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Review: Superconductivity in ultrasmall metallic grainsJan 03 2001We review recent experimental and theoretical work on superconductivity in ultrasmall metallic grains, i.e. grains sufficiently small that the conduction electron energy spectrum becomes discrete. The discrete excitation spectrum of an individual grain ... More

Decoherence of interacting electrons in disordered conductors: on the relation between influence functional and diagrammatic approachesOct 29 2002We establish a connection between the influence functional approach of Golubev and Zaikin (GZ) and Keldysh diagrammatic perturbation theory for calculating the decoherence time of interacting electrons in disordered metals; we show how the standard diagrams ... More

Sum-rule Conserving Spectral Functions from the Numerical Renormalization GroupJul 19 2006Aug 20 2007We show how spectral functions for quantum impurity models can be calculated very accurately using a complete set of ``discarded'' numerical renormalization group eigenstates, recently introduced by Anders and Schiller. The only approximation is to judiciously ... More

Comment on ``Point-Contact Study of Fast and Slow Two-Level Fluctuators in Metallic Glasses'' by Keijsers, Shklyarevskii and van KempenJan 23 1998We point out that a recent experiment by Keijsers, Shklyarevskii and van Kempen [Phys. Rev. Lett. 77, 3411 (1996)] on metallic glass point contacts containing two-level systems (TLS) effectively measures for the first time the conductance contributions ... More

Observing the Nonequilibrium Dynamics of the Quantum Transverse-Field Ising Chain in Circuit QEDAug 07 2012Jan 10 2013We show how a quantum Ising spin chain in a time-dependent transverse magnetic field can be simulated and experimentally probed in the framework of circuit QED with current technology. The proposed setup provides a new platform for observing the nonequilibrium ... More

Reply to Comment on "Superradiant Phase Transitions and the Standard Description of Circuit QED"Feb 14 2012Jun 25 2012A Reply to the Comment by C. Ciuti and P. Nataf [arXiv:1112.0986v1] on our Letter "Superradiant Phase Transitions and the Standard Description of Circuit QED" [Phys. Rev. Lett. 107, 113602 (2011)].

Poor man's derivation of the Bethe-Ansatz equations for the Dicke modelAug 11 2010We present an elementary derivation of the exact solution (Bethe-Ansatz equations) of the Dicke model, using only commutation relations and an informed Ansatz for the structure of its eigenstates.

Finite-Size Bosonization of 2-Channel Kondo Model: a Bridge between Numerical Renormalization Group and Conformal Field TheoryJul 06 1998We generalize Emery and Kivelson's (EK) bosonization-refermionization treatment of the 2-channel Kondo model to finite system size and on the EK-line analytically construct its exact eigenstates and finite-size spectrum. The latter crosses over to conformal ... More

Spin tunneling in the Kagomé antiferromagnetNov 03 1992The collective tunneling of a small cluster of spins between two degenerate ground state configurations of the Kagom\'{e}-lattice quantum Heisenberg antiferromagnet is \mbox{studied}. The cluster consists of the six spins on a hexagon of the lattice. ... More

Destructive quantum interference in spin tunneling problemsAug 15 1992In some spin tunneling problems, there are several different but symmetry-related tunneling paths that connect the same initial and final configurations. The topological phase factors of the corresponding tunneling amplitudes can lead to destructive interference ... More

Anderson Orthogonality and the Numerical Renormalization GroupApr 15 2011Anderson Orthogonality (AO) refers to the fact that the ground states of two Fermi seas that experience different local scattering potentials, say |G_I> and |G_F>, become orthogonal in the thermodynamic limit of large particle number N, in that |<G_I|G_F>| ... More

Superradiant Phase Transitions and the Standard Description of Circuit QEDMar 23 2011We investigate the equilibrium behaviour of a superconducting circuit QED system containing a large number of artificial atoms. It is shown that the currently accepted standard description of circuit QED via an effective model fails in an important aspect: ... More

Equilibrium Fermi-liquid coefficients for the fully screened N-channel Kondo modelMar 03 2014May 25 2014We analytically and numerically compute three equilibrium Fermi-liquid coefficients of the fully screened $N$-channel Kondo model, namely $c_B$, $c_T$ and $c_\varepsilon$, characterizing the magnetic field and temperature dependence of the resisitivity, ... More

The dephasing rate formula in the many body contextSep 08 2009Nov 11 2009We suggest a straightforward approach to the calculation of the dephasing rate in a fermionic system, which correctly keeps track of the crucial physics of Pauli blocking. Starting from Fermi's golden rule, the dephasing rate can be written as an integral ... More

The Kondo Box: A Magnetic Impurity in an Ultrasmall Metallic GrainSep 30 1998We study the Kondo effect generated by a single magnetic impurity embedded in an ultrasmall metallic grain, to be called a ``Kondo box''. We find that the Kondo resonance is strongly affected when the mean level spacing in the grain becomes larger than ... More

Filling-driven Mott transition in SU(N) Hubbard modelsOct 11 2017We study the filling-driven Mott transition involving the metallic and paramagnetic insulating phases in SU(N) Fermi-Hubbard models, using dynamical mean-field theory (DMFT) and the numerical renormalization group (NRG) as impurity solver. The compressibility ... More

Generalized Schrieffer-Wolff transformation of multi-flavor Hubbard modelsOct 03 2017Dec 06 2017We give a self-contained derivation of the low-energy effective interactions of the SU($N$) Hubbard model, a multiflavor generalization of the one-band Hubbard model, by using a generalized Schrieffer-Wolff transformation (SWT). The effective interaction ... More

Interplay of mesoscopic and Kondo effects for transmission amplitude of few-level quantum dotsMay 20 2008The magnitude and phase of the transmission amplitude of a multi-level quantum dot is calculated for the mesoscopic regime of level spacing large compared to level width. The interplay between Kondo correlations and the influence by neighboring levels ... More

Numerical renormalization group calculation of near-gap peaks in spectral functions of the Anderson model with superconducting leadsMar 08 2008Jun 12 2008We 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, in contrast to previous belief, that NRG iterations can ... More

Hexagon-singlet solid ansatz for the spin-1 kagome antiferromagnetDec 22 2014Jun 25 2015We perform a systematic investigation on the hexagon-singlet solid (HSS) states, which are a class of spin liquid candidates for the spin-1 kagome antiferromagnet. With the Schwinger boson representation, we show that all HSS states have exponentially ... More

Transmission Phase Shift of a Quantum Dot with Kondo CorrelationsSep 28 1999Apr 26 2000We study the effects of Kondo correlations on the transmission phase shift of a quantum dot in an Aharonov-Bohm ring. We predict in detail how the development of a Kondo resonance should affect the dependence of the phase shift on transport voltage, gate ... More

Functional Renormalization Group treatment of the 0.7-analog in quantum point contactsMay 16 2018We use a recently developed fRG method (extendend Coupled-Ladder Approximation) to study the 0.7-analog in quantum point contacts, arising at the crossing of the 1st and 2nd band at suf- ficiently high magnetic fields. We reproduce the main features of ... More

Doublon-holon origin of the subpeaks at the Hubbard band edgesMay 10 2017Dec 06 2017Dynamical mean-field theory (DMFT) studies frequently observe a fine structure in the local spectral function of the SU(2) Fermi-Hubbard model at half filling: In the metallic phase close to the Mott transition, subpeaks emerge at the inner edges of the ... More

Critical and strong-coupling phases in one- and two-bath spin-boson modelsOct 28 2011Mar 06 2012For phase transitions in dissipative quantum impurity models, the existence of a quantum-to-classical correspondence has been discussed extensively. We introduce a variational matrix product state approach involving an optimized boson basis, rendering ... More

Non-Fermi-liquid Kondo screening under Rabi drivingMay 29 2019We investigate a Rabi-Kondo model describing an optically driven two-channel quantum dot device featuring a non-Fermi liquid Kondo effect. Optically induced Rabi oscillation between the valence and conduction levels of the dot give rise to a two-stage ... More

Lindblad-Driven Discretized Leads for Non-Equilibrium Steady-State Transport in Quantum Impurity Models: Recovering the Continuum LimitApr 07 2016The description of interacting quantum impurity models in steady-state non-equilibrium is an open challenge for computational many-particle methods: the numerical requirement of using a finite number of lead levels and the physical requirement of describing ... More

Flavor fluctuations in 3-level quantum dots: Generic SU(3)-Kondo fixed point in equilibrium and non-Kondo fixed points in nonequilibriumFeb 27 2018We study a $3$-level quantum dot in the singly occupied cotunneling regime coupled via a generic tunneling matrix to several multi-channel leads in equilibrium or nonequilibrium. We derive an effective model where also each reservoir has three channels ... More

Density matrix renormalization group study of a quantum impurity model with Landau-Zener time-dependent HamiltonianOct 16 2008Apr 01 2009We use the adaptive time-dependent density matrix renormalization group method (t-DMRG) to study the nonequilibrium dynamics of a benchmark quantum impurity system which has a time-dependent Hamiltonian. This model is a resonant-level model, obtained ... More

Signatures of Mottness and Hundness in archetypal correlated metalsAug 18 2017Jan 15 2019Physical properties of multi-orbital materials depend not only on the strength of the effective interactions among the valence electrons but also on their type. Strong correlations are caused by either Mott physics that captures the Coulomb repulsion ... More

Emergent spin-1 trimerized valence bond crystal in the spin-1/2 Heisenberg model on the star latticeAug 14 2015We explore the frustrated spin-$1/2$ Heisenberg model on the star lattice with antiferromagnetic (AF) couplings inside each triangle and ferromagnetic (FM) inter-triangle couplings ($J_e<0$), and calculate its magnetic and thermodynamic properties. We ... More

At which magnetic field, exactly, does the Kondo resonance begin to split? A Fermi liquid description of the low-energy properties of the Anderson modelSep 20 2016Jul 17 2018This paper is a corrected version of Phys. Rev. B 95, 165404 (2017), which we have retracted because it contained a trivial but fatal sign error that lead to incorrect conclusions. --- We extend a recently-eveloped Fermi-liquid (FL) theory for the asymmetric ... More

Simplex valence-bond crystal in the spin-1 kagome Heisenberg antiferromagnetJun 23 2014Mar 19 2015We investigate the ground state properties of a spin-1 kagome antiferromagnetic Heisenberg model using tensor-network (TN) methods. We obtain the energy per site {$e_0=-1.41090(2)$ with $D^*=8$ multiplets retained (i.e., a bond dimension of $D=24$), and ... More

Nonequilibrium Kondo effect in a magnetic field: Auxiliary master equation approachAug 18 2017Mar 01 2018We study the single-impurity Anderson model out of equilibrium under the influence of a bias voltage $\phi$ and a magnetic field $B$. We investigate the interplay between the shift ($\omega_B$) of the Kondo peak in the spin-resolved density of states ... More

Two-color Fermi liquid theory for transport through a multilevel Kondo impurityFeb 01 2018Mar 27 2018We consider a quantum dot with ${\cal K}{\geq} 2$ orbital levels occupied by two electrons connected to two electric terminals. The generic model is given by a multi-level Anderson Hamiltonian. The weak-coupling theory at the particle-hole symmetric point ... More

Emergent spin-1 trimerized valence bond crystal in the spin-1/2 Heisenberg model on the star latticeAug 14 2015Feb 26 2018We explore the frustrated spin-$1/2$ Heisenberg model on the star lattice with antiferromagnetic (AF) couplings inside each triangle and ferromagnetic (FM) inter-triangle couplings ($J_e<0$), and calculate its magnetic and thermodynamic properties. We ... More

Two-bath spin-boson model: Phase diagram and critical propertiesOct 14 2014The spin-boson model, describing a two-level system coupled to a bath of harmonic oscillators, is a generic model for quantum dissipation, with manifold applications. It has also been studied as a simple example for an impurity quantum phase transition. ... More

Thermal Tensor Renormalization Group Simulations of Square-Lattice Quantum Spin ModelsApr 12 2019In this work, we benchmark the well-controlled and numerically accurate exponential thermal tensor renormalization group (XTRG) in the simulation of interacting spin models in two dimensions. Finite temperature introduces a thermal correlation length, ... More

Anatomy of quantum critical wave functions in dissipative impurity problemsAug 02 2016Feb 03 2017Quantum phase transitions reflect singular changes taking place in a many-body ground state, however, computing and analyzing large-scale critical wave functions constitutes a formidable challenge. New physical insights into the sub-Ohmic spin-boson model ... More

Open Wilson chains for quantum impurity models: Keeping track of all bath modesNov 16 2016Apr 03 2017When constructing a Wilson chain to represent a quantum impurity model, the effects of truncated bath modes are neglected. We show that their influence can be kept track of systematically by constructing an "open Wilson chain" in which each site is coupled ... More

Frequency-dependent transport through a quantum dot in the Kondo regimeJun 14 2004May 24 2005We study the AC conductance and equilibrium current fluctuations of a Coulomb blockaded quantum dot. A relation between the equilibrium spectral function and the linear AC conductance is derived which is valid for frequencies well below the charging energy ... More

The spin-boson model with a structured environment: A comparison of approachesOct 10 2003In the spin-boson model, the properties of the oscillator bath are fully characterized by the spectral density of oscillators $J(\omega)$. We study the case when this function is of Breit-Wigner shape and has a sharp peak at a frequency $\Omega$ with ... More

Influence Functional for Decoherence of Interacting Electrons in Disordered ConductorsOct 21 2005Apr 10 2008We have rederived the controversial influence functional approach of Golubev and Zaikin (GZ) for interacting electrons in disordered metals in a way that allows us to show its equivalence, before disorder averaging, to diagrammatic Keldysh perturbation ... More

Superconductivity in Ultrasmall Grains: Introduction to Richardson's Exact SolutionNov 04 1999Studies of pairing correlations in ultrasmall metallic grains have commonly been based on a simple reduced BCS-model describing the scattering of pairs of electrons between discrete energy levels that come in time-reversed pairs. This model has an exact ... More

Fixed-N Superconductivity: The Exact Crossover from the Bulk to the Few-Electron LimitJul 26 1999We use two truly canonical approaches to describe superconductivity in ultrasmall metallic grains: (a) a variational fixed-N projected BCS-like theory and (b) an exact solution of the model Hamiltonian developed by Richardson in context with Nuclear Physics. ... More

Simple Bosonization Solution of the 2-channel Kondo Model: I. Analytical Calculation of Finite-Size Crossover SpectrumDec 10 1998We present in detail a simple, exact solution of the anisotropic 2-channel Kondo (2CK) model at its Toulouse point. We reduce the model to a quadratic resonant-level model by generalizing the bosonization-refermionization approach of Emery and Kivelson ... More

Nonequilibrium excitations in Ferromagnetic NanoparticlesOct 17 2001In recent measurements of tunneling transport through individual ferromagnetic Co nanograins, Deshmukh, Gu\'eron, Ralph et al. \cite{mandar,gueron} (DGR) observed a tunneling spectrum with discrete resonances, whose spacing was much smaller than what ... More

Bosonization for Beginners --- Refermionization for ExpertsMay 21 1998Oct 30 1998This tutorial gives an elementary and self-contained review of abelian bosonization in 1 dimension in a system of finite size $L$, following and simplifying Haldane's constructive approach. As a non-trivial application, we rigorously resolve (following ... More

Algebraic Bethe Ansatz for a discrete-state BCS pairing modelJun 20 2001We show in detail how Richardson's exact solution of a discrete-state BCS (DBCS) model can be recovered as a special case of an algebraic Bethe Ansatz solution of the inhomogeneous XXX vertex model with twisted boundary conditions: by implementing the ... More

Fixed-N Superconductivity: The Crossover from the Bulk to the Few-Electron LimitOct 13 1998Jan 18 1999We present a truly canonical theory of superconductivity in ultrasmall metallic grains by variationally optimizing fixed-N projected BCS wave-functions, which yields the first full description of the entire crossover from the bulk BCS regime (mean level ... More

Superconductivity in Ultrasmall Metallic GrainsJan 16 1998We develop a theory of superconductivity in ultrasmall (nm-scale) metallic grains having a discrete electronic eigenspectrum with a mean level spacing of order of the bulk gap. The theory is based on calculating the eigenspectrum using a generalized BCS ... More

Functional Renormalization Group Approach for Inhomogeneous Interacting Fermi-SystemsNov 13 2013Jan 23 2014The functional renormalization group (fRG) approach has the property that, in general, the flow equation for the two-particle vertex generates $\mathcal{O}(N^4)$ independent variables, where $N$ is the number of interacting states (e.g. sites of a real-space ... More

DMFT+NRG study of spin-orbital separation in a three-band Hund's metalMar 22 2015We show that the numerical renormalization group (NRG) is a viable multi-band impurity solver for Dynamical Mean Field Theory (DMFT), offering unprecedent real-frequency spectral resolution at arbitrarily low energies and temperatures. We use it to obtain ... More

Fermi-edge singularity and the functional renormalization groupJun 21 2017May 13 2018We study the Fermi-edge singularity, describing the response of a degenerate electron system to optical excitation, in the framework of the functional renormalization group (fRG). Results for the (interband) particle-hole susceptibility from various implementations ... More

Multiloop functional renormalization group that sums up all parquet diagramsMar 19 2017Feb 14 2018We present a multiloop flow equation for the four-point vertex in the functional renormalization group (fRG) framework. The multiloop flow consists of successive one-loop calculations and sums up all parquet diagrams to arbitrary order. This provides ... More

Derivation of exact flow equations from the self-consistent parquet relationsJul 08 2018Dec 27 2018We exploit the parquet formalism to derive exact flow equations for the two-particle-reducible four-point vertices, the self-energy, and typical response functions, circumventing the reliance on higher-point vertices. This includes a concise, algebraic ... More

Measuring the size of a Schroedinger cat stateSep 01 2006We propose a measure for the "size" of a Schroedinger cat state, i.e. a quantum superposition of two many-body states with (supposedly) macroscopically distinct properties, by counting how many single-particle operations are needed to map one state onto ... More

Functional Renormalization Group Approach for Inhomogeneous One-Dimensional Fermi Systems with Finite-Ranged InteractionsSep 23 2016Jan 16 2017We introduce an equilibrium formulation of the functional renormalization group (fRG) for inhomogeneous systems capable of dealing with spatially finite-ranged interactions. In the general third order truncated form of fRG, the dependence of the two-particle ... More

Identifying Symmetry-Protected Topological Order by Entanglement EntropyJun 24 2013Jan 08 2014According to the classification using projective representations of the SO(3) group, there exist two topologically distinct gapped phases in spin-1 chains. The symmetry-protected topological (SPT) phase possesses half-integer projective representations ... More

The quantum transverse-field Ising chain in circuit QED: effects of disorder on the nonequilibrium dynamicsJan 16 2013Apr 19 2013We study several dynamical properties of a recently proposed implementation of the quantum transverse-field Ising chain in the framework of circuit QED. Particular emphasis is placed on the effects of disorder on the nonequilibrium behavior of the system. ... More

Josephson effect between superconducting nanograins with discrete energy levelsMay 15 2003We investigate the Josephson effect between two coupled superconductors, coupled by the tunneling of pairs of electrons, in the regime that their energy level spacing is comparable to the bulk superconducting gap, but neglecting any charging effects. ... More

Matrix product state approach for a two-lead, multi-level Anderson impurity modelApr 03 2008Mar 16 2010We exploit the common mathematical structure of the numerical renormalization group and the density matrix renormalization group, namely, matrix product states, to implement an efficient numerical treatment of a two-lead, multi-level Anderson impurity ... More

Decoherence without dissipation?Jun 03 2003In a recent article, Ford, Lewis and O'Connell (PRA 64, 032101 (2001)) discuss a thought experiment in which a Brownian particle is subjected to a double-slit measurement. Analyzing the decay of the emerging interference pattern, they derive a decoherence ... More

Multiloop functional renormalization group for general modelsJul 14 2017Feb 14 2018We present multiloop flow equations in the functional renormalization group (fRG) framework for the four-point vertex and self-energy, formulated for a general fermionic many-body problem. This generalizes the previously introduced vertex flow [F. B. ... More

Spectroscopy of discrete energy levels in ultrasmall metallic grainsJan 02 2001Jan 03 2001We review recent experimental and theoretical work on ultrasmall metallic grains, i.e. grains sufficiently small that the conduction electron energy spectrum becomes discrete. The discrete excitation spectrum of an individual grain can be measured by ... More

Functional Renormalization Group Approach for Inhomogeneous One-Dimensional Fermi Systems with Finite-Ranged InteractionsSep 23 2016We introduce an equilibrium formulation of the functional renormalization group (fRG) for inhomogeneous systems capable of dealing with spatially finite-ranged interactions. In the general third order truncated form of fRG, the dependence of the two-particle ... More

Efficient simulation of infinite tree tensor network states on the Bethe latticeSep 11 2012Nov 27 2012We show that the simple update approach proposed by Jiang et. al. [H.C. Jiang, Z.Y. Weng, and T. Xiang, Phys. Rev. Lett. 101, 090603 (2008)] is an efficient and accurate method for determining the infinite tree tensor network states on the Bethe lattice. ... More

Matrix product state comparison of the numerical renormalization group and the variational formulation of the density matrix renormalization groupApr 01 2008Wilson's numerical renormalization group (NRG) method for solving quantum impurity models yields a set of energy eigenstates that have the form of matrix product states (MPS). White's density matrix renormalization group (DMRG) for treating quantum lattice ... More

Transport and Dephasing in a Quantum Dot: Multiply Connected Graph ModelOct 10 2011Using the theory of diffusion in graphs, we propose a model to study mesoscopic transport through a diffusive quantum dot. The graph consists of three quasi-1D regions: a central region describing the dot, and two identical left- and right- wires connected ... More

Flow equation renormalization of a spin-boson model with a structured bathFeb 18 2003We discuss the dynamics of a spin coupled to a damped harmonic oscillator. This system can be mapped to a spin-boson model with a structured bath, i.e. the spectral function of the bath has a resonance peak. We diagonalize the model by means of infinitesimal ... More

Symmetric Minimally Entangled Typical Thermal StatesJun 10 2015Sep 05 2015We extend White's minimally entangled typically thermal states approach (METTS) to allow Abelian and non-Ablian symmetries to be exploited when computing finite-temperature response functions in one-dimensional (1D) quantum systems. Our approach, called ... More

Kondo quantum dot coupled to ferromagnetic leads: Numerical renormalization group studyJun 27 2007We systematically study the influence of ferromagnetic leads on the Kondo resonance in a quantum dot tuned to the local moment regime. We employ Wilson's numerical renormalization group method, extended to handle leads with a spin asymmetric density of ... More

Proposed Rabi-Kondo Correlated State in a Laser-Driven Semiconductor Quantum DotNov 29 2012Oct 11 2013Spin 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 ... More

Nonequilibrium dynamics in an optical transition from a neutral quantum dot to a correlated many-body stateApr 05 2013Nov 04 2013We investigate the effect of many-body interactions on the optical absorption spectrum of a charge-tunable quantum dot coupled to a degenerate electron gas. A constructive Fano interference between an indirect path, associated with an intra dot exciton ... More

Magnetic Anisotropy Variations and Non-Equilibrium Tunneling in a Cobalt NanoparticleAug 09 2001We present detailed measurements of the discrete electron-tunneling level spectrum within nanometer-scale cobalt particles as a function of magnetic field and gate voltage, in this way probing individual quantum many-body eigenstates inside ferromagnetic ... More

The effects of ion mass variation and domain size on octupolar out-of-plane magnetic field generation in collisionless magnetic reconnectionMar 18 2015Mar 26 2015J. Graf von der Pahlen and D. Tsiklauri, Phys. Plas. 21, 060705 (2014), established that the generation of octupolar out-of-plane magnetic field structure in a stressed $X$-point collapse is due to ion currents. The field has a central region, comprising ... More

Theoretical compensation of static deformations of freeform multi mirror substratesMay 30 2018Varying temperatures influence the figure errors of freeform metal mirrors by thermal expansion. Furthermore, different materials lead to thermo-elastic bending effects. The article presents a derivation of a compensation approach for general static loads. ... More

Effect of spin-orbit interactions on the 0.7 anomaly in quantum point contactsAug 04 2014Jan 05 2015We study how the conductance of a quantum point contact is affected by spin-orbit interactions, for systems at zero temperature both with and without electron-electron interactions. In the presence of spin-orbit coupling, tuning the strength and direction ... More

Diagnostics of low and atmospheric pressure plasmas by means of mass spectrometryMay 13 2011The knowledge of absolute fluxes of reactive species such as radicals or energetic ions to the surface is crucial for understanding the growth or etching of thin films. These species have due to their high reactivity very low densities and their detection ... More

Keldysh Derivation of Oguri's Linear Conductance Formula for Interacting FermionsApr 19 2017We present a Keldysh-based derivation of a formula, previously obtained by Oguri using the Matsubara formalisum, for the linear conductance through a central, interacting region coupled to non-interacting fermionic leads. Our starting point is the well-known ... More

Dephasing in Metals by Two-Level Systems in the 2-Channel-Kondo RegimeFeb 11 1999Sep 28 1999We point out a novel, non-universal contribution to the dephasing rate 1/\tau_\phi \equiv \gamma_\phi of conduction electrons in metallic systems: scattering off non-magnetic two-level systems (TLSs) having almost degenerate Kondo ground states. In the ... More

Decoherence in weak localization II: Bethe-Salpeter calculation of CooperonOct 21 2005This is the second in a series of two papers (I and II) on the problem of decoherence in weak localization. In paper I, we discussed how the Pauli principle could be incorporated into an influence functional approach for calculating the Cooperon propagator ... More

Decoherence in weak localization I: Pauli principle in influence functionalOct 21 2005This is the first in a series of two papers (I and II), in which we revisit the problem of decoherence in weak localization. The basic challenge addressed in our work is to calculate the decoherence of electrons interacting with a quantum-mechanical environment, ... More

At which magnetic field, exactly, does the Kondo resonance begin to split?Sep 20 2016We extend a recently-developed Fermi-liquid (FL) theory for the asymmetric single-impurity Anderson model [C. Mora et al., Phys. Rev. B, 92, 075120 (2015)] to the case of an arbitrary local magnetic field. To describe the system's low-lying quasiparticle ... More

Well-defined quasiparticles in interacting metallic grainsApr 26 2004We analyze spectral functions of mesoscopic systems with large dimensionless conductance, which can be described by a universal Hamiltonian. We show that an important class of spectral functions are dominated by one single state only, which implies the ... More

Dynamic structure factor of the spin-1/2 XXZ chain in a transverse fieldJun 10 2016Aug 22 2016The spin-$\frac{1}{2}$ XXZ chain with easy-plane anisotropy in a transverse field describes well the thermodynamic properties of the material ${\rm Cs_2CoCl_4}$ in a wide range of temperatures and fields including the region close to the spin-flop Ising ... More

Paramagnetic Breakdown of Superconductivity in Ultrasmall Metallic GrainsApr 22 1997Jul 31 1997We study the magnetic-field-induced breakdown of superconductivity in nm-scale metal grains having a mean electron level spacing $d \simeq \tilde\Delta$ (bulk gap). Using a generalized variational BCS approach that yields good qualitative agreement with ... More

Hundness versus Mottness in a three-band Hubbard-Hund model: On the origin of strong correlations in Hund metalsAug 29 2018Dec 21 2018Hund metals are multi-orbital systems with moderate Coulomb interaction, $U$, and sizeable Hund's rule coupling, $J<U$, that aligns the spins in different orbitals. They show strong correlation effects, like very low Fermi-liquid coherence scales and ... More

Fermi-liquid theory for the single-impurity Anderson modelSep 11 2014Aug 25 2015We generalize Nozi\`eres' Fermi-liquid theory for the low-energy behavior of the Kondo model to that of the single-impurity Anderson model. In addition to the electrons' phase shift at the Fermi energy, the low-energy Fermi-liquid theory is characterized ... More

Nonequilibrium Steady-State Transport in Quantum Impurity Models: a Thermofield and Quantum Quench Approach using Matrix Product StatesAug 21 2017Jan 03 2019The numerical renormalization group (NRG) is tailored to describe interacting impurity models in equilibrium, but faces limitations for steady-state nonequilibrium, arising, e.g., due to an applied bias voltage. We show that these limitations can be overcome ... More

Spin fluctuations in the 0.7-anomaly in quantum point contactsMar 08 2017It has been argued that the 0.7 anomaly in quantum point contacts (QPCs) is due to an enhanced density of states at the top of the QPC-barrier (van Hove ridge), which strongly enhances the effects of interactions. Here, we analyze their effect on dynamical ... More

SU(3) Anderson impurity model: A numerical renormalization group approach exploiting non-Abelian symmetriesAug 03 2012We show how the density-matrix numerical renormalization group (DM-NRG) method can be used in combination with non-Abelian symmetries such as SU(N), where the decomposition of the direct product of two irreducible representations requires the use of a ... More

The 2-Channel Kondo Model II: CFT Calculation of Non-Equilibrium Conductance through a Nanoconstriction containing 2-Channel Kondo ImpuritiesFeb 05 1997Sep 20 1999Recent experiments by Ralph and Buhrman on zero-bias anomalies in quenched Cu nanoconstrictions (reviewed in the preceding paper, I), are in accord with the assumption that the interaction between electrons and nearly degenerate two-level systems in the ... More

Theory of inelastic scattering from magnetic impuritiesMar 29 2004Mar 31 2004We use the numerical renormalization group method tocalculate the single particle matrix elements $\cal T$ of the many body $T$-matrix of the conduction electrons scattered by a magnetic impurity at T=0 temperature. Since $\cal T$ determines both the ... More

A numerical algorithm for the explicit calculation of SU(N) and SL(N,C) Clebsch-Gordan coefficientsSep 02 2010Mar 28 2011We present an algorithm for the explicit numerical calculation of SU(N) and SL(N,C) Clebsch-Gordan coefficients, based on the Gelfand-Tsetlin pattern calculus. Our algorithm is well-suited for numerical implementation; we include a computer code in an ... More

Charge oscillations in Quantum Dots: Renormalization group and Hartree method calculationsAug 04 2004Nov 08 2005We analyze the local level occupation of a spinless, interacting two-level quantum dot coupled to two leads by means of Wilson's numerical renormalization group method. A gate voltage sweep, causing a rearrangement of the charge such that the system's ... More

Fermi-edge exciton-polaritons in doped semiconductor microcavities with finite hole massJul 26 2017Oct 27 2017The coupling between a 2D semiconductor quantum well and an optical cavity gives rise to combined light-matter excitations, the exciton-polaritons. These were usually measured when the conduction band is empty, making the single polariton physics a simple ... More

Shedding light on non-equilibrium dynamics of a spin coupled to fermionic reservoirJul 22 2009A single confined spin interacting with a solid-state environment has emerged as one of the fundamental paradigms of mesoscopic physics. In contrast to standard quantum optical systems, decoherence that stems from these interactions can in general not ... More

A note on quadratic forms of stationary functional time series under mild conditionsMay 30 2019We study the distributional properties of a quadratic form of a stationary functional time series under mild moment conditions. As an important application, we obtain consistency rates of estimators of spectral density operators and prove joint weak convergence ... More

Effects of periodic forcing on a Paleoclimate delay modelAug 07 2018Jan 11 2019We present a study of a delay differential equation (DDE) model for the Mid-Pleistocene Transition (MPT). We investigate the behavior of the model when subjected to periodic forcing. The unforced model has a bistable region consisting of a stable equilibrium ... More

The gluon propagator close to criticalityOct 28 2011Mar 15 2012The deconfinement phase transition of pure Yang-Mills theory at finite temperature is reflected in the behavior of gauge-fixed gluonic correlation functions. This is one of many examples of how physical information can be extracted from gauge-dependent ... More