Magnetic structure and excitations of the topological semimetal YbMnBi2

Abstract

We investigated the magnetic structure and dynamics of YbMnBi2, with elastic and inelastic neutron scattering, to shed light on the topological nature of the charge carriers in the antiferromagnetic phase. We confirm C-type antiferromagnetic ordering of the Mn spins below TN = 290 K, and determine that the spins point along the c-axis to within about 3 • . The observed magnon spectrum can be described very well by the same effective spin Hamiltonian as was used previously to model the magnon spectrum of CaMnBi2. Our results show conclusively that the creation of Weyl nodes in YbMnBi2 by the time-reversal-symmetry breaking mechanism can be excluded in the bulk.

Spin dynamics of a magnetic Weyl semimetal Sr1−xMn1−ySb2

“…Note that we used the longest axis as c, which is the same as that in Refs. [21,34] but different from that in Refs. [37,40].…”

“…In YbMnBi 2 , nearly wave-vector-independent damping in the INS spectra was taken as a signature of the spin-fermion coupling [51]. In contrast, another INS work did not detect any anomalous features in the magnetic spectra, implying the absence of the coupling between magnons and topological fermions [34].…”

“…[31][32][33]). However, in the AMnBi 2 materials, the strong spin-orbital coupling (SOC) of Bi atoms might induce a gap that prevented the formation of the Dirac point, and made the fermions massive [13,30,34]. One way to avoid the SOC-induced electronic gap opening and preserve the Dirac band structure is to replace Bi with lighter elements that have weaker SOC, e.g., Sb (Ref.…”

Spin dynamics in antiferromagnetic oxypnictides and fluoropnictides: LaMnAsO, LaMnSbO, and BaMnAsF

“…In fact, INS studies of other layered MnP n compounds, such as BaMn 2 Bi 2 [16], and the topological semimentals AMnBi 2 (A = Sr, Ca) [7] and YbMnBi 2 . [17], have also established the presence of competing AFM J 1 − J 2 exchange couplings. Another class of AFM compounds that shares similar MnP n planes is RMnP nB (R = La, Ce, Pr, Ba, ...and B = O and F, referred to here as Mn-1111 compounds) [18][19][20][21][22][23][24][25][26].…”

Magnetic structures, spin-flop transition, and coupling of Eu and Mn magnetism in the Dirac semimetal EuMnBi2

“…In addition, due to coupling of the magnetic layer and Bi square-net layer with Dirac fermions, a strong influence of magnetic order on electronic transport properties was found [6,9,11,35,36], and Dirac fermions were also reported to enhance the exchange coupling between magnetic moments in AMnBi 2 [10]. EuMnBi 2 and YbMnBi 2 were recently discovered as two possible candidates; in particular, YbMnBi 2 , whose magnetic structures and excitations were studied by neutron scattering in previous works [5,37], shows significant coupling of Dirac bands with spins [5]. By spontaneous or externally induced time-reversal symmetry breaking, EuMnBi 2 and YbMnBi 2 could also be driven to host Weyl physics.…”