It is predicted that a vortex in a topological superconductor contains a Majorana zero mode (MZM). The confirmative Majorana signature, i.e., the $2e^2/h$ quantized conductance, however, is easily sabotaged by unavoidable interruptions, e.g., instrument broadening, non-Majorana signal, and extra particle channels. To avoid these interruptions, we propose to obtain strong Majorana evidence following our novel Majorana hunting protocol that relies on dissipation introduced by disorders at, e.g., the sample-substrate interface. Within this protocol, we highlight three features, each of which alone can provide a strong evidence to identify MZM. First, dissipation suppresses a finite-energy Caroli-de Gennes-Matricon (CdGM) conductance peak into a valley, while it does not split MZM zero-bias conductance peak (ZBCP). Second, we predict a dissipation-dependent scaling feature of the ZBCP. Third, the introduced dissipation manifests the MZM signal by suppressing nontopological CdGM modes. Importantly, the observation of these features does not require a quantized conductance value $2e^2/h$.

Long-range aperiodically ordered dodecagonal oxide quasicrystals (OQCs) have been observed on Pt(111), together with a variety of related approximants. All structures contain barium, titanium, and oxygen atoms in ${\mathrm{Ti}}_n{\mathrm{O}}_n$ ring structures with rings of $n$ = 4, 7, and 10. Barium decorates the larger rings and forms a dodecagonal square-triangle-rhombus tiling. In contrast to these studies on Pt(111), we report here on Ba-Ti-O layers on Pd(111), which has a 1% smaller lattice constant than Pt(111). We find a series of quasicrystal approximants with unit cells consisting of up to 60 triangles, 22 squares, and eight rhombuses. The latter resembles the largest quasicrystal approximant reported to date. The basis for these structures are local patches of the $\sigma$-phase square-triangle approximant, into which rhombuses are incorporated due to the formation of ordered antiphase domain boundaries in two orthogonal directions. A structural phase diagram of all quasicrystal approximants on Pd(111) system is presented.

We study the origin of the anomalous spin resonance detected electrically in a strongly correlated two-dimensional electron system. Such resonance reveals itself around nominally nonmagnetic even filling factors $\nu$ of the integer quantum Hall effect and is a consequence of strong electron-electron interactions. We directly demonstrate that while the spin resonance at odd $\nu$ manifests itself as an increase in the longitudinal resistance of the two-dimensional channel induced by the usual heating due to the radiation absorption, the anomalous resonance around even fillings is detected as a drop in the resistance, as if the electron system is cooled. In contrast, if the magnetic field is tilted so that the ground state of the system becomes ferromagnetic at even $\nu$, the spin resonance around even fillings turns to a more conventional “heating”-like behavior. Analysis of both the evolution of the spin resonance with increasing tilt angle and the measured temperature dependencies allowed us to put forth a possible mechanism of anomalous spin resonance around even fillings that qualitatively explains all of the puzzling experimental findings.

The Seebeck coefficient, which is proportional to a ratio of the thermoelectric conductivity to electrical conductivity, has been examined for Dirac electrons in the organic conductor $\alpha$-(BEDT-TTF)${}_2{\mathrm{I}}_3$ [BEDT-TTF denotes a molecule given by bis(ethylenedithio)tetrathiafulvalene] under a uniaxial pressure using a two-dimensional tight-binding model with both impurity and electron-phonon (e-p) scatterings. We calculate an anomalous temperature ($T$) dependence of the Seebeck coefficient $S_{\nu }$ with $\nu =x$ (perpendicular to the molecular stacking axis) and $y$, which shows $S_{\nu }>0$ with a maximum at high temperatures and $S_{\nu }<0$ with a minimum at low temperatures. The microscopic mechanism of such a sign change of $S_{\nu }$ is clarified in terms of the spectral conductivity. The result is compared with experiments on $\alpha$-(BEDT-TTF)${}_2{\mathrm{I}}_3$.

The formation of pseudomagnetic fields is a well-known consequence due to lattice strain, which has considerable effects on the electronic properties of graphene. To this end, strain engineering remains an effective route to enable unconventional electronic properties. Particularly, pseudomagnetic fields due to compressive strain have demonstrated unique advantages such as remarkably high intensities at relatively low magnitude of strains (e.g., < 5%) in several experiments. For example, pseudomagnetic fields as high as 300 T have been observed in buckled graphene nanobubbles. Recently, strong pseudomagnetic fields as high as 108 T have been measured in periodically buckled monolayer graphene, responsible for its band flattening and correlated states. Nevertheless, the general features and sensitivities of compressive strain-induced pseudomagnetic fields have been rarely explored, posing challenges for realizing their full potential. In this paper, we carry out large-scale molecular dynamics simulations to explore the properties of pseudomagnetic fields in buckled graphene nanobubbles, which are the basic representative graphene structures under compressive strains. We reveal that compressive strain can induce strong and sensitive pseudomagnetic fields for a variety of nanobubble shapes and boundary relaxation conditions. We also discuss the effect of the microscopy probe tip, which is frequently used to tune the morphologies and strain patterns. These results may offer guidance for designing electronic two-dimensional structures enabled by compressive strain engineering.

Recently topological states of matter have witnessed a new physical phenomenon where both edge modes and gapless bulk coexist at topological quantum criticality. The presence and absence of edge modes on a critical line can lead to an unusual class of topological phase transition between the topological and nontopological critical phases. We explore the existence of this new class of topological phase transitions in a generic model representing the topological insulators and superconductors and we show that such transition occurs at a multicritical point, i.e., at the intersection of two critical lines. To characterize these transitions we reconstruct the theoretical frameworks, which include bound state solution of the Dirac equation, winding number, correlation factors, and scaling theory of the curvature function to work for the criticality. Critical exponents and scaling laws are discussed to distinguish between the multicritical points, which separate the critical phases. Entanglement entropy and its scaling in the real space provide further insights into the unique transition at criticality revealing the interplay between fixed point and critical point at the multicriticalities.

In low dimensions, the combined effects of interactions and quantum fluctuations can lead to dramatically new physics distinct from that existing in higher dimensions. Here, we investigate the electronic and optical properties of ${\mathrm{CeIr}}_3{\mathrm{B}}_2$, a quasione-dimensional (1D) Kondo lattice system, using $abinitio$ calculations. The Ce atoms in the hexagonal crystal structure form 1D chains along the $c$ axis, with extremely short Ce-Ce distances. The quasi-1D nature of the crystal structure is well reflected in its electronic structure. Extremely flat bands emerge within the $ab$ plane of the Brillouin zone, yielding sharp optical transitions in the corresponding optical conductivity. Our calculations indicate that these prominent peaks in the optical conductivity provide a clear signature of quasi-1D heavy fermion systems.

$\mathrm{HfS}_2|\mathrm{HfO}_2$ interfaces present a uniquely interesting study in band alignment. The band alignment between materials determines the viability of many electronic devices. We have modeled a variety of two-dimensional|three-dimensional (2D|3D) interfaces $\mathrm{HfS}_2|\mathrm{HfO}_2$ interfaces, showing that the band alignment can change substantially depending on the geometric alignment. Our results have shown that there exists almost no electronic reconstruction when layers of $\mathrm{HfS}_2$ are placed on a $\mathrm{HfO}_2$ substrate. Conversely, when the in-plane connection between $\mathrm{HfS}_2$ and $\mathrm{HfO}_2$ is made (lateral), there is a more significant interface reconstruction present. In the latter case, all examples considered yielded a type I alignment, whereas in the case that layers were parallel to the $\mathrm{HfO}_2$ substrate (stacked) we found that the alignment was either type I or type II with a very small difference between the valance band offsets of the two constituents. We show that the range in the barrier heights between these two systems can vary by up to 2.46 $\mathrm{e}\mathrm{V}$. This variation is driven by the amount of charge transfer across the interface and indicate that 2D|3D interfaces have considerably more tunability in their band alignment than 2D|2D or 3D|3D interfaces.

We consider coherent dynamics of graphene charged carriers exposed to an intense few-cycle linearly polarized laser pulse. The results, obtained by solving the generalized semiconductor Bloch equations numerically in the Hartree-Fock approximation, taking into account many-body Coulomb interaction, demonstrate strong dependence of the valley polarization on the carrier-envelope phase (CEP), which is interpolated by the simple sinusoidal law. Then we consider harmonic generation in a multicycle laser field by graphene preliminarily exposed to an intense few-cycle laser pulse. We show that the second harmonic's intensity is a robust observable quantity that provides a gauge of CEP for pulse durations up to two optical cycles, corresponding to 40 $\mathrm{fs}$ at the wavelength of 6.2 $\mu \mathrm{m}$.

The dispersion of any given material is crucial for its charge carriers' dynamics. For all-electronic, gate-defined cavities in gapped bilayer graphene, we developed a trajectory-tracing algorithm aware of the material's electronic properties and details of the confinement. We show how the anisotropic dispersion of bilayer graphene induces chaotic and regular dynamics depending on the gate voltage, despite the high symmetry of the circular cavity. Our results demonstrate the emergence of nonstandard fermion optics solely due to anisotropic material characteristics.

Signatures of nematic nodal superconductivity have been experimentally observed in magic angle twisted bilayer graphene (MATBG). Here, we propose a general topological mechanism explaining how a nematic pairing leads to nodal superconductivity in MATBG. By focusing on the intervalley $C_{2z}\mathcal{T}$-invariant Cooper pairing order parameter, we show that the pairing order parameter can always be split into a trivial channel and an Euler obstructed channel, owing to the nontrivial normal-state band topology. When the pairing is spontaneously nematic, we find that a sufficiently-dominant Euler obstructed channel with two zeros typically leads to nodal superconductivity. The mechanism is general since it is independent of the specific interaction that accounts for the required pairing. Under the approximation of exactly-flat bands, we analytically find that the mean-field zero-temperature superfluid weight is bounded from below, and thus the Berezinksii-Kosterlitz-Thouless (BKT) critical temperature can be nonzero, even if the Euler obstructed pairing is dominant. We also numerically find that a spontaneously-nematic dominant Euler obstructed pairing can arise from a local attractive interaction.

We use inelastic neutron scattering to study spin fluctuations in ${\mathrm{Sr}}_{1.8}{\mathrm{La}}_{0.2}{\mathrm{RuO}}_4$, where Lanthanum doping triggers a Lifshitz transition by pushing the van Hove singularity in the $\gamma$ band to the Fermi energy. Strong spin fluctuations emerge at an incommensurate wave vector ${\mathbf{Q}}_{ic}=(0.3,0.3)$, corresponding to the nesting vector between $\alpha$ and $\beta$ Fermi sheets. The incommensurate antiferromagnetic fluctuations shift toward (0.25,0.25) with increasing energy up to $\sim 110$ meV. By contrast, scatterings near the ferromagnetic wave vectors $\mathbf{Q}=(1,0)$ and (1,1) remain featureless at all energies. This contradicts the weak-coupling perspective that suggests a sharp enhancement of ferromagnetic susceptibility due to the divergence of density of states in the associated $\gamma$ band. Our findings imply that ferromagnetic fluctuations in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and related materials do not fit into the weak-coupling paradigm, but instead are quasilocal fluctuations induced by Hund's coupling. This imposes significant constraints for the pairing mechanism involving spin fluctuations.

We investigate the effects of the electron-electron interactions on the quantum transport through a charge Kondo circuit. The setup consists of a quantum dot sandwiched between two leads by two nearly transparent single mode quantum point contacts. The size of the interacting area $L$ in the Luttinger liquid formed in the vicinities of the narrow constrictions is assumed to be much smaller compared to the size of the quantum dot $a$. We predict that the interplay between the electron-electron interactions in the Luttinger liquid and the fingerprints of the non-Fermi liquid behavior in the vicinity of the two channel Kondo intermediate coupling fixed point allows one to determine the interaction strength through the power-law temperature scaling of the electric conductance.

We propose an analytical Landau-Ginzburg (LG) theory of the charge density waves coupled with lattice and electronic long-range order parameters. Examples of long-range order include the electronic wave function of superconducting Cooper pairs, structural distortions, electric polarization, and magnetization. We formulate the LG free energy density as a power expansion with respect to the charge density and other long-range order parameters as well as their spatial gradients and biquadratic coupling terms. We introduced a biquadratic coupling between the charge density gradient and long-range order parameters as well as nonlinear higher gradients of the long-range order parameters. The biquadratic gradient coupling is critical to the appearance of different spatially modulated phases in charge-ordered ferroics and high-temperature superconductors. We derived the thermodynamic conditions for the stability of the spatially modulated phases, which are the intertwined spatial waves of charge density and lattice/electronic long-range order. The analytical expressions for the energies of different phases, corresponding order parameters, charge density waves amplitudes, and modulation periods obtained in this paper can be employed to guide the comprehensive physical explanation, deconvolution, and Bayesian analysis of experimental data on quantum materials ranging from charge-ordered ferroics to high-temperature superconductors.

The rainbow trapping effect, which enables field amplification of multiple wavelengths in topological insulators, offers unprecedented opportunities for integrated ultrasonic sensors and energy harvesting. However, until now, the realization of the rainbow trapping effect has been limited to a one-dimensional (1D) or 2D interface in the electromagnetic and acoustic systems. Here, we propose a method to realize rainbow trapping based on higher-order topological corner modes (HOTCMs), where the elastic wave is localized at 0D corners rather than at the interface. We strategically design the two-dimensional elastic locally resonant metamaterial plate and construct multiple HOTCMs at the interfacial corners formed by trivial and nontrivial domains. We further investigate the interplay between nearest-neighbor couplings and next-nearest-neighbor couplings. Remarkably, the HOTCMs localized at corners with different geometric configurations are shown to be frequency dependent, providing a platform for trapping elastic waves at different corners. Moreover, we demonstrate rainbow trapping based on the HOTCMs at the corners and show the agreement between the experimental results and theoretical modeling. Our results provide a mechanism to realize the trapping of multiple frequencies and extend the use of elastic integrated devices toward higher order topological insulators.

Two-dimensional (2D) superconductivity in artificial interfaces and atomic-thin layers has gained attention for its exotic quantum phenomena and practical applications. Although bulk van der Waals layered materials have been explored for 2D superconductivity, most of these compounds do not exhibit remarkable properties despite exhibiting 2D characteristics. Here we report a comprehensive analysis of single crystals of Li-intercalated $2H{\text{-TaS}}_2$ superconductor, suggesting weakly coupled anisotropic superconductivity. Angle-dependent magnetotransport and the Berezinskii-Kosterlitz-Thouless transition confirm quasi-2D superconductivity in $2H{\text{-Li}}_x{\mathrm{TaS}}_2$.