A5028623311- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Rare-earth and actinide compounds
- Iron-based superconductors research
- Superconductivity in MgB2 and Alloys
- High-pressure geophysics and materials
- Magnetic properties of thin films
- Magnetic Properties of Alloys
- Superconducting Materials and Applications
- Dyeing and Modifying Textile Fibers
- Color Science and Applications
- Quantum, superfluid, helium dynamics
- Color perception and design
- Nuclear Materials and Properties
- Inorganic Fluorides and Related Compounds
- Electronic and Structural Properties of Oxides
- Inorganic Chemistry and Materials
- X-ray Diffraction in Crystallography
- Copper-based nanomaterials and applications
- Cold Atom Physics and Bose-Einstein Condensates
- Theoretical and Computational Physics
- Thermal Expansion and Ionic Conductivity
- Textile materials and evaluations
- Atomic and Subatomic Physics Research
Argonne National Laboratory
2005-2020
North Carolina State University
2010-2020
Brookhaven National Laboratory
2017
North Central State College
2008-2016
Jiangnan University
2014
Northwestern University
1990-2006
University of Wisconsin–Milwaukee
2002-2006
National High Magnetic Field Laboratory
2006
Illinois Institute of Technology
2000
Izmir Institute of Technology
2000
In situ neutron powder diffraction measurements show that the orthorhombic-to-tetragonal phase transition in $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$, which occurs near 700\ifmmode^\circ\else\textdegree\fi{}C a pure oxygen atmosphere, is an order-disorder disordering of atoms into normally vacant site destroys one-dimensional Cu-O chains present room-temperature orthorhombic structure. For both structures, stoichiometry decreases monotonically with...
Muon-spin-relaxation and bulk measurements of the magnetic-field penetration depth suggest that cuprate high-${\mathit{T}}_{\mathit{c}}$, bismuthate, organic Chevrel-phase, heavy-fermion systems possibly belong to a unique group superconductors characterized by high transition temperatures ${\mathit{T}}_{\mathit{c}}$ relative values ${\mathit{n}}_{\mathit{s}}$/${\mathit{m}}^{\mathrm{*}}$ (carrier density/effective mass). This feature distinguishes these exotic from ordinary BCS superconductors.
We have determined the crystal structure of single-phase stoichiometric high-temperature superconductor in Y-Ba-Cu-O system using high-resolution neutron powder diffraction. This compound has an orthorhombic with space group Pmmm and lattice constants a=3.8231 Å, b=3.8864 c=11.6807 Å. The consists ‘‘dimpled’’ CuO2 layers a-b planes loosely bonded by one-dimensional fencelike square-planar CuO3 chains b-c planes.
${\mathrm{La}}_{1.85}$${\mathrm{Ba}}_{0.15}$${\mathrm{CuO}}_{4}$ exhibits high-${\mathrm{T}}_{\mathrm{c}}$ superconductivity with an onset temperature near 33 K as measured by resistivity and magnetic susceptibility. The nonsuperconducting end-member compound, ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$, which has orthorhombic, Cmca structure, semiconducting behavior. orthorhombic distortion is proposed to result from a Peierls 2${\mathrm{k}}_{\mathrm{F}}$ instability or soft zone-boundary...
Measurements of the specific heat ${\mathrm{Mg}}^{11}{\mathrm{B}}_{2}$ from 1 to 50 K, in magnetic fields 9 T, give Debye temperature, $\ensuremath{\Theta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1050\mathrm{K}$, coefficient normal-state electron contribution, ${\ensuremath{\gamma}}_{n}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.6\mathrm{mJ}{\mathrm{mol}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}2}$, and a discontinuity zero-field...
Using Rietveld refinement of neutron powder diffraction data, we show that the excess oxygen in ${\mathrm{La}}_{2}$${\mathrm{NiO}}_{4+\mathrm{\ensuremath{\delta}}}$ (0.13<\ensuremath{\delta}<0.18) is incorporated as an interstitial defect. The defect located near ((1/4, 1/B) / 4 ,(1/4) site orthorhombic Fmmm structure, which provides a favorable coordination to four La atoms but requires nearby be displaced from their normal positions. concentration determined structural agrees well with...
High-resolution photoemission is used to study the electronic structure of cuprate superconductor, Bi(2)Sr(2)CaCu(2)O(8+delta), as a function hole doping and temperature. A kink observed in band dispersion nodal line superconducting state associated with coupling resonant mode neutron scattering. From measured real part self-energy it possible extract constant which largest underdoped regime, then decreasing continuously into overdoped regime.
The study of the anisotropic superconductor MgB2 using a combination scanning tunneling microscopy and spectroscopy reveals two distinct energy gaps at Delta(1)=2.3 meV Delta(2)=7.1 4.2 K. Different spectral weights partial superconducting density states are reflection different directions in this multiband system. Temperature evolution spectra follows BCS scenario [Phys. Rev. Lett. 3, 552 (1959)]] with both vanishing bulk T(c). data confirm importance Fermi-surface sheet dependent...
The photoemission line shape near $(\ensuremath{\pi},0)$ in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ below ${T}_{c}$ is characterized by a sharp peak, followed at higher energy dip and hump. We study the evolution of this as function momentum, temperature, doping. find hump scales with peak persists above pseudogap state. present strong evidence that peak-dip-hump structure arises from interaction electrons collective mode wave vector...
We show that the specific heat of superconductor MgB2 in zero field, for which significant non-BCS features have been reported, can be fitted, essentially within experimental error, over entire range temperature to Tc by a phenomenological two-gap model. The resulting gap parameters agree with previous determinations from band structure calculations, and various spectroscopic experiments. determination heat, bulk property, shows presence two superconducting gaps is volume effect.
Tunneling measurements are reported for break junctions on ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{O}_{8\ensuremath{-}\ensuremath{\delta}}$ single crystals with various oxygen concentrations. Superconducting energy gaps $\ensuremath{\Delta}$ observed in the underdoped samples which considerably larger $(\ensuremath{\sim}30%)$ than found optimal doped crystals. The trend of decreasing and $2\ensuremath{\Delta}{/kT}_{c}$ increasing hole doping is continued into overdoped region....
We present measurements of longitudinal ultrasonic velocity on single crystals the heavy-fermion superconductor ${\mathrm{UPt}}_{3}$. The show clear signatures second-order phase transitions in superconducting state, with anomalies well accounted for by Ginzburg-Landau theory. From these we construct a diagram ${\mathrm{UPt}}_{3}$ that reveals all boundary lines have been identified as possible transitions. are able to track transition tetracritical point, located upper-critical-field curve,...
Temperature-dependent neutron diffraction studies on melt-grown crystals of the layered compound ${\mathrm{La}}_{1.2}$${\mathrm{Sr}}_{1.8}$${\mathrm{Mn}}_{2}$${\mathrm{O}}_{7}$ reveal a dramatic structural response to onset ferromagnetism and coincident insulator-metal transition. Unlike related manganite perovskites, whose Jahn-Teller distorted octahedra become more regular at temperatures below transition, ${\mathrm{MnO}}_{6}$ this material are severely when charge is itinerant than it localized.
New tunneling data are reported in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ which show quasiparticle excitation gaps, \ensuremath{\Delta}, reaching values as high 60 meV for underdoped crystals with ${T}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}70\mathrm{K}$. These energy gaps nearly 3 times larger than those of overdoped similar ${T}_{c}$. Despite the large differences gap magnitude, spectra display qualitatively...