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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 (ρLaAuGe = 59.05 μΩ cm and ρLaAPtSb = 27.81 μΩ cm at 2 K) and high carrier density (nh ∼ 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. When combined with predicted ferroelectric hexagonal Heuslers, these materials provide a new platform for fully epitaxial, multiferroic heterostructures.
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Correlating polar distortions and interfacial charge at the polar/non-polar LaCrO3/SrTiO3 (001) interface
The relationship between the sheet carrier concentration, ns, of LaCrO3(LCO)/SrTiO3(STO) heterostructures and their structural properties has been investigated. Under low oxygen partial pressure, the STO substrate is reduced during growth as evidenced by a high ns of 1016 cm−2. By controlling the post-growth annealing conditions, heterostructures with ns of 1013–1016 cm−2 are achieved. The atomic-scale structure of the samples is obtained using high-resolution synchrotron x-ray diffraction measurements. For heterostructures with ns at or below 3 × 1013 cm−2, polar distortions are present within the LCO layers and increase in magnitude with a decrease in sheet carrier concentration. These distortions are absent for samples with ns on the order of 1015–1016 cm−2 where interfacial carriers play a role in alleviating the polar discontinuity at the LCO/STO interface. These results suggest that interfacial charge carriers and polar distortions can act as complementary mechanisms to alleviate the polar discontinuity at polar/non-polar complex oxide interfaces.
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- Award ID(s):
- 1751455
- PAR ID:
- 10597179
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- AIP Advances
- Volume:
- 10
- Issue:
- 4
- ISSN:
- 2158-3226
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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