Different Topological Quantum States in Ternary Zintl compounds: BaCaX (X = Si, Ge, Sn and Pb)

Abstract

Topological quantum states require stringent combination of crystal symmetry and spin-orbit coupling (SOC) strength. Here, we report that the ternary Zintl compound series BaCaX (X = Si, Ge, Sn and Pb, Group IV) in the same crystal structure having eight valence electrons per formula unit can host two different topological quantum phases, controlled by atomic size and SOC strength. BaCaSi is a nodal-line semimetal (NLSM) with band inversion protected by mirror symmetry and hosts a strong topological insulator (TI) state when SOC is turned on, thus, a NLSM-TI phase. Moving to larger atomic sizes and heavier atoms, BaCaGe and BaCaSn are normal insulators (NIs); then, with the strongest SOC in BaCaPb, a different band inversion is induced, giving a strong TI phase without the need of NLSM. Thus, we also predict two types of topological transitions in a phase diagram for BaCaX: (1) NLSM-TI to NI, then to TI by tuning atomic size and SOC strength via alloying, and (2) NI or TI to NLSM-TI via pressure. Disciplines

Antiferromagnetic semiconductor Eu3Sn2P4 with Sn–Sn dimer and crown-wrapped Eu

“…8,9,40 Many series of these compounds, for example BaCaX (X = Si, Ge, Sn and Pb, Group IV), XNiSn and XCoSb (X = Ti, Zr or Hf), AELi 2 In 2 Ge 2 (AE = Sr, Ba, Eu), exhibit a crossover from semiconducting to metallic behavior upon doping or alloying with larger atomic sizes and heavier atoms. [41][42][43] It should be noted that varying U value does not change qualitatively results of the electronic structure calculations in Eu 3 Sn 2 P 4 . However, the size of the gap is sensitive to the value of the U parameter, due to changes of the energy separation, e.g.…”

“…Magnetic measurements demonstrate an antiferromagnetic transition (T N ) around 14 K. The high-temperature data (50-300K) can be fitted using the Curie-Weiss law, which gives  = 6.5(2) K with an effective magnetic moment ~7. 41(3) B /Eu. The electric resistivity measurements and band structure calculations confirm the semiconducting character.…”

Prediction of topological Dirac semimetal in Ca-based Zintl layered compounds CaM2X2 (M = Zn or Cd; X = N, P, As, Sb, or Bi)

“…Interestingly, some of the TE materials may exhibit topological properties due to their strong spin–orbit coupling (SOC) effect and small bandgap 46 . Interestingly, a new group of Zintl materials 47 – 51 have been attracting attention because of their possible applications in the design and discovery of new quantum materials. Specifically, EuSn 2 P 2 47 and EuCd 2 As 2 48 have been recently experimentally and theoretically investigated.…”

Superconductivity in layered Zintl phase LiSn2As2

“…There is usually a complete electron transfer from the more electropositive metal to anion clusters (Zintl ion), such as (Si 4 ) 4− [3], (Tl 4 ) 8− [4] and (As 7 ) 3− [5]. When the Zintl ion is composed of infinite 2D layers, these compounds are called layered Zintl phase with numerous features including superconductivity [6,7], topological properties [8][9][10][11] and thermoelectricity [12,13]. NaSn 2 As 2 , with a superconducting transition temperature at 1.6 K, has recently attracted a lot of attention [6,14].…”