Damir R. Islamov

Superconductivity on the localization threshold and magnetic-field-tuned superconductor-insulator transition in TiN films

Temperature-and magnetic-field-dependent measurements of the resistance of ultrathin superconducting TiN films are presented. The analysis of the temperature dependence of the zero-field resistance indicates an underlying insulating behavior, when the contribution of Aslamazov-Larkin fluctuations is taken into account. This demonstrates the possibility of the coexistence of the superconducting and insulating phases and of a direct transition from the one to the other. The scaling behavior of magnetic field data is in accordance with a superconductor-insulator transition (SIT) driven by quantum phase fluctuations in two-dimensional superconductor. The temperature dependence of the isomagnetic resistance data on the high-field side of the SIT has been analyzed, and the presence of an insulating phase is confirmed. A transition from the insulating to a metallic phase is found at high magnetic fields, where the zero-temperature asymptotic value of the resistance is equal to h/e2.

Giant magnetoresistance oscillations induced by microwave radiation and a zero-resistance state in a 2D electron system with a moderate mobility

The effect of a microwave field in the frequency range from 54 to 140 GHz on the magnetotransport in a GaAs quantum well with AlAs/GaAs superlattice barriers and with an electron mobility no higher than 106 cm2/V s is investigated. In the given two-dimensional system under the effect of microwave radiation, giant resistance oscillations are observed with their positions in the magnetic field being determined by the ratio of the radiation frequency to the cyclotron frequency. Earlier, such oscillations had only been observed in GaAs/AlGaAs heterostructures with much higher mobilities. When the samples under study are irradiated with a 140-GHz microwave field, the resistance corresponding to the main oscillation minimum, which occurs near the cyclotron resonance, appears to be close to zero. The results of the study suggest that a mobility value lower than 106 cm2/V s does not prevent the formation of zero-resistance states in a magnetic field in a two-dimensional system under the effect of microwave radiation.

Origin of traps and charge transport mechanism in hafnia

In this study, we demonstrated experimentally and theoretically that oxygen vacancies are responsible for the charge transport in HfO2. Basing on the model of phonon-assisted tunneling between traps, and assuming that the electron traps are oxygen vacancies, good quantitative agreement between the experimental and theoretical data of current-voltage characteristics was achieved. The thermal trap energy of 1.25 eV in HfO2 was determined based on the charge transport experiments.

Charge transport in amorphous Hf0.5Zr0.5O2

In this study, we demonstrated experimentally and theoretically that the charge transport mechanism in amorphous Hf0.5Zr0.5O2 is phonon-assisted tunneling between traps like in HfO2 and ZrO2. The thermal trap energy of 1.25 eV and optical trap energy of 2.5 eV in Hf0.5Zr0.5O2 were determined based on comparison of experimental data on transport with different theories of charge transfer in dielectrics. A hypothesis that oxygen vacancies are responsible for the charge transport in Hf0.5Zr0.5O2 was discussed.

Percolation conductivity in hafnium sub-oxides

In this study, we demonstrated experimentally that formation of chains and islands of oxygen vacancies in hafnium sub-oxides (HfOx, x < 2) leads to percolation charge transport in such dielectrics. Basing on the model of Efros-Shklovskii percolation theory, good quantitative agreement between the experimental and theoretical data of current-voltage characteristics was achieved. Based on the percolation theory suggested model shows that hafnium sub-oxides consist of mixtures of metallic Hf nanoscale clusters of 1–2 nm distributed onto non-stoichiometric HfOx. It was shown that reported approach might describe low resistance state current-voltage characteristics of resistive memory elements based on HfOx.

Bipolar conductivity in amorphous HfO2

This study calculates the contribution of electrons and holes to HfO2 conductivity in Si/HfO2/Ni structures using experiments on injection of minority carriers from n- and p-type silicon. Results show that electrons and holes contribute to the conductivity of HfO2, allowing HfO2 to exhibit two-band conductivity.

Charge transport mechanism in thin films of amorphous and ferroelectric Hf0.5Zr0.5O2

The charge transport mechanism in thin amorphous and ferroelectric Hf0.5Zr0.5O2 films has been studied. It has been shown that the transport mechanism in studied materials does not depend on the crystal phase and is phonon-assisted tunneling between traps. The comparison of the experimental current–voltage characteristics of TiN/Hf0.5Zr0.5O2/Pt structures with the calculated ones provides the trap parameters: thermal energy of 1.25 eV and the optical energy of 2.5 eV. The trap concentration has been estimated as ~1019–1020 cm–3.

Josephson junction arrays on the basis of superconducting PtSi films

Abstract We present the results of low-temperature transport measurements on Josephson junction arrays fabricated on the basis of superconducting polycrystalline PtSi films of thickness 6 nm . To fabricate a two-dimensional array of superconductor—normal-metal–superconductor Josephson weak links, we patterned a square lattice of holes with a period of 600 nm by means of electron lithography and subsequent plasma etching. A periodic variation of the resistance of these arrays with a period corresponding to the magnetic flux quantum per unit cell, including a secondary minimum at the half-quantum points, has been observed.

Microwave Photoresistance of a Double Quantum Well at High Filling Factors

The effect of millimeter wave radiation on the electronic transport in a GaAs double quantum well at a temperature of 4.2 K in a magnetic field of up to 2 T has been studied. Resistance (conductance) oscillations have been shown to appear in the two-dimensional electronic system under investigation at high filling factors. The magnetic field positions of the oscillation maxima are determined by the condition ΔSAS/ħ = lωc, where ΔSAS = (E2 − E1) is the size quantization sublevel splitting in the quantum well, ωc is the cyclotron frequency, and l is a positive integer. It has been found that the microwave field substantially modifies the oscillations in the double quantum well, which results in alternating two-frequency oscillations of photoresistance with the inverse magnetic field.

Absolute negative resistance in a nonequilibrium two-dimensional electron system in a strong magnetic field

The effect of microwave electromagnetic radiation on the resistance of the 2D electron gas in a GaAs/AlAs heterostructure in a strong magnetic field is investigated. It is shown that, under the nonequilibrium conditions caused by microwave radiation, the aforementioned 2D system exhibits giant oscillations of its resistance with varying magnetic field. When the measuring current density is small, an increase in the microwave power leads to the appearance of an absolute negative resistance at the main minimum of these oscillations, which lies near the cyclotron resonance. The experimental data are found to be in qualitative agreement with the theory of multiphoton photoinduced impurity scattering [J. Inarrea and G. Platero, Appl. Phys. Lett. 89, 052109 (2006)].