Quantitative comparison of Anderson impurity solvers applied to transport in quantum dots.

We study the single impurity Anderson model (SIAM) using the equations of motion method (EOM), the non-crossing approximation (NCA), the one-crossing approximation (OCA), and Wilson's numerical renormalization group (NRG). We calculate the density of states and the linear conductance focusing on their dependence on the chemical potential and on the temperature paying special attention to the Kondo and Coulomb blockade regimes for a large range of model parameters. We report that some standard approximations based on the EOM technique display a rather unexpected poor behavior in the Coulomb blockade regime even at high temperatures.

Toward Realistic Amorphous Topological Insulators.

The topological properties of materials are, until now, associated with the features of their crystalline structure, although translational symmetry is not an explicit requirement of the topological phases. Recent studies of hopping models on random lattices have demonstrated that amorphous model systems show a nontrivial topology. Using calculations, we show that two-dimensional amorphous materials can also display topological insulator properties.

Landauer-Büttiker Approach to Strongly Coupled Quantum Thermodynamics: Inside-Outside Duality of Entropy Evolution.

We develop a Landauer-Büttiker theory of entropy evolution in time-dependent, strongly coupled electron systems. The formalism naturally avoids the problem of the system-bath distinction by defining the entropy current in the attached leads. This current can then be used to infer changes of the entropy of the system which we refer to as the inside-outside duality.

Conductance and Kondo Interference beyond Proportional Coupling.

The transport properties of nanostructured systems are deeply affected by the geometry of the effective connections to metallic leads. In this work we derive a conductance expression for a class of interacting systems whose connectivity geometries do not meet the Meir-Wingreen proportional coupling condition. As an interesting application, we consider a quantum dot connected coherently to tunable electronic cavity modes.

Multi-scale approach for strain-engineering of phosphorene.

A multi-scale approach for the theoretical description of deformed phosphorene is presented. This approach combines a valence-force model to relate macroscopic strain to microscopic displacements of atoms and a tight-binding model with distance-dependent hopping parameters to obtain electronic properties. The resulting self-consistent electromechanical model is suitable for large-scale modeling of phosphorene devices.

A 50/50 electronic beam splitter in graphene nanoribbons as a building block for electron optics.

Based on the investigation of the multi-terminal conductance of a system composed of two graphene nanoribbons, in which one is on top of the other and rotated by [Formula: see text], we propose a setup for a 50/50 electronic beam splitter that neither requires large magnetic fields nor ultra low temperatures. Our findings are based on an atomistic tight-binding description of the system and on the Green function method to compute the Landauer conductance. We demonstrate that this system acts as a perfect 50/50 electronic beam splitter, in which its operation can be switched on and off by varying the doping (Fermi energy).

A tight-binding model for MoS2 monolayers.

We propose an accurate tight-binding parametrization for the band structure of MoS2 monolayers near the main energy gap. We introduce a generic and straightforward derivation for the band energies equations that could be employed for other monolayer dichalcogenides. A parametrization that includes spin-orbit coupling is also provided.

Conductance peaks in open quantum dots.

We present a simple measure of the conductance fluctuations in open ballistic chaotic quantum dots, extending the number of maxima method originally proposed for the statistical analysis of compound nuclear reactions. The average number of extreme points (maxima and minima) in the dimensionless conductance T as a function of an arbitrary external parameter Z is directly related to the autocorrelation function of T(Z). The parameter Z can be associated with an applied gate voltage causing shape deformation in quantum dot, an external magnetic field, the Fermi energy, etc.

Disorder and electronic transport in graphene.

In this review, we provide an account of the recent progress in understanding electronic transport in disordered graphene systems. Starting from a theoretical description that emphasizes the role played by band structure properties and lattice symmetries, we describe the nature of disorder in these systems and its relation to transport properties. While the focus is primarily on theoretical and conceptual aspects, connections to experiments are also included.

Nonlinear conductance in a ballistic Aharonov-Bohm ring.

The nonlinear electronic transport properties of a ballistic Aharonov-Bohm ring are investigated. It is demonstrated how the electronic interaction breaks the phase rigidity in a two-probe mesoscopic device as the voltage bias is increased. The possibility of studying interference effects in the nonlinear regime is addressed.

Decay of the Loschmidt echo in a time-dependent environment.

We study the decay rate of the Loschmidt echo or fidelity in a chaotic system under a time-dependent perturbation V(q,t) with typical strength Planck's/tau(v) . The perturbation represents the action of an uncontrolled environment interacting with the system, and is characterized by a correlation length xi(0) and a correlation time tau(0). For small perturbation strengths or rapid fluctuating perturbations, the Loschmidt echo decays exponentially with a rate predicted by the Fermi "golden rule," 1/approximately tau =tau(c)/tau(v)(2), where tau(c) approximately min[tau(0), xi(0)/upsilon] and upsilon is the typical particle velocity.

Universal transport properties of open microwave cavities with and without time-reversal symmetry.

We measure the transmission through asymmetric and reflection-symmetric chaotic microwave cavities in dependence on the number of attached waveguides. Ferrite cylinders are placed inside the cavities to break time-reversal symmetry. The phase-breaking properties of the ferrite and its range of applicability are discussed in detail.

Classical-quantum correspondence for the scattering dwell time.

Using results from the theory of dynamical systems, we derive a general expression for the classical average scattering dwell time tau . Remarkably, tau depends only on a ratio of phase space volumes. We further show that, for a wide class of systems, the average classical dwell time is not in correspondence with the energy average of the quantum Wigner time delay.

Distribution of reflection coefficients in absorbing chaotic microwave cavities.

The distribution of reflection coefficients P(R) for chaotic microwave cavities with time-reversal symmetry is investigated in different absorption and antenna coupling regimes. For all regimes the agreement between experimental distributions and random-matrix theory predictions is very good, provided both the antenna coupling T(a) and the wall absorption strength T(w) are taken into account in an appropriate way. These parameters are determined by independent experimental quantities.

Coherent versus sequential electron tunneling in quantum dots.

Manifestations of quantum coherence in the electronic conductance through nearly closed quantum dots in the Coulomb-blockade regime are addressed. We show that quantum coherent tunneling processes explain some puzzling statistical features of the conductance peak heights observed in recent experiments at low temperatures. We employ the constant interaction model and the random matrix theory to model the quantum dot electronic interactions and its single-particle statistical fluctuations, taking full account of the finite decay width of the quantum dot levels.

Conductance fluctuations and weak localization in chaotic quantum dots.

We study the conductance statistical features of ballistic electrons flowing through a chaotic quantum dot. We show how the temperature affects the universal conductance fluctuations by analyzing the influence of dephasing and thermal smearing. This leads us to two main findings.

Measuring the Lyapunov exponent using quantum mechanics.

We study the time evolution of two wave packets prepared at the same initial state, but evolving under slightly different Hamiltonians. For chaotic systems, we determine the circumstances that lead to an exponential decay with time of the wave packet overlap function. We show that for sufficiently weak perturbations, the exponential decay follows a Fermi golden rule, while by making the difference between the two Hamiltonians larger, the characteristic exponential decay time becomes the Lyapunov exponent of the classical system.

Semiclassical spatial correlations in chaotic wave functions.

We study the spatial autocorrelation of energy eigenfunctions psi(n)(q) corresponding to classically chaotic systems in the semiclassical regime. Our analysis is based on the Weyl-Wigner formalism for the spectral average C(epsilon)(q(+),q(-),E) of psi(n)(q(+))psi(*)(n)(q(-)), defined as the average over eigenstates within an energy window epsilon centered at E. In this framework C(epsilon) is the Fourier transform in the momentum space of the spectral Wigner function W(x,E;epsilon).

Transmission fluctuations in chaotic microwave billiards with and without time-reversal symmetry.

Transmission fluctuations have been studied in a microwave billiard in dependence to the number of attached wave guides on its entrance and exit. To investigate the influence of breaking time-reversal symmetry, ferrite cylinders were introduced into the billiard. The obtained transmission intensity distributions are compared with predictions from the random matrix theory.

Quantum transport through ballistic cavities: soft vs hard quantum chaos.

We study transport through a two-dimensional billiard attached to two infinite leads by numerically calculating the Landauer conductance and the Wigner time delay. In the generic case of a mixed phase space we find a power-law distribution of resonance widths and a power-law dependence of conductance increments apparently reflecting the classical dwell time exponent, in striking difference to the case of a fully chaotic phase space. Surprisingly, these power laws appear on energy scales below the mean level spacing, in contrast to semiclassical expectations.