Found 36 papers in cond-mat Integrating nanoscale opto-electronic functions is vital for applications
such as optical emitters, detectors, and quantum information. Lanthanide atoms
show great potential in this endeavor due to their intrinsic transitions. Here,
we investigate Er adatoms on Si(100)-2x1 at 9K using a scanning tunneling
microscope (STM) coupled to a tunable laser. Er adatoms display two main
adsorption configurations that are optically excited between 800 nm and 1200 nm
while the STM reads the resulting photocurrents. Our spectroscopic method
reveals that various photocurrent signals stem from the bare silicon surface or
Er adatoms. Additional photocurrent peaks appear as the signature of the Er
adatoms relaxation, triggering efficient dissociation of nearby trapped
excitons. Calculations using the density functional theory with spin-orbit
coupling correction highlight the origin of the observed photocurrent peaks as
specific 4f->4f or 4f->5d transitions. This spectroscopic technique can pave
the way to an optoelectronic analysis of atomic and molecular assemblies by
offering unique insight into their intrinsic quantum properties.
Higher-order topological insulators in two spatial dimensions display
fractional corner charges. While fractional charges in one dimension are known
to be captured by a many-body bulk invariant, computed by the Resta formula, a
many-body bulk invariant for higher-order topology and the corresponding
fractional corner charges remains elusive despite several attempts. Inspired by
recent work by Tada and Oshikawa, we propose a well-defined many-body bulk
invariant for $C_n$ symmetric higher-order topological insulators, which is
valid for both non-interacting and interacting systems. Instead of relating
them to the bulk quadrupole moment as was previously done, we show that in the
presence of $C_n$ rotational symmetry, this bulk invariant can be directly
identified with quantized fractional corner charges. In particular, we prove
that the corner charge is quantized as $e/n$ with $C_n$ symmetry, leading to a
$\mathbb{Z}_n$ classification for higher-order topological insulators in two
dimensions.
The antiferromagnetic layered compound EuCd$_2$As$_2$ is widely considered as
a leading candidate of ideal Weyl semimetal, featuring a single pair of Weyl
nodes in its field-induced ferromagnetic (FM) state. Nevertheless, this view
has recently been challenged by an optical spectroscopy study, which suggests
that it is a magnetic semiconductor. In this study, we have successfully
synthesized highly insulating EuCd$_2$As$_2$ crystals with carrier density
reaching as low as $2\times 10^{15}$ $\text{cm}^{-3}$. The magneto-transport
measurements revealed a progressive decrease of the anomalous Hall conductivity
(AHC) by several orders of magnitude as the carrier density decreases. This
behavior contradicts with what is expected from the intrinsic AHC generated by
the Weyl points, which is independent of carrier density as the Fermi level
approaches the charge neutrality point. In contrast, the scaling relationship
between AHC and longitudinal conductivity aligns with the characteristics of
variable range hopping insulators. Our results suggest that EuCd$_2$As$_2$ is a
magnetic semiconductor rather than a topological Weyl semimetal.
We numerically study the coarsening of topological defects in 2D polar active
matter and make several interesting observations and predictions. (i) The long
time state is characterized by nonzero density of defects, in stark contrast to
theoretical expectations. (ii) The kinetics of defect coarsening shows power
law decay to steady state, as opposed to exponential decay in thermal
equilibrium. (iii) Observations (i) and (ii) together suggest emergent
screening of topological charges due to activity. (iv) Nontrivial defect
coarsening in the active model leads to nontrivial steady state patterns. We
investigate, characterize, and validate these patterns and discuss their
biological significance.
We investigate edge and bulk states in Weyl-orbit based quantum Hall effect
by measuring a Corbino-type device fabricated from a topological Dirac
semimetal (Cd1-xZnx)3As2 film. Clear quantum Hall plateaus are observed when
measuring one-sided terminals of the Corbino-type device. This indicates that
edge states of the Weyl-orbit quantum Hall effect form closed trajectories
consisting of Fermi arcs and chiral zero modes independently on inner and outer
sides. On the other hand, the bulk resistance does not diverge at fields where
the quantum Hall plateau appears, suggesting that the Weyl orbits in the bulk
region are not completely localized when applying electric current through the
bulk region.
Exploring the physics of low-dimensional spin systems and their
pressure-driven electronic and magnetic transitions are thriving research field
in modern condensed matter physics. In this context, recently antiferromagnetic
Cr-based compounds such as CrI3, CrBr3, CrGeTe3 have been investigated
experimentally and theoretically for their possible spintronics applications.
Motivated by the fundamental and industrial importance of these materials, we
theoretically studied the electronic and magnetic properties of a relatively
less explored Cr-based chalcogenide, namely LaCrS3 where 2D layers of magnetic
Cr3+ ions form a rectangular lattice. We employed density functional theory +
Hubbard U approach in conjunction with constrained random-phase approximation
(cRPA) where the later was used to estimate the strength of U. Our findings at
ambient pressure show that the system exhibits semiconducting antiferromagnetic
ground state with a gap of 0.5 eV and large Cr moments that corresponds to
nominal S=3/2 spin-state. The 1st nearest neighbor (NN) interatomic exchange
coupling (J1) is found to be strongly antiferromagnetic (AFM), while 2nd NN
couplings are relatively weaker ferromagnetic (FM), making this system a
candidate for 1D non-frustrated antiferromagnetic spin-chain family of
materials. Based on orbital resolved interactions, we demonstrated the reason
behind two different types of interactions among 1st and 2nd NN despite their
very similar bond lengths. We observe a significant spin-orbit coupling effect,
giving rise to a finite magneto crystalline anisotropy, and
Dzyaloshinskii-Moriya (DM) interaction. Further, we found that by applying
uniaxial tensile strain along crystallographic a and b-axis, LaCrS3 exhibits a
magnetic transition to a semi-conducting FM ground state, while compression
gives rise to the realization of novel gapless semiconducting antiferromagnetic
ground state.
Nanoparticle-Enhanced Phase Change Materials (NePCM) have been a subject of
intensive research owing to their potential for enhanced thermo-physical
properties. However, their behavior during phase change processes, such as
melting or solidification, remains inadequately understood\@. This
investigation focuses on the melting process of NePCM in a square cavity,
exploring distinct cases of melting from both the top and bottom sides. The
NePCM comprises copper nanoparticles (2 nm in size) suspended in water. Our
study involves different combinations of constant temperature boundary
conditions and particle volume fractions\@. Utilizing a numerical model based
on the one-fluid mixture approach combined with the single-domain
enthalpy-porosity model, we account for the phase change process and particles'
interaction with the solid-liquid interface. When melting NePCM from the top
side, convection effects are suppressed, resulting in a melting process
primarily governed by conduction. Both NePCM and pure water melt at the same
rate under these conditions. However, melting NePCM from the bottom side
induces convection-dominated melting. For pure water, thermal convection leads
to the formation of convection cells during melting. Contrastingly, melting
NePCM triggers thermosolutal convection due to temperature and particle
concentration gradients. The flow cells formed from thermosolutal convection in
NePCM differ from those in pure water driven by pure thermal convection. Our
simulations reveal that thermosolutal convection contributes to decelerating
the solid-liquid interface, thereby prolonging NePCM melting compared to pure
water. Surprisingly, the viscosity increase in NePCM plays a minimal role in
the deceleration process, contrary to prior literature attributing slow-downs
of the melting process of the NePCM primarily to increased viscosity.
In condensed matter physics, the Kagome lattice and its inherent flat bands
have attracted considerable attention for their potential to host a variety of
exotic physical phenomena. Despite extensive efforts to fabricate thin films of
Kagome materials aimed at modulating the flat bands through electrostatic
gating or strain manipulation, progress has been limited. Here, we report the
observation of a novel $d$-orbital hybridized Kagome-derived flat band in
Ag/Si(111) $\sqrt{3}\times\sqrt{3}$ as revealed by angle-resolved photoemission
spectroscopy. Our findings indicate that silver atoms on a silicon substrate
form a Kagome-like structure, where a delicate balance in the hopping
parameters of the in-plane $d$-orbitals leads to destructive interference,
resulting in a flat band. These results not only introduce a new platform for
Kagome physics but also illuminate the potential for integrating
metal-semiconductor interfaces into Kagome-related research, thereby opening a
new avenue for exploring ideal two-dimensional Kagome systems.
We study populations of oscillators, all-to-all coupled by means of quenched
disordered phase shifts. While there is no traditional synchronization
transition with a nonvanishing Kuramoto order parameter, the system
demonstrates a specific order as the coupling strength increases. This order is
characterized by partial phase locking, which is put into evidence by the
introduced correlation order parameter and via frequency entrainment.
Simulations with phase oscillators, Stuart-Landau oscillators, and chaotic
Roessler oscillators demonstrate similar scaling of the correlation order
parameter with the coupling and the system size and also similar behavior of
the frequencies with maximal entrainment at some finite coupling.
The Ginzburg-Landau (GL) theory is very successful in describing the pairing
symmetry, a fundamental characterization of the broken symmetries in a paired
superfluid or superconductor. However, GL theory does not describe fermionic
excitations such as Bogoliubov quasiparticles or Andreev bound states that are
directly related to topological properties of the superconductor. In this work,
we show that the symmetries of the fermionic excitations are captured by a
Projective Symmetry Group (PSG), which is a group extension of the bosonic
symmetry group in the superconducting state. We further establish a
correspondence between the pairing symmetry and the fermion PSG. When the
normal and superconducting states share the same spin rotational symmetry,
there is a simpler correspondence between the pairing symmetry and the fermion
PSG, which we enumerate for all 32 crystalline point groups. We also discuss
the general framework for computing PSGs when the spin rotational symmetry is
spontaneously broken in the superconducting state. This PSG formalism leads to
experimental consequences, and as an example, we show how a given pairing
symmetry dictates the classification of topological superconductivity.
A single nanotube synthesized from a transition metal dichalcogenide (TMDC)
exhibits strong exciton resonances and, in addition, can support optical
whispering gallery modes. This combination is promising for observing
exciton-polaritons without an external cavity. However, traditional
energy-momentum-resolved detection methods are unsuitable for this tiny object.
Instead, we propose to use split optical modes in a twisted nanotube with the
flattened cross-section, where a gradually decreasing gap between the opposite
walls leads to a change in mode energy, similar to the effect of the barrier
width on the eigenenergies in the double-well potential. Using
micro-reflectance spectroscopy, we investigated the rich pattern of polariton
branches in single MoS$_2$ tubes with both variable and constant gaps. Observed
Rabi splitting in the 40 - 60 meV range is comparable to that for a MoS$_2$
monolayer in a microcavity. Our results, based on the polariton dispersion
measurements and polariton dynamics analysis, present a single TMDC nanotube as
a perfect polaritonic structure for nanophotonics.
Integer or fractional quantum Hall crystals, states postulating the
coexistence of charge order with integer or fractional quantum Hall effect,
have long been proposed in theoretical studies in Landau levels. Inspired by
recent experiments on integer or fractional quantum anomalous Hall (IQAH/FQAH)
states in MoTe2 and rhombohedral multilayer graphene, this work examines the
archetypal correlated flat band model on a checkerboard lattice at filling
{\nu} = 2/3. Interestingly, at this filling level, we find that this
topological flatband does not stabilize conventional FQAH states. Instead, the
unique interplay between smectic charge order and topological order gives rise
to two intriguing quantum states. As the interaction strength increases, the
system first transitions from a Fermi liquid into FQAH smectic (FQAHS) states,
where FQAH topological order coexists cooperatively with smectic charge order.
With a further increase in interaction strength, the system undergoes another
quantum phase transition and evolves into a polar smectic metal. Contrary to
conventional smectic order and FQAHS states, this gapless state spontaneously
breaks the two-fold rotational symmetry, resulting in a nonzero electric dipole
moment and ferroelectric order. In addition to identifying the ground states,
large-scale numerical simulations are also used to study low-energy excitations
and thermodynamic characteristics. We find that FQAHS states exhibit two
distinct temperature scales: the onset of charge order and the onset of the
fractional Hall plateau, respectively. Interestingly, the latter is dictated by
charge-neutral low-energy excitations with finite momenta, known as
magnetorotons. Our studies suggest that these nontrivial phenomena could, in
principle, be accessed in future experiments with moir\'e systems.
The interplay between lattice geometry, band topology and electronic
correlations in the newly discovered kagome compounds AV3Sb5 (A=K, Rb, Cs)
makes this family a novel playground to investigate emergent quantum phenomena,
such as unconventional superconductivity, chiral charge density wave and
electronic nematicity. These exotic quantum phases naturally leave nontrivial
fingerprints in transport properties of AV3Sb5, both in electrical and thermal
channels, which are prominent probes to uncover the underlying mechanisms. In
this brief review, we highlight the unusual electrical and thermal transport
properties observed in the unconventional charge ordered state of AV3Sb5,
including giant anomalous Hall, anomalous Nernst, ambipolar Nernst and
anomalous thermal Hall effects. Connections of these anomalous transport
properties to time-reversal symmetry breaking, topological and multiband
fermiology, as well as electronic nematicity, are also discussed. Finally, a
perspective together with challenges of this rapid growing field are given.
A recent study has demonstrated that a fermionic two-leg ladder model,
threaded by a flux and characterized by a spatially varying interleg hopping
term, gives rise to a quasiflat low-energy band. This band exhibits an unusual
ground state at half filling in the presence of interaction -- a ferromagnetic
Mott insulator. In this paper, we extend the study of this model to other
fillings of the quasiflat band and explore the magnetic properties of the
ground state at these fillings. In particular, we study four fillings:
one-quarter, three-quarters, slightly above half filling (half filling plus two
electrons), and slightly below half-filling (half filling minus two electrons).
Incorporating interaction within the Hubbard model and using the Density Matrix
Renormalization Group method to find the ground states, we find that the
spin-spin correlation is ferromagnetic at fillings less than half, similar to
that observed at half filling, but is antiferromagnetic beyond half filling.
Interestingly, these results hold only when mixing between the lowest quasiflat
band and the next-to-lowest dispersive band is negligible; once mixing between
the two bands is facilitated by increasing the interaction strength, the
correlation becomes ferromagnetic above half filling as well. Additionally, by
reducing the strength of the interaction in comparison to the bandwidth, a
transition from the ferromagnetic to the antiferromagnetic state is observed in
all the cases.
By virtue of being atomically thin, the electronic properties of
heterostructures built from two-dimensional materials are strongly influenced
by atomic relaxation where the atomic layers should be thought of as membranes
rather than rigid 2D crystals. We develop an analytical treatment of lattice
relaxation for twisted 2D moir\'e materials obtaining semi-analytical results
for lattice displacements, real and momentum space moir\'e potentials,
pseudomagnetic fields and electronic band structures. We benchmark our results
for twisted bilayer graphene and twisted homobilayers of tungsten diselenide
using large-scale molecular dynamics simulations finding that our theory is
valid for magic angle twisted bilayer graphene (angles $\gtrsim 1^\circ$), and
for twisted TMDs for twist angles $\gtrsim$ 7 degrees.
Higher-order cellular automata (HOCA) are a type of cellular automata that
evolve over multiple time steps. These HOCA generate intricate patterns within
the spacetime lattice, which can be utilized to create symmetry-protected
topological (SPT) phases. The symmetries of these phases are not global, but
act on lower-dimensional subsystems of the lattice, such as lines or fractals.
These are referred to as HOCA generated SPT (HGSPT) phases. These phases
naturally encompass previously studied phases with subsystem symmetries,
including symmetry-protected topological phases protected by symmetries
supported on regular (e.g., line-like, membrane-like) and fractal subsystems.
Moreover, these phases include models with subsystem symmetries that extend
beyond previously studied phases. They include mixed-subsystem SPT (MSPT) that
possess two types of subsystem symmetries simultaneously (for example, fractal
and line-like subsystem symmetries or two different fractal symmetries), and
chaotic SPT (CSPT) that have chaos-like symmetries, beyond the classification
of fractal or regular subsystems. We propose that each HOCA pattern with a
finite initial condition can be represented by a mathematical object $X=(d,M)$,
and HOCA rules $\mathbf{f}$ can be categorized into different classes
$[\mathbf{f}]$ based on the pattern that the rule can generate. The class of
the HOCA rule of a given HGSPT can be identified by what we dub as the
multi-point strange correlator, as a generalization of the strange correlator.
We have raised a general procedure to construct multi-point strange correlators
to detect the nontrivial SPT orders in the gapped ground states of HGSPT models
and the their classes.
We consider a Josephson junction built with the two-dimensional semi-Dirac
semimetal, which features a hybrid of linear and quadratic dispersion around a
nodal point. We model the weak link between the two superconducting regions by
a Dirac delta potential because it mimics the thin-barrier limit of a
superconductor-barrier-superconductor configuration. Assuming a homogeneous
pairing in each region, we set up the BdG formalism for electronlike and
holelike quasiparticles propagating along the quadratic-in-momentum dispersion
direction. This allows us to compute the discrete bound-state energy spectrum
$\varepsilon $ of the subgap Andreev states localized at the junction. In
contrast with the Josephson effect investigated for propagation along linearly
dispersing directions, we find a pair of doubly degenerate Andreev bound
states. Using the dependence of $\varepsilon $ on the superconducting phase
difference $\phi$, we compute the variation of Josephson current as a function
of $\phi$.
The kagome lattice is an exciting solid state physics platform for the
emergence of nontrivial quantum states driven by electronic correlations:
topological effects, unconventional superconductivity, charge and spin density
waves, and unusual magnetic states such as quantum spin liquids. While kagome
lattices have been realized in complex multi-atomic bulk compounds, here we
demonstrate from first-principles a process that we dub kagomerization, in
which we fabricate a two-dimensional kagome lattice in monolayers of transition
metals utilizing a hexagonal boron nitride (h-BN) overlayer. Surprisingly, h-BN
induces a large rearrangement of the transition metal atoms supported on a
fcc(111) heavy-metal surface. This reconstruction is found to be rather generic
for this type of heterostructures and has a profound impact on the underlying
magnetic properties, ultimately stabilizing various topological magnetic
solitons such as skyrmions and bimerons. Our findings call for a
reconsideration of h-BN as merely a passive capping layer, showing its
potential for not only reconstructing the atomic structure of the underlying
material, e.g. through the kagomerization of magnetic films, but also enabling
electronic and magnetic phases that are highly sought for the next generation
of device technologies.
We demonstrate that non-Hermitian perturbations can probe topological phase
transitions and unambiguously detect non-Abelian zero modes. We show that under
carefully designed non-Hermitian perturbations, the Loschmidt echo(LE) decays
into 1/N where N is the ground state degeneracy in the topological non-trivial
phase, while it approaches 1 in the trivial phase. This distinction is robust
against small parameter deviations in the non-Hermitian perturbations. We
further study four well-known models that support Majorana or parafermionic
zero modes. By calculating their dynamical responses to specific non-Hermitian
perturbations, we prove that the steady-state LE can indeed differentiate
between different phases. This method avoids the ambiguity introduced by
trivial zero-energy states and thus provides an alternative and promising way
to demonstrate the emergence of topologically non-trivial phases. The
experimental realizations of non-Hermitian perturbations are discussed.
We present measurements and theoretical modeling demonstrating the capability
of Doppler Broadened annihilation gamma Spectroscopy (DBS) to provide
element-specific information from the topmost atomic layer of surfaces that are
either clean or covered with adsorbates or thin films. Our measurements show
that the energy spectra of Doppler-shifted annihilation gamma photons emitted
following the annihilation of positrons from the topmost atomic layers of clean
gold (Au) and copper (Cu) differ significantly. With the aid of the positron
annihilation-induced Auger electron spectroscopy (PAES) performed
simultaneously with DBS, we show that measurable differences between the
Doppler broadened gamma spectra from Au and Cu surfaces in the high energy
region of the gamma spectra can be used for the quantification of surface
chemical composition. Modeling the measured Doppler spectra from clean Au and
Cu surfaces using gamma spectra obtained from ab initio calculations after
considering the detector energy resolution and surface positronium formation
pointed to an increase in the relative contribution of gamma from positron
annihilation with valence shell electrons. The fit result also suggests that
the surface-trapped positrons predominantly annihilated with the delocalized
valence shell (s and p) electrons that extended into the vacuum as compared to
the highly localized d electrons. Simultaneous DBS and PAES measurements from
adsorbate (sulfur, oxygen, carbon) or thin film (selenium (Se), graphene)
covered Cu surface showed that it is possible to distinguish and quantify the
surface adsorbate and thin-film composition just based on DBS. DBS of elemental
surfaces presents a promising avenue for developing a characterization tool
that can be used to probe external and internal surfaces that are inaccessible
by conventional surface science techniques.
Nonlinear charge transport, including nonreciprocal longitudinal resistance
and nonlinear Hall effect, has garnered significant attention due to its
ability to explore inherent symmetries and topological properties of novel
materials. An exciting recent progress along this direction is the discovery of
significant nonreciprocal longitudinal resistance and nonlinear Hall effect in
the intrinsic magnetic topological insulator MnBi2Te4 induced by the quantum
metric dipole. Given the importance of this finding, the inconsistent response
with charge density, and conflicting requirement of C3z symmetry, it is
imperative to elucidate every detail that may impact the nonlinear transport
measurement. In this study, we reveal an intriguing experimental factor that
inevitably gives rise to sizable nonlinear transport signal in MnBi2Te4. We
demonstrate that this effect stems from the gate voltage oscillation caused by
the application of a large alternating current to the sample. Furthermore, we
propose a methodology to significantly suppress this effect by individually
grounding the voltage electrodes during the second-harmonic measurements. Our
investigation emphasizes the critical importance of thoroughly assessing the
impact of gate voltage oscillation before determining the intrinsic nature of
nonlinear transport in all 2D material devices with an electrically connected
operative gate electrode.
In planar superconductor thin films, the places of nucleation and
arrangements of moving vortices are determined by structural defects. However,
various applications of superconductors require reconfigurable steering of
fluxons, which is hard to realize with geometrically predefined vortex pinning
landscapes. Here, on the basis of the time-dependent Ginzburg-Landau equation,
we present an approach for steering of vortex chains and vortex jets in
superconductor nanotubes containing a slit. The idea is based on tilting of the
magnetic field $\mathbf{B}$ at an angle $\alpha$ in the plane perpendicular to
the axis of a nanotube carrying an azimuthal transport current. Namely, while
at $\alpha=0^\circ$ vortices move paraxially in opposite directions within each
half-tube, an increase of $\alpha$ displaces the areas with the
close-to-maximum normal component $|B_\mathrm{n}|$ to the
close(opposite)-to-slit regions, giving rise to descending (ascending) branches
in the induced-voltage frequency spectrum $f_\mathrm{U}(\alpha)$. At lower $B$,
upon reaching the critical angle $\alpha_\mathrm{c}$, close-to-slit vortex
chains disappear, yielding $f_\mathrm{U}$ of the $nf_1$-type ($n\geq1$: an
integer; $f_1$: vortex nucleation frequency). At higher $B$, $f_\mathrm{U}$ is
largely blurry because of multifurcations of vortex trajectories, leading to
the coexistence of a vortex jet with two vortex chains at $\alpha=90^\circ$. In
addition to prospects for tuning of GHz-frequency spectra and steering of
vortices as information bits, our findings lay foundations for on-demand tuning
of vortex arrangements in 3D superconductor membranes in tilted magnetic
fields.
Magnetization dynamics in magnetic materials are well described by the
modified semiclassical Landau-Lifshitz-Gilbert (LLG) equation, which includes
the magnetic damping $\alpha$ and the magnetic moment of inertia $\mathrm{I}$
tensors as key parameters. Both parameters are material-specific and physically
represent the time scales of damping of precession and nutation in
magnetization dynamics. $\alpha$ and $\mathrm{I}$ can be calculated quantum
mechanically within the framework of the torque-torque correlation model. The
quantities required for the calculation are torque matrix elements, the real
and imaginary parts of the Green's function and its derivatives. Here, we
calculate these parameters for the elemental magnets such as Fe, Co and Ni in
an ab initio framework using density functional theory and Wannier functions.
We also propose a method to calculate the torque matrix elements within the
Wannier framework. We demonstrate the effectiveness of the method by comparing
it with the experiments and the previous ab initio and empirical studies and
show its potential to improve our understanding of spin dynamics and to
facilitate the design of spintronic devices.
Recent advances in ultrafast electron emission, microscopy, and diffraction
reveal our capacity to manipulate free electrons with remarkable quantum
coherence using light beams. Here, we present a framework for exploring free
electron fractional charge in ultrafast electron-light interactions. An
explicit Jackiw-Rebbi solution of free electron is constructed by a
spatiotemporally twisted laser field, showcasing a flying topological quantum
number with a fractional charge of e/2 (we call it "half-electron"), which is
dispersion-free due to its topological nature. We also propose an Aharonov-Bohm
interferometry for detecting these half-electrons. The half-electron is a
topologically protected bound state in free-space propagation, expands its
realm beyond quasiparticles with fractional charges in materials, enabling to
advance our understanding of exotic quantum and topological effects of free
electron wavefunction.
We identify two-dimensional three-state Potts paramagnets with gapless edge
modes on a triangular lattice protected by $(\times Z_3)^3\equiv Z_3\times
Z_3\times Z_3$ symmetry and smaller $Z_3$ symmetry. We derive microscopic
models for the gapless edge, uncover their symmetries, and analyze the
conformal properties. We study the properties of the gapless edge by employing
the numerical density-matrix renormalization group (DMRG) simulation and exact
diagonalization. We discuss the corresponding conformal field theory, its
central charge, and the scaling dimension of the corresponding primary field.
We argue that the low energy limit of our edge modes is defined by the
$SU_k(3)/SU_k(2)$ coset conformal field theory with the level $k=2$. The
discussed two-dimensional models realize a variety of symmetry-protected
topological phases, opening a window for studies of the unconventional quantum
criticalities between them.
Superconducting circuits are an extremely versatile platform to realize
quantum information hardware and to emulate topological materials. We here show
how a simple arrangement of capacitors and conventional
superconductor-insulator-superconductor junctions can realize an even broader
class of systems, in the form of a nonlinear capacitive element which is
quasiperiodic with respect to the quantized Cooper-pair charge. Our setup
allows to create protected Dirac points defined in the transport degrees of
freedom, whose presence leads to a suppression of the classical
finite-frequency current noise. Furthermore, the quasiperiodicity can emulate
Anderson localization in charge space, measurable via vanishing charge quantum
fluctuations. The realization by means of the macroscopic transport degrees of
freedom allows for a straightforward generalization to arbitrary dimensions and
implements truly non-interacting versions of the considered models. As an
outlook, we discuss potential ideas to simulate a transport version of the
magic-angle effect known from twisted bilayer graphene.
Recent experiments have confirmed the presence of interlayer excitons in the
ground state of transition metal dichalcogenide (TMD) bilayers. The interlayer
excitons are expected to show remarkable transport properties when they undergo
Bose condensation. In this work, we demonstrate that quantum geometry of Bloch
wavefunctions plays an important role in the phase stiffness of the Interlayer
Exciton Condensate (IEC). Notably, we identify a geometric contribution that
amplifies the stiffness, leading to the formation of a robust condensate with
an increased BKT temperature. Our results have direct implications for the
ongoing experimental efforts on interlayer excitons in materials that have
non-trivial quantum geometry. We provide quantitative estimates for the
geometric contribution in TMD bilayers through a realistic continuum model with
gated Coulomb interaction, and find that the substantially increased stiffness
allows for an IEC to be realized at amenable experimental conditions.
In our previous work, we synthesized a metal/2D material heterointerface
consisting of $L1_0$-ordered iron-palladium (FePd) and graphene (Gr) called
FePd(001)/Gr. This system has been explored by both experimental measurements
and theoretical calculations. In this study, we focus on a heterojunction
composed of FePd and multilayer graphene referred to as
FePd(001)/$m$-Gr/FePd(001), where $m$ represents the number of graphene layers.
We perform first-principles calculations to predict their spin-dependent
transport properties. The quantitative calculations of spin-resolved
conductance and magnetoresistance (MR) ratio (150-200%) suggest that the
proposed structure can function as a magnetic tunnel junction in spintronics
applications. We also find that an increase in $m$ not only reduces conductance
but also changes transport properties from the tunneling behavior to the
graphite $\pi$-band-like behavior. Additionally, we investigate the
spin-transfer torque-induced magnetization switching behavior of our
\color{blue} junction structures \color{black} using micromagnetic simulations.
Furthermore, we examine the impact of lateral displacements (``sliding'') at
the interface and find that the spin transport properties remain robust despite
these changes; this is the advantage of two-dimensional material
hetero-interfaces over traditional insulating barrier layers such as MgO.
We investigate symmetry breaking in the Dirac fermion phase of the organic
compound $\alpha$-(BEDT-TTF)$_2$I$_3$ under pressure, where BEDT-TTF denotes
bis(ethylenedithio)tetrathiafulvalene. The exchange interaction resulting from
inter-molecule Coulomb repulsion leads to broken time-reversal symmetry and
particle-hole symmetry while preserving translational symmetry. The system
breaks time-reversal symmetry by creating fluxes in the unit cell. This
symmetry-broken state exhibits a large Nernst signal as well as thermopower. We
compute the Nernst signal and thermopower, demonstrating their consistency with
experimental results.
Spin-current density functional theory (SCDFT) is a formally exact framework
designed to handle the treatment of interacting many-electron systems including
spin-orbit coupling at the level of the Pauli equation. In practice, robust and
accurate calculations of the electronic structure of these systems call for
functional approximations that depend not only on the densities, but also on
spin-orbitals. Here we show that the call can be answered by resorting to an
extension of the Kohn-Sham formalism, which admits the use of non-local
effective potentials, yet it is firmly rooted in SCDFT. The power of the
extended formalism is demonstrated by calculating the spin-orbit-induced
band-splittings of inversion-asymmetric MoSe$_2$ monolayer and
inversion-symmetric bulk $\alpha$-MoTe$_2$. We show that quantitative agreement
with experimental data is obtainable via global hybrid approximations by
setting the fraction of Fock exchange at the same level which yields accurate
values of the band gap. Key to these results is the ability of the method to
self-consistently account for the spin currents induced by the spin-orbit
interaction. The widely used method of refining spin-density functional theory
by a second-variational treatment of spin-orbit coupling is unable to match our
SCDFT results.
In this paper, we investigate different thermodynamic properties of
$T\bar{T}+J\bar{T }$ deformed 2D-gravity. First, we compute the partition
function of $U(1)$ coupled 2D-gravity with fixed chemical potential, obtained
from the dimensional reduction of the four-dimensional Einstein-Maxwell theory.
Then, we compute the partition function of the deformed theory and study the
genus expansion of the one and two-point correlation function of the partition
function of the theory. Subsequently, we use the one-point function to compute
the ``Annealed'' and ``Quenched'' free energy in low-temperature limits and
make a qualitative comparison with the undeformed theory. Then, using the
two-point function, we compute the Spectral Form Factor of the deformed theory
in early and late time. We find a dip and ramp structure in early and late
time, respectively. We also get a plateau structure in the $\tau$-scaling
limit. Last but not least, we comment on the late-time topology change to give
a physical interpretation of the ramp of the Spectral Form Factor for our
theory.
The concept of torsion in geometry, although known for a long time, has not
gained considerable attention by the physics community until relatively
recently, due to its diverse and potentially important applications to a
plethora of contexts of physical interest. These range from novel materials,
such as graphene and graphene-like materials, to advanced theoretical ideas,
such as string theory and supersymmetry/supergravity and applications thereof
in understanding the dark sector of our Universe. This work reviews such
applications of torsion at different physical scales.
Neuromorphic devices have gained significant attention as potential building
blocks for the next generation of computing technologies owing to their ability
to emulate the functionalities of biological nervous systems. The essential
components in artificial neural network such as synapses and neurons are
predominantly implemented by dedicated devices with specific functionalities.
In this work, we present a gate-controlled transition of neuromorphic functions
between artificial neurons and synapses in monolayer graphene transistors that
can be employed as memtransistors or synaptic transistors as required. By
harnessing the reliability of reversible electrochemical reactions between C
atoms and hydrogen ions, the electric conductivity of graphene transistors can
be effectively manipulated, resulting in high on/off resistance ratio,
well-defined set/reset voltage, and prolonged retention time. Overall, the
on-demand switching of neuromorphic functions in a single graphene transistor
provides a promising opportunity to develop adaptive neural networks for the
upcoming era of artificial intelligence and machine learning.
Nonlinear optics lies at the heart of classical and quantum light generation.
The invention of periodic poling revolutionized nonlinear optics and its
commercial applications by enabling robust quasi-phase-matching in crystals
such as lithium niobate. However, reaching useful frequency conversion
efficiencies requires macroscopic dimensions, limiting further technology
development and integration. Here we realize a periodically poled van der Waals
semiconductor (3R-MoS$_2$). Due to its exceptional nonlinearity, we achieve
macroscopic frequency conversion efficiency over a microscopic thickness of
only 1.2${\mu}$m, $10-100\times$ thinner than current systems with similar
performances. Due to unique intrinsic cavity effects, the thickness-dependent
quasi-phase-matched second harmonic signal surpasses the usual quadratic
enhancement by $50\%$. Further, we report the broadband generation of photon
pairs at telecom wavelengths via quasi-phase-matched spontaneous parametric
down-conversion. This work opens the new and unexplored field of phase-matched
nonlinear optics with microscopic van der Waals crystals, unlocking
applications that require simple, ultra-compact technologies such as on-chip
entangled photon-pair sources for integrated quantum circuitry and sensing.
A recent theory described strange metal behavior in a model of a Fermi
surface coupled a two-dimensional quantum critical bosonic scalar field with a
spatially random Yukawa coupling. With the assumption of self-averaging
randomness, similar to that in the Sachdev-Ye-Kitaev model, numerous observed
properties of a strange metal were obtained for wide range of intermediate
temperatures, including the linear-in-temperature resistivity. The Harris
criterion implies that spatial fluctuations in the local position of the
critical point must dominate at low temperatures, and these were not fully
accounted for in the recent theory. We use multiple graphics processing units
to compute the real frequency spectrum of the boson propagator in a
self-consistent mean-field treatment of the boson self-interactions, but an
exact treatment of multiple realizations of the spatial randomness from the
random boson mass. We find that Landau damping from the fermions leads to
behavior consistent with the emergence of the physics of the random
transverse-field Ising model, as has been proposed by Hoyos, Kotabage, and
Vojta. This emergent low temperature regime, controlled by localized overdamped
eigenmodes of the bosonic scalar field, also has a resistivity which is nearly
linear-in-temperature, and extends into a `quantum critical phase' away from
the quantum critical point, as observed in several cuprates.
We reveal that optical saturation of the low-energy states takes place in
graphene for arbitrarily weak electromagnetic fields. This effect originates
from the diverging field-induced interband coupling at the Dirac point. Using
semiconductor Bloch equations to model the electronic dynamics of graphene, we
argue that the charge carriers undergo ultrafast Rabi oscillations leading to
the anomalous saturation effect. The theory is complemented by a many-body
study of the carrier relaxations dynamics in graphene. It will be demonstrated
that the carrier relaxation dynamics is slow around the Dirac point, which in
turn leads to a more pronounced saturation. The implications of this effect to
the nonlinear optics of graphene is then discussed. Our analysis show that the
conventional perturbative treatment of the nonlinear optics, i.e., expanding
the polarization field in a Taylor series of the electric field, is problematic
for graphene, in particular at small Fermi levels and large field amplitudes.

Date of feed: Tue, 02 Jan 2024 01:30:00 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) **Optoelectronic Readout of single Er Adatom's Electronic States Adsorbed on the Si(100) Surface at Low Temperature (9K). (arXiv:2401.00034v1 [physics.app-ph])**

Eric Duverger, Damien Riedel

**Many-body higher-order topological invariant for $C_n$-symmetric insulators. (arXiv:2401.00050v1 [cond-mat.str-el])**

Ammar Jahin, Yuan-Ming Lu, Yuxuan Wang

**Absence of Weyl nodes in EuCd$_2$As$_2$ revealed by the carrier density dependence of the anomalous Hall effect. (arXiv:2401.00138v1 [cond-mat.mtrl-sci])**

Yue Shi, Zhaoyu Liu, Logan A. Burnett, Seokhyeong Lee, Chaowei Hu, Qianni Jiang, Jiaqi Cai, Xiaodong Xu, Cheng-Chien Chen, Jiun-Haw Chu

**Coarsening of topological defects in 2D polar active matter. (arXiv:2401.00203v1 [cond-mat.soft])**

Soumyadeep Mondal, Pankaj Popli, Sumantra Sarkar

**Edge and bulk states in Weyl-orbit quantum Hall effect as studied by Corbino measurements. (arXiv:2401.00224v1 [cond-mat.mes-hall])**

Yusuke Nakazawa, Ryosuke Kurihara, Masatoshi Miyazawa, Shinichi Nishihaya, Markus Kriener, Masashi Tokunaga, Masashi Kawasaki, Masaki Uchida

**Strain induced electronic and magnetic transition in S = 3/2 antiferromagnetic spin chain compound LaCrS3. (arXiv:2401.00239v1 [cond-mat.str-el])**

Kuldeep Kargeti, Aadit Sen, S. K. Panda

**The Impact of Thermosolutal Convection on Melting Dynamics of Nano-enhanced Phase Change Materials (NePCM). (arXiv:2401.00251v1 [physics.flu-dyn])**

Yousef El Hasadi

**An unconventional platform for two-dimensional Kagome flat bands on semiconductor surfaces. (arXiv:2401.00265v1 [cond-mat.mtrl-sci])**

Jae Hyuck Lee, GwanWoo Kim, Inkyung Song, Yejin Kim, Yeonjae Lee, Sung Jong Yoo, Deok-Yong Cho, Jun-Won Rhim, Jongkeun Jung, Gunn Kim, Changyoung Kim

**Dynamics of oscillator populations with disorder in the coupling phase shifts. (arXiv:2401.00281v1 [nlin.AO])**

Arkady Pikovsky, Franco Bagnoli

**Pairing Symmetry and Fermion Projective Symmetry Groups. (arXiv:2401.00321v1 [cond-mat.supr-con])**

Xu Yang, Shuangyuan Lu, Sayak Biswas, Mohit Randeria, Yuan-Ming Lu

**Direct observation of split-mode exciton-polaritons in a single MoS$_2$ nanotube. (arXiv:2401.00348v1 [cond-mat.mes-hall])**

A.I. Galimov, D.R. Kazanov, A.V. Poshakinskiy, M.V. Rakhlin, I.A. Eliseyev, A.A. Toropov, M. Remskar, T.V. Shubina

**From Fractional Quantum Anomalous Hall Smectics to Polar Smectic Metals: Nontrivial Interplay Between Electronic Liquid Crystal Order and Topological Order in Correlated Topological Flat Bands. (arXiv:2401.00363v1 [cond-mat.str-el])**

Hongyu Lu, Han-Qing Wu, Bin-Bin Chen, Kai Sun, Zi Yang Meng

**Electrical and thermal transport properties of kagome metals AV3Sb5 (A=K, Rb, Cs). (arXiv:2401.00410v1 [cond-mat.str-el])**

Xinrun Mi, Kunya Yang, Yuhan Gan, Long Zhang, Aifeng Wang, Yisheng Chai, Xiaoyuan Zhou, Mingquan He

**Magnetic properties at various fillings of the quasiflat band in a fermionic two-leg ladder model. (arXiv:2401.00483v1 [cond-mat.str-el])**

Paban Kumar Patra, Yixuan Huang, Hridis K. Pal

**Analytical Model for Atomic Relaxation in Twisted Moir\'e Materials. (arXiv:2401.00498v1 [cond-mat.str-el])**

Mohammed M. Al Ezzi, Gayani N. Pallewela, Shaffique Adam

**Higher-Order Cellular Automata Generated Symmetry-Protected Topological Phases and Detection Through Multi-Point Strange Correlators. (arXiv:2401.00505v1 [cond-mat.str-el])**

Jie-Yu Zhang, Meng-Yuan Li, Peng Ye

**Andreev bound states in Josephson junctions of semi-Dirac semimetals. (arXiv:2401.00506v1 [cond-mat.supr-con])**

Ipsita Mandal

**Kagomerization of transition metal monolayers induced by two-dimensional hexagonal boron nitride. (arXiv:2401.00516v1 [cond-mat.mtrl-sci])**

Hangyu Zhou, Manuel dos Santos Dias, Youguang Zhang, Weisheng Zhao, Samir Lounis

**Probing topological phase transition with non-Hermitian perturbations. (arXiv:2401.00530v1 [quant-ph])**

Jingcheng Liang, Chen Fang, Jiangping Hu

**Measurement and analysis of the Doppler broadened energy spectra of annihilation gamma radiation originating from clean and adsorbate-covered surfaces. (arXiv:2401.00581v1 [cond-mat.other])**

S. Lotfimarangloo, V. A. Chirayath, P. A. Sterne, H. Mahdy, R. W. Gladen, J. Driscoll, M. Rooks, M. Chrysler, A. R. Koymen, J. Asaadi, A. H. Weiss

**Nonlinear charge transport induced by gate voltage oscillation in few-layer MnBi2Te4. (arXiv:2401.00679v1 [cond-mat.mtrl-sci])**

Liangcai Xu, Zichen Lian, Yongchao Wang, Xinlei Hao, Shuai Yang, Chang Liu, Yang Feng, Yayu Wang, Jinsong Zhang

**Steering of vortices by magnetic-field tilting in superconductor nanotubes. (arXiv:2401.00712v1 [cond-mat.supr-con])**

Igor Bogush, Oleksandr V. Dobrovolskiy, Vladimir M. Fomin

**Calculation of Gilbert damping and magnetic moment of inertia using torque-torque correlation model within ab initio Wannier framework. (arXiv:2401.00714v1 [cond-mat.mtrl-sci])**

Robin Bajaj, Seung-Cheol Lee, H. R. Krishnamurthy, Satadeep Bhattacharjee, Manish Jain

**"half-electron (e/2)" -- free electron fractional charge induced by twisted light. (arXiv:2401.00723v1 [quant-ph])**

Yiming Pan, Ruoyu Yin, Yongcheng Ding, Daniel Podolsky, Bin Zhang

**$Z_3$ and $(\times Z_3)^3$ symmetry protected topological paramagnets. (arXiv:2210.01187v4 [cond-mat.str-el] UPDATED)**

Hrant Topchyan, Vasilii Iugov, Mkhitar Mirumyan, Shahane A. Khachatryan, Tigran S. Hakobyan, Tigran A. Sedrakyan

**Quasiperiodic circuit quantum electrodynamics. (arXiv:2212.12382v2 [cond-mat.mes-hall] UPDATED)**

Tobias Herrig, Jedediah H. Pixley, Elio J. König, Roman-Pascal Riwar

**Geometric Stiffness in Interlayer Exciton Condensates. (arXiv:2307.01253v2 [cond-mat.mes-hall] UPDATED)**

Nishchhal Verma, Daniele Guerci, Raquel Queiroz

**First-principle study of spin transport property in $L1_0$-FePd(001)/graphene heterojunction. (arXiv:2308.02171v5 [cond-mat.mtrl-sci] UPDATED)**

Hayato Adachi, Ryuusuke Endo, Hikari Shinya, Hiroshi Naganuma, Tomoya Ono, Mitsuharu Uemoto

**Time-reversal symmetry-breaking flux state in an organic Dirac fermion system. (arXiv:2308.11141v2 [cond-mat.str-el] UPDATED)**

Takao Morinari

**Generalized Kohn-Sham Approach for the Electronic Band Structure of Spin-Orbit Coupled Materials. (arXiv:2309.11158v2 [cond-mat.mtrl-sci] UPDATED)**

Jacques K. Desmarais, Giacomo Ambrogio, Giovanni Vignale, Alessandro Erba, Stefano Pittalis

**Aspects of $T\bar{T}+J\bar{T }$ deformed 2D topological gravity : from partition function to late-time SFF. (arXiv:2309.16658v3 [hep-th] UPDATED)**

Arpan Bhattacharyya, Saptaswa Ghosh, Sounak Pal

**Torsion at different scales: from materials to the Universe. (arXiv:2310.13150v3 [gr-qc] UPDATED)**

Nick E. Mavromatos, Pablo Pais, Alfredo Iorio

**Gate-controlled neuromorphic functional transition in an electrochemical graphene transistor. (arXiv:2312.04934v2 [physics.app-ph] UPDATED)**

Chenglin Yu, Shaorui Li, Zhoujie Pan, Yanming Liu, Yongchao Wang, Siyi Zhou, Zhiting Gao, He Tian, Kaili Jiang, Yayu Wang, Jinsong Zhang

**Quasi-phase-matched up- and down-conversion in periodically poled layered semiconductors. (arXiv:2312.05444v2 [physics.optics] UPDATED)**

Chiara Trovatello, Carino Ferrante, Birui Yang, Josip Bajo, Benjamin Braun, Xinyi Xu, Zhi Hao Peng, Philipp K. Jenke, Andrew Ye, Milan Delor, D. N. Basov, Jiwoong Park, Philip Walther, Lee A. Rozema, Cory Dean, Andrea Marini, Giulio Cerullo, P. James Schuck

**Localization of overdamped bosonic modes and transport in strange metals. (arXiv:2312.06751v2 [cond-mat.str-el] UPDATED)**

Aavishkar A. Patel, Peter Lunts, Subir Sachdev

**Anomalous optical saturation of low-energy Dirac states in graphene and its implication for nonlinear optics. (arXiv:1806.10123v2 [cond-mat.mes-hall] CROSS LISTED)**

Behrooz Semnani, Roland Jago, Safieddin Safavi-Naeini, Amir Hamed Majedi, Ermin Malic, Philippe Tassin

Found 2 papers in comm-phys **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) **Synthesizing 2 h/e^{2} resistance plateau at the first Landau level confined in a quantum point contact**

Yoshiro Hirayama

Communications Physics, Published online: 20 December 2023; doi:10.1038/s42005-023-01491-8

In the quantum Hall regime, electrical current flows along the edges in a chiral fashion and they determine the Hall resistance plateaus. This work reports on experiments on fractional and integer quantum Hall edge channel mixing in a quantum point contact, which lead to unexpectedly anomalous resistance plateaus, shedding light onto the edge reconstruction and equilibration processes. Communications Physics, Published online: 20 December 2023; doi:10.1038/s42005-023-01447-y Transition metal dichalcogenide-based photovoltaics offer the prospect of increased specific power compared to incumbent solar technologies but there are engineering challenges that come with integrating these materials into high-efficiency devices. Here, the authors develop a model to describe the relationship between material quality and the performance limits of single junction solar cells built with various transition metal dichalcogenides. |