P. C. Canfield

Use of frit-disc crucibles for routine and exploratory solution growth of single crystalline samples

Solution growth of single crystals from high temperature solutions often involves the separation of residual solution from the grown crystals. For many growths of intermetallic compounds, this separation has historically been achieved with the use of plugs of silica wool. Whereas this is generally efficient in a mechanical sense, it leads to a significant contamination of the decanted liquid with silica fibres. In this paper, we present a simple design for frit-disc alumina crucible sets that has made their use in the growth single crystals from high temperature solutions both simple and affordable. An alumina frit-disc allows for the clean separation of the residual liquid from the solid phase. This allows for the reuse of the decanted liquid, either for further growth of the same phase, or for subsequent growth of other, related phases. In this paper, we provide examples of the growth of isotopically substituted TbCd and icosahedral i-RCd quasicrystals, as well as the separation of (i) the closely related and phases and (ii) and .

Strong cooperative coupling of pressure-induced magnetic order and nematicity in FeSe

A hallmark of the iron-based superconductors is the strong coupling between magnetic, structural and electronic degrees of freedom. However, a universal picture of the normal state properties of these compounds has been confounded by recent investigations of FeSe where the nematic (structural) and magnetic transitions appear to be decoupled. Here, using synchrotron-based high-energy x-ray diffraction and time-domain Mössbauer spectroscopy, we show that nematicity and magnetism in FeSe under applied pressure are indeed strongly coupled. Distinct structural and magnetic transitions are observed for pressures between 1.0 and 1.7u2009GPa and merge into a single first-order transition for pressures ≳1.7u2009GPa, reminiscent of what has been found for the evolution of these transitions in the prototypical system Ba(Fe1−xCox)2As2. Our results are consistent with a spin-driven mechanism for nematic order in FeSe and provide an important step towards a universal description of the normal state properties of the iron-based superconductors.

Origin of the Resistivity Anisotropy in the Nematic Phase of FeSe.

The in-plane resistivity anisotropy is studied in strain-detwinned single crystals of FeSe. In contrast to other iron-based superconductors, FeSe does not develop long-range magnetic order below the tetragonal-to-orthorhombic transition at T_{s}≈90u2009u2009K. This allows for the disentanglement of the contributions to the resistivity anisotropy due to nematic and magnetic orders. Comparing direct transport and elastoresistivity measurements, we extract the intrinsic resistivity anisotropy of strain-free samples. The anisotropy peaks slightly below T_{s} and decreases to nearly zero on cooling down to the superconducting transition. This behavior is consistent with a scenario in which the in-plane resistivity anisotropy is dominated by inelastic scattering by anisotropic spin fluctuations.

Asymmetric mass acquisition in LaBi. Topological semimetal candidate

We use our high resolution He-lamp-based, tunable laser-based angle-resolved photoemission spectroscopy measurements and density functional theory calculations to study the electronic properties of LaBi, a binary system that was proposed to be a member of a new family of topological semimetals. Both bulk and surface bands are present in the spectra. Furthermore, the dispersion of the surface state is highly unusual. It resembles a Dirac cone, but upon closer inspection we can clearly detect an energy gap. The bottom band follows roughly a parabolic dispersion. The dispersion of the top band remains very linear, “V” -shape like, with the tip approaching very closely to the extrapolated location of Dirac point. Finally, such asymmetric mass acquisition is highly unusual and opens a possibility of a new topological phenomenon that has yet to be understood.

Nonmonotonic pressure evolution of the upper critical field in superconducting FeSe

The pressure dependence of the upper critical field, Hc2,c, of single crystalline FeSe was studied using measurements of the interplane resistivity, ρc, in magnetic fields parallel to tetragonal c axis. Hc2,c(T) curves obtained under hydrostatic pressures up to 1.56 GPa, the range over which the superconducting transition temperature, Tc, of FeSe exhibits a nonmonotonic dependence with local maximum at p1 ≈ 0.8 GPa and local minimum at p2 ≈ 1.2 GPa. The slope of the upper critical field at Tc,(dHc2,c/dT)Tc, also exhibits a nonmonotonic pressure dependence with distinct changes at p1 and p2. For p p2 the slope is in good semiquantitative agreement with a single band, orbital Helfand-Werthamer theory with Fermi velocities determined from Shubnikov–de Haas measurements. Lastly, this finding indicates that Fermi surface changes are responsible for the local minimum of Tc(p) at p2 ≈ 1.2 GPa.

Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

S. Teknowijoyo, K. Cho, M. A. Tanatar, J. Gonzales, A. E. Böhmer, O. Cavani, V. Mishra, 4 P. J. Hirschfeld, S. L. Bud’ko, P. C. Canfield, and R. Prozorov ∗ Ames Laboratory and Department of Physics & Astronomy, Iowa State University, Ames, IA 50011, USA Laboratoire des Solides Irradís, École Polytechnique, CNRS, CEA, Universit Paris-Saclay, 91128 Palaiseau Cedex, France Joint Institute of Computational Sciences, University of Tennessee, Knoxville, TN-37996, USA Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN-37831, USA Department of Physics, University of Florida, Gainesville, Florida 32611, USA (Dated: 13 May 2016)

Variation of transition temperatures and residual resistivity ratio in vapor-grown FeSe

The study of the iron-based superconductor FeSe has blossomed with the availability of high-quality single crystals, obtained through flux/vapor-transport growth techniques below the structural transformation temperature of its tetragonal phase,

X-Ray diffraction on large single crystals using a powder diffractometer

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Discovery of ferromagnetism with large magnetic anisotropy in ZrMnP and HfMnP

. Here, we report on the variation of sample morphology and properties due to small modifications in the growth conditions. A considerable variation of the superconducting transition temperature

Super-heavy electron material as metallic refrigerant for adiabatic demagnetization cooling

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