Enhanced Two-Channel Kondo Physics in a Quantum Box Device

We propose a design for a one-dimensional quantum box device where the charge fluctuations are described by an anisotropic two-channel Kondo model. The device consists of a quantum box in the Coulomb blockade regime, weakly coupled to a quantum wire by a single-mode point contact. The electron correlations in the wire produce strong back scattering at the contact, significantly increasing the Kondo temperature as compared to the case of non-interacting electrons. By employing boundary conformal field theory techniques we show that the differential capacitance of the box exhibits manifest two-channel Kondo scaling with temperature and gate voltage, uncontaminated by the one-dimensional electron correlations. We discuss the prospect to experimentally access the Kondo regime with this type of device.Comment: EPL style, 5 pages, 1 figure, final published versio

Time-Loop Formalism for Irreversible Quantum Problems: Steady State Transport in Junctions with Asymmetric Dynamics

Non-unitary quantum mechanics has been used in the past to study irreversibility, dissipation and decay in a variety of physical systems. In this letter, we propose a general scheme to deal with systems governed by non-Hermitian Hamiltonians. We argue that the Schwinger-Keldysh formalism gives a natural description for those problems. To elucidate the method, we study a simple model inspired by mesoscopic physics --an asymmetric junction. The system is governed by a non-Hermitian Hamiltonian which captures essential aspects of irreversibility.Comment: 4 pages, 4 figure

Signatures of Strong Correlations in One-Dimensional Ultra-Cold Atomic Fermi Gases

Recent success in manipulating ultra-cold atomic systems allows to probe different strongly correlated regimes in one-dimension. Regimes such as the (spin-coherent) Luttinger liquid and the spin-incoherent Luttinger liquid can be realized by tuning the inter-atomic interaction strength and trap parameters. We identify the noise correlations of density fluctuations as a robust observable (uniquely suitable in the context of trapped atomic gases) to discriminate between these two regimes. Finally, we address the prospects to realize and probe these phenomena experimentally using optical lattices.Comment: 4 pages, 2 figure

Local Spectral Weight of a Luttinger Liquid: Effects from Edges and Impurities

We calculate the finite-temperature local spectral weight (LSW) of a Luttinger liquid with an "open" (hard wall) boundary. Close to the boundary the LSW exhibits characteristic oscillations indicative of spin-charge separation. The line shape of the LSW is also found to have a Fano-like asymmetry, a feature originating from the interplay between electron-electron interaction and scattering off the boundary. Our results can be used to predict how edges and impurities influence scanning tunneling microscopy (STM) of one-dimensional electron systems at low temperatures and voltage bias. Applications to STM on single-walled carbon nanotubes are discussed.Comment: 15 pages, 10 figues, The latest version in pdf format is available at http://www.physik.uni-kl.de/eggert/papers/LSW-LL.pd

Local height probabilities in a composite Andrews-Baxter-Forrester model

We study the local height probabilities in a composite height model, derived from the restricted solid-on-solid model introduced by Andrews, Baxter and Forrester, and their connection with conformal field theory characters. The obtained conformal field theories also describe the critical behavior of the model at two different critical points. In addition, at criticality, the model is equivalent to a one-dimensional chain of anyons, subject to competing two- and three-body interactions. The anyonic-chain interpretation provided the original motivation to introduce the composite height model, and by obtaining the critical behaviour of the composite height model, the critical behaviour of the anyonic chains is established as well. Depending on the overall sign of the hamiltonian, this critical behaviour is described by a diagonal coset-model, generalizing the minimal models for one sign, and by Fateev-Zamolodchikov parafermions for the other.Comment: 34 pages, 5 figures; v2: expanded introduction, references added and other minor change

Spin-Imbalance in a One-Dimensional Fermi Gas

Superconductivity and magnetism generally do not coexist. Changing the relative number of up and down spin electrons disrupts the basic mechanism of superconductivity, where atoms of opposite momentum and spin form Cooper pairs. Nearly forty years ago Fulde and Ferrell and Larkin and Ovchinnikov proposed an exotic pairing mechanism (FFLO) where magnetism is accommodated by formation of pairs with finite momentum. Despite intense theoretical and experimental efforts, however, polarized superconductivity remains largely elusive. Here we report experimental measurements of density profiles of a two spin mixture of ultracold 6Li atoms trapped in an array of one dimensional (1D) tubes, a system analogous to electrons in 1D wires. At finite spin imbalance, the system phase separates with an inverted phase profile in comparison to the three-dimensional case. In 1D we find a partially polarized core surrounded by wings composed of either a completely paired BCS superfluid or a fully polarized Fermi gas, depending on the degree of polarization. Our observations are in quantitative agreement with theoretical calculations in which the partially polarized phase is found to be a 1D analogue of the FFLO state. This study demonstrates how ultracold atomic gases in 1D may be used to create non-trivial new phases of matter, and also paves the way for direct observation and further study of the FFLO phase.Comment: 30 pages, 7 figure

\eta-superconductivity in the Hubbard chain with pair hopping

The ground state phase diagram of the 1D Hubbard chain with pair-hopping interaction is studied. The analysis of the model is performed using the continuum-limit field theory approach and exact diagonalization studies. At half-filling the phase diagram is shown to consist of two superconducting states with Cooper pair center-of-mass momentum Q=0 (BCS-\eta_0 phase) and Q=\pi (\eta_\pi-phase) and four insulating phases corresponding to the Mott antiferromagnet, the Peierls dimerized phase, the charge-density-wave (CDW) insulator as well as an unconventional insulating phase characterized by the coexistence of a CDW and a bond-located staggered magnetization. Away from half-filling the phase diagram consists of the superconducting BCS-\eta_0 and \eta_\pi phases and the metallic Luttinger-liquid phase. The BCS-\eta_0 phase exhibits smooth crossover from a weak-coupling BCS type to a strong coupling local-pair regime. The \eta_\pi phase shows properties of the doublon (zero size Cooper pair) superconductor with Cooper pair center-of-mass momentum Q=\pi. The transition into the \eta_\pi- paired state corresponds to an abrupt change in the groundstate structure. After the transition the conduction band is completely destroyed and a new \eta_\pi-pair band corresponding to the strongly correlated doublon motion is created.Comment: 15 pages Revtex, 15 embedded eps figure

Metamorphosis and Taxonomy of Andreev Bound States

We analyze the spatial and energy dependence of the local density of states in a SNS junction. We model our system as a one-dimensional tight-binding chain which we solve exactly by numerical diagonalization. We calculate the dependence of the Andreev bound states on position, phase difference, gate voltage, and coupling with the superconducting leads. Our results confirm the physics predicted by certain analytical approximations, but reveal a much richer set of phenomena beyond the grasp of these approximations, such as the metamorphosis of the discrete states of the normal link (the normal bound states) into Andreev bound states as the leads become superconducting.Comment: 23 pages, 15 figure