We report a doping study directed to intentionally induce disorder in ${\mathrm{PdTe}}_2$ by the isoelectronic substitution of Pt. Two single-crystalline batches ${\mathrm{Pd}}_{1-x}{\mathrm{Pt}}_x{\mathrm{Te}}_2$ have been prepared with nominal doping concentrations $x=0.05$ and $x=0.10$. Sample characterization by energy dispersive x-ray spectroscopy revealed Pt did not dissolve homogeneously in the crystals. For the nominal value $x=0.10$ small single crystals cut from the batch appeared to have $x=0.09$, as well as the nonstoichiometric composition ${\mathrm{Pd}}_{0.97}{\mathrm{Pt}}_{<0.004}{\mathrm{Te}}_{2.03}$. Magnetic and heat capacity measurements demonstrate a transition from type-I to type-II superconducting behavior upon increasing disorder. From transport measurements we calculate a residual resistivity ${\rho }_0=1.4\mu \mathrm{\Omega }\mathrm{cm}$ suffices to turn ${\mathrm{PdTe}}_2$ into a superconductor of the second kind.

Wake patterns due to a uniformly traveling source are a result of the resonant emission of the medium's collective excitations. When there exists a frequency range where such excitations possess a negative group velocity, their interference leads to a wake pattern resembling the Kelvin ship wake: while there are “transverse” and “divergent” wave fronts trailing the source, they are oriented oppositely to Kelvin's. This is illustrated by an explicit calculation of “roton” wake patterns in superfluid ${}^4\mathrm{He}$ where a Kelvin-like wake emerges when the speed of the source marginally exceeds the Landau critical roton velocity.

We studied in situ the local atomic structure evolution of an equiatomic ${\mathrm{Zr}}_{50}{\mathrm{Cu}}_{50}$ metallic glassy alloy under high pressure compression inside a diamond anvil cell using synchrotron x-ray total scattering. The empirical potential structure refinement method was used to reconstruct the three-dimensional atomic models at each pressure step, and to analyze the spatially averaged local atomic structure configurations. The interatomic distances of different atomic pairs are reduced at different rates with increasing pressure and the Cu-Cu pairs exhibit the highest percentage reduction. Between ambient pressure and 36.85 GPa, the atomic separation of the Cu-Cu pairs is reduced by ∼12% compared to ∼5% for Zr-Zr and Zr-Cu pairs. Such disproportional decrease in interatomic distance results in inhomogeneous atom reconfiguration in the short atomic range. With the increase of pressure, the Zr atoms move preferentially towards the Zr-Zr pairs, while the Cu atoms move preferentially towards the Cu-Cu pairs, creating inhomogeneous atom reconfiguration with positive short-range order coefficients of 0.0309 and 0.0464 for Zr-Zr and Cu-Cu respectively, but a negative value of −0.0464 for Zr-Cu pairs. Voronoi tessellation method was also used to study the evolution of the short-range atom packing versus pressure, elucidating the cause for the bimodal distribution of the bond angle distributions. The research sheds light on understanding of the atomic reconfiguration of equiatomic alloys under high pressure.

We report a theoretical study of the nonlinear magnetoelectric response of $\mathrm{Gd}\mathrm{Fe}{\mathrm{O}}_3$ through an analytical approach combined with a Heisenberg model, which is fitted against first-principles calculations. Our theory reproduces the nonlinear change of polarization under applied magnetic field reported experimentally such that it allows us to analyze the origin of the large responses in different directions. We show that the nonlinear character of the response in these materials originates from the fact that the antiferromagnetic order of Gd atoms changes nonlinearly with respect to the applied magnetic field. Our model can be generalized to other materials in which the antiferromagnetic ordering breaks inversion symmetry.

Through density-functional calculations, we systematically studied the exchange bias effect of the antiferromagnetic Cr(001) substrate on a single magnetic molecule $\mathrm{Co}{\mathrm{Cp}}_2$. The magnetic moment and magnetic anisotropy of $\mathrm{Co}{\mathrm{Cp}}_2$ are largely tuned by the charge transfer between the molecule and substrate. A large exchange energy of ∼94 meV is found, which essentially pins the spin orientation of $\mathrm{Co}{\mathrm{Cp}}_2$. This makes $\mathrm{Co}{\mathrm{Cp}}_2/\mathrm{Cr}\left(001\right)$ an ideal combination for quantum sensing as its quantum spin states are well decoupled from those of the target magnetic entities. This work paves a way for the development of local quantum sensing with scanning probe techniques.

The charge density wave instability in one-dimensional semimetals is usually explained through a Peierls-like mechanism, where the coupling of electrons and phonons induces a periodic lattice distortion along certain modes of vibration, leading to a gap opening in the electronic band structure and to a lowering of the symmetry of the lattice. In this work, we study two prototypical Peierls systems: the one-dimensional carbon chain and the monatomic hydrogen chain with accurate ab initio calculations based on quantum Monte Carlo and hybrid density functional theory. We demonstrate that in one-dimensional semimetals at $T=0$, a purely electronic instability can exist independently of a lattice distortion. It is induced by spontaneous formation of low energy electron-hole pairs resulting in the electronic band gap opening, i.e., the destabilization of the semimetallic phase is due to an excitonic mechanism.

First-principles calculation of nonlinear magneto-optical effects has become an indispensable tool to reveal the geometric and topological nature of electronic states and to understand light-matter interactions. While intriguingly rich physics could emerge in magnetic materials, further methodological developments are required to deal with time-reversal symmetry breaking, due to the degeneracy and gauge problems caused by symmetry and the low-frequency divergence problem in the existing calculation formalism. Here we present a gauge-covariant and low-frequency convergent formalism for the first-principles computation. Remarkably, this formalism generally works for both nonmagnetic and magnetic materials with or without band degeneracy. Reliability and capability of our method are demonstrated by studying example materials (i.e., bilayers of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ and ${\mathrm{CrI}}_3$) and comparing with published results. Moreover, an importance correction term that ensures gauge covariance of degenerate states is derived, whose influence on physical responses is systematically checked. Our method enables computation of nonlinear magneto-optical effects in magnetic materials and paves the way for exploring rich physics created by the interplay of light and magnetism.

Weyl semimetals harbor topological Fermi arc surface states that determine the nontrivial charge current response to external fields. We study here the quasiparticle decay rate of Fermi arc states arising from their coupling to acoustic phonons, as well as the phonon-limited conductivity tensor for a clean Weyl semimetal slab. Using the phonon modes for an isotropic elastic continuum with a deformation potential coupling to electrons, we determine the temperature dependence of the quasiparticle decay rate, both near and far away from the arc termination points. By solving the coupled Boltzmann equations for the bulk and arc state distribution functions in the slab geometry, we show how the linear-response conductivity depends on key parameters such as the temperature, the chemical potential, the geometric shape of the Fermi arcs, or the slab width. The chiral nature of Fermi arc states causes an enhancement of the longitudinal conductivity along the chiral direction at low temperatures, together with a $1/T^2$ scaling regime at intermediate temperatures without counterpart for the conductivity along the perpendicular direction.

Rare-earth orthoferrites $\left(R{\mathrm{FeO}}_3\right)$ provide a flexible playground for magnetic materials design, combining the magnetic properties arising from complex interactions between $R^{3+}$ and ${\mathrm{Fe}}^{3+}$ cations within the robust framework of the perovskite structure. The most important magnetic property common to most orthoferrites is a spin reorientation transition in which the magnetic moments of ${\mathrm{Fe}}^{3+}$ cations rotate with respect to a crystallographic axis. ${\mathrm{SmFeO}}_3$ is unique among orthoferrites due to its high-temperature spin reorientation. It is possible to tune the spin reorientation transition to occur at room temperature by replacing Sm with Tm in the ${\mathrm{Sm}}_{0.70}{\mathrm{Tm}}_{0.30}{\mathrm{FeO}}_3$ perovskite. In this study, we show how small changes in composition in the ${\mathrm{Sm}}_{1-x}{\mathrm{Tm}}_x\mathrm{Fe}{\mathrm{O}}_3$ $\left(x=0.30\text{–}0.50\right)$ series provide a high degree of control over the magnetic properties. This work also offers a rather unusual look into the magnetic structure of a samarium-based perovskite by means of neutron powder diffraction, which was made possible by using ${}^{152}\mathrm{Sm}$. The combination of these results and magnetization measurements allowed the construction of the magnetic phase diagram of the series.

Braiding Majorana zero modes (MZMs) is the key procedure toward topological quantum computation. We show such braiding can be well performed in a parallel semiconductor-superconductor nanowire structure. Considering the fact that the low-energy Andreev bound states (ABSs) usually mix with the MZMs in the present setup, we further investigate the braiding properties of MZMs when an ABS is presented. Our numerical simulation suggests that ABS can be regarded as a pair of weakly coupled MZMs. The dynamical hybridization of MZMs plus the non-Abelian braiding of MZMs would induce an arbitrary rotation on the Bloch sphere of a single qubit. Remarkably, such rotation is manipulable since the rotation parameters could be individually modulated. Thus, the dynamic evolution can be eliminated and the non-Abelian braiding statistics, independent of the braiding time, retrieves.

Dimer models arise as effective descriptions in a variety of physical contexts, and provide paradigmatic examples of systems subject to strong local constraints. Here we present a quantum version of the venerable Kasteleyn model, which has an unusual phase transition from a dimer solid to a U(1) liquid. We show how the phase structure of the quantum model can be understood in terms of the quantum mechanics of one-dimensional strings and determine the exact value of the critical coupling. By constructing effective models to describe the properties of these strings, we calculate properties such as the dimer–dimer correlation function in the neighborhood of the transition. We also discuss the full phase structure of the model, in the ground state and at nonzero temperature.

We study the crystal structure of the tetragonal iron selenide FeSe and its nematic phase transition to the low-temperature orthorhombic structure using synchrotron x-ray and neutron scattering analyzed in both real space and reciprocal space. We show that in the local structure the orthorhombic distortion associated with the electronically driven nematic order is more pronounced at short length scales. It also survives to temperatures above 90 K, where reciprocal-space analysis suggests tetragonal symmetry. Additionally, the real-space pair distribution function analysis of the synchrotron x-ray diffraction data reveals a tiny broadening of the peaks corresponding to the nearest Fe-Fe, nearest Fe-Se, and next-nearest Fe-Se bond distances as well as the tetrahedral torsion angles at a short length scale of 20 Å. This broadening appears below 20 K and is attributed to a pseudogap. However, we did not observe any further reduction in local symmetry below orthorhombic down to 3 K. Our results suggest that the superconducting gap anisotropy in FeSe is not associated with any symmetry-lowering short-range structural correlations.

Emergent Lorentz symmetry and chiral anomaly are well known for playing an essential role in anomalous transport phenomena of Weyl metals. In particular, the former causes a Berry-curvature-induced orbital magnetic moment to modify the group velocity of Weyl electrons, and the latter results in the chiral magnetic effect to be responsible for a “dissipationless” longitudinal current channel of the bulk. In this study, we verify that these two effects can be measured in Shubnikov–de Haas (SdH) quantum oscillations, where a double-peak structure of the SdH oscillation appears to cause a kink in the Landau fan diagram. We examine three different cases which cover all possible experimental situations under external electric/magnetic fields and identify the experimental condition for the existence of the double-peak structure. We claim that interplay of the orbital magnetic moment and the chiral magnetic effect in SdH quantum oscillations is an interesting feature of the Weyl metal state.

Qubits encoded in the spin state of heavy holes confined in Si- and Ge-based semiconductor quantum dots are currently leading the efforts toward spin-based quantum information processing. The virtual absence of spinful nuclei in purified samples yields long qubit coherence times and the intricate coupling between spin and momentum in the valence band can provide very fast spin-orbit-based qubit control, e.g., via electrically induced modulations of the heavy-hole $g$-tensor. A thorough understanding of all aspects of the interplay between spin-orbit coupling, the confining potentials, and applied magnetic fields is thus essential for the development of the optimal hole-spin-based qubit platform. Here we theoretically investigate the manifestation of the effective $g$-tensor and effective mass of heavy holes in two-dimensional hole gases as well as in lateral quantum dots. We include the effects of the anisotropy of the effective Luttinger Hamiltonian (particularly relevant for Si-based systems) and we focus on the detailed role of the orientation of the transverse confining potential. We derive general analytic expressions for the anisotropic $g$-tensor and we present a general and straightforward way to calculate corrections to this $g$-tensor for localized holes due to various types of spin-orbit interaction, exemplifying the approach by including a simple linear Rashba-like term. Our results thus contribute to the understanding needed to find optimal points in parameter space for hole-spin qubits, where confinement is effective and spin-orbit-mediated electric control over the spin states is efficient.

Breaking Hermiticity in topological systems gives rise to intriguing phenomena, such as the exceptional topology and the non-Hermitian skin effect. In this work, we study a non-Hermitian topological crystalline insulator sitting on the Kekulé texture-modulated honeycomb lattice with balanced gain and loss. We find that the gaplessness of the topological edge states in the non-Hermitian system is insensitive to edge geometries under moderate strength of gain and loss, unlike the cases of Hermitian topological crystalline insulators that depend on edge geometries crucially. We focus on two types of gain and loss configurations, which are $PT$ symmetric and $PT$ asymmetric, respectively. For the $PT$-symmetric configuration, the Dirac point of the topological edge states in the Hermitian molecular-zigzag-terminated ribbons splits into a pair of exceptional points. The edge gap in the Hermitian armchair-terminated ribbons vanishes and a Dirac point forms as far as moderate gain and loss is induced. The band gaps of edge and bulk states in the Hermitian armchair-terminated ribbons close simultaneously for the $PT$-asymmetric configuration.

Non-Abelian states of matter, in which the final state depends on the order of the interchanges of two quasiparticles, can encode information immune from environmental noise with the potential to provide a robust platform for topological quantum computation. We demonstrate that phonons can carry non-Abelian frame charges at the band-crossing points of their frequency spectrum, and that external stimuli can drive their braiding. We present a general framework to understand the topological configurations of phonons from first-principles calculations using a topological invariant called Euler class, and provide a complete analysis of phonon braiding by combining different topological configurations. Taking a well-known dielectric material ${\mathrm{Al}}_2{\mathrm{O}}_3$ as a representative example, we demonstrate that electrostatic doping gives rise to phonon band inversions that can induce redistribution of the frame charges, leading to non-Abelian braiding of phonons. Our work provides a quasiparticle platform for realizable non-Abelian braiding in reciprocal space, and expands the tool set for studying braiding processes.

Light emitters in a single-mode nanolaser interact with the same cavity field that gives rise to polarization correlations which transform the cavity mode. Usually these correlations are ignored, however, collective phenomena can lead to the distinct sub- and superradiance, whose fully quantum description is challenging. Here we develop a simple yet rigorous picture of radiative transitions in single-mode nanolasers that accounts for polarization correlations. We show that the collective behavior of emitters modifies the photonic density of states leading to gain-dependent Purcell enhancement of spontaneous emission. Moreover, the stimulated emission rate is dependent on both the photon number and the laser line shape. As the laser line narrows, stimulated emission becomes stronger than predicted by Einstein's relations and the nanolaser reaches the threshold earlier. Finally, we provide concise, ready-to-use expressions for spontaneous and stimulated emission rates seamlessly describing both conventional and superradiant nanolasers.

In three-dimensional (3D) crystals, emergent particles arise when two or multiple bands contact and form degeneracy (band crossing) in the Brillouin zone. Recently a complete classification of emergent particles in 3D nonmagnetic crystals, described by the type-II magnetic space groups (MSGs), has been established. However, symmetries become complex in magnetically ordered structures. Consequently, we further perform a systematic investigation of emergent particles in magnetic crystals, and here we address this challenging task by exploring the possibilities of the emergent particles in the 674 type-III MSGs. Based on effective $\mathit{k}·\mathit{p}$ Hamiltonian and our classification of emergent particles [Yu et al., Sci. Bull. (2022)], we identify all possible emergent particles, including spinful and spinless, essential and accidental particles in the type-III MSGs. We find that all emergent particles in type-III MSGs also exist in type-II MSGs, with only one exception, i.e., the combined quadratic nodal line and nodal surface. Moreover, tabulations of the emergent particles in each of the 674 type-III MSGs, together with the symmetry operations, the small corepresentations, the effective $\mathit{k}·\mathit{p}$ Hamiltonians, and the topological character of these particles, are explicitly presented. Remarkably, combining this work and our homemade $\mathtt{SpaceGroupIrep}\text{and}\mathtt{MSGCorep}$ packages will provide an efficient way to search topological magnetic materials with novel quasiparticles.

We present a comparative density-functional theory plus dynamical mean-field theory study of the two known superconducting members of the rare-earth $\left(R\right)$ layered nickelate family: hole-doped ${R\text{NiO}}_2$ $(n=\infty )$ and $R_6{\mathrm{Ni}}_5{\mathrm{O}}_{12}$ $(n=5)$. At the same nominal carrier concentration, these two materials exhibit nearly identical electronic structures and many-body correlation effects: mass enhancements, self-energies, and occupations. However, the fermiology of the quintuple-layer nickelate is more two-dimensional-like than its infinite-layer counterpart, making this new superconducting quintuple-layer nickelate more cupratelike without the need for chemical doping.