arXiv subjects

M. Krawiec

Publications and source records attributed to M. Krawiec.

At least 19 recordsLinked to original sources

arXiv2016

Spilling of electronic states in Pb Quantum Wells

Energy-dependent apparent step heights of two-dimensional ultra-thin Pb islands grown on the Si(111)6$\times$6Au surface have been investigated by a combination of scanning tunneling microscopy, first-principles density functional theory and the particle in a box model calculations. The apparent step height shows the thickness and energy dependent oscillatory behavior, which is directly related to the spilling of electron states into the vacuum exhibiting a quantum size effect. This has been unambiguously proven by extensive first-principles scanning tunneling microscopy and spectroscopy simulations. An electronic contribution to the apparent step height is directly determined. At certain energies it reaches values as high as a half of the atomic contribution. The applicability of the particle in a box model to the spilling of electron states is also discussed.

cond-mat.mes-hall↗

arXiv2015

Silicene on metallic quantum wells - an efficient way of tuning silicene-substrate interaction

We propose a powerful method of controlling interaction between silicene and a substrate utilizing quantum size effect, which allows to grow silicene with tailored electronic properties. As an example we consider silicene on ultrathin Pb(111) layers, and demonstrate how the properties of silicene, including the binding energy, and the Dirac bands, can easily be tuned by quantum well states of the substrate. We also discover a novel mechanism of protecting the Dirac electrons from the influence of the substrate. This is associated with special arrangement of a part of Si atoms in silicene. These findings emphasize the essential role of interfacial coupling and open new routes to create silicene-like two-dimensional structures with controlled electronic properties.

cond-mat.mes-hall↗

arXiv2014

Ag adatoms on Si(111)5x2-Au surface

Using scanning tunneling microscopy together with the first-principles density functional theory calculations we study structural properties of the Si(111)5x2-Au surface covered by Ag adatoms. The STM topography data show that a submonolayer coverage of Ag does not lead to a well-ordered adatom chain structure with a periodicity 5x4, as it was observed for Si, Pb and In adatoms. Instead of that, we observe Ag adatoms located in different nonequivalent positions within the unit cell, which confirms the electronic nature of stabilization of the Si(111)5x2-Au surface. Moreover, the DFT calculations give five different structural models of the Si(111)5x2-Au/Ag surface. All the models are almost degenerate in energy, which further supports the above scenario.

cond-mat.mes-hall↗

arXiv2007

STM tunneling through a quantum wire with a side-attached impurity

The STM tunneling through a quantum wire (QW) with a side-attached impurity (atom, island) is investigated using a tight-binding model and the nonequilibrium Keldysh Green function method. The impurity can be coupled to one or more QW atoms. The presence of the impurity strongly modifies the local density of states of the wire atoms, thus influences the STM tunneling through all the wire atoms. The transport properties of the impurity itself are also investigated mainly as a function of the wire length and the way it is coupled to the wire. It is shown that the properties of the impurity itself and the way it is coupled to the wire strongly influence the STM tunneling which is reflected in the density of states and differential conductance.

cond-mat.mes-hall↗

arXiv2007

Thermoelectric phenomena in a quantum dot asymmetrically coupled to external leads

We study thermoelectric phenomena in a system consisting of strongly correlated quantum dot coupled to external leads in the Kondo regime. We calculate linear and nonlinear electrical and thermal conductance and thermopower of the quantum dot and discuss the role of asymmetry in the couplings to external electrodes. In the linear regime electrical and thermal conductances are modified, while thermopower remains unchanged. In the nonlinear regime the Kondo resonance in differential conductance develops at non-zero source-drain voltage, which has important consequences on thermoelectric properties of the system and the thermopower starts to depend on the asymmetry. We also discuss Wiedemann-Franz relation, thermoelectric figure of merit and validity of the Mott formula for thermopower.

cond-mat.mes-hall↗

arXiv2006

Thermoelectric effects in STM tunneling through a monoatomic chain

We study thermoelectric properties of the system composed of a monoatomic chain on a surface and additional electrode coupled to the chain, which can be an STM tip. In particular, we are interested in thermopower, electric and thermal conductance, Wiedemann-Franz relation and thermoelectric figure of merit, which is a direct measure of the usefulness of the system for applications. We discuss the modifications of the STM wire topography due to temperature gradient between the electrodes. Finally, we also make connection to STM experiment, in which the thermopower has been directly measured, showing different structure, not visible in topography spectra.

cond-mat.mes-hall↗

arXiv2006

Properties of the $π$ state induced by impurities in a d-wave superconductor

We study the properties of a quantum impurity embedded in a superconducting host of a d-wave symmetry. The superconductor is described by the extended negative $U$ Hubbard model while the impurity introduces a repulsive interaction to the system around the central site. We discuss the influence of this repulsion on the local properties (density of states, electron pairing and spontaneous current around the impurity) of the superconductor. We show the condition of $π$ - like behaviour, defined as two subsystems having a phase difference of $π$, in the system by using a proper combination of attractive pairing bond interaction and repulsive one between electrons located at the impurity and nearest neighbour sites.

cond-mat.supr-con↗

arXiv2006

Thermoelectric effects in a strongly interacting quantum dot coupled to ferromagnetic leads

We study thermoelectric effects in Kondo correlated quantum dot coupled to ferromagnetic electrodes by calculating thermopower S in the Kondo regime as function of on-dot energy level and temperature. The system is represented by the Anderson model and the results agree well with those recently measured for a quantum dot coupled to nonmagnetic leads. For magnetic electrodes one observes marked dependence of S on the degree of their polarization.

cond-mat.mes-hall↗

arXiv2006

Double non-equivalent chain structure on vicinal Si(557)-Au surface

We study electronic and topographic properties of the vicinal Si(557)-Au surface using scanning tunneling microscopy and reflection of high energy electron diffraction technique. STM data reveal double wire structures along terraces. Moreover behavior of the voltage dependent STM tip - surface distance is different in different chains. While the one chain shows oscillations of the distance which are sensitive to the sign of the voltage bias, the oscillations in the other chain remain unchanged with respect to the positive/negative biases. This suggests that one wire has metallic character while the other one - semiconducting. The experimental results are supplemented by theoretical calculations within tight binding model suggesting that the observed chains are made of different materials, one is gold and the other one is silicon chain.

cond-mat.mes-hall↗

arXiv2005

High resolution scanning tunneling spectroscopy of ultrathin Pb on Si(111)-(6x6) substrate

The electronic structure of Si(111)-(6x6)Au surface covered with submonolayer amount of Pb is investigated using scanning tunneling spectroscopy. Already in small islands of Pb with thickness of 1 ML Pb$_{(111)}$ and with the diameter of only about 2 nm we detected the quantized electronic state with energy 0.55 eV below the Fermi level. Similarly, the I(V) characteristics made for the Si(111)-(6x6)Au surface reveal a localized energy state 0.3 eV below the Fermi level. These energies result from fitting of the theoretical curves to the experimental data. The calculations are based on tight binding Hubbard model. The theoretical calculations clearly show prominent modification of the I(V) curve due to variation of electronic and topographic properties of the STM tip apex.

cond-mat.mes-hall↗

arXiv2005

Electron transport through a strongly correlated monoatomic chain

We study transport properties of a strongly correlated monoatomic chain coupled to metallic leads. Our system is described by tight binding Hubbard-like model in the limit of strong on-site electron-electron interactions in the wire. The equation of motion technique in the slave boson representation has been applied to obtain analytical and numerical results. Calculated linear conductance of the system shows oscillatory behavior as a function of the wire length. We have also found similar oscillations of the electron charge in the system. Moreover our results show spontaneous spin polarization in the wire. Finally, we compare our results with those for non-interacting chain and discuss their modifications due to the Coulomb interactions in the system.

cond-mat.mes-hall↗

arXiv2005

Origin of Spontaneous Currents in a Superconductor-Ferromagnet Proximity System

We have previously shown that a ferromagnet-superconductor heterostructure may possess a spontaneous current circulation parallel to the interface. This current is caused by Andreev bound states in the thin ferromagnetic layer, and can be fully spin-polarized. Here we investigate the total energy of the system in cases where the current either does or does not flow. We show that the current is a true quantum ground state effect, and examine the effect of the current on the different contributions to the total energy.

cond-mat.supr-con↗

arXiv2005

Scanning tunneling microscopy of monoatomic gold chains on vicinal Si(335) surface: experimental and theoretical study

We study electronic and topographic properties of the Si(335) surface, containing Au wires parallel to the steps. We use scanning tunneling microscopy (STM) supplemented by reflection of high energy electron diffraction (RHEED) technique. The STM data show the space and voltage dependent oscillations of the distance between STM tip and the surface which can be explained within one band tight binding Hubbard model. We calculate the STM current using nonequilibrium Keldysh Green function formalism.

cond-mat.mes-hall↗

arXiv2005

Thermoelectric effects in strongly interacting quantum dot coupled to ferromagnetic leads

We study thermoelectric effects in Kondo correlated quantum dot coupled to ferromagnetic electrodes by calculating conductance, thermopower and thermal conductance in the Kondo regime. We also study the effect of the asymmetry in the coupling to the leads, which has important consequences for anti-parallel magnetization configuration. We discuss the thermoelectric figure of merit, tunnel magnetoresistance and violation of the Wiedemann-Franz law in this system. The results agree with recently measured thermopower of the quantum dot defined in a two dimensional electron gas.

cond-mat.mes-hall↗

arXiv2005

Spontaneous currents in a ferromagnet - normal metal - superconductor trilayer

We discuss the ground state properties of the system composed of a normal metal sandwiched between ferromagnet and superconductor within a tight binding Hubbard model. We have solved the spin-polarized Hartree-Fock-Gorkov equations together with the Maxwell's equation (Ampere's law) and found a proximity induced Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in this system. Here we show that the inclusion of the normal metal layer in between those subsystems does not necessarily lead to the suppression of the FFLO phase. Moreover, we have found that depending on the thickness of the normal metal slab the system can be switched periodically between the state with the spontaneous current flowing to that one with no current. All these effects can be explained in terms of the Andreev bound states formed in such structures.

cond-mat.mes-hall↗

arXiv2004

Fulde-Ferrell-Larkin-Ovchinnikov-like state in Ferromagnet-Superconductor Proximity System

We discuss some properties of the ferromagnet-superconductor proximity system. In particular, the emphasis is put on the physics of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state. In addition to Andreev reflections it features a number of unusual thermodynamic and transport properties, like: oscillatory behavior of the pairing amplitude, density of states and superconducting transition temperature as a function of the ferromagnet thickness. Surprisingly, under certain conditions spontaneous spin polarized current is generated in the ground state of such a system. We provide some informations regarding experimental observations of this exotic state.

cond-mat.supr-con↗

arXiv2004

Aspects of electron transport through a quantum dot

The work of the Lublin group on the non-equillibrium transport through the quantum dot coupled to external leads (normal or superconducting) and subject to external time dependent fields has been reviewed.

cond-mat.mes-hall↗

arXiv2003

Electron transport through strongly interacting quantum dot coupled to normal metal and superconductor

We study the electron transport through the quantum dot coupled to the normal metal and BCS-like superconductor (N - QD - S) in the presence of the Kondo effect and Andreev scattering. The system is described by the single impurity Anderson model in the limit of strong on-dot interaction. We use recently proposed equation of motion technique for Keldysh nonequilibrium Green's function together with the modified slave boson approach to study the electron transport. We derive formula for the current which contains various tunneling processes and apply it to study the transport through the system. We find that the Andreev conductance is strongly suppressed and there is no zero-bias (Kondo) anomaly in the differential conductance. We discuss effects of the particle-hole asymmetry in the electrodes as well as the asymmetry in the couplings.

cond-mat.mes-hall↗