6 research outputs found
Direct imaging of spatial heterogeneities in type II superconductors
Understanding the exotic properties of quantum materials, including
high-temperature superconductors, remains a formidable challenge that demands
direct insights into electronic conductivity. Current methodologies either
capture a bulk average or near-atomically-resolved information, missing direct
measurements at the critical intermediate length scales. Here, using the
superconductor Fe(Se,Te) as a model system, we use low-temperature conductive
atomic force microscopy (cAFM) to bridge this gap. Contrary to the uniform
superconductivity anticipated from bulk assessments, cAFM uncovers micron-scale
conductive intrusions within a relatively insulating matrix. Subsequent
compositional mapping through atom probe tomography, shows that differences in
conductivity correlated with local changes in composition. cAFM, supported by
advanced microscopy and microanalysis, represents a methodological breakthrough
that can be used to navigate the intricate landscape of high-temperature
superconductors and the broader realm of quantum materials. Such fundamental
information is critical for theoretical understanding and future guided design
Insulating improper ferroelectric domain walls as robust barrier layer capacitors
We report the dielectric properties of improper ferroelectric h-ErMnO.
From the bulk characterisation we observe a temperature and frequency range
with two distinct relaxation-like features, leading to high and even 'colossal'
values for the dielectric permittivity. One feature trivially originates from
the formation of a Schottky barrier at the electrode-sample interface, whereas
the second one relates to an internal barrier layer capacitance (BLC). The
calculated volume fraction of the internal BLC (of 8 %) is in good agreement
with the observed volume fraction of insulating domain walls (DWs). While it is
established that insulating DWs can give rise to high dielectric constants,
studies typically focused on proper ferroelectrics where electric fields can
remove the DWs. In h-ErMnO, by contrast, the insulating DWs are
topologically protected, facilitating operation under substantially higher
electric fields. Our findings provide the basis for a conceptually new approach
to engineer materials exhibiting colossal dielectric permittivities using
domain walls in improper ferroelecctrics with potential applications in
electroceramic capacitors.Comment: 7 pages, 4 figure
Charged ferroelectric domain walls for deterministic ac signal control at the nanoscale
[Image: see text] The direct current (dc) conductivity and emergent functionalities at ferroelectric domain walls are closely linked to the local polarization charges. Depending on the charge state, the walls can exhibit unusual dc conduction ranging from insulating to metallic-like, which is leveraged in domain-wall-based memory, multilevel data storage, and synaptic devices. In contrast to the functional dc behaviors at charged walls, their response to alternating currents (ac) remains to be resolved. Here, we reveal ac characteristics at positively and negatively charged walls in ErMnO(3), distinctly different from the response of the surrounding domains. By combining voltage-dependent spectroscopic measurements on macroscopic and local scales, we demonstrate a pronounced nonlinear response at the electrode-wall junction, which correlates with the domain-wall charge state. The dependence on the ac drive voltage enables reversible switching between uni- and bipolar output signals, providing conceptually new opportunities for the application of charged walls as functional nanoelements in ac circuitry
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Charged Ferroelectric Domain Walls for Deterministic ac Signal Control at the Nanoscale.
The direct current (dc) conductivity and emergent functionalities at ferroelectric domain walls are closely linked to the local polarization charges. Depending on the charge state, the walls can exhibit unusual dc conduction ranging from insulating to metallic-like, which is leveraged in domain-wall-based memory, multilevel data storage, and synaptic devices. In contrast to the functional dc behaviors at charged walls, their response to alternating currents (ac) remains to be resolved. Here, we reveal ac characteristics at positively and negatively charged walls in ErMnO3, distinctly different from the response of the surrounding domains. By combining voltage-dependent spectroscopic measurements on macroscopic and local scales, we demonstrate a pronounced nonlinear response at the electrode-wall junction, which correlates with the domain-wall charge state. The dependence on the ac drive voltage enables reversible switching between uni- and bipolar output signals, providing conceptually new opportunities for the application of charged walls as functional nanoelements in ac circuitry
Insulating improper ferroelectric domain walls as robust barrier layer capacitors
We report the dielectric properties of improper ferroelectric hexagonal (h-)ErMnO3. From the bulk characterization, we observe a temperature and frequency range with two distinct relaxation-like features, leading to high and even “colossal” values for the dielectric permittivity. One feature trivially originates from the formation of a Schottky barrier at the electrode–sample interface, whereas the second one relates to an internal barrier layer capacitance (BLC). The calculated volume fraction of the internal BLC (of 8%) is in good agreement with the observed volume fraction of insulating domain walls (DWs). While it is established that insulating DWs can give rise to high dielectric constants, studies typically focused on proper ferroelectrics where electric fields can remove the DWs. In h-ErMnO3, by contrast, the insulating DWs are topologically protected, facilitating operation under substantially higher electric fields. Our findings provide the basis for a conceptually new approach to engineer materials exhibiting colossal dielectric permittivities using domain walls in improper ferroelectrics