arXiv subjects

Y. Syryanyy

Publications and source records attributed to Y. Syryanyy.

4 recordsLinked to original sources

arXiv2026

Molecular Nitrogen Formation in Nitrogen-Implanted (100) $\beta-Ga_2O_3$ Revealed by Temperature-Dependent $N$ $K$-edge XANES

The realization of $p$-type doping in wide-band-gap oxide semiconductors remains a major challenge, particularly in $\beta-Ga_2O_3$ where nitrogen has long been considered a potential acceptor dopant but has consistently failed to produce hole conductivity. Here we investigate the microscopic configuration of implanted nitrogen in (100) $\beta-Ga_2O_3$ using temperature-dependent $N$ $K$-edge x-ray absorption spectroscopy. The spectra reveal a pronounced $\pi^*$ resonance characteristic of molecular nitrogen, which becomes increasingly dominant upon thermal annealing. First-principles calculations and multiple-scattering simulations reveal a pronounced tendency for nitrogen atoms to form $N-N$ bonded configurations in the $Ga_2O_3$ matrix, particularly in defect-rich environments created by ion implantation, reproducing the characteristic spectral features observed in the $N$ $K$-edge XANES spectra. Structural analysis further indicates that implantation induces a defect-rich near-surface layer with local $\beta$-to-$\gamma$-like structural motifs, highlighting the strongly nonequilibrium structural environment in which nitrogen incorporation occurs. Reported results show that implanted nitrogen preferentially forms molecular $N_2$-like configurations rather than substitutional acceptors. Our results provide a microscopic explanation for the long-standing failure of nitrogen acceptor doping in $\beta-Ga_2O_3$ and reveal dopant molecularization as a previously overlooked pathway for impurity incorporation under strongly nonequilibrium implantation conditions.

cond-mat.mtrl-sci↗

arXiv2020

Properties of YBa$_2$Cu$_3$O$_{7-δ}$ films grown by pulsed laser deposition on CeO$_2$-buffered sapphire

In the present work we study the growth by pulsed laser deposition of YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) films on the r-cut sapphire substrates. To improve the matching of the lattice parameters between the substrate and the film we use CeO$_{2}$ buffer layer, recrystallized prior to the deposition of YBCO. The optimal thickness and temperature of recrystallization of the buffer layer is first determined using atomic force microscopy (AFM) and X-ray diffraction. Next, we use the AFM to examine the dependence of YBCO film roughness on the film thickness, and we study the homogeneity of magnetic flux penetration into the films by magneto-optical imaging. We find that the superconducting critical temperature and critical current density of these films are very similar to those of YBCO films grown on well-matched substrates. It appears that the microstructure of YBCO films is affected by structural defects in the buffer layer as well as variations in oxygen deficiency, which results in high values of critical current density suitable for application.

cond-mat.supr-con↗

arXiv2020

Upper critical field and superconductor-metal transition in ultrathin niobium films

Recent studies suggests that in disordered ultrathin films superconducting (SC) state may be intrinsically inhomogeneous. Here we investigate the nature of SC state in ultrathin Nb films, of thickness $d$ ranging from 1.2 nm to 20 nm, which undergo a transition from amorphous to polycrystalline structure at the thickness $d \simeq 3.3$ nm. We show that the properties of SC state are very different in polycrystalline and amorphous films. The upper critical field ($H_{c2}$) is orbitally limited in the first case, and paramagnetically limited in the latter. The magnetic field induced superconductor-metal transition is observed, with the critical field approximately constant or decreasing as a power-law with the film conductance in polycrystalline or amorphous films, respectively. The scaling analysis indicates distinct scaling exponents in these two types of films. Negative contribution of the SC fluctuations to conductivity exists above $H_{c2}$, particularly pronounced in amorphous films, signaling the presence of fluctuating Cooper pairs. These observations suggest the development of local inhomogeneities in the amorphous films, in the form of proximity-coupled SC islands. An usual evolution of SC correlations on cooling is observed in amorphous films, likely related to the effect of quantum fluctuations on the proximity-induced phase coherence.

cond-mat.supr-con↗

arXiv2011

Spin-glass behavior in Ni-doped La1:85Sr0:15CuO4

The dynamic and static magnetic properties of La1:85Sr0:15Cu1-yNiyO4 with Ni concentration up to y=0.63 are reported. All the features that characterize the spin-glass (SG) behavior are found: bifurcation of the dc susceptibility chi vs temperature curve, a peak in the zero-field cooling branch of this curve accompanied by a step in the imaginary part of the ac susceptibility chi_ac, frequency dependence of the peak position in the real part of chi_ac and scaling behavior. The decay of remnant magnetization is described by a stretched-exponential function. The characteristic time from the critical slowing-down formula that governs the dynamics of the system suggests the existence of the spin clusters. The strongest interactions between the fluctuating entities are at y equal to the charge carriers concentration in the system. The SG transition temperature decreases linearly with decreasing y for y<0.30 and extrapolates to 0 K at y=0 what means that Ni display a magnetic character in the surrounding Cu-O network starting from the smallest concentration y. The static critical exponents characterizing the scaling behavior of the nonlinear part of chi lie between those typical for three dimensional Ising-like and Heisenberg-like systems

cond-mat.supr-con↗