11 research outputs found
Acquisition of Single Crystal Growth and Characterization Equipment
Final Report for DOE Grant No. DE-FG02-04ER46178 'Acquisition of Single Crystal Growth and Characterization Equipment'. There is growing concern in the condensed matter community that the need for quality crystal growth and materials preparation laboratories is not being met in the United States. It has been suggested that there are too many researchers performing measurements on too few materials. As a result, many user facilities are not being used optimally. The number of proficient crystal growers is too small. In addition, insufficient attention is being paid to the enterprise of finding new and interesting materials, which is the driving force behind much of condensed matter research and, ultimately, technology. While a detailed assessment of this situation is clearly needed, enough evidence of a problem already exists to compel a general consensus that the situation must be addressed promptly. This final report describes the work carried out during the last four years in our group, in which a state-of-the-art single crystal growth and characterization facility was established for the study of novel oxides and intermetallic compounds of rare earth, actinide and transition metal elements. Research emphasis is on the physics of superconducting (SC), magnetic, heavy fermion (HF), non-Fermi liquid (NFL) and other types of strongly correlated electron phenomena in bulk single crystals. Properties of these materials are being studied as a function of concentration of chemical constituents, temperature, pressure, and magnetic field, which provide information about the electronic, lattice, and magnetic excitations at the root of various strongly correlated electron phenomena. Most importantly, the facility makes possible the investigation of material properties that can only be achieved in high quality bulk single crystals, including magnetic and transport phenomena, studies of the effects of disorder, properties in the clean limit, and spectroscopic and scattering studies through efforts with numerous collaborators. These endeavors will assist the effort to explain various outstanding theoretical problems, such as order parameter symmetries and electron-pairing mechanisms in unconventional superconductors, the relationship between superconductivity and magnetic order in certain correlated electron systems, the role of disorder in non-Fermi liquid behavior and unconventional superconductivity, and the nature of interactions between localized and itinerant electrons in these materials. Understanding the mechanisms behind strongly correlated electron behavior has important technological implications
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Annual Scientific Progress Report: National Nuclear Security Administration Stockpile Stewardship: Academic Alliance Research Grant #DE-FG52-06NA26205
The focus of this grant, entitled 'Experimental investigations of magnetic, superconducting, and other phase transitions in novel f-electron materials at ultra-high pressures using designer diamond anvils', is to explore the novel properties of f-electron compounds under pressure, with a particular emphasis on the physics of superconductivity, magnetism, and their interactions. This report is a synopsis of the research that was undertaken from 6/2007-6/2008
Anisotropic Physical Properties of the Kondo Semimetal CeCuAs
The recently proposed novel materials class called Weyl-Kondo semimetal
(WKSM) is a time reversal invariant but inversion symmetry broken Kondo
semimetal in which Weyl nodes are pushed to the Fermi level by the Kondo
interaction. Here we explore whether CeCuAs may be a new WKSM
candidate. We report on its single-crystal growth, structure determination and
physical properties investigation. Previously published studies on
polycrystalline samples suggest that it is indeed a Kondo semimetal, which is
confirmed by our investigations on single crystals. X-ray diffraction reveals
that CeCuAs crystallizes in a tetragonal centrosymmetric structure,
although the inversion symmetry could still be broken locally due to partially
occupied Cu sites. Chemical analysis results in an average occupation =
0.11(1). The electrical resistivity increases logarithmically with decreasing
temperature, and saturates below 10 K. A Kondo temperature
4 K is extracted from entropy, estimated from the specific heat
measurements. From Hall effect experiments, a charge carrier density of cm is extracted, a value characteristic of a semimetal.
The magnetization shows pronounced anisotropy, with no evidence of magnetic
ordering down to 0.4 K. We thus classify CeCuAs as a tetragonal
Kondo semimetal with anisotropic magnetic properties, with a possibly broken
inversion symmetry, thus fulfilling the necessary conditions for a WKSM state.Comment: 6 pages, 4 figures, Proceedings of the International Conference on
Strongly Correlated Electron Systems (SCES2019
Author Correction: Control of electronic topology in a strongly correlated electron system
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Quenching a Weyl-Kondo semimetal by magnetic field
With the advent of topology in electronic materials the number of predicted
quantum phases has literally exploded. Most of them, however, still await firm
experimental identification. In strongly correlated electron systems, scanning
their low-temperature phase diagrams by varying a nonthermal control parameter
has been instrumental in delineating phases defined by a Landau order
parameter. Here we show that this approach is versatile also for strongly
correlated topological phases. We use Hall effect measurements to probe how the
time reversal symmetry invariant Weyl-Kondo semimetal CeBiPd
transforms under magnetic-field tuning. We detect an intriguing two-stage
transition, which we associate with an annihilation of the Weyl nodes, making
the system more insulating, and a consecutive transition to a heavy fermion
metal phase. We expect our work to stimulate tuning studies in related systems,
thereby advancing the much needed identification of organizing principles for
strongly correlated electronic topology.Comment: 4 figures, 19 page
Universal V-shaped temperature-pressure phase diagram in the iron-based superconductors KFe
Strain-Driven Approach to Quantum Criticality in AFe2As2 with A=K, Rb, and Cs
The iron-based superconductors AFe2As2 with A=K, Rb, Cs exhibit large Sommerfeld coefficients approaching those of heavy-fermion systems. We have investigated the magnetostriction and thermal expansion of this series to shed light on this unusual behavior. Quantum oscillations of the magnetostriction allow identifying the band-specific quasiparticle masses which by far exceed the band-structure derived masses. The divergence of the Grüneisen ratio derived from thermal expansion indicates that with increasing volume along the series a quantum critical point is approached. The critical fluctuations responsible for the enhancement of the quasiparticle masses appear to weaken the superconducting state
Determining the local low-energy excitations in the Kondo semimetal CeRu4Sn6 using resonant inelastic x-ray scattering
We have investigated the local low-energy excitations in CeRu4Sn6, a material discussed recently in the framework of strongly correlated Weyl semimetals, by means of Ce M-5 resonant inelastic x-ray scattering (RIXS). The availability of both F-2(5/2) and F-2(7/2) excitations of the Ce 4f(1) configuration in the spectra allows for the determination of the crystal-electric field (CEF) parameters that explain quantitatively the high-temperature anisotropy of the magnetic susceptibility. The absence of an azimuthal dependence in the spectra indicates that all CEF states are close to being rotational symmetric. We show further that the non-negligible impact of the (sic)(6)(0) parameter on the ground state of CeRu4Sn6 leads to a reduction of the magnetic moment mu(c) due to multiplet intermixing. This improves the agreement between CEF calculations and the experimentally determined magnetic susceptibility considerably at low temperatures. Deviations that persist at low temperatures for fields within the tetragonal plane are attributed to the Kondo interaction between 4f and conduction electrons. The RIXS results are consistent with inelastic neutron scattering data and are compared to the predictions from ab initio based electronic structure calculations