arXiv subjects

T. Domanski

Publications and source records attributed to T. Domanski.

At least 37 records · Page 2Linked to original sources

arXiv2013

In-gap states of the quantum dot coupled between a normal and superconducting lead

We study the in-gap states of the quantum dot hybridized to a conducting and superconducting electrode. The usual proximity effect suppresses electronic states over the entire subgap regime $|ω| < Δ$, where $Δ$ denotes the energy gap of superconductor. Owing to the Andreev scattering there can, however, emerge additional in-gap states whose line-broadening (inverse life-time) depends on the coupling to a normal electrode. We show that even number of such bound states appears in the quantum dot spectrum, depending on a competition between the Coulomb repulsion and the induced on-dot pairing. We discuss signatures of these in-gap states showing up in the tunneling conductance, especially in a low-bias regime dominated by the Andreev channel.

cond-mat.mes-hall↗

arXiv2013

Replicas of the Fano resonances induced by phonons in a subgap Andreev tunneling

We study influence of the phonon modes on a subgap spectrum and Andreev conductance for the double quantum dot vertically coupled between a metallic and superconducting lead. For the monochromatic phonon reservoir we obtain replicas of the interferometric Fano-type structures appearing simultaneously in the particle and hole channels. We furthermore confront the induced on-dot pairing with the electron correlations and investigate how the phonon modes affect the zero-bias signature of the Kondo effect in Andreev conductance.

cond-mat.str-el↗

arXiv2012

Decoherence effect on the Fano lineshapes in double quantum dots coupled between normal and superconducting leads

We investigate the Fano-type spectroscopic lineshapes of the T-shape double quantum dot coupled between the conducting and superconducting electrodes and analyze their stability on a decoherence. Because of the proximity effect the quantum interference patterns appear simultaneously at +/- epsilon_2, where epsilon_2 is an energy of the side-attached quantum dot. We find that decoherence gradually suppresses both such interferometric structures. We also show that at low temperatures another tiny Fano-type structure can be induced upon forming the Kondo state on the side-coupled quantum dot due to its coupling to the floating lead.

cond-mat.mes-hall↗

arXiv2011

Flow equation approach to the linear response theory of superconductors

We apply the flow equation method for studying the current-current response function of electron systems with the pairing instability. To illustrate the specific scheme in which the flow equation procedure determines the two-particle Green's functions we reproduce the standard response kernel of the BCS superconductor. We next generalize this non-perturbative treatment considering the pairing field fluctuations. Our study indicates that the residual diamagnetic behavior detected above the transition temperature in the cuprate superconductors can originate from the noncondensed preformed pairs.

cond-mat.supr-con↗

arXiv2011

Fano-type interference in quantum dots coupled between metallic and superconducting leads

We analyze the quantum interference effects appearing in the charge current through the double quantum dots coupled in T-shape configuration to an isotropic superconductor and metallic lead. Owing to proximity effect the quantum dots inherit a pairing which has the profound influence on nonequilibrium charge transport, especially in the subgap regime |eV| < Delta. We discuss under what conditions the Fano-type lineshapes might appear in such Andreev conductance and consider a possible interplay with the strong correlation effects.

cond-mat.str-el↗

arXiv2011

Spectroscopic Bogoliubov features near the unitary limit

We analyze the single particle excitation spectrum of the ultracold fermion atom system close to the unitary limit where there has been found experimental evidence for the Bogoliubov quasiparticles below as well as above the transition temperature Tc. We consider the short-range correlations originating from the preformed pairs and try to reproduce the experimental data adapting phenomenological selfenergy previously used for description of the anti-nodal spectra of the underdoped cuprate superconductors. We show that it fairly fits the lineshapes obtained by the momentum resolved RF spectroscopy for {40}^K atoms.

cond-mat.supr-con↗

arXiv2010

Real space inhomogeneities in high temperature superconductors: the perspective of two-component model

The two-component model of high temperature superconductors in its real space version has been solved using Bogoliubov-de Gennes equations. The disorder in the electron and boson subsystem has been taken into account. It strongly modifies the superconducting properties and leads to local variations of the gap parameter and density of states. The assumption that the impurities mainly modify boson energies offers natural explanation of the puzzling positive correlation between the positions of impurities and the values of the order parameter found in the scanning tunnelling microscopy experiments.

cond-mat.supr-con↗

arXiv2010

Boson-Fermion Duality and Metastability in Cuprate Superconductors

The intrinsic structural metastability in cuprate high T$_c$ materials, evidenced in a checker-board domain structure of the CuO$_2$ planes, locally breaks translational and rotational symmetry. Dynamical charge - deformation fluctuations of such nano-size unidirectional domains, involving Cu-O-Cu molecular bonds, result in resonantly fluctuating diamagnetic pairs embedded in a correlated Fermi liquid. As a consequence, the single-particle spectral properties acquire simultaneously (i) fermionic low energy Bogoliubov branches for propagating Cooper pairs and (ii) bosonic localized glassy structures for tightly bound states of them at high energies. The partial localization of the single-particle excitations results in a fractionation of the Fermi surface as the strength of the exchange coupling between itinerant fermions and partially localized fermion pairs increases upon moving from the nodal to the anti-nodal point. This is also the reason why, upon hole doping, bound fermion pairs predominantly accumulate near the anti-nodal points and ultimately condense in an anisotropic fashion, tracking the gap in the single particle spectrum.

cond-mat.supr-con↗

arXiv2009

Localization-delocalization dichotomy: Inherent spectral properties of the cuprates

We consider hole pairing in the pseudopgap phase of High T_c cuprates, as arising from resonant scattering on dynamically deformable molecular units. As a result, localized and delocalized features coexist in the one-particle spectra: the pseudogap and propagating diffusive Bogoliubov modes. Due to the anisotropy of the electron dispersion and pairing interaction, these two manifestations have different impact in the different regions of the Brillouin zone. We illustrate that for k-vectors crossing the arc, determined by the chemical potential, joining the anti-nodal and the nodal point.

cond-mat.supr-con↗

arXiv2009

Electron pair current through the correlated quantum dot

We study the charge current transmitted through the correlated quantum dot characterized by a finite magnitude of the Coulomb interaction |U|. At low temperatures the correlations can lead to appearance of the spin (for U>0) or charge (for U<0) Kondo states qualitatively affecting the transport properties. We explore an influence of the charge Kondo effect on the electron pair tunneling introducing the auxiliary two-component model which describes the fluctuations between empty and doubly occupied states of the quantum dot.

cond-mat.str-el↗

arXiv2008

Meservey-Tedrow-Fulde effect in a quantum dot embedded between metallic and superconducting electrodes

Magnetic field applied to the quantum dot coupled between one metallic and one superconducting electrode can produce a similar effect as has been experimentally observed by Meservey, Tedrow and Fulde [Phys. Rev. Lett. 25, 1270 (1970)] for the planar normal metal -- superconductor junctions. We investigate the tunneling current and show that indeed the square root singularities of differential conductance exhibit the Zeeman splitting near the gap edge features V = +/- Delta/e. Since magnetic field affects also the in-gap states of quantum dot it furthermore imposes a hyperfine structure on the anomalous (subgap) Andreev current which has a crucial importance for a signature of the Kondo resonance.

cond-mat.supr-con↗

arXiv2008

Unconventional particle-hole mixing in the systems with strong superconducting fluctuations

Development of the STM and ARPES spectroscopies enabled to reach the resolution level sufficient for detecting the particle-hole entanglement in superconducting materials. On a quantitative level one can characterize such entanglement in terms of the, so called, Bogoliubov angle which determines to what extent the particles and holes constitute the spatially or momentum resolved excitation spectra. In classical superconductors, where the phase transition is related to formation of the Cooper pairs almost simultaneously accompanied by onset of their long-range phase coherence, the Bogoliubov angle is slanted all the way up to the critical temperature Tc. In the high temperature superconductors and in superfluid ultracold fermion atoms near the Feshbach resonance the situation is different because of the preformed pairs which exist above Tc albeit loosing coherence due to the strong quantum fluctuations. We discuss a generic temperature dependence of the Bogoliubov angle in such pseudogap state indicating a novel, non-BCS behavior. For quantitative analysis we use a two-component model describing the pairs coexisting with single fermions and study their mutual feedback effects by the selfconsistent procedure originating from the renormalization group approach.

cond-mat.supr-con↗

arXiv2008

Comment on `Evidence for pairing above Tc from the dispersion in the pseudogap phase of cuprates' by A. Kanigel et al

In a recent preprint [0803.3052] A. Kanigel et al report evidence for Bogoliubov-type excitations in the pseudogap phase in the anti-nodal region, where a robust pseudogap remains well above Tc. This important experimental result has been theoretically predicted by us almost 6 years ago on a basis of the phenomenological boson fermion model. An earlier theoretical prediction on the basis of this model was that of a pseudogap in the electron DOS, setting in at some temperature T* and evolving into the superconducting gap upon approaching Tc. A natural logical pursuit of this early work was to show that, in order to have a superconducting state evolved out of a pseudogap state, the diamagnetic bosonic pair fluctuations (characterizing the pseudogap phase) have to be propagating modes, which are phase correlated over finite distances above Tc. If so, then the pseudogap feature has to be reflected in characteristic features of the single particle excitations, showing remnants of the Bogoliubov modes inherent in the superconducting phase. Such Bogoliubov modes result from dynamical feedback effects between single electron excitations and dynamical local pairing fluctuations. We briefly recollect here our theoretical results and confront them with the recent experimental findings.

cond-mat.supr-con↗

arXiv2007

Correlation effects in the transport through quantum dots

We study the charge and heat transport through the correlated quantum dot with a finite value of the charging energy U \neq \infty . The Kondo resonance appearing at temperatures below T_K is responsible for several qualitative changes of the electric and thermal transport. We show that under such conditions the semiclassical Mott relation between the thermopower and electric conductivity is violated. We also analyze the other transport properties where a finite charging energy U has a significant influence. They are considered here both, in the limit of small and for arbitrarily large values of the external voltage eV and/or temperature difference. In particular, we check validity of the Wiedemann-Franz law and the semiclassical Mott relation.

cond-mat.str-el↗

arXiv2006

The flow equation approach to the pairing instability problem

By means of the continuous unitary transformation similar to a general scheme of the Renormalization Group (RG) procedure we study the issue of symmetry breaking and pairing instability in the system of interacting fermions. Constructing a generalized version of the Bogoliubov transformation we show that formation of the fermion pairs and their superconductivity/superfluidity can appear at different temperatures. It is shown that strong quantum fluctuations can destroy the long-range order without breaking the fermion pairs which may still exist as incoherent and/or damped entities. Such unusual phase is characterized by a partial suppression of the density of states near the Fermi energy and by residual collective features like the sound-wave mode in the fermion pair spectrum.

cond-mat.supr-con↗

arXiv2006

Flow equation approach to the pairing problems

We apply the flow equation method for studying the fermion systems where pairing interactions can either trigger the BCS instability with the symmetry breaking manifested by the off-diagonal order parameter or lead to the gaped single particle spectrum without any symmetry breaking. We construct the continuous Bogoliubov transformation in a scheme resembling the renormalization group procedure. We further extend this continuous transformation to a case where fermion pairs interact with the boson field. Due to temporal quantum fluctuations the single particle excitation spectrum develops a gap which is centered around the renormalized boson energy. When bosons undergo the Bose Einstein condensation this structure evolves into the BCS spectrum.

cond-mat.supr-con↗

arXiv2005

Quantum fluctuations of the ultracold atom-molecule mixtures

We investigate evolution of the quantum coherence in the ultracold mixture of fermionic atoms and bosonic dimer molecules. Interactions are there experimentally controlled via tuning the external magnetic field. Consequently, the fermionic atoms and their bosonic counterparts can be driven to a behavior resembling the usual BCS to BEC crossover. We analyze in some detail how this quantum coherence evolves with respect to time upon a smooth and abrupt sweep across the Feshbach resonance inducing the atom-molecule quantum fluctuations.

cond-mat.supr-con↗

arXiv2004

Remnant superfluid collective phase oscillations in the normal state of systems with resonant pairing

The signature of superfluidity in bosonic systems is a sound wave-like spectrum of the single particle excitations which in the case of strong interactions is roughly temperature independent. In fermionic systems, where fermion pairing arises as a resonance phenomenon between free fermions and paired fermionic states (examples are: the atomic gases of lithium or potassium controlled by a Feshbach resonance, polaronic systems in the intermediary coupling regime, d-wave hole pairing in the strongly correlated Hubbard system), remnants of such superfluid characteristics are expected to be visible in the normal state. The single particle excitations maintain there a sound wave like structure for wave vectors above a certain q_{min}(T) where they practically coincide there with the spectrum of the superfluid phase for T<T_{c}. Upon approaching the transition from above this region in q-space extends down to small momenta, except for a narrow region around q=0 where such modes change into damped free particle

cond-mat.supr-con↗