142 research outputs found
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
Tuning the magnetic and structural phase transitions of PrFeAsO via Fe/Ru spin dilution
Neutron diffraction and muon spin relaxation measurements are used to obtain
a detailed phase diagram of Pr(Fe,Ru)AsO. The isoelectronic substitution of Ru
for Fe acts effectively as spin dilution, suppressing both the structural and
magnetic phase transitions. The temperature of the tetragonal-orthorhombic
structural phase transition decreases gradually as a function of x. Slightly
below the transition temperature coherent precessions of the muon spin are
observed corresponding to static magnetism, possibly reflecting a significant
magneto-elastic coupling in the FeAs layers. Short range order in both the Fe
and Pr moments persists for higher levels of x. The static magnetic moments
disappear at a concentration coincident with that expected for percolation of
the J1-J2 square lattice model
PULSEE: A software for the quantum simulation of an extensive set of magnetic resonance observables
We present an open-source software for the simulation of observables in
magnetic resonance experiments, including nuclear magnetic/quadrupole resonance
NMR/NQR and electron spin resonance (ESR), developed to assist experimental
research in the design of new strategies for the investigation of fundamental
quantum properties of materials, as inspired by magnetic resonance protocols
that emerged in the context of quantum information science (QIS). The package
introduced here enables the simulation of both standard NMR spectroscopic
observables and the time-evolution of an interacting single-spin system subject
to complex pulse sequences, i.e. quantum gates. The main purpose of this
software is to facilitate in the development of much needed novel NMR-based
probes of emergent quantum orders, which can be elusive to standard
experimental probes. The software is based on a quantum mechanical description
of nuclear spin dynamics in NMR/NQR experiments and has been widely tested on
available theoretical and experimental results. Moreover, the structure of the
software allows for basic experiments to easily be generalized to more
sophisticated ones, as it includes all the libraries required for the numerical
simulation of generic spin systems. In order to make the program easily
accessible to a large user base, we developed a user-friendly graphical
interface, Jupyter notebooks, and fully-detailed documentation. Lastly, we
portray several examples of the execution of the code that illustrate the
potential of a novel NMR paradigm, inspired by QIS, for efficient investigation
of emergent phases in strongly correlated materials.Comment: 51 page
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
Strain-tuning of nematicity and superconductivity in single crystals of FeSe
Strain is a powerful experimental tool to explore new electronic states and
understand unconventional superconductivity. Here, we investigate the effect of
uniaxial strain on the nematic and superconducting phase of single crystal FeSe
using magnetotransport measurements. We find that the resistivity response to
the strain is strongly temperature dependent and it correlates with the sign
change in the Hall coefficient being driven by scattering, coupling with the
lattice and multiband phenomena. Band structure calculations suggest that under
strain the electron pockets develop a large in-plane anisotropy as compared
with the hole pocket. Magnetotransport studies at low temperatures indicate
that the mobility of the dominant carriers increases with tensile strain. Close
to the critical temperature, all resistivity curves at constant strain cross in
a single point, indicating a universal critical exponent linked to a
strain-induced phase transition. Our results indicate that the superconducting
state is enhanced under compressive strain and suppressed under tensile strain,
in agreement with the trends observed in FeSe thin films and overdoped
pnictides, whereas the nematic phase seems to be affected in the opposite way
by the uniaxial strain. By comparing the enhanced superconductivity under
strain of different systems, our results suggest that strain on its own cannot
account for the enhanced high superconductivity of FeSe systems.Comment: 11 pages, 8 figure
Anomalous local lattice disorder and distortion in A2Mo2O7 pyrochlores
We present an extended X-ray absorption fine structure study of the pyrochlores A2Mo2O7 (A Œ Gd, Dy,
Ho, Er), as a function of temperature. While in the three spin-glass compositions Dy2Mo2O7, Ho2Mo2O7
and Er2Mo2O7 the Debye temperatures are in accordance with other pyrochlores and the static disorder
contributions are compatible with a lattice frustration, in the low-temperature-ferromagnetic Gd2Mo2O7
system we point out an anomalous enhancement of the local structure disorder below about 225 K down
to low temperatures. Moreover, considering the general pyrochlore predisposition towards structural
disorder, we prove the presence on a local scale of at least a bimodal distribution of the Mo-O(1)
octahedral interatomic distances for all the studied compounds, consisting of two shorter and four
longer bond lengths.
Our results suggest that the local structure order parameter plays an important role in the ferromagnetic or spin-glass phase stabilization.We gratefully acknowledge the Spanish CRG at the ESRF for
providing beamtime under experiment HC-2414. F.R.-M. is also
indebted to MINECO for a âRamon y Cajalâ contract (ref: RyC-2015-
18626), which is co-financed by the European Social Fund 2014-20.
G.L. thanks M. Lucaccini and G. Tavilla for their valuable technical
support and C. Robustelli for the supply of cryogenic liquids during
the magnetization measurements
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
Effects of charge doping on Mott insulator with strong spin-orbit coupling, Ba2Na1âxCaxOsO6
The effects of doping on the electronic evolution of the Mott insulating state have been extensively studied in efforts to understand mechanisms of emergent quantum phases of materials. The study of these effects becomes ever more intriguing in the presence of entanglement between spin and orbital degrees of freedom. Here, we present a comprehensive investigation of charge doping in the double perovskite Ba2NaOsO6, a complex Mott insulator where such entanglement plays an important role. We establish that the insulating magnetic ground state evolves from canted antiferromagnet (cAFM) [Lu et al., Nat. Commun. 8, 14407 (2017)] to Neel order for dopant levels exceeding approximate to 10%. Furthermore, we determine that a broken local point symmetry (BLPS) phase, precursor to the magnetically ordered state, occupies an extended portion of the (H-T) phase diagram with increased doping. This finding reveals that the breaking of the local cubic symmetry is driven by a multipolar order, most likely of the antiferro-quadrupolar type [Khaliullin et al., Phys. Rev. Res. 3, 033163 (2021); Churchill and Kee, Phys. Rev. B 105, 014438 (2022)]. Future dynamical measurements will be instrumental in determination of the precise nature of the identified multipolar order
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
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