We present a theoretical study of dolerophanite ${\mathrm{Cu}}_2{\mathrm{OSO}}_4$, a layered kagomelike spin-$\frac{1}{2}$ magnetic insulator that can be described either as a system of chains coupled through dimers or as a kagome lattice where every third spin is replaced by a ferromagnetic spin dimer. Building on insights from ab initio calculations, classical numerical minimizations, and semiclassical expansions, we arrive at a minimal microscopic description that accounts for the experimental data reported so far, including the nature of the magnetic order, the reported spin length, and the observed anisotropy. The latter arises by a peculiar competition between the antisymmetric (Dzyaloshinskii-Moriya) and the symmetric part of the exchange anisotropy, which gives rise to a two-step reorientation process involving two successive continuous phase transitions. In this paper, we uncover mechanisms stabilizing canted ferrimagnetic order in kagome systems and highlight strong magnetic anisotropy in the presence of dissimilar magnetic orbitals on crystallographically nonequivalent Cu sites. We also show how these anisotropy terms affect the spin-wave spectrum and how they can be tracked experimentally.

We analyze possible nodal superconducting phases that emerge from a doped nodal-line semimetal. We show that nodal-line superconducting phases are favored by interactions mediated by short-range ferromagnetic fluctuations or Hund's coupling. It is found that the leading pairing channels are momentum-independent, orbital-singlet and spin-triplet. In the pairing state, we show that the Bogoliubov-de Gennes Hamiltonian hosts a pair of topologically protected nodal rings on the equators of the torus Fermi surface (FS). Using a topological classification for gapless systems with inversion symmetry, we find that these nodal rings are topologically nontrivial and protected by integer-valued monopole charges $\nu =\pm 2$. In the scenario of pairing driven by ferromagnetic fluctuations, we analyze the fate of superconductivity in the magnetically ordered phase. Based on Ginzburg-Landau free energy analysis, we find the energetically favored superconducting state is characterized by the coexistence of two pairing orders whose $\mathbf{d}$ vectors are perpendicular to the magnetization axis $\mathbf{M}$ with their phases unfixed. In this case, each nodal loop in the pairing state splits into two, carrying a $\pm 1$ monopole charge. For bulk-boundary correspondence, these nodal rings enclose flat-band Majorana zero modes on top and bottom surface Brillouin zones with distinct $\mathbb{Z}$-valued topological invariants.

The emergence of superconductivity is often accompanied by competing charge/magnetic orders, such as charge/spin density waves and antiferromagnetism in correlated systems. The superconducting temperature $T_{\mathrm{C}}$ can often be significantly enhanced once the competing order is suppressed via external stimuli. Recently, ${\mathrm{Re}}_3{\mathrm{Ge}}_7$ has attracted considerable attention due to its temperature-induced metal-insulator-like transition, which is inexplicably related to superconductivity. In this study, we have discovered that ${\mathrm{Re}}_3{\mathrm{Ge}}_7$ single crystals exhibit pressure-induced superconductivity due to the suppression of charge order. ${\mathrm{Re}}_3{\mathrm{Ge}}_7$ displays an insulatorlike upturn of electronic resistivity bellow 60 K at ambient pressure without triggering a structure transition. The dominant carrier changes from electrons to holes at low temperatures. The temperature-dependent angle-resolved photoemission spectroscopy investigations indicated that the band structure of ${\mathrm{Re}}_3{\mathrm{Ge}}_7$ does not appear to alter significantly between 70 K and 7 K. After ruling out some possible competing orders based on experimental evidence, we suggest that the insulatorlike state could be the unconventional charge ordering's plausible ground state. Our findings indicate that the emergence of superconductivity can be achieved at a relatively low pressure of 0.2 GPa by restraining the charge order. With increasing pressure, $T_C$ is slightly enhanced, reaching a maximum value of 5.3 K at 24.1 GPa, while the charge order is rapidly inhibited until it becomes imperceptible. The superconductivity shows an unusual platform-shaped phase diagram, suggesting the possibility of unconventional electronic contributions. The current research poses important questions concerning the ${\mathrm{Re}}_3{\mathrm{Ge}}_7$ unconventional charge order and how it competes with the appearance of superconductivity.

In conformal field theory (CFT), the four-point correlator is a fundamental object that encodes CFT properties, constrains CFT structures, and connects to the gravitational scattering amplitude in holography theory. However, the four-point correlator of CFTs in dimensions higher than two-dimensional remains largely unexplored due to the lack of nonperturbative tools. In this paper, we introduce a new approach for directly computing four-point correlators of three-dimensional (3D) CFTs. Our method employs the recently proposed fuzzy (noncommutative) sphere regularization, and we apply it to the paradigmatic 3D Ising CFT. Specifically, we have computed three different four-point correlators: $\langle \sigma \sigma \sigma \sigma \rangle , \langle \sigma \sigma \epsilon \epsilon \rangle$, and $\langle \sigma \sigma T_{\mu \nu }{T}_{\rho \eta }\rangle$. Additionally, we verify the crossing symmetry of $\langle \sigma \sigma \sigma \sigma \rangle$, which is a notable property arising from conformal symmetry. Remarkably, the computed four-point correlators exhibit continuous crossing ratios, showcasing the continuum nature of the fuzzy sphere regularization scheme. This characteristic renders them highly suitable for future theoretical applications, enabling further advancements and insights in 3D CFT.

Bernstein modes are formed as a result of nonlocal coupling of collective excitations and cyclotron harmonics in magnetized plasma. In degenerate solid-state plasma they are typically associated with magnetoplasmons. A different type of Bernstein modes arise in two-dimensional electron liquid at sufficiently strong quasiparticle interaction. We consider Bernstein modes originating from coupling between quasiparticle cyclotron harmonics and shear magnetosound waves. The latter may be responsible for the giant peak in radiofrequency photoresistance observed in high-quality GaAs quantum wells. Using Landau-Silin kinetic equation with an arbitrary strength of the interparticle Landau interaction, we trace the reconstruction of Bernstein mode spectrum in high-quality 2D electron systems across the crossover between weakly interacting degenerate electron gas and the correlated electron liquid. Sensitivity of Bernstein modes to the strength of quasiparticle interaction allows one to use them for spectroscopy of Landau interaction function in the electron Fermi liquids.

The origin of the nonhydrogenic hole transition at $\sim 23\mathrm{meV}$ in the boron-doped silicon is still under debate. Here we employ the scanning tunneling microscope to uncover that a boron-containing complex on the silicon (111) surface shows three shallow acceptor states. Among them, the first excited state has the typical energy of the nonhydrogenic hole transition. We then show that this energy gap originates from the strain-induced mixing of the valence bands, unraveling a distinct origin for the nonhydrogenic hole transition in the boron-doped silicon.

Local measurements of heat flux in quantum Hall devices can deviate from the expected equilibrium heat flux due to interactions. We present a model of a simple mesoscopic device consisting of an Ohmic reservoir contacted by chiral edge states. In contrast to the well studied heat Coulomb blockade (HCB) effect, we report the opposite phenomenon, an enhancement of the heat flux carried by an edge state in the HCB regime due to an additional contribution of the collective charge mode via the fluctuating potential of the Ohmic contact. We discuss the thermometry of these correlated states and discuss their detectability. The enhancement effect is also reflected in modified correlation functions, which influences the electrical and thermal linear response coefficients in a tunneling probe measurement. On a technical level, we introduce a Langevin formalism that elucidates the role of these extra fluctuations in electrical and thermal transport, both in uniformly heated and Joule heated devices, and argue that our approach has advantages in the latter scenario compared to the standard $P\left(E\right)$ theory. We report a violation of the Wiedemann-Franz law, which is modified by the external resistance of the mesoscopic circuit.

The effect of a time-periodic perturbation, such as radiation, on a system otherwise at equilibrium has been studied in the context of Floquet theory with stationary states replaced by Floquet states and the energy replaced by quasienergy. These quasienergy bands in general differ from the energy bands in their dispersion and, especially in the presence of spin-orbit coupling, in their states. This may, in some cases, alter the topology when the quasienergy bands exhibit different topological invariants than their stationary counterparts. In this paper, motivated by advances in pump-probe techniques, we consider the optical response of driven topological systems when the drive is not purely periodic but is instead multiplied by a pulse shape/envelope function. We use real time-evolved states to calculate the optical conductivity and compare it to the response calculated using Floquet theory. We find that the conductivity bears a memory of the initial equilibrium state even when the pump is turned on slowly and the measurement is taken well after the ramp. The response of the time-evolved system is interpreted as coming from Floquet bands whose population has been determined by their overlap with the initial equilibrium state. In particular, at band inversion points in the Brillouin zone the population of the Floquet bands is inverted as well.

By means of molecular beam epitaxy, x-ray diffraction, transmission electron microscopy, and in situ scanning tunneling microscopy, we successfully prepare type-II Dirac semimetal $1T-{\mathrm{NiTe}}_2$ films and investigate their surface morphology, electronic structure, and topological characteristics on the atomic scale. Atomically flat ${\mathrm{NiTe}}_2$ films can be readily prepared on ${\mathrm{SrTiO}}_3$(001) substrates at $\sim 210{}^{\circ }\mathrm{C}$. For ${\mathrm{NiTe}}_2$ multilayers ($\sim 17$ layers), the predominant surface defect is identified as intercalated Ni atoms inside the van der Waals gap. Besides, we observe spin-splitting and resonant topological surface states near $E_{\text{F}}$ and at $\sim -0.65$ eV, respectively. They are suppressed at the step edges and in ultrathin monolayer and bilayer films. By exploring the quasiparticle interference, we visualize a backscattering suppression within $140\pm 40$ meV in multilayer ${\mathrm{NiTe}}_2$, which is associated possibly with the type-II Dirac node.

We investigate the role of disorder in the edge transport of axion insulator films. We predict by first-principles calculations that even-number-layer ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ have gapped helical edge states. The random potential will dramatically modify the edge spectral function to become gapless. However, such gapless helical state here is fundamentally different from that in the quantum spin Hall insulator or topological Anderson insulator. We further study the edge transport in this system by Landauer-Büttiker formalism, and find such gapless edge state is dissipative and not immune to backscattering, which would explain the dissipative nonlocal transport in the axion insulator state observed in six-septuple-layer ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ experimentally. Transport experiments with floating leads are proposed to verify our theory on the dissipative helical edge channels. In particular, the longitudinal resistance can be greatly reduced by adding an extra floating probe, even if it is not used. These results will facilitate the observation of the long-sought topological magnetoelectric effect in axion insulators.

We use the energy loss method (ELM) to evaluate the drift mobility tensor of doped phosphorene due to scattering of its carriers on an ensemble of charged impurities located in a substrate. The ELM makes it possible to circumvent the endeavor of numerically solving the Boltzmann transport equation for the same problem, whereby it yields an explicit expression for the mobility tensor components as a double integral, making it straightforward to survey various model layouts and parameters. This enabled us to perform a statistical analysis of the effects of spatial correlation among the impurities by means of a geometric structure factor for the hard-disk model of a planar distribution of pointlike impurities. We found that the correlation distance between impurities plays an important role at doping densities of phosphorene that are lower than the areal density of impurities. Moreover, the ELM naturally brings about the dielectric function of phosphorene, allowing us to explore the role of interband electron transitions in static screening of the impurities, in addition to the role played by the intraband transitions, which we treat in the random phase approximation. We found that the interband transitions augment the screening when impurities are close to phosphorene and when its doping density increases, thereby increasing the mobility tensor components while decreasing their asymmetry ratio.

Linear magnetoresistance (LMR) is of particular interest for memory, electronics, and sensing applications, especially when it does not saturate over a wide range of magnetic fields. Structural disorder, however, also tends to limit the mobility and hence the overall LMR amplitude. An alternative route to achieve large LMR is via nonstructural inhomogeneities which do not affect the zero field mobility, like magnetic domains. Here, we report a colossal positive linear magnetoresistance in $\mathrm{La}{\mathrm{TiO}}_3/\mathrm{Sr}{\mathrm{TiO}}_3$ heterostructures, with amplitude up to 6500% at 9T at low temperature. The colossal amplitude of the LMR, one of the largest in oxide heterostructure, stems from the unusual combination of a very high heterostructure mobility, up to 40 000 ${\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$, and a very large coverage of low-mobility regions. Low-temperature Lorentz transmission electron microscopy measurements further reveals a striped magnetic structure at the sub-$\mu \mathrm{m}$ scale in the $\mathrm{La}{\mathrm{TiO}}_3$ layer, compatible with in-plane spiral magnetism, with very high surface coverage. We propose that the low-mobility regions and striped magnetic regions are correlated, we model the increase in scattering induced by the magnetic texture, and we show that the non saturating LMR fits the Parish-Littlewood scenario. Our results provide a novel route for the engineering of large-LMR systems, using magnetic texture.

The spin of a single electron confined in a semiconductor quantum dot is a natural qubit candidate. Fundamental building blocks of spin-based quantum computing have been demonstrated in double quantum dots with significant spin-orbit coupling. Here, we show that spin-orbit-coupled double quantum dots can be categorised in six classes, according to a partitioning of the multidimensional space of their $g$ tensors. The class determines physical characteristics of the double dot, i.e., features in transport, spectroscopy, and coherence measurements, as well as qubit control, shuttling, and readout experiments. In particular, we predict that the spin physics is highly simplified due to pseudospin conservation, whenever the external magnetic field is pointing to special directions (“magic directions”), where the number of special directions is determined by the class. We also analyze the existence and relevance of magic loops in the space of magnetic-field directions, corresponding to equal local Zeeman splittings. These results present an important step toward precise interpretation and efficient design of spin-based quantum computing experiments in materials with strong spin-orbit coupling.

The magneto-optical properties of (001)-oriented NbAs single crystals have been studied in the spectral range from 5 to 150 meV and in magnetic fields of up to 13 T. A rich spectrum of inter-Landau-level transitions is revealed by these measurements. The transitions follow a square-root-like dependence with magnetic field, but the simple linear-band approximation is unable to accurately reproduce the observed behavior of the transitions in applied fields. We argue that the detected magneto-optical spectra should be related to crossing hyperbolic bands, which form the W1 cones. We propose a model Hamiltonian, which describes coupled hyperbolic bands and reproduces the shape of the relevant bands in NbAs. The magneto-optical spectra computed from this Hamiltonian nicely reproduce our observations. We conclude that the hyperbolic-band approach is a minimal model to adequately describe the magneto-optical response of NbAs and that the chiral (conical) bands do not explicitly manifest themselves in the spectra.

The complexity of the competition between nonradiative energy transfer and charge transfer is presented in this work. This study uses ZnO nanocrystals as a donor component and rhodamine B (RhB) dye as an acceptor component. Investigations reveal that the concentration of intrinsic defects and their localization, particularly oxygen vacancies, zinc interstitials, and oxygen interstitials, play a vital role in nonradiative energy transfer from ZnO nanocrystals to RhB dye. Additionally, photoluminescent spectra indicate that ZnO nanocrystals degrade the emission signals of RhB dye via charge transfer. It is possible that a part of oxygen vacancies may also contribute to the photocatalytic oxidation of the RhB molecule. The correlation between electron paramagnetic resonance, photoluminescence, and the RhB emission decay rates indicates two processes that one may encounter when dealing with semiconductor-dye conjugates. First is a complex energy transfer from ZnO to RhB indicating a photoluminescent up-conversion and second is a charge transfer from photoexcited intrinsic defect species in ZnO suppressing the RhB emission signals, which occur together. The defect species involved in photoluminescent up-conversion in $\mathrm{ZnO}+\mathrm{RhB}$ is due to a nonradiative energy transfer from photoexcited zinc interstitials or doubly charged oxygen vacancies in ZnO to RhB. Additionally, the suppression of RhB emission occurs due to charge transfer from oxygen vacancies in ZnO.

In this work, we investigate quenches in a free-fermion chain with long-range hopping, which decay with the distance with an exponent $\nu$ and has range $D$. By exploring the exact solution of the model, we found that the dynamic free energy is nonanalytical in the thermodynamic limit, whenever the sudden quench crosses the equilibrium quantum critical point. We were able to determine the nonanalyticities of dynamic free energy $f\left(t\right)$ at some critical times $t^c$ by solving nonlinear equations. We also show that the Yang-Lee-Fisher (YLF) zeros cross the real-time axis at those critical times. We found that the number of nontrivial critical times, $N_s,$ depends on $\nu$ and $D$. In particular, we show that for small $\nu$ and large $D$ the dynamic free energy presents nonanalyticities in any time interval $\mathrm{\Delta }t\sim 1/D\ll 1$, i.e., there are nonanalyticities at almost all times. For the spacial case $\nu =0$, we obtain the critical times in terms of a simple expression of the model parameters and also show that $f\left(t\right)$ is nonanalytical even for finite system under antiperiodic boundary condition, when we consider some special values of quench parameters. We also show that, generically, the first derivative of the dynamic free energy is discontinuous at the critical time instant when the YLF zeros are nondegenerate. On the other hand, when they become degenerate, all derivatives of $f\left(t\right)$ exist at the associated critical instant.

We report the magnetic properties of tetragonal compounds $R{\mathrm{Cd}}_{1-\delta }{\mathrm{Sb}}_2$ ($R=\mathrm{Ce}–\mathrm{Nd}$) by means of magnetic susceptibility, heat capacity, and electrical resistivity measurements. A ferromagnetic ordering at $T_{\mathrm{C}}\approx 3\mathrm{K}$, a nonmagnetic singlet ground state, and an antiferromagnetic ordering at $T_{\mathrm{N}}\approx 2.4\mathrm{K}$ is observed in ${\mathrm{CeCd}}_{1-\delta }{\mathrm{Sb}}_2, {\mathrm{PrCd}}_{1-\delta }{\mathrm{Sb}}_2$, and ${\mathrm{NdCd}}_{1-\delta }{\mathrm{Sb}}_2$, respectively. The trivalent nature of the rare-earth atoms has been confirmed from the effective magnetic moment estimated from the paramagnetic susceptibility data. The isothermal magnetization shows that the easy axis of magnetization is along the [100] direction for both ${\mathrm{CeCd}}_{1-\delta }{\mathrm{Sb}}_2$ and ${\mathrm{NdCd}}_{1-\delta }{\mathrm{Sb}}_2$. From the crystal electric field (CEF) analysis, based on the point charge model, we have analyzed the magnetic susceptibility, magnetization, and the heat capacity data and estimated the CEF split energy levels of ${\mathrm{CeCd}}_{1-\delta }{\mathrm{Sb}}_2$ and ${\mathrm{NdCd}}_{1-\delta }{\mathrm{Sb}}_2$.

Fe/MgO system is the one of the most important material prototypes in modern magnetic devices owing to its rich physics such as large perpendicular magnetic anisotropy and magnetoresistance effect. However, both large Dzyaloshinskii-Moriya interaction (DMI) and the topological magnetism that are mostly observed in heavy metals/ferromagnet (oxide) heterostructures have not been reported in this system. Here, we present evidence for sizable DMI that is even comparable to the Co/Pt interface can also be realized at pure and oxidized Fe/MgO bilayers due to the Rashba effect. More importantly, we find that both the strength and chirality of DMI can be engineered via interfacial oxygen manipulation, e.g., oxidization degree. The microscopic mechanism of oxidization inducing $3d$ orbitals reconstruction of Fe atoms dominates the variation of DMI is also unveiled. Using micromagnetic simulations, we further confirm that zero-field chiral spin textures can be achieved at the designed Fe/MgO films. These results not only enrich the physics of Fe/MgO interface but also provide a possible strategy to tailor noncolinear magnetic interaction and topological magnetism in the ferromagnet/oxide system.

Resonant inelastic x-ray spectroscopy (RIXS) has emerged as an important tool to explore magnetism in two-dimensional (2D) antiferromagnets realized in strongly correlated materials. Here, we consider the Heisenberg model with nearest- and next-nearest-neighbor hopping relevant to the study of magnetic excitations of the cuprate family. We compute the RIXS cross-section within the ultrashort core-hole lifetime expansion of the Kramers-Heisenberg scattering amplitude that allows a perturbative solution within linear spin wave theory (LSWT). We report detailed results for both spin-conserving and nonconserving channels. Apart from the widely discussed single-magnon and bimagnon contributions, we show that three-magnon contributions in the spin-nonconserving channel are useful to explain certain features of the RIXS data for 2D cuprates. We confirm the qualitative correctness of the LSWT conclusions for the three-magnon excitation with exact diagonalization. In this paper, we put constraints on the dispersion of the three-magnon in the Brillouin zone, opening avenues for realizing higher modes of quasiparticles using RIXS.