. In addition, Li2IrO3 undergoes a sluggish structural rearrangement at the pressure range 20-40 GPa coinciding with a significant decrease in resistance. Despite dissimilar structural evolution and different mechanisms of the electrical conductivity, Arrhenius conductivity for Na2IrO3 and Mott variable-range hopping in Li2IrO3, both systems show a very similar R(P) behavior. Namely, after a nonmonotonic decrease of the resistance R and the charge gap Δ, the Δ stabilizes at about 45 GPa and even increases slightly with pressure; the R(T) shows insulating behavior up to the highest pressure measured, 80 and 55 GPa, respectively. This resilient nonmetallic behavior of the studied iridates suggests a formation close to a localized-itinerant crossover of unusual electronic states, whose possible features are discussed. Unforeseeably, the R(P) behavior is not dependent on the buffer element A, which seems essential for understanding the nature of the electrical conductivity in iridates.
| Original language | English |
|---|---|
| Article number | 085156 |
| Journal | Physical Review B |
| Volume | 102 |
| Issue number | 8 |
| DOIs | |
| State | Published - 15 Aug 2020 |
| Externally published | Yes |
Bibliographical note
Publisher Copyright:© 2020 American Physical Society.
Funding
This research was supported by the Israel Science Foundation (Grants No. 1189/14 and No. 1552/18). S.L. thankfully acknowledges the Planning and Budgeting Committee (PBC) of the Council for Higher Education in Israel for a postdoctoral fellowship. Other members of the Soleil Synchrotron are gratefully acknowledged for their help with XRD measurements. Y.S. acknowledges a discussion with R. Valenti after the 2016 APS March meeting and G.K.R. acknowledges a discussion with D. Khomskii. We acknowledge the x-ray facility at IISER Mohali. K.M. acknowledges UGC-CSIR India for a fellowship. Y.S. acknowledges DST, India for support through Ramanujan Grant No. SR/S2/RJN-76/2010 and through DST Grant No. SB/S2/CMP-001/2013. Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation – Earth Sciences (EAR – 1634415) and Department of Energy – GeoSciences (Grant No. DE-FG02-94ER14466). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Use of the COMPRES-GSECARS gas loading system was also supported by COMPRES under NSF Cooperative Agreement EAR -1606856.
| Funders | Funder number |
|---|---|
| COMPRES | |
| National Science Foundation – Earth Sciences | EAR – 1634415 |
| UGC-CSIR | |
| National Science Foundation | EAR -1606856 |
| U.S. Department of Energy | DE-FG02-94ER14466 |
| Office of Science | |
| Argonne National Laboratory | DE-AC02-06CH11357 |
| Department of Science and Technology, Ministry of Science and Technology, India | SR/S2/RJN-76/2010, SB/S2/CMP-001/2013 |
| Israel Science Foundation | 1552/18, 1189/14 |
| Council for Higher Education |