Highly mismatched alloys (HMAs) have band structures strongly modified due to the introduction of the alloying element. We consider HMAs where the isolated state of the alloying element is near the host conduction band, which causes the conduction band to split into two bands. We determine the bulk plasma frequency when the lower-energy band is partially occupied, as by doping, using a semianalytical method based on a disorder-averaged Green's function. We include the nontrivial effects of interband transitions to the higher-energy band, which limit the plasma frequency to be less than an effective band gap. We show that the distribution of states in the split bands causes plasmons in HMAs to behave differently than plasmons in standard metals and semiconductors. The effective mass of the lower split band $m^{*}$ changes with alloy fraction, and we find that the plasmon frequency with small carrier concentration $n$ scales with $\sqrt{n}/m^{*}$ rather than the $\sqrt{n/m^{*}}$ that is expected in standard materials. We suggest experiments to observe these phenomena. Considering the typical range of material parameters in this group of alloys and taking a realistic example, we suggest that HMAs can serve as highly tunable low-frequency plasmonic materials.

We carried out a comprehensive study of electronic transport, thermal, and thermodynamic properties in $\mathrm{Fe}{\mathrm{Cr}}_2{\mathrm{Te}}_4$ single crystals. It exhibits bad-metallic behavior and anomalous Hall effect (AHE) below a weak-itinerant paramagnetic-to-ferrimagnetic transition $T_c\sim 123$ K. The linear scaling between the anomalous Hall resistivity ${\rho }_{xy}$ and the longitudinal resistivity ${\rho }_{xx}$ implies that the AHE in $\mathrm{Fe}{\mathrm{Cr}}_2{\mathrm{Te}}_4$ is most likely dominated by an extrinsic skew-scattering mechanism rather than an intrinsic KL or an extrinsic side-jump mechanism, which is supported by our Berry phase calculations.

We show theoretically that a quantum dot circuit quantum electrodynamics device can be used as a probe of the Overhauser field in quantum dots. By coupling a transmission line to the interdot tunneling gate, an electromagnetically induced transparency scheme can be established, whose Fano-type interference leads to a sharp curvature in the reflection spectrum around resonance. This sharp feature persists even in the presence of the fluctuating spin bath, rendering a high-resolution method to extract the bath's statistical information. For strong nuclear spin fields, the reflection spectrum exhibits an Autler-Townes splitting, where the peak locations indicate the strengths of the Overhauser field gradient.

We investigate the electron transport in smooth graphene $p-n$ junctions, generated by gradually varying electrostatic potentials. The numerically calculated coherent current flow patterns can be understood largely in terms of semiclassical trajectories, equivalent to the ones obtained for light beams in a medium with a gradually changing refractive index. In smooth junctions, energetically forbidden regions emerge, which increase reflections and can generate pronounced interference patterns, for example, whispering gallery modes. The investigated devices do not only demonstrate the feasibility of the gradient-index electron optics in graphene $p-n$ junctions, such as Luneburg and Maxwell lenses, but may have also technological applications, for example, as electron beam splitters, focusers, and waveguides. The semiclassical trajectories offer an efficient tool to estimate the current flow paths in such nanoelectronic devices.

For the pristine phosphorene nanoribbons (PNRs) with edge states, there exist two categories of edge bands near the Fermi energy ($E_F$), i.e., the shuttle-shaped twofold-degenerate and the near-flat simple degenerate edge bands. However, the usual experimental measurement may not distinguish the difference between the two categories of edge bands. Here we study the varying rule for the edge bands of PNRs under an external electrostatic field. By using the KWANT code based on the tight-binding approach, we find that the twofold-degenerate edge bands can be divided into two separated shuttles until the degeneracy is completely removed and a gap near $E_F$ is opened under a sufficiently strong in-plane electric field. Importantly, each shuttle from the ribbon upper or lower edge outmost atoms is identified according to the local density of states. However, under a small off-plane field the shuttle-shaped bands are easily induced into two near-flat bands contributed from the edge atoms of the top and bottom sublayers, respectively. The evidence provides the edge and sublayer degrees of freedom (DOF) for the PNRs with shuttle-shaped edge bands, which is obviously different from another category of PNRs intrinsically with near-flat edge bands. This is because the former category of ribbons solely have four zigzaglike atomic configurations at the edges in each unit cell, which also results in that the property is robust against the point defect in the ribbon center area. As an application, furthermore, based on this issue we propose a homogenous junction of a shuttle-edge-band PNR attached by two electric gates. Interestingly, the transport property of the junction with field manipulation well reflects the characteristics of the two DOFs. These findings may provide a further understanding on PNRs and initiate new developments in PNR-based electronics.

Both Zn doping and $c$-axis magnetic fields have been observed to increase the spin stripe order in ${\mathrm{La}}_{2\text{−}x}{\mathrm{Ba}}_x{\mathrm{CuO}}_4$ with $x$ close to 1/8. For $x=0.095$, the applied magnetic field also causes superconducting layers to decouple, presumably by favoring pair-density-wave order that consequently frustrates interlayer Josephson coupling. Here we show that introducing 1% Zn also leads to an initial onset of two-dimensional (2D) superconductivity, followed by 3D superconductivity at lower temperatures, even in zero field. We infer that the Zn pins pair-density-wave order locally, establishing the generality of such behavior.

We investigate the interplay of magnetic fluctuations and Cooper pairing in twisted bilayer graphene from a purely microscopic model within a large-scale tight-binding approach resolving the angstrom scale. For local on-site repulsive interactions and using the random-phase approximation for spin fluctuations, we derive a microscopic effective pairing interaction that we use for self-consistent solutions of the Bogoliubov–de Gennes equations of superconductivity. We study the predominant pairing types as a function of interaction strength, temperature, and band filling. For large regions of this parameter space, we find chiral $d$-wave pairing regimes, spontaneously breaking time-reversal symmetry, separated by magnetic instabilities at integer band fillings. Interestingly, the $d$-wave pairing is strongly concentrated in the $AA$ regions of the moiré unit cell and exhibits phase windings of integer multiples of $2\pi$ around these superconducting islands, i.e., pinned vortices. The spontaneous circulating current creates a distinctive magnetic field pattern. This signature of the chiral pairing should be measurable by state-of-the-art experimental techniques.

The time evolution of the entanglement entropy is a key concept to understand the structure of a nonequilibrium quantum state. In a large class of models, such evolution can be understood in terms of a semiclassical picture of moving quasiparticles spreading the entanglement throughout the system. However, it is not yet known how the entanglement splits between the sectors of an internal local symmetry of a quantum many-body system. Here, guided by the examples of conformal field theories and free-fermion chains, we show that the quasiparticle picture can be adapted to this goal, leading to a general conjecture for the charged entropies whose Fourier transform gives the desired symmetry-resolved entanglement $S_n\left(q\right)$. We point out two physically relevant effects that should be easily observed in atomic experiments: a delay time for the onset of $S_n\left(q\right)$ which grows linearly with $\left|\mathrm{\Delta }q\right|$ (the difference between the charge $q$ and its mean value) and an effective equipartition when $\left|\mathrm{\Delta }q\right|$ is much smaller than the subsystem size.

Topological electronics has extended its richness to nonelectronic systems where bosonic quasiparticles can play the role of spin and heat carriers. In particular, topological magnons can be enabled by the Dzyaloshinskii-Moriya interaction (DMI) which acts as an effective spin-orbit coupling. We show that, besides DMI, an alternating arrangement of Heisenberg exchange interactions critically determines the magnon band topology, realizing a magnonic analog of the Su-Schrieffer-Heeger model. On a honeycomb ferromagnet with perpendicular anisotropy, we calculate the topological phase diagram, the chiral edge states, and the associated magnon Hall effect with tunable relative strength of exchange interactions on different links. Including weak phonon-magnon hybridization does not change the result. Candidate materials are discussed.

We construct a lattice model of topological order (kagome quantum spin liquids) and solve it with unbiased quantum Monte Carlo simulations. A three-stage anyon condensation with two transitions from a ${\mathbb{Z}}_2⊠{\mathbb{Z}}_2$ topological order to a ${\mathbb{Z}}_2$ topological order and eventually to a trivial symmetric phase is revealed. These results provide concrete examples of phase transitions between topological orders in quantum magnets. The designed quantum spin liquid model and its numerical solution offer a playground for further investigations on vestigial anyon condensation.

Recent experiments revealed a remarkable possibility for the absence of the disparity between the phase diagrams of electron- and hole-doped cuprate superconductors, while such an aspect should also be reflected in the dressing of the electrons. Here the phase diagrams of electron-doped cuprate superconductors and the related exotic features of the anisotropic dressing of the electrons are studied based on kinetic-energy-driven superconductivity. It is shown that although the optimized $T_{\mathrm{c}}$ in the electron-doped side is much smaller than that in the hole-doped case, the electron- and hole-doped cuprate superconductors rather resemble each other in the doping range of the superconducting dome, indicating an absence of the disparity between the phase diagrams of electron- and hole-doped cuprate superconductors. In particular, the anisotropic dressing of the electrons due to strong electron coupling to strongly dispersive spin excitation leads to the truncation of the electron Fermi surface to form the disconnected Fermi arcs centered around the nodal region. Concomitantly, the dip in the peak-dip-hump structure of the quasiparticle excitation spectrum is directly associated with the corresponding peak in the quasiparticle scattering rate, while the dispersion kink is always accompanied by the corresponding inflection point in the total self-energy as the dip in the peak-dip-hump structure and the dispersion kink in the hole-doped counterparts. The theory also predicts that both normal and anomalous self-energies exhibit well-pronounced low-energy peak structures.

As key signatures of topological superconductors (TSCs), the chiral and helical Majorana edge states (MESs) have received increasing attention recently. One prudent mechanism for realizing the MESs is by magnetizing topological surface states (TSSs) associated with conventional superconductivity. Here we construct comprehensive phase diagrams in the parameter space of magnetization and superconductivity for TSSs, based on tight-binding model analyses. In addition to the chiral MESs hosted by the quantum anomalous Hall (QAH), the half-plateau surface QAH and the zero-plateau QAH states, we find that the axion insulator state can realize helical MES, where the opened Zeeman gaps in two TSSs with antiferromagnetic exchange fields eliminate the requirement of the opposite phases between the superconducting gaps in two TSSs. We also demonstrate that the TSC phase is robust against the increase of interaction between two TSSs when the square of the sum of two superconducting gaps is smaller than that of two Zeeman energies. Furthermore, using first-principles approach, we predict $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4/{\mathrm{Bi}}_2{\mathrm{Te}}_3$ film placed on a superconducting substrate to be an ideal experimental platform to realize the chiral MESs within a wide energy range (∼80 meV), which persist even down to one quintuple layer of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. Our findings shed light on fundamental understanding of TSC phase and paving another avenue to search for TSC materials.

Pressure is an efficient tool to tune the electronic structure of iron-based superconductors. Here, we performed systematic high pressure transport and magnetization measurements on (${\mathrm{Ca}}_{0.73}{\mathrm{La}}_{0.27}){\mathrm{FeAs}}_2$ single crystal samples. Filamentary superconductivity is induced under a small applied pressure $P=1.6$ GPa. At $P=3.2$ GPa, the superconductivity becomes bulk. It is found that $T_c$ increases initially and then decreases with further increasing pressure, forming a dome shape. Hall resistivity is measured simultaneously and the Hall coefficient $R_H$ at 50 K shows nonmonotonic dependence on pressure. In addition, $R_H$ reverse sign at a critical pressure $P_c=3.9$ GPa, where $T_c$ reaches the maximum and there is a sudden increase in superconducting diamagnetism. Theoretical calculation results show a pressure induced Lifshitz transition of the Fermi surface which might be responsible for the appearance of superconductivity.

Evidence for broken time reversal symmetry (TRS) has been found in the superconducting states of the $R_5{\mathrm{Rh}}_6{\mathrm{Sn}}_{18}$ ($R=\text{Sc}$, Y, Lu) compounds with a centrosymmetric caged crystal structure, but the origin of this phenomenon is unresolved. Here, we report neutron diffraction measurements of single crystals with $R=\text{Lu}$, as well as measurements of the temperature dependence of the magnetic penetration depth using a self-induced tunnel-diode-oscillator (TDO)-based technique, together with band structure calculations using density functional theory. Neutron diffraction measurements reveal that the system crystallizes in a tetragonal caged structure, and that one of the nominal Lu sites in the ${\mathrm{Lu}}_5{\mathrm{Rh}}_6{\mathrm{Sn}}_{18}$ structure is occupied by Sn, yielding a composition ${\mathrm{Lu}}_{5-x}{\mathrm{Rh}}_6{\mathrm{Sn}}_{18+x}$ ($x=1$). The low temperature penetration depth shift $\mathrm{\Delta }\lambda \left(T\right)$ exhibits an exponential temperature dependence below around $0.3T_c$, giving clear evidence for fully gapped superconductivity. The derived superfluid density is reasonably well accounted for by a single-gap $s$-wave model, whereas agreement cannot be found for models of TRS breaking states with two-component order parameters. Moreover, band structure calculations reveal multiple bands crossing the Fermi level, and indicate that the aforementioned TRS breaking states would be expected to have nodes on the Fermi surface, in contrast to the observations.

A resistivity study of a single crystal of ${\mathrm{U}}_2{\mathrm{Ni}}_2\mathrm{Sn}$ has been performed at ambient pressure and under hydrostatic pressure up to $p=3.3\mathrm{GPa}$. It revealed Fermi-liquid behavior accompanied by spin excitations with an energy gap $\mathrm{\Delta }=30\text{–}55\mathrm{K}$ in the whole pressure range. The Néel temperature varies with pressure in a nonmonotonous way. It increases at the rate $d{T}_{\mathrm{N}}/dp=+0.6\mathrm{K}/\mathrm{GPa}$, and later, after passing through the maximum at ≈3 GPa, it starts to decrease quickly. High-pressure x-ray diffraction indicated that an orthorhombic distortion of the tetragonal structure takes place around the pressure of this $T_{\mathrm{N}}$ maximum. The computational study based on the density functional theory illustrates that the loss of magnetism in ${\mathrm{U}}_2{\mathrm{Ni}}_2\mathrm{Sn}$ with pressure is primarily due to $5f$-band broadening, which results from the collapse of the U spacing within the U-U dimers.

Recently layered compound $\mathrm{TaNi}{\mathrm{Te}}_5$ was proposed to be two-dimensional (2D) topological semimetals. Here we report the detailed investigation on $\mathrm{TaNi}{\mathrm{Te}}_5$ single crystals through magnetotransport and de Hass−van Alphen (dHvA) effect studies. Strong quantum oscillations with multiple periodicities have been observed. By analyzing the quantum oscillations, we provide evidence of nontrivial Berry phase with a 3D Fermi surface character in layered $\mathrm{TaNi}{\mathrm{Te}}_5$. Our work suggested that layered $\mathrm{TaNi}{\mathrm{Te}}_5$ should be 3D topological semimetal which offers a platform to explore exotic properties in low-dimensional topological semimetals.

Many-body theories such as dynamical mean field theory (DMFT) have enabled the description of the electron-electron correlation effects that are missing in current density functional theory (DFT) calculations. However, there has been relatively little focus on the wave functions from these theories. We present the methodology of the newly developed elk-triqs interface and how to calculate the DFT with DMFT ($\mathrm{DFT}+\mathrm{DMFT}$) wave functions, which can be used to calculate $\mathrm{DFT}+\mathrm{DMFT}$ wave-function-dependent quantities. We illustrate this by calculating the electron localization function (ELF) in monolayer ${\mathrm{SrVO}}_3$ and ${\mathrm{CaFe}}_2{\mathrm{As}}_2$, which provides a means of visualizing their chemical bonds. Monolayer ${\mathrm{SrVO}}_3$ ELFs are sensitive to the charge redistribution between the DFT, one-shot $\mathrm{DFT}+\mathrm{DMFT}$, and fully charge self-consistent $\mathrm{DFT}+\mathrm{DMFT}$ calculations. In both tetragonal and collapsed tetragonal ${\mathrm{CaFe}}_2{\mathrm{As}}_2$ phases, the ELF changes weakly with correlation-induced charge redistribution of the hybridized As $p$ and Fe $d$ states. Nonetheless, the interlayer As-As bond in the collapsed tetragonal structure is robust to the changes at and around the Fermi level.