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Magnetic phases of the quasi-two-dimensional antiferromagnet CuCrO 2 on a triangular lattice
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Antiferromagnetism enables electron-phonon coupling in iron-based superconductors
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Interlayer electronic transport in CaMnBi 2 antiferromagnet
Here, we report interlayer electronic transport in CaMnBi 2 single crystals. Quantum oscillations and angular magnetoresistance suggest coherent electronic conduction and valley polarized conduction of Dirac states. Furthermore, the small cyclotron mass, high mobility of carriers, and nontrivial Berry's phase are consistent with the presence of Dirac fermions on the side wall of the warped cylindrical Fermi surface. Similarly to SrMnBi 2 , which features an anisotropic Dirac cone, our results suggest that magnetic-field-induced changes in interlayer conduction are also present in layered bismuth-based materials with a zero-energy line in momentum space created by the staggered alkaline earth atoms.
Noncollinear antiferromagnetism of coupled spins and pseudospins in the double perovskite La 2 CuIrO 6
This article reports the structural, magnetic, and thermodynamic properties of the double perovskite compound La 2 CuIrO 6 from x-ray, neutron diffraction, neutron depolarization, dc magnetization, ac susceptibility, specific heat, muon-spin-relaxation ( μ SR ) , electron-spin-resonance (ESR) and nuclear magnetic resonance (NMR) measurements. Below ~113 K, short-range spin-spin correlations occur within the Cu 2+ sublattice.
Magnetotransport study of Dirac fermions in YbMnBi 2 antiferromagnet
We report quantum transport and Dirac fermions in YbMnBi 2 single crystals. YbMnBi 2 is a layered material with anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, and small cyclotron mass indicate the presence of Dirac fermions. Lastly, angular-dependent magnetoresistance indicates a possible quasi-two-dimensional Fermi surface, whereas the deviation from the nontrivial Berry phase expected for Dirac states suggests the contribution of parabolic bands at the Fermi level or spin-orbit coupling.
Pressure-driven phase transition from antiferromagnetic semiconductor to nonmagnetic metal in the two-leg ladders A Fe 2 X 3 ( A = Ba , K ; X = S , Se )
The recent discovery of superconductivity in BaFe 2 S 3 has stimulated considerable interest in 123-type iron chalcogenides. This material is the first reported iron-based two-leg ladder superconductor, as opposed to the prevailing two-dimensional layered structures of the iron superconductor family. Once the hydrostatic pressure exceeds 11 GPa, BaFe 2 S 3 changes from a semiconductor to a superconductor below 24 K. Although previous calculations correctly explained its ground-state magnetic state and electronic structure, the pressure-induced phase transition was not successfully reproduced. In this work, our first-principles calculations show that with increasing pressure the lattice constants as well as local magnetic moments are gradually suppressed, followed by a first-order magnetic transition at a critical pressure, with local magnetic moments dropping to zero suddenly. Our calculations suggest that the self-doping caused by electrons transferred from S to Fe may play a key role in this transition. The development of a nonmagnetic metallic phase at high pressure may pave the way to superconductivity. As extensions of this effort, two other 123-type iron chalcogenides, KFe 2 S 3 and KFe 2 Se 3 , have also been investigated. KFe 2 S 3 also displays a first-order transition with increasing pressure, but KFe 2 Se 3 shows instead a second-order or weakly first-order transition. Here, the required pressures for KFe 2 S 3 and KFe 2 Se 3 to quench the magnetism are higher than for BaFe 2 S 3 . Further experiments could confirm the predicted first-order nature of the transition in BaFe 2 S 3 and KFe 2 S 3 , as well as the possible metallic/superconductivity state in other 123-type iron chalcogenides under high pressure.
Global phase diagram and quantum spin liquids in a spin- 1 2 triangular antiferromagnet
For this research, we study the spin-1/2 Heisenberg model on the triangular lattice with the nearest-neighbor J 1 > 0 , the next-nearest-neighobr J 2 > 0 Heisenberg interactions, and the additional scalar chiral interaction Jχ ($\vec{S}$ i × $\vec{S}$ j ) · $\vec{S}$ k for the three spins in all the triangles using large-scale density matrix renormalization group calculation on cylinder geometry. With increasing J 2 (J 2 / J 1 ≤ 0.3 ) and Jχ (Jχ / J 1 ≤ 1.0 ) interactions, we establish a quantum phase diagram with the magnetically ordered 120°, stripe, and noncoplanar tetrahedral phase. In between these magnetic order phases, we find a chiral spin liquid (CSL) phase, which is identified as a ν = 1/2 bosonic fractional quantum Hall state with possible spontaneous rotational symmetry breaking. By switching on the chiral interaction, we find that the previously identified spin liquid in the J 1 - J 2 triangular model (0.08 ≲ J 2 / J 1 ≲ 0.15) shows a phase transition to the CSL phase at very small Jχ. We also compute the spin triplet gap in both spin liquid phases, and our finite-size results suggest a large gap in the odd topological sector but a small or vanishing gap in the even sector. Lastly, we discuss the implications of our results on the nature of the spin liquid phases.
Magnetic structure and magnetization of helical antiferromagnets in high magnetic fields perpendicular to the helix axis at zero temperature
The zero-temperature angles of magnetic moments in a helix or sinusoidal fan confined to the x y plane, with respect to an in-plane magnetic field H x applied perpendicular to the z axis of a helix or fan, are calculated for commensurate helices and fans with field-independent turn angles k d between moments in adjacent layers of the helix or fan using the classical J 0 - J 1 - J 2 Heisenberg model. For 0 < k d < 4 π / 9 , first-order transitions from helix to a fan structure occur at fields H t as previously inferred, where the fan is found to be approximately sinusoidal. However, for 4 π / 9 ≤ k d ≤ π , different behaviors are found depending on the value of k d and these properties vary nonmonotonically with k d . In this k d range, the change from helix to fanlike structure is usually a crossover with no phase transition between them, although first-order transitions are found for k d = 3 π / 5 and 8 π / 11 and a second-order transition for k d = 3 π / 4 . At a critical field H c , the fan or fanlike structures exhibit a second-order transition to the paramagnetic state. The H c for a helix undergoing a field-induced change to a fan or fanlike structure is found to be the same as for a sinusoidal fan with the same k d and interlayer interactions. We present analytical expressions for H c versus k d. We also calculated the average x -axis moment per spin μ x ave versus H x for helices and fans with crossovers and phase transitions between them. When smooth helix to fanlike crossovers occur in the range 4 π / 9 ≤ k d ≤ π , μ x ave exhibits an S-shape behavior with increasing H x . The behavior we predict is consistent with μ x ave ( H x ) data previously reported by Sangeetha et al. [Phys. Rev. B 94, 014422 (2016)] for single-crystal EuCo 2 P 2 possessing a helix ground state with k d ≈ 0.85 π . The low-field magnetic susceptibility and the ratio H t / H c are calculated analytically or numerically versus k d for helices, and are shown to approach the respective known limits for k d → 0 .
Search for a nematic phase in the quasi-two-dimensional antiferromagnet CuCrO 2 by NMR in an electric field
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Charge density wave behavior and order-disorder in the antiferromagnetic metallic series Eu ( Ga 1 - x Al x ) 4
The solid solution Eu(Ga 1-x Al x ) 4 was grown in single crystal form to reveal a rich variety of crystallographic, magnetic, and electronic properties that differ from the isostructural end compounds EuGa 4 and EuAl 4 , despite the similar covalent radii and electronic configurations of Ga and Al. In this work we present the onset of magnetic spin reorientation and metamagnetic transitions for x=0-1 evidenced by magnetization and temperature-dependent specific heat measurements. T N changes nonmonotonously with x, and it reaches a maximum around 20 K for x=0.50, where the a lattice parameter also reflects an extreme (minimum) value. Anomalies in the temperature-dependent resistivity consistent with charge density wave behavior exist only for x=0.50 and 1. Density functional theory calculations show increased polarization between the Ga-Al covalent bonds in the x=0.50 structure compared to the end compounds, such that crystallographic order and chemical pressure are proposed as the causes of the charge density wave behavior.
Averievite: A copper oxide kagome antiferromagnet
Averievite, Cu 5 V 2 O 10 (CsCl) , is an oxide mineral composed of Cu 2+ kagome layers sandwiched by Cu 2+ -V 5+ honeycomb layers. We have synthesized this oxide and investigated its properties from ab initio calculations along with susceptibility and specific heat measurements. The data imply a Curie-Weiss temperature of 185K as well as long-range magnetic order at 24 K due to the significant interlayer coupling from the honeycomb copper ions. This order is suppressed by substituting copper by isoelectronic zinc, suggesting that Zn-substituted averievite is a promising spin liquid candidate. A further proposed substitution that replaces V 5+ by Ti 4+ not only dopes the material but is predicted to give rise to a two-dimensional electronic structure featuring Dirac crossings. Thus, averievite is an attractive platform for S =1/2 kagome physics with the potential for realizing novel electronic states.