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Emmanouilidou, Eve; Shen, Bing; Deng, Xiaoyu; Chang, Tay-Rong; Shi, Aoshuang; Kotliar, Gabriel; Xu, Su; Ni, Ni

doi:10.1103/physrevb.95.245113

Cited by 80 publications

(74 citation statements)

References 45 publications

(26 reference statements)

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“…Based on n =B/eρ yx , the estimated carrier density is ≈6.5×10 20 /cm 3 . This value is significantly greater than Dirac semimetals Cd 3 As 2 [22], Na 3 Bi [23] and Weyl semimetal TaAs [24], but comparable to the Dirac nodal-line semimetal candidates ZrSiSe [25] and CaAgAs [26].…”

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Magnetic order induces symmetry breaking in the single-crystalline orthorhombic CuMnAs semimetal

et al. 2017

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Recently, orthorhombic CuMnAs has been proposed to be a magnetic material where topological fermions exist around the Fermi level. Here we report the magnetic structure of the orthorhombic Cu0.95MnAs and Cu0.98Mn0.96As single crystals. While Cu0.95MnAs is a commensurate antiferromagnet (C-AFM) below 360 K with a propagation vector of k = 0, Cu0.98Mn0.96As undergoes a second-order paramagnetic to incommensurate antiferromagnetic (IC-AFM) phase transition at 320 K with k = (0.1,0,0), followed by a second-order IC-AFM to C-AFM phase transition at 230 K. In the C-AFM state, the Mn spins order parallel to the b-axis but antiparallel to their nearest-neighbors with the easy axis along the b axis. This magnetic order breaks Ry gliding and S2z rotational symmetries, the two crucial for symmetry analysis, resulting in finite band gaps at the crossing point and the disappearance of the massless topological fermions. However, the spin-polarized surface states and signature induced by non-trivial topology still can be observed in this system, which makes orthorhombic CuMnAs promising in antiferromagnetic spintronics.Dirac cones have been proposed and observed in many non-magnetic materials, including Cd 3 As 2 [1, 2] and Na 3 Bi [3,4]. By breaking inversion symmetry (P) or time-reversal symmetry (T ), a Dirac point can be split into a pair of Weyl points. To break T , we can either apply an external magnetic field or use the spontaneous magnetic moment inside the material. For the latter case, the correlation between spontaneous magnetism and Weyl fermions has been studied in the AMnPn 2 (A = rare earth or alkali earth and Pn = Sb or Bi) system [5][6][7][8][9][10][11][12] and the half-Heusler compound GdPtBi [13,14]. Recently, CuMnAs was proposed to be an interesting material with non-trivial topology. CuMnAs has two polymorphs; the tetragonal (TET) CuMnAs, which crystalizes in the space group P 4/nmm, and the orthorhombic (ORT) CuMnAs crystalizing in the non-symmorphic P nma space group. The TET phase consists of alternating layers of edge-sharing CuAs 4 and MnAs 4 tetrahedra. It has been proposed to be a candidate with favourable applications in spintronics [18,19] and a topological metal-insulator transition driven by the Néel vector [17]. On the other hand, the ORT phase consists of a 3D network of edge-sharing CuAs 4 and MnAs 4 tetrahedra (Fig. 2(c)), where the Mn atoms form a 3D distorted honeycomb lattice (Fig. 2(d)). ORT CuMnAs was proposed to be an antiferromagnetic topological semimetal when the spin-orbit coupling is fully considered [15,17]. In such a system, two gapless points, named as coupled Weyl fermions, are robust if the combination of PT is * Corresponding author: nini@physics.ucla.edu reserved and the non-symmorphic screw symmetry S 2z is not broken. Thus, the anti-ferromagnetic ORT CuMnAs provides an ideal system to study the interplay between antiferromagnetism (AFM) and Dirac fermions [15]. In this paper, we will focus on the ORT CuMnAs. We experimentally determine its magnetic order, which breaks th...

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Magnetic order induces symmetry breaking in the single-crystalline orthorhombic CuMnAs semimetal

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“…With strong spin-orbit coupling (SOC), the nodal lines in these materials are either protected by reflection or mirror symmetry, or gapped out due to the lack of such symmetries [18][19][20][21][22] realizing a clean, "hydrogen-atom-like" NLSM is therefore of urgent need. Single-crystalline CaAgAs is theoretically predicted to be among the best candidate NLSMs since its theoretical Fermi surface contains no more than a circular nodal contour linked by the topological surface state [36], which gives rise to the ultralow magnetoresistance found by transport measurements [37]. In this Rapid Communication, we systematically investigate the NLSM state of CaAgAs which is solely protected by mirror reflection symmetry through a comparison between angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations.…”

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“…[37]. ARPES measurements were performed at the "Dreamline" beamline of the Shanghai Synchrotron Radiation Facility (SSRF) with a Scienta DA30 analyzer.…”

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Topological surface electronic states in candidate nodal-line semimetal CaAgAs

Wang

Emmanouilidou

et al. 2017

Phys. Rev. B

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We investigate systematically the bulk and surface electronic structure of the candidate nodal-line semimetal CaAgAs by angle-resolved photoemission spectroscopy and density functional calculations. We observed a metallic, linear, non-k z -dispersive surface band that coincides with the high-binding-energy part of the theoretical topological surface state, proving the topological nontriviality of the system. An overall downshift of the experimental Fermi level points to a rigid-band-like p doping of the samples, due possibly to Ag vacancies in the as-grown crystals. DOI: 10.1103/PhysRevB.96.161112 The discovery of topologically nontrivial systems has dominated the field of condensed matter physics over the past decade. Unique nontrivial topological properties in these fermionic systems relate concepts from high-energy physics to various quasiparticle excitations in condensed matter, causing the systems to resist small perturbations due to the protection by particular topological invariants [1,2]. In the so-called topological semimetals, such nontrivialities appear as the touching of valence and conduction bands at isolated points, closed lines, or planes in momentum space. Such materials exhibit chiral anomaly [3,4], topological surface Fermi arcs [5][6][7][8][9][10][11][12][13], and/or superconducting zero modes [14][15][16], whose quasiparticle excitations correspond directly to the Dirac, Weyl, and Majorana fermions. These quasiparticles differ from the actual entities in high-energy physics, but obey the same underlying principles in quantum field theory, offering the opportunity to investigate the fundamental physical laws that govern a large subset of quantum condensed matter as well as creating a new approach for developing a broad range of low-power, high-efficiency spintronic and quantum computing devices [1,2,17].Topological nodal-line semimetals (NLSMs) exhibit novel topological properties that are manifested by surface states in the form of a drumlike membrane living in the continuous toroidal isosurface gap in three-dimensional (3D) momentum space. With strong spin-orbit coupling (SOC), the nodal lines in these materials are either protected by reflection or mirror symmetry, or gapped out due to the lack of such symmetries [18][19][20][21][22] realizing a clean, "hydrogen-atom-like" NLSM is therefore of urgent need. Single-crystalline CaAgAs is theoretically predicted to be among the best candidate NLSMs since its theoretical Fermi surface contains no more than a circular nodal contour linked by the topological surface state [36], which gives rise to the ultralow magnetoresistance found by transport measurements [37]. In this Rapid Communication, we systematically investigate the NLSM state of CaAgAs which is solely protected by mirror reflection symmetry through a comparison between angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations. Our DFT calculations show that without SOC, a topological nodal ring enclosing appears in the first Bri...

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“…These range from elemental solids 11,14 to ternary compounds 7,8 , to highlight just a few. Promising experimental advances in synthesizing and characterizing candidate materials have also been reported for PtSn 4 18 , PbTaSe 2 19 , ZrSiS [20][21][22] , ZrSiSe 23 , and CaAgP 24,25 .…”

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Finite size and volume effects in line node semimetals: A first-principles investigation

Narayan

2019

Journal of Physics and Chemistry of Solids

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We systematically study the bulk and finite size effects on the band structure of prototypical line node materials using density functional theory based computations. For the bulk system, we analyze quantum oscillations with changes in the Fermi surface topology. We show that ultra thin slabs are gapped, with the first signatures of the line node appearing beyond a critical thickness.Further, motivated by possibility of tuning the bulk line node, we find that the line node radius is rather sensitive to bulk volume change. Based on this observation, we propose that application of pressure or suitable substrate engineering can be used as an effective means to control and tune the line node and the accompanying surface drumhead states.

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Magnetotransport properties of the single-crystalline nodal-line semimetal candidatesCaTX(T=Ag,Cd;X=As,Ge)

Cited by 80 publications

References 45 publications

Magnetic order induces symmetry breaking in the single-crystalline orthorhombic CuMnAs semimetal

Magnetic order induces symmetry breaking in the single-crystalline orthorhombic CuMnAs semimetal

Topological surface electronic states in candidate nodal-line semimetal CaAgAs

Finite size and volume effects in line node semimetals: A first-principles investigation

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