An experiment is proposed to measure the out-of-equilibrium splitting of the Kondo resonance in an ultrasmall quantum dot, by adding a third, weakly coupled lead to the standard two-lead quantumdot system, and sweeping the chemical potential of that lead. Fixing the voltage bias between the source and drain leads, we show that the differential conductance for the current through the third lead traces the out-of-equilibrium dot density of states (DOS) for the two-lead system. This enables one to measure the dot DOS in the presence of an applied voltage bias. We show that this method is robust, and extends also to the case where the coupling to the third lead is no longer weak.

The charging of a quantum box connected to a lead by a single-mode point contact is solved for arbitrary temperatures, tunneling amplitudes, and gate voltages, using a variant of Wilson's numerical renormalization group. The charge inside the box and the capacitance of the junction are calculated on equal footing for all physical regimes, including weak tunneling, near perfect transmission, and the crossover regime in between. At the charge plateaus, perturbation theory is found to break down at fairly small tunneling amplitudes. Near perfect transmission, we confirm Matveev's scenario for the smearing of the Coulomb-blockade staircase. A surprising reentrance of the Coulomb-blockade staircase is found for large tunneling amplitudes. At the degeneracy points, we obtain two-channel Kondo behavior directly from the Coulomb-blockade Hamiltonian, without the restriction to two charge configurations or the introduction of an effective cutoff.PACS numbers: 73.23. Hk, 72.15.Qm, 73.40.Gk The Coulomb blockade 1,2 is one of the fundamental phenomena in mesoscopic physics. When a quantum box, either a small metallic grain or a large semiconducting quantum dot, is coupled by weak tunneling to a lead, its charging is governed by the finite energy barrier E C for adding a single electron to the box. This gives rise to the well-known Coulomb-blockade staircase for the charge of the box as a function of gate voltage. 1,2 Increasing the coupling to the lead smears the Coulomb staircase, as thermal fluctuations do at k B T > E C .A large diversity of theoretical approaches have been applied to the Coulomb blockade, ranging from perturbation theory 3,4,5,6 and diagrammatic techniques, 7,8,9 to renormalization-group treatments 4,5,10,11,12 and Monte Carlo simulations. 11,12,13,14 However, to date there is no single unified approach encompassing all regimes of the Coulomb blockade. The reason being that different starting points are required for describing the different physical regimes of the Coulomb blockade. For weak tunneling and k B T ≪ E C , the charge inside the box is essentially quantized at the charge plateaus. Hence, one can start from a well-defined charge configuration and apply the perturbation theory in the tunneling amplitude. This approach collapses at the degeneracy points between adjacent charge plateaus, where strong charge fluctuations give rise to exotic many-body physics in the form of the two-channel Kondo effect. 5,15 For large transmission, the Coulomb-blockade staircase is smeared out and the notion of well-defined charge configurations breaks down.In this paper, we devise such a unified approach for all temperatures and parameter regimes of the Coulomb blockade using Wilson's numerical renormalization-group method. 16 Focusing on single-mode point contacts, we accurately calculate the charge and the capacitance of the quantum box, for arbitrary gate voltages, temperatures, and tunneling amplitudes. These quantities were recently measured by Berman et al. for single-mode point contacts, 17 revealing sign...

We present a theory for the memory effect in electron glasses. In fast gate voltage sweeps it is manifested as a dip in the conductivity around the equilibration gate voltage. We show that this feature, also known as anomalous field effect, arises from the long-time persistence of correlations in the electronic configuration. We argue that the gate voltage at which the memory dip saturates is related to an instability caused by the injection of a critical number of excess carriers. This saturation threshold naturally increases with temperature. On the other hand, we argue that the gate voltage beyond which memory is erased, is temperature independent. Using standard percolation arguments, we calculate the anomalous field effect as a function of gate voltage, temperature, carrier density and disorder. Our results are consistent with experiments, and in particular, they reproduce the observed scaling of the width of the memory dip with various parameters.

The noncrossing approximation (NCA) is generalized to the multi-channel Kondo-spin Hamiltonian with arbitrary anisotropic exchange couplings and an external magnetic field, and appliedin the framework of Matveev's mapping -to the charge fluctuations in a single-electron box at the Coulomb blockade. The temperature dependences of the charge step and the capacitance are calculated for a narrow point contact. At low temperatures and close to the degeneracy point, the capacitance line shape exhibits an approximate scaling with U/ √ T , where U is the deviation in gate voltage from the degeneracy point. This scaling relation is proposed as a sharp experimental diagnostic for the non-Fermi-liquid physics of the system at low temperatures. Both the reliability and shortcomings of the Kondo NCA are discussed in detail. Through comparison with poor-man's scaling, we are able to pinpoint the omission of particle-particle processes as the origin of the NCA flaws. An extended diagrammatic scheme is devised to amend the NCA flaws.

∞ m=−∞ m|m m| andN ± = ∞ m=−∞ |m ± 1 m|, we replace the tunneling term between the dot and the box in Eq. (1) with k,σ t B N + c † Bkσ d σ + H.c. , while the charging-energy term is converted to E C (N − N B ) 2 .

We show how the electron gas methods of Luttinger, Ward and Nozières can be applied to an SU (N ), multi-channel generalization of the infinite U Anderson impurity model within a Schwinger boson treatment. Working to all orders in a 1/N expansion, we show how the Friedel Langreth relationship, the Yamada-Yosida-Yoshimori and the Shiba-Korringa relations can be derived, under the assumption that the spinon and holon fields are gapped. One of the remarkable features of this treatment, is that the Landau amplitudes depend on the exchange of low energy virtual spinons and holons. We end the paper with a discussion on the extension of our approach to the lattice, where the spinon-holon gap is expected to close at a quantum critical point.

Using a Luttinger-Ward scheme for interacting gauge particles, we present a conserving many body treatment of a family of fully screened infinite-U Anderson models that has a smooth crossover into the Fermi-liquid state, with a finite scattering phase shift at zero temperature and a Wilson ratio greater than 1. We illustrate our method, computing the temperature dependence of the thermodynamics, resistivity, and electron dephasing rate and discuss its future application to nonequilibrium quantum dots and quantum critical mixed valent systems.

We discuss the history dependence and memory effects which are observed in the out-of-equilibrium conductivity of electron glasses. The experiments can be understood by assuming that the local density of states retains a memory of the sample history. We provide analytical arguments for the consistency of this assumption, and discuss the saturation of the memory effect with increasing gate voltage change. This picture is bolstered by numerical simulations at zero temperature, which moreover demonstrate the incompressibility of the Coulomb glass on short timescales.Comment: 4 pages, 1 figur