Andreev scattering in the asymmetric ladder with preformed bosonic pairs

We discuss the phase coherence which emanates from the ladder-like proximity effect between a ``weak superconductor'' with preformed bosonic pairs (here, a single-chain Luther-Emery liquid with superconducting correlations that decay approximately as $x^{-1}$) and a Fermi gas with unpaired fermions. Carefully studying tunneling mechanism(s), we show that the boson-mediated Cooper pairing between remaining unpaired electrons results in a quasi long-range superconductivity: Superconducting correlations decay very slowly as $x^{-\eta}$ with $\eta\approx 1/2$. This process is reminiscent of the coupling of fermions to preformed bosonic pairs introduced in the context of high-Tc cuprates.Comment: 5 pages, final version (To appear in PRB Rapid Communication

Zeeman smearing of the Coulomb blockade

Charge fluctuations of a large quantum dot coupled to a two-dimensional lead via a single-mode good Quantum Point Contact (QPC) and capacitively coupled to a back-gate, are investigated in the presence of a parallel magnetic field. The Zeeman term induces an asymmetry between transmission probabilities for the spin-up and spin-down channels at the QPC, producing noticeable effects on the quantization of the grain charge already at low magnetic fields. Performing a quantitative analysis, I show that the capacitance between the gate and the lead exhibits - instead of a logarithmic singularity - a reduced peak as a function of gate voltage. Experimental applicability is discussed.Comment: 5 pages, 3 figures (Final version

Quasi-particle scattering and protected nature of topological states in a parent topological insulator Bi2_2Se3_3

We report on angle resolved photoemission spectroscopic studies on a parent topological insulator (TI), Bi$_2$Se$_3$. The line width of the spectral function (inverse of the quasi-particle lifetime) of the topological metallic (TM) states shows an anomalous behavior. This behavior can be reasonably accounted for by assuming decay of the quasi-particles predominantly into bulk electronic states through electron-electron interaction and defect scattering. Studies on aged surfaces reveal that topological metallic states are very much unaffected by the potentials created by adsorbed atoms or molecules on the surface, indicating that topological states could be indeed protected against weak perturbations.Comment: accepted for publication in Phys. Rev. B(R

Time-reversal symmetry breaking in circuit-QED based photon lattices

Breaking time-reversal symmetry is a prerequisite for accessing certain interesting many-body states such as fractional quantum Hall states. For polaritons, charge neutrality prevents magnetic fields from providing a direct symmetry breaking mechanism and similar to the situation in ultracold atomic gases, an effective magnetic field has to be synthesized. We show that in the circuit QED architecture, this can be achieved by inserting simple superconducting circuits into the resonator junctions. In the presence of such coupling elements, constant parallel magnetic and electric fields suffice to break time-reversal symmetry. We support these theoretical predictions with numerical simulations for realistic sample parameters, specify general conditions under which time-reversal is broken, and discuss the application to chiral Fock state transfer, an on-chip circulator, and tunable band structure for the Kagome lattice.Comment: minor revisions, version published in PRA; 19 pages, 13 figures, 2 table

Critical Ising modes in low-dimensional Kondo insulators

We present an Ising-like intermediate phase for one-dimensional Kondo insulator systems. Resulting from a spinon splitting, its low-energy excitations are critical Ising modes, whereas the triplet sector has a spectral gap. It should occur as long as the RKKY oscillation amplitude dominates over any direct exchange between localized spins. The chiral fixed point, however, becomes unstable in the far Infra-Red limit due to prevalent fluctuations among localized spins which induce gapless triplet excitations in the spectrum. Based on previous numerical results, we obtain a paramagnetic disordered state ruled by the correlation length of the single impurity Kondo model.Comment: 7 pages, RevTeX; last version: to be published in Physical Review

The electronic structure of the heavy fermion metal LiV2O4LiV_2O_4

The electronic structure of the first reported heavy fermion compound without f-electrons LiV_2O_4 was studied by an ab-initio calculation method. In the result of the trigonal splitting and d-d Coulomb interaction one electron of the $d^{1.5}$ configuration of V ion is localized and the rest partially fills a relatively broad conduction band. The effective Anderson impurity model was solved by Non-Crossing-Approximation method, leading to an estimation for the single-site Kondo energy scale T_K. Then, we show how the so-called exhaustion phenomenon of Nozi\`eres for the Kondo lattice leads to a remarkable decrease of the heavy-fermion (or coherence) energy scale $T_{coh}\equiv {T_K}^2/D$ (D is the typical bandwidth), comparable to the experimental result.Comment: 4 pages, RevTeX; 3 figures in format .eps. submitted to PR

Electron fractionalization induced dephasing in Luttinger liquids

Using the appropriate fractionalization mechanism, we correctly derive the temperature (T) and interaction dependence of the electron lifetime $\tau_F$ in Luttinger liquids. For strong enough interactions, we report that $(T\tau_F)\propto g$, with $g\ll 1$ being the standard Luttinger exponent; This reinforces that electrons are {\it not} good quasiparticles. We immediately emphasize that this is of importance for the detection of electronic interferences in ballistic 1D rings and carbon nanotubes, inducing ``dephasing'' (strong reduction of Aharonov-Bohm oscillations).Comment: 5 pages, 1 figure (Final version for PRB Brief Report