High electrical conductivity in the epitaxial polar metals LaAuGe and LaPtSb

Journal Article · 16 December 2019 · APL Materials

DOI: https://doi.org/10.1063/1.5132339 · OSTI ID:1599066

Du, Dongxue  ^[1]; Lim, Amber  ^[1]; Zhang, Chenyu ^[1]; Strohbeen, Patrick J. ^[1]; Shourov, Estiaque H. ^[1]; Rodolakis, Fanny  ^[2]; McChesney, Jessica L.  ^[2]; Voyles, Paul  ^[1]; Fredrickson, Daniel C.  ^[1]; Kawasaki, Jason K.  ^[1]

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1. Univ. of Wisconsin, Madison, WI (United States)
2. Argonne National Lab. (ANL), Argonne, IL (United States)

Polar metals are an intriguing class of materials that simultaneously host free carriers and polar structural distortions. Despite the name “polar metal,” however, most well-studied polar metals are poor electrical conductors. Here, we demonstrate the molecular beam epitaxial growth of LaPtSb and LaAuGe, two polar metal compounds whose electrical resistivity is an order of magnitude lower than the well studied oxide polar metals. These materials belong to a broad family of ABC intermetallics adopting the stuffed wurtzite structure, also known as hexagonal Heusler compounds. Scanning transmission electron microscopy reveals a polar structure with unidirectionally buckled BC (PtSb and AuGe) planes. Magnetotransport measurements demonstrate good metallic behavior with low residual resistivity (ρ_LaAuGe = 59.05 μΩ cm and ρ_LaAPtSb = 27.81 μΩ·cm at 2 K) and high carrier density (n_h ~ 10²¹ cm^-3). Photoemission spectroscopy measurements confirm the band metallicity and are in quantitative agreement with density functional theory (DFT) calculations. Through DFT-chemical pressure and crystal orbital Hamilton population analyses, the atomic packing factor is found to support the polar buckling of the structure although the degree of direct interlayer B–C bonding is limited by repulsion at the A–C contacts. Furthermore, when combined with predicted ferroelectric hexagonal Heuslers, these materials provide a new platform for fully epitaxial, multiferroic heterostructures.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: Army Research Office; National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division; Univ. of Wisconsin Materials Research Science and Engineering Center (MRSEC)
• Grant/Contract Number: AC02-06CH11357; FG02-08ER46547
• OSTI ID: 1599066
• Journal Information: APL Materials, Journal Name: APL Materials Journal Issue: 12 Vol. 7; ISSN 2166-532X
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English