A5011802261- Iron-based superconductors research
- Magnetic and transport properties of perovskites and related materials
- Rare-earth and actinide compounds
- Multiferroics and related materials
- Corporate Taxation and Avoidance
- Advanced Condensed Matter Physics
- Physics of Superconductivity and Magnetism
- Intellectual Capital and Performance Analysis
- Ferroelectric and Piezoelectric Materials
- Magnetic Properties of Alloys
- Electronic and Structural Properties of Oxides
- Superconductivity in MgB2 and Alloys
- Magnetic properties of thin films
- Inorganic Chemistry and Materials
- Amyloidosis: Diagnosis, Treatment, Outcomes
- Photonic Crystals and Applications
- Solid-state spectroscopy and crystallography
- Copper-based nanomaterials and applications
- Acoustic Wave Resonator Technologies
- Gas Sensing Nanomaterials and Sensors
- nanoparticles nucleation surface interactions
- Advanced Memory and Neural Computing
- Thermodynamic and Structural Properties of Metals and Alloys
- ZnO doping and properties
Beijing Normal University
2011-2021
Rice University
2017
University of Tennessee at Knoxville
2011-2014
Institute of Physics
2003-2005
Tsinghua University
2004-2005
National Laboratory for Superconductivity
2005
Chinese Academy of Sciences
2003
Imperial College London
2000
In conventional Bardeen-Cooper-Schrieffer (BCS) superconductors, superconductivity occurs when electrons form coherent Cooper pairs below the superconducting transition temperature Tc. Although kinetic energy of paired increases in state relative to normal state, reduction ion lattice is sufficient give condensation energy. For iron pnictide superconductors derived from electron or hole doping their antiferromagnetic (AF) parent compounds, microscopic origin for supercnductivity unclear....
Triangular lattice of rare-earth ions with interacting effective spin-1/2 local moments is an ideal platform to explore the physics quantum spin liquids (QSLs) in presence strong spin-orbit coupling, crystal electric fields, and geometrical frustration. The Yb delafossites, NaYbCh2 (Ch=O, S, Se) forming a perfect triangular lattice, have been suggested be candidates for QSLs. Previous thermodynamics, nuclear magnetic resonance, powder-sample neutron scattering measurements on supported...
Topological vortices with swirling ferroelectric, magnetic and structural anti-phase relationship in hexagonal RMnO3 (R = Ho to Lu, Y Sc) have attracted much attention because of their intriguing behaviors. Herein, we report the structure multiferroic vortex domains YMnO3 at atomic scale using state-of-the-art aberration-corrected scanning transmission electron microscopy (STEM). Two types displacements were identified among six domain walls (DWs); translation-ferroelectric denoted by α+,...
We use inelastic neutron scattering to study spin waves in the antiferromagnetic ordered phase of iron pnictide NaFeAs throughout Brillouin zone. Comparing with well-studied $A{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ ($A=\mathrm{Ca}$, Sr, Ba) family, have considerably lower zone boundary energies and more isotropic effective in-plane magnetic exchange couplings. These results are consistent calculations from a combined density functional theory dynamical mean field provide strong evidence that...
Neutron diffraction has been used to study the lattice and magnetic structures of insulating superconducting Rb${}_{y}$Fe${}_{1.6+x}$Se${}_{2}$. For Rb${}_{y}$Fe${}_{1.6+x}$Se${}_{2}$, neutron polarization analysis single-crystal unambiguously confirm earlier proposed $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}$ block antiferromagnetic structure. samples (${T}_{c}=30$ K), we find that in addition tetragonal superlattice structure transition at 513 K, material develops a separate...
A determination of the superconducting (SC) electron pairing symmetry forms basis for establishing a microscopic mechanism superconductivity. For iron pnictide superconductors, ${s}^{\ifmmode\pm\else\textpm\fi{}}$-pairing theory predicts presence sharp neutron spin resonance at an energy below sum hole and SC gap energies ($E\ensuremath{\le}2\ensuremath{\Delta}$) ${T}_{c}$. On other hand, ${s}^{++}$-pairing expects broad excitation enhancement above $2\ensuremath{\Delta}$ Although has been...
High-temperature superconductivity is closely adjacent to a long-range antiferromagnet, which called parent compound. In cuprates, all compounds are alike and carrier doping leads superconductivity, so unified phase diagram can be drawn. However, the properties of for iron-based superconductors show significant diversity both isovalent dopings cause casts doubt on idea that there exists them. Here we ordered moments in variety iron pnictides inversely proportional effective Curie constants...
We use inelastic neutron scattering to show that superconductivity in electron-underdoped NaFe0.985Co0.015As induces a dispersive sharp resonance near E(r1)=3.25 meV and broad dispersionless mode at E(r2)=6 meV. However, similar measurements on overdoped superconducting NaFe0.935Co0.045As find only single E(r)=7 connect these results with the observations of angle-resolved photoemission spectroscopy gaps electron Fermi pockets are anisotropic underdoped material but become isotropic case....
In this letter, the electrical and magnetic properties of La{sub(1-x)}Te{sub(x)}MnO{sub(3)}(x=0.1, 0.15), which is a new material shows good colossal magnetoresistance (CMR) behavior, have been investigated. These compounds rhombohedral structure. materical, Te replaced part La ions, induced lattice cell constriction Mn-O-Mn bond angle widening. X-ray photoemission spectroscopy (XPS) measurement revealed that ions were in tetravalent state manganese could be considered as mixture Mn{sup(2+)}...
We use unpolarized and polarized inelastic neutron scattering to study low-energy spin excitations in NaFeAs, which exhibits a tetragonal-to-orthorhombic lattice distortion at ${T}_{s}\ensuremath{\approx}58$ K followed by collinear antiferromagnetic (AF) order below ${T}_{N}\ensuremath{\approx}45$ K. In the AF ordered state ($T<{T}_{N}$), waves are entirely $c$-axis $\ensuremath{\sim}$10 meV, exhibiting gap of $\ensuremath{\sim}$4 meV zone center disperse $\ensuremath{\sim}$7 near...
Iron-arsenide superconductor Na$_{1-\delta}$FeAs is highly reactive with the environment. Due to high mobility of Na ions, this reaction affects entire bulk crystals and leads an effective stoichiometry change. Here we use effect study doping evolution normal superconducting properties \emph{the same} single crystals. Controlled air increases transition temperature, $T_c$, from initial value 12 K 27 as probed by transport magnetic measurements. Similar effects are observed in samples reacted...
We study the normal-state and superconducting properties of NaFe${}_{1\ensuremath{-}x}$Co${}_{x}$As system by specific heat measurements. Both Sommerfeld coefficient condensation energy are strongly suppressed in underdoped heavily overdoped samples. The low-temperature electronic can be well fitted either a one-gap or two-gap BCS-type function for all ratio ${\ensuremath{\gamma}}_{N}{T}_{c}^{2}/{H}_{c}^{2}(0)$ nicely associate neutron spin resonance as bosons standard Eliashberg model....
We use polarized inelastic neutron scattering (INS) to study spin excitations in superconducting NaFe0.985Co0.015As (C15) with static antiferromagnetic (AF) order along the a-axis of orthorhombic structure and NaFe0.935Co0.045As (C45) without AF order. In previous unpolarized INS work, C15 were found have a dispersive sharp resonance near Er1=3.25 meV broad dispersionless mode at Er2=6 meV. Our polarization analysis reveals that is highly anisotropic a- c-axis, while isotropic similar C45....
We use polarized inelastic neutron scattering (INS) to study spin excitations of optimally hole-doped superconductor Ba${}_{0.67}$K${}_{0.33}$Fe${}_{2}$As${}_{2}$ (${T}_{c}=38$ K). In the normal state, imaginary part dynamic susceptibility, ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}(Q,\ensuremath{\omega})$, shows magnetic anisotropy for energies below $\ensuremath{\sim}$7 meV with $c$-axis larger than that in-plane component. Upon entering into superconducting previous unpolarized...
Abstract Triangular lattice of rare-earth ions with interacting effective spin-1/2 local moments is an ideal platform to explore the physics quantum spin liquids (QSLs) in presence strong spin-orbit coupling, crystal electric fields, and geometrical frustration. The Yb delafossites, NaYb Ch 2 ( =O, S, Se) forming a perfect triangular lattice, have been suggested be candidates for QSLs. Previous thermodynamics, nuclear magnetic resonance, powder sample neutron scattering measurements on...
Using polarization-resolved electronic Raman scattering we study underdoped, optimally doped, and overdoped ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ samples in the normal superconducting states. We show that low-energy nematic fluctuations are universal for all studied doping ranges. In state, observe two distinct pair-breaking peaks corresponding to one large small gap. addition, detect a collective mode below transition ${B}_{2g}$ channel...
We report structural transformation of sixfold vortex domains into two-, four-, and eightfold vortices via a different type topological defect in hexagonal manganites. Combining high-resolution electron microscopy Landau-theory-based numerical simulations, we investigate the remarkable atomic arrangement intertwined relationship between structures defects. The roles their displacement field, formation temperature, nucleation sites are revealed. All conceivable system topologically classified...
We report the structural, magnetic, and electrical transport properties of pervoskite oxide La0.9Te0.1MnO3. This material, with space group R-3C, shows spin-glasslike features at low temperature has a good colossal magnetoresistance behavior. The ratio MR=[ρ(0)−ρ(H)]/ρ(0) is about 51% 200 K in field 4 T. X-ray photoemission spectroscopy measurements suggest that Te ions are Te4+ state, while Mn may be Mn2+ Mn3+ valence state.
We present a high-pressure NMR study of the overdoped iron pnictide superconductor ${\mathrm{NaFe}}_{0.94}{\mathrm{Co}}_{0.06}\mathrm{As}$. The low-energy antiferromagnetic spin fluctuations in normal state, manifest as Curie-Weiss upturn spin-lattice relaxation rate $1/^{75}T_{1}T$, first increase strongly with pressure but fall again at $P>{P}_{\mathrm{opt}}=2.2\text{ }\text{ }\mathrm{GPa}$. Neither long-ranged magnetic order nor structural phase transition is encountered up to 2.5 GPa....
Although topological defects, such as domain walls (DWs) or vortices, are naturally protected by invariance, yet, we discover an exception that the six-state topology of vortex with Z2 × Z3 symmetry is broken a partial edge dislocation (PED) in hexagonal Y0.67Lu0.33MnO3, where topologies four-state closed DWs emerges. Using aberration-corrected scanning transmission electron microscopy, found PED plays important role changing phase translation domain. The at core leads to formation vortex,...
Because of the unconventional nature high-temperature superconductors, it has been proposed that magnons, rather than phonons, play an important role in Cooper pair formation. It is therefore great importance to understand how magnetic excitations behave and evolve between superconducting nonsuperconducting compounds. In this work, authors present a comprehensive study electron-doped NaFe${}_{1-x}$Co${}_{x}$As several samples across phase diagram, including both They find strong suppression...
We use polarized inelastic neutron scattering to study the temperature and energy dependence of spin space anisotropies in optimally hole-doped iron pnictide Ba$_{0.67}$K$_{0.33}$Fe$_{2}$As$_{2}$ ($T_{{\rm c}}=38$ K). In superconducting state, while high-energy part magnetic spectrum is nearly isotropic, low-energy displays a pronouced anisotropy, manifested by $c$-axis resonance. also observe that anisotropy extends higher energies compared electron-doped BaFe$_{2-x}TM_{x}$As$_{2}$...
In this study, electron-doped manganese oxide thin films La1−xTexMnO3 (x=0.1,0.15) have been fabricated and their magnetic properties colossal magnetoresistance effect investigated. The experimental results show that the a high metal–insulator transition temperature TMI of ∼300 K large ratio ∼80% at 4 T. addition, resistivity has similar change an on–off function near room might be advantageous in technological application materials.
We use inelastic neutron scattering and dielectric constant measurements to study the doping influence on spin dynamics magnetoelectric (ME) effect in hexagonal${\mathrm{Y}}_{0.7}{\mathrm{Lu}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$. In undoped $\mathrm{Y}\mathrm{Mn}{\mathrm{O}}_{3}$ $\mathrm{Lu}\mathrm{Mn}{\mathrm{O}}_{3}$, Mn trimerization distortion has been suggested play a key role determining magnetic structure effect. ${\mathrm{Y}}_{0.7}{\mathrm{Lu}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$, at...