High Hole Mobility and Nonsaturating Giant Magnetoresistance in the New 2D Metal NaCu4Se4 Synthesized by a Unique Pathway

• Published in: Journal of the American Chemical Society Vol. 141; no. 1; pp. 635 - 642
• Main Authors: Chen, Haijie, Rodrigues, João N. B, Rettie, Alexander J. E, Song, Tze-Bin, Chica, Daniel G, Su, Xianli, Bao, Jin-Ke, Chung, Duck Young, Kwok, Wai-Kwong, Wagner, Lucas K, Kanatzidis, Mercouri G
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 09.01.2019; American Chemical Society (ACS)
• Subjects: cations; copper; cupric oxide; flux synthesis; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; magnetoresistance; metal; slabs; sodium; two-dimensional material; X-ray photoelectron spectroscopy
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.8b11911

The new compound NaCu4Se4 forms by the reaction of CuO and Cu in a molten sodium polyselenide flux, with the existence of CuO being unexpectedly critical to its synthesis. It adopts a layered hexagonal structure (space group P63/mmc with cell parameters a = 3.9931(6) Å and c = 25.167(5) Å), consisting of infinite two-dimensional [Cu4Se4]− slabs separated by Na+ cations. X-ray photoelectron spectroscopy suggests that NaCu4Se4 is mixed-valent with the formula (Na+)­(Cu+)4(Se2–)­(Se–)­(Se2)2–. NaCu4Se4 is a p-type metal with a carrier density of ∼1021 cm–3 and a high hole mobility of ∼808 cm2 V–1 s–1 at 2 K based on electronic transport measurements. First-principles calculations suggest the density of states around the Fermi level are composed of Cu-d and Se-p orbitals. At 2 K, a very large transverse magnetoresistance of ∼1400% was observed, with a nonsaturating, linear dependence on field up to 9 T. Our results indicate that the use of metal oxide chemical precursors can open reaction paths to new low-dimensional compounds.