216 research outputs found
Real-space Observation of Unidirectional Charge Density Wave and Complex Structural Modulation in the Pnictide Superconductor BaSrNiAs
Here we use low-temperature and variable-temperature scanning tunneling
microscopy to study the pnictide superconductor, BaSrNiAs.
In the low-temperature phase (triclinic phase) of BaNiAs, we observe
the unidirectional charge density wave (CDW) with = 1/3 on both the Ba and
NiAs surfaces. On the NiAs surface of the triclinic BaNiAs, there are
structural-modulation-induced chain-like superstructures with distinct
periodicities. In the high-temperature phase (tetragonal phase) of
BaNiAs, the NiAs surface appears as the periodic 1 by 2 superstructure.
Interestingly, in the triclinic phase of BaSrNiAs, the
unidirectional CDW is suppressed on both the Ba/Sr and NiAs surfaces, and the
Sr substitution stabilizes the periodic 1 by 2 superstructure on the NiAs
surface, which enhance the superconductivity in
BaSrNiAs. Our results provide important microscopic
insights for the interplay among the unidirectional CDW, structural modulation,
and superconductivity in this class of pnictide superconductors.Comment: 15 pages, 4 figure
Non-locally sensing the magnetic states of nanoscale antiferromagnets with an atomic spin sensor
The ability to sense the magnetic state of individual magnetic nano-objects
is a key capability for powerful applications ranging from readout of
ultra-dense magnetic memory to the measurement of spins in complex structures
with nanometer precision. Magnetic nano-objects require extremely sensitive
sensors and detection methods. Here we create an atomic spin sensor consisting
of three Fe atoms and show that it can detect nanoscale antiferromagnets
through minute surface-mediated magnetic interaction. Coupling, even to an
object with no net spin and having vanishing dipolar stray field, modifies the
transition matrix element between two spin states of the Fe-atom-based spin
sensor that changes the sensor's spin relaxation time. The sensor can detect
nanoscale antiferromagnets at up to three nanometers distance and achieves an
energy resolution of 10 micro-electronvolts surpassing the thermal limit of
conventional scanning probe spectroscopy. This scheme permits simultaneous
sensing of multiple antiferromagnets with a single spin sensor integrated onto
the surface.Comment: 30 pages main text, 6 figures, Supplementary materials not inculde
Probing hidden Mott gap and incommensurate charge modulation on the polar surfaces of PdCrO
Here we report a combined study of low-temperature scanning tunneling
microscopy (STM) and dynamical mean-field theory (DMFT) on PdCrO, a
delafossite metal with an antiferromagnetic order below ~37.5 K. First, on the
CrO-terminated polar surface we detect a gap-like feature both below and
above the N\'eel temperature. The DMFT calculations indicate that this gap is
opened due to the strong correlations of Cr-3d electrons, suggesting the hidden
Mott nature of the gap. Then, we observe two kinds of Pd-terminated polar
surfaces. One is a well-ordered Pd surface with the
Fermi-surface-nesting-induced incommensurate charge modulation, while the other
one is a reconstructed Pd surface with the individual nano-scale non-periodic
domain structures. On the well-ordered Pd surface, the interference between the
incommensurate charge modulation and the atomic lattice forms the periodic
moir\'e pattern. Our results provide important microscopic information for
fully understanding the correlated electronic properties of this class of
materials.Comment: 11 pages, 4 figure
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