Found 39 papers in cond-mat Rhombohedral graphene multilayers provide a clean and highly reproducible
platform to explore the emergence of superconductivity and magnetism in a
strongly interacting electron system. Here, we use electronic compressibility
and local magnetometry to explore the phase diagram of this material class in
unprecedented detail. We focus on rhombohedral trilayer in the quarter metal
regime, where the electronic ground state is characterized by the occupation of
a single spin and valley isospin flavor. Our measurements reveal a subtle
competition between valley imbalanced (VI) orbital ferromagnets and intervalley
coherent (IVC) states in which electron wave functions in the two momentum
space valleys develop a macroscopically coherent relative phase. Contrasting
the in-plane spin susceptibility of the IVC and VI phases reveals the influence
of graphene's intrinsic spin-orbit coupling, which drives the emergence of a
distinct correlated phase with hybrid VI and IVC character. Spin-orbit also
suppresses the in-plane magnetic susceptibility of the VI phase, which allows
us to extract the spin-orbit coupling strength of $\lambda \approx 50\mu$eV for
our hexagonal boron nitride-encapsulated graphene system. We discuss the
implications of finite spin-orbit coupling on the spin-triplet superconductors
observed in both rhombohedral and twisted graphene multilayers.
We propose a general framework to characterize gapped infra-red (IR) phases
of theories with non-invertible (or categorical) symmetries. In this paper we
focus on (1+1)d gapped phases with fusion category symmetries. The approach
that we propose uses the Symmetry Topological Field Theory (SymTFT) as a key
input: associated to a field theory in d spacetime dimensions, the SymTFT lives
in one dimension higher and admits a gapped boundary, which realizes the
categorical symmetries. It also admits a second, physical, boundary, which is
generically not gapped. Upon interval compactification of the SymTFT by
colliding the gapped and physical boundaries, we regain the original theory. In
this paper, we realize gapped symmetric phases by choosing the physical
boundary to be a gapped boundary condition as well. This set-up provides
computational power to determine the number of vacua, the symmetry breaking
pattern, and the action of the symmetry on the vacua. The SymTFT also
manifestly encodes the order parameters for these gapped phases, thus providing
a generalized, categorical Landau paradigm for (1+1)d gapped phases. We find
that for non-invertible symmetries the order parameters involve multiplets
containing both untwisted and twisted sector local operators, and hence can be
interpreted as mixtures of conventional and string order parameters. We also
observe that spontaneous breaking of non-invertible symmetries can lead to
vacua that are physically distinguishable: unlike the standard symmetries
described by groups, non-invertible symmetries can have different actions on
different vacua of an irreducible gapped phase. This leads to the presence of
relative Euler terms between physically distinct vacua. We also provide a
mathematical description of symmetric gapped phases as 2-functors from
delooping of fusion category characterizing the symmetry to Euler completion of
2-vector spaces.
We propose a unified framework to classify gapped infra-red (IR) phases with
categorical symmetries, leading to a generalized, categorical Landau paradigm.
This is applicable in any dimension and gives a succinct, comprehensive, and
computationally powerful approach to classifying gapped symmetric phases. The
key tool is the symmetry topological field theory (SymTFT), which is a one
dimension higher TFT with two boundaries, which we choose both to be
topological. We illustrate the general idea for (1+1)d gapped phases with
categorical symmetries and suggest higher-dimensional extensions.
Topological insulator/superconductor two-dimensional heterostructures are
promising candidates for realizing topological superconductivity and Majorana
modes. In these systems, a vortex pinned by a pre-fabricated antidot in the
superconductor can host Majorana zero-energy modes (MZMs), which are exotic
quasiparticles that may enable quantum information processing. However, a major
challenge is to design devices that can manipulate the information encoded in
these MZMs. One of the key factors is to create small and clean antidots, so
that the MZMs, localized in the vortex core, have a large gap to other
excitations. If the antidot is too large or too disordered, the level spacing
for the subgap vortex states may become smaller than temperature. In this
paper, we numerically investigate the effects of disorder, chemical potential,
and antidot size on the subgap vortex spectrum, using a two-dimensional
effective model of the topological insulator surface. Our model allows us to
simulate large system sizes with vortices up to 1.8 $\mu$m in diameter. We also
compare our disorder model with the transport data from existing experiments.
We find that the spectral gap can exhibit a non-monotonic behavior as a
function of disorder strength, and that it can be tuned by applying a gate
voltage.
Under plastic flow, multi-element high/medium-entropy alloys (HEAs/MEAs)
commonly exhibit complex intermittent and collective dislocation dynamics owing
to inherent lattice distortion and atomic-level chemical complexities. Using
atomistic simulations, we report on an avalanche study of slowly-driven model
face-centered cubic (fcc) NiCoCrFeMn and NiCoCr chemically complex alloys
aiming for microstructural/topological characterization of associated
dislocation avalanches. The results of our avalanche simulations reveal a close
correspondence between the observed serration features in the stress response
of the deforming HEA/MEA and the incurred slip patterns within the bulk
crystal. We show that such correlations become quite pronounced within the
rate-independent (quasi-static) regime exhibiting scale-free statistics and
critical scaling features as universal signatures of dislocation avalanches.
Topological nodal-line semimetals are characterized by symmetry-protected
one-dimensional band-touching lines or loops, which give rise to their peculiar
Fermi surfaces at low energies. Furthermore, if time-reversal or inversion
symmetry breaking tilts the bands, anisotropic Fermi surfaces hosting electron
and hole carriers simultaneously can also appear. We analytically investigate
the linear density-density response function of a two-dimensional tilted
nodal-line semimetal in the intrinsic and doped regimes. Despite the
anisotropic electronic bands, the polarizability remains isotropic in our model
system. We find that the plasmon dispersion in the long wavelength limit
exhibits a standard behavior that is proportional to the square root of the
wave vector, characteristic of two-dimensional electron liquids. Tilting tends
to enhance the plasmon frequency, and the Drude weight does not depend on the
carrier density at low doping levels. In these regimes, unlike the intrinsic
and highly-doped ones, the static polarizability has two distinct singularities
at finite wave vectors. This results in beat patterns in the Friedel
oscillations.
We predict the limit cycle solution for a ring-shape bosonic condensate of
exciton-polaritons confined in an optically induced rotating trap. The limit
cycle manifests itself with polarization oscillations on a characteristic
timescale of tens of picoseconds. The effect arises due to the interplay
between orbital motion and the polarization degree of freedom. It is specific
to spinor bosonic condensates and would be absent in a scalar case, where a
bi-stability of stationary solutions would be observed instead. This work
offers a tool of initialisation and control of qubits based on superpositions
of polariton condensates characterised by different topologic charges.
We consider a smooth interface between a topological nodal-line semimetal and
a topologically trivial insulator (e.g., the vacuum) or another semimetal with
a nodal ring of different radius. Using a low-energy effective Hamiltonian
including only the two crossing bands, we show that these junctions accommodate
a two-dimensional zero-energy level and a set of two-dimensional dispersive
bands, corresponding to states localized at the interface. We characterize the
spectrum, identifying the parameter ranges in which these states are present,
and highlight the role of the nodal radius and the smoothness of the interface.
We also suggest material-independent ways to detect and identify these states,
using optical conductivity and infrared absorption spectroscopy in magnetic
field.
In the presence of external magnetic field, the Kitaev model could either
hosts gapped topological anyon or gapless Majorana fermions. In
$\alpha$-RuCl$_3$, the gapped and gapless cases are only separated by a
thirty-degree rotation of the in-plane magnetic field vector. The
presence/absence of the spectral gap is key for understanding the thermal
transport behavior in $\alpha$-RuCl$_3$. Here, we study the anisotropy of the
oscillatory features of thermal conductivity in $\alpha$-RuCl$_3$. We examine
the oscillatory features of thermal conductivities (k//a, k//b) with fixed
external fields and found distinct behavior for the gapped (B//a) and gapless
(B//b) scenarios. Furthermore, we track the evolution of thermal resistivity
($\lambda_{a}$) and its oscillatory features with the rotation of in-plane
magnetic fields from B//b to B//a. The thermal resistivity $\lambda (B,\theta)$
display distinct rotational symmetries before and after the emergence of the
field induced Kitaev spin liquid phase. These experiment data suggest close
correlations between the oscillatory features of thermal conductivity, the
underlying Kitaev spin liquid phase and the fermionic excitation it holds.
Phonon-polaritons are electromagnetic waves resulting from the coherent
coupling of photons with optical phonons in polar dielectrics. Due to their
exceptional ability to confine electric fields to deep subwavelength scales
with low loss, they are uniquely poised to enable a suite of applications
beyond the reach of conventional photonics, such as sub-diffraction imaging and
near-field energy transfer. The conventional approach to exciting
phonon-polaritons through optical methods, however, necessitates costly
mid-infrared and terahertz coherent light sources along with near-field
scanning probes, and generally leads to low excitation efficiency due to the
substantial momentum mismatch between phonon-polaritons and free-space photons.
Here, we demonstrate that under proper conditions, phonon-polaritons can be
excited all-electrically by flowing charge carriers. Specifically, in hexagonal
boron nitride (hBN)/graphene heterostructures, by electrically driving charge
carriers in ultra-high-mobility graphene out of equilibrium, we observe bright
electroluminescence of hBN's hyperbolic phonon-polaritons (HPhPs) at mid-IR
frequencies. The HPhP electroluminescence shows a temperature and carrier
density dependence distinct from black-body or super-Planckian thermal
emission. Moreover, the carrier density dependence of HPhP electroluminescence
spectra reveals that HPhP electroluminescence can arise from both inter-band
transition and intra-band Cherenkov radiation of charge carriers in graphene.
The HPhP electroluminescence offers fundamentally new avenues for realizing
electrically-pumped, tunable mid-IR and THz phonon-polariton lasers, and
efficient cooling of electronic devices.
The development of two-dimensional (2D) room temperature magnets is of great
significance to the practical application of spintronic devices. However, the
number of synthesized intrinsic 2D magnets is limited and the performances of
them are not satisfactory, e.g. typically with low Curie temperature and poor
environmental stability. Magnetic modulation based on developed 2D materials,
especially non-magnetic 2D materials, can bring us new breakthroughs. Herein,
we report room temperature ferromagnetism in halogenated MoS2 monolayer under
the synergistic effect of strain engineering and charge injection, and the
combined implementation of these two processes is based on the halogenation of
MoS2. The adsorbed halogen atoms X (X = F, Cl, and Br) on the surface leads to
lattice superstretching and hole injection, resulting in MoS2 monolayer
exhibiting half-metallic properties, with one spin channel being gapless in the
band structure. The Curie temperature of halogenated MoS2 monolayer is 513~615
K, which is much higher than the room temperature. In addition, large magnetic
anisotropy energy and good environmental stability make halogenated MoS2
display great advantages in practical spintronic nanodevices.
Topological phononics enabling backscattering-immune transport is expected to
improve the performance of electromechanical systems for classical and quantum
information technologies. Nonetheless, most of the previous demonstrations
utilized macroscale and low-frequency structures and thus offered little
experimental insight into ultrahigh frequency phonon transport, especially in
chip-scale circuits. Here, we report microwave phonon transmissions in a
microscopic topological ring-waveguide coupled system, which is an important
building block for wave-based signal processing. The elastic waves in the
topological waveguide evanescently couple to the ring resonator, while
maintaining the valley pseudospin polarization. The resultant waves are robust
to backscattering even in the tiny hexagonal ring, generating a resonant phonon
circulation. Furthermore, the evanescently coupled structure allows for a
critical coupling, where valley-dependent ring-waveguide interference enables
blocking of the topological edge transmission. Our demonstrations reveal the
capability of using topological phenomena to manipulate ultrahigh frequency
elastic waves in intricate phononic circuits for classical and quantum
signal-processing applications.
Superconductivity (SC) was experimentally observed for the first time in
antimony polyhydride. The diamond anvil cell combined with laser heating system
was used to synthesize the antimony polyhydride sample at high pressure and
high temperature conditions. In-situ high pressure transport measurements as
function of temperature with applied magnet are performed to study the SC
properties. It was found that the antimony polyhydride samples show
superconducting transition with critical temperature $T_c = 116^\circ$K at 184
GPa. The investigation of SC at magnetic field revealed that the
superconducting coherent length ~40 angstroms based on Ginzburg Landau (GL)
equation. Antimony polyhydride superconductor has the second highest Tc in
addition to sulfur hydride among the polyhydrides of elements from main group
IIIA to VIIA in periodic table.
In a recent experiment on the interlayer magnetoresistance in the
quasi-two-dimensional organic salt, $\alpha$-(BEDT-TTF)$_2$I$_3$, it has been
observed that at low temperatures, interlayer tunneling attains phase
coherence, leading to the emergence of a three-dimensional electronic
structure. Theoretically and experimentally it has been suggested that the
system exhibits characteristics of a three-dimensional Dirac semimetal as a
consequence of broken time-reversal symmetry and inversion symmetry. Here, we
perform a theoretical calculation of the magnetoconductivity under an in-plane
magnetic field and demonstrate that the system displays a planar Hall effect.
Our calculations are based on a realistic model for
$\alpha$-(BEDT-TTF)$_2$I$_3$ incorporating interlayer tunneling and the tilt of
the Dirac cone. Given that the planar Hall effect is anticipated as a
consequence of chiral anomaly, our findings provide support for the
classification of $\alpha$-(BEDT-TTF)$_2$I$_3$ as a three-dimensional Dirac
semimetal.
Recent experiments in twisted bilayer WTe$_2$ revealed the existence of
anisotropic Luttinger liquid behavior. To generically characterize such
anisotropic twisted bilayer systems, we study a model of twisted bilayer of 2D
arrays of coupled wires, which effectively form an array of coupled moir\'e
wires. We solve the model by transfer matrix method, and identify quasi-1D
electron bands in the system at small twist angles. With electron interactions
added, we show that the moir\'e wires have an effective Luttinger parameter
$g_\text{eff}$ much lower than that of the microscopic wires. This leads to a
sliding Luttinger liquid (SLL) temperature regime, in which power-law current
voltage relations arise. For parameters partly estimated from WTe$_2$, a
microscopic interaction $U\sim0.7$eV yields a temperature regime of SLL similar
to that in the WTe$_2$ experiments.
Few-layer graphene possesses low-energy carriers which behave as massive
fermions, exhibiting intriguing properties in both transport and light
scattering experiments. By lowering the excitation energy of resonance Raman
spectroscopy down to 1.17 eV we target these massive quasiparticles in the
low-energy split bands close to the K point. The low excitation energy
suppresses some of the Raman processes which are resonant in the visible, and
induces a clearer frequency-separation of the sub-structures of the resonant 2D
peak. Studying the different intensities of the sub-structures and comparing
experimental measurements with fully ab initio theoretical calculations, in the
case of bilayer graphene we unveil an enhanced coupling between the massive
fermions and the lattice vibrations at the K point, in analogy to what found
for the massless fermions of monolayer graphene, and also suggesting that what
governs the enhancement is the vicinity of the electron-hole pair momentum to K
rather than how small the electron-hole pair energy is.
The silicide superconductors (Ta, Nb, Zr)OsSi are among the best candidate
materials for investigating the interplay of topological order and
superconductivity. Here, we investigate in detail the normal-state topological
properties of (Ta, Nb, Zr)OsSi, focusing on ZrOsSi, by employing a combination
of $^{29}$Si nuclear magnetic resonance (NMR) measurements and first-principles
band-structure calculations. We show that, while (Ta, Nb)OsSi behave as almost
ideal metals, characterized by weak electronic correlations and a relatively
low density of states, the replacement of Ta (or Nb) with Zr expands the
crystal lattice and shifts ZrOsSi towards an insulator. Our ab initio
calculations indicate that ZrOsSi is a $Z_2$ topological metal with clear
surface Dirac cones and properties similar to a doped strong topological
insulator.
Two-dimensional MoS$_2$ combines many interesting properties that make the
material a top candidate for a variety of applications. It exhibits a high
electron mobility comparable to graphene, a direct fundamental band gap,
relatively strongly bound excitons, and moderate spin-orbit coupling. For a
thorough understanding of all these properties, an accurate description of the
electronic structure is mandatory. Surprisingly, published band gaps of MoS$_2$
obtained with $GW$, the state-of-the-art in electronic-structure calculations,
are quite scattered, ranging from 2.31 to 2.97 eV. The details of $G_0W_0$
calculations, such as the underlying geometry, the starting point, the
inclusion of spin-orbit coupling, and the treatment of the Coulomb potential
can critically determine how accurate the results are. In this manuscript, we
employ the linearized augmented planewave + local orbital method to
systematically investigate how all these aspects affect the quality of $G_0W_0$
calculations, and also provide a summary of literature data. We conclude that
the best overall agreement with experiments and coupled-cluster calculations is
found for $G_0W_0$ results with HSE06 as a starting point including spin-orbit
coupling, a truncated Coulomb potential, and an analytical treatment of the
singularity at $q=0$.
Atmospheric water harvesting is urgently needed given increasing global water
scarcity. Current sorbent-based devices that cycle between water capture and
release have low harvesting rates. We envision a radically different
multi-material architecture with segregated and simultaneous capture and
release. This way, proven fast-release mechanisms that approach theoretical
limits can be incorporated; however, no capture mechanism exists to supply
liquid adequately for release. Inspired by tree frogs and airplants, our
capture approach transports water through a hydrogel membrane ``skin'' into a
liquid desiccant. We report an extraordinarily high capture rate of 5.50
$\text{kg}\,\text{m}^{-2}\,\text{d}^{-1}$ at a low humidity of 35%, limited by
the convection of air to the device. At higher humidities, we demonstrate up to
16.9 $\text{kg}\,\text{m}^{-2}\,\text{d}^{-1}$, exceeding theoretical limits
for release. Simulated performance of a hypothetical one-square-meter device
shows that water could be supplied to two to three people in dry environments.
This work is a significant step toward providing new resources to water-scarce
regions.
Within ten years, flat band (FB) superconductivity has gained a huge interest
for its remarkable features and connection to quantum geometry. We investigate
the superconductivity in a FB system whose orbitals are inequivalent and in
which the gap and the quantum metric are tunable. The key feature of the
present theoretical study is to show a unique and simple constrain relation
that pairings obey. Furthermore, pairings and superfluid weight in partially
filled FB are shown to be controlled by those of the half-filled lattice. We
argue that the geometry of the lattice or the complexity of the hopping terms
have no impact on the features revealed in this work as far as the system is
bipartite.
Kagome metals are reported to exhibit remarkable properties, including
superconductivity, charge density wave order, and a large anomalous Hall
conductivity, which facilitate the implementation of spintronic devices. In
this work, we study a novel kagome metal based on Mn magnetic sites in a
KMn$_3$Sb$_5$ stoichiometry. By means of first-principles density functional
theory calculations, we demonstrate that the studied compound is dynamically
stable, locking the ferromagnetic order as the ground state configuration, thus
preventing the charge-density-wave state as reported in its vanadium-based
counterpart KV$_3$Sb$_5$. Our calculations predict that KMn$_3$Sb$_5$ exhibits
an out-of-plane (001) ferromagnetic response as the ground state, allowing for
the emergence of topologically protected Weyl nodes near the Fermi level and
nonzero anomalous Hall conductivity ($\sigma_{ij}$) in this centrosymmetric
system. We obtain a tangible $\sigma_{xy} = 314$ S$\cdot$cm$^{-1}$ component,
which is comparable to that of other kagome metals. Finally, we explore the
effect of the on-site Coulomb repulsion ($+U$) on the structural and electronic
properties and find that, although the lattice parameters and $\sigma_{xy}$
moderately vary with increasing $+U$, KMn$_3$Sb$_5$ stands as an ideal stable
ferromagnetic kagome metal with a large anomalous Hall conductivity response.
We construct the simplest density functional for the problem of a single
impurity interacting with a Fermi gas via a long--ranged potential using the
Thomas--Fermi approach. We find that the Fermi polaron is fully bosonized in
two dimensions, as the model results in a suitable Landau--Pekar functional
known from the Bose polaron problem which describes a self--interacting
impurity. In other dimensions, the impurity self--interacts with an infinite
number of its own images, and no bosonization occurs. We discuss applications
of our theory for the $2d$ exciton--polaron and the ionic polaron problem and
compute the effective mass for these cases, finding a self--trapping transition
with order depending on the dimensionality.
We carry out a theoretical study of unconventional superconductivity in
twisted bilayer cuprates as a function of electron density and layer twist
angle. The bilayer $t$-$J$-$U$ model is employed and analyzed within the
framework of a generalized variational wave function approach in the
statistically-consistent Gutzwiller formulation. The constructed phase diagram
encompasses both gapless $d$-wave state (reflecting the pairing symmetry of
untwisted copper-oxides) and gapped $d+\mathrm{e}^{i\varphi}d$ phase that
breaks spontaneously time-reversal-symmetry (TRS) and is characterized by
nontrivial Chern number. We find that $d+\mathrm{e}^{i\varphi}d$ state occupies
a non-convex butterfly-shaped region in the doping vs. twist-angle plane, and
demonstrate the presence of previously unreported reentrant TRS-breaking phase
on the underdoped side of the phase diagram. This circumstance supports the
emergence of topological superconductivity for fine-tuned twist angles away
from $45^\circ$. Our analysis of the microscopically derived Landau free energy
functional points toward sensitivity of the superconducting order parameter to
small perturbations close to the topological state boundary.
We study the impact of atomic interactions on an in-situ collimation method
for matter-waves. Building upon an earlier study with $^{87}$Rb, we apply a
lensing protocol to $^{39}$K where the atomic scattering length can be tailored
by means of magnetic Feshbach resonances. Minimizing interactions, we show an
enhancement of the collimation compared to the strong interaction regime,
realizing ballistic 2D expansion energies of 438(77) pK in our experiment. Our
results are supported by an accurate simulation, describing the ensemble
dynamics, which we further use to study the behavior of various trap
configurations for different interaction strengths. Based on our findings we
propose an advanced scenario which allows for 3D expansion energies below 16 pK
by implementing an additional pulsed delta-kick collimation directly after
release from the trapping potential. Our results pave the way to achieve
state-of-the-art quantum state in typical dipole trap setups required to
perform ultra-precise measurements without the need of complex micro-gravity or
long baselines environments.
We use polarization resolved Raman spectroscopy to show that for 3D giant
Rashba system the bulk plasmon collective mode directly couples to the Raman
response even in the long wavelength $\mathbf q \rightarrow 0$ limit although
the standard theory predicts that the plasmon spectral weight should scale as
the square of its quasi-momentum and hence be negligibly weak in the Raman
spectra. Such plasmon coupling to the Raman response at $\mathbf q \rightarrow
0$ arises for a polar system with spin-orbit coupling when the incoming photon
excitation is turned to a resonance with Rashba-split intermediates states
involved in the resonant Raman process. As an example, we identify special
features of BiTeI's chiral band structure that enable the appearance of plasmon
mode in the Raman spectrum.
We study by large-scale Monte Carlo simulation the $RP^3$ model, which can be
regarded as an effective low-energy model of a triangular lattice Heisenberg
antiferromagnet. $Z_2$ vortices appear as elementary excitations in the
triangular lattice Heisenberg antiferromagnet. Such $Z_2$ vortices are
ubiquitous in other frustrated Heisenberg spin systems that have noncollinear
long-range orders. In this study, we investigate a possible topological phase
transition driven by the binding--unbinding of $Z_2$ vortices. By extracting
important degrees of freedom, we map a frustrated spin system to an effective
$RP^3$ model. From large-scale Monte Carlo simulation, we obtain an order
parameter and a correlation length of up to $L=16384$. Concerning the existence
of a $Z_2$-vortex transition, by extrapolating the order parameter to the
thermodynamics limit assuming the $Z_2$-vortex transition, we obtain a finite
transition temperature as $T_v/\tilde{J} \simeq 0.25$. Our estimate of the
correlation length at $T_v$ is much larger than $L=16384$, which is beyond the
previous estimate obtained with the triangular lattice Heisenberg model.
We reveal how symmetry protected nodal points in topological semimetals may
be promoted to pairs of generically stable exceptional points (EPs) by
symmetry-breaking fluctuations at the onset of long-range order. This novel
route to non-Hermitian (NH) topology is exemplified by a magnetic NH Weyl phase
spontaneously emerging at the surface of a strongly correlated
three-dimensional topological insulator when entering the ferromagnetic regime
from a high temperature paramagnetic phase. Here, electronic excitations with
opposite spin acquire significantly different life-times, thus giving rise to
an anti-Hermitian structure in spin that is incompatible with the chiral spin
texture of the nodal surface states, and hence facilitates the spontaneous
formation of EPs. We present numerical evidence of this phenomenon by solving a
microscopic multi-band Hubbard model non-perturbatively in the framework of
dynamical mean-field theory.
The gapped Dirac-like surface states of compensated magnetic topological
insulator MnBi$_{2-x}$Sb$_x$Te$_4$ (MBST) are a promising host for exotic
quantum phenomena such as the quantum anomalous Hall effect and axion
insulating states. However, it has become clear that atomic defects undermine
the stabilization of such quantum phases as they lead to spatial variations in
the surface state gap and doping levels. The large number of possible defect
configurations in MBST make studying the influence of individual defects
virtually impossible. Here, we present a statistical analysis of the nanoscale
effect of defects in MBST with $x=0.64$, by scanning tunneling
microscopy/spectroscopy (STM/S). We identify (Bi,Sb)$_{\rm Mn}$ anti-site
defects to be the main source of the observed doping fluctuations, leading
towards the formation of nanoscale charge puddles and effectively closing the
transport gap. Our findings will guide further optimization of this material
system via defect engineering, to enable exploitation of its promising
properties.
The complex energy bands of non-Hermitian systems braid in momentum space
even in one dimension. Here, we reveal that the non-Hermitian braiding
underlies the Hermitian topological physics with chiral symmetry under a
general framework that unifies Hermitian and non-Hermitian systems.
Particularly, we derive an elegant identity that equates the linking number
between the knots of braiding non-Hermitian bands and the zero-energy loop to
the topological invariant of chiral-symmetric topological phases in one
dimension. Moreover, we find an exotic class of phase transitions arising from
the critical point transforming different knot structures of the non-Hermitian
braiding, which are not included in the conventional Hermitian topological
phase transition theory. Nevertheless, we show the bulk-boundary correspondence
between the bulk non-Hermitian braiding and boundary zero-modes of the
Hermitian topological insulators. Finally, we construct typical topological
phases with non-Hermitian braidings, which can be readily realized by
artificial crystals.
The flat band is a key ingredient for the realization of interesting quantum
states for novel functionalities. In this work, we investigate the conditions
for the flat band in both monolayer and bilayer graphene under periodic strain.
We find topological nearly flat bands with homogeneous distribution of Berry
curvature in both systems. The quantum metric of the nearly flat band closely
resembles that for Landau levels. For monolayer graphene, the strain field can
be regarded as an effective gauge field, while for Bernal-stacked (AB-stacked)
bilayer graphene, its role is beyond the description of gauge field. We also
provide an understanding of the origin of the nearly flat band in monolayer
graphene in terms of the Jackiw-Rebbi model for Dirac fermions with
sign-changing mass. Our work suggests strained graphene as a promising platform
for strongly correlated quantum states.
Recent experimental study unveiled highly unconventional phenomena in the
superconducting twisted bilayer graphene (TBG) with ultra flat bands, which
cannot be described by the conventional BCS theory. For example, given the
small Fermi velocity of the flat bands, the superconducting coherence length
predicted by BCS theory is more than 20 times shorter than the measured values.
A new theory is needed to understand many of the unconventional properties of
flat band superconductors. In this work, we establish a Ginzburg-Landau (GL)
theory from a microscopic flat band Hamiltonian. The GL theory shows how the
properties of the physical quantities such as the critical temperature, the
superconducting coherence length, the upper critical field and the superfluid
density are governed by the quantum metric of the Bloch states. One key
conclusion is that the superconducting coherence length is not determined by
the Fermi velocity but by the size of the optimally localized Wannier functions
which is limited by quantum metric. Applying the theory to TBG, we calculated
the superconducting coherence length and the upper critical fields. The results
match the experimental ones well without fine tuning of parameters. The
established GL theory provides a new and general theoretical framework for
understanding flat band superconductors with quantum metric.
Topological excitations or defects such as solitons are ubiquitous throughout
physics, supporting numerous interesting phenomena like zero energy modes with
exotic statistics and fractionalized charges. In this paper, we study such
objects through the lens of symmetry-resolved entanglement entropy.
Specifically, we compute the charge-resolved entanglement entropy for a single
interval in the low-lying states of the Su-Schrieffer-Heeger model in the
presence of topological defects. Using a combination of exact and asymptotic
analytical techniques, backed up by numerical analysis, we find that, compared
to the unresolved counterpart and to the pure system, a richer structure of
entanglement emerges. This includes a redistribution between its
configurational and fluctuational parts due to the presence of the defect and
an interesting interplay with entanglement equipartition. In particular, in a
subsystem that excludes the defect, equipartition is restricted to charge
sectors of the same parity, while full equipartition is restored if the
subsystem includes the defect, as long as the associated zero mode remains
unoccupied. Additionally, by exciting zero modes in the presence of multiple
defects, we observe a significant enhancement of entanglement in certain charge
sectors, due to charge splitting on the defects. The two different scenarios
featuring the breakdown of entanglement equipartition are underlied by a joint
mechanism, which we unveil by relating them to degeneracies in the spectrum of
the entanglement Hamiltonian. In addition, equipartition is shown to stem from
an equidistant entanglement spectrum.
In an altermagnet, the symmetry that relates configurations with flipped
magnetic moments is a rotation. This makes it qualitatively different from a
ferromagnet, where no such symmetry exists, or a collinear antiferromagnet,
where this symmetry is a lattice translation. In this paper, we investigate the
impact of the crystalline environment on the magnetic and electronic properties
of an altermagnet. We find that, because each component of the magnetization
acquires its own angular dependence, the Zeeman splitting of the bands has
symmetry-protected nodal lines residing on mirror planes of the crystal. Upon
crossing the Fermi surface, these nodal lines give rise to pinch points that
behave as single or double type-II Weyl nodes. We show that an external
magnetic field perpendicular to these mirror planes can only move the nodal
lines, such that a critical field value is necessary to collapse the nodes and
make the Weyl pinch points annihilate. This unveils the topological nature of
the transition from a nodal to a nodeless Zeeman splitting of the bands. We
also classify the altermagnetic states of common crystallographic point groups
in the presence of spin-orbit coupling, revealing that a broad family of
magnetic orthorhombic perovskites can realize altermagnetism.
Geometrical frustration in correlated systems can give rise to a plethora of
novel ordered states and intriguing phases. Here, we analyze theoretically
vertex-sharing frustrated Kagome lattice of Josephson junctions and identify
various classical and quantum phases. The frustration is provided by
periodically arranged $0$- and $\pi$- Josephson junctions. In the frustrated
regime the macroscopic phases are composed of different patterns of
vortex/antivortex penetrating each basic element of the Kagome lattice, i.e., a
superconducting triangle interrupted by three Josephson junctions. We obtain
that numerous topological constraints, related to the flux quantization in any
hexagon loop, lead to highly anisotropic and long-range interaction between
well separated vortices (antivortices). Taking into account this interaction
and a possibility of macroscopic "tunneling" between vortex and antivortex in
single superconducting triangles we derive an effective Ising-type spin
Hamiltonian with strongly anisotropic long-range interaction. In the
classically frustrated regime we calculate numerically the
temperature-dependent spatially averaged spins polarization, $\overline{m}(T)$,
characterizing the crossover between the ordered and disordered
vortex/antivortex states. In the coherent quantum regime we analyze the lifting
of the degeneracy of the ground state and the appearance of the highly
entangled states.
Defects in graphene are both a boon and a bane for applications - they can
induce uncontrollable effects but can also provide novel ways to manipulate the
properties of pristine graphene. Nanoporous Graphene, which contains nanoscopic
holes, has found impactful applications in sustainability domains, e.g. gas
separation, water filtration membranes and battery technologies. For this
report, we investigate pore formation in graphene with no defect, one and two
mono-vacancies, and two di-vacancies using bespoke Dimensionally Restricted
Molecular Dynamics (DR-MD) designed for the purpose. We show DR-MD to be
superior to free-standing or substrate suspended configurations for simulating
stable defected structures. Applying DR-MD, stable pore configurations are
identified, and their formation mechanisms elucidated. We also investigated
formation mechanisms due to two Stone-Wales 55-77 defects, and the formation
energies of their linearly extended structures, along the zigzag and armchair
directions, and when they are placed in different relative orientations. This
study offers a way to identify stable porous defect structures in graphene and
insights into atomistic pore formation mechanisms for an environmentally
important material.
Motivated by recent observation of the quantum spin Hall effect in monolayer
germanene and twisted bilayer transition-metal-dichalcogenides (TMDs), we study
the topological phases of moir\'e twisted bilayers with time-reversal symmetry
and spin $s_z$ conservation. By using a continuum model description which can
be applied to both germanene and TMD bilayers, we show that at small twist
angles, the emergent moir\'e flatbands can be topologically nontrivial due to
inversion symmetry breaking. Each of these flatbands for each spin projection
admits a lowest-Landau-level description in the chiral limit and at magic twist
angle. This allows for the construction of a many-body Laughlin state with
time-reversal symmetry which can be stabilized by a short-range
pseudopotential, and therefore serves as an ideal platform for realizing the
so-far elusive fractional quantum spin Hall effect with emergent spin-1/2 U(1)
symmetry.
The elastic response of mechanical, chemical, and biological systems is often
modeled using a discrete arrangement of Hookean springs, either modeling finite
material elements or even the molecular bonds of a system. However, to date,
there is no direct derivation of the relation between discrete spring network,
and a general elastic continuum. Furthermore, understanding the networks'
mechanical response requires simulations that may be expensive computationally.
Here we report a method to derive the exact elastic continuum model of any
discrete network of springs, requiring network geometry and topology only. We
identify and calculate the so-called "non-affine" displacements. Explicit
comparison of our calculations to simulations of different crystalline and
disordered configurations, shows we successfully capture the mechanics even of
auxetic materials. Our method is valid for residually stressed systems with
non-trivial geometries, is easily generalizable to other discrete models, and
opens the possibility of a rational design of elastic systems.
In the field of 2D materials, transition metal dichalcogenides (TMDs) are
gaining attention for electronic applications. Our study delves into the
H-phase monolayer VS$_2$ of the TMD family, analyzing its electronic structure
and how strain affects its band structure using Density Functional Theory
(DFT). Using a variety of computational methods, we provide an in-depth view of
the electronic band structure. We find that strains between -5\% and +5\%
significantly affect the energy gap, with uniaxial strains having a stronger
effect than biaxial strains. Remarkably, compressive strains induce a phase
shift from semiconducting to metallic, associated with symmetry breaking and
changes in bond length. These findings not only deepen our understanding of the
electronic nuances of monolayer VS$_2$ under varying strains but also suggest
potential avenues for creating new electronic devices through strain
engineering.
We give a general derivation of Ginsparg-Wilson relations for both Dirac and
Majorana fermions in any dimension. These relations encode continuous and
discrete chiral, parity and time reversal anomalies and will apply to the
various classes of free fermion topological insulators and superconductors (in
the framework of a relativistic quantum field theory in Euclidean spacetime).
We show how to formulate the exact symmetries of the lattice action and the
relevant index theorems for the anomalies.

Date of feed: Mon, 09 Oct 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) **Intervalley coherence and intrinsic spin-orbit coupling in rhombohedral trilayer graphene. (arXiv:2310.03781v1 [cond-mat.mes-hall])**

Trevor Arp, Owen Sheekey, Haoxin Zhou, C.L. Tschirhart, Caitlin L. Patterson, H. M. Yoo, Ludwig Holleis, Evgeny Redekop, Grigory Babikyan, Tian Xie, Jiewen Xiao, Yaar Vituri, Tobias Holder, Takashi Taniguchi, Kenji Watanabe, Martin E. Huber, Erez Berg, Andrea F. Young

**Gapped Phases with Non-Invertible Symmetries: (1+1)d. (arXiv:2310.03784v1 [hep-th])**

Lakshya Bhardwaj, Lea E. Bottini, Daniel Pajer, Sakura Schafer-Nameki

**Categorical Landau Paradigm for Gapped Phases. (arXiv:2310.03786v1 [cond-mat.str-el])**

Lakshya Bhardwaj, Lea E. Bottini, Daniel Pajer, Sakura Schafer-Nameki

**Influence of disorder on antidot vortex Majorana states in 3D topological insulators. (arXiv:2310.03810v1 [cond-mat.mes-hall])**

Rafał Rechciński, Aleksei Khindanov, Dmitry I. Pikulin, Jian Liao, Leonid P. Rokhinson, Yong P. Chen, Roman M. Lutchyn, Jukka I. Väyrynen

**Serrated plastic flow in slowly-deforming complex concentrated alloys: universal signatures of dislocation avalanches. (arXiv:2310.03828v1 [cond-mat.mtrl-sci])**

Kamran Karimi, Amin Esfandiarpour, Stefanos Papanikolaou

**Collective excitations and screening in two-dimensional tilted nodal-line semimetals. (arXiv:2310.03835v1 [cond-mat.mes-hall])**

Hamid Rahimpoor, Saeed H. Abedinpour

**Persistent polarization oscillations in ring-shape polariton condensates. (arXiv:2310.03836v1 [physics.optics])**

A. V. Yulin, E. S. Sedov, A. V. Kavokin, I. A. Shelykh

**Dispersive Drumhead States in Nodal-Line Semimetal Junctions. (arXiv:2310.03896v1 [cond-mat.mes-hall])**

Francesco Buccheri, Reinhold Egger, Alessandro De Martino

**Anisotropy of thermal conductivity oscillations in relation to the Kitaev spin liquid phase. (arXiv:2310.03917v1 [cond-mat.str-el])**

Heda Zhang, Hu Miao, Thomas Z Ward, David G Mandrus, Stephen E Nagler, Michael A McGuire, Jiaqiang Yan

**Hyperbolic phonon-polariton electroluminescence in graphene-hBN van der Waals heterostructures. (arXiv:2310.03926v1 [cond-mat.mes-hall])**

Qiushi Guo, Iliya Esin, Cheng Li, Chen Chen, Song Liu, James H. Edgar, Selina Zhou, Eugene Demler, Gil Refael, Fengnian Xia

**Turning non-magnetic two-dimensional molybdenum disulfide into room temperature magnets by the synergistic effect of strain engineering and charge injection. (arXiv:2310.03995v1 [cond-mat.mtrl-sci])**

Jing Wu, Ruyi Guo, Daoxiong Wu, Xiuling Li, Xiaojun Wu

**Evanescently coupled topological ring-waveguide systems for chip-scale ultrahigh frequency phononic circuits. (arXiv:2310.04008v1 [cond-mat.mes-hall])**

Daiki Hatanaka, Hiroaki Takeshita, Motoki Kataoka, Hajime Okamoto, Kenji Tsuruta, Hiroshi Yamaguchi

**Superconductivity with Tc 116 K discovered in antimony polyhydrides. (arXiv:2310.04033v1 [cond-mat.supr-con])**

K. Lu, X. He, C.L. Zhang, Z.W. Li, S.J. Zhang, B. S. Min, J. Zhang, J.F. Zhao, L.C. Shi, Y. Peng, S.M. Feng, Q.Q. Liu, J. Song, R.C. Yu, X.C. Wang, Y. Wang, M. Bykov, C. Q. Jin

**Theory for Planar Hall Effect in Organic Dirac Fermion System. (arXiv:2310.04066v1 [cond-mat.str-el])**

Yuki Nakamura, Takao Morinari

**Twisted Coupled Wire Model for moir\'e Sliding Luttinger Liquid. (arXiv:2310.04070v1 [cond-mat.str-el])**

Yichen Hu, Yuanfeng Xu, Biao Lian

**Enhanced coupling between massive fermions and zone-boundary phonons probed by infrared resonance Raman in bilayer graphene. (arXiv:2310.04071v1 [cond-mat.mes-hall])**

Lorenzo Graziotto, Francesco Macheda, Tommaso Venanzi, Simone Sotgiu, Taoufiq Ouaj, Elena Stellino, Claudia Fasolato, Paolo Postorino, Marvin Metzelaars, Paul Kögerler, Bernd Beschoten, Matteo Calandra, Michele Ortolani, Christoph Stampfer, Francesco Mauri, Leonetta Baldassarre

**ZrOsSi: A $Z_2$ topological metal with a superconducting ground state. (arXiv:2310.04105v1 [cond-mat.supr-con])**

S. K. Ghosh, B. Li, C. Xu, A. D. Hillier, P. K. Biswas, X. Xu, T. Shiroka

**Electronic structure of MoS$_2$ revisited: a comprehensive assessment of $G_0W_0$ calculations. (arXiv:2310.04198v1 [cond-mat.mtrl-sci])**

Ronaldo Rodrigues Pela, Cecilia Vona, Sven Lubeck, Ben Alex, Ignacio Gonzalez Oliva, Claudia Draxl

**High-yield atmospheric water capture via bioinspired material segregation. (arXiv:2310.04254v1 [physics.flu-dyn])**

Yiwei Gao, Santiago Ricoy, Addison Cobb, Ryan Phung, Areianna Lewis, Aaron Sahm, Nathan Ortiz, Sameer Rao, H. Jeremy Cho

**Constrain relations for superfluid weight and pairings in a chiral flat band superconductor. (arXiv:2310.04325v1 [cond-mat.supr-con])**

M. Thumin, G. Bouzerar

**Kagome KMn$_3$Sb$_5$ metal: Magnetism, lattice dynamics, and anomalous Hall conductivity. (arXiv:2310.04339v1 [cond-mat.str-el])**

Sobhit Singh, A.C. Garcia-Castro

**The long-range interacting Fermi polaron. (arXiv:2310.04351v1 [cond-mat.quant-gas])**

Krzysztof Myśliwy, Krzysztof Jachymski

**Tuning topological superconductivity within the $t$-$J$-$U$ model of twisted bilayer cuprates. (arXiv:2310.04379v1 [cond-mat.supr-con])**

Maciej Fidrysiak, Bartłomiej Rzeszotarski, Józef Spałek

**Matter-wave collimation to picokelvin energies with scattering length and potential shape control. (arXiv:2310.04383v1 [physics.atom-ph])**

Alexander Herbst, Timothé Estrampes, Henning Albers, Robin Corgier, Knut Stolzenberg, Sebastian Bode, Eric Charron, Ernst M. Rasel, Naceur Gaaloul, Dennis Schlippert

**Direct Photon Scattering by Plasmons in BiTeI. (arXiv:2310.04394v1 [cond-mat.str-el])**

A. C. Lee, S. Sarkar, K. Du, H.-H. Kung, C. J. Won, K. Wang, S.-W. Cheong, S. Maiti, G. Blumberg

**Possibility of a Topological Phase Transition in Two-dimensional $RP^3$ Model. (arXiv:2112.15053v2 [cond-mat.stat-mech] UPDATED)**

Tsuyoshi Okubo, Naoki Kawashima

**Spontaneous Formation of Exceptional Points at the Onset of Magnetism. (arXiv:2207.05097v2 [cond-mat.str-el] UPDATED)**

Lorenzo Crippa, Giorgio Sangiovanni, Jan Carl Budich

**Anti-site defect-induced disorder in compensated topological magnet MnBi$_{2-x}$Sb$_x$Te$_4$. (arXiv:2208.13374v3 [cond-mat.mes-hall] UPDATED)**

Felix Lüpke, Marek Kolmer, Jiaqiang Yan, Hao Chang, Paolo Vilmercati, Hanno H. Weitering, Wonhee Ko, An-Ping Li

**Hermitian Topologies originating from non-Hermitian braidings. (arXiv:2212.13736v2 [cond-mat.mes-hall] UPDATED)**

W. B. Rui, Y. X. Zhao, Z. D. Wang

**Nearly flat Chern band in periodically strained monolayer and bilayer graphene. (arXiv:2302.07199v2 [cond-mat.mes-hall] UPDATED)**

Xiaohan Wan, Siddhartha Sarkar, Kai Sun, Shi-Zeng Lin

**The Ginzburg-Landau theory of flat band superconductors with quantum metric. (arXiv:2303.15504v4 [cond-mat.supr-con] UPDATED)**

Shuai A. Chen, K. T. Law

**Charge-resolved entanglement in the presence of topological defects. (arXiv:2306.15532v2 [quant-ph] UPDATED)**

David X. Horvath, Shachar Fraenkel, Stefano Scopa, Colin Rylands

**Topological transition from nodal to nodeless Zeeman splitting in altermagnets. (arXiv:2307.12380v3 [cond-mat.mes-hall] UPDATED)**

Rafael M. Fernandes, Vanuildo S. de Carvalho, Turan Birol, Rodrigo G. Pereira

**Long-range Ising spins models emerging from frustrated Josephson junctions arrays with topological constraints. (arXiv:2308.07143v2 [quant-ph] UPDATED)**

Oliver Neyenhuys, Mikhail V. Fistul, Ilya M. Eremin

**Generating Nanoporous Graphene from Point and Stone-Wales Defects: A Study with Dimensionally Restricted Molecular Dynamics (DR-MD). (arXiv:2308.13810v2 [cond-mat.mtrl-sci] UPDATED)**

Ji Wei Yoon

**Time-Reversal Invariant Topological Moir\'e Flatband: A Platform for the Fractional Quantum Spin Hall Effect. (arXiv:2309.07222v2 [cond-mat.mes-hall] UPDATED)**

Yi-Ming Wu, Daniel Shaffer, Zhengzhi Wu, Luiz H. Santos

**Predicting the mechanical properties of spring networks. (arXiv:2309.07844v2 [cond-mat.soft] UPDATED)**

Doron Grossman, Arezki Boudaoud

**Electronic Phase Transformations and Energy Gap Variations in Uniaxial and Biaxial Strained Monolayer VS$_2$ TMDs: A Comprehensive DFT and Beyond-DFT Study. (arXiv:2309.08393v3 [cond-mat.mtrl-sci] UPDATED)**

Oguzhan Orhan, Şener Özönder, Soner Ozgen

**Generalized Ginsparg-Wilson relations. (arXiv:2309.08542v2 [hep-lat] UPDATED)**

Michael Clancy, David B. Kaplan, Hersh Singh

Found 1 papers in sci-rep **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) **Synthesis and optical properties of WS _{2} nanotubes with relatively small diameters**

Kazuhiro Yanagi

Scientific Reports, Published online: 08 October 2023; doi:10.1038/s41598-023-44072-z

Synthesis and optical properties of WS