98 research outputs found
Anomalous lattice contraction and emergent electronic phases in Bi-doped EuIrO
We study the pyrochlore series (EuBi)IrO for . We show that for small , the lattice undergoes an anomalous
contraction but the all-in/all-out and metal-to-insulator transitions remain
robust, and the resistivity approaches a dependence at low-T, suggesting
proximity to the Weyl semimetallic phase, as previously predicted
theoretically. At the boundary between EuIrO and BiIrO
a qualitatively different ground state emerges, which is characterized by its
unusual metallic behavior and absence of magnetic ordering at least down to
K.Comment: 5 Pages, 4 figure
Evidence for impurity-induced frustration in La2CuO4
Zero-field muon spin rotation and magnetization measurements were performed
in La2Cu{1-x}MxO4, for 0<x< 0.12, where Cu2+ is replaced either by M=Zn2+ or by
M=Mg2+ spinless impurity. It is shown that while the doping dependence of the
sublattice magnetization (M(x)) is nearly the same for both compounds, the
N\'eel temperature (T_N(x)) decreases unambiguously more rapidly in the
Zn-doped compound. This difference, not taken into account within a simple
dilution model, is associated with the frustration induced by the Zn2+ impurity
onto the Cu2+ antiferromagnetic lattice. In fact, from T_N(x) and M(x) the spin
stiffness is derived and found to be reduced by Zn doping more significantly
than expected within a dilution model. The effect of the structural
modifications induced by doping on the exchange coupling is also discussed.Comment: 4 pages, 4 figure
Cluster charge-density-wave glass in hydrogen-intercalated TiSe
The topotactic intercalation of transition-metal dichalcogenides with atomic
or molecular ions acts as an efficient knob to tune the electronic ground state
of the host compound. A representative material in this sense is
1-TiSe, where the electric-field-controlled intercalations of lithium
or hydrogen trigger superconductivity coexisting with the charge-density wave
phase. Here, we use the nuclear magnetic moments of the intercalants in
hydrogen-intercalated 1-TiSe as local probes for nuclear magnetic
resonance experiments. We argue that fluctuating mesoscopic-sized domains
nucleate already at temperatures higher than the bulk critical temperature to
the charge-density wave phase and display cluster-glass-like dynamics in the
MHz range tracked by the H nuclear moments. Additionally, we observe a
well-defined independent dynamical process at lower temperatures that we
associate with the intrinsic properties of the charge-density wave state. In
particular, we ascribe the low-temperature phenomenology to the collective
phason-like motion of the charge-density wave being hindered by structural
defects and chemical impurities and resulting in a localized oscillating
motion.Comment: 9 pages, 4 figure
Monopole-limited nucleation of magnetism in EuIrO
We present an in-depth analysis of muon-spin spectroscopy measurements of
EuIrO under the effect of the EuBi isovalent
and diamagnetic substitution as well as of external pressure. Our results
evidence an anomalously slow increase of the magnetic volume fraction upon
decreasing temperature only for stoichiometric EuIrO,
pointing towards highly unconventional properties of the magnetic phase
developing therein. We argue that magnetism in EuIrO develops
based on the nucleation of magnetic droplets at , whose successive
growth is limited by the need of a continuous generation of magnetic hedgehog
monopoles.Comment: 9 pages, 4 figure
Direct evidence for the emergence of a pressure induced nodal superconducting gap in the iron-based superconductor Ba_0.65Rb_0.35Fe_2As_2
Identifying the superconducting (SC) gap structure of the iron-based
high-temperature superconductors (Fe-HTS's) remains a key issue for the
understanding of superconductivity in these materials. In contrast to other
unconventional superconductors, in the Fe-HTS's both -wave and extended
s-wave pairing symmetries are close in energy, with the latter believed to be
generally favored over the former. Probing the proximity between these very
different SC states and identifying experimental parameters that can tune them,
are of central interest. Here we report high-pressure muon spin rotation
experiments on the temperature-dependent magnetic penetration depth (lambda) in
the optimally doped Fe-HTS Ba_0.65Rb_0.35Fe_2As_2. At ambient pressure this
material is known to be a nodeless s-wave superconductor. Upon pressure a
strong decrease of (lambda) is observed, while the SC transition temperature
remains nearly constant. More importantly, the low-temperature behavior of
(1/lambda^{2}) changes from exponential saturation at zero pressure to a
power-law with increasing pressure, providing unambiguous evidence that
hydrostatic pressure promotes nodal SC gaps. Comparison to microscopic models
favors a d-wave over a nodal s^{+-}-wave pairing as the origin of the nodes.
Our results provide a new route of understanding the complex topology of the SC
gap in Fe-HTS's.Comment: 33 pages and 12 figures (including supplementary information
Mutual independence of critical temperature and superfluid density under pressure in optimally electron-doped superconducting LaFeAsOF
The superconducting properties of LaFeAsOF in conditions of
optimal electron-doping are investigated upon the application of external
pressure up to kbar. Measurements of muon-spin spectroscopy and dc
magnetometry evidence a clear mutual independence between the critical
temperature and the low-temperature saturation value for the ratio
(superfluid density over effective band mass of Cooper pairs).
Remarkably, a dramatic increase of % is reported for at
the maximum pressure value while is substantially unaffected in the
whole accessed experimental window. We argue and demonstrate that the
explanation for the observed results must take the effect of non-magnetic
impurities on multi-band superconductivity into account. In particular, the
unique possibility to modify the ratio between intra-band and inter-bands
scattering rates by acting on structural parameters while keeping the amount of
chemical disorder constant is a striking result of our proposed model.Comment: 8 pages (Main text: 5 pages. Paper merged with supplemental
information), 5 figure
Magnetic properties of spin diluted iron pnictides from muSR and NMR in LaFe1-xRuxAsO
The effect of isoelectronic substitutions on the microscopic properties of
LaFe1-xRuxAsO, for 0< x< 0.8, has been investigated by means of muSR and 139La
NMR. It was found that Ru substitution causes a progressive reduction of the
N\`eel temperature (T_N) and of the magnetic order parameter without leading to
the onset of superconductivity. The temperature dependence of 139La nuclear
spin-lattice relaxation rate 1/T_1 can be suitably described within a two-band
model. One band giving rise to the spin density wave ground-state, while the
other one is characterized by weakly correlated electrons. Fe for Ru
substitution yields to a progressive decrease of the density of states at the
Fermi level close to the one derived from band structure calculations. The
reduction of T_N with doping follows the predictions of the J_1-J_2 model on a
square lattice, which appears to be an effective framework to describe the
magnetic properties of the spin density wave ground-state.Comment: 6 pages, 8 figure
Entanglement between Muon and I > 1/2 Nuclear Spins as a Probe of Charge Environment
We report on the first example of quantum coherence between the spins of muons and quadrupolar nuclei. We reveal that these entangled states are highly sensitive to a local charge environment and thus, can be deployed as a functional quantum sensor of that environment. The quantum coherence effect was observed in vanadium intermetallic compounds which adopt the A15 crystal structure, and whose members include all technologically pertinent superconductors. Furthermore, the extreme sensitivity of the entangled states to the local structural and electronic environments emerges through the quadrupolar interaction with the electric field gradient due to the charge distribution at the nuclear (I >1/2) sites. This case study demonstrates that positive muons can be used as a quantum sensing tool to also probe structural and charge-related phenomena in materials, even in the absence of magnetic degrees of freedom
Effect of external pressure on the magnetic properties of LnFeAsO (Ln = La, Ce, Pr, Sm)
We investigate the effect of external pressure on magnetic order in undoped
LnFeAsO (Ln = La, Ce, Pr, La) by using muon-spin relaxation measurements and
ab-initio calculations. Both magnetic transition temperature and Fe
magnetic moment decrease with external pressure. The effect is observed to be
lanthanide dependent with the strongest response for Ln = La and the weakest
for Ln = Sm. The trend is qualitatively in agreement with our DFT calculations.
The same calculations allow us to assign a value of 0.68(2) to the Fe
moment, obtained from an accurate determination of the muon sites. Our data
further show that the magnetic lanthanide order transitions do not follow the
simple trend of Fe, possibly as a consequence of the different -electron
overlap.Comment: 16 pages, 11 figure
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