86 research outputs found
On the origin of the anomalous behaviour of 2+ excitation energies in the neutron-rich Cd isotopes
Recent experimental results obtained using decay and isomer
spectroscopy indicate an unusual behaviour of the energies of the first excited
2 states in neutron-rich Cd isotopes approaching the N=82 shell closure.
To explain the unexpected trend, changes of the nuclear structure far-off
stability have been suggested, namely a quenching of the N=82 shell gap already
in Cd, only two proton holes away from doubly magic Sn. We
study the behaviour of the 2 energies in the Cd isotopes from N=50 to N=82,
i.e. across the entire span of a major neutron shell using modern beyond mean
field techniques and the Gogny force. We demonstrate that the observed low
2 excitation energy in Cd close to the N=82 shell closure is a
consequence of the doubly magic character of this nucleus for oblate
deformation favoring thereby prolate configurations rather than spherical ones.Comment: 10 pages, 4 figures, to be publised in Phys. Lett.
Incommensurate charge-stripe correlations in the kagome superconductor CsVSbSn
We track the evolution of charge correlations in the kagome superconductor
CsVSb as its parent, long-ranged charge density order is destabilized.
Upon hole-doping doping, interlayer charge correlations rapidly become
short-ranged and their periodicity is reduced by half along the interlayer
direction. Beyond the peak of the first superconducting dome, the parent charge
density wave state vanishes and incommensurate, quasi-1D charge correlations
are stabilized in its place. These competing, unidirectional charge
correlations demonstrate an inherent electronic rotational symmetry breaking in
CsVSb, independent of the parent charge density wave state and reveal a
complex landscape of charge correlations across the electronic phase diagram of
this class of kagome superconductors. Our data suggest an inherent 2
charge instability and the phenomenology of competing charge instabilities is
reminiscent of what has been noted across several classes of unconventional
superconductors.Comment: 6 pages, 4 figure
Fermi surface mapping and the nature of charge density wave order in the kagome superconductor CsVSb
The recently discovered family of AVSb (A: K, Rb Cs) kagome metals
possess a unique combination of nontrivial band topology, superconducting
ground states, and signatures of electron correlations manifest via competing
charge density wave order. Little is understood regarding the nature of the
charge density wave (CDW) instability inherent to these compounds and the
potential correlation with the accompanying onset of a large anomalous Hall
response. To understand the impact of the CDW order on the electronic structure
in these systems, we present quantum oscillation measurements on single
crystals of CsVSb. Our data provides direct evidence that the CDW
invokes a substantial reconstruction of the Fermi surface pockets associated
with the vanadium orbitals and the kagome lattice framework. In conjunction
with density functional theory modeling, we are able to identify split
oscillation frequencies originating from reconstructed pockets built from
vanadium orbitals and Dirac-like bands. Complementary diffraction measurements
are further able to demonstrate that the CDW instability has a correlated
phasing between neighboring VSb planes. These results provide critical
insights into the underlying CDW instability in AVSb kagome metals and
support minimal models of CDW order arising from within the vanadium-based
kagome lattice.Comment: 12 pages, 9 figure
Frustrated charge order and cooperative distortions in ScV6Sn6
Here we study the stability of charge order in the kagome metal ScV6Sn6.
Synchrotron x-ray diffraction measurements reveal high-temperature, short-range
charge correlations at the wave vectors along q=(1/3,1/3,1/2) whose inter-layer
correlation lengths diverge upon cooling. At the charge order transition, this
divergence is interrupted and long-range order freezes in along
q=(1/3,1/3,1/3), as previously reported, while disorder enables the charge
correlations to persist at the q=(1/3,1/3,1/2) wave vector down to the lowest
temperatures measured. Both short-range and long-range charge correlations
seemingly arise from the same instability and both are rapidly quenched upon
the introduction of larger Y ions onto the Sc sites. Our results validate the
theoretical prediction of the primary lattice instability at q=(1/3,1/3,1/2),
and we present a heuristic picture for viewing the frustration of charge order
in this compound
YbVSb and EuVSb, vanadium-based kagome metals with Yb and Eu zig-zag chains
Here we present YbVSb and EuVSb, two new compounds exhibiting
slightly distorted vanadium-based kagome nets interleaved with zig-zag chains
of divalent Yb and Eu ions. Single crystal growth methods are
reported alongside magnetic, electronic, and thermodynamic measurements.
YbVSb is a nonmagnetic metal with no collective phase transitions
observed between 60mK and 300K. Conversely, EuVSb is a magnetic kagome
metal exhibiting easy-plane ferromagnetic-like order below =32K
with signatures of noncollinearity under low field. Our discovery of
YbVSb and EuVSb demonstrate another direction for the discovery
and development of vanadium-based kagome metals while incorporating the
chemical and magnetic degrees of freedom offered by a rare-earth sublattice
Discovery of unconventional chiral charge order in kagome superconductor KV3Sb5
Intertwining quantum order and nontrivial topology is at the frontier of
condensed matter physics. A charge density wave (CDW) like order with orbital
currents has been proposed as a powerful resource for achieving the quantum
anomalous Hall effect in topological materials and for the hidden phase in
cuprate high-temperature superconductors. However, the experimental realization
of such an order is challenging. Here we use high-resolution scanning
tunnelling microscopy (STM) to discover an unconventional charge order in a
kagome material KV3Sb5, with both a topological band structure and a
superconducting ground state. Through both topography and spectroscopic
imaging, we observe a robust 2x2 superlattice. Spectroscopically, an energy gap
opens at the Fermi level, across which the 2x2 charge modulation exhibits an
intensity reversal in real-space, signaling charge ordering. At
impurity-pinning free region, the strength of intrinsic charge modulations
further exhibits chiral anisotropy with unusual magnetic field response.
Theoretical analysis of our experiments suggests a tantalizing unconventional
chiral CDW in the frustrated kagome lattice, which can not only lead to large
anomalous Hall effect with orbital magnetism, but also be a precursor of
unconventional superconductivity.Comment: Orbital magnetism calculation adde
Irsch, Nikolaus: Die Trierer Abteikirche St. Matthias und die Trierisch-Lothringische Bautengruppe
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