61 research outputs found
Criticality of tuning in athermal phase transitions
We experimentally address the importance of tuning in athermal phase
transitions, which are triggered only by a slowly varying external field acting
as tuning parameter. Using higher order statistics of fluctuations, a singular
critical instability is detected for the first time in spite of an apparent
universal self-similar kinetics over a broad range of driving force. The
results as well as the experimental technique are likely to be of significance
to many slowly driven non-equilibrium systems from geophysics to material
science which display avalanche dynamics.Comment: 5 pages, 4 figure
Evidence for defect-mediated tunneling in hexagonal boron nitride-based junctions
We investigate tunneling in metal-insulator-metal junctions employing few
atomic layers of hexagonal boron nitride (hBN) as the insulating barrier. While
the low-bias tunnel resistance increases nearly exponentially with barrier
thickness, subtle features are seen in the current-voltage curves, indicating
marked influence of the intrinsic defects present in the hBN insulator on the
tunneling transport. In particular, single electron charging events are
observed, which are more evident in thicker-barrier devices where direct
tunneling is substantially low. Furthermore, we find that annealing the devices
modifies the defect states and hence the tunneling signatures.Comment: 5 pages, 5 figure
Emergent phases in graphene flat bands
Electronic correlations in two-dimensional materials play a crucial role in
stabilising emergent phases of matter. The realisation of correlation-driven
phenomena in graphene has remained a longstanding goal, primarily due to the
absence of strong electron-electron interactions within its low-energy bands.
In this context, magic-angle twisted bilayer graphene has recently emerged as a
novel platform featuring correlated phases favoured by the low-energy flat
bands of the underlying moir\'e superlattice. Notably, the observation of
correlated insulators and superconductivity has garnered significant attention,
leading to substantial progress in theoretical and experimental studies aiming
to elucidate the origin and interplay between these two phases. A wealth of
correlated phases with unprecedented tunability was discovered subsequently,
including orbital ferromagnetism, Chern insulators, strange metallicity,
density waves, and nematicity. However, a comprehensive understanding of these
closely competing phases remains elusive. The ability to controllably twist and
stack multiple graphene layers has enabled the creation of a whole new family
of moir\'e superlattices with myriad properties being discovered at a fast
pace. Here, we review the progress and development achieved so far,
encompassing the rich phase diagrams offered by these graphene-based moir\'e
systems. Additionally, we discuss multiple phases recently observed in
non-moir\'e multilayer graphene systems. Finally, we outline future
opportunities and challenges for the exploration of hidden phases in this new
generation of moir\'e materials
Signature of Martensite transformation on conductivity noise in thin films of NiTi shape memory alloys
Slow time-dependent fluctuations, or noise, in the electrical resistance of
dc magnetron sputtered thin films of Nickel Titanium shape memory alloys have
been measured. Even in equilibrium, the noise was several orders of magnitude
larger than that of simple diffusive metallic films, and was found to be
non-monotonic around the martensitic transformation regime. The results are
discussed in terms of dynamics of structural defects, which also lay foundation
to a new noise-based characterization scheme of martensite transformation.Comment: 4 pages, 3 figure
Spin-orbit coupling-enhanced valley ordering of malleable bands in twisted bilayer graphene on WSe2
New phases of matter can be stabilized by a combination of diverging
electronic density of states, strong interactions, and spin-orbit coupling.
Recent experiments in magic-angle twisted bilayer graphene (TBG) have uncovered
a wealth of novel phases as a result of interaction-driven spin-valley flavour
polarization. In this work, we explore correlated phases appearing due to the
combined effect of spin-orbit coupling-enhanced valley polarization and large
density of states below half filling () of the moir\'e band in
a TBG coupled to tungsten diselenide. We observe anomalous Hall effect,
accompanied by a series of Lifshitz transitions, that are highly tunable with
carrier density and magnetic field. Strikingly, the magnetization shows an
abrupt sign change in the vicinity of half-filling, confirming its orbital
nature. The coercive fields reported are about an order of magnitude higher
than previous studies in graphene-based moir\'e systems, presumably aided by a
Stoner instability favoured by the van Hove singularities in the malleable
bands. While the Hall resistance is not quantized at zero magnetic fields,
indicative of a ground state with partial valley polarization, perfect
quantization and complete valley polarization are observed at finite fields.
Our findings illustrate that singularities in the flat bands in the presence of
spin-orbit coupling can stabilize ordered phases even at non-integer moir\'e
band fillings.Comment: 17 pages, 15 figure
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