302 research outputs found
Superconductivity in Weyl semimetal NbP: Bulk vs. surface
Transition metal monopnictides belong to the new class of semimetals where the bulk properties are determined by the presence of pairs of nodes with different chirality formed by linear dispersive states in the k-space. Beside the anomaly in the bulk magnetotransport superconductivity is frequently found in some Weyl semimetals. We found signatures of superconductivity in ac and dc magnetization measurements of highly pure and stoichiometric NbP powder. We determined the lower and upper critical field and the Ginzburg-Landau parameter. The relative small superconducting volume fraction is related to either effect of finite grain size and/or surface superconductivity. The last mentioned may originate from either off stoichiometric (Nb-rich) surface layers or a strained surface with different electronic properties. Furthermore the intrinsic normal state susceptibility is determined taking into account a paramagnetic contribution of a few ppm of magnetic impurities
Nuclear spin-lattice relaxation time in TaP and the Knight shift of Weyl semimetals
We first analyze the recent experimental data on the nuclear spin-lattice
relaxation rate of the Weyl semimetal TaP. We argue that its non-monotonic
temperature dependence is explained by the temperature dependent chemical
potential of Weyl fermions. We also develop the theory of the Knight shift in
Weyl semimetals, which contains two counteracting terms. The diamagnetic term
follows with , and being the high
energy cutoff, chemical potential and temperature, respectively, and is always
negative. The paramagnetic term scales with and changes sign depending on
the doping level. Altogether, the Knight shift is predicted to vanish or even
change sign upon changing the doping or the temperature, making it a sensitive
tool to identify Weyl points. We also calculate the Korringa relation for Weyl
semimetals which shows an unusual energy dependence rather than being constant
as expected for a non-interacting Fermi system.Comment: 9 pages, 3 figure
Quantum phase transition in the dioptase magnetic lattice
The study of quantum phase transitions, which are zero-temperature phase
transitions between distinct states of matter, is of current interest in
research since it allows for a description of low-temperature properties based
on universal relations. Here we show that the crystal green dioptase
Cu_6Si_6O_18 . 6H_2O, known to the ancient Roman as the gem of Venus, has a
magnetic crystal structure, formed by the Cu(II) ions, which allows for a
quantum phase transition between an antiferromagnetically ordered state and a
quantum spin liquid.Comment: 6 pages, 5 figures, EPL, in pres
121,123Sb NQR as a microscopic probe in Te doped correlated semimetal FeSb2 : emergence of electronic Griffith phase, magnetism and metallic behavior %
nuclear quadrupole resonance (NQR) was applied to
in the low doping regime (\emph{x = 0, 0.01} and
\emph{0.05}) as a microscopic zero field probe to study the evolution of
\emph{3d} magnetism and the emergence of metallic behavior. Whereas the NQR
spectra itself reflects the degree of local disorder via the width of the
individual NQR lines, the spin lattice relaxation rate (SLRR) probes
the fluctuations at the - site. The fluctuations originate either from
conduction electrons or from magnetic moments. In contrast to the semi metal
with a clear signature of the charge and spin gap formation in
, the 1\% doped system exhibits
almost metallic conductivity and a almost filled gap. A weak divergence of the
SLRR coefficient points towards the
presence of electronic correlations towards low temperatures wheras the
\textit{5\%} doped sample exhibits a much larger divergence in the SLRR
coefficient showing . According to the specific heat
divergence a power law with is expected for the SLRR.
Furthermore -doped as a disordered paramagnetic metal might be a
platform for the electronic Griffith phase scenario. NQR evidences a
substantial asymmetric broadening of the NQR spectrum for the
\emph{5\%} sample. This has purely electronic origin in agreement with the
electronic Griffith phase and stems probably from an enhanced - bond
polarization and electronic density shift towards the atom inside
- dumbbell
Complex Chiral Modulations in FeGe close to Magnetic Ordering
We report on detailed polarized small-angle neutron scattering on cubic FeGe
in magnetic fields applied either along (transverse) the scattering vector or
parallel (longitudinal)to the neutron beam. The () phase diagrams for all
principal axes contain a segmented -phase region just below the onset of
magnetic order. Hexagonal Bragg-spot patterns were observed across the entire
-phase region for the longitudinal geometry. Scattering intensity was
observed in parts of the A phase for both scattering configurations. Only in a
distinct pocket () vanishing scattering intensity was found in the
transverse geometry.Comment: This paper has been withdrawn by the author due to misunderstanding
with some of the co-author
Field tuned critical fluctuations in YFe2Al10: Evidence from magnetization, 27Al (NMR, NQR) investigations
We report magnetization, specific heat, and NMR investigations on YFe2Al10
over a wide range in temperature and magnetic field and zero field (NQR)
measurements. Magnetic susceptibility, specific heat and spin-lattice
relaxation rate divided by T (1/T1T) follow a weak power law (T^-0.4)
temperature dependence, which is a signature of critical fluctuations of Fe
moments. The value of the Sommerfeld-Wilson ratio and linear relation between
1/T1T and chi(T) suggest the existence of ferromagnetic correlations in this
system. No magnetic ordering down to 50 mK in Cp(T) and the unusual temperature
and field scaling of the bulk and NMR data are associated with a magnetic
instability which drives the system to quantum criticality. The magnetic
properties of the system are tuned by field wherein ferromagnetic fluctuations
are suppressed and a crossover from quantum critical to FL behavior is observed
with increasing magnetic field
Magnetism and superconductivity in Eu0.2Sr0.8(Fe0.86Co0.14)2As2 probed by 75As NMR
We report bulk superconductivity (SC) in
EuSr(FeCo)As single crystals by
means of electrical resistivity, magnetic susceptibility, and specific heat
measurements with 20 K with an antiferromagnetic
(AFM) ordering of Eu moments at 2.0 K in
zero field. As NMR experiments have been performed in the two external
field directions (H) and (H). As-NMR spectra are analyzed in
terms of first order quadrupolar interaction. Spin-lattice relaxation rates
(1/) follow a law in the temperature range 4.2-15 K. There is no
signature of Hebel-Slichter coherence peak just below the SC transition
indicating a non s-wave or s type of superconductivity. The increase of
1/ with lowering the temperature in the range 160-18 K following
law reflecting 2D AFM spin fluctuations
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