Tatyana Baturina - Academia.edu (original) (raw)
Papers by Tatyana Baturina
Measurements of the current-voltage (I-V) characteristics of TiN thin superconducting films revea... more Measurements of the current-voltage (I-V) characteristics of TiN thin superconducting films reveal strongly nonlinear switching behavior in both parallel and perpendicular magnetic fields near the superconductor-insulator transition. At moderate temperatures, T > 60 mK in perpendicular fields and over the whole temperature range in parallel field, the I-V curves are well described by a simple overheating instability model. At low temperatures in perpendicular magnetic fields we observe pre-switching I \propto V^(alpha) dependences with an exponent alpha rapidly growing with decreasing temperature, which constitutes evidence for the charge-Berezinskii-Kosterlitz-Thouless (BKT) mechanism of the insulator-superinsulator transition. Comment: 4 pages, 4 figures
We investigate experimentally the electric transport at the insulating side of the superconductor... more We investigate experimentally the electric transport at the insulating side of the superconductor to insulator transition in thin TiN-films. At temperatures T > 50 mK we observe an Arrhenius-type conductance, with an activation energy depending logarithmically on the sample size. At high bias the current voltage (I-V) characteristics display a large current jump into an electron heating dominated regime. For the largest samples, and below 50 mK we observe a low-bias power law I ~ V^alpha characteristics with an exponent alpha > 1 rapidly growing with decreasing temperature, which is expected for a binding-unbinding crossover of the charge-Berezinskii-Kosterlitz-Thouless type.
A superconducting state is characterized by the gap in the electronic density of states (DOS) whi... more A superconducting state is characterized by the gap in the electronic density of states (DOS) which vanishes at the superconductor transition temperature T c . It was discovered that in high temperature superconductors (HTS) a noticeable depression in the density of states still remains even at temperatures above T c ; this feature being called pseudogap [1, 2, 3, 4]. Here we show that a pseudogap exists in a conventional superconductor: ultrathin titanium nitride films in the vicinity of the disorder-driven superconductorinsulator transition (D-SIT) [5, 6], over a surprisingly wide range of temperatures above T c . We demonstrate that this pseudogap results from quasi-two-dimensional superconducting fluctuations enhanced by the closeness to the disorderdriven superconductor-insulator transition. A general character of the observed phenomenon offers new insight into the origin of the pseudogap state in the layered HTS compounds.
ABSTRACT We report the use of atomic layer deposition (ALD) to synthesize thin superconducting fi... more ABSTRACT We report the use of atomic layer deposition (ALD) to synthesize thin superconducting films and multilayer superconductor-insulator (S-I) heterostructures. The ALD technique applied to superconducting films opens the way for a variety of applications, including improving the performance and decreasing the cost of high energy particle accelerators, superconducting wires for energy storage, and bolometers for radiation detection. Furthermore, the atomic-scale thickness control afforded by ALD enables the study of superconductivity and associated phenomena in homogeneous layers in the ultra-thin film limit. In this respect, we will present results of ALD-grown transition metal-based superconductors, including nitrides, carbides, and silicides of niobium, nitrides of molybdenum and titanium, and Nb1-xTixN/AlN-based S-I heterostructures. Transport measurement for various composition and film thicknesses will be presented.
We develop an analytical theory of the localization-delocalization transition for a disordered Bo... more We develop an analytical theory of the localization-delocalization transition for a disordered Bose system, focusing on a Cooper-pair insulator. We consider a chain of small superconducting granules coupled via Josephson links and show that the low-temperature tunnelling transport of Cooper pairs is mediated by a self-generated environment of dipole excitations comprised of the same particles as the tunnelling charge carriers in accord with the early notion by Fleishman, Licciardello, and Anderson [1]. We derive an analytical expression for the current-voltage characteristic and find that at temperatures, T , below the the charging energy of a single junction, Ec, the dc transport is completely locked by Coulomb blockade effect at all voltages except for a discrete set of resonant ones. At T > Ec the combined action of disorder and temperature unlocks the charge transport, since the environment excitation spectrum becomes quasi-continuous according to a Landau-Hopflike [2-5] scenario of turbulence, and the conductivity acquires an Arrhenius-like thermal activation form. The transition from the localized to delocalized behaviour occurs at T = Ec which corresponds to the onset of turbulence in the spectral flow of environmental excitations with Reynolds number Re ≡ (kBT /Ec) = 1. The proposed theory breaks ground for a quantitative description of dynamic and quantum phase transitions in a wealth of physical systems ranging from cold atoms in optical lattices, through disordered films and wires to granular and nanopatterned materials.
We report in this paper the temperature and mangetic field dependence of the conductance in the p... more We report in this paper the temperature and mangetic field dependence of the conductance in the polycrystalline film of titanium nitride, before and after heating at ambient conditions. The difference between the two films is the room temperature sheet resistance which remains within 15 percent and both the films show superconducting transition at lower temperatures. The zero field and the high field data, respectively, corresponds to the superconducting and the normal states. Both the films display Atshuler-Aronov zero bias anamoly in their normal states, and the superconducting gap openeing up at low fields. However the heated film has a smaller gap owing to more pronounced zero bias suppression of the density of states. The normal states in both the films are similar to the quasi-2d-disordered metal and its behavior is studied with temperature. Our data suggests that the zero bias anamoly suppresses the superconducting gap with increase in the disorder.
We report in this paper the atomic level imaging in the polycrystalline film of titanium nitride.... more We report in this paper the atomic level imaging in the polycrystalline film of titanium nitride. The crystalline boundaries are resolved at several places on the film surface, and the atomic positions are clearly seen with different orientations. We also observed presence of electronic charge density modulations, with their wave vectors varying over a large range, and in several directions. We associate the presence of charge density modulations to the disorder scattering of electronic waves at the low angle crystalline boundaries. We further consider the effect of Charge density modulations on the superconducting phase. In the STS measurement, we find that the conductance fluctuations at energies close to the superconducting gap are strongly influenced by the charge modulation patterns. At quasi-particle peak position and near zero bias, the conductance fluctuations are relatively suppressed.
Physical Properties of Nanosystems, 2011
ABSTRACT We construct a nonequilibrium theory for the charge transfer through a diffusive array o... more ABSTRACT We construct a nonequilibrium theory for the charge transfer through a diffusive array of alternating normal (N) and superconducting (S) islands comprising an SNSNS junction, with the size of the central S-island being smaller than the energy relaxation length. We demonstrate that in the nonequilibrium regime the central island acts as Andreev retransmitter with the Andreev conversions at both NS interfaces of the central island correlated via over-the-gap transmission and Andreev reflection. This results in a synchronized transmission at certain resonant voltages which can be experimentally observed as a sequence of spikes in the differential conductivity.
Physical Properties of Nanosystems, 2011
A theory of far-from-equilibrium transport in arrays of tunnel junctions is developed. We show th... more A theory of far-from-equilibrium transport in arrays of tunnel junctions is developed. We show that at low temperatures the energy relaxation ensuring tunneling current can become a cascade two-stage process. First, charge carriers lose their energy to a bosonic environment via non-phonon energy exchange. The role of such an environment can be taken by electromagnetic fluctuations or dipole excitations (electron-hole pairs). The environment, in its turn, relaxes the energy to the thermostat by means of phonon irradiation. We derive the current-voltage characteristics for the arrays and demonstrate that opening the energy gap in the spectrum of the environmental excitations completely suppresses the tunneling current. The consequences of the cascade relaxation in various physical systems are discussed.
Physical Review Letters, 2008
Scanning tunneling spectroscopy at very low temperatures on homogeneously disordered superconduct... more Scanning tunneling spectroscopy at very low temperatures on homogeneously disordered superconducting titanium nitride thin films reveals strong spatial inhomogeneities of the superconducting gap Á in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature T c towards zero, enhancement of spatial fluctuations in Á, and growth of the Á=T c ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductorinsulator transition.
Physical Review Letters, 2012
We discuss fluctuations near the second-order phase transition where the free energy has an addit... more We discuss fluctuations near the second-order phase transition where the free energy has an additional non-Hermitian term. The spectrum of the fluctuations changes when the odd-parity potential amplitude exceeds the critical value corresponding to the P T -symmetry breakdown in the topological structure of the Hilbert space of the effective non-Hermitian Hamiltonian. We calculate the fluctuation contribution to the differential resistance of a superconducting weak link and find the manifestation of the P T -symmetry breaking in its temperature evolution. We successfully validate our theory by carrying out measurements of far from equilibrium transport in mesoscale-patterned superconducting wires.
Physical Review B, 2011
ABSTRACT The interplay between the superconducting order parameter and elastic fields, which are ... more ABSTRACT The interplay between the superconducting order parameter and elastic fields, which are intimately connected to the very existence of the superconductivity itself, can result in a novel superconducting state: a regular self-organized texture of superconducting islands. We study the formation of these islands in a system of a thin superconducting film coupled elastically to a more rigid substrate and derive the phase diagram below the superconducting critical temperature depending on the elastic coupling constant of both subsystems. The fact that this pattern is a result of the Ginzburg-Landau description of superconductivity indicates that the formation of regular structures may be a common feature of the superconductor transition in the presence of long-range coupling.
Physical Review B, 2010
We construct a nonequilibrium theory for the charge transfer through a diffusive array of alterna... more We construct a nonequilibrium theory for the charge transfer through a diffusive array of alternating normal (N) and superconducting (S) islands comprising an SNSNS junction, with the size of the central S-island being smaller than the energy relaxation length. We demonstrate that in the nonequilibrium regime the central island acts as Andreev retransmitter with the Andreev conversions at both NS interfaces of the central island correlated via over-the-gap transmission and Andreev reflection. This results in a synchronized transmission at certain resonant voltages which can be experimentally observed as a sequence of spikes in the differential conductivity.
Physica C: Superconductivity, 2008
We investigate low temperature transport properties of thin TiN superconducting films, differing ... more We investigate low temperature transport properties of thin TiN superconducting films, differing by the degree of disorder. At zero magnetic field we find an extremely sharp separation between the superconducting-and insulating phases, indicating a direct superconductor-insulator transition without an intermediate metallic phase. We show that in the critical region of the transition a peculiar highly inhomogeneous insulating state with superconducting correlations forms. The insulating films exhibit thermally activated conductivity and huge positive magnetoresistance at low magnetic fields. A sharp depinning transition at some voltage V T is observed in the I-V curves at very low temperatures. We propose a percolation type of depinning with the threshold voltage determined by the Coulomb blockade energy for the Cooper pairs between neighboring self-induced superconducting islands, with V T being the total voltage along the first conduction path. The observed hysteretic behavior of the threshold and steps on the dI/dV vs. V curves support this percolation picture of the depinning transition.
Physica C: Superconductivity, 2010
ABSTRACT We present the results of the comparative study of low-temperature transport properties ... more ABSTRACT We present the results of the comparative study of low-temperature transport properties of critically disordered nanoperforated titanium nitride films of the thickness less than the superconducting coherence length, ξd. The samples were patterned by the electron beam lithography and the subsequent plasma etching to form a square array of holes, with the hole diameter being ⩾2ξd and the center to center separation being 80nm. In the wide temperature region below the superconducting critical temperature, Tc, we observe a periodic dependence of the resistance upon the external magnetic field, with the period corresponding to the magnetic flux quantum per unit cell. On top of that we see secondary minima at the half-integer quanta points. We find that the effect of perforation on the low-temperature (⩽0.1Tc) magnetoresistance depends drastically on the degree of disorder. Namely, in the moderately disordered films (kFl≃3) the perforation results in the shift of magnetoresistance curves towards higher fields as compared to those of the original films, while in the more disordered films (kFl≃1), the perforation gives rise to the shift of the magnetoresistance in the opposite direction.
Physica C: Superconductivity, 2010
We present an experimental study of transport properties of a large two-dimensional array of supe... more We present an experimental study of transport properties of a large two-dimensional array of superconductor -normal-metal -superconductor (SNS) junctions comprised of the nanopatterned superconducting film, ensuring that NS interfaces of our SNS junctions are highly transparent. We find the anomalously high charge transmission at certain applied voltages commensurate with the magnitude of the gap in superconducting islands. This indicates the nonlocal nature of the charge transfer in multiply connected SNS systems. We propose the mechanism of the correlated transmission of Cooper pairs in large arrays of SNS junctions based on the combined action of the proximity effect and the simultaneous Andreev conversion processes at many NS-interfaces.
Physica C: Superconductivity, 2010
ABSTRACT We derive the current–voltage (I–V) characteristics of far from equilibrium superconduct... more ABSTRACT We derive the current–voltage (I–V) characteristics of far from equilibrium superconducting tunneling arrays and find that the energy relaxation ensuring the charge transfer occurs in two stages: (i) the energy exchange between charge carriers and the intermediate bosonic agent, environment, and (ii) relaxing the energy further to the (phonon) thermostat, the bath, provided the rate of the environmental modes-phonon interactions is slower than their energy exchange rate with the tunneling junction. For a single junction we find I∝(V/RT)ln(Λ/V), where RT is the bare tunnel resistance of the junction and Λ is the high energy cut-off of the electron-environment interaction. In large tunneling arrays comprised of macroscopic number of junctions, low-temperature transport is governed by the cotunneling processes losing energy to the electron–hole environment. Below some critical temperature, T∗, the Coulomb interactions open a finite gap in the environment excitations spectrum blocking simultaneously Cooper pair and normal excitations currents through the array; this is the microscopic mechanism of the insulator-to-superinsulator transition.
Nature Communications, 2010
A superconducting state is characterized by the gap in the electronic density of states, which va... more A superconducting state is characterized by the gap in the electronic density of states, which vanishes at the superconducting transition temperature T c . It was discovered that in high-temperature superconductors, a noticeable depression in the density of states, the pseudogap, still remains even at temperatures above T c . Here, we show that a pseudogap exists in a conventional superconductor, ultrathin titanium nitride films, over a wide range of temperatures above T c . our study reveals that this pseudogap state is induced by superconducting fluctuations and favoured by two-dimensionality and by the proximity to the transition to the insulating state. A general character of the observed phenomenon provides a powerful tool to discriminate between fluctuations as the origin of the pseudogap state and other contributions in the layered high-temperature superconductor compounds.
Measurements of the current-voltage (I-V) characteristics of TiN thin superconducting films revea... more Measurements of the current-voltage (I-V) characteristics of TiN thin superconducting films reveal strongly nonlinear switching behavior in both parallel and perpendicular magnetic fields near the superconductor-insulator transition. At moderate temperatures, T > 60 mK in perpendicular fields and over the whole temperature range in parallel field, the I-V curves are well described by a simple overheating instability model. At low temperatures in perpendicular magnetic fields we observe pre-switching I \propto V^(alpha) dependences with an exponent alpha rapidly growing with decreasing temperature, which constitutes evidence for the charge-Berezinskii-Kosterlitz-Thouless (BKT) mechanism of the insulator-superinsulator transition. Comment: 4 pages, 4 figures
We investigate experimentally the electric transport at the insulating side of the superconductor... more We investigate experimentally the electric transport at the insulating side of the superconductor to insulator transition in thin TiN-films. At temperatures T > 50 mK we observe an Arrhenius-type conductance, with an activation energy depending logarithmically on the sample size. At high bias the current voltage (I-V) characteristics display a large current jump into an electron heating dominated regime. For the largest samples, and below 50 mK we observe a low-bias power law I ~ V^alpha characteristics with an exponent alpha > 1 rapidly growing with decreasing temperature, which is expected for a binding-unbinding crossover of the charge-Berezinskii-Kosterlitz-Thouless type.
A superconducting state is characterized by the gap in the electronic density of states (DOS) whi... more A superconducting state is characterized by the gap in the electronic density of states (DOS) which vanishes at the superconductor transition temperature T c . It was discovered that in high temperature superconductors (HTS) a noticeable depression in the density of states still remains even at temperatures above T c ; this feature being called pseudogap [1, 2, 3, 4]. Here we show that a pseudogap exists in a conventional superconductor: ultrathin titanium nitride films in the vicinity of the disorder-driven superconductorinsulator transition (D-SIT) [5, 6], over a surprisingly wide range of temperatures above T c . We demonstrate that this pseudogap results from quasi-two-dimensional superconducting fluctuations enhanced by the closeness to the disorderdriven superconductor-insulator transition. A general character of the observed phenomenon offers new insight into the origin of the pseudogap state in the layered HTS compounds.
ABSTRACT We report the use of atomic layer deposition (ALD) to synthesize thin superconducting fi... more ABSTRACT We report the use of atomic layer deposition (ALD) to synthesize thin superconducting films and multilayer superconductor-insulator (S-I) heterostructures. The ALD technique applied to superconducting films opens the way for a variety of applications, including improving the performance and decreasing the cost of high energy particle accelerators, superconducting wires for energy storage, and bolometers for radiation detection. Furthermore, the atomic-scale thickness control afforded by ALD enables the study of superconductivity and associated phenomena in homogeneous layers in the ultra-thin film limit. In this respect, we will present results of ALD-grown transition metal-based superconductors, including nitrides, carbides, and silicides of niobium, nitrides of molybdenum and titanium, and Nb1-xTixN/AlN-based S-I heterostructures. Transport measurement for various composition and film thicknesses will be presented.
We develop an analytical theory of the localization-delocalization transition for a disordered Bo... more We develop an analytical theory of the localization-delocalization transition for a disordered Bose system, focusing on a Cooper-pair insulator. We consider a chain of small superconducting granules coupled via Josephson links and show that the low-temperature tunnelling transport of Cooper pairs is mediated by a self-generated environment of dipole excitations comprised of the same particles as the tunnelling charge carriers in accord with the early notion by Fleishman, Licciardello, and Anderson [1]. We derive an analytical expression for the current-voltage characteristic and find that at temperatures, T , below the the charging energy of a single junction, Ec, the dc transport is completely locked by Coulomb blockade effect at all voltages except for a discrete set of resonant ones. At T > Ec the combined action of disorder and temperature unlocks the charge transport, since the environment excitation spectrum becomes quasi-continuous according to a Landau-Hopflike [2-5] scenario of turbulence, and the conductivity acquires an Arrhenius-like thermal activation form. The transition from the localized to delocalized behaviour occurs at T = Ec which corresponds to the onset of turbulence in the spectral flow of environmental excitations with Reynolds number Re ≡ (kBT /Ec) = 1. The proposed theory breaks ground for a quantitative description of dynamic and quantum phase transitions in a wealth of physical systems ranging from cold atoms in optical lattices, through disordered films and wires to granular and nanopatterned materials.
We report in this paper the temperature and mangetic field dependence of the conductance in the p... more We report in this paper the temperature and mangetic field dependence of the conductance in the polycrystalline film of titanium nitride, before and after heating at ambient conditions. The difference between the two films is the room temperature sheet resistance which remains within 15 percent and both the films show superconducting transition at lower temperatures. The zero field and the high field data, respectively, corresponds to the superconducting and the normal states. Both the films display Atshuler-Aronov zero bias anamoly in their normal states, and the superconducting gap openeing up at low fields. However the heated film has a smaller gap owing to more pronounced zero bias suppression of the density of states. The normal states in both the films are similar to the quasi-2d-disordered metal and its behavior is studied with temperature. Our data suggests that the zero bias anamoly suppresses the superconducting gap with increase in the disorder.
We report in this paper the atomic level imaging in the polycrystalline film of titanium nitride.... more We report in this paper the atomic level imaging in the polycrystalline film of titanium nitride. The crystalline boundaries are resolved at several places on the film surface, and the atomic positions are clearly seen with different orientations. We also observed presence of electronic charge density modulations, with their wave vectors varying over a large range, and in several directions. We associate the presence of charge density modulations to the disorder scattering of electronic waves at the low angle crystalline boundaries. We further consider the effect of Charge density modulations on the superconducting phase. In the STS measurement, we find that the conductance fluctuations at energies close to the superconducting gap are strongly influenced by the charge modulation patterns. At quasi-particle peak position and near zero bias, the conductance fluctuations are relatively suppressed.
Physical Properties of Nanosystems, 2011
ABSTRACT We construct a nonequilibrium theory for the charge transfer through a diffusive array o... more ABSTRACT We construct a nonequilibrium theory for the charge transfer through a diffusive array of alternating normal (N) and superconducting (S) islands comprising an SNSNS junction, with the size of the central S-island being smaller than the energy relaxation length. We demonstrate that in the nonequilibrium regime the central island acts as Andreev retransmitter with the Andreev conversions at both NS interfaces of the central island correlated via over-the-gap transmission and Andreev reflection. This results in a synchronized transmission at certain resonant voltages which can be experimentally observed as a sequence of spikes in the differential conductivity.
Physical Properties of Nanosystems, 2011
A theory of far-from-equilibrium transport in arrays of tunnel junctions is developed. We show th... more A theory of far-from-equilibrium transport in arrays of tunnel junctions is developed. We show that at low temperatures the energy relaxation ensuring tunneling current can become a cascade two-stage process. First, charge carriers lose their energy to a bosonic environment via non-phonon energy exchange. The role of such an environment can be taken by electromagnetic fluctuations or dipole excitations (electron-hole pairs). The environment, in its turn, relaxes the energy to the thermostat by means of phonon irradiation. We derive the current-voltage characteristics for the arrays and demonstrate that opening the energy gap in the spectrum of the environmental excitations completely suppresses the tunneling current. The consequences of the cascade relaxation in various physical systems are discussed.
Physical Review Letters, 2008
Scanning tunneling spectroscopy at very low temperatures on homogeneously disordered superconduct... more Scanning tunneling spectroscopy at very low temperatures on homogeneously disordered superconducting titanium nitride thin films reveals strong spatial inhomogeneities of the superconducting gap Á in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature T c towards zero, enhancement of spatial fluctuations in Á, and growth of the Á=T c ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductorinsulator transition.
Physical Review Letters, 2012
We discuss fluctuations near the second-order phase transition where the free energy has an addit... more We discuss fluctuations near the second-order phase transition where the free energy has an additional non-Hermitian term. The spectrum of the fluctuations changes when the odd-parity potential amplitude exceeds the critical value corresponding to the P T -symmetry breakdown in the topological structure of the Hilbert space of the effective non-Hermitian Hamiltonian. We calculate the fluctuation contribution to the differential resistance of a superconducting weak link and find the manifestation of the P T -symmetry breaking in its temperature evolution. We successfully validate our theory by carrying out measurements of far from equilibrium transport in mesoscale-patterned superconducting wires.
Physical Review B, 2011
ABSTRACT The interplay between the superconducting order parameter and elastic fields, which are ... more ABSTRACT The interplay between the superconducting order parameter and elastic fields, which are intimately connected to the very existence of the superconductivity itself, can result in a novel superconducting state: a regular self-organized texture of superconducting islands. We study the formation of these islands in a system of a thin superconducting film coupled elastically to a more rigid substrate and derive the phase diagram below the superconducting critical temperature depending on the elastic coupling constant of both subsystems. The fact that this pattern is a result of the Ginzburg-Landau description of superconductivity indicates that the formation of regular structures may be a common feature of the superconductor transition in the presence of long-range coupling.
Physical Review B, 2010
We construct a nonequilibrium theory for the charge transfer through a diffusive array of alterna... more We construct a nonequilibrium theory for the charge transfer through a diffusive array of alternating normal (N) and superconducting (S) islands comprising an SNSNS junction, with the size of the central S-island being smaller than the energy relaxation length. We demonstrate that in the nonequilibrium regime the central island acts as Andreev retransmitter with the Andreev conversions at both NS interfaces of the central island correlated via over-the-gap transmission and Andreev reflection. This results in a synchronized transmission at certain resonant voltages which can be experimentally observed as a sequence of spikes in the differential conductivity.
Physica C: Superconductivity, 2008
We investigate low temperature transport properties of thin TiN superconducting films, differing ... more We investigate low temperature transport properties of thin TiN superconducting films, differing by the degree of disorder. At zero magnetic field we find an extremely sharp separation between the superconducting-and insulating phases, indicating a direct superconductor-insulator transition without an intermediate metallic phase. We show that in the critical region of the transition a peculiar highly inhomogeneous insulating state with superconducting correlations forms. The insulating films exhibit thermally activated conductivity and huge positive magnetoresistance at low magnetic fields. A sharp depinning transition at some voltage V T is observed in the I-V curves at very low temperatures. We propose a percolation type of depinning with the threshold voltage determined by the Coulomb blockade energy for the Cooper pairs between neighboring self-induced superconducting islands, with V T being the total voltage along the first conduction path. The observed hysteretic behavior of the threshold and steps on the dI/dV vs. V curves support this percolation picture of the depinning transition.
Physica C: Superconductivity, 2010
ABSTRACT We present the results of the comparative study of low-temperature transport properties ... more ABSTRACT We present the results of the comparative study of low-temperature transport properties of critically disordered nanoperforated titanium nitride films of the thickness less than the superconducting coherence length, ξd. The samples were patterned by the electron beam lithography and the subsequent plasma etching to form a square array of holes, with the hole diameter being ⩾2ξd and the center to center separation being 80nm. In the wide temperature region below the superconducting critical temperature, Tc, we observe a periodic dependence of the resistance upon the external magnetic field, with the period corresponding to the magnetic flux quantum per unit cell. On top of that we see secondary minima at the half-integer quanta points. We find that the effect of perforation on the low-temperature (⩽0.1Tc) magnetoresistance depends drastically on the degree of disorder. Namely, in the moderately disordered films (kFl≃3) the perforation results in the shift of magnetoresistance curves towards higher fields as compared to those of the original films, while in the more disordered films (kFl≃1), the perforation gives rise to the shift of the magnetoresistance in the opposite direction.
Physica C: Superconductivity, 2010
We present an experimental study of transport properties of a large two-dimensional array of supe... more We present an experimental study of transport properties of a large two-dimensional array of superconductor -normal-metal -superconductor (SNS) junctions comprised of the nanopatterned superconducting film, ensuring that NS interfaces of our SNS junctions are highly transparent. We find the anomalously high charge transmission at certain applied voltages commensurate with the magnitude of the gap in superconducting islands. This indicates the nonlocal nature of the charge transfer in multiply connected SNS systems. We propose the mechanism of the correlated transmission of Cooper pairs in large arrays of SNS junctions based on the combined action of the proximity effect and the simultaneous Andreev conversion processes at many NS-interfaces.
Physica C: Superconductivity, 2010
ABSTRACT We derive the current–voltage (I–V) characteristics of far from equilibrium superconduct... more ABSTRACT We derive the current–voltage (I–V) characteristics of far from equilibrium superconducting tunneling arrays and find that the energy relaxation ensuring the charge transfer occurs in two stages: (i) the energy exchange between charge carriers and the intermediate bosonic agent, environment, and (ii) relaxing the energy further to the (phonon) thermostat, the bath, provided the rate of the environmental modes-phonon interactions is slower than their energy exchange rate with the tunneling junction. For a single junction we find I∝(V/RT)ln(Λ/V), where RT is the bare tunnel resistance of the junction and Λ is the high energy cut-off of the electron-environment interaction. In large tunneling arrays comprised of macroscopic number of junctions, low-temperature transport is governed by the cotunneling processes losing energy to the electron–hole environment. Below some critical temperature, T∗, the Coulomb interactions open a finite gap in the environment excitations spectrum blocking simultaneously Cooper pair and normal excitations currents through the array; this is the microscopic mechanism of the insulator-to-superinsulator transition.
Nature Communications, 2010
A superconducting state is characterized by the gap in the electronic density of states, which va... more A superconducting state is characterized by the gap in the electronic density of states, which vanishes at the superconducting transition temperature T c . It was discovered that in high-temperature superconductors, a noticeable depression in the density of states, the pseudogap, still remains even at temperatures above T c . Here, we show that a pseudogap exists in a conventional superconductor, ultrathin titanium nitride films, over a wide range of temperatures above T c . our study reveals that this pseudogap state is induced by superconducting fluctuations and favoured by two-dimensionality and by the proximity to the transition to the insulating state. A general character of the observed phenomenon provides a powerful tool to discriminate between fluctuations as the origin of the pseudogap state and other contributions in the layered high-temperature superconductor compounds.