Engineering topics

Gong, Dongliang

Publications and source records attributed to Gong, Dongliang.

7 records

DOE OSTI2024

Anomalous proximitized transport in metal/quantum magnet heterostructure Bi 2 Ir 2 O 7 /Yb 2 Ti 2 O 7

Fluctuations of quantum spins play a crucial role in the emergence of exotic magnetic phases and excitations. The lack of the charge degree of freedom in insulating quantum magnets, however, precludes such fluctuations from mediating electronic transport. Here, we show that the quantum fluctuations of a localized frustrated magnet induce strong proximitized charge transport of the conduction electrons in a synthetic heterostructure comprising an epitaxial Bi 2 Ir 2 O 7 ultrathin film on a single crystal of Yb 2 Ti 2 O 7 . The proximity effects are evidenced by the scaling behavior of the Bi 2 Ir 2 O 7 resistance in correspondence with the dynamic scaling of the dynamic spincorrelation function of Yb 2 Ti 2 O 7 , which is a result of quantum fluctuations near a multiphase quantum critical point. The proximitized transport in Bi 2 Ir 2 O 7 can be effectively tuned by a magnetic field through suppressing the quantum spin fluctuations (QSFs) as well as inducing transitions via magnetic anisotropy in Yb 2 Ti 2 O 7 . In this study, we establish a pathway for harnessing QSFs in magnetic insulators with electric transport, offering exciting prospects for potential applications in the realm of quantum spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Spin excitations in the kagome-lattice metallic antiferromagnet Fe 0.89 Co 0.11 Sn

Kagome-lattice materials have attracted tremendous interest due to the broad prospect for seeking superconductivity, quantum spin liquid states, and topological electronic structures. Among them, the transition-metal kagome lattices are high-profile objects for the combination of topological properties, rich magnetism, and multiple-orbital physics. Here we report an inelastic neutron scattering study on the spin dynamics of a kagome-lattice antiferromagnetic metal Fe 0.89 Co 0.11 Sn. Although the magnetic excitations can be observed up to ~250 meV, well-defined spin waves are only identified below ~90 meV and can be modeled using Heisenberg exchange with ferromagnetic in-plane nearest-neighbor coupling J 1 , in-plane next-nearest-neighbor coupling J 2 , and antiferromagnetic (AFM) interlayer coupling J c under linear spin-wave theory. Above ~90 meV, the spin waves enter the itinerant Stoner continuum and become highly damped particle-hole excitations. At the K point of the Brillouin zone, we reveal a possible band crossing of the spin wave, which indicates a potential Dirac magnon. Finally, our results uncover the evolution of the spin excitations from the planar AFM state to the axial AFM state in Fe 0.89 Co 0.11 Sn, solve the magnetic Hamiltonian for both states, and confirm the significant influence of the itinerant magnetism on the spin excitations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Reconciling monolayer and bilayer Jeff = 1/2 square lattices in hybrid oxide superlattice

The number of atomic layers confined in a two-dimensional structure is crucial for the electronic and magnetic properties. Single-layer and bilayer J eff = 1/2 square lattices are well-known examples where the presence of the extra layer turns the XY anisotropy to the c-axis anisotropy. We report on experimental realization of a hybrid SrIrO 3 /SrTiO 3 superlattice that integrates monolayer and bilayer square lattices in one layered structure. By synchrotron x-ray diffraction, resonant x-ray magnetic scattering, magnetization, and resistivity measurements, we found that the hybrid superlattice exhibits properties that are distinct from both the single-layer and bilayer systems and cannot be explained by a simple addition of them. In particular, the entire hybrid superlattice orders simultaneously through a single antiferromagnetic transition at temperatures similar to the bilayer system but with all the J eff = 1/2 moments mainly pointing in the ab plane similar to the single-layer system. The results show that bringing monolayer and bilayer with orthogonal properties in proximity to each other in a hybrid superlattice structure is a powerful way to stabilize a unique state not obtainable in a uniform structure.

2-dimensional systems↗

DOE OSTI2022

Tracking the nematicity in cuprate superconductors: a resistivity study under uniaxial pressure

Overshadowing the superconducting dome in hole-doped cuprates, the pseudogap state is still one of the mysteries that no consensus can be achieved. It has been suggested that the rotational symmetry is broken in this state and may result in a nematic phase transition, whose temperature seems to coincide with the onset temperature of the pseudogap state $T^{\,*}$ around optimal doping level, raising the question whether the pseudogap results from the establishment of the nematic order. Here we report results of resistivity measurements under uniaxial pressure on several hole-doped cuprates, where the normalized slope of the elastoresistivity ζ can be obtained as illustrated in iron-based superconductors. The temperature dependence of ζ along particular lattice axis exhibits kink feature at Tk and shows Curie–Weiss-like behavior above it, which may suggest a spontaneous nematic transition. While Tk seems to be the same as $T^{\,*}$ around the optimal doping and in the overdoped region, they become very different in underdoped La$_{2-x}$SrxCuO 4 . Our results suggest that the nematic order, if indeed existing, is an electronic phase within the pseudogap state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Nematic Fluctuations in the Non-Superconducting Iron Pnictide BaFe 1.9-x Ni 0.1 Cr x As 2

The main driven force of the electronic nematic phase in iron-based superconductors is still under debate. Here, we report a comprehensive study on the nematic fluctuations in a non-superconducting iron pnictide system BaFe 1.9-x Ni 0.1 Cr x As 2 by electronic transport, angle-resolved photoemission spectroscopy (ARPES), and inelastic neutron scattering (INS) measurements. Previous neutron diffraction and transport measurements suggested that the collinear antiferromagnetism persists to x = 0.8, with similar Néel temperature TN and structural transition temperature Ts around 32 K, but the charge carriers change from electron type to hole type around x = 0.5. In this study, we have found that the in-plane resistivity anisotropy also highly depends on the Cr dopings and the type of charge carriers. While ARPES measurements suggest possibly weak orbital anisotropy onset near Ts for both x = 0.05 and x = 0.5 compounds, INS experiments reveal clearly different onset temperatures of low-energy spin excitation anisotropy, which is likely related to the energy scale of spin nematicity. These results suggest that the interplay between the local spins on Fe atoms and the itinerant electrons on Fermi surfaces is crucial to the nematic fluctuations of iron pnictides, where the orbital degree of freedom may behave differently from the spin degree of freedom, and the transport properties are intimately related to the spin dynamics.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Evidence for topological semimetallicity in a chain-compound TaSe 3

Among one-dimensional transition-metal trichalcogenides, TaSe 3 is unconventional in many respects. One is its strong topological semimetallicity as predicted by first-principles calculations. We report the experimental investigations of the electronic properties of one-dimensional-like TaSe 3 single crystals. While the b-axis electrical resistivity shows good metallicity with a high residual resistivity ratio greater than 100, an extremely large magnetoresistance is observed reaching ≈7 × 10 3 % at 1.9 K for 14 T. Interestingly, the magnetoresistance follows the Kohler’s rule with nearly quadratic magnetic field dependence, consistent with the electron–hole compensation scenario as confirmed by our Hall conductivity data. Both the longitudinal and Hall conductivities show Shubnikov-de Haas oscillations with two frequencies: F α ≈ 97 T and F β ≈ 186 T. Quantitative analysis indicates that F α results from the two-dimensional-like electron band with the non-trivial Berry phase [1.1π], and Fβ from the hole band with the trivial Berry phase [0(3D) -0.16π(2D)]. Our experimental findings are consistent with the predictions based on first-principles calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Canted Eu magnetic structure in EuMnSb 2

Magnetic ordering breaks the time-reversal symmetry, greatly impacting material topological properties. Here, we report the investigation of the magnetic properties of the layered EuMnSb 2 , which has two sets of magnetic sublattices. Both the magnetization and electrical resistivity reveal two phase transitions with one at T N,Eu ~21K and the other at T N,Mn ~346K. Single crystal neutron diffraction refinement indicates that both transitions are originated from magnetic ordering. Below T N,Mn , the Mn sublattice forms the C-type antiferromagnetic (AFM) structure with moments [(4.5±0.6)μB at 7 K] pointing along the a axis. Below T N,Eu , the Eu sublattice forms the canted A-type AFM structure with moments [(5.9±0.8)μB at 7 K] lying in the ac plane but pointing (41 ± 1)° away from the a axis. Quantitative analysis indicates that the spin-spin correlation length, while anisotropic, has long-range characteristic in all directions for both the Eu and Mn sublattices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗