Influence of magnetism on Dirac semimetallic behavior in nonstoichiometric Sr1−yMn1−zSb2(y

Abstract

Nonstoichiometric Sr1−yMn1−zSb2 (y, z <0.1) is known to exhibit a coexistence of magnetic order and the nontrivial semimetallic behavior related to Dirac or Weyl fermions. Here, we report inelastic neutron scattering analyses of the spin dynamics and density functional theory studies on the electronic properties of Sr1−yMn1−zSb2. We observe a relatively large spin excitation gap ≈ 8.5 meV at 5 K, and the interlayer magnetic exchange constant only 2.8 % of the dominant intralayer magnetic interaction, providing evidence that Sr1−yMn1−zSb2 exhibits a quasi-2D magnetism. Using density functional theory, we find a strong influence of magnetic orders on the electronic band structure and the Dirac dispersions near the Fermi level along the Y-S direction in the presence of a ferromagnetic ordering. Our study unveils novel interplay between the magnetic order, magnetic transition, and electronic property in Sr1−yMn1−zSb2, and opens new pathways to control the relativistic band structure through magnetism in ternary compounds.Topological semimetals [1, 2] are a newly emerged frontier in condensed matter physics and have stimulated tremendous research interest because they give access to new quantum phenomena and are very attractive for both fundamental research and technological application. Particular attention has focused on Weyl or Dirac semimetals that exibit a coexistence with magnetism as a promising route to modify and control Weyl/Dirac fermions, electronic transport properties and band topology, among which SrMnSb 2 has attracted much interest recently. Liu et al.[3] reported a nontrivial semimetallic behavior related to Dirac or Weyl fermions including nearly massless quasiparticles with a π Berry phase coupled to ferromagnetism in nonstoichiometric Sr 1−y Mn 1−z Sb 2 . For the magnetic behavior, it displays ferromagnetic (FM) order below T C ∼ 565 K, followed by a transition to canted antiferromagnetic (AFM) order with a net FM component below T F M −AF M ≈ 304 K [3]. The nontrivial topological semimetal behavior was further supported by optical conductivity and ultrafast optical pump-probe measurements [4]. Nevertheless, Ramankutty et al.[5] reported zero Berry phase indicative of trivial topology in nearly stoichiometric SrMnSb 2 . Previous density functional theory (DFT) calculations [5][6][7] showed that the lattice distortion in the orthorhombic structure prevents the formation of the Dirac points near the Fermi level by opening a gap. Both results cannot account for the observed topological semimetallic behavior reported in Ref.[3]. It is therefore challenging to explore whether there are indeed Dirac/Weyl points in proximity to the Fermi level and what drives their formation in Sr 1−y Mn 1−z Sb 2 . Furthermore, SrMnSb 2 offers a wonderful opportunity to address an important question whether there is a close correlation between magnetic order and band topology in 3D Dirac compounds.In addition to SrMnSb 2 , other Alkaline earth ternary AMnC 2 "112" compounds (A =Sr, Ca, Ba, C= Bi or Sb) [8][9][10][11][12]...

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

“…Combining the above Eq. (11) and the susceptibilities at T = 2 K in Fig. 2(a), the uniaxial magnetic anisotropy parameter can be obtained, K u = 3.35 T (0.19 meV).…”

“…Furthermore, a potential coupling of Dirac/Weyl fermions to other degrees of freedom such as magnetism [5,6] may open up other avenues for the exploration and tuning of physical properties. Recently, particular attention has been focused on magnetic Dirac/Weyl materials, in which it is possible to tune the electronic transport properties by utilizing the interaction between the relativistic quasiparticles and magnetism [7][8][9][10][11]. A few candidates of magnetic Dirac/Weyl materials have already been theoretically proposed or experimentally verified, like Co 3 Sn 2 S 2 [12,13], MnBi 2 Te 4 [14][15][16], and the layered manganese pnictides AMnBi 2 (A = rare/alkaline earth) "112" system [17][18][19][20][21][22].…”

“…A few candidates of magnetic Dirac/Weyl materials have already been theoretically proposed or experimentally verified, like Co 3 Sn 2 S 2 [12,13], MnBi 2 Te 4 [14][15][16], and the layered manganese pnictides AMnBi 2 (A = rare/alkaline earth) "112" system [17][18][19][20][21][22]. Among them, the experimental evidence for the coexistence of Dirac fermions and AFM order was found in AMnBi 2 compounds by different methods [6,10,11,21,[23][24][25][26][27][28][29][30][31][32][33][34], such as quantum oscillation, magnetoresistant behavior, angle-resolved photon emission spectroscopy, and optical conductivity. 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].…”

“…Among them, the experimental evidence for the coexistence of Dirac fermions and AFM order was found in AMnBi 2 compounds by different methods [6,10,11,21,[23][24][25][26][27][28][29][30][31][32][33][34], such as quantum oscillation, magnetoresistant behavior, angle-resolved photon emission spectroscopy, and optical conductivity. 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].…”

Anderson-Mott transition in a disordered Hubbard chain with correlated hopping

“…These terms emerge naturally in the derivation of an effective low-energy model starting from the three-band Hubbard Hamiltonian that describes the Cu-O planes of the superconducting cuprates. [53][54][55] In some limit, it is equivalent to the so called extended Hubbard model with bondcharge interaction which has been investigated in the context of low-dimensional organic superconductors [56][57][58] as well as in the context of non-conventional superconducting mechanisms, like hole-superconductivity 59,60 and η-pairing superconductivity, 61,62 mesoscopic transport, 63 and quantum information. 64,65 More recently, this model was also investigated in optical lattices and cold atoms [66][67][68][69][70][71] and was also found to provide the effective theory of the Hubbard Hamiltonian in driven lattices.…”