27 research outputs found
Numerical tests of the large charge expansion
We perform Monte-Carlo measurements of two and three point functions of
charged operators in the critical O(2) model in 3 dimensions. Our results are
compatible with the predictions of the large charge superfluid effective field
theory. To obtain reliable measurements for large values of the charge, we
improved the Worm algorithm and devised a measurement scheme which mitigates
the uncertainties due to lattice and finite size effects.Comment: 16 pages, 12 figures. v2: Improved finite size scaling. v3: Added
comparison between Monte Carlo update
From Bloch Oscillations to a Steady-State Current in Strongly Biased Mesoscopic Devices
It has long been known that quantum particles in a periodic lattice exhibit
an oscillatory motion that is solely driven by a constant and uniform force
field. In a strongly biased mesoscopic device, this would appear as an ongoing
time-dependent current oscillation (a Bloch oscillation) but, even when
electrons can move coherently and without scattering, a steady-state regime of
charge transport (a Landauer current) have been seen to quickly emerge. Here,
we theoretically investigate the non-equilibrium current dynamics of a strongly
biased two-terminal mesoscopic device, in order to show that such a system can
exhibit Bloch oscillations as a transient regime that relaxes into a Landauer
steady-state from charge being drained into the leads. Analytical results from
the one-dimensional Wannier-Stark ladder problem are combined with numerical
quantum time-evolution of a tight-binding toy model with finite leads to
characterize the decay times of transient Bloch oscillations and establish the
conditions under which they can occur.Comment: Preliminary Version (13 pages + 12 Figures). Comments and Suggestions
are Welcome
Twisted bilayer graphene: low-energy physics, electronic and optical properties
Van der Waals (vdW) heterostructures ---formed by stacking or growing
two-dimensional (2D) crystals on top of each other--- have emerged as a new
promising route to tailor and engineer the properties of 2D materials. Twisted
bilayer graphene (tBLG), a simple vdW structure where the interference between
two misaligned graphene lattices leads to the formation of a moir\'e pattern,
is a test bed to study the effects of the interaction and misalignment between
layers, key players for determining the electronic properties of these
stackings. In this chapter, we present in a pedagogical way the general theory
used to describe lattice mismatched and misaligned vdW structures. We apply it
to the study of tBLG in the limit of small rotations and see how the coupling
between the two layers leads both to an angle dependent renormalization of
graphene's Fermi velocity and appearance of low-energy van Hove singularities.
The optical response of this system is then addressed by computing the optical
conductivity and the dispersion relation of tBLG surface plasmon-polaritons
Anomalous Transport Signatures in Weyl Semimetals with Point Defects
We present the first theoretical study of transport properties of Weyl
semimetals with point defects. Focusing on a class of time-reversal symmetric
Weyl lattice models, we show that dilute lattice vacancies induce a finite
density of quasi-localized states at and near the nodal energy, causing strong
modifications to the low-energy spectrum. This generates novel transport
effects, namely (i) an oscillatory behaviour of the dc-conductivity with the
charge carrier density in the absence of magnetic fields, and (ii) a
plateau-shaped dissipative optical response for photon frequencies below the
inter-band threshold, .Our
results provide a path to engineer unconventional quantum transport effects in
Weyl semimetals by means of common point defects.Comment: 6 pages + 1 page of Supplementary Material; 4 + 2 Figures. Slight
Changes Relative to V