arXiv subjects

T. I. Baturina

Publications and source records attributed to T. I. Baturina.

At least 19 recordsLinked to original sources

arXiv2020

Quantum criticality and multiple crossing points in the magnetoresistance of thin TiN-films

We have measured $R(T,B)$ of a TiN thin-film very close to the disorder-driven superconductor-insulator transition but still superconducting at zero field and low temperatures. In a magnetic field we find three distinct crossing point of the magnetoresistance isotherms occur at magnetic fields $B_{cX}$ in three different temperature regions. Each crossing point in $R(T,B)$ corresponds to a plateau in $R(T,B_{cX})$. We systematically study the evolution of these crossing point near the disorder-induced superconductor/insulator transition, identify the most promising candidate for a quantum phase transition, and provide estimates for the two critical exponents $z$ and $ν$.

cond-mat.supr-con↗

arXiv2018

Magnetic field-tuned superconductor/insulator transition in TiN nanostrips

We have measured the electric transport properties of TiN nanostrips with different widths. At zero magnetic field the temperature dependent resistance R(T) saturates at a finite resistance towards low temperatures, which results from quantum phase slips in the narrower strips. We find that the current-voltage (I-V) characteristics of the narrowest strips are equivalent to those of small Josephson junctions. Applying a transverse magnetic field drives the devices into a reentrant insulating phase, with I-V-characteristics dual to those in the superconducting regime. The results evidence that our critically disordered superconducting nanostrips behave like small self-organized random Josephson networks.

cond-mat.mes-hall↗

arXiv2014

Hotspots in two-phase conducting media

We study electric properties of random resistor networks consisting of resistors of two kinds numerically, focusing on the power loss across each bond. Tuning the ratio of the resistances $r$ and their respective fraction $α$ we find that at large $r$ the conductance of the network is dominated by a few optimal, percolation-like, conducting paths. We demonstrate that the distribution of the local power losses $P$ is exponential, $\propto\exp(-P/\langle P\rangle)$, and reveal the spatial distribution of hotspots concentrating the main part of the dissipated power.

cond-mat.mes-hall↗

arXiv2012

Stimulation of the fluctuation superconductivity by the PT-symmetry

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 PT-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 PT-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.

cond-mat.supr-con↗

arXiv2011

Localization-Delocalization Transition and Current Fractalization

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. 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, E_c, the dc transport is completely locked by Coulomb blockade effect at all voltages except for a discrete set of resonant ones. At T>E_c the combined action of disorder and temperature unlocks the charge transport, since the environment excitation spectrum becomes quasi-continuous according to a Landau-Hopf-like scenario of turbulence, and the conductivity acquires an Arrhenius-like thermal activation form. The transition from the localized to delocalized behaviour occurs at T=E_c which corresponds to the onset of turbulence in the spectral flow of environmental excitations with Reynolds number Re=(k_B T/E_c)=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.

cond-mat.mes-hall↗

arXiv2011

Superconducting phase transitions in ultrathin TiN films

We investigate transition to the superconducting state in the ultrathin titanium nitride films on approach to superconductor-insulator transition. Building on the complete account of quantum contributions to conductivity, we demonstrate that the resistance of thin superconducting films exhibits a non-monotonic temperature behaviour due to the competition between weak localization, electron-electron interaction, and superconducting fluctuations. We show that superconducting fluctuations give rise to an appreciable decrease in the resistance even at temperatures well exceeding the superconducting transition temperature, T_c, with this decrease being dominated by the Maki-Thompson process.The transition to a global phase-coherent superconducting state occurs via the Berezinskii-Kosterlitz-Thouless (BKT) transition, which we observe both by power-law behaviour in current-voltage characteristics and by flux flow transport in the magnetic field. The ratio T_{BKT}/T_c follows the universal Beasley-Mooij-Orlando relation. Our results call for revisiting the past data on superconducting transition in thin disordered films.

cond-mat.supr-con↗

arXiv2011

Out-of-equilibrium heating of electron liquid: fermionic and bosonic temperatures

We investigate out-of-the equilibrium properties of the electron liquid in a two-dimensional disordered superconductor subject to the electric bias and temperature gradient. We calculate kinetic coefficients and Nyquist noise, and find that they are characterized by distinct effective temperatures: $T_{\mathrm{e}}$, characterizing single-particle excitations, $T_{\mathrm{Cp}}$, describing the Cooper pairs, and $T_{\mathrm{eh}}$, corresponding to electron-hole or dipole excitations. Tuning the ratio between the electric $j$ and thermal $j_{\mathrm{th}}$ currents and the boundary conditions one can heat different kind of excitations and control their corresponding temperatures. We propose the experimental setting for determining these effective temperatures.

cond-mat.str-el↗

arXiv2010

Pseudogap in a thin film of a conventional superconductor

A superconducting state is characterized by the gap in the electronic density of states which vanishes at the superconducting transition temperature Tc. It was discovered that in high temperature superconductors a noticeable depression in the density of states still remains even at temperatures above Tc; this feature being called pseudogap. Here we show that a pseudogap exists in a conventional superconductor: ultrathin titanium nitride films over a wide range of temperatures above Tc. Our study reveals that this pseudogap state is induced by superconducting fluctuations and favored 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.

cond-mat.supr-con↗

arXiv2010

Intrinsic non-linear conduction in the super-insulating state of thin TiN films

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.

cond-mat.supr-con↗

arXiv2010

Nanopattern-stimulated superconductor-insulator transition in thin TiN films

We present the results of the comparative study of the influence of disorder on transport properties in continuous and nanoperforated TiN films. We show that nanopatterning turns a thin TiN film into an array of superconducting weak links and stimulates both, the disorder- and magnetic field-driven superconductor-to-insulator transitions, pushing them to lower degree of disorder. We find that nanopatterning enhances the role of the two-dimensional Coulomb interaction in the system transforming the originally insulating film into a more pronounced insulator. We observe magnetoresistance oscillations reflecting collective behaviour of the multiconnected nanopatterned superconducting film in the wide range of temperatures and uncover the physical mechanism of these oscillations as phase slips in superconducting weak link network.

cond-mat.supr-con↗

arXiv2010

Synchronized Andreev Transmission in Chains of SNS Junctions

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.

cond-mat.mes-hall↗

arXiv2010

Low temperature transport in tunnel junction arrays: Cascade energy relaxation

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.

cond-mat.str-el↗

arXiv2010

Synchronized Andreev Transmission in SNS Junction Arrays

cond-mat.mes-hall↗

arXiv2009

Hierarchical energy relaxation in mesoscopic tunnel junctions: Effect of nonequilibrium environment on low-temperature transport

We develop a theory of far from the equilibrium transport in arrays of tunnel junctions. We find that if the rate of the electron-electron interactions exceeds the rate of the electron-phonon energy exchange, the energy relaxation ensuring the charge transfer may occur sequentially. In particular, cotunneling transport in arrays of junctions is dominated by the relaxation via the intermediate bosonic environment, the electron-hole excitations, rather than by the electron-phonon mechanism. The current-voltage characteristics are highly sensitive to the spectrum of the environmental modes and to the applied bias, which sets the lower bound for the effective temperature. We demonstrate that the energy gap in the electron-hole spectrum which opens below some critical temperature T* due to long-range Coulomb interactions gives rise to the suppression of the tunneling current.

cond-mat.mes-hall↗

arXiv2009

Optical Properties of TiN Thin Films close to the Superconductor-Insulator Transition

We present the intrinsic optical properties over a broad spectral range of TiN thin films deposited on a Si/SiO$_2$ substrate. We analyze the measured reflectivity spectra of the film-substrate multilayer structure within a well-establish procedure based on the Fresnel equation and extract the real part of the optical conductivity of TiN. We identify the metallic contribution as well as the finite energy excitations and disentangle the spectral weight distribution among them. The absorption spectrum of TiN bears some similarities with the electrodynamic response observed in the normal state of the high-temperature superconductors. Particularly, a mid-infrared feature in the optical conductivity is quite reminiscent of a pseudogap-like excitation.

cond-mat.mtrl-sci↗

arXiv2009

Hyperactivated resistance in TiN films on the insulating side of the disorder-driven superconductor-insulator transition

We investigate the insulating phase that forms in a titanium nitride film in a close vicinity of the disorder-driven superconductor-insulator transition. In zero magnetic field the temperature dependence of the resistance reveals a sequence of distinct regimes upon decreasing temperature crossing over from logarithmic to activated behavior with the variable-range hopping squeezing in between. In perpendicular magnetic fields below 2 T, the thermally activated regime retains at intermediate temperatures, whereas at ultralow temperatures, the resistance increases faster than that of the thermally activated type. This indicates a change of the mechanism of the conductivity. We find that at higher magnetic fields the thermally activated behavior disappears and the magnetoresistive isotherms saturate towards the value close to quantum resistance h/e^2.

cond-mat.supr-con↗

arXiv2008

Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition

Scanning tunneling spectroscopy at very low temperature on homogeneously disordered superconducting Titanium Nitride thin films reveals strong spatial inhomogeneities of the superconducting gap $Δ$ 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 $Δ$, and growth of the $Δ/T_c$ ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition.

cond-mat.mes-hall↗

arXiv2008

Macroscopic Coulomb blockade in large Josephson junction arrays

We investigate theoretically transport properties of one- and two-dimensional regular Josephson junction arrays (JJAs) in an insulating state. We derive the low-temperature current-voltage characteristics for the current mediated by the Cooper pair transfer across the system. In the case where the screening length associated with the capacitance of the islands to the ground is much larger than the island's size, we find that transport is governed by the macroscopic Coulomb blockade effect with the gap well exceeding a single island charging energy. In the limit when the screening length is much larger than the linear size of the array, the gap establishes the dependence on the array size, namely, the Coulomb gap grows linearly with the system size in 1D and grows as logarithm of the system size in the two-dimensional array. We find two transport regimes: At moderate temperatures, above the BKT-like charge binding-unbinding transition the low bias transport is thermally activated, the activation energy being equal to the Coulomb blockade energy. At low temperatures, below the binding-unbinding transition, a JJA falls into a superinsulating state with the resistance exhibiting a double-exponential temperature dependence.

cond-mat.supr-con↗