Found 34 papers in cond-mat We uncover a useful connection between the integrated current noise
$S(\omega)$ and the topological band gap in dispersionless quantum states,
$\int d \omega [ \mathcal S^{\text{flat}}_{xx} + \mathcal S^{\text{flat}}_{yy}
] = C e^2 \Delta^2$ (in units $\hbar$$=$$1$), where $C$ is the Chern number,
$e$ is electric charge, and $\Delta$ is the topological band gap. This
relationship may serve as a working principle for a new experimental probe of
topological band gaps in flat band materials. Possible applications include
moir\'e systems, such as twisted bilayer graphene and twisted transition metal
dichalcogenides, where a band gap measurement in meV regime presents an
experimental challenge.
Valley magnetic moments play a crucial role in valleytronics in 2D hexagonal
materials. Traditionally, based on studies of quantum states in homogeneous
bulks, it is widely believed that only materials with broken structural
inversion symmetry can exhibit nonvanishing valley magnetic moments. Such
constraint excludes from relevant applications those with inversion symmetry,
as specifically exemplified by gapless monolayer graphene despite its
technological advantage in routine growth and production. This work revisits
valley-derived magnetic moments in a broad context covering inhomogeneous
structures as well. It generalizes the notion of valley magnetic moment for a
state from an integrated total quantity to the local field called "local valley
magnetic moment" with space-varying distribution. In suitable
inversion-symmetric structures with inhomogeneity, e.g., zigzag nanoribbons of
gapless monolayer graphene, it is shown that the local moment of a state can be
nonvanishing with sizable magnitude, while the corresponding total moment is
subject to the broken symmetry constraint. Moreover, it is demonstrated that
such local moment can interact with space-dependent electric and magnetic
fields manifesting pronounced field effects and making possible a local valley
control with external fields. Overall, a path to "local valleytronics" is
illustrated which exploits local valley magnetic moments for device
applications, relaxes the broken symmetry constraint on materials, and expands
flexibility in the implementation of valleytronics.
$\nu$=1/2 is among the most enigmatic many-body phases in two-dimensional
electron systems as it appears in the ground-state rather than an excited
Landau level. It is observed in wide quantum wells where the electrons have a
bilayer charge distribution with finite tunneling. Whether this 1/2 FQHS is
two-component (Abelian) or one-component (non-Abelian) has been debated since
its experimental discovery over 30 years ago. Here, we report strong 1/2 FQHSs
in ultrahigh-quality, wide, GaAs quantum wells, with transport energy gaps up
to $\simeq$4K, among the largest gaps reported for any even-denominator FQHS.
The 1/2 FQHS is flanked by numerous, Jain-sequence FQHSs at
$\nu$=$p$/(2$p$$\pm$1) up to $\nu$=8/17 and 9/17. Remarkably, as we raise the
density and strengthen the 1/2 FQHS, the 8/17 and 7/13 FQHSs suddenly become
strong, much stronger than their neighboring high-order FQHSs. Insofar as FQHSs
at $\nu$=8/17 and 7/13 are precisely the theoretically-predicted, simplest,
daughter states of the one-component Pfaffian 1/2 FQHS, our data suggest a
topological phase-transition of 8/17 and 7/13 FQHSs from the Jain-states to the
daughter states of the Pfaffian, and that the parent 1/2 FQHS we observe is the
Pfaffian state.
We examine properties of the mean-field wave function of the one-dimensional
Kitaev model supporting Majorana Zero Modes (MZMs) \emph{when restricted} to a
fixed number of particles. Such wave functions can in fact be realized as exact
ground states of interacting number-conserving Hamiltonians and amount to a
more realistic description of the finite isolated superconductors. Akin to
their mean-field parent, the fixed-number wave functions encode a single
electron spectral function at zero energy that decays exponentially away from
the edges, with a localization length that agrees with the mean-field value.
Based purely on the structure of the number-projected ground states, we
construct the fixed particle number generalization of the MZM operators. They
can be used to compute the edge tunneling conductance; however, notably the
value of the zero-bias conductance remains the same as in the mean-field case,
quantized to $2e^2/h$. We also compute the topological entanglement entropy for
the number-projected wave functions and find that it contains a `robust'
$\log(2)$ component as well as a logarithmic correction to the mean field
result, which depends on the precise partitioning used to compute it. The
presence of the logarithmic term in the entanglement entropy indicates the
absence of a spectral gap above the ground state; as one introduces
fluctuations in the number of particles, the correction vanishes smoothly.
We have investigated the effects of strain on two-dimensional square lattices
and examined the methods for inducing pseudo-magnetic fields. In both the
columnar and staggered $\pi$-flux square lattices, we have found that strain
only modulates Fermi velocities rather than inducing pseudo-magnetic fields.
However, spatially non-uniform on-site potentials (anisotropic hoppings) can
create pseudo-magnetic fields in columnar (staggered) $\pi$-flux square
lattices. On the other hand, we demonstrate that strain does induce
pseudo-magnetic fields in staggered zero-flux square lattices. By breaking a
quarter of the bonds, we clarify that a staggered zero-flux square lattice is
topologically equivalent to a honeycomb lattice and displays pseudo-vector
potentials and pseudo-Landau levels at the Dirac points.
Chirality, a fundamental structural property of crystals, can induce many
unique topological quantum phenomena. In kagome lattice, unconventional
transports have been reported under tantalizing chiral charge order. Here, we
show how by deforming the kagome lattice to obtain a three-dimensional (3D)
chiral kagome lattice in which the key band features of the non-chiral 2D
kagome lattice - flat energy bands, van Hove singularities (VHSs), and
degeneracies - remain robust in both the $k_z$ = 0 and $\pi$ planes in momentum
space. Given the handedness of our kagome lattice, degenerate momentum points
possess quantized Chern numbers, ushering in the realization of Weyl fermions.
Our 3D chiral kagome lattice surprisingly exhibits 1D behavior on its surface,
where topological surface Fermi arc states connecting Weyl fermions are
dispersive in one momentum direction and flat in the other direction. These 1D
Fermi arcs open up unique possibilities for generating unconventional non-local
transport phenomena at the interfaces of domains with different handedness, and
the associated enhanced conductance as the separation of the leads on the
surface is increased. Employing first-principles calculations, we investigate
in-depth the electronic and phononic structures of representative materials
within the ten space groups that can support topological chiral kagome
lattices. Our study opens a new research direction that integrates the
advantages of structural chirality with those of a kagome lattice and thus
provides a new materials platform for exploring unique aspects of correlated
topological physics in chiral lattices.
Type-II Weyl semimetal MoTe$_2$ exhibits a first-order structural transition
at $T_s$ $\sim$250~K and superconducts at $T_c$ $\sim$0.1~K at ambient
pressure. Both $T_s$ and $T_c$ can be manipulated by several tuning parameters,
such as hydrostatic pressure and chemical substitution. It is often reported
that suppressing $T_s$ enhances $T_c$, but our study shows a different
behaviour when MoTe$_2$ is hole-doped by Ta. When $T_s$ is suppressed by Ta
doping, $T_c$ is also suppressed. Our findings suggest that the suppression of
$T_s$ does not necessarily enhance superconductivity in MoTe$_2$. By connecting
with the findings of electron-doped MoTe$_2$, we argue that varying electron
carrier concentration can effectively tune $T_c$. In addition, the Hall
coefficient is enhanced around the doping region, where $T_s$ is completely
suppressed, suggesting that the critical scattering around the structural
transition may also play a role in suppressing $T_c$.
The interplay among frustrated lattice geometry, nontrivial band topology and
correlations yields rich quantum states of matter in Kagome systems. A class of
recent Kagome metals, AV3Sb5 (A= K, Rb, Cs), exhibit a cascade of
symmetry-breaking transitions, involving 3Q chiral charge ordering, electronic
nematicity, roton pair density wave and superconductivity. The interdependence
among multiple competing orders suggests unconventional superconductivity, the
nature of which is yet to be resolved. Here, we report the electronic evidence
for chiral superconducting domains with boundary supercurrent, a smoking-gun of
chiral superconductivity, in intrinsic CsV3Sb5 akes. Magnetic field-free
superconducting diode effects are observed with its polarity modulated by
thermal histories, unveiling a spontaneous time-reversal-symmetry breaking
within dynamical order parameter domains in the superconducting phase.
Strikingly, the critical current exhibits double-slit superconducting
interference patterns, when subjected to external magnetic field. This is
attributed to the periodic modulation of supercurrent owing along chiral domain
boundaries constrained by fluxoid quantization. Our results provide the direct
demonstration of a time-reversal symmetry breaking superconducting order in
Kagome systems, opening a potential for exploring exotic physics, e.g. Majorana
zero modes, in this intriguing topological Kagome system.
Atomic engineering in a solid-state material has the potential to
functionalize the host with novel phenomena. STM-based lithographic techniques
have enabled the placement of individual phosphorus atoms at selective lattice
sites of silicon with atomic precision. Here, we show that by placing four
phosphorus donors spaced 10-15 nm apart from their neighbours in a linear
chain, it is possible to realize coherent spin coupling between the end dopants
of the chain, analogous to the superexchange interaction in magnetic materials.
Since phosphorus atoms are a promising building block of a silicon quantum
computer, this enables spin coupling between their bound electrons beyond
nearest neighbours, allowing the qubits to be spaced out by 30-45 nm. The added
flexibility in architecture brought about by this long-range coupling not only
reduces gate densities but can also reduce correlated noise between qubits from
local noise sources that are detrimental to error correction codes. We base our
calculations on a full configuration interaction technique in the atomistic
tight-binding basis, solving the 4-electron problem exactly, over a domain of a
million silicon atoms. Our calculations show that superexchange can be tuned
electrically through gate voltages where it is less sensitive to charge noise
and donor placement errors.
We present a simple proof of a sufficient condition for the uniqueness of
non-equilibrium steady states of Gorini-Kossakowski-Sudarshan-Lindblad
equations. We demonstrate the applications of the sufficient condition using
examples of the transverse-field Ising model, the XYZ model, and the
tight-binding model with dephasing.
Generalized string-net models have been recently proposed in order to enlarge
the set of possible topological quantum phases emerging from the original
string-net construction. In the present work, we do not consider vertex
excitations and restrict to plaquette excitations, or fluxons, that satisfy
important identities. We explain how to compute the energy-level degeneracies
of the generalized string-net Hamiltonian associated to an arbitrary unitary
fusion category. In contrast to the degeneracy of the ground state, which is
purely topological, that of excited energy levels depends not only on the
Drinfeld center of the category, but also on internal multiplicities obtained
from the tube algebra defined from the category. For a noncommutative category,
these internal multiplicities result in extra nontopological degeneracies. Our
results are valid for any trivalent graph and any orientable surface. We
illustrate our findings with nontrivial examples.
We argue that doped twisted bilayer graphene with magical twist angle can
become superconducting. In our theoretical scenario the superconductivity
coexists with the spin-density-wave-like ordering. Numerical mean field
analysis demonstrates that the spin-density wave order, which is much stronger
than the superconductivity, leaves parts of the Fermi surface ungapped. This
Fermi surface serves as a host for the superconductivity. Since the magnetic
texture at finite doping breaks the point group of the twisted bilayer
graphene, the stabilized superconducting order parameter is nematic. We also
explore the possibility of purely Coulomb-based mechanism of the
superconductivity in the studied system. The screened Coulomb interaction is
calculated within the random phase approximation. It is shown that near the
half-filling the renormalized Coulomb repulsion indeed induces the
superconducting state, with the order parameter possessing two nodes on the
Fermi surface. We estimate the superconducting transition temperature, which
turns out to be very low. The implications of our proposal are discussed.
A topological transition in high-temperature superconductors FeTe1-xSex,
occurring at a critical range of Se concentration x, underlies their intrinsic
topological superconductivity and emergence of Majorana states within vortices.
Nonetheless, the influence of Se concentration and distribution on the
electronic states in FeTe1-xSex remains unclear, particularly concerning their
relationship with the presence or absence of Majorana states. In this study, we
combine density functional theory (DFT) calculations, pz-dxz/yz-based and
Wannier-based Hamiltonian analysis to systematically explore the electronic
structures of diverse FeTe1-xSex compositions. Our investigation reveals a
nonlinear variation of the spin-orbit coupling (SOC) gap between pz and dxz/yz
bands in response to x, with the maximum gap occurring at x = 0.5. The pz-pz
and dx2-y2-pz interactions are found to be critical for pd band inversion.
Furthermore, we ascertain that the distribution of Se significantly modulates
the SOC gap, thereby influencing the presence or absence of Majorana states
within local vortices.
The Casimir-Polder force between atoms or nanoparticles and graphene-coated
dielectric substrates is investigated in the region of large separations.
Graphene coating with any value of the energy gap and chemical potential is
described in the framework of the Dirac model using the formalism of the
polarization tensor. It is shown that the Casimir-Polder force from a
graphene-coated substrate reaches the limit of large separations at
approximately 5.6 $\mu$m distance between an atom or a nanoparticle and
graphene coating independently of the values of the energy gap and chemical
potential. According to our results, however, the classical limit, where the
Casimir-Polder force no longer depends on the Planck constant and the speed of
light, may be attained at much larger separations depending on the values of
the energy gap and chemical potential. In addition, we have found a simple
analytic expression for the Casimir-Polder force from a graphene-coated
substrate at large separations and determined the region of its applicability.
It is demonstrated that the asymptotic results for the large-separation
Casimir-Polder force from a graphene-coated substrate are in better agreement
with the results of numerical computations for the graphene sheets with larger
chemical potential and smaller energy gap. Possible applications of the
obtained results in nanotechnology and bioelectronics are discussed.
In Landau's Fermi liquid, transport is governed by scattering between
quasi-particles. The normal liquid $^3$He conforms to this picture, but only
when T$< 0.02$ T$_F$. Here, we observe that the deviation from the standard
behavior is concomitant with the fermion-fermion scattering time falling below
the Planckian time, $\frac{\hbar}{k_BT}$. The thermal diffusivity of this
quantum liquid is bounded by a minimum set by fundamental physical constants
and earlier observed in classical liquids. This implies that collective
excitations of the liquid (a sound mode) are carrying heat. We argue that if
heat is carried by 2k$_F$ hydrodynamic sound mode, both the amplitude and the
hitherto unexplained $T^{1/2}$ temperature dependence of thermal conductivity
find an explanation with no other adjustable parameter.
We delve into the statistical properties of regions within complex networks
that are distant from vertices with high centralities, such as hubs or highly
connected clusters. These remote regions play a pivotal role in shaping the
asymptotic behaviours of various spreading processes and the features of
associated spectra. We investigate the probability distribution $P_{\geq m}(s)$
of the number $s$ of vertices located at distance $m$ or beyond from a randomly
chosen vertex in an undirected network. Earlier, this distribution and its
large $m$ asymptotics $1/s^2$ were obtained theoretically for undirected
uncorrelated networks [S. N. Dorogovtsev, J. F. F. Mendes, A. N. Samukhin,
Nucl. Phys. B 653 (2003) 307]. Employing numerical simulations and analysing
empirical data, we explore a wide range of real undirected networks and their
models, including trees and loopy networks, and reveal that the inverse square
law is valid even for networks with strong correlations. We observe this law in
the networks demonstrating the small-world effect and containing vertices with
degree $1$ (so-called leaves or dead ends). We find the specific classes of
networks for which this law is not valid. Such networks include the
finite-dimensional networks and the networks embedded in finite-dimensional
spaces. We notice that long chains of nodes in networks reduce the range of $m$
for which the inverse square law can be spotted. Interestingly, we detect such
long chains in the remote regions of the undirected projection of a large Web
domain.
Fast quantum gates are of paramount importance for enabling efficient and
error-resilient quantum computations. In the present work we analyze
Landau-Zener-St\"uckelberg-Majorana (LSZM) strong driving protocols, tailored
to implement fast gates with particular emphasis on small gap qubits. We derive
analytical equations to determine the specific set of driving parameters for
the implementation of single qubit and two qubit gates employing single period
sinusoidal pulses. Our approach circumvents the need to scan experimentally a
wide range of parameters and instead it allows to focus in fine-tuning the
device near the analytically predicted values. We analyze the dependence of
relaxation and decoherence on the amplitude and frequency of the pulses,
obtaining the optimal regime of driving parameters to mitigate the effects of
the environment. Our results focus on the study of the single qubit
$X_{\frac{\pi}{2}}$, $Y_{\frac{\pi}{2}}$ and identity gates. Also, we propose
the $\sqrt{\rm{bSWAP}}$ as the simplest two-qubit gate attainable through a
robust LZSM driving protocol.
(1) Introduction: Nanoparticles have multiple applications, including drug
delivery systems, biosensing, and carbon capture. Non-Einstein-like viscosity
reduction has been reported in nanoparticle-polymer blends at low nanoparticle
concentrations. More recently, a similar non-Einsteinian viscosity reduction
effect has been observed in aqueous ultra-low concentration carbon-based
nanofluids. (2) Methods: We use a boron nitride nanotube functionalized with
hydrophilic groups in rheological experiments to investigate the viscosity
reduction in ultra-low concentration nanofluids (0.1-10 ppm). We measure the
dynamic viscosity in an air atmosphere and methane (0-5 MPag) at low
temperatures (0-10 C). (3) Results: A negligible effect on the temperature
dependence of viscosity was found. Ultra-low concentrations of BNNT reduced the
viscosity of the nanofluid by up to 29% at 10 ppm in the presence of methane.
The results presented here were compared to similar studies on O-GNF and
O-MWCNT nanofluids, which also reported significant viscosity reductions. (4)
Conclusions: This work identified a non-Einsteinian viscosity reduction in BNNT
nanofluids, which was exacerbated by methane dissolved in the nanofluid.
Broken symmetries in topological condensed matter systems have implications
for the spectrum of Fermionic excitations confined on surfaces or topological
defects. The Fermionic spectrum of confined (quasi-2D) $^3$He-A consists of
branches of chiral edge states. The negative energy states are related to the
ground-state angular momentum, $L_z = (N/2) \hbar$, for $N/2$ Cooper pairs. The
power law suppression of the angular momentum, $L_z(T) \simeq (N/2)\,\hbar\,[1
- \frac{2}{3}(\pi T/\Delta)^2 ]$ for $0 \le T \ll T_c$, in the fully gapped 2D
chiral A-phase reflects the thermal excitation of the chiral edge Fermions. We
discuss the effects of wave function overlap, and hybridization between edge
states confined near opposing edge boundaries on the edge currents,
ground-state angular momentum and ground-state order parameter of superfluid
$^3$He thin films. Under strong lateral confinement, the chiral A phase
undergoes a sequence of phase transitions, first to a pair density wave (PDW)
phase with broken translational symmetry at $D_{c2} \sim 16 \xi_0$. The PDW
phase is described by a periodic array of chiral domains with alternating
chirality, separated by domain walls. The period of PDW phase diverges as the
confinement length $D\rightarrow D_{c_2}$. The PDW phase breaks time-reversal
symmetry, translation invariance, but is invariant under the combination of
time-reversal and translation by a one-half period of the PDW. The mass current
distribution of the PDW phase reflects this combined symmetry, and originates
from the spectra of edge Fermions and the chiral branches bound to the domain
walls. Under sufficiently strong confinement a second-order transition occurs
to the non-chiral ``polar phase'' at $D_{c1} \sim 9\xi_0$, in which a single
p-wave orbital state of Cooper pairs is aligned along the channel.
In the thermodynamic limit, the steady states of open quantum many-body
systems can undergo nonequilibrium phase transitions due to a competition
between coherent and driven-dissipative dynamics. Here, we consider Markovian
systems and elucidate structures of the Liouville super-operator that generates
the time evolution. In many cases of interest, an operator-basis transformation
can bring the Liouvillian into a block-triangular form, making it possible to
assess its spectrum. The spectral gap sets the asymptotic decay rate. The
super-operator structure can be used to bound gaps from below, showing that, in
a large class of systems, dissipative phase transitions are actually impossible
and that the convergence to steady states follows an exponential temporal
decay. Furthermore, when the blocks on the diagonal are Hermitian, the
Liouvillian spectra obey Weyl ordering relations. The results apply, for
example, to Davies generators and quadratic systems, and are also demonstrated
for various spin models.
Two spatially separated magnetic impurities coupled to itinerant electrons
give rise to a dynamically generated exchange (RKKY) inter-impurity interaction
that competes with the individual Kondo screening of the impurities. It has
been recently shown by Yevtushenko and Yudson (2018), that the RKKY interaction
and the RKKY vs. Kondo competition become nontrivial on helical edges of
two-dimensional topological insulators where there is lock-in relation between
the electron spin and its direction of motion. Kondo screening always takes
over and dominates at large inter-impurity distances and it can also dominate
all the way to short distances if the Kondo coupling is sufficiently large and
anisotropic. In the present paper, we study the Kondo-RKKY competition in
detail on a qualitative and quantitative level. For this we employ the
numerically exact numerical renormalization group (NRG) for a broad parameter
scan of two Kondo coupled impurities vs. magnetic anisotropy, impurity distance
and temperature, and comment on the role of finite bandwidth. We give a
pedagogical introduction on the the setup of the two-impurity setting within
the NRG in the helical context. Overall we establish a plain crossover from
RKKY to Kondo with increasing impurity distance which permits an intuitive
physical picture by simply comparing length scales set by the Kondo screening
cloud, the thermal length scale vs. the impurity distance.
We derive the response of non-Hermitian topological phases with intrinsic
point gap topology to localized magnetic flux insertions. In two spatial
dimensions, we identify the necessary and sufficient conditions for a flux skin
effect that localizes an extensive number of in-gap modes at a flux core. In
three dimensions, we furthermore establish the existence of: a flux spectral
jump, where flux tube insertion fills up the entire point gap only at a single
parallel crystal momentum; a higher-order flux skin effect, which occurs at the
ends of flux tubes in presence of pseudo-inversion symmetry; and a flux
Majorana mode that represents a spectrally isolated mid-gap state in the
complex energy plane. We uniquely associate each non-Hermitian symmetry class
with intrinsic point gap topology with one of these cases or a trivial flux
response, and discuss possible experimental realizations.
We theoretically investigate the consequences of proximity-induced
conventional superconductivity in metals that break time-reversal and inversion
symmetries through their energy dispersion. We discover behaviors impossible in
an isolated superconductor such as an equilibrium supercurrent that apparently
violates a no-go theorem and, at suitable topological defects, non-conservation
of electric charge reminiscent of the chiral anomaly. The equilibrium
supercurrent is expected to be trainable by a helical electromagnetic field in
the normal state. Remarkably, if the band asymmetry exceeds the critical
current of the parent superconductor in appropriate units, we predict a perfect
superconducting diode effect with diode coefficient unity. We propose toroidal
metals such as UNi$_{4}$B and metals with directional scalar spin chiral order
as potential platforms.
Robust and tunable topological Josephson junctions (TJJs) are highly
desirable platforms for investigating the anomalous Josephson effect and
topological quantum computation applications. Experimental demonstrations have
been done in hybrid superconducting-two dimensional topological insulator
(2DTI) platforms, sensitive to magnetic disorder and interactions with phonons
and other electrons. In this work, we propose a robust and electrostatically
tunable TJJ by combining the physics of the integer quantum Hall (IQH) regime
and of superconductors. We provide analytical insights about the corresponding
Andreev bound state spectrum, the Josephson current and the anomalous current.
We demonstrate the existence of protected zero-energy crossings, that can be
controlled through electrostatic external gates. This electrostatic tunability
has a direct advantage to compensate for non-ideal interfaces and undesirable
reflections that may occur in any realistic samples. TJJs in the IQH regime
could be realized in graphene and other 2D materials. They are of particular
relevance towards scalable and robust Andreev-qubit platforms, and also for
efficient phase batteries.
We study dynamic correlations for current and mass, as well as the associated
power spectra, in the one-dimensional conserved Manna sandpile. We show that,
in the thermodynamic limit, the variance of cumulative bond current up to time
$T$ grows subdiffusively as $T^{1/2-\mu}$ with the exponent $\mu \ge 0$
depending on the density regimes considered and, likewise, the power spectra of
current and mass at low frequency $f$ varies as $f^{1/2+\mu}$ and
$f^{-3/2+\mu}$, respectively; our theory predicts that, far from criticality,
$\mu = 0$ and, near criticality, $\mu = (\beta+1)/2 \nu_{\perp} z > 0$ with
$\beta$, $\nu_{\perp}$ and $z$ being the order-parameter, correlation-length
and dynamic exponents, respectively. The anomalous suppression of fluctuations
near criticality signifies a "dynamic hyperuniformity", characterized by a set
of fluctuation relations, in which current, mass and tagged-particle
displacement fluctuations are shown to have a precise quantitative relationship
with the density-dependent activity (or, it's derivative). In particular, the
relation, ${\mathcal{D}}_s(\bar{\rho}) = a(\bar{\rho}) / \bar{\rho}$, between
the self-diffusion coefficient ${\mathcal{D}}_s(\bar{\rho})$, activity
$a(\bar{\rho})$ and density $\bar{\rho}$ explains a previous simulation
observation [Eur. Phys. J. B \textbf{72}, 441 (2009)] that, near criticality,
the self-diffusion coefficient in the Manna sandpile has the same scaling
behavior as the activity.
We investigate electronic states in a two-dimensional network consisting of
interacting quantum wires, a model adopted for twisted bilayer systems. We
construct general operators which describe various scattering processes in the
system. In a twisted bilayer structure, the moir\'e periodicity allows for
generalized umklapp scatterings, leading to a class of correlated states at
certain fractional fillings. We identify scattering processes which can lead to
an insulating gapped bulk with gapless chiral edge modes at fractional
fillings, resembling the quantum anomalous Hall effect recently observed in
twisted bilayer graphene. Finally, we demonstrate that the description can be
useful in predicting spectroscopic and transport features to detect and
characterize the chiral edge modes in the moir\'e-induced correlated states.
A bicircular light (BCL) consists of left and right circularly polarized
lights with different frequencies, and draws a rose-like pattern with a
rotational symmetry determined by the ratio of the two frequencies. Here we
show that an application of a BCL to centrosymmetric systems allows a
photocurrent generation through introduction of an effective polarity to the
system. We derive formulas for the BCL-induced photocurrent from a standard
perturbation theory, which is then applied to a simple 1D model and 3D
Dirac/Weyl semimetals. A nonperturbative effect with strong light intensity is
also discussed with the Floquet technique.
The salient property of the electronic band structure of twisted bilayer
graphene (TBG), at the so-called magic angle (MA), is the emergence of flat
bands around the charge neutrality point. These bands are associated with the
observed superconducting phases and the correlated insulating states. Scanning
tunneling microscopy combined with angle resolved photoemission spectroscopy
are usually used to visualize the flatness of the band structure of TBG at the
MA. Here, we theoretically argue that spin pumping (SP) provides a direct probe
of the flat bands of TBG and an accurate determination of the MA. We consider a
junction separating a ferromagnetic insulator and a heterostructure of TBG
adjacent to a monolayer of a transition metal dichalcogenide. We show that the
Gilbert damping of the ferromagnetic resonance experiment, through this
junction, depends on the twist angle of TBG, and exhibits a sharp drop at the
MA. We discuss the experimental realization of our results which open the way
to a twist switchable spintronics in twisted van der Waals heterostructures.
The Dzyaloshinskii-Moriya interaction (DMI), which is the antisymmetric part
of the exchange interaction between neighboring local spins, winds the spin
manifold and can stabilize non-trivial topological spin textures. Since
topology is a robust information carrier, characterization techniques that can
extract the DMI magnitude are important for the discovery and optimization of
spintronic materials. Existing experimental techniques for quantitative
determination of DMI, such as high-resolution magnetic imaging of spin textures
and measurement of magnon or transport properties, are time consuming and
require specialized instrumentation. Here we show that a convolutional neural
network can extract the DMI magnitude from minor hysteresis loops, or magnetic
"fingerprints" of a material. These hysteresis loops are readily available by
conventional magnetometry measurements. This provides a convenient tool to
investigate topological spin textures for next-generation information
processing.
The classification of point gap topology in all local non-Hermitian symmetry
classes has been recently established. However, many entries in the resulting
periodic table have only been discussed in a formal setting and still lack a
physical interpretation in terms of their bulk-boundary correspondence. Here,
we derive the edge signatures of all two-dimensional phases with intrinsic
point gap topology. While in one dimension point gap topology invariably leads
to the non-Hermitian skin effect, non-Hermitian boundary physics is
significantly richer in two dimensions. We find two broad classes of
non-Hermitian edge states: (1) Infernal points, where a skin effect occurs only
at a single edge momentum, while all other edge momenta are devoid of edge
states. Under semi-infinite boundary conditions, the point gap thereby closes
completely, but only at a single edge momentum. (2) Non-Hermitian exceptional
point dispersions, where edge states persist at all edge momenta and furnish an
anomalous number of symmetry-protected exceptional points. Surprisingly, the
latter class of systems allows for a finite, non-extensive number of edge
states with a well defined dispersion along all generic edge terminations.
Instead, the point gap only closes along the real and imaginary eigenvalue
axes, realizing a novel form of non-Hermitian spectral flow.
We discuss the dynamics of the formation of a Bose polaron when an impurity
is injected into a weakly interacting one-dimensional Bose condensate. While
for small impurity-boson couplings this process can be described within the
Froehlich model as generation, emission and binding of Bogoliubov phonons, this
is no longer adequate if the coupling becomes strong. To treat this regime we
consider a mean-field approach beyond the Froehlich model which accounts for
the backaction to the condensate, complemented with Truncated Wigner
simulations to include quantum fluctuation. For the stationary polaron we find
an energy-momentum relation that displays a smooth crossover from a convex to a
concave dependence associated with a non-monotonous relation between impurity
velocity and polaron momentum. For larger momenta the energy is a periodic
function including regions of negative impurity velocity. Studying the polaron
formation after turning on the impurity-boson coupling quasi adiabatically and
in a sudden quench, we find a very rich scenario of dynamical regimes. Due to
the build-up of an effective mass, the impurity is slowed down even if its
initial velocity is below the Landau critical value. For larger initial
velocities we find deceleration and even backscattering caused by emission of
density waves or grey solitons and subsequent formation of stationary polaron
states in different momentum sectors. In order to analyze the effect of quantum
fluctuations we consider a trapped condensate to avoid 1D infrared
divergencies. Using Truncated Wigner simulations in this case we show under
what conditions the influence of quantum fluctuations is small.
We consider here a dynamic model for a gas in which a variable number of
particles $N \in \mathbb{N}_0 := \mathbb{N} \cup \{0\}$ can be located at a
site. This point of view leads us to the grand-canonical framework and the need
for a chemical potential. The dynamics is played by the shift acting on the set
of sequences $\Omega := \mathcal{A}^\mathbb{N}$, where the alphabet is
$\mathcal{A} := \mathbb{N} \cup \{0\}$. Introducing new variables like the
number of particles $N$ and the chemical potential $\mu$, we adapt the concept
of grand-canonical partition sum of thermodynamics of gases to a symbolic
dynamical setting considering a Lipschitz family of potentials $% (A_N)_{N \in
\mathbb{N}_0}$, $A_N:\Omega \to \mathbb{R}$. Our main results will be obtained
from adapting well-known %properties the results will be obtained through the
use of known properties of the Thermodynamic Formalism for IFS with weights to
our setting. In this direction, we introduce the grand-canonical transfer
(Ruelle) operator: $\mathcal{L}_{\beta, \mu}(f)=g$, when, $\beta>0,\mu<0,$ and
$$g(x)= \mathcal{L}_{\beta, \mu}(f) (x) =\sum_{N \in \mathbb{N}_0} e^{\beta \,
\mu\, N }\, \sum_{j \in \mathcal{A}} e^{- \,\beta\, A_N(jx)} f(jx). $$ We show
the existence of the main eigenvalue, an associated eigenfunction, and an
eigenprobability for $\mathcal{L}_{\beta, \mu}$. Considering the concept of
entropy for holonomic probabilities on $\mathbb{N}_0\times \Omega$% , we relate
these items with the variational problem of maximizing grand-canonical
pressure. In another direction, in the appendix, we briefly digress on a
possible interpretation of the concept of topological pressure as related to
the gas pressure of gas thermodynamics.
Following the general theory of categorified quantum groups developed by the
author previously (arxiv:2304.07398), we construct the 2-Drinfel'd double
associated to a finite group $N=G_0$. For $N=\mathbb{Z}_2$, we explicitly
compute the braided 2-categories of 2-representations of certain version of
this 2-Drinfel'd double, and prove that they characterize precisely the 4d
toric code and its spin-$\mathbb{Z}_2$ variant. This result relates the two
descriptions (categorical vs. field theoretical) of 4d gapped topological
phases in existing literature and, perhaps more strikingly, displays the first
ever instances of higher Tannakian duality for braided 2-categories. In
particular, we show that particular twists of the underlying 2-Drinfel'd double
is responsible for much of the higher-structural properties that arise in 4d
topological orders.
Using the Lieb-Mattis ordering theorem of electronic energy levels, we
identify the Hilbert space of the low energy sector of U($N$) quantum
Hall/Heisenberg ferromagnets at filling factor $M$ for $L$ Landau/lattice sites
with the carrier space of irreducible representations of U($N$) described by
rectangular Young tableaux of $M$ rows and $L$ columns, and associated with
Grassmannian phase spaces U($N$)/U($M$)$\times$U($N-M$). We embed this
$N$-component fermion mixture in Fock space through a Schwinger-Jordan (boson
and fermion) representation of U($N$)-spin operators. We provide different
realizations of basis vectors using Young diagrams, Gelfand-Tsetlin patterns
and Fock states (for an electron/flux occupation number in the
fermionic/bosonic representation). U($N$)-spin operator matrix elements in the
Gelfand-Tsetlin basis are explicitly given. Coherent state excitations above
the ground state are computed and labeled by complex $(N-M)\times M$ matrix
points $Z$ on the Grassmannian phase space. They adopt the form of a U($N$)
displaced/rotated highest-weight vector, or a multinomial Bose-Einstein
condensate in the flux occupation number representation. Replacing U($N$)-spin
operators by their expectation values in a Grassmannian coherent state allows
for a semi-classical treatment of the low energy (long wavelength)
U($N$)-spin-wave coherent excitations (skyrmions) of U($N$) quantum Hall
ferromagnets in terms of Grasmannian nonlinear sigma models.

Date of feed: Mon, 04 Sep 2023 00:30:00 GMT**Search terms: **(topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)|(flatband)|(flat.{1}band)|(LK.{1}99) **Noise probing of topological band gaps in dispersionless quantum states. (arXiv:2309.00042v1 [cond-mat.str-el])**

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J. G. Oliveira, S. N. Dorogovtsev, J. F. F. Mendes

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Hao Wu, J. A. Sauls

**Super-operator structures and no-go theorems for dissipative quantum phase transitions. (arXiv:2012.05505v3 [quant-ph] UPDATED)**

Thomas Barthel, Yikang Zhang

**RKKY to Kondo crossover in Helical Edge of a Topological Insulator. (arXiv:2208.02275v3 [cond-mat.str-el] UPDATED)**

Pol Alonso-Cuevillas Ferrer, Oleg M. Yevtushenko, Andreas Weichselbaum

**Magnetic Flux Response of Non-Hermitian Topological Phases. (arXiv:2208.11712v2 [cond-mat.mes-hall] UPDATED)**

M. Michael Denner, Frank Schindler

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Pavan Hosur, Daniel Palacios

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**Grand-canonical Thermodynamic Formalism via IFS: volume, temperature, gas pressure and grand-canonical topological pressure. (arXiv:2305.01590v2 [math.DS] UPDATED)**

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Found 1 papers in scipost **Search terms: **(topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)|(flatband)|(flat.{1}band)|(LK.{1}99) **Visualizing near-coexistence of massless Dirac electrons and ultra-massive saddle point electrons, by Abhay Kumar Nayak, Jonathan Reiner, Hengxin Tan, Huixia Fu, Henry Ling, Chandra Shekhar, Claudia Felser, Tami Pereg-Barnea, Binghai Yan, Haim Beidenkopf, Nurit Avraham**

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Submitted on 2023-09-03, refereeing deadline 2023-09-03.