42 research outputs found
Two step disordering of the vortex lattice across the peak effect in a weakly pinned Type II superconductor, Co0.0075NbSe2
The vortex lattice in a Type II superconductor provides a versatile model
system to investigate the order-disorder transition in a periodic medium in the
presence of random pinning. Here, using scanning tunnelling spectroscopy in a
weakly pinned Co0.0075NbSe2 single crystal, we show that at low temperatures,
the vortex lattice in a 3-dimensional superconductor disorders in two steps
across the peak effect. At the onset of the peak effect, the equilibrium Bragg
glass transforms into an orientational glass through the proliferation of
dislocations. At a higher field, the dislocations dissociate into isolated
disclination giving rise to an amorphous vortex glass. We also show the
existence of a variety of additional non-equilibrium metastable states, which
can be accessed through different thermomagnetic cycling.Comment: The analysis of the positional and orientational correlation
functions have been refined in this version of the manuscrip
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
Realization of Z Topological Metal in Single-Crystalline Nickel Deficient NiVSe
Temperature-dependent electronic and magnetic properties are reported for a
Z2 topological metal single-crystalline nickel-deficient NiVSe. It is
found to crystallize in the monoclinic Cr3S4 structure type with space group
I2=m. From single-crystal x-ray diffraction, we find that there are vacancies
on the Ni site, resulting in the composition Ni0:85V2Se4 in agreement with our
electron-probe microanalysis. The electrical resistivity shows metallic
behavior with a broad anomaly around 150{200 K that is also observed in the
heat capacity data. This anomaly indicates a change of state of the material
below 150 K. We believe that this anomaly could be due to spin fluctuations or
charge-density-wave (CDW) fluctuations, where the lack of long-range order is
caused by vacancies at the Ni site of Ni0:85V2Se4. Although we fail to observe
any structural distortion in this crystal down to 1.5 K, its electronic and
thermal properties are anomalous. The observation of non-linear temperature
dependence of resistivity as well as an enhanced value of the Sommerfeld
coefficient = 104.0(1) mJ/molK2 suggests strong electron-electron correlations
in this material. The first-principles calculations performed for
NiVSe, which are also applicable to Ni0:85V2Se4, classify this material
as a topological metal with Z2 = (1; 110) and coexisting electron and hole
pockets at the Fermi level. The phonon spectrum lacks any soft phonon mode,
consistent with the absence of periodic lattice distortion in the present
experiments.Comment: arXiv admin note: text overlap with arXiv:cond-mat/0610166 by other
author