We study the full-counting statistics of charges transmitted through a single-level quantum dot weakly coupled to a local Einstein phonon which causes fluctuations in the dot energy. An analytic expression for the cumulant generating-function, accurate up to second order in the electron-phonon coupling and valid for finite voltages and temperatures, is obtained in the extended wide-band limit. The result accounts for nonequilibrium phonon distributions induced by the source-drain bias voltage, and concomitantly satisfies the fluctuation theorem. Extending the counting field to the complex plane, we investigate the locations of possible singularities of the cumulant generatingfunction, and exploit them to identify regimes in which the electron transfer is affected differently by the coupling to the phonons. Within a large-deviation analysis, we find a kink in the probability distribution, analogous to a first-order phase transition in thermodynamics, which would be a unique hallmark of the electron-phonon correlations. This kink reflects the fact that although inelastic scattering by the phonons once the voltage exceeds their frequency can scatter electrons opposite to the bias, this will never generate current flowing against the bias at zero temperature, in accordance with the fluctuation theorem.

We theoretically study the resonant tunneling and Fano resonance in quantum dots with electronphonon (e-ph) interaction. We examine the bias-voltage (V ) dependence of the decoherence, using Keldysh Green function method and perturbation with respect to the e-ph interaction. With optical phonons of energy ω 0 , only the elastic process takes place when eV < ω 0 , in which electrons emit and absorb phonons virtually. The process suppresses the resonant amplitude. When eV > ω 0 , the inelastic process is possible which is accompanied by real emission of phonons. It results in the dephasing and broadens the resonant width. The bias-voltage dependence of the decoherence cannot be obtained by the canonical transformation method to consider the e-ph interaction if its effect on the tunnel coupling is neglected. With acoustic phonons, the asymmetric shape of the Fano resonance grows like a symmetric one as the bias voltage increases, in qualitative accordance with experimental results.

We investigate the conductance of an Aharonov-Bohm (AB) interferometer coupled to a quantum dot and two Majorana bound states on the edge of the topological superconductor with finite length. When the tunnel couplings between the Majorana bound states and the Aharonov-Bohm interferometer are fixed to the specific phase, the differential conductance becomes zero irrespective of all the parameters as long as the hoppings to the two Majorana fermions on the opposite side are equal. The conductance at the zero bias voltage does not change with the magnetic flux penetrating the ring for all cases. When the energy level of the quantum dot is equal to the energy of the Majorana bound states, the AB oscillation shows π periodicity due to the particle-hole symmetry. The breaking of the time-reversal symmetry of the topological superconductor results in 2π periodicity of the AB oscillation for the specific phase of the tunnel coupling while the time-reversal symmetry breaking leads to the mixing of the triplet and singlet states in the quantum dot in another specific phase. PACS numbers: 74.45.+c, 73.63.Kv, Exotic features of Majorana fermions [1] have been studied not only from the interest of the fundamental physics, but also from the application for quantum computing [2][3][4][5][6]. In recent years, Majorana fermions have been predicted in several setups with s-wave or d-wave superconductors [7-10]. It has been shown that Majorana fermions are manifested as a zero bias conductance peak in the normal metal/topological superconductor (TS) junctions [11][12][13]. Recently, the zero bias conductance peak due to Majorana bound states (MBSs) has been observed in these systems [14][15][16][17][18]. However, the signature is not enough to prove the existence of MBSs. The observed zero bias conductance peak is not quantized and it could occur even without MBSs in the presence of disorders [19][20][21][22][23]. Thus, alternative setups are necessary. Other setups are proposed to detect the phase information of transport electrons due to existence of the MBSs using interferometry of electron waves [24,25].These studies mentioned above have examined the class D TSs, in which one Majorana fermion emerges at the edge. When the time-reversal symmetry is preserved, the TS is classified into the class BDI. Then, two Majorana fermions can exist on the edge of the TS which has the integer topological number of 2 [26][27][28][29][30]. The BDI topological superconductors can be realized with superconductors coupled to the AIII topological insulators which show the quantum anomalous Hall effect [27,29,30]. Yamakage and Sato have reported that the zero bias conductance of the normal metal(N)-TS junction shows zero or 4e 2 /h value depending on the phase of the tunnel coupling between the normal metal and the TS [30].The Aharonov-Bohm (AB) ring with an embedded quantum dot attached to the normal lead has been studied in 2DEG in GaAs/AlGaAs heterostructures [31]. The high-order interference called the Fano resonance appears in the conductance ...

Lead iodide (PbI2) clusters were synthesized from the chemical reaction of NaI (or KI) with Pb(NO3)2 in H2O, D2O, CH3OH, and C3H7OH solvents. The observation of absorption features between the 550 and 350 nm region obtained with an integrating sphere strongly suggests PbI2 quantum dot formation in solution. Comparison of spectra of PbI2 clusters in solution with PbI2 clusters formed by impregnation of PbI2 in four different pore-sized porous silica substrates indicates that the PbI2 cluster size in solution is less than 2.5 nm in the lateral dimension. Atomic force microscopy (AFM) measurements of PbI2 solutions deposited on mica and highly oriented pyrolytic graphite surfaces indicate that the clusters are single layered. The measured height is 1.0 ± 0.1 nm, which is ∼0.3 nm larger than the layer thickness observed for the bulk materials. The swollen layer thickness can be attributed to the intralayer contraction from the strong lateral interaction among PbI2 molecules, which is supported by ab initio calculations. Raman scattering measurements of the LO and TO modes of PbI2 in bulk and in the confined state were also conducted in 50−150 cm-1 region. Three bands observed at 74, 96, and 116 cm-1 for the confined materials are assigned to the TO2, LO2, and LO1 modes, respectively. The relatively small red shift in the LO modes for PbI2 in the porous hosts may be caused by the surface phonon of PbI2 nanoparticles confined in the porous silica.

MeV implantation of gold ions into MgO(100) followed by annealing is a method to form gold nanoparticles for obtaining modified optical properties. We show from variable-energy positron spectroscopy that clusters of 2 Mg and 2 O vacancies ͑y 4 ͒ are attached to the gold nanoparticle surfaces within the projected range ͑R p ͒. We also find that y 4 vacancy clusters are created at depths less than R p , and extend into the region greater than R p due to damage induced by knock-on collisions. PACS numbers: 61.72.Ji, 78.70.Bj As studies of nanoparticles gain attention [1], understanding of the surface structures of nanoparticles becomes more urgent since the surface-to-bulk ratio is much larger at nanometer scales than it is for macroscopic samples. In this Letter we show that positron spectroscopic measurements, combined with detailed electronic structure calculations which include the effect of the positron [2], can provide new information about defect structures on the surfaces of colloidal gold particles embedded in crystalline MgO. We have discovered a correlation between vacancy clusters and Au nanoparticles. In fact, the Au implants are not visible by the positron probe until they form nanoclusters that are associated with vacancies. Implantation [3] of metal ions into single crystal MgO followed by annealing creates colloidal metal particles with a diameter of a few nm [4,5]. These composite materials, consisting of metal colloids in a dielectric host, have new optical properties, such as a high optical nonlinearity associated with the surface plasmon or Mie resonances of the colloidal particles [6,7]. The implantation process, of course, generates vacancy-type defects, such as F centers (oxygen vacancies occupied by two electrons) and V centers (magnesium vacancies), as well as interstials. These defects can become associated with the interface between the nanoparticle and host material during the heat treatment processes. On the other hand, such interfacial defects can affect the apparent nanoparticle bulk properties since the surface-to-bulk ratio becomes very large for nanoscale particles. An understanding of the defect structure of nanoparticle surfaces is then essential in explaining the properties of nanoscale composites.Au nanoparticles formed in Au 1 implanted MgO can be detected by the surface plasmon resonance [4,5] and observed directly by transmission electron microscopy [8]. Some vacancy structures can be measured with limited sensitivity using optical spectroscopy. For example, isolated F centers and F 2 centers can be studied in optical absorption spectra [9]. Depth profiling using variable energy positron spectroscopy [10] is uniquely sensitive for the detection of vacancy clusters at low concentrations, since injected positrons are preferably trapped in these defect sites. In this Letter we use both the positron lifetime spectroscopy and Doppler broadening of annihilation radiation techniques to specify that there are significant numbers of vacancy clusters located on the surfaces of Au n...