SdH Oscillations from the Dirac Surface State in the Fermi-Arc Antiferromagnet NdBi.

The recent progress in CuMnAs and Mn3X (X = Sn, Ge, Pt) shows that antiferromagnets (AFMs) provide a promising platform for advanced spintronics device innovations. Most recently, a switchable Fermi-arc is discovered by the ARPES technique in antiferromagnet NdBi, but the knowledge about electron-transport property and the manipulability of the magnetic structure in NdBi is still vacant to date. In this study, SdH oscillations are successfully verified from the Dirac surface states (SSs) with 2-dimensionality and nonzero Berry phase. Particularly, it is observed that the spin-flop transition only appears when the external magnetical field is applied along [001] direction, and features obvious hysteresis for the first time in NdBi, which provides a powerful handle for adjusting the spin texture in NdBi. Crucially, the DFT shows the Dirac cone and the Fermi arc strongly depend on the high-order magnetic structure of NdBi and further reveals the orbital magnetic moment of Nd plays a crucial role in fostering the peculiar SSs, leading to unveil the mystery of the band-splitting effect and to manipulate the electronic transport, high-effectively, in the thin film works in NdBi. It is believed that this study provides important guidance for the development of new antiferromagnet-based spintronics devices based on cutting-edge rare-earth monopnictides.

Field-induced quantum spin disordered state in spin-1/2 honeycomb magnet Na2Co2TeO6.

Spin-orbit coupled honeycomb magnets with the Kitaev interaction have received a lot of attention due to their potential of hosting exotic quantum states including quantum spin liquids. Thus far, the most studied Kitaev systems are 4d/5d-based honeycomb magnets. Recent theoretical studies predicted that 3d-based honeycomb magnets, including Na2Co2TeO6 (NCTO), could also be a potential Kitaev system. Here, we have used a combination of heat capacity, magnetization, electron spin resonance measurements alongside inelastic neutron scattering (INS) to study NCTO's quantum magnetism, and we have found a field-induced spin disordered state in an applied magnetic field range of 7.5 T < B (⊥ b-axis) < 10.5 T. The INS spectra were also simulated to tentatively extract the exchange interactions. As a 3d-magnet with a field-induced disordered state on an effective spin-1/2 honeycomb lattice, NCTO expands the Kitaev model to 3d compounds, promoting further interests on the spin-orbital effect in quantum magnets.

Two-dimensional magnetic interplay in the tensile-strained LaCoO3 thin films.

High-quality epitaxial LaCoO3 (LCO) thin films have been deposited on SrTiO3 (STO) substrates with pulsed laser deposition (PLD). We find that the LCO films undergo a typical ferromagnetic-paramagnetic (FM-PM) phase transition at ∼80 K. To understand the nature of magnetic phase transition, various methods, including the modified Arrott plot and critical isotherm analysis, were used to determine the critical exponents, which are ß = 0.754(1) with a Curie temperature TC = 79.8(8) K and γ = 1.52(2) with TC = 79.9(2) K. The reliability of these critical exponents was confirmed using the Widom scaling relation and the scaling hypothesis. Further analysis revealed that the spin coupling within the LCO films exhibits two-dimensional (2D) long-range magnetic interaction and the magnetic exchange distance decays as J(r) ∼r-(3.46). Our critical behavior analysis may shed new light on the further understanding of the origin of FM and the relatively fixed TC in LCO thin films.

Disorder-driven non-Fermi liquid behavior in itinerant ferromagnet α-Co5Ge3.

The physical properties of itinerant ferromagnet [Formula: see text]-Co5Ge3 with both strong disorder and spin fluctuations was studied. The dc and ac susceptibility show that both spin fluctuations and disorder dominate the physical properties. In the spin glass phase, with a coexisting ferromagnetic state ([Formula: see text]30 K), both non-Fermi liquid behavior and large exponent of scaling relation of [Formula: see text] are observed and attributed to the spin fluctuations and disorder induced by cobalt defects. Upon the increase of external field, Fermi liquid behavior restores due to the suppression of spin fluctuations and disorder. In addition, a large anomalous Hall coefficient R s is observed. Our results suggest that [Formula: see text]-Co5Ge3 is a typical itinerant ferromagnet to explore the interplay of disorder and spin fluctuations.

Nontrivial superconductivity in topological MoTe2-x S x crystals.

Topological Weyl semimetals (TWSs) with pairs of Weyl points and topologically protected Fermi arc states have broadened the classification of topological phases and provide superior platform for study of topological superconductivity. Here we report the nontrivial superconductivity and topological features of sulfur-doped Td -phase MoTe2 with enhanced Tc compared with type-II TWS MoTe2 It is found that Td -phase S-doped MoTe2 (MoTe2-x S x , x ∼ 0.2) is a two-band s-wave bulk superconductor (∼0.13 meV and 0.26 meV), where the superconducting behavior can be explained by the s+- pairing model. Further, measurements of the quasi-particle interference (QPI) patterns and a comparison with band-structure calculations reveal the existence of Fermi arcs in MoTe2-x S x More interestingly, a relatively large superconducting gap (∼1.7 meV) is detected by scanning tunneling spectroscopy on the sample surface, showing a hint of topological nontrivial superconductivity based on the pairing of Fermi arc surface states. Our work demonstrates that the Td -phase MoTe2-x S x is not only a promising topological superconductor candidate but also a unique material for study of s+- superconductivity.

Anisotropic magnetic coupling with a two-dimensional characteristic in noncentrosymmetric Cr11Ge19.

In this work, we successfully synthesize the single crystal Cr11Ge19. The magnetism of the noncentrosymmetric Cr11Ge19 with itinerant ferromagnetic ground state is thoroughly investigated on the single crystal. Based on the variation measurements including the angular rotation, temperature, and magnetic field dependence of magnetization, we find that this material exhibits strong magnetic anisotropy along the c-axis. To clearly reveal the magnetic interactions, the critical behavior is studied using the modified Arrott plot, the Kouvel-Fisher method, and the critical isotherm technique. Combining these different methods, three main critical exponents (ß, γ, and δ) are obtained. The critical exponent ß is close to the theoretical prediction of a three-dimensional XY model with spin-dimensionality n = 2, indicating two-dimensional magnetic coupling. Meanwhile, the critical exponent γ suggests that the magnetic interaction is of long-range type with magnetic exchange distance decaying as J(r) ≈ r-4.61. We propose that the ferromagnetic ground state of Cr11Ge19 is formed by the polarized magnetic moments along the c-axis, while the long-range magnetic coupling is established within the ab plane.

Superconductivity and Charge Density Wave in ZrTe3-xSex.

Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe3 when the long range CDW order is gradually suppressed. Superconducting critical temperature Tc(x) in ZrTe3-xSex (0 ≤ x ≤ 0.1) increases up to 4 K plateau for 0.04 ≤ x ≤ 0.07. Further increase in Se content results in diminishing Tc and filametary superconductivity. The CDW modes from Raman spectra are observed in x = 0.04 and 0.1 crystals, where signature of ZrTe3 CDW order in resistivity vanishes. The electronic-scattering for high Tc crystals is dominated by local CDW fluctuations at high temperatures, the resistivity is linear up to highest measured T = 300 K and contributes to substantial in-plane anisotropy.

Gapless quantum spin liquid ground state in the two-dimensional spin-1/2 triangular antiferromagnet YbMgGaO4.

Quantum spin liquid (QSL) is a novel state of matter which refuses the conventional spin freezing even at 0 K. Experimentally searching for the structurally perfect candidates is a big challenge in condensed matter physics. Here we report the successful synthesis of a new spin-1/2 triangular antiferromagnet YbMgGaO4 with symmetry. The compound with an ideal two-dimensional and spatial isotropic magnetic triangular-lattice has no site-mixing magnetic defects and no antisymmetric Dzyaloshinsky-Moriya (DM) interactions. No spin freezing down to 60 mK (despite θw ~ -4 K), the power-law temperature dependence of heat capacity and nonzero susceptibility at low temperatures suggest that YbMgGaO4 is a promising gapless (≤|θw|/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO4, approaches zero (<0.6%). This indicates that the possible QSL ground state (GS) of the frustrated spin system has been experimentally achieved at the lowest measurement temperatures.

Detection of a superconducting phase in a two-atom layer of hexagonal Ga film grown on semiconducting GaN(0001).

The recent observation of the superconducting state at atomic scale has motivated the pursuit of exotic condensed phases in two-dimensional (2D) systems. Here we report on a superconducting phase in two-monolayer crystalline Ga films epitaxially grown on wide-band-gap semiconductor GaN(0001). This phase exhibits a hexagonal structure and only 0.552 nm in thickness, nevertheless, brings about a superconducting transition temperature Tc as high as 5.4 K, confirmed by in situ scanning tunneling spectroscopy and ex situ electrical magnetotransport and magnetization measurements. The anisotropy of critical magnetic field and Berezinski-Kosterlitz-Thouless-like transition are observed, typical for the 2D superconductivity. Our results demonstrate a novel platform for exploring atomic-scale 2D superconductors, with great potential for understanding the interface superconductivity.

Oxygen-vacancy-induced antiferromagnetism to ferromagnetism transformation in Eu0.5Ba0.5TiO3₋δ multiferroic thin films.

Oxygen vacancies (V(O)) effects on magnetic ordering in Eu0.5Ba0.5TiO3₋δ (EBTO3₋δ) thin films have been investigated using a combination of experimental measurements and first-principles density-functional calculations. Two kinds of EBTO3₋δ thin films with different oxygen deficiency have been fabricated. A nuclear resonance backscattering spectrometry technique has been used to quantitatively measure contents of the V(O). Eu0.5Ba0.5TiO3 ceramics have been known to exhibit ferroelectric (FE) and G-type antiferromagnetic (AFM) properties. While, a ferromagnetic (FM) behavior with a Curie temperature of 1.85 K has been found in the EBTO3₋δ thin films. Spin-polarized Ti(3+) ions, which originated from the V(O), has been proven to mediate a FM coupling between the local Eu 4f spins and were believed to be responsible for the great change of the magnetic ordering. Considering the easy formation of V(O), our work opens up a new avenue for achieving co-existence of FM and FE orders in oxide materials.

A racemic polar cobalt phosphonate with weak ferromagnetism.

Comfortably nemp: A novel polar compound [Co(2)(nemp)(2)(H(2)O)(2) ] incorporating racemic [1-(1-naphthyl)ethylamino]methylphosphonate (nemp(2-)) as a ligand is reported (see packing structure). This compound shows nonlinear optical properties at room temperature and weak ferromagnetism below 2 K.

The great effect of magnetic Fe(2+) ions on electromagnetic behavior in the Cu(1-x)Fe(x)Ir(2)S(4) system.

The substitution of magnetic Fe(2+) for nonmagnetic Cu(+) in the Cu(1-x)Fe(x)Ir(2)S(4) system causes drastic changes in electromagnetic behavior. For x = 0.01 and 0.025, the Peierls-like phase transition step ΔM in magnetization increases with x increasing, and an unexpected spin transition occurs at T(*)≈120 K. This may be attributed to the spin-polarization of the Ir(4+) ions by the Fe(2+) ions. When x exceed 0.1, the Peierls-like phase transition is suppressed completely. The magnetic state for Fe doped samples transforms from ferromagnetic (FM) to paramagnetic (PM), and back to the FM state again with the increase of x. For the highly doped samples, the FM domains formed by Fe(2+) ions result in another transition at T(**)≈110 K and the cluster-spin glass transition.