Showing papers on "Ground state published in 2013"
TL;DR: In this article, the root-mean-square (rms) nuclear charge radii R obtained by combined analysis of two types of experimental data: (i) radii changes determined from optical and, to a lesser extent, K α X-ray isotope shifts and (ii) absolute radii measured by muonic spectra and electronic scattering experiments.
1,172 citations
Journal Article•
TL;DR: The research expands the understanding of the nature of hydrogen bonding by delineating the interaction between hydrogen bonds and photons, thereby providing a basis for excited-state hydrogen bonding studies in photophysics, photochemistry, and photobiology.
Abstract: Because of its fundamental importance in many branches of science, hydrogen bonding is a subject of intense contemporary research interest. The physical and chemical properties of hydrogen bonds in the ground state have been widely studied both experimentally and theoretically by chemists, physicists, and biologists. However, hydrogen bonding in the electronic excited state, which plays an important role in many photophysical processes and photochemical reactions, has scarcely been investigated.Upon electronic excitation of hydrogen-bonded systems by light, the hydrogen donor and acceptor molecules must reorganize in the electronic excited state because of the significant charge distribution difference between the different electronic states. The electronic excited-state hydrogen-bonding dynamics, which are predominantly determined by the vibrational motions of the hydrogen donor and acceptor groups, generally occur on ultrafast time scales of hundreds of femtoseconds. As a result, state-of-the-art femtos...
886 citations
TL;DR: It is found that chiral magnetic effect is absent in both the semimetal and the insulator phase, and the reasons for this discrepancy are elucidated.
Abstract: It has been suggested recently, based on subtle field-theoretical considerations, that the electromagnetic response of Weyl semimetals and the closely related Weyl insulators can be characterized by an axion term θE·B with space and time dependent axion angle θ(r,t). Here we construct a minimal lattice model of the Weyl medium and study its electromagnetic response by a combination of analytical and numerical techniques. We confirm the existence of the anomalous Hall effect expected on the basis of the field theory treatment. We find, contrary to the latter, that chiral magnetic effect (that is, ground state charge current induced by the applied magnetic field) is absent in both the semimetal and the insulator phase. We elucidate the reasons for this discrepancy.
425 citations
TL;DR: In this paper, a variational approach is proposed to solve a class of Schrodinger equations involving the fractional Laplacian, which is variational in nature and based on minimization on the Nehari manifold.
Abstract: We construct solutions to a class of Schrodinger equations involving the fractional Laplacian. Our approach is variational in nature, and based on minimization on the Nehari manifold.
419 citations
TL;DR: In this article, the ionization dynamics of single nitrogen-vacancy center (NV) in bulk diamond at room temperature during illumination and its dependence on the excitation wavelength and power were investigated.
Abstract: The nitrogen–vacancy centre (NV) has drawn much attention for over a decade, yet detailed knowledge of the photophysics needs to be established. Under typical conditions, the NV can have two stable charge states, negative (NV−) or neutral (NV0), with photo-induced interconversion of these two states. Here, we present detailed studies of the ionization dynamics of single NV centres in bulk diamond at room temperature during illumination and its dependence on the excitation wavelength and power. We apply a recent method which allows us to directly measure the charge state of a single NV centre, and observe its temporal evolution. We find that the steady-state NV− population is always ⩽75% for 450–610 nm excitation wavelength. In combination with saturation measurements, we show that the optimal excitation wavelength is around 510–540 nm. Furthermore, the relative absorption cross-section of NV− is determined for 540–610 nm, revealing a double-peak structure. Finally, the energy of the NV− ground state of 2.6 eV below the conduction band is measured. These results reveal new insights into the charge state dynamics of the NV centre.
335 citations
TL;DR: The authors' observed in-gap Fermi surface oddness tied with the Kramers' point topology, their coexistence with the two-dimensional transport anomaly in the Kondo hybridization regime, as well as their robustness against thermal recycling, collectively provide strong evidence for protected surface metallicity with a Fermani surface whose topology is consistent with the theoretically predicted topological FermI surface.
Abstract: The Kondo insulator SmB6 has long been known to exhibit low-temperature transport anomalies whose origin is of great interest. Here we uniquely access the surface electronic structure of the anomalous transport regime by combining state-of-the-art laser and synchrotron-based angle-resolved photoemission techniques. We observe clear in-gap states (up to ~4 meV), whose temperature dependence is contingent on the Kondo gap formation. In addition, our observed in-gap Fermi surface oddness tied with the Kramers' point topology, their coexistence with the two-dimensional transport anomaly in the Kondo hybridization regime, as well as their robustness against thermal recycling, taken together, collectively provide strong evidence for protected surface metallicity with a Fermi surface whose topology is consistent with the theoretically predicted topological Fermi surface. Our observations of systematic surface electronic structure provide the fundamental electronic parameters for the anomalous Kondo ground state of correlated electron material SmB6.
291 citations
TL;DR: In this article, the ground state entanglement Hamiltonian and the physical stress tensor within the path integral formalism were derived for spherical entangling surfaces in a CFT, and the resulting reduced density matrix can be characterized by a spatially varying “entanglement temperature.
Abstract: We derive a general relation between the ground state entanglement Hamiltonian and the physical stress tensor within the path integral formalism. For spherical entangling surfaces in a CFT, we reproduce the local ground state entanglement Hamiltonian derived by Casini, Huerta and Myers. The resulting reduced density matrix can be characterized by a spatially varying “entanglement temperature”. Using the entanglement Hamiltonian, we calculate the first order change in the entanglement entropy due to changes in conserved charges of the ground state, and find a local first law-like relation for the entanglement entropy. Our approach provides a field theory derivation and generalization of recent results obtained by holographic techniques. However, we note a discrepancy between our field theoretically derived results for the entanglement entropy of excited states with a non-uniform energy density and current holographic results in the literature. Finally, we give a CFT derivation of a set of constraint equations obeyed by the entanglement entropy of excited states in any dimension. Previously, these equations were derived in the context of holography.
279 citations
University College London1, Old Dominion University2, California Institute of Technology3, Joseph Fourier University4, Eötvös Loránd University5, University of Reims Champagne-Ardenne6, National Institute of Standards and Technology7, Russian Academy of Sciences8, Harvard University9, Belgian Institute for Space Aeronomy10
TL;DR: In this paper, the authors presented experimental line positions, experimental-quality energy levels, and validated labels for rotational-vibrational transitions of the most abundant isotopologue of water, H216O.
Abstract: This is the third of a series of articles reporting critically evaluated rotational–vibrational line positions, transition intensities, and energy levels, with associated critically reviewed labels and uncertainties, for all the main isotopologues of water. This paper presents experimental line positions, experimental-quality energy levels, and validated labels for rotational–vibrational transitions of the most abundant isotopologue of water, H216O. The latest version of the MARVEL (Measured Active Rotational–Vibrational Energy Levels) line-inversion procedure is used to determine the rovibrational energy levels of the electronic ground state of H216O from experimentally measured lines, together with their self-consistent uncertainties, for the spectral region up to the first dissociation limit. The spectroscopic network of H216O containstwo components, an ortho (o) and a para (p) one. For o-H216O and p-H216O, experimentally measured, assigned, and labeled transitions were analyzed from more than 100 sources. The measured lines come from one-photon spectra recorded at room temperature in absorption, from hot samples with temperatures up to 3000 K recorded in emission, and from multiresonance excitation spectra which sample levels up to dissociation. The total number of transitions considered is 184 667 of which 182 156 are validated: 68 027 between para states and 114 129 ortho ones. These transitions give rise to 18 486 validated energy levels, of which 10 446 and 8040 belong to o-H216O and p-H216O, respectively. The energy levels, including their labeling with approximate normal-mode and rigid-rotor quantum numbers, have been checked against ones determined from accurate variational nuclear motion computations employing exact kinetic energy operators as well as against previous compilations of energy levels. The extensive list of MARVEL lines and levels obtained are deposited in the supplementary data of this paper, as well as in a distributed information system applied to water, W@DIS, where they can easily be retrieved.
237 citations
TL;DR: In this article, a scalar field equation involving a fractional Laplacian was studied and a positive ground state was obtained under the general Berestycki-Lions type assumptions.
Abstract: This paper focuses on the following scalar field equation involving a fractional Laplacian: where N ≥ 2, α ∈ (0, 1), (−Δ)α stands for the fractional Laplacian. Using some minimax arguments, we obtain a positive ground state under the general Berestycki–Lions type assumptions.
235 citations
TL;DR: In this article, a spin-1/2 Heisenberg antiferromagnetic chain was modeled as a singlet entangling all spins in the chain, and the existence of higher-order spinon states was quantified to within 99(8)%.
Abstract: One of the simplest quantum many-body systems is the spin-1/2 Heisenberg antiferromagnetic chain, a linear array of interacting magnetic moments. Its exact ground state is a macroscopic singlet entangling all spins in the chain. Its elementary excitations, called spinons, are fractional spin-1/2 quasiparticles created and detected in pairs by neutron scattering. Theoretical predictions show that two-spinon states exhaust only 71% of the spectral weight and higher-order spinon states, yet to be experimentally located, are predicted to participate in the remaining. Here, by accurate absolute normalization of our inelastic neutron scattering data on a spin-1/2 Heisenberg antiferromagnetic chain compound, we account for the full spectral weight to within 99(8)%. Our data thus establish and quantify the existence of higher-order spinon states. The observation that, within error bars, the experimental line shape resembles a rescaled two-spinon one with similar boundaries allows us to develop a simple picture for understanding multi-spinon excitations.
233 citations
TL;DR: In this paper, the energy and the static spin structure factor of the ground state of the spin-$1/2$ quantum Heisenberg antiferromagnetic model on the kagome lattice were studied.
Abstract: We study the energy and the static spin structure factor of the ground state of the spin-$1/2$ quantum Heisenberg antiferromagnetic model on the kagome lattice. By the iterative application of a few Lanczos steps on accurate projected fermionic wave functions and the Green's function Monte Carlo technique, we find that a gapless (algebraic) $U(1)$ Dirac spin liquid is competitive with previously proposed gapped (topological) ${\mathbb{Z}}_{2}$ spin liquids. By performing a finite-size extrapolation of the ground-state energy, we obtain an energy per site $E/J=\ensuremath{-}0.4365(2)$, which is equal, within three error bars, to the estimates given by the density-matrix renormalization group (DMRG). Our estimate is obtained for a translationally invariant system, and, therefore, does not suffer from boundary effects, like in DMRG. Moreover, on finite toric clusters at the pure variational level, our energies are lower compared to those from DMRG calculations.
TL;DR: A novel restricted-open-shell configuration interaction with singles (ROCIS) approach for the calculation of transition metal L-edge X-ray absorption spectra is introduced and it is advantageous to employ Kohn-Sham rather than Hartree-Fock orbitals thus defining the density functional theory∕R OCIS method.
Abstract: A novel restricted-open-shell configuration interaction with singles (ROCIS) approach for the calculation of transition metal L-edge X-ray absorption spectra is introduced. In this method, one first calculates the ground state and a number of excited states of the non-relativistic Hamiltonian. By construction, the total spin is a good quantum number in each of these states. For a ground state with total spin S excited states with spin S′ = S, S − 1, and S + 1 are constructed. Using Wigner-Eckart algebra, all magnetic sublevels with MS = S, …, −S for each multiplet of spin S are obtained. The spin-orbit operator is represented by a mean-field approximation to the full Breit-Pauli spin-orbit operator and is diagonalized over this N-particle basis. This is equivalent to a quasi-degenerate treatment of the spin-orbit interaction to all orders. Importantly, the excitation space spans all of the molecular multiplets that arise from the atomic Russell-Saunders terms. Hence, the method represents a rigorous first-principles approach to the complicated low-symmetry molecular multiplet problem met in L-edge X-ray absorption spectroscopy. In order to gain computational efficiency, as well as additional accuracy, the excitation space is restricted to single excitations and the configuration interaction matrix is slightly parameterized in order to account for dynamic correlation effects in an average way. To this end, it is advantageous to employ Kohn-Sham rather than Hartree-Fock orbitals thus defining the density functional theory/ROCIS method. However, the method can also be used in an entirely non-empirical fashion. Only three global empirical parameters are introduced and have been determined here for future application of the method to any system containing any transition metal. The three parameters were carefully calibrated using the L-edge X-ray absorption spectroscopy spectra of a test set of coordination complexes containing first row transition metals. These parameters are universal and transferable. Hence, there are no adjustable parameters that are used to fit experimental X-ray absorption spectra. Thus, the new approach classifies as a predictive first-principles method rather than an analysis tool. A series of calculations on transition metal compounds containing Cu, Ti, Fe, and Ni in various oxidation and spin states is investigated and a detailed comparison to experimental data is reported. In most cases, the approach yields good to excellent agreement with experiment. In addition, the origin of the observed spectral features is discussed in terms of the electronic structure of the investigated compounds.
TL;DR: This work adopted hardness as the fitness function in combination with the first-principles calculation to construct the hardness vs. energy map by seeking a proper balance between hardness and energy for a better mechanical description of given chemical systems.
Abstract: We reported a developed methodology to design superhard materials for given chemical systems under external conditions (here, pressure). The new approach is based on the CALYPSO algorithm and requires only the chemical compositions to predict the hardness vs. energy map, from which the energetically preferable superhard structures are readily accessible. In contrast to the traditional ground state structure prediction method where the total energy was solely used as the fitness function, here we adopted hardness as the fitness function in combination with the first-principles calculation to construct the hardness vs. energy map by seeking a proper balance between hardness and energy for a better mechanical description of given chemical systems. To allow a universal calculation on the hardness for the predicted structure, we have improved the earlier hardness model based on bond strength by applying the Laplacian matrix to account for the highly anisotropic and molecular systems. We benchmarked our approach in typical superhard systems, such as elemental carbon, binary B-N, and ternary B-C-N compounds. Nearly all the experimentally known and most of the earlier theoretical superhard structures have been successfully reproduced. The results suggested that our approach is reliable and can be widely applied into design of new superhard materials.
TL;DR: A global ground-state potential energy surface for N4 suitable for treating high-energy vibrational-rotational energy transfer and collision-induced dissociation in N2-N2 collisions is presented.
Abstract: We present a global ground-state potential energy surface for N4 suitable for treating high-energy vibrational-rotational energy transfer and collision-induced dissociation in N2–N2 collisions. To obtain the surface, complete active space second-order perturbation theory calculations were performed for the ground singlet state with an active space of 12 electrons in 12 orbitals and the maug-cc-pVTZ triple zeta basis set. About 17 000 ab initio data points have been calculated for the N4 system, distributed along nine series of N2 + N2 geometries and three series of N3 + N geometries. The six-dimensional ground-state potential energy surface is fitted using least-squares fits to the many-body component of the electronic energies based on permutationally invariant polynomials in bond order variables.
TL;DR: By analyzing diatomic molecules, this paper reveals size consistency errors up to several electron volts and finds that binding energies cannot be predicted reliably and consequences of the consistent ground-state use of the tuning approach are potential energy surfaces that are qualitatively in error and an incorrect prediction of spin states.
Abstract: Optimally tuned range separated hybrid functionals are a new class of implicitly defined functionals. Their important new aspect is that the range separation parameter in these functionals is determined individually for each system by iteratively tuning it until a fundamental, non-empirical condition is fulfilled. Such functionals have been demonstrated to be extremely successful in predicting electronic excitations. In this paper, we explore the use of the tuning approach for predicting ground state properties. This sheds light on one of its downsides – the violation of size consistency. By analyzing diatomic molecules, we reveal size consistency errors up to several electron volts and find that binding energies cannot be predicted reliably. Further consequences of the consistent ground-state use of the tuning approach are potential energy surfaces that are qualitatively in error and an incorrect prediction of spin states. We discuss these failures, their origins, and possibilities for overcoming them.
TL;DR: In this paper, the feasibility of tensor network solutions for lattice gauge theories in Hamiltonian formulation by applying matrix product states algorithms to the Schwinger model with zero and non-vanishing fermion mass was shown.
Abstract: We show the feasibility of tensor network solutions for lattice gauge theories in Hamiltonian formulation by applying matrix product states algorithms to the Schwinger model with zero and non-vanishing fermion mass. We introduce new techniques to com- pute excitations in a system with open boundary conditions, and to identify the states corresponding to low momentum and different quantum numbers in the continuum. For the ground state and both the vector and scalar mass gaps in the massive case, the MPS technique attains precisions comparable to the best results available from other techniques.
TL;DR: A redox active dinuclear complex displays single molecule magnet behaviour with M(J) = ±7/2 ground state demonstrating the correlation between magnetic and optical properties.
TL;DR: Kinetic Monte Carlo simulations agree well with the temporal evolution of the magnetic state when including disorder, and the experimental results can be explained by considering the effective interaction energy associated with the separation of pairs of vertex excitations.
Abstract: We study the thermal relaxation of artificial spin ice with photoemission electron microscopy, and are able to directly observe how such a system finds its way from an energetically excited state to the ground state. On plotting vertex-type populations as a function of time, we can characterize the relaxation, which occurs in two stages, namely a string and a domain regime. Kinetic Monte Carlo simulations agree well with the temporal evolution of the magnetic state when including disorder, and the experimental results can be explained by considering the effective interaction energy associated with the separation of pairs of vertex excitations.
TL;DR: In this paper, the authors analyzed the landscape of general smooth Gaussian functions on the sphere in dimension N, when N is large, and gave an explicit formula for the asymptotic complexity of the mean number of critical points of finite and diverging index at any level of energy and for the mean Euler characteristic of level sets.
Abstract: We analyze the landscape of general smooth Gaussian functions on the sphere in dimension N, when N is large. We give an explicit formula for the asymptotic complexity of the mean number of critical points of finite and diverging index at any level of energy and for the mean Euler characteristic of level sets. We then find two possible scenarios for the bottom landscape, one that has a layered structure of critical values and a strong correlation between indexes and critical values and another where even at levels below the limiting ground state energy the mean number of local minima is exponentially large. We end the paper by discussing how these results can be interpreted in the language of spin glasses models.
TL;DR: The second J(π)=2+ state of 12C, predicted over 50 years ago as an excitation of the Hoyle state, has been unambiguously identified using the 12C(γ,α0)(8)Be reaction.
Abstract: The second Jπ=2 + state of C12, predicted over 50 years ago as an excitation of the Hoyle state, has been unambiguously identified using the C12(γ,α 0 )Be8 reaction. The alpha particles produced by the photodisintegration of C12 were detected using an optical time projection chamber. Data were collected at beam energies between 9.1 and 10.7 MeV using the intense nearly monoenergetic gamma-ray beams at the HIγS facility. The measured angular distributions determine the cross section and the E1-E2 relative phases as a function of energy leading to an unambiguous identification of the second 2 + state in C12 at 10.03(11) MeV, with a total width of 800(130) keV and a ground state gamma-decay width of 60(10) meV; B(E2:22+→01+)=0.73(13)e2 fm4 [or 0.45(8) W.u.]. The Hoyle state and its rotational 2 + state that are more extended than the ground state of C12 presents a challenge and constraints for models attempting to reveal the nature of three alpha-particle states in C12. Specifically, it challenges the ab initio lattice effective field theory calculations that predict similar rms radii for the ground state and the Hoyle state. © 2013 American Physical Society.
TL;DR: This work investigates how the initially excited metal-to-ligand charge transfer (MLCT) singlet state deactivates to the final metastable high-spin state and determines all the intermediate electronic states along the pathway from low spin to high spin and gives estimates for the deactivation times of the different stages.
Abstract: The mechanism of the light- induced spin crossover of the (Fe- A3) 2 + complex (bpy = 2,2'-bipyri- dine) has been studied by combining accurate electronic-structure calcula- tions and time-dependent approaches to calculate intersystem-crossing rates. We investigate how the initially excited metal-to-ligand charge transfer (MLCT) singlet state deactivates to the final metastable high-spin state. Al- though ultrafast X-ray free-electron spectroscopy has established that the total timescale of this process is on the order of a few tenths of a picosecond, the details of the mechanisms still remain unclear. We determine all the intermediate electronic states along the pathway from low spin to high spin and give estimates for the deactivation times of the different stages. The calcu- lations result in a total deactivation time on the same order of magnitude as the experimentally determined rate and indicate that the complex can reach the final high-spin state by means of different deactivation chan- nels. The optically populated excited singlet state rapidly decays to a triplet state with an Fe d 6 (t 5e 1) configuration either directly or by means of a triplet MLCT state. This triplet ligand-field state could in principle decay directly to the final quintet state, but a much faster channel is provided by internal conversion to a lower-lying triplet state and subsequent intersystem crossing to the high-spin state. The deactivation rate to the low-spin ground state is much smaller, which is in line with the large quantum yield reported for the process.
TL;DR: In this paper, the mutual Renyi information of disjoint compact spatial regions A and B in the ground state of a d + 1-dimensional conformal field theory was studied.
Abstract: We consider the mutual Renyi information of disjoint compact spatial regions A and B in the ground state of a d + 1-dimensional conformal field theory (CFT), in the limit when the separation r between A and B is much greater than their sizes RA, B. We show that in general , where α is the smallest sum of the scaling dimensions of operators whose product has the quantum numbers of the vacuum, and the constants depend only on the shape of the regions and universal data of the CFT. For a free massless scalar field, where α = d − 1, we show that is proportional to the capacitance of a thin conducting slab in the shape of A in d + 1-dimensional electrostatics, and give explicit formulae for this when A is the interior of a sphere Sd − 1 or an ellipsoid. For spherical regions in d = 2 and 3 we obtain explicit results for C(n) for all n and hence for the leading term in the mutual information by taking n → 1. We also compute a universal logarithmic correction to the area law for the Renyi entropies of a single spherical region for a scalar field theory with a small mass.
TL;DR: In this article, a review of the available spectroscopic data for {Fe−NO}7 and {Fe-NO}8 mono-and dinuclear non-heme iron-nitrosyls are summarized and the implications of these results with respect to the electronic structures and reactivities of these species, in particular towards NO reduction, are discussed.
TL;DR: In this article, the existence of a positive ground state solution for the following class of elliptic equations was investigated: Δ u + V (x ) u = K ( x ) f ( u ) in R N, where N ⩾ 3, V, K are nonnegative continuous functions and f is a continuous function with a quasicritical growth.
TL;DR: Through exact diagonalization studies, it is shown that, even for moderate interactions, the many-body ground states consist of bosonic fractional quantum Hall states, including the Laughlin state and the Moore-Read (Pfaffian) state.
Abstract: We present a robust scheme by which fractional quantum Hall states of bosons can be achieved for ultracold atomic gases. We describe a new form of optical flux lattice, suitable for commonly used atomic species with ground state angular momentum ${J}_{g}=1$, for which the lowest energy band is topological and nearly dispersionless. Through exact diagonalization studies, we show that, even for moderate interactions, the many-body ground states consist of bosonic fractional quantum Hall states, including the Laughlin state and the Moore-Read (Pfaffian) state. These phases are shown to have energy gaps that are larger than temperature scales achievable in ultracold gases.
TL;DR: The nature and magnitude of the magnetic anisotropy of heptacoordinate mononuclear Ni( II) and Co(II) complexes were investigated by a combination of experiment and ab initio calculations to rationalize the magnitude and the sign of D.
Abstract: The nature and magnitude of the magnetic anisotropy of heptacoordinate mononuclear Ni(II) and Co(II) complexes were investigated by a combination of experiment and ab initio calculations. The zero-field splitting (ZFS) parameters D of [Ni(H(2)DAPBH)(H(2)O)(2)](NO(3))(2)⋅2 H(2)O (1) and [Co(H(2)DAPBH)(H(2)O)(NO(3))](NO(3)) [2; H(2)DAPBH = 2,6-diacetylpyridine bis- (benzoyl hydrazone)] were determined by means of magnetization measurements and high-field high-frequency EPR spectroscopy. The negative D value, and hence an easy axis of magnetization, found for the Ni(II) complex indicates stabilization of the highest M(S) value of the S = 1 ground spin state, while a large and positive D value, and hence an easy plane of magnetization, found for Co(II) indicates stabilization of the M(S) = ±1/2 sublevels of the S = 3/2 spin state. Ab initio calculations were performed to rationalize the magnitude and the sign of D, by elucidating the chemical parameters that govern the magnitude of the anisotropy in these complexes. The negative D value for the Ni(II) complex is due largely to a first excited triplet state that is close in energy to the ground state. This relatively small energy gap between the ground and the first excited state is the result of a small energy difference between the d(xy) and d(x(2)-y(2)) orbitals owing to the pseudo-pentagonal-bipyramidal symmetry of the complex. For Co(II), all of the excited states contribute to a positive D value, which accounts for the large magnitude of the anisotropy for this complex.
Posted Content•
TL;DR: A new proof for the area law for general 1D gapped systems, which exponentially improves Hastings' famous result, and establishes a new, “random-walk like”, bound on the entanglement rank of an arbitrary power of a 1D Hamiltonian.
Abstract: We give a new proof for the area law for general 1D gapped systems, which exponentially improves Hastings' famous result [1]. Specifically, we show that for a chain of d-dimensional spins, governed by a 1D local Hamiltonian with a spectral gap e > 0, the entanglement entropy of the ground state with respect to any cut in the chain is upper bounded by O(log^3 d/e ). Our approach uses the framework of Refs. [2, 3] to construct a Chebyshev-based AGSP (Approximate Ground Space Projection) with favorable factors. However, our construction uses the Hamiltonian directly, instead of using the Detectability lemma, which allows us to work with general (frustrated) Hamiltonians, as well as slightly improving the 1/e dependence of the bound in Ref. [3]. To achieve that, we establish a new, “random-walk like”, bound on the entanglement rank of an arbitrary power of a 1D Hamiltonian, which might be of independent interest: ER(H^l) ≤ (ld)O(√l). Finally, treating d as a constant, our AGSP shows that the ground state is well approximated by a matrix product state with a sublinear bond dimension B = e ^O(log^(3/4) n/e^(1/4)). Using this in conjunction with known dynamical programing algorithms, yields an algorithm for a 1=poly(n) approximation of the ground energy with a subexponential running time T ≤ exp (eO(log^(3/4) n/e^(1/4))).
TL;DR: The interface between two non-magnetic band insulators, LaAlO3 and SrTiO3, can exhibit conductivity, superconductivity and magnetism as discussed by the authors.
Abstract: The interface between two non-magnetic band insulators, LaAlO3 and SrTiO3, can exhibit conductivity, superconductivity and magnetism. These interfacial phenomena can be reconciled by a theory that predicts a spiral magnetic ground state.
TL;DR: Semihydrogenated graphitic BN (sh-BN) sheet is a potential metal-free visible-light driven photocatalyst for water splitting and the probability densities of valence and conduction bands are distributed apart spatially leading to a well- separation of photogenerated electrons and holes.
Abstract: Based on first principles calculations, we predict semihydrogenated graphitic BN (sh-BN) sheet is a potential metal-free visible-light driven photocatalyst for water splitting. The ground state of sh-BN is a strip-like antiferromagnetic semiconductor with a band gap suitable for visible-light absorption. The redox potentials of water splitting are all located inside the band gap and the probability densities of valence and conduction bands are distributed apart spatially leading to a well-separation of photogenerated electrons and holes.
TL;DR: The cyclic alkyl(amino) carbene (cAAC:)-stabilized acyclic germylones were prepared utilizing a one-pot synthesis of GeCl2(dioxane), cAAC:, and KC8 in a 1:2:2.1 molar ratio and suggested a singlet diradicaloid character of 1 and 2.
Abstract: The cyclic alkyl(amino) carbene (cAAC:)-stabilized acyclic germylones (Me2-cAAC:)2Ge (1) and (Cy2-cAAC:)2Ge (2) were prepared utilizing a one-pot synthesis of GeCl2(dioxane), cAAC:, and KC8 in a 1:2:2.1 molar ratio. Dark green crystals of compounds 1 and 2 were produced in 75 and 70% yields, respectively. The reported methods for the preparation of the corresponding silicon compounds turned out to be not applicable in the case of germanium. The single-crystal X-ray structures of 1 and 2 feature the C–Ge–C bent backbone, which possesses a three-center two-electron π-bond system. Compounds 1 and 2 are the first acyclic germylones containing each one germanium atom and two cAAC: molecules. EPR measurements on compounds 1 and 2 confirmed the singlet spin ground state. DFT calculations on 1/2 revealed that the singlet ground state is more stable by ∼16 to 18 kcal mol–1 than that of the triplet state. First and second proton affinity values were theoretically calculated to be of 265.8 (1)/267.1 (2) and 180.4 (1...