24 research outputs found
Microscopic study of the impurity effect in the kagome superconductor La(RuFe)Si
We report on the effect of magnetic impurities on the microscopic
superconducting (SC) properties of the kagome-lattice superconductor
La(RuFe)Si using muon spin relaxation/rotation
(SR). A strong suppression of the superconducting critical temperature
, the SC volume fraction, and the superfluid density was observed.
We furthermore find a correlation between the superfluid density and which is considered a hallmark feature of unconventional superconductivity.
Most remarkably, measurements of the temperature-dependent magnetic penetration
depth reveal a change in the low-temperature behavior from
exponential saturation to a linear increase, which indicates that Fe doping
introduces nodes in the superconducting gap structure at concentrations as low
as ~0.015. Our results point to a rare example of unconventional
superconductivity in the correlated kagome lattice and accessible tunability of
the superconducting gap structure, offering new insights into the microscopic
mechanisms involved in superconducting order.Comment: 7 page article with 4 figure
Designing the stripe-ordered cuprate phase diagram through uniaxial-stress
The ability to efficiently control charge and spin in the cuprate
high-temperature superconductors is crucial for fundamental research and
underpins technological development. Here, we explore the tunability of
magnetism, superconductivity and crystal structure in the stripe phase of the
cuprate La_2-xBa_xCuO_4, with x = 0.115 and 0.135, by employing
temperature-dependent (down to 400 mK) muon-spin rotation and AC
susceptibility, as well as X-ray scattering experiments under compressive
uniaxial stress in the CuO_2 plane. A sixfold increase of the 3-dimensional
(3D) superconducting critical temperature T_c and a full recovery of the 3D
phase coherence is observed in both samples with the application of extremely
low uniaxial stress of 0.1 GPa. This finding demonstrates the removal of the
well-known 1/8-anomaly of cuprates by uniaxial stress. On the other hand, the
spin-stripe order temperature as well as the magnetic fraction at 400 mK show
only a modest decrease under stress. Moreover, the onset temperatures of 3D
superconductivity and spin-stripe order are very similar in the large stress
regime. However, a substantial decrease of the magnetic volume fraction and a
full suppression of the low-temperature tetragonal structure is found at
elevated temperatures, which is a necessary condition for the development of
the 3D superconducting phase with optimal T_c. Our results evidence a
remarkable cooperation between the long-range static spin-stripe order and the
underlying crystalline order with the three-dimensional fully coherent
superconductivity. Overall, these results suggest that the stripe- and the SC
order may have a common physical mechanism.Comment: 11 pages, 5 figures. This work builds on our earlier findings on
LBCO, arXiv:2008.01159, and substantially expands i
Hidden magnetism uncovered in charge ordered bilayer kagome material ScV_6Sn_6
Charge ordered kagome lattices have been demonstrated to be intriguing
platforms for studying the intertwining of topology, correlation, and
magnetism. The recently discovered charge ordered kagome material ScV_6Sn_6
does not feature a magnetic groundstate or excitations, thus it is often
regarded as a conventional paramagnet. Here, using advanced muon-spin rotation
spectroscopy, we uncover an unexpected hidden magnetism of the charge order. We
observe a striking enhancement of the internal field width sensed by the muon
ensemble, which takes place within the charge ordered state. More remarkably,
the muon spin relaxation rate below the charge ordering temperature is
substantially enhanced by applying an external magnetic field. Taken together
with the hidden magnetism found in AV_3Sb_5 (A = K, Rb, Cs) and FeGe kagome
systems, our results suggest ubiqitous time-reversal symmetry-breaking in
charge ordered kagome lattices.Comment: 9 pages, 4 figure
Low-temperature magnetic crossover in the topological kagome magnet TbMn6Sn6
Magnetic topological phases of quantum matter are an emerging frontier in physics and materials science, of which kagome magnets appear as a highly promising platform. Here, we explore magnetic correlations in the recently identified topological kagome system TbMnSnusing muon spin rotation, combined with local field analysis and neutron diffraction. Our studies identify an out-of-plane ferrimagnetic structure with slow magnetic fluctuations which exhibit a critical slowing down below ≃ 120 K and finally freeze into static patches with ideal out-of-plane order belowT ≃ 20 K. We further show that hydrostatic pressure of 2.1 GPa stabilises the static out-of-plane topological ferrimagnetic ground state in the whole volume of the sample. Therefore the exciting perspective arises of a magnetically-induced topological system whose magnetism can be controlled through external parameters. The present results will stimulate theoretical investigations to obtain a microscopic understanding of the relation between the low-temperature volume-wise magnetic evolution of the staticc-axis ferrimagnetic patches and the topological electronic properties in TbMnSn
Charge order above room-temperature in a prototypical kagome superconductor La(RuFe)Si
The kagome lattice is an intriguing and rich platform for discovering, tuning
and understanding the diverse phases of quantum matter, which is a necessary
premise for utilizing quantum materials in all areas of modern and future
electronics in a controlled and optimal way. The system LaRuSi was
shown to exhibit typical kagome band structure features near the Fermi energy
formed by the Ru- orbitals and the highest superconducting transition
temperature 7K among the kagome-lattice materials.
However, the effect of electronic correlations on the normal state properties
remains elusive. Here, we report the discovery of charge order in
La(RuFe)Si ( = 0, 0.01, 0.05) beyond
room-temperature. Namely, single crystal X-ray diffraction reveals charge order
with a propagation vector of (,0,0) below
400K in all three compounds. At lower temperatures, we see the
appearance of a second set of charge order peaks with a propagation vector of
(,0,0). The introduction of Fe, which is known to quickly suppress
superconductivity, does not drastically alter the onset temperature for charge
order. Instead, it broadens the scattered intensity such that diffuse
scattering appears at the same onset temperature, however does not coalesce
into sharp Bragg diffraction peaks until much lower in temperature. Our results
present the first example of a charge ordered state at or above room
temperature in the correlated kagome lattice with bulk superconductivity.Comment: 15 pages, 8 figure
Cognitive impairment and World Trade Centre-related exposures
On 11 September 2001 the World Trade Center (WTC) in New York was attacked by terrorists, causing the collapse of multiple buildings including the iconic 110-story ‘Twin Towers’. Thousands of people died that day from the collapse of the buildings, fires, falling from the buildings, falling debris, or other related accidents. Survivors of the attacks, those who worked in search and rescue during and after the buildings collapsed, and those working in recovery and clean-up operations were exposed to severe psychological stressors. Concurrently, these ‘WTC-affected’ individuals breathed and ingested a mixture of organic and particulate neurotoxins and pro-inflammogens generated as a result of the attack and building collapse. Twenty years later, researchers have documented neurocognitive and motor dysfunctions that resemble the typical features of neurodegenerative disease in some WTC responders at midlife. Cortical atrophy, which usually manifests later in life, has also been observed in this population. Evidence indicates that neurocognitive symptoms and corresponding brain atrophy are associated with both physical exposures at the WTC and chronic post-traumatic stress disorder, including regularly re-experiencing traumatic memories of the events while awake or during sleep. Despite these findings, little is understood about the long-term effects of these physical and mental exposures on the brain health of WTC-affected individuals, and the potential for neurocognitive disorders. Here, we review the existing evidence concerning neurological outcomes in WTC-affected individuals, with the aim of contextualizing this research for policymakers, researchers and clinicians and educating WTC-affected individuals and their friends and families. We conclude by providing a rationale and recommendations for monitoring the neurological health of WTC-affected individuals