87 research outputs found
Correlated Insulating States in Twisted Double Bilayer Graphene
We present a combined experimental and theoretical study of twisted double
bilayer graphene with twist angles between 1{\deg} and 1.35{\deg}. Consistent
with moir\'e band structure calculations, we observe insulators at integer
moir\'e band fillings one and three, but not two. An applied transverse
electric field separates the first moir\'e conduction band from neighbouring
bands, and favors the appearance of correlated insulators at 1/4, 1/2, and 3/4
band filling. Insulating states at 1/4 and 3/4 band filling emerge only in a
parallel magnetic field (B_{||}), whereas the resistance at half band filling
is weakly dependent on B_{||}. These findings suggest that correlated
insulators are favored when a moir\'e flat band is spectrally isolated, with
spin polarization at 1/4 and 3/4 band filling and valley polarization at 1/2
band filling.Comment: 5 pages, 4 figures, includes supplementary materia
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The Misdiagnosis of Hypertension: The Role of Patient Anxiety
Background: The white coat effect (defined as the difference between blood pressure [BP] measurements taken at the physician's office and those taken outside the office) is an important determinant of misdiagnosis of hypertension, but little is known about the mechanisms underlying this phenomenon. We tested the hypothesis that the white coat effect may be a conditioned response as opposed to a manifestation of general anxiety.
Methods: A total of 238 patients in a hypertension clinic wore ambulatory blood pressure monitors on 3 separate days 1 month apart. At each clinic visit, BP readings were manually triggered in the waiting area and the examination room (in the presence and absence of the physician) and were compared with the mercury sphygmomanometer readings taken by the physician in the examination room. Patients completed trait and state anxiety measures before and after each BP assessment.
Results: A total of 35% of the sample was normotensive, and 9%, 37%, and 19% had white coat, sustained, and masked hypertension, respectively. The diagnostic category was associated with the state anxiety measure (F3,237 = 6.4, P < .001) but not with the trait anxiety measure. Patients with white coat hypertension had significantly higher state anxiety scores (t = 2.67, P < .01), with the greatest difference reported during the physician measurement. The same pattern was observed for BP changes, which generally paralleled the changes in state anxiety (t = 4.86, P < .002 for systolic BP; t = 3.51, P < .002 for diastolic BP).
Conclusions: These findings support our hypothesis that the white coat effect is a conditioned response. The BP measurements taken by physicians appear to exacerbate the white coat effect more than other means. This problem could be addressed with uniform use of automated BP devices in office settings
Emergence of Interlayer Coherence in Twist-Controlled Graphene Double Layers
We report enhanced interlayer tunneling with reduced linewidth at zero
interlayer bias in a twist-controlled double monolayer graphene heterostructure
in the quantum Hall regime, when the top () and bottom
() layer filling factors are near and , and the total filling factor
or . The zero-bias interlayer conductance peaks are stable
against variations of layer filling factor, and signal the emergence of
interlayer phase coherence. Our results highlight twist control as a key
attribute in revealing interlayer coherence using tunneling.Comment: 5 pages, 4 figures, includes supplementary materia
Topological Edge Transport in Twisted Double-Bilayer Graphene
Topological insulators realized in materials with strong spin-orbit
interactions challenged the long-held view that electronic materials are
classified as either conductors or insulators. The emergence of controlled,
two-dimensional moire patterns has opened new vistas in the topological
materials landscape. Here we report on evidence, obtained by combining
thermodynamic measurements, local and non-local transport measurements, and
theoretical calculations, that robust topologically non-trivial, valley Chern
insulators occur at charge neutrality in twisted double-bilayer graphene
(TDBG). These time reversal-conserving valley Chern insulators are enabled by
valley-number conservation, a symmetry that emerges from the moir\'e pattern.
The thermodynamic gap extracted from chemical potential measurements proves
that TDBG is a bulk insulator under transverse electric field, while transport
measurements confirm the existence of conducting edge states. A
Landauer-Buttiker analysis of measurements on multi-terminal samples allows us
to quantitatively assess edge state scattering and demonstrate that it does not
destroy the edge states, leaving the bulk-boundary correspondence largely
intact
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