Quantum anomalies in Weyl semimetal (for either $\mathbf{E}·\mathbf{B}\ne 0$ or $\mathbf{\nabla }T·\mathbf{B}\ne 0$) leads to chiral charge and energy pumping between the opposite chirality nodes. This results in chiral charge and energy imbalance between the Weyl nodes which manifests in several intriguing magneto-transport phenomena. Here, we investigate the role of electrical-, thermal-, and gravitational chiral anomaly on magneto-transport in Weyl semimetals. We predict the planar Ettinghausen and Righi-Leduc effect to be a distinct signature of these quantum anomalies. We also demonstrate a significant enhancement in the thermoelectric conductivity, Seebeck effect, Nernst effect, and thermal conductivity with increasing temperature. Interestingly, this anomaly induced transport violates the Wiedemann-Franz law and Mott relation.

We develop ab initio relativistic QED theory for elastic electron scattering on hydrogen-like highly charged ions for impact energies where, in addition to direct (Coulomb) scattering, the process can also proceed via formation and consequent Auger decay of autoionizing states of the corresponding helium-like ions. Even so, the primary goal of the theory is to treat electron scattering on highly charged ions, a comparison with experiment shows that it can also be applied for relatively light ions covering thus a very broad range of the scattering systems. Using the theory we performed calculations for elastic electron scattering on ${\mathrm{B}}^{4+}, {\mathrm{Ca}}^{19+}, {\mathrm{Fe}}^{25+}, {\mathrm{Kr}}^{35+}$, and ${\mathrm{Xe}}^{53+}$. The theory was also generalized for collisions of hydrogen-like highly charged ions with atoms considering the latter as a source of (quasi)free electrons.

We study Coulomb drag in a system consisting of a carbon nanotube and monolayer graphene. Within the Fermi liquid theory, we calculate the drag resistivity and find that the dimensional mismatch of the system components leads to a dependence of the drag rate on the carrier density, temperature, and spacing, which is substantially different from what is known for graphene double layers. Because of the competing effects of forward and backward scattering, we identify features of the drag dependence on the electron density, which allows us to control their relative contribution to the drag resistivity.

Hard-core bosons on honeycomb lattice ribbons with zigzag edges are studied using exact numerical simulations. We map out the phase diagrams of ribbons with different widths, which contain superfluid and insulator phases at various fillings. We show that charge domain walls are energetically favorable, in sharp contrast to the more typical occupation of a set of sites on a single sublattice of the bipartite geometry at $\rho =\frac{1}{2}$ filling. This “self-organized domain wall” separates two charge-density-wave regions with opposite Berry curvatures. Associated with the change of topological properties, superfluid transport occurs down the domain wall. Our results provide a concrete context to observe bosonic topological phenomena and can be simulated experimentally using bosonic cold atoms trapped in designed optical lattices.

The production of correlated Stokes (S) and anti-Stokes (aS) photons (SaS process) mediated by real or virtual phonon exchange has been reported in many transparent materials. In this work, we investigate the polarization and time correlations of SaS photon pairs produced in a diamond sample. We demonstrate that both S and aS photons have mainly the same polarization of the excitation laser. We also perform a pump-and-probe experiment to measure the decay rate of the SaS pair production, evidencing the fundamental difference between the real and virtual (phonon exchange) processes. In real processes, the rate of SaS pair production is governed by the phonon lifetime of $(2.8\pm 0.3)\mathrm{ps}$, while virtual processes only take place within the time width of the pump laser pulses of approximately $0.4\mathrm{ps}$. We explain the difference between real and virtual SaS processes by a phenomenological model, based on the probabilities of phonon creation and decay.

We consider a system of stacked tunnel-coupled two-dimensional electron- and hole-gas layers with Rashba spin-orbit interaction subjected to a staggered Zeeman field. The interplay of different intralayer tunnel couplings results in a topological insulator phase characterized by the presence of gapless helical surface states. The staggered Zeeman field further enriches the topological phase diagram by generating a second-order topological insulator phase characterized by the presence of gapless hinge states. The emergence of these topological phases is proven analytically in the regime of small Zeeman field and confirmed by numerical simulations in the nonperturbative region of the phase diagram. The topological phases are stable against external perturbations and disorder.

The molecular coordination complex ${\mathrm{NiI}}_2{(3,5-\mathrm{lut})}_4$ [where (3,5-lut) $=$ (3,5-lutidine) $=({\mathrm{C}}_7{\mathrm{H}}_9\mathrm{N}$)] has been synthesized and characterized by several techniques including synchrotron x-ray diffraction, electron-spin resonance, superconducting quantum interference device magnetometry, pulsed-field magnetization, inelastic neutron scattering, and muon spin relaxation. Templated by the configuration of 3,5-lut ligands the molecules pack in-registry with the Ni–$\mathrm{I}\cdots \mathrm{I}$–Ni chains aligned along the $c$ axis. This arrangement leads to an uncommon through-space $\mathrm{I}\cdots \mathrm{I}$ magnetic coupling which is directly measured in this work. The net result is a near-ideal realization of the $S=1$ Haldane chain with $J=17.5\mathrm{K}$ and energy gaps of ${\mathrm{\Delta }}^{\parallel }=5.3\mathrm{K} {\mathrm{\Delta }}^{\perp }=7.7\mathrm{K}$, split by the easy-axis single-ion anisotropy $D=-1.2\mathrm{K}$. The ratio $D/J=-0.07$ affords one of the most isotropic Haldane systems yet discovered, while the ratio ${\mathrm{\Delta }}_0/J=0.40\left(1\right)$ (where ${\mathrm{\Delta }}_0$ is the average gap size) is close to its ideal theoretical value, suggesting a very high degree of magnetic isolation of the spin chains in this material. The Haldane gap is closed by orientation-dependent critical fields ${\mu }_0{H}_{\mathrm{c}}^{\parallel }=5.3\mathrm{T}$ and ${\mu }_0{H}_{\mathrm{c}}^{\perp }=4.3\mathrm{T}$, which are readily accessible experimentally and permit investigations across the entirety of the Haldane phase, with the fully polarized state occurring at ${\mu }_0{H}_{\mathrm{s}}^{\parallel }=46.0\mathrm{T}$ and ${\mu }_0{H}_{\mathrm{s}}^{\perp }=50.7\mathrm{T}$. The results are explicable within the so-called fermion model, in contrast to other reported easy-axis Haldane systems. Zero-field magnetic order is absent down to $20\mathrm{mK}$ and emergent end-chain effects are observed in the gapped state, as evidenced by detailed low-temperature measurements.

The modified $XY$ model is a variation of the $XY$ model extended by a half-period term, exhibiting a rich phase structure. As the Goldstone model, also known as the linear O(2) model, can be obtained as a continuum and regular model for the $XY$ model, we define the modified Goldstone model as that of the modified $XY$ model. We construct a vortex, a soliton (domain wall), and a molecule of two half-quantized vortices connected by a soliton as regular solutions of this model. Then we investigate its phase structure in two Euclidean dimensions via the functional renormalization group formalism and full numerical simulations. We argue that the field dependence of the wave function renormalization factor plays a crucial role in the existence of the line of fixed points describing the Berezinskii-Kosterlitz-Thouless (BKT) transition, which can ultimately terminate not only at one but at two end points in the modified model. This structure confirms that a two-step phase transition of the BKT and Ising types can occur in the system. We compare our renormalization group results with full numerical simulations, which also reveal that the phase transitions show a richer scenario than expected.

We study the annihilation of topological defect pairs in the quasi-two-dimensional geometry of freely suspended smectic films. This elementary process is at the basis of all models describing the statistics of complex defect patterns. We prepare pairs with opposite topological charges and retrieve the interaction mechanisms from their trajectories. The square-root dependence of the defect separation on the time until annihilation and the asymmetry in propagation velocities of the opponents predicted by theory are confirmed. The importance of defect orientations is demonstrated. Trajectories are, in general, curved, depending on the mutual orientations (phase mismatch) of the defects and on the orientation of the pair respective to the far, undisturbed director. The experiments provide the basis for an adaption of the theoretical models to the real complexity of the annihilation.

We measure collective excitations of a harmonically trapped two-dimensional (2D) SU($N$) Fermi gas of ${}^{173}\mathrm{Yb}$ confined to a stack of layers formed by a one-dimensional optical lattice. Quadrupole and breathing modes are excited and monitored in the collisionless regime $|ln(k_F{a}_{2D}\left)\right|\gg 1$ with tunable spin. We observe that the quadrupole mode frequency decreases with increasing number of spin components due to the amplification of the interaction effect by $N$ in agreement with a theoretical prediction based on 2D kinetic equations. The breathing mode frequency, however, is measured to be twice the dipole oscillation frequency regardless of $N$. We also follow the evolution of collective excitations in the dimensional crossover from two to three dimensions and characterize the damping rate of quadrupole and breathing modes for tunable SU($N$) fermions, both of which reveal the enhanced interparticle collisions for larger spin. Our result paves the way to investigate the collective property of 2D SU($N$) Fermi liquid with enlarged spin.

We investigate the intrinsic magnon spin current in a noncollinear antiferromagnetic insulator. We introduce a definition of the magnon spin current in a noncollinear antiferromagnet and find that it is in general nonconserved, but for certain symmetries and spin polarizations the averaged effect of nonconserving terms can vanish. We formulate a general linear response theory for magnons in noncollinear antiferromagnets subject to a temperature gradient and analyze the effect of symmetries on the response tensor. We apply this theory to single-layer potassium iron jarosite ${\mathrm{KFe}}_3{\left(\mathrm{OH}\right)}_6{\left({\mathrm{SO}}_4\right)}_2$ and predict a measurable spin current response.

I construct a diagrammatic technique for non-Hermitian fermionic systems which allows addressing correlation effects in the steady state by systematic expansion. Applying this method to exceptional points or rings, I find that nodal objects in non-Hermitian systems are generically displaced in momentum-space due to interactions. This is a consequence of the fact that exceptional points invariably break a class of orthonormal symmetries that are generally present for nodal points in Hermitian systems and which protect the integrity of the node at low energy scales.

Bravais lattices are the most fundamental building blocks of crystallography. They are classified into groups according to their translational, rotational, and inversion symmetries. In computational analysis of Bravais lattices, fulfillment of symmetry conditions is usually determined by analysis of the metric tensor, using either a numerical tolerance to produce a binary (i.e., yes or no) classification or a distance function which quantifies the deviation from an ideal lattice type. The metric tensor, though, is not scale invariant, which complicates the choice of threshold and the interpretation of the distance function. Here, we quantify the distance of a lattice from a target Bravais class using strain. For an arbitrary lattice, we find the minimum-strain transformation needed to fulfill the symmetry conditions of a desired Bravais lattice type; the norm of the strain tensor is used to quantify the degree of symmetry breaking. The resulting distance is invariant to scale and rotation, and is a physically intuitive quantity. By symmetrizing to all Bravais classes, each lattice can be placed in a 14-dimensional space, which we use to create a map of the space of Bravais lattices and the transformation paths between them. A software implementation is available online under a permissive license.

Pioneering studies in transition metal dichalcogenides have demonstrated convincingly the coexistence of multiple angular momentum degrees of freedom—of spin ($1/2s_z=\pm 1/2$), valley ($\tau =K, K^{\prime }$ or $\pm 1$), and atomic orbital $(l_z=\pm 2)$ origins—in the valence band with strong interlocking among them, which results in noise-resilient pseudospin states ideal for spintronic-type applications. With field modulation a powerful, universal means in physics studies and applications, this work develops, from bare models in the context of complicated band structure, a general effective theory of field-modulated spin valley orbital pseudospin physics that is able to describe both intra- and intervalley dynamics. Based on the theory, it predicts and discusses the linear response of a pseudospin to external fields of arbitrary orientations. Paradigm field configurations are identified for pseudospin control, including pseudospin flipping. For a nontrivial example, it presents a spin valley orbital quantum computing proposal, where the theory is applied to address all-electrical, simultaneous control of $s_z, \tau$, and $l_z$ for qubit manipulation. It demonstrates the viability of such control with static field effects and an additional dynamic electric field. An optimized qubit manipulation time $\sim O$ (ns) is given.

Lamellar gel networks are creamy formulations extensively used in cosmetics and pharmaceutics. The basic units of these networks are lipid bilayers assembled from mixtures of fatty alcohols, surfactants, and water. Despite being an essential step for the preparation of the dispersions, the nature of the mixtures at high temperature has defied understanding. Here we show, by atomistic molecular dynamics simulations, that aqueous mixtures of cetyl (${\mathrm{C}}_{16}\mathrm{OH}$) and stearyl (${\mathrm{C}}_{18}\mathrm{OH}$) alcohols, and cetyl-trimethylammonium chloride (CTAC), lead to fluid bilayers, which are the units of the lamellar $L_{\alpha }$ phase. By providing a consistent numerical simulation model able to describe the structure and properties of fatty alcohol lamellae stabilized by a surfactant, our work paves the way for the elucidation of the forces regulating this family of industrially important gels.

We propose a condition, called convex quasilinearity, for deterministic nonlinear quantum evolutions. Evolutions satisfying this condition do not allow for arbitrary fast signaling, therefore, they cannot be ruled out by a standard argument. We also give an explicit example of a nonlinear qubit evolution satisfying quasilinearity.

Coherent nonlinear multipulse processes, nonlinear waves, and echo effects in resonant media are the topical problems of modern optics and important tools of coherent spectroscopy and quantum information science. We generalize the McCall-Hahn area theorem to the formation of an arbitrary photon echo generated during the multipulse excitation of the optically dense resonant media. The derived theorem made it possible to reveal the nonlinear mechanism of generation and evolution of the photon echo signals inside the media after a two-pulse excitation. We find that a series of self-reviving echo signals with a total area of $2\pi$ or $0\pi$ is excited and propagates in the media depth, with each pulse having an individual area less than $\pi$. The resulting echo pulse train is an alternative to the well-known soliton or breather. The developed pulse-area approach paves the way for more precise coherent spectroscopy, studies of different photon echo signals, and quantum control of light pulses in the optically dense media.

We describe a general procedure for associating a minimal informationally complete quantum measurement with a purely probabilistic representation of the Born rule. Such representations provide a way to understand the Born rule as a consistency condition between probabilities assigned to the outcomes of one experiment in terms of the probabilities assigned to the outcomes of other experiments. In this setting, the difference between quantum and classical physics is the way their physical assumptions augment bare probability theory: Classical physics corresponds to a trivial augmentation—one just applies the law of total probability (LTP) between the scenarios—while quantum theory makes use of the Born rule expressed in one or another of the forms of our general procedure. To mark the irreducible difference between quantum and classical, one should seek the representations that minimize the disparity between the expressions. We prove that the representation of the Born rule obtained from a symmetric informationally complete measurement minimizes this distinction in at least two senses, the first to do with unitarily invariant distance measures between the rules and the second to do with available volume in a reference probability simplex (roughly speaking, a different kind of uncertainty principle). Both of these arise from a useful result in majorization theory. This work complements recent studies in quantum computation where the deviation of the Born rule from the LTP is measured in terms of negativity of Wigner functions.

Weyl semimetals are materials with topologically nontrivial band structures both in the bulk and on the surface, hosting chiral nodes which are sinks and sources of Berry curvature. Weyl semimetals have been predicted and recently measured to exhibit large nonlinear optical responses. This discovery, along with their high mobilities, makes Weyl semimetals relevant to a broad spectrum of applications in optoelectronic, nanophotonic, and quantum optical devices. Although there is growing interest in understanding and characterizing the linear and nonlinear behaviors of Weyl semimetals, an ab initio calculation of the linear optical and optoelectronic responses at finite temperature remains largely unexplored. Here, we specifically address the temperature dependence of the linear optical response in type-I Weyl semimetals TaAs and NbAs. We evaluate, from first principles, the scattering lifetimes due to electron-phonon and electron-electron interactions and incorporate these lifetimes in evaluating an experimentally relevant frequency-, polarization-, and temperature-dependent complex dielectric function for each semimetal. From these calculations, we present linear optical conductivity predictions which agree well where experiment exists (for TaAs) and guide the way for future measurements of type-I Weyl semimetals. Importantly, we also examine the optical conductivity's dependence on the chemical potential, a crucial physical parameter which can be controlled experimentally and can elucidate the role of the Weyl nodes in optoelectronic response. Throughout this paper, we present design principles for Weyl optoelectronic devices that use photogenerated carriers in type-I Weyl semimetals.

Kitaev materials are promising for realizing exotic quantum spin liquid phases, such as a non-Abelian chiral spin liquid. Motivated by recent experiments in these materials, we theoretically study the novel field-induced quantum phase transitions from the non-Abelian chiral spin liquid to the symmetry-broken zigzag phase and to the trivial polarized state. Utilizing the recently developed dualities of gauge theories, we find these transitions can be described by critical bosons or gapless fermions coupled to emergent non-Abelian gauge fields, and the critical theories are of the type of a ${\mathrm{QCD}}_3$-Chern-Simons theory. We propose that all these exotic quantum phase transitions can potentially be direct and continuous in Kitaev materials, and we present sound evidence for this proposal. Therefore, besides being systems with intriguing quantum magnetism, Kitaev materials may also serve as table-top experimental platforms to study the interesting dynamics of emergent strongly interacting quarks and gluons in $2+1$ dimensions.