Emergence of Spinons in Layered Trimer Iridate Ba_{4}Ir_{3}O_{10}

Spinons are well known as the elementary excitations of one-dimensional antiferromagnetic chains, but means to realize spinons in higher dimensions is the subject of intense research. Here, we use resonant x-ray scattering to study the layered trimer iridate Ba_{4}Ir_{3}O_{10}, which shows no magnetic order down to 0.2 K. An emergent one-dimensional spinon continuum is observed that can be well described by XXZ spin-1/2 chains with a magnetic exchange of ∼55  meV and a small Ising-like anisotropy. With 2% isovalent Sr doping, magnetic order appears below T_{N}=130  K along with sharper excitations in (Ba_{1-x}Sr_{x})_{4}Ir_{3}O_{10}. Combining our data with exact diagonalization calculations, we find that the frustrated intratrimer interactions effectively reduce the system into decoupled spin chains, the subtle balance of which can be easily tipped by perturbations such as chemical doping. Our results put Ba_{4}Ir_{3}O_{10} between the one-dimensional chain and two-dimensional quantum spin liquid scenarios, illustrating a new way to suppress magnetic order and realize fractional spinons.

Global Phase Diagram of a Spin-Orbital Kondo Impurity Model and the Suppression of Fermi-Liquid Scale

Many correlated metallic materials are described by Landau Fermi-liquid theory at low energies, but for Hund metals the Fermi-liquid coherence scale T_{FL} is found to be surprisingly small. In this Letter, we study the simplest impurity model relevant for Hund metals, the three-channel spin-orbital Kondo model, using the numerical renormalization group (NRG) method and compute its global phase diagram. In this framework, T_{FL} becomes arbitrarily small close to two new quantum critical points that we identify by tuning the spin or spin-orbital Kondo couplings into the ferromagnetic regimes. We find quantum phase transitions to a singular Fermi-liquid or a novel non-Fermi-liquid phase. The new non-Fermi-liquid phase shows frustrated behavior involving alternating overscreenings in spin and orbital sectors, with universal power laws in the spin (ω^{-1/5}), orbital (ω^{1/5}) and spin-orbital (ω^{1}) dynamical susceptibilities. These power laws, and the NRG eigenlevel spectra, can be fully understood using conformal field theory arguments, which also clarify the nature of the non-Fermi-liquid phase.

Nonequilibrium Steady-State Transport in Quantum Impurity Models: A Thermofield and Quantum Quench Approach Using Matrix Product States

The numerical renormalization group (NRG) is tailored to describe interacting impurity models in equilibrium, but it faces limitations for steady-state nonequilibrium, arising, e.g., due to an applied bias voltage. We show that these limitations can be overcome by describing the thermal leads using a thermofield approach, integrating out high energy modes using NRG, and then treating the nonequilibrium dynamics at low energies using a quench protocol, implemented using the time-dependent density matrix renormalization group. This yields quantitatively reliable results for the current (with errors ≲3%) down to the exponentially small energy scales characteristic of impurity models. We present results of benchmark quality for the temperature and magnetic field dependence of the zero-bias conductance peak for the single-impurity Anderson model.

Dynamical Mean-Field Theory Plus Numerical Renormalization-Group Study of Spin-Orbital Separation in a Three-Band Hund Metal

We show that the numerical renormalization group is a viable multi-band impurity solver for dynamical mean-field theory (DMFT), offering unprecedented real-frequency spectral resolution at arbitrarily low energies and temperatures. We use it to obtain a numerically exact DMFT solution to the Hund metal problem for a three-band model on a Bethe lattice at 1/3 filling. The ground state is a Fermi liquid. The one-particle spectral function undergoes a coherence-incoherence crossover with increasing temperature, with spectral weight being transferred from low to high energies. Further, it exhibits a strong particle-hole asymmetry. In the incoherent regime, the self-energy displays approximate power-law behavior for positive frequencies only. The spin and orbital spectral functions show "spin-orbital separation": spin screening occurs at much lower energies than orbital screening. The renormalization group flows clearly reveal the relevant physics at all energy scales.

Transmission phase in the Kondo regime revealed in a two-path interferometer

We report on the direct observation of the transmission phase shift through a Kondo correlated quantum dot by employing a new type of two-path interferometer. We observed a clear π/2-phase shift, which persists up to the Kondo temperature TK. Above this temperature, the phase shifts by more than π/2 at each Coulomb peak, approaching the behavior observed for the standard Coulomb blockade regime. These observations are in remarkable agreement with two-level numerical renormalization group calculations. The unique combination of experimental and theoretical results presented here fully elucidates the phase evolution in the Kondo regime.

Proposed Rabi-Kondo correlated state in a laser-driven semiconductor quantum dot

Spin exchange between a single-electron charged quantum dot and itinerant electrons leads to an emergence of Kondo correlations. When the quantum dot is driven resonantly by weak laser light, the resulting emission spectrum allows for a direct probe of these correlations. In the opposite limit of vanishing exchange interaction and strong laser drive, the quantum dot exhibits coherent oscillations between the single-spin and optically excited states. Here, we show that the interplay between strong exchange and nonperturbative laser coupling leads to the formation of a new nonequilibrium quantum-correlated state, characterized by the emergence of a laser-induced secondary spin screening cloud, and examine the implications for the emission spectrum.

Non-Fermi-liquid behavior in transport through Co-doped Au chains

We calculate the conductance as a function of temperature G(T) through Au monatomic chains containing one Co atom as a magnetic impurity, and connected to two conducting leads with a fourfold symmetry axis. Using the information derived from ab initio calculations, we construct an effective model Ĥ(eff) that hybridizes a 3d(7) quadruplet at the Co site with two 3d(8) triplets through the hopping of 5d(xz) and 5d(yz) electrons of Au. The quadruplet is split by spin anisotropy due to spin-orbit coupling. Solving Ĥ(eff) with the numerical renormalization group we find that at low temperatures G(T)=a-b√[T] and the ground state impurity entropy is ln(2)/2, a behavior similar to the two-channel Kondo model. Stretching the chain leads to a non-Kondo phase, with the physics of the underscreened Kondo model at the quantum critical point.

Many-body dynamics of exciton creation in a quantum dot by optical absorption: a quantum quench towards Kondo correlations

We study a quantum quench for a semiconductor quantum dot coupled to a fermionic reservoir, induced by the sudden creation of an exciton via optical absorption. The subsequent emergence of correlations between spin degrees of freedom of dot and reservoir, culminating in the Kondo effect, can be read off from the absorption line shape and understood in terms of the three fixed points of the single-impurity Anderson model. At low temperatures the line shape is dominated by a power-law singularity, with an exponent that depends on gate voltage and, in a universal, asymmetric fashion, on magnetic field, indicative of a tunable Anderson orthogonality catastrophe.

Quantum criticality perspective on the charging of narrow quantum-dot levels

Understanding the charging of exceptionally narrow levels in quantum dots in the presence of interactions remains a challenge within mesoscopic physics. We address this fundamental question in the generic model of a narrow level capacitively coupled to a broad one. Using bosonization we show that for arbitrary capacitive coupling charging can be described by an analogy to the magnetization in the anisotropic Kondo model, featuring a low-energy crossover scale that depends in a power-law fashion on the tunneling amplitude to the level. Explicit analytical expressions for the exponent are derived and confirmed by detailed numerical and functional renormalization-group calculations.

Kondo decoherence: finding the right spin model for iron impurities in gold and silver

We exploit the decoherence of electrons due to magnetic impurities, studied via weak localization, to resolve a long-standing question concerning the classic Kondo systems of Fe impurities in the noble metals gold and silver: which Kondo-type model yields a realistic description of the relevant multiple bands, spin, and orbital degrees of freedom? Previous studies suggest a fully screened spin S Kondo model, but the value of S remained ambiguous. We perform density functional theory calculations that suggest S=3/2. We also compare previous and new measurements of both the resistivity and decoherence rate in quasi-one-dimensional wires to numerical renormalization group predictions for S=1/2, 1, and 3/2, finding excellent agreement for S=3/2.

Numerical renormalization group calculation of near-gap peaks in spectral functions of the Anderson model with superconducting leads

We use the numerical renormalization group method (NRG) to investigate a single-impurity Anderson model with a coupling of the impurity to a superconducting host. Analysis of the energy flow shows that, contrary to previous belief, NRG iterations can be performed up to a large number of sites, corresponding to energy differences far below the superconducting gap Δ. This allows us to calculate the impurity spectral function A(ω) very accurately for frequencies |ω|∼Δ, and to resolve, in a certain parameter regime, sharp peaks in A(ω) close to the gap edge.

Mesoscopic to universal crossover of the transmission phase of multilevel quantum dots

Transmission phase alpha measurements of many-electron quantum dots (small mean level spacing delta) revealed universal phase lapses by pi between consecutive resonances. In contrast, for dots with only a few electrons (large delta), the appearance or not of a phase lapse depends on the dot parameters. We show that a model of a multilevel quantum dot with local Coulomb interactions and arbitrary level-lead couplings reproduces the generic features of the observed behavior. The universal behavior of alpha for small delta follows from Fano-type antiresonances of the renormalized single-particle levels.

Spatially resolved manipulation of single electrons in quantum dots using a scanned probe

The scanning metallic tip of a scanning force microscope was coupled capacitively to electrons confined in a lithographically defined gate-tunable quantum dot at a temperature of 300 mK. Single electrons were made to hop on or off the dot by moving the tip or by changing the tip bias voltage owing to the Coulomb-blockade effect. Spatial images of conductance resonances map the interaction potential between the tip and individual electronic quantum dot states. Under certain conditions this interaction is found to contain a tip-voltage induced and a tip-voltage-independent contribution.

Potential landscapes and induced charges near metallic islands in three dimensions

We calculate electrostatic potential landscapes for an external probe charge in the presence of a set of metallic islands. Our numerical calculation in three dimensions (3D) uses an efficient grid relaxation technique. The well-known relaxation algorithm for solving the Poisson equation in two dimensions is generalized to 3D. In addition, all charges on the system, free as well as induced charges, are determined accurately and self-consistently to satisfy the desired boundary conditions. This allows the straightforward calculation of the potential on the outer boundary using the free space electrostatic Green's function, as well as the calculation of the entire capacitance matrix of the system. Physically interesting examples of nanoscale systems are presented and analyzed.

Lyophilisates for drug delivery in ophthalmology: pharmacokinetics of fluorescein in the human anterior segment

AIMS

To assess the ocular bioavailability of fluorescein from a novel water free, freeze dried ophthalmic drug delivery system compared to conventional preservative-free fluorescein eye drops.

METHODS

Sodium fluorescein 0.17% was dissolved in an aqueous solution of hydroxypropylmethyl cellulose 1.0% (HPMC), deposited on sterilised flexible hydrophobic poly(tetrafluoroethylene) (PTFE) carrier strips and freeze dried under aseptic conditions. The fluorescein dose of the lyophilisate was 68 micro g, corresponding to a single conventional drop of 40 micro l fluorescein 0.17% solution. In a randomised, open label study 12 healthy volunteers applied the lyophilised fluorescein to one eye and one drop of conventional fluorescein ophthalmic solution to the fellow eye. Fluorophotometry measurements of fluorescein concentrations in the anterior segment were performed with the Fluorotron Master II (Ocumetrics, USA) before and +15, 30, 45, 60, 120, and 180 minutes after application.

RESULTS

At all times anterior chamber fluorescein concentration was greater in the lyophysilate treated eye than the solution treated eye. The magnitude of this difference ranged from 2-5.3 times and was statistically significant.

CONCLUSION

The greater intraocular bioavailability of fluorescein from the lyophilisate relative to the solution suggests that it may be a useful method for delivering substances to the eye.

The effect of human fallopian tube epithelium on human sperm velocity motility and binding

PURPOSE

A prospective, controlled in vitro study was conducted to evaluate the effects of human fallopian tube epithelium on the motility, velocity, and binding of human spermatozoa.

METHODS

Eleven fallopian tubes from six women undergoing hysterectomy and semen samples from 14 male partners of women undergoing in vitro fertilization were collected. Human spermatozoa were cultured with monolayer of human fallopian tube epithelial cells. The motility and velocity were analyzed subsequently at 0, 2, 6, 24, and 48 hr of incubation. The sperm binding capacity was analyzed after 48 hr in the hemizona assay (HZA).

RESULTS

The presence of the human fallopian tube epithelial cells did not have any beneficial effects on sperm motility and velocity. On the other hand, significant promoting effect was observed in the ability of the sperm to bind to the zona pellucida.

CONCLUSIONS

The interaction of human spermatozoa with fallopian tube epithelial cells significantly increases sperm binding in the HZA.

High progesterone levels and ciliary dysfunction--a possible cause of ectopic pregnancy

OBJECTIVES

To investigate the effects of different levels of hormones on the ciliary activity of human oviducts and, consequently, to assess their possible role in tubal implantation of the fertilized egg.

DESIGN

Fallopian tube epithelial samples were incubated in media with the addition of Estradiol (E2), progesterone (P), human menopausal gonadotropin (hMG), LH, or pure FSH (Metrodin) in different concentrations. The ciliary beat frequency (CBF) was measured after 24 h of incubation. Then the media were exchanged to media without the addition of hormones and the CBF was measured again 24 h later by using the photoelectric technique.

SETTING

University teaching hospital, IVF unit.

RESULTS

Twenty-four hr after the addition of P to the culture medium in concentrations of 0.5 or 1 ng/ml a significant decline of the CBF down to 63% of the control level was observed (P < 0.001) and with P in concentration of 2 ng/ml or greater, 50-70% of the cilia were paralyzed. These effects of P were found to be reversible. Incubation with E2 induced a slight increase of 4% in the mean CBF (P = 0.002). Twenty-four hr incubation with Metrodin, Pergonal, or LH did not affect ciliary motility.

CONCLUSIONS

Higher levels of progesterone cause ciliary dysfunction and subsequently may be a possible cause of ectopic pregnancy.

Laser scattering instrument for real time in-vivo measurement of ciliary activity in human fallopian tubes

Based on a laser light scattering technique and fibre optic probe, we have developed and tested a simple and practical device for real time measurements of ciliary activity in human Fallopian tubes during laparoscopy and laparotomy. A further aim was to investigate the relationship between the ciliary beat frequency (CBF) and the morphology of the ciliary epithelium. The mean +/- SE of CBF in the fimbria and in the ampulla were 5.4 +/- 0.3 Hz and 5.0 +/- 0.1 Hz respectively. Small pieces of fimbria and ampulla epithelium were taken from the same sites at which the CBF was measured, and the percentage of ciliary cells was determined by scanning electron microscopy. A high positive correlation was found between CBF and the percentage of ciliary cells in the fimbria (r = 0.84) and in the ampulla (r = 0.88). The instrument presented in this study provided, for the first time, a quantitative examination of the CBF in intact human Fallopian tubes and may be used for the investigation of ciliary activity in patients with infertility.