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arXiv2009

Coulomb Blockade in Hierarchical Quantum Hall Droplets

The degeneracy of energy levels in a quantum dot of Hall fluid, leading to conductance peaks, can be readily derived from the partition functions of conformal field theory. Their complete expressions can be found for Hall states with both Abelian and non-Abelian statistics, upon adapting known results for the annulus geometry. We analyze the Abelian states with hierarchical filling fractions, ν=m/(mp \pm 1), and find a non trivial pattern of conductance peaks. In particular, each one of them occurs with a characteristic multiplicity, that is due to the extended symmetry of the m-folded edge. Experimental tests of the multiplicity can shed more light on the dynamics of this composite edge.

cond-mat.mes-hall↗
arXiv2009

Quantum Transport in Bridge Systems

We study electron transport properties of some molecular wires and a unconventional disordered thin film within the tight-binding framework using Green's function technique. We show that electron transport is significantly affected by quantum interference of electronic wave functions, molecule-to-electrode coupling strengths, length of the molecular wire and disorder strength. Our model calculations provide a physical insight to the behavior of electron conduction across a bridge system.

cond-mat.mes-hall↗
arXiv2009

Heat release in clusterization of nanoparticles

We show that the effect of size dependence of the melting temperature of nanocrystals may be used to govern anomalies of thermodynamic properties of nanocrystals in the premelting range. For example, if temperature of nanocrystals is near the melting point, their mechanical contact should result in a change of the temperature and release of some heat. We discuss fundamental possibility of construction of a "heat pump" to extract thermal energy from a low-temperature medium.

cond-mat.mtrl-sci↗
arXiv2009

Shot noise in electron transport through a double quantum dot: A master equation approach

We study shot noise in tunneling current through a double quantum dot connected to two electric leads. We derive two master equations in the occupation-state basis and the eigenstate basis to describe the electron dynamics. The approach based on the occupation-state basis, despite widely used in many previous studies, is valid only when the interdot coupling strength is much smaller than the energy difference between the two dots. In contrast, the calculations using the eigenstate basis are valid for an arbitrary interdot coupling. We show that the master equation in the occupation-state basis includes only the low-order terms with respect to the interdot coupling compared with the more accurate master equation in the eigenstate basis. Using realistic model parameters, we demonstrate that the predicted currents and shot-noise properties from the two approaches are significantly different when the interdot coupling is not small. Furthermore, properties of the shot noise predicted using the eigenstate basis successfully reproduce qualitative features found in a recent experiment.

cond-mat.mes-hall↗
arXiv2009

Comment on "Formation Mechanism and Low-Temperature Instability of Exciton Rings"

This is an extended version of the Comment that contains the criticism against an applicability of the diffusive transport model for the explanation of the ring-shaped spatial pattern formation in the exciton photoluminescence for the GaAs/AlGaAs double quantum wells [Phys. Rev. Lett. 92, 117404 (2004)]. The model has been used in other similar papers published in the PRL and the PRB afterwards.

cond-mat.mes-hall↗
arXiv2009

A Hot Electron Thermocouple and the Diffusion Thermopower of Two-Dimensional Electrons in GaAs

A simple hot electron thermocouple is realized in a two-dimensional electron system (2DES) and used to measure the diffusion thermopower of the 2DES at zero magnetic field. This hot electron technique, which requires no micron-scale patterning of the 2DES, is much less sensitive than conventional methods to phonon-drag effects. Our thermopower results are in good agreement with the Mott formula for diffusion thermopower for temperatures up to T ~ 2 K.

cond-mat.mes-hall↗
arXiv2010

Nonequilibrium Extension of Onsager Relations for Thermoelectric Effects of Mesoscopic Conductors

We discuss a consequence of time reversal symmetry on thermoelectric effect in nonequilibrium coherent quantum transport. Starting with a quantum version of the fluctuation theorem, we show that there exist universal relations between the Peltier coefficient and the Seebeck coefficient of general mesoscopic systems with Coulomb interaction in a nonlinear regime. This extended Kelvin-Onsager relation may be used to obtain useful information on heat current, e.g. the nonlinear Peltier coefficient, which is difficult to be measured in a usual setup of experiments, only from electric current measurement.

cond-mat.mes-hall↗
arXiv2009

Angle resolved photon spectrum and quasiparticle excitation spectrum in an exciton superfluid

There have been extensive experimental search for possible exciton superfluid in semiconductor electron-hole bilayer systems below liquid Helium temperature. However, exciton superfluid are meta-stable and will eventually decay through emitting photons. Here we show that the light emitted from the excitonic superfluid has unique and unusual features not shared by any other atomic or condensed matter systems. We evaluate angle resolved photon spectrum, momentum distribution curve, energy distribution curve and quasiparticle excitation spectrum in the exciton superfluid and comment on relevant experimental data in both exciton and exciton-polariton systems.

cond-mat.mes-hall↗
arXiv2009

Adiabatic quantum pumping and rectification effects in interacting quantum dots

We derive a formula describing the adiabatically pumped charge through an interacting quantum dot within the scattering matrix and Green's function approach. We show that when the tunneling rates between the leads and the dot are varied adiabatically in time, both in modulus and phase, the current induced in the dot consists of two terms, the pumping current and a rectification-like term. The last contribution arises from the time-derivative of the tunneling phase and can have even or odd parity with respect to the pumping phase φ. The rectification-like term is also discussed in relation to some recent experiments in quantum-dots.

cond-mat.mes-hall↗
arXiv2009

Kondo physics versus spin gap physics in fully spin-split quantum wires

Linear and nonlinear transport of quantum wires is investigated at a magnetic field where spin-split one-dimensional (1D) subbands are equidistant in energy. In this seldom-studied regime, experiments are consistent with a density-dependent energy gap between spin subbands, and with a complete spin polarization of the first 1D subband under a large source-drain bias at zero field.

cond-mat.mes-hall↗
arXiv2009

Fractional Quantum Hall Effect and vortex lattices.II

It is demonstrated that all observed fractions at moderate Landau level fillings for the quantum Hall effect can be obtained without recourse to the phenomenological concept of composite fermions. The possibility to have the special topologically nontrivial many-electron wave functions is considered. Their group classification indicates the special values of of electron density in the ground states separated by a gap from excited states. These gaps were calculated for some lattices in a simplified model.

cond-mat.mes-hall↗
arXiv2009

Noise-induced phase transition in the electronic Mach-Zehnder interferometer

We consider dephasing in the electronic Mach-Zehnder interferometer strongly coupled to current noise created by a voltage biased quantum point contact (QPC). We find the visibility of Aharonov-Bohm oscillations as a function voltage bias and express it via the cumulant generating function of noise. In the large-bias regime, high-order cumulants of current add up to cancel the dilution effect of a QPC. This leads to an abrupt change in the dependence of the visibility on voltage bias which occurs at the QPC's transparency T=1/2. Quantum fluctuations in the vicinity of this point smear out the sharp transition.

cond-mat.mes-hall↗
arXiv2009

New Theoretical Approach to Quantum Size Effects of Interactive Electron-hole in Spherical Semiconductor Quantum Dots

The issue of quantum size effects of interactive electron-hole systems in spherical semiconductor quantum dots is put to question. A sharper theoretical approach is suggested based on a new pseudo-potential method. In this new setting, analytical computations can be performed in most intermediate steps lending stronger support to the adopted physical assumptions. The resulting numerical values for physical quantities are found to be much closer to the experimental values than those existing so far in the literature.

cond-mat.mtrl-sci↗
arXiv2009

Graphene - a nearly perfect fluid

Hydrodynamics and collision dominated transport are crucial to understand the slow dynamics of many correlated quantum liquids. The ratio η/s of the shear viscosity ηto the entropy density s is uniquely suited to determine how strongly the excitations in a quantum fluid interact. We determine η/s in clean undoped graphene using a quantum kinetic theory. As a result of the quantum criticality of this system the ratio is smaller than in many other correlated quantum liquids and, interestingly, comes close to a lower bound conjectured in the context of the quark gluon plasma. We discuss possible consequences of the low viscosity, including pre-turbulent current flow.

cond-mat.mes-hall↗
arXiv2009

Does a Fermi liquid on a half-filled Landau level have Pomeranchuk instabilities?

We present a theory of spontaneous Fermi surface deformations for half-filled Landau levels (filling factors of the form $ν=2n+1/2$). We assume the half-filled level to be in a compressible, Fermi liquid state with a circular Fermi surface. The Landau level projection is incorporated via a modified effective electron-electron interaction and the resulting band structure is described within the Hartree-Fock approximation. We regulate the infrared divergences in the theory and probe the intrinsic tendency of the Fermi surface to deform through Pomeranchuk instabilities. We find that the corresponding susceptibility never diverges, though the system is asymptotically unstable in the $n \to \infty$ limit.

cond-mat.mes-hall↗
arXiv2009

Electrostatic Field of Charged Infinite Metallic Plane Contacting with Metallic Sphere

The problem concerning the form of the electrostatic field potential of the infinite charged metallic plane contacting with the metallic sphere is solved. The distributions of the surface charge densities both on the plane and the sphere and also the force acting on the sphere that causing to tear away from the plane are found. The expressions found for the charge of the sphere and the force of tear from the plane permits estimate the frequency of the shuttle motion of the nanoparticles and the charge transfer between metallic electrodes and also use them for the measurement of their sizes and to make use of their separation in progress.

physics.gen-ph↗
arXiv2009

First observation of spin-helical Dirac fermions and topological phases in undoped and doped Bi2Te3 demonstrated by spin-ARPES spectroscopy

Electron systems that possess light-like dispersion relations or the conical Dirac spectrum, such as graphene and bismuth, have recently been shown to harbor unusual collective states in high magnetic fields. Such states are possible because their light-like electrons come in spin pairs that are chiral,which means that their direction of propagation is tied to a quantity called pseudospin that describes their location in the crystal lattice. An emerging direction in quantum materials research is the manipulation of atomic spin-orbit coupling to simulate the effect of a spin dependent magnetic field,in attempt to realize novel spin phases of matter. This effect has been proposed to realize systems consisting of unpaired Dirac cones that are helical, meaning their direction of propagation is tied to the electron spin itself, which are forbidden to exist in graphene or bismuth. The experimental existence of topological order can not be determined without spin-resolved measurements. Here we report a spin-and angle-resolved photoemission study of the hexagonal surface of the Bi2Te3 and Bi{2-x}MnxTe3 series, which is found to exhibit a single helical Dirac cone that is fully spin-polarized. Our observations of a gap in the bulk spin-degenerate band and a spin-resolved surface Dirac node close to the chemical potential show that the low energy dynamics of Bi2Te3 is dominated by the unpaired spin-helical Dirac modes. Our spin-texture measurements prove the existence of a rare topological phase in this materials class for the first time, and suggest its suitability for novel 2D Dirac spin device applications beyond the chiral variety or traditional graphene.

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