29 research outputs found
Evolution and control of the phase competition morphology in a manganite film
The competition among different phases in perovskite manganites is pronounced
since their energies are very close under the interplay of charge, spin,
orbital and lattice degrees of freedom. To reveal the roles of underlying
interactions, many efforts have been devoted towards directly imaging phase
transitions at microscopic scales. Here we show images of the charge-ordered
insulator (COI) phase transition from a pure ferromagnetic metal with reducing
field or increasing temperature in a strained phase-separated manganite film,
using a home-built magnetic force microscope. Compared with the COI melting
transition, this reverse transition is sharp, cooperative and martensitic-like
with astonishingly unique yet diverse morphologies. The COI domains show
variable-dimensional growth at different temperatures and their distribution
can illustrate the delicate balance of the underlying interactions in
manganites. Our findings also display how phase domain engineering is possible
and how the phase competition can be tuned in a controllable manner.Comment: Published versio
Atomic-scale coexistence of short-range magnetic order and superconductivity in FeSeTe
The ground state of the parent compounds of many high temperature
superconductors is an antiferromagnetically (AFM) ordered phase, where
superconductivity emerges when the AFM phase transition is suppressed by doping
or application of pressure. This behaviour implies a close relation between the
two orders. Understanding the interplay between them promises a better
understanding of how the superconducting condensate forms from the AFM ordered
background. Here we explore this relation in real space at the atomic scale
using low temperature spin-polarized scanning tunneling microscopy (SP-STM) and
spectroscopy. We investigate the transition from antiferromagnetically ordered
via the spin glass phase in
to superconducting
. In
we observe an
atomic-scale coexistence of superconductivity and short-ranged bicollinear
antiferromagnetic order.Comment: 7 pages, 6 figure
Imaging de Haas-van Alphen quantum oscillations and milli-Tesla pseudomagnetic fields
A unique attribute of atomically thin quantum materials is the in-situ
tunability of their electronic band structure by externally controllable
parameters like electrostatic doping, electric field, strain, electron
interactions, and displacement or twisting of atomic layers. This unparalleled
control of the electronic bands has led to the discovery of a plethora of
exotic emergent phenomena. But despite its key role, there is currently no
versatile method for mapping the local band structure in advanced 2D materials
devices in which the active layer is commonly embedded in various insulating
layers and metallic gates. Utilizing a scanning superconducting quantum
interference device, we image the de Haas-van Alphen quantum oscillations in a
model system, the Bernal-stacked trilayer graphene with dual gates, which
displays multiple highly-tunable bands. By resolving thermodynamic quantum
oscillations spanning over 100 Landau levels in low magnetic fields, we
reconstruct the band structure and its controllable evolution with the
displacement field with unprecedented precision and spatial resolution of 150
nm. Moreover, by developing Landau level interferometry, we reveal
shear-strain-induced pseudomagnetic fields and map their spatial dependence. In
contrast to artificially-induced large strain, which leads to pseudomagnetic
fields of hundreds of Tesla, we detect naturally occurring pseudomagnetic
fields as low as 1 mT corresponding to graphene twisting by just 1 millidegree
over one {\mu}m distance, two orders of magnitude lower than the typical angle
disorder in high-quality twisted bilayer graphene devices. This ability to
resolve the local band structure and strain on the nanoscale opens the door to
the characterization and utilization of tunable band engineering in practical
van der Waals devices.Comment: Nature (2023
Scanning SQUID-on-tip microscope in a top-loading cryogen-free dilution refrigerator
The scanning superconducting quantum interference device (SQUID) fabricated
on the tip of a sharp quartz pipette (SQUID-on-tip) has emerged as a versatile
tool for nanoscale imaging of magnetic, thermal, and transport properties of
microscopic devices of quantum materials. We present the design and performance
of a scanning SQUID-on-tip microscope in a top-loading probe of a cryogen-free
dilution refrigerator. The microscope is enclosed in a custom-made vacuum-tight
cell mounted at the bottom of the probe and is suspended by springs to suppress
vibrations caused by the pulse tube cryocooler. Two capillaries allow in-situ
control of helium exchange gas pressure in the cell that is required for
thermal imaging. A nanoscale heater is used to create local temperature
gradients in the sample, which enables quantitative characterization of the
relative vibrations between the tip and the sample. The spectrum of the
vibrations shows distinct resonant peaks with maximal power density of about 27
nm/Hz in the in-plane direction. The performance of the SQUID-on-tip
microscope is demonstrated by magnetic imaging of the MnBiTe magnetic
topological insulator, magnetization and current distribution imaging in a
SrRuO ferromagnetic oxide thin film, and by thermal imaging of dissipation
in graphene.Comment: Submitted to Review of Scientific Instrument
Atomic-scale coexistence of short-range magnetic order and superconductivity in Fe1+ySe0.1Te0.9
Funding: UK EPSRC (EP/I031014/1) (HZ, J-PR, and PW)The ground state of the parent compounds of many high-temperature superconductors is an antiferromagnetically ordered phase, where superconductivity emerges when the antiferromagnetic phase transition is suppressed by doping or application of pressure. This behavior implies a close relation between the two orders. Examining the interplay between them promises a better understanding of how the superconducting condensate forms from the antiferromagnetically ordered background. Here we explore this relation in real space at the atomic scale using low-temperature spin-polarized scanning tunneling microscopy and spectroscopy. We investigate the transition from antiferromagnetically ordered Fe1+yTe via the spin-glass phase in Fe1+ySe0.1Te0.9 to superconducting Fe1+ySe0.15Te0.85. In Fe1+ySe0.1Te0.9 we observe an atomic-scale coexistence of superconductivity and short-ranged bicollinear antiferromagnetic order. However, a direct correlation between the two orders is not observed, supporting the scenario of s± superconducting symmetry in this material. Our work demonstrates a direct probe of the relation between the two orders, which is indispensable for our understanding of high-temperature superconductivity.Publisher PDFPeer reviewe
Roald Dahl Centenary Cardiff Conference
This is a report on the Roald Dahl Centenary Cardiff Conference held in Cardiff, United Kingdom from 16th to 18th June 2016