We investigate the effects of nonuniform uniaxial strain and triaxial strain on the $\alpha \text{−}{T}_3$ lattice. The analytical expressions of the pseudo-Landau levels (pLLs) are derived based on low-energy Hamiltonians, and are verified by tight-binding calculations. We find that the pseudo magnetic field leads to oscillating density of states, and the first pLL is sublattice polarized, which is distributed on only two of the three sets of sublattices. For nonuniform uniaxial strain, we show that pLLs become dispersive due to renormalization of the Fermi velocity, and a valley polarized current emerges. Our results generalize the study of pseudo magnetic fields to the $\alpha \text{−}{T}_3$ lattice, which will not only deepen the understanding of the intriguing effects of mechanical strains but also provide a theoretical foundation for possible experimental studies of the effects of strain on the $\alpha \text{−}{T}_3$ lattice.

Using the normal incidence x-ray standing-wave technique as well as low-energy electron microscopy we have investigated the structure of quasifreestanding monolayer graphene (QFMLG) obtained by intercalation of antimony under the $(6\sqrt{3}\times 6\sqrt{3})R{30}^{\circ }$ reconstructed graphitized $6H$-SiC(0001) surface, also known as zeroth-layer graphene. We found that Sb intercalation decouples the QFMLG well from the substrate. The distance from the QFMLG to the Sb layer almost equals the expected van der Waals bonding distance of C and Sb. The Sb intercalation layer itself is monoatomic, flat, and located much closer to the substrate, at almost the distance of a covalent Sb-Si bond length. All data is consistent with Sb located on top of the uppermost Si atoms of the SiC bulk.

In a recent paper [M. M. Roberts and T. Wiseman, Phys. Rev. B 105, 195412 (2022)], based on methods typical of the condensed-matter literature (the real-space gradient expansion applied to the tight-binding model), conclude that the curved-space Dirac description of the low-energy conductivity electrons of monolayer graphene is incorrect when only strain is present (elastic monolayer graphene). In this Comment we point out that, in a much earlier paper [A. Iorio and P. Pais, Phys. Rev. D 92, 125005 (2015)], basing our analysis on methods typical of quantum field theory in curved space-time, we had concluded the same. Unfortunately, the authors of [M. M. Roberts and T. Wiseman, Phys. Rev. B 105, 195412 (2022)] have missed that result (even though it is very clearly stated in various places, starting from the Abstract), to the extent of citing our paper as one where strain is actually used for that wrong purpose. Since the paper in point is written with the declared intent of bringing clarity into the debate, we believe that this Comment of ours is very much due, precisely to give it another try to achieve the latter purpose.

We respond to the Comment on our paper [Phys. Rev. B 105, 195412 (2022)]. The authors of the Comment claim our paper arrived at similar conclusions to their earlier paper [Phys. Rev. D 92, 125005 (2015)]. In this response to their Comment, we outline why we believe our paper is fundamentally different in nature, we review its conclusions, and detail how these are different to those of their earlier work.

In this article, we propose a simple but general scaling relation between interactions in a gapped bulk topological matter and gapless interacting surface states. We explicitly illustrate such a generic bulk-boundary relation (BBR) for a few specific interactions in a topological quantum matter, where we can perform dimensional reduction of a microscopic bulk theory to project out interacting surfaces. We have examined renormalization effects of the gapped bulk fermions on the interacting topological surface fermions. As simple applications, we utilize effective interacting quantum fields implied by BBR to explore feasibility of routes to various fascinating emergent phenomena on surfaces including emergent Majorana fermions induced by spontaneous symmetry breaking. We obtain sufficient conditions for these interacting surface phenomena to take place. We have also found that for given bulk electron-phonon interactions and when ${\mathrm{\Omega }}_D\ge m$, the phonon-mediated interactions on the surface are strongest if the bulk Debye frequency ${\mathrm{\Omega }}_D$ matches $m$, the mass gap of the topological matter.

Plasmonic antennas channel incoming light into a confined near field that comes along with strong field gradients at the edges. Transverse field gradients are capable of driving quadrupole transitions in a more effective way than the weak longitudinal field gradient in dipolar light. Cuprous oxide Rydberg excitons with principal quantum number $n$ between 5 and 15 are several tens to a few hundreds of nanometers in diameter and can have different orbital angular momentum quantum numbers. Usually, only $P$- and $F$-excitons are electric dipole allowed, while $S$- and $D$-excitons remain dark. Here, we use 30-nm-wide and 60- to 110-nm-long plasmonic aluminum nanoantennas deposited on the cuprous oxide crystal surface to create transverse field gradients in similar spatial dimensions as the size of the Rydberg excitons. This way, light field and matter wave function overlap spatially and quadrupole transitions of $S$excitons are enhanced. The relative enhancement of the $S$-exciton oscillator strength with respect to the $P$-exciton oscillator accounts for a factor of up to 1.4.

We report a theoretic study of the supercurrent rectification effect in the graphene-based superconductor (GS) junction without invoking any spin-related interaction. By introducing the valley coupling effect through the Kekulé lattice distortion as well as the valley polarization interaction, we demonstrate that the GS/G/GS Josephson junction (JJ) can exhibit not only a $\pi$-state JJ but also a ${\varphi }_0$-state one, in which a nonzero supercurrent can flow without the superconducting phase difference between the two GS electrodes. A supercurrent rectification effect, that the critical supercurrent is asymmetric between the two opposite flowing directions, is identified. The conditions for the optimal supercurrent rectification effect are also discussed.

Being motivated by intriguing phenomena, such as the breakdown of conventional bulk boundary correspondence and the emergence of skin modes in the context of non-Hermitian (NH) topological insulators, we here propose a NH second-order topological superconductor (SOTSC) model that hosts Majorana zero modes (MZMs). Employing the non-Bloch form of the NH Hamiltonian, we topologically characterize the above modes by biorthogonal nested polarization and resolve the apparent breakdown of the bulk boundary correspondence. Unlike the Hermitian SOTSC, we note that the MZMs inhabit only one corner out of four in the two-dimensional NH SOTSCs. Such a localization profile of MZMs is protected by mirror rotation symmetry and remains robust under on-site random disorder. We extend the static MZMs into the realm of the Floquet drive. We find the anomalous $\pi$ mode following low-frequency mass kick in addition to the regular 0 mode that is usually engineered in a high-frequency regime. We further characterize the regular 0 mode with biorthogonal Floquet nested polarization. Our proposal is not limited to the $d$-wave superconductivity only and can be realized in the experiment with strongly correlated optical lattice platforms.

Flat bands are an ideal environment to realize unconventional electronic phases. Here, we show that fermionic systems with dissipation governed by a Bloch Lindbladian can realize dispersionless bands for sufficiently strong coupling to an appropriately engineered bath. These flat bands emerge in a “dark space” of the system-environment coupling and are long-lived by virtue of symmetry protection from dissipation. We exhibit the robustness of this mechanism for general one- and two-band models with and without spin, and discuss conditions for their experimental realization such as in a two-dimensional material on a superconducting substrate.

The control of flying qubits is at the core of quantum networks. When the flying qubits are carried by single-photon fields, the control involves not only their logical states but also their shapes. In this paper we explore a variety of flying-qubit control problems using a three-level atom with time-varying tunable couplings to two input-output channels. It is shown that one can tune the couplings of a $\mathrm{\Lambda }$-type atom to distribute a single photon into the two channels with arbitrary shapes, or use a $\mathrm{\Lambda }$-type atom or a $V$-type atom to catch an arbitrary-shape distributed single photon. The $\mathrm{\Lambda }$-type atom can also be designed to transfer a flying qubit from one channel to the other, with both the central frequency and the photon shape being converted. With a $\mathrm{\Xi }$-type atom, one can shape a pair of correlated photons via cascaded emission. In all cases, analytical formulas are derived for the coupling functions to fulfill these control tasks. Their correlation properties and physical limitations are discussed as well. These results provide useful control protocols for high-fidelity quantum information transmission over complex quantum networks.

Symmetries (and their spontaneous rupturing) can be used to protect and engender novel quantum phases and lead to interesting collective phenomena. In the work of K. Agarwal and I. Martin [Phys. Rev. Lett. 125, 080602 (2020)], the authors described a general dynamical decoupling (polyfractal) protocol that can be used to engineer multiple discrete symmetries in many-body systems. This work expands on the former by studying the effect of quasiperiodic and random noise on such a dynamical scheme. We find generally that relaxation of engineered symmetry generators proceeds by (i) an initial relaxation on microscopic timescales to a prethermal plateau whose height is independent of noise, (ii) a linear relaxation regime with a noise-dependent rate, followed by (iii) a slow logarithmic relaxation regime that is only present for quasiperiodic noise. We glean the essential features of these regimes via scaling collapses and show that they can be generally explained by the spectral properties of the various noise waveforms considered. In particular, the quasiperiodic noise is characterized by highly time-dependent spectrum with a noise floor that mimics white noise, and peaks that grow sharper with time. We argue that both the noise floor and peaks contribute to the initial linear-in-time relaxation while the logarithmic regime is initiated when the peaks become sufficiently well resolved and cease to contribute to further relaxation. We provide numerical evidence to justify these findings.

Heusler alloy-based spin gapless semiconductors (SGSs) with very high Curie temperatures $\left(T_C\right)$ have recently gained enormous attention because of their unconventional electronic structures. They exhibit a nonzero band gap in one of the spin channels and a zero band gap in the other spin channel, making them an important class of materials for tunable spin transport. Here, we report the experimental observation of anomalous Nernst effect (ANE) in ${\mathrm{Co}}_{1+x}{\mathrm{Fe}}_{1-x}\mathrm{CrGa}$ ($x=0$, 0.2, 0.4, and 0.5), which are the emerging quaternary Heusler alloy-based SGSs. While the electron-electron elastic scattering and the disorder-mediated weak localization effect play the major roles in electrical transport for all the samples at low temperatures, the magnon-drag effect was found to dominate the longitudinal thermoelectric transport. The ANE coefficient at room temperature increases from $\approx 0.018\mu \mathrm{V}{\mathrm{K}}^{-1}$ for $x=0$ to $\approx 0.063\mu \mathrm{V}{\mathrm{K}}^{-1}$ for $x=0.5$, which is higher than that for ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ and compressively strained $\mathrm{SrRu}{\mathrm{O}}_3$ films. Our analysis indicates that the observed ANE in these samples originates from asymmetric skew scattering of charge carriers.

It is well known that in the absence of the spin-orbit (SO) splitting the zero-temperature ferromagnetic phase transition in two-dimensional (2D) and three-dimensional (3D) electron gas is discontinuous (first order). The physical reason for this effect lies in the infrared catastrophe brought by the long-range particle-hole fluctuations near the Fermi surface. It is widely believed that a finite SO splitting is able to regularize this infrared catastrophe, and therefore, to stabilize the ferromagnetic quantum critical point. In contrast to this, we show that the infrared catastrophe persists at arbitrary SO splitting and the zero-temperature ferromagnetic phase transition in the itinerant 2D and 3D electron gas is always discontinuous. We also find that SO splitting reduces the symmetry of the ferromagnetic ground state down to the symmetry of the spin-orbit term. For example, Rashba SO splitting in 2D electron gas leads to the easy-plane symmetry of the ferromagnetic ground state. A combination of the Rashba SO splitting with the Dresselhaus term reduces the symmetry of the ferromagnetic ground state down to the in-plane Ising ferromagnet. The infrared catastrophe can be measured via the nonanalytic dependence of the spin susceptibility on magnetic field. This dependence is strongly anisotropic and follows the symmetry of SO splitting.

We present the quantitative investigation of the submicron structure in the bulk of porous graphite by using the dark-field x-ray imaging with Hartmann masks. By scanning the correlation length and measuring the mask visibility reduction, we obtain the average pore size, relative pore fraction, fractal dimension, and Hurst exponent of the structure in a simple and flexible setup with relaxed requirements on beam coherence. Profiting from the dimensionality of the mask, we obtain scattering signals in two orthogonal directions, which reveals the anisotropy of pore sizes.

We have investigated scaling properties near the quantum critical point between the extended phase and the critical phase in the Aubry-André-Harper model with $p$-wave pairing, which have rarely been exploited as most investigations focus on the localization transition from the critical phase to the localized phase. We find that the spectrum-averaged entanglement entropy and the generalized fidelity susceptibility act as eminent universal order parameters of the corresponding critical point without gap closing. We introduce a Widom scaling Ansatz for these criticality probes to develop a unified theory of critical exponents and scaling functions. We thus extract the correlation-length critical exponent $\nu$ and the dynamical exponent $z$ through the finite-size scaling given the system size increase in the Fibonacci sequence. The retrieved values of $\nu \simeq 1.000$ and $z\simeq 3.610$ indicate that the transition from the extended phase to the critical phase belongs to a different universality class from the localization transition. Our approach sets the stage for exploring the unconventional quantum criticality and the associated universal information of quasiperiodic systems in state-of-the-art quantum simulation experiments.

We study spin pumping into an anisotropic Dirac electron system induced by microwave irradiation to an adjacent ferromagnetic insulator theoretically. We formulate the Gilbert damping enhancement due to the spin current flowing into the Dirac electron system using second-order perturbation with respect to the interfacial exchange coupling. As an illustration, we consider the anisotropic Dirac system realized in bismuth to show that the Gilbert damping varies according to the magnetization direction in the ferromagnetic insulator. Our results indicate that this setup can provide helpful information on the anisotropy of the Dirac electron system.

Magnetoelectric (ME) effect triggered by spiral spin orders in various hexaferrites develops both the theory and application of ME coupling. However, the strength of such ME effect is restricted by the small spin-orbit coupling (SOC) of $3d$ electrons in M-type hexaferrite. Here, we introduce the $5d$ element Ir with large SOC into $\mathrm{Sr}{\mathrm{Fe}}_{12}{\mathrm{O}}_{19}$. It is found that a low ${\mathrm{Ir}}^{4+}\text{−}\mathrm{doping}$ level (about 4.2% of total ${\mathrm{Fe}}^{3+}$ ions) can induce conical spin order in $\mathrm{Sr}{\mathrm{Mg}}_x{\mathrm{Ir}}_x{\mathrm{Fe}}_{12-2x}{\mathrm{O}}_{19}$ ceramics, mainly because ${\mathrm{Ir}}^{4+}$ ions prefer to enter a crucial $4f_2$ magnetic-interacted site and thus strengthen the local Dzyaloshinskii-Moriya interaction. Spin-order-induced polarization $\left(P_{\mathrm{spin}}\right)$ is achieved and displays a synchronous temperature-dependent behavior with the displacive polarization $\left(P_{\mathrm{disp}}\right)$. This interesting ME effect is discussed via $d\text{−}p$ hybridization emerging at $\mathrm{Fe}{\mathrm{O}}_5$ trigonal bipyramids. Moreover, $P_{\mathrm{spin}}$ response decreases step by step during the periodical ME test, reflecting the controllable helicity and the possible multilevel states. These results demonstrate the impact of the $5d$ element with strong SOC on the formation of conical spin order and the enhancement of ME effect in M-type hexaferrite, and also reveal the interconnectedness between $P_{\mathrm{spin}}$ and $P_{\mathrm{disp}}$.

We analyze resonant magnetoelastic interactions between standing perpendicular spin wave modes (exchange magnons) and longitudinal acoustic phonon modes in free-standing hybrid metal-ferromagnet bilayer and trilayer structures. Whereas the ferromagnetic layer acts as a magnetic cavity, all metal layers control the frequencies and eigenmodes of acoustic vibrations. The design proposed here allows for achieving and tuning the spectral and spatial mode overlap between phonons and magnons that results in their strong resonant interaction. Realistic simulations for gold-nickel multilayers show that sweeping the external magnetic field should allow for observing resonantly enhanced interactions between individual magnon and phonon modes in a broad range of frequencies spanning from tens of gigahertz up to several hundreds of gigahertz, which can be finely tuned through the multilayer design. Our results would enable the systematic study and the deep understanding of resonantly enhanced magnetoelastic coupling between individual phonon and magnon modes up to frequencies of great contemporary fundamental and applied interest.

The deconfined quantum critical point (DQCP) between the Néel and valence bond solid order was originally proposed in quantum spin systems with a local Hamiltonian. In the last few years analogs of DQCPs with nonlocal interactions have been explored, which can lead to rich possibilities. The nonlocal interactions can either arise from an instantaneous long-range interaction in the Hamiltonian, or from gapless modes that reside in one higher spatial dimension. Here, we consider another mechanism of generating nonlocal interactions by coupling the DQCP to the “hot spots” of a Fermi surface. We demonstrate that at least within a substantial energy window, the physics of the DQCP is controlled by a new fixed point with a dynamical exponent $z>1$.