Spin-valley locking and bulk quantum Hall effect in a noncentrosymmetric Dirac semimetal BaMnSb2

Abstract

Spin-valley locking in monolayer transition metal dichalcogenides has attracted enormous interest, since it offers potential for valleytronic and optoelectronic applications. Such an exotic electronic state has sparsely been seen in bulk materials. Here, we report spin-valley locking in a Dirac semimetal BaMnSb2. This is revealed by comprehensive studies using first principles calculations, tight-binding and effective model analyses, angle-resolved photoemission spectroscopy measurements. Moreover, this material also exhibits a stacked quantum Hall effect (QHE). The spin-valley degeneracy extracted from the QHE is close to 2. This result, together with the Landau level spin splitting, further confirms the spin-valley locking picture. In the extreme quantum limit, we also observed a plateau in the z-axis resistance, suggestive of a two-dimensional chiral surface state present in the quantum Hall state. These findings establish BaMnSb2 as a rare platform for exploring coupled spin and valley physics in bulk single crystals and accessing 3D interacting topological states.

Magnetotransport studies of the Sb square-net compound LaAgSb2 under high pressure and rotating magnetic fields

“…Materials with the formula MT P 2 (M is a rare-earth or alkali-earth metal, T is a transition metal, and P is a pnictogen element such as Bi and Sb) serve as versatile square-net compounds [2][3][4][5][6][7][8][9][10][11][12]. One remarkable advantage of these materials is that systematic investigation is possible by choosing the appropriate M and/or T from a wide range of materials, including nonmagnetic and magnetic elements.…”

“…One remarkable advantage of these materials is that systematic investigation is possible by choosing the appropriate M and/or T from a wide range of materials, including nonmagnetic and magnetic elements. The prominent quantum oscillation with the nontrivial Berry phase [2][3][4][5][6][7][8][9][10][11][12] and the quantum Hall effect in a bulk crystal [4,11,12] have been regarded as hallmarks of Dirac fermions derived from the Bi-or Sb-square-net layers.…”

Exploration of two surfaces observed in Weyl semimetal BaMnSb2

“…On the other hand, by considering both SOC and the canted antiferromagnetic ordering of Mn, Dirac crossings remain in a centrosymmetric I4/mmm structure scenario (i.e., assuming X square lattice) 6 . However, recent single crystal x-ray diffraction, scanning transmission electron microscopy and neutron scattering studies revealed that BaMnSb 2 actually forms an orthorhombic structure (Imm2), which is noncentrosymmetric 1,7,8 . With the Imm2 structure, Dirac cones are gapped without 7 or with the consideration of the magnetism (assuming the G-type magnetic ordering in ref.…”

“…However, recent single crystal x-ray diffraction, scanning transmission electron microscopy and neutron scattering studies revealed that BaMnSb 2 actually forms an orthorhombic structure (Imm2), which is noncentrosymmetric 1,7,8 . With the Imm2 structure, Dirac cones are gapped without 7 or with the consideration of the magnetism (assuming the G-type magnetic ordering in ref. 8 ).…”

Magnetic tuning of band topology evidenced by exotic quantum oscillations in the Dirac semimetal EuMnSb$_2$

“…The angular dependent oscillation splitting should be attributed to the dominating spin splitting of the Dirac bands. As adopted from a previous study for BaMnSb 2 [41], the g-factor is estimated to 9.2 at 0.4K by using F(1/B + -1/B − ) = (1/2)g(m*/m e ), with F=95 T (Fig. 2(f)), (1/B + -1/B − )=0.005 T −1 (Fig.…”