Abstract: Thouless introduced the idea of a topological charge pump: the quantized motion of charge due to the slow cyclic variation of a periodic potential. This topologically protected transport has now been realized with ultracold bosonic atoms.

Abstract: The spin–momentum locking of Dirac surface states offers intriguing possibilities for converting between charge and spin currents. Experiments show that fine tuning of the Fermi level is critical for maximizing the efficiency of such conversions.

Abstract: The dispersion of charge carriers in a metal is distinctly different from that of free electrons owing to their interactions with the crystal lattice. These interactions may lead to quasiparticles mimicking the massless relativistic dynamics of high-energy particle physics, and they can twist the quantum phase of electrons into topologically non-trivial knots-producing protected surface states with anomalous electromagnetic properties. These effects intertwine in materials known as Weyl semimetals, and in their crystal-symmetry-protected analogues, Dirac semimetals. The latter show a linear electronic dispersion in three dimensions described by two copies of the Weyl equation (a theoretical description of massless relativistic fermions). At the surface of a crystal, the broken translational symmetry creates topological surface states, so-called Fermi arcs, which have no counterparts in high-energy physics or conventional condensed matter systems. Here we present Shubnikov-de Haas oscillations in focused-ion-beam-prepared microstructures of Cd3As2 that are consistent with the theoretically predicted 'Weyl orbits', a kind of cyclotron motion that weaves together Fermi-arc and chiral bulk states. In contrast to conventional cyclotron orbits, this motion is driven by the transfer of chirality from one Weyl node to another, rather than momentum transfer of the Lorentz force. Our observations provide evidence for direct access to the topological properties of charge in a transport experiment, a first step towards their potential application.

Abstract: We study charge diffusion in holographic scaling theories with a particle-hole symmetry. We show that these theories have a universal regime in which the diffusion constant is given by D_{c}=Cv_{B}^{2}/(2πT), where v_{B} is the velocity of the butterfly effect. The constant of proportionality C depends only on the scaling exponents of the infrared theory. Our results suggest an unexpected connection between transport at strong coupling and quantum chaos.

Abstract: Bekenstein proved that in Einstein’s gravity minimally coupled to one (or many) real, Abelian, Proca field, stationary black holes (BHs) cannot have Proca hair. Dropping Bekenstein’s assumption that matter inherits spacetime symmetries, we show this model admits asymptotically flat, stationary, axisymmetric, regular on and outside an event horizon BHs with Proca hair, for an even number of real (or an arbitrary number of complex) Proca fields. To establish it, we start by showing that a test, complex Proca field can form bound states, with real frequency, around Kerr BHs: stationary Proca clouds. These states exist at the threshold of superradiance. It was conjectured in [1, 2], that the existence of such clouds at the linear level implies the existence of a new family of BH solutions at the non-linear level. We confirm this expectation and explicitly construct examples of such Kerr black holes with Proca hair (KBHsPH). For a single complex Proca field, these BHs form a countable number of families with three continuous parameters (ADM mass, ADM angular momentum and Noether charge). They branch off from the Kerr solutions that can support stationary Proca clouds and reduce to Proca stars [3] when the horizon size vanishes. We present the domain of existence of one family of KBHsPH, as well as its phase space in terms of ADM quantities. Some physical properties of the solutions are discussed; in particular, and in contrast with Kerr BHs with scalar hair, some spacetime regions can be counter-rotating with respect to the horizon. We further establish a no-Proca-hair theorem for static, spherically symmetric BHs but allowing the complex Proca field to have a harmonic time dependence, which shows BHs with Proca hair in this model require rotation and have no static limit. KBHsPH are also disconnected from Kerr-Newman BHs with a real, massless vector field. ∗herdeiro@ua.pt †eugen.radu@ua.pt ‡helgi.runarsson@gmail.com 1 ar X iv :1 60 3. 02 68 7v 1 [ gr -q c] 8 M ar 2 01 6

Abstract: The standard boundary state of a topological insulator in 3+1 dimensions has gapless charged fermions. We present model systems that reproduce this standard gapless boundary state in one phase, but also have gapped phases with topological order. Our models are weakly coupled and all the dynamics is explicit. We rederive some known boundary states of topological insulators and construct new ones. Consistency with the standard spin/charge relation of condensed matter physics places a nontrivial constraint on models.

Abstract: We demonstrate a 12 quantum dot device fabricated on an undoped Si/SiGe heterostructure as a proof-of-concept for a scalable, linear gate architecture for semiconductor quantum dots. The device consists of 9 quantum dots in a linear array and 3 single quantum dot charge sensors. We show reproducible single quantum dot charging and orbital energies, with standard deviations less than 20% relative to the mean across the 9 dot array. The single quantum dot charge sensors have a charge sensitivity of 8.2 x 10^{-4} e/root(Hz) and allow the investigation of real-time charge dynamics. As a demonstration of the versatility of this device, we use single-shot readout to measure a spin relaxation time T1 = 170 ms at a magnetic field B = 1 T. By reconfiguring the device, we form two capacitively coupled double quantum dots and extract a mutual charging energy of 200 microeV, which indicates that 50 GHz two-qubit gate operation speeds are feasible.

Abstract: We study some (conformal) field theories with global symmetries in the sector where the value of the global charge $Q$ is large. We find (as expected) that the low energy excitations of this sector are described by the general form of Goldstone's theorem in the non-relativistic regime. We also derive the unexpected result, first presented in [Hellerman et al. 2015], that the effective field theory describing such sector of fixed $Q$ contains effective couplings $\lambda_{\text{eff}}\sim \lambda^b /Q^{a}$, where $\lambda$ is the original coupling. Hence, large charge leads to weak coupling. In the last section of the paper we present an outline of how to compute anomalous dimensions of the $O(n)$ model in this limit.

Abstract: DOI: 10.1002/aenm.201601325 nonradiative energy loss mechanisms is highly desirable. We note that nonradiative recombination processes can also occur, for instance, because of poor contacts at the electrodes and, in the case of nongeminate recombination, not only via singlet 1CT states but also via triplet 3CT states[30] (a topic of future studies in our group). Up to now, the theoretical investigations of the NR recombination process in organic solar cells have been conducted under the Born-Oppenheimer (BO) approximation.[31–35] Thus, the possible impact of nonadiabatic vibronic coupling due to the breakdown of the BO approximation (for instance, in particular, when the energy difference between the initial and final states is small) has been neglected. We note that the nonradiative recombination via nonadiabatic coupling (NAC) was initially investigated in inorganic semiconductors in the early 1950s; there, it was found to play an important role in reducing the number of photogenerated carriers, suppressing luminescence, and decreasing the carrier lifetimes.[36–38] In molecular systems, the NR transition between two excited states or between an excited state and the ground state (with the same spin multiplicity) due to nonadiabatic coupling, is referred to as internal conversion.[39] In the case of organic emitters, the theoretical studies of Shuai and co-workers have demonstrated that internal conversion significantly limits the fluorescence quantum yields.[40,41] Compared to the energies (usually in the range 2.0–4.0 eV) of the first excited states in organic emitters, the CT1-state energies are generally much lower in organic solar cells, on the order of 0.5–1.7 eV.[22,23,29,42] Thus, the nonadiabatic coupling between the CT1 state and the ground state can be expected to be large and it becomes important to evaluate the role that nonadiabatic coupling can play in the NR recombination of CT1 states at donor–acceptor interfaces. We emphasize that the NR recombination rates of interfacial CT1 states are difficult to measure experimentally since the distribution of the CT1 states in transient experiments is far from equilibrium.[43,44] Here, we have chosen the pentacene–C60 interface as a re presentative system to study the factors determining the NR recombination rates in the context of OPV applications, since a large number of data are available from earlier experimental and theoretical studies.[31,45–48] As the recombination process is expected to depend on the local D–A interface geometry, we have considered both edge-on and face-on interfacial orientations of the pentacene molecules relative to C60. Also, we consider two different packing modes of the pentacene molecules: (i) a herringbone-type packing (referred to as [P:herringbone] hereafter) directly taken from the pentacene crystal structure;[49] and (ii) a co-facial-type packing (referred to as [P:co-facial] Organic photovoltaic (OPV)[1–8] devices have a great potential to become a low-cost technology for producing large-area, flexible solar modules that can be exploited, for instance, in portable and building-integrated applications. The organic electron donor (D) and acceptor (A) materials, used as active layer in an OPV device, are assembled into either a bilayer or bulk heterojunction structure.[9,10] In high-performance organic solar cells, external quantum efficiencies can reach 70%–80% with internal quantum efficiencies approaching 100%.[11–14] In these cases, nearly all photons absorbed by the donors or acceptors can be converted into collected electrons at short circuit and, hence, the achieved short-circuit currents (JSC) are close to their predicted maximum. However, in contrast, the open-circuit voltages (VOC) of these devices remain low,[15,16] which limits the power conversion efficiencies (PCEs); to date, the highest PCEs reach 11.7% in a single-junction device,[17] to be compared to ≈25% in silicon solar cells.[18,19] Thus, it is crucial to better understand the factors limiting the open-circuit voltage in OPV devices in order to ultimately improve efficiency. In an organic solar cell, the photogenerated excitons dissociate across a donor–acceptor interface, resulting in immediate long-range charge separation[20] or formation of interfacial charge-transfer states with singlet character, which vibrationally relax to the lowest CT1 state.[21] The CT1 states can separate into free charge carriers or decay to the ground state via either radiative emission or a nonradiative (NR) process. Numerous experimental investigations have demonstrated that the VOC values correlate linearly with the energies of the CT1 states. An empirical relation has been deduced: qVOC = E(CT1) – (0.6 ± 0.1 eV), with the 0.6 eV energy difference (loss) between E(CT1) and qVOC attributed to radiative and nonradiative recombinations.[22–28] Electroluminescence measurements on polymer-fullerene complexes show that the electroluminescent external quantum efficiency (EQEEL) is very low, on the order of <10−6, which means that the CT1 nonradiative recombination rates are expected to dominate the decay to the ground state and represent the major voltage loss between E(CT1)/q and VOC. Therefore, a better understanding of the

Abstract: The charge distribution method describes non-molecular crystal structures in a Madelung-type approach in which the formal oxidation number (`charge') of each atom is distributed among its neighbours. The sum of the distributed charges gives back the input charge when a structure is correctly refined and well balanced, so that the method can be used for structure validation and for the analysis of over- and underbonding effects. A new version of the software used to compute the charge distribution is presented, now with a CIF parser and graphical user interface.

Abstract: We provide a general formulation for calculating conserved charges for solutions to generally covariant gravitational theories with possibly other internal gauge symmetries, in any dimensions and with generic asymptotic behaviors. These solutions are generically specified by a number of exact (continuous, global) symmetries and some parameters. We define ``parametric variations'' as field perturbations generated by variations of the solution parameters. Employing the covariant phase space method, we establish that the set of these solutions (up to pure gauge transformations) form a phase space, the solution phase space, and that the tangent space of this phase space includes the parametric variations. We then compute conserved charge variations associated with the exact symmetries of the family of solutions, caused by parametric variations. Integrating the charge variations over a path in the solution phase space, we define the conserved charges. In particular, we revisit ``black hole entropy as a conserved charge'' and the derivation of the first law of black hole thermodynamics. We show that the solution phase space setting enables us to define black hole entropy by an integration over any compact, codminesion-2, smooth spacelike surface encircling the hole, as well as to a natural generalization of Wald and Iyer-Wald analysis to cases involving gauge fields.

Abstract: Large Gauge Transformations (LGT) are gauge transformations that do not vanish at infinity. Instead, they asymptotically approach arbitrary functions on the conformal sphere at infinity. Recently, it was argued that the LGT should be treated as an infinite set of global symmetries which are spontaneously broken by the vacuum. It was established that in QED, the Ward identities of their induced symmetries are equivalent to the Soft Photon Theorem. In this paper we study the implications of LGT on the S-matrix between physical asymptotic states in massive QED. In appose to the naively free scattering states, physical asymptotic states incorporate the long range electric field between asymptotic charged particles and were already constructed in 1970 by Kulish and Faddeev. We find that the LGT charge is independent of the particles' momenta and may be associated to the vacuum. The soft theorem's manifestation as a Ward identity turns out to be an outcome of not working with the physical asymptotic states.

Abstract: Large Gauge Transformations (LGT) are gauge transformations that do not vanish at infinity. Instead, they asymptotically approach arbitrary functions on the conformal sphere at infinity. Recently, it was argued that the LGT should be treated as an infinite set of global symmetries which are spontaneously broken by the vacuum. It was established that in QED, the Ward identities of their induced symmetries are equivalent to the Soft Photon Theorem. In this paper we study the implications of LGT on the S-matrix between physical asymptotic states in massive QED. In appose to the naively free scattering states, physical asymptotic states incorporate the long range electric field between asymptotic charged particles and were already constructed in 1970 by Kulish and Faddeev. We find that the LGT charge is independent of the particles’ momenta and may be associated to the vacuum. The soft theorem’s manifestation as a Ward identity turns out to be an outcome of not working with the physical asymptotic states.

Abstract: Quantum anomalies, breakdown of classical symmetries by quantum effects, provide a sharp definition of symmetry protected topological phases. In particular, they can diagnose interaction effects on the noninteracting classification of fermionic symmetry protected topological phases. In this paper, we identify quantum anomalies in two kinds of (3+1)d fermionic symmetry protected topological phases: (i) topological insulators protected by CP (charge conjugation $\ifmmode\times\else\texttimes\fi{}$ reflection) and electromagnetic $\mathrm{U}(1)$ symmetries, and (ii) topological superconductors protected by reflection symmetry. For the first example, which is related to, by CPT-theorem, time-reversal symmetric topological insulators, we show that the CP-projected partition function of the surface theory is not invariant under large $\mathrm{U}(1)$ gauge transformations, but picks up an anomalous sign, signaling a ${\mathbb{Z}}_{2}$ topological classification. Similarly, for the second example, which is related to, by CPT-theorem, class DIII topological superconductors, we discuss the invariance/noninvariance of the partition function of the surface theory, defined on the three-torus and its descendants generated by the orientifold projection, under large diffeomorphisms (coordinate transformations). The connection to the collapse of the noninteracting classification by an integer ($\mathbb{Z}$) to ${\mathbb{Z}}_{16}$, in the presence of interactions, is discussed.

Abstract: We discuss the limitations of the covariant derivative expansion prescription advocated to compute the one-loop Standard Model (SM) effective lagrangian when the heavy fields couple linearly to the SM. In particular, one-loop contributions resulting from the exchange of both heavy and light fields must be explicitly taken into account through matching because the proposed functional approach alone does not account for them. We review a simple case with a heavy scalar singlet of charge $-1$ to illustrate the argument. As two other examples where this matching is needed and this functional method gives a vanishing result, up to renormalization of the heavy sector parameters, we re-evaluate the one-loop corrections to the T--parameter due to a heavy scalar triplet with vanishing hypercharge coupling to the Brout-Englert-Higgs boson and to a heavy vector-like quark singlet of charged $2/3$ mixing with the top quark, respectively. In all cases we make use of a new code for matching fundamental and effective theories in models with arbitrary heavy field additions.

Abstract: Two-nucleon axial charge and current operators are derived in chiral effective field theory up to one loop. The derivation is based on time-ordered perturbation theory and accounts for cancellations between the contributions of irreducible diagrams and the contributions owing to nonstatic corrections from energy denominators of reducible diagrams. Ultraviolet divergencies associated with the loop corrections are isolated in dimensional regularization. The resulting axial current is finite and conserved in the chiral limit, while the axial charge requires renormalization. A complete set of contact terms for the axial charge up to the relevant order in the power counting is constructed.

Abstract: We generalize current holographic models with homogeneous breaking of translation symmetry by incorporating higher derivative couplings, in the spirit of effective field theories. Focusing on charge transport, we specialize to two simple couplings between the charge and translation symmetry breaking sectors. We obtain analytical charged black brane solutions and compute their DC conductivity in terms of horizon data. We constrain the allowed values of the couplings and note that the DC conductivity can vanish at zero temperature for strong translation symmetry breaking, thus showing that in general there is no lower bound on the conductivity.

Abstract: We present the complete derivation of the nuclear axial charge and current operators as well as the pseudoscalar operators to fourth order in the chiral expansion relative to the dominant one-body contribution using the method of unitary transformation. We demonstrate that the unitary ambiguity in the resulting operators can be eliminated by the requirement of renormalizability and by matching of the pion-pole contributions to the nuclear forces. We give expressions for the renormalized single-, two- and three-nucleon contributions to the charge and current operators and pseudoscalar operators including the relevant relativistic corrections. We also verify explicitly the validity of the continuity equation.

Abstract: We demonstrate that topological Dirac semimetals, which possess two Dirac nodes, separated in momentum space along a rotation axis and protected by rotational symmetry, exhibit an additional quantum anomaly, distinct from the chiral anomaly. This anomaly, which we call the Z_{2} anomaly, is a consequence of the fact that the Dirac nodes in topological Dirac semimetals carry a Z_{2} topological charge. The Z_{2} anomaly refers to nonconservation of this charge in the presence of external fields due to quantum effects and has observable consequences due to its interplay with the chiral anomaly. We discuss possible implications of this for the interpretation of magnetotransport experiments on topological Dirac semimetals. We also provide a possible explanation for the magnetic field dependent angular narrowing of the negative longitudinal magnetoresistance, observed in a recent experiment on Na_{3}Bi.

Abstract: The formalism of matrix product states is used to perform a numerical study of (1 + 1)-dimensional QED—also known as the (massive) Schwinger model—in the presence of an external static “quark” and “antiquark”. We obtain a detailed picture of the transition from the confining state at short interquark distances to the broken-string “hadronized” state at large distances, and this for a wide range of couplings, recovering the predicted behavior both in the weak- and strong-coupling limit of the continuum theory. In addition to the relevant local observables like charge and electric field, we compute the (bipartite) entanglement entropy and show that subtraction of its vacuum value results in a UV-finite quantity. We find that both string formation and string breaking leave a clear imprint on the resulting entropy profile. Finally, we also study the case of fractional probe charges, simulating for the first time the phenomenon of partial string breaking.

Abstract: Fluid models including charge generation and transport function of time and space need to be further developed, especially when the object under study is a HVDC cable. In the present paper, we propose an evolution of a 1D fluid bipolar charge transport model, taking into account the cylindrical geometry, and its associated effects, i.e. a non-homogeneity of the field and the temperature within the dielectric. Simulations are performed using this one-dimensional cylindrical model, featuring charge injection, transport, trapping, detrapping and recombination, in order to highlight the effects of the cylindrical geometry, i.e. a temperature and a field gradient, on the space charge profiles. A long term simulation is performed until stationary state, to study the capabilities of the model in describing the behaviour of space charge in a MV cable, and the future improvements that need to be performed.

Abstract: The already overcrowded phase diagram of cuprate superconductors has recently accommodated a region characterized by incommensurate charge density waves (CDW), partly overlapping with superconductivity, and included in the pseudogap regime. Although charge order is strengthened by high magnetic fields and competes with superconductivity, its role in Cooper pairing is still unassessed, calling for more complete characterization in different families of cuprates. The authors present an extensive x-ray scattering study of charge order in single layer La-doped Bi2201, and they show it extends up to optimal-doping (OP33K, $p$=0.16) in this family too. The CDW peak sharpens at ${T}_{c}$ and disappears above the pseudogap onset at temperature ${T}^{*}$. They also demonstrate that in the underdoped sample (OD15K, $p$=0.115) the charge density wave has no out-of-plane correlation and has dominant unidirectional nature within the planes.

Abstract: Interplays between charge and electric field, which play a critical role in determining the charge transport, recombination, storage and hysteresis in the perovskite solar cell, have been systematically investigated by both electrical transient experiments and theoretical calculations. It is found that the light illumination can increase the carrier concentration in the perovskite absorber, thus enhancing charge recombination and causing the co-existence of high electric field and free carriers. Meanwhile, the cell shows a similar charge storage and junction mechanism to that of the multicrystalline silicon solar cell, where the junction electric field determines the charge collection and distribution. Furthermore, it is demonstrated that the static charge of both the doping and defect coming from ion (vacancy) migration can significantly influence the electric field inside the cell, thus affecting the charge collection and recombination, which could be the origins for the widely-concerned hysteresis behaviors.

Abstract: The differential cross section and charge asymmetry for inclusive pp → W± + X → μ±ν + X production at √ s = 8 TeV are measured as a function of muon pseudorapidity. The data sample corresponds to an integrated luminosity of 18.8 fb−1 recorded with the CMS detector at the LHC. These results provide important constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10−3 to 10−1.

Abstract: Hellerman et al. (arXiv:1505.01537) have shown that in a generic CFT the spectrum of operators carrying a large U(1) charge can be analyzed semiclassically in an expansion in inverse powers of the charge. The key is the operator state correspondence by which such operators are associated with a finite density superfluid phase for the theory quantized on the cylinder. The dynamics is dominated by the corresponding Goldstone hydrodynamic mode and the derivative expansion coincides with the inverse charge expansion. We illustrate and further clarify this situation by first considering simple quantum mechanical analogues. We then systematize the approach by employing the coset construction for non-linearly realized space-time symmetries. Focussing on CFT3 we illustrate the case of higher rank and non-abelian groups and the computation of higher point functions. Three point function coefficients turn out to satisfy universal scaling laws and correlations as the charge and spin are varied.

Abstract: Charge exchange X-ray emission provides unique insights into the interactions between cold and hot astrophysical plasmas. Besides its own profound science, this emission is also technically crucial to all observations in the X-ray band, since charge exchange with the solar wind often contributes a significant foreground component that contaminates the signal of interest. By approximating the cross sections resolved to $n$ and $l$ atomic subshells, and carrying out complete radiative cascade calculation, we create a new spectral code to evaluate the charge exchange emission in the X-ray band. Comparing to collisional thermal emission, charge exchange radiation exhibits enhanced lines from large-$n$ shells to the ground, as well as large forbidden-to-resonance ratios of triplet transitions. Our new model successfully reproduces an observed high-quality spectrum of comet C/2000 WM1 (LINEAR), which emits purely by charge exchange between solar wind ions and cometary neutrals. It demonstrates that a proper charge exchange model will allow us to probe remotely the ion properties, including charge state, dynamics, and composition, at the interface between the cold and hot plasmas.

Abstract: Planar AdS black holes with axionic charge have finite DC conductivity due to momentum relaxation. We obtain a new family of exact asymptotically AdS$_4$ black branes with scalar hair, carrying magnetic and axion charge, and we study the thermodynamics and dynamic stability of these, as well as of a number of previously known electric and dyonic solutions with axion charge and scalar hair. The scalar hair for all solutions satisfy mixed boundary conditions, which lead to modified holographic Ward identities, conserved charges and free energy, relative to those following from the more standard Dirichlet boundary conditions. We show that properly accounting for the scalar boundary conditions leads to well defined first law and other thermodynamic relations. Finally, we compute the holographic quantum effective potential for the dual scalar operator and show that dynamical stability of the hairy black branes is equivalent to positivity of the energy density.

Abstract: Charge exchange X-ray emission provides unique insight into the interactions between cold and hot astrophysical plasmas. Besides its own profound science, this emission is also technically crucial to all observations in the X-ray band, since charge exchange with the solar wind often contributes a significant foreground component that contaminates the signal of interest. By approximating the cross sections resolved to n and l atomic subshells and carrying out complete radiative cascade calculation, we have created a new spectral code to evaluate the charge exchange emission in the X-ray band. Compared to collisional thermal emission, charge exchange radiation exhibits enhanced lines from large-n shells to the ground, as well as large forbidden-to-resonance ratios of triplet transitions. Our new model successfully reproduces an observed high-quality spectrum of comet C/2000 WM1 (LINEAR), which emits purely by charge exchange between solar wind ions and cometary neutrals. It demonstrates that a proper charge exchange model will allow us to probe the ion properties remotely, including charge state, dynamics, and composition, at the interface between the cold and hot plasmas.

Abstract: Domain walls in three-dimensional Weyl semimetals, formed by localized magnetic moments, are investigated. There appear bound states around the domain wall with the discrete spectrum, among which we find ``Fermi arc'' states with the linear dispersion. The Fermi arc modes contribute to the electric charge and current localized at the domain wall, which reveal a universal behavior depending only on chemical potential and the splitting of the Weyl nodes. This equilibrium current can be traced back to the chiral magnetic effect, or the edge counterpart of the anomalous Hall effect in the bulk. We propose a way to manipulate the motion of the domain wall, accompanied with the localized charge, by applying an external electric field.