P. Szabo - TIMA

P. Szabo
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P. Szabo
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TIMA
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Physics - Superconductivity (28)
 
Physics - Materials Science (6)
 
Physics - Statistical Mechanics (4)
 
Computer Science - Other (2)
 
Mathematics - Combinatorics (2)
 
Physics - Soft Condensed Matter (2)
 
Physics - General Physics (1)
 
Physics - Disordered Systems and Neural Networks (1)
 
Physics - Strongly Correlated Electrons (1)
 
High Energy Physics - Phenomenology (1)
 
High Energy Astrophysical Phenomena (1)
 
Computer Science - Computational Engineering; Finance; and Science (1)
 
Physics - Fluid Dynamics (1)

Publications Authored By P. Szabo

With the advent of new wide-field, high-cadence optical transient surveys, our understanding of the diversity of core-collapse supernovae has grown tremendously in the last decade. However, the pre-supernova evolution of massive stars, that sets the physical backdrop to these violent events, is theoretically not well understood and difficult to probe observationally. Here we report the discovery of the supernova iPTF13dqy = SN 2013fs, a mere ~3 hr after explosion. Read More

Plastic deformation of crystalline and amorphous matter often involves intermittent local strain burst events. To understand the physical background of the phenomenon a minimal stochastic mesoscopic model was introduced, where microstructural details are represented by a fluctuating local yielding threshold. In the present paper, we propose a method for determining this yield stress distribution by lower scale discrete dislocation dynamics simulations and using a weakest link argument. Read More

We use sub-Kelvin scanning tunneling spectroscopy to investigate the suppression of superconductivity in homogeneously disordered ultrathin MoC films. We observe that the superconducting state remains spatially homogeneous even on the films of 3 nm thickness. The vortex imaging suggests the global phase coherence in our films. Read More

Gaplessness was observed in the disordered films of MoC on approaching to the superconductor to insulator transition by reducing the film thickness. The gaplessness is attributed to the enhanced Coulomb interactions due to the loss of screening in the presence of strong disorder in the films. Read More

We have implemented the log-conformation method for two-dimensional viscoelastic flow in COMSOL, a commercial high-level finite element package. The code is verified for an Oldroyd-B fluid flowing past a confined cylinder. We are also able to describe the well-known bistability of the viscoelastic flow in a cross-slot geometry for a FENE-CR fluid, and we describe the changes required for performing simulations with the Phan-Thien-Tanner (PTT), Giesekus and FENE-P models. Read More

Size-dependence of plastic flow is studied by discrete dislocation dynamical simulation of systems with various numbers of interacting linear edge dislocations while the stress is slowly increased. Regions between avalanches in the individual stress curves as functions of the plastic strain were found nearly linear and reversible, where the plastic deformation obeys an effective equation of motion with a nearly linear force. For small plastic deformation, the means of the stress-strain curves are power law over two decades. Read More

We investigate the complex conductivity of a highly disordered MoC superconducting film with $k_Fl\approx 1$, where $k_F$ is the Fermi wavenumber and $l$ is the mean free path, derived from experimental transmission characteristics of coplanar waveguide resonators in a wide temperature range below the superconducting transition temperature $T_c$. We find that the original Mattis-Bardeen model with a finite quasiparticle lifetime, $\tau$, offers a perfect description of the experimentally observed complex conductivity. We show that $\tau$ is appreciably reduced by scattering effects. Read More

Let $\mathcal{H}$ be a $k$-uniform hypergraph. A chain in $\mathcal{H}$ is a sequence of its vertices such that every $k$ consecutive vertices form an edge. In 1999 Katona and Kierstead suggested to use chains in hypergraphs as the generalisation of paths. Read More

We studied a thin superconducting NbN film in magnetic fields up to 8 T above the zero- temperature limit by means of time-domain terahertz and scanning tunneling spectroscopies in order to understand the vortex response. Scanning tunneling spectroscopy was used to determine the optical gap and the upper critical field of the sample. The obtained values were subsequently used to fit the terahertz complex conductivity spectra in the magnetic field in the Faraday geometry above the zero temperature limit. Read More

We present heat capacity measurements on a series of superconducting Cu$_x$TiSe$_2$ single crystals with different Cu content down to 600 mK and up to 1 T performed by ac microcalorimetry. The samples cover a large portion of the phase diagram from an underdoped to a slightly overdoped region with an increasing superconducting critical temperature and the charge density wave (CDW) order gradually suppressed. The electronic heat capacity as a function of normalized temperature $T/T_c$ shows no difference regardless of the concentration of copper, i. Read More

Previous investigations have shown that SrPd2Ge2, a compound isostructural with "122" iron pnictides but iron- and pnictogen-free, is a conventional superconductor with a single s-wave energy gap and a strongly three-dimensional electronic structure. In this work we reveal the Abrikosov vortex lattice formed in SrPd2Ge2 when exposed to magnetic field by means of scanning tunneling microscopy and spectroscopy. Moreover, by examining the differential conductance spectra across a vortex and estimating the upper and lower critical magnetic fields by tunneling spectroscopy and local magnetization measurements, we show that SrPd2Ge2 is a strong type II superconductor with \kappa >> sqrt(2). Read More

Electronic structure of SrPd2Ge2 single crystals is studied by angle-resolved photoemission spectroscopy (ARPES), scanning tunneling spectroscopy (STS) and band-structure calculations within the local-density approximation (LDA). The STS measurements show single s-wave superconducting energy gap \Delta(0) = 0.5 meV. Read More

Specific heat has been measured down to 600 mK and up to 8 Tesla by the highly sensitive AC microcalorimetry on the MgCNi3 single crystals with Tc ~ 7 K. Exponential decay of the electronic specific heat at low temperatures proved that a superconducting energy gap is fully open on the whole Fermi surface, in agreement with our previous magnetic penetration depth measurements on the same crystals. The specific-heat data analysis shows consistently the strong coupling strength 2D/kTc ~ 4. Read More

Relaxation processes of dislocation systems are studied by two-dimensional dynamical simulations. In order to capture generic features, three physically different scenarios were studied and power-law decays found for various physical quantities. Our main finding is that all these are the consequence of the underlying scaling property of the dislocation velocity distribution. Read More

The messengers of Gauge-Mediation Models can couple to standard-model matter fields through renormalizable superpotential couplings. These matter-messenger couplings generate generation-dependent sfermion masses and are therefore usually forbidden by discrete symmetries. However, the non-trivial structure of the standard-model Yukawa couplings hints at some underlying flavor theory, which would necessarily control the sizes of the matter-messenger couplings as well. Read More

A brief overview of the superconducting energy gap studies on 122-type family of iron pnictides is given. It seems that the situation in the hole-doped Ba1-xKxFe2As2 is well resolved. Most of the measurements including the presented here point-contact Andreev reflection spectra agree on existence of multiple nodeless gaps in the excitation spectrum of this multiband system. Read More

Directional point-contact Andreev-reflection spectroscopy measurements on the Ba$_{0.55}$K$_{0.45}$Fe$_2$As$_2$ single crystals are presented. Read More

We consider a three dimensional, generalized version of the original SPP model for collective motion. By extending the factors influencing the ordering, we investigate the case when the movement of the self-propelled particles (SPP-s) depends on both the velocity and the acceleration of the neighboring particles, instead of being determined solely by the former one. By changing the value of a weight parameter s determining the relative influence of the velocity and the acceleration terms, the system undergoes a kinetic phase transition as a function of a behavioral pattern. Read More

Systematic studies of the NdFeAsOF superconducting energy gap via the point-contact Andreev-reflection (PCAR) spectroscopy are presented. The PCAR conductance spectra show at low temperatures a pair of gap-like peaks at about 4 - 7 mV indicating the superconducting energy gap and in most cases also a pair of humps at around 10 mV. Fits to the s-wave two-gap model of the PCAR conductance allowed to determine two superconducting energy gaps in the system. Read More

Thermal functional circuits are an interesting and perspectivic group of the MEMS elements. A practical realization is called Quadratic Transfer Characteristic (QTC) element which driving principle is the Seebeck-effect. In this paper we present the analyses of a QTC element from different perspectives. Read More

Thermal qualification of the die attach of semiconductor devices is a very important element in the device characterization as the temperature of the chip is strongly affected by the quality of the die attach. Voids or delaminations in this layer may cause higher temperature elevation and thus damage or shorter lifetime. Thermal test of each device in the manufacturing process would be the best solution for eliminating the devices with wrong die attach layer. Read More

Our paper presents a non-destructive thermal transient measurement method that is able to reveal differences even in the micron size range of MEMS structures. Devices of the same design can have differences in their sacrificial layers as consequence of the differences in their manufacturing processes e.g. Read More

Thermal measurement and modeling of multi-die packages became a hot topic recently in different fields like RAM chip packaging or LEDs / LED assemblies, resulting in vertical (stacked) and lateral arrangement. In our present study we show results for a mixed arrangement: an opto-coupler device has been investigated with 4 chips in lateral as well as vertical arrangement. In this paper we give an overview of measurement and modeling techniques and results for stacked and MCM structures, describe our present measurement results together with our structure function based methodology of validating the detailed model of the package being studied. Read More

The two-band/two-gap superconductivity in aluminium and carbon doped MgB$_2$ has been addressed by the point-contact spectroscopy. Two gaps are preserved in all samples with $T_c's$ down to 22 K. The evolution of two gaps as a function of the critical temperature in the doped systems suggest the dominance of the band-filling effects but for the increased Al-doping the enhanced interband scattering approaching two gaps must be considered. Read More

The lower ($H_{c1}$) and upper ($H_{c2}$) critical fields of Mg$_{1-x}$Al$_{x}$B$_2$ single crystals (for $x = 0$, 0.1 and $\gtrsim 0.2$) have been deduced from specific heat and local magnetization measurements, respectively. Read More

In a recent Physical Review Letter Kortus et al. claim that the observed decrease of $T_c$ in Al and C doped MgB$_2$ samples is mainly due to the band filling by the electron doping but for a fuller understanding of the different behavior of the superconducting energy gaps in Al and C doped samples it is necessary to also include an increased interband scattering for the carbon doped samples. We argue in the following that this latter statement is misleading and is based on the assumption that for carbon doping the two superconducting gaps merge near 10 % carbon doping: an assumption that contradicts most of the existing experimental data. Read More

Point-contact measurements on the carbon-substituted Mg(B$_{1-x}$C$_x$)$_2$ filament/powder samples directly reveal a retention of the two superconducting energy gaps in the whole doping range from $x = 0$ to $x \approx 0.1$. The large gap on the $\sigma$-band is decreased in an essentially linear fashion with increasing the carbon concentrations. Read More

The temperature dependence of the London penetration depth ($\lambda$) and coherence length ($\xi$) has been deduced from Hall probe magnetization measurements in high quality MgB$_2$ single crystals in the two main crystallographic directions. We show that, in contrast to conventional superconductors, MgB$_2$ is characterized by two different anisotropy parameters ($\Gamma_\lambda = \lambda_c/\lambda_{ab}$ and $\Gamma_\xi = \xi_{ab}/\xi_c$) which strongly differ at low temperature and merge at $T_c $. These results are in very good agreement with recent calculations in weakly coupled two bands suprerconductors (Phys. Read More

The Andreev reflection measurements of the superconducting energy gap in the carbon-substituted MgB$_2$ are presented. Despite the strong suppression of the transition temperature by 17 K in comparison with the pure MgB$_2$, the same reduced value of the small superconducting energy gap with $2\Delta/kT_c \approx$ 1.7 has been systematically observed. Read More

Point-contact spectroscopy measurements on magnesium diboride reveal the existence of two superconducting energy gaps closing at the same transition temperature in line with the multiband model of superconductivity. The sizes of the two gaps ($\Delta_{\pi}$ = 2.8 meV and $\Delta_{\sigma}$ = 6. Read More

We report on specific heat, high magnetic field transport and $ac-$susceptibility measurements on magnesium diboride single crystals. The upper critical field $H_{c2}$ for magnetic fields perpendicular and parallel to the Mg and B planes is presented for the first time in the entire temperature range. A very different temperature dependence has been observed in the two directions which yields to a temperature dependent anisotropy with $\Gamma \sim$ 5 at low temperatures and about 2 near $T_c$. Read More

We study the emergency of mutual cooperation in evolutionary prisoner's dilemma games when the players are located on a square lattice. The players can choose one of the three strategies: cooperation (C), defection (D) or "tit for tat" (T), and their total payoffs come from games with the nearest neighbors. During the random sequential updates the players adopt one of their neighboring strategies if the chosen neighbor has higher payoff. Read More

Thermodynamic (specific heat, reversible magnetization, tunneling spectroscopy) and transport measurements have been performed on high quality (K,Ba)BiO$_3$ single crystals. The temperature dependence of the magnetic field $H_{Cp}$ corresponding to the onset of the specific heat anomaly presents a clear positive curvature. $H_{Cp}$ is significantly smaller than the field $H_\Delta$ for which the superconducting gap vanishes but is closely related to the irreversibility line deduced from transport data. Read More

The temperature and angular dependencies of the resistive upper critical magnetic field $B_{c2}$ reveal a dimensional crossover of the superconducting state in the highly anisotropic misfit-layer single crystal of (LaSe)$_{1.14}$(NbSe$_2$) with the critical temperature $T_c$ of 1.23 K. Read More

Magnetotransport measurements are presented on polycrystalline MgB2 samples. The resistive upper critical magnetic field reveals a temperature dependence with a positive curvature from Tc = 39.3 K down to about 20 K, then changes to a slightly negative curvature reaching 25 T at 1. Read More

Experimental support is found for the multiband model of the superconductivity in the recently discovered system MgB2 with the transition temperature Tc = 39 K. By means of Andreev reflection evidence is obtained for two distinct superconducting energy gaps. The sizes of the two gaps (Delta_S = 2. Read More

Elastic tunneling is used as a powerful direct tool to determine the upper critical field $H_{c2}(T)$ in the high-$T_c$ oxide Ba$_{1-x}$K$_x$BiO$_3$. The temperature dependence of $H_{c2}$ inferred from the tunneling follows the Werthamer-Helfand-Hohenberg prediction for type-II superconductors. A comparison will be made with resistively determined critical field data. Read More

We show that the interlayer transport in a two-dimensional superconductor can reveal a peak in the temperature as well as the magnetic field dependence of the resistivity near the superconducting transition. The magnetotransport experiment was performed on the highly anisotropic misfit-layer superconductor (LaSe)$_{1.14}$(NbSe$_2$) with critical tempertaure $T_c$ of 1. Read More

The de Gennes and Maki theory of gapless superconductivity for dirty superconductors is used to interpret the tunneling measurements on the strongly type-II high-Tc oxide-superconductor Ba1-xKxBiO3 in high magnetic fields up to 30 Tesla. We show that this theory is applicable at all temperatures and in a wide range of magnetic fields starting from 50 percent of the upper critical field Bc2. In this magnetic field range the measured superconducting density of states (DOS) has the simple energy dependence as predicted by de Gennes from which the temperature dependence of the pair-breaking parameter alpha(T), or Bc2(T), has been obtained. Read More

The emergence of mutual cooperation is studied in a spatially extended evolutionary prisoner's dilemma game in which the players are located on the sites of cubic lattices for dimensions d=1, 2, and 3. Each player can choose one of the three strategies: cooperation (C), defection (D) or Tit for Tat (T). During the evolutionary process the randomly chosen players adopt one of their neighboring strategies if the chosen neighbor has higher payoff. Read More