The pseudospin of heavy holes (HHs) confined in a semiconductor quantum dot (QD) represents a promising candidate for a fast and robust qubit. While hole spin manipulation by a classical electric field utilizing the Dresselhaus spin-orbit interaction (SOI) has been demonstrated, our work explores cavity-based qubit manipulation and coupling schemes for inversion-symmetric crystals forming a planar HH QD. Choosing the exemplary material germanium (Ge), we derive an effective cavity-mediated ground state spin coupling that harnesses the cubic Rashba SOI. In addition, we propose an optimal set of parameters which allows for Rabi frequencies in the MHz range, thus entering the strong coupling regime of cavity quantum electrodynamics.

We perform magnetotransport and microwave (MW) photovoltage (PV) measurements in bulk tantalum arsenide (TaAs) crystal with $c$-(001) crystalline surface at low temperature ($T$). Two sets of quantum oscillations from different topological Weyl electron pockets are found in magnetoresistance and PV. Similar to the magnetoresistance, PV oscillates with the density of states around the Fermi level. Our observation qualitatively countenances a model which holds that the PV oscillations originate from nonequilibrium chiral Weyl fermions. Moreover, as a probe for detecting local electron states, PV is proved to be more sensitive than magnetoresistances. Microwave photovoltaic effect provides an effective method to explore topological electron structure and novel quantum phases in three-dimensional Weyl systems.

Motivated by the recent prediction of the Magnus Hall effect in systems with broken inversion symmetry, in this paper we study the Magnus Nernst effect and the Magnus thermal Hall effect. In the presence of an inbuilt electric field, the wave packets of electrons with finite Berry curvature generate a Magnus velocity perpendicular to both the inbuilt electric field and the Berry curvature. This anomalous Magnus velocity gives rise to the Magnus Hall transport, which manifests in all four electrothermal transport coefficients. In this paper we demonstrate the existence of the Magnus Nernst and Magnus thermal Hall effect in monolayer ${\mathrm{WTe}}_2$ and gapped bilayer graphene using the semiclassical Boltzmann formalism. We show that the Magnus velocity can also give rise to the Magnus valley Hall effect in gapped graphene. Magnus velocity can be useful for experimentally probing the Berry curvature and designing novel electrical and electrothermal devices.

In this work we examine the evolution of the electronic structure in twisted bilayers of $\mathrm{Mo}{\mathrm{Se}}_2$, assuming the moiré potential to be a small perturbation to the untwisted limit. Its role in modifying the electronic structure is probed by mapping the calculated band structure for the moiré cell onto the primitive cell direction which represents the untwisted limit. At large twist angles such as $19.{03}^{\circ }$, we find that the moiré cell band structure is identical to the primitive cell one in the low-energy window. There are, however, significant deviations for small twist angles such as $3.{48}^{\circ }$ which have large patches of high-symmetry regions of AA and ${\mathrm{AB}}^{\prime }$ stackings. These lead to enhanced interlayer hopping interaction strengths in some regions, and hence stronger perturbations leading to subband formation of the highest occupied band, which has a bandwidth of 19 meV and is found to be localized both in real space as well as in momentum space.

The two-dimensional structure of graphene makes it difficult to realize flexibility and auxeticity (negative Poisson's ratio) in graphene-based structures. Using molecular dynamics simulations, we demonstrate for graphene origami structures effective tuning of both the flexibility and Poisson's ratio through the geometry, including the potential to combine superflexibility with a highly tunable negative Poisson's ratio in contrast to any existing graphene-based structure. Auxeticity even can be achieved under large applied strain, both tensile and compressive.

We investigate diffusion of excitation in one- and two-dimensional lattices with random onsite energies and deterministic long-range couplings (hopping) inversely proportional to the distance. Three regimes of diffusion are observed in strongly disordered systems: ballistic motion at short time, standard diffusion for intermediate times, and a stationary phase (saturation) at long times. We propose an analytical solution valid in the strong-coupling regime which explains the observed dynamics and relates the ballistic velocity, diffusion coefficient, and asymptotic diffusion range to the system size and disorder strength via simple formulas. We show also that in the long-time asymptotic limit of diffusion from a single site the occupations form a heavy-tailed power-law distribution.

We show that local correlators in a wide class of kicked chains can be calculated exactly at light-cone edges. Extending previous works on circuit lattice systems, the correlators between local operators are expressed through the expectation values of transfer matrices $\mathbf{T}$ with small dimensions. For dual-unitary kicked chains, with spatial-temporal symmetry of the dynamics, this provides a full characterization of local correlators. Furthermore, we identify a remarkable family of dual-unitary models where an explicit information on the spectrum of $\mathbf{T}$ is available. For this class of models we provide a closed analytical formula for the corresponding two-point correlators. The results are exemplified on the kicked Ising spin chain model.

We show that the spin pumping from ferromagnetic insulator into the adjacent metallic spin sink can be strongly stimulated by the superconducting correlations. The key physical mechanism responsible for this effect is the presence of Andreev bound states at the ferromagnetic insulator/superconductor interface. We consider the minimal model when these states appear because of the suppressed pairing constant within the interfacial normal layer. For thin normal layers we obtain a strongly peaked temperature dependence of the Gilbert damping coefficient which has been recently observed in such systems. For thicker normal layers the Gilbert damping monotonically increases down to the temperatures much smaller than the critical one. The suggested model paves the way to controlling the temperature dependence of the spin pumping by fabricating hybrid normal metal–superconductor spin sinks.

Near the accidental degeneracy of two symmetry-distinct orders, i.e., where both transition temperatures almost coincide, phase interactions significantly reshape the ordering behavior. Strong attraction between the parent phases are known to induce a joint first-order transition. For weak interactions, I report a second-order transition of both primary orders, preceded by a fluctuation-driven state of matter. Due to symmetry mixing, this antecedent bound-state order exhibits unique signatures, incompatible with either parent phase. Within a field-theoretical formalism, I derive the generic phase diagram for a system with bound-state order, study its response to strain, and evaluate analytic expressions for a specific model. As the realization of a perfect degeneracy between symmetry-distinct orders is accidental by nature, interpretations of that kind—such as $(d+ig)$-superconducting state as a candidate for ${\mathrm{Sr}}_2\mathrm{Ru}{\mathrm{O}}_4$—have inarguably a weak point. The results presented here raise the plausibility for realizing such a situation by widening the degeneracy point to an extended line. Finally, I discuss how a trainable Kerr effect under strain provides strong evidence for a bound-state phase of symmetry-distinct orders.

An $A$-type antiferromagnet, ${\mathrm{NaNiO}}_2$, was examined by means of positive muon spin rotation and relaxation (${\mu }^{+}\mathrm{SR}$) measurements and first-principles calculations based on a density functional theory (DFT). Below $T_{\mathrm{N}}=20$ K, a clear muon spin precession signal was observed in the ${\mu }^{+}\mathrm{SR}$ time spectrum recorded under zero field, due to the formation of a static internal magnetic field. The microscopic origin of such an internal field was computed as a sum of dipolar and hyperfine contact fields at the site (0.624, 0, 0.854), where both the muon site and the local spin density at such a site were predicted with DFT calculations. While the computed values were consistent with experimentally obtained ones, in both the antiferromagnetic and the paramagnetic states, the contribution of the hyperfine contact field was shown to be insignificant even below $T_{\mathrm{N}}$. Finally, measurements at higher temperatures signified thermally activated Na-ion diffusion with $E_{\mathrm{a}}=50\left(20\right)$ meV and $D_{\mathrm{Na}}\left(300\mathrm{K}\right)=8.8\times {10}^{-11}{\mathrm{cm}}^2$/s, commonly observed in layered-type compounds.

We develop a theory to compute the domain-wall magnetoresistance (DWMR) in antiferromagnetic metals with different spin structures. In the diffusive transport regime, the DWMR can be either negative or positive depending on the domain-wall orientation and spin structure. In contrast, when the transport is in the ballistic regime, the DWMR is always positive, and the magnitude depends on the width and orientation of the domain wall. Our results pave the way for using electrical measurements for probing the internal spin structure in antiferromagnetic metals.

We study a disordered weakly coupled superconductor around the Anderson transition by solving numerically the Bogoliubov–de Gennes (BdG) equations in a three-dimensional lattice of size up to $20\times 20\times 20$ in the presence of a random potential. The spatial average of the order parameter is moderately enhanced as disorder approaches the transition but decreases sharply in the insulating region. The spatial distribution of the order parameter is sensitive to the disorder strength: for intermediate disorders below the transition, we already observe a highly asymmetric distribution with an exponential tail. Around the transition, it is well described by a log-normal distribution and a parabolic singularity spectrum. These features are typical of a multifractal measure. We determine quantitatively the critical disorder at which the insulator transition occurs by an analysis of level statistics in the spectral region that contributes to the formation of the order parameter. Interestingly, spectral correlations at the transition are similar to those found in noninteracting disordered systems at the Anderson transition. A percolation analysis suggests that the loss of phase coherence may occur around the critical disorder.

The projector-augmented-wave (PAW) method of Blöchl makes smooth but nonorthogonal orbitals. Here we show how to make a PAW orthogonal using a cheap transformation of the wave functions. We show that the resulting orthogonal PAW (OPAW), applied for density functional theory, reproduces (for a large variety of solids) band gaps from the abinit package. OPAW combines the underlying orthogonality of norm-conserving pseudopotentials with the large grid spacings and small energy cutoffs in PAW. The OPAW framework can also be combined with other electronic structure theory methods.

By performing a detailed study of hydrogen adsorbates on graphene using density functional theory (DFT), we propose a general tight-binding (TB) formalism for a simultaneous treatment of multiple impurities of arbitrary species. To elucidate the details of the hydrogen-graphene bonding, we systematically examine the effects of hybridization and deformation on the band structure and the spectral function. An enhanced understanding of the binding mechanisms leads to a TB model whose predicted spectral function compares favorably with the DFT calculations on the scale of the supercell, as well as the individual adsorbates and carbon atoms. The computational load of our model scales with the number of impurities, not their separation, making it especially useful for experimentally relevant clustered impurity configurations that are too computationally expensive for DFT. The formalism described here allows for the treatment of Anderson impurities and impurities that bind to multiple carbon atoms.

A theory is developed of the time-dependent magnetization of the metacrystal composed of magnetoferritin macromolecules. Such superstructures, comprising up to several million superparamagnetic nanoparticles encapsulated in protein shells, can be created artificially using biochemical assembling technologies. They have been also shown to occur naturally in sensitive cells of the inner ear of birds, which suggests their possible involvement in the detection of the geomagnetic field for orientation and navigation of migratory animals. The dynamics of the magnetic system of the magnetoferritin metacrystal, comprising a very large number of magnetic moments coupled by long-range dipole forces, is exceedingly complex. In order to find the response of the metacrystal to high-frequency magnetic fields, we used a thermodynamic approach borrowed from the theory of nuclear spin systems of solids. The resulting theory yields the time-dependent superspin temperature and magnetization induced by oscillating magnetic fields of arbitrary strength. The predicted dependence of the high-frequency response on the static magnetic field can be used for experimental detection and characterization of magnetoferritin metacrystals in biological tissues.

The transport of quantum information between different nodes of a quantum device is among the challenging functionalities of a quantum processor. In the context of spin qubits, this requirement can be met by coherent electron spin shuttling between semiconductor quantum dots. Here we theoretically study a minimal version of spin shuttling between two quantum dots. To this end, we analyze the dynamics of an electron during a detuning sweep in a silicon double quantum dot (DQD) occupied by one electron. Possibilities and limitations of spin transport are investigated. Spin-orbit interaction and the Zeeman effect in an inhomogeneous magnetic field play an important role for spin shuttling and are included in our model. Interactions that couple the position, spin, and valley degrees of freedom open a number of avoided crossings in the spectrum allowing for diabatic transitions and interfering paths. The outcomes of single and repeated spin shuttling protocols are explored by means of numerical simulations and an approximate analytical model based on the solution of the Landau-Zener problem. We find that a spin infidelity as low as $1-F_s\lesssim 0.002$ with a relatively fast level velocity of $\alpha =600\mu {\mathrm{eV}\mathrm{ns}}^{-1}$ is feasible for optimal choices of parameters or by making use of constructive interference.

We show that the first-order transition related to charge ordering (CO) follows power-law scaling with external hydrostatic pressure ($P$) and magnetic field ($H$). This is an experimental evidence of a scaling relation through magnetization measurement across the CO transition temperature ($T_{\mathrm{CO}}$) in three manganese-oxide systems under the simultaneous influence of $H$ and $P$. The melting of CO instability obeys a simple scaling relation, $\mathrm{\Delta }{T}_{\mathrm{CO}}=f(H{P}^{\alpha }$), where $\mathrm{\Delta }{T}_{\mathrm{CO}}$ is the suppression of $T_{\mathrm{CO}}$ by $P$ and $H$ and $\alpha$ is the nonuniversal scaling exponent that crucially depends on lattice, charge, and spin coupled dynamics. Our results suggest that the instability point of a first-order transition scales with the strength of the perturbations, $H$ and $P$. The $H\text{−}P\text{−}T$ scaling should allow us controlled manipulation of the transition in a three-dimensional space. The scaling relations should be applicable to other first-order transitions as well with the relevant parameters.

We show the existence of non-Hermitian degeneracies, known as exceptional points, in the collective mode spectrum of Fermi liquids with quadrupolar interactions. Through a careful analysis of the analytic properties of the dynamic quadrupolar susceptibility, we show that, in the weak attractive region, two stable collective modes coalesce to an exceptional point. We completely characterize this singularity, explicitly showing its topological properties. Experimental signatures are also discussed.

In two dimensions, the topological order described by ${\mathbb{Z}}_2$ gauge theory coupled to free or weakly interacting fermions with a nonzero spectral Chern number $\nu$ is classified by $\nu \mathrm{mod}16$ as predicted by Kitaev [Ann. Phys. 321, 2 (2006)]. Here, we provide a systematic and complete construction of microscopic models realizing this so-called sixteenfold way of anyon theories. These models are defined by $\mathrm{\Gamma }$ matrices satisfying the Clifford algebra, enjoy a global $\mathrm{SO}\left(\nu \right)$ symmetry, and live on either square or honeycomb lattices depending on the parity of $\nu$. We show that all these models are exactly solvable by using a Majorana representation and characterize the topological order by calculating the topological spin of an anyonic quasiparticle and the ground-state degeneracy. The possible relevance of the $\nu =2$ and $\nu =3$ models to materials with Kugel-Khomskii-type spin-orbital interactions is discussed.