The ScAu2Al superconducting Heusler-type compound was recently characterized to have the highest critical temperature of Tc=5.12 K and the strongest electron-phonon coupling among the Heusler family. In this work, the...
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The ScAu2Al superconducting Heusler-type compound was recently characterized to have the highest critical temperature of Tc=5.12 K and the strongest electron-phonon coupling among the Heusler family. In this work, the electronic structure, phonons, electron-phonon coupling, and superconductivity of ScAu2Al are studied using ab initio calculations. The spin-orbit coupling significantly changes the electronic structure removing the van Hove singularity from the vicinity of the Fermi level. In the phonon spectrum, low-frequency acoustic modes, additionally softened by the spin-orbit interaction, strongly couple with electrons, leading to the electron-phonon coupling constant λ=1.25, a record high among Heuslers. The density functional theory for superconductors is then used to analyze superconducting state in this two-band superconductor. The effect of spin fluctuations (SF) on superconductivity is also analyzed. The calculated critical temperatures of Tc=5.16 K (4.79 K with SF) agree very well with the experiment, confirming the electron-phonon mechanism of superconductivity and showing a weak spin-fluctuation effect. The superconducting gaps formed on two Fermi surface sheets exhibit moderate anisotropy. Their magnitudes confirm the strong coupling regime, as the reduced average values are 2Δb1/kBTc≃4.1 and 2Δb2/kBTc≃4.3. Anisotropy of the gaps and large spread in their values significantly affect the calculated quasiparticle density of states.
Local distortions of the crystal structure and their influence on the electronic structure, electron-phonon interaction, and superconductivity are theoretically studied in the superconducting high-entropy alloy (TaNb)...
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Local distortions of the crystal structure and their influence on the electronic structure, electron-phonon interaction, and superconductivity are theoretically studied in the superconducting high-entropy alloy (TaNb)0.67(HfZrTi)0.33. Distortions of the crystal lattice are caused by the relaxation of atomic positions and are studied in the twelve models of supercells. The largest relative changes in the interatomic distances due to relaxation reach 8%. On average, local distortions tend to lower the density of states at the Fermi level and significantly reduce the electron-phonon coupling parameter λ. As a result, the calculated superconducting critical temperature is reduced to about 50% of the initial value, which shows the strong impact of structural disorder on superconductivity in this prototype high-entropy alloy. With the reduced value of λ, the theoretical Tc is closer to the experiment for typical values of the Coulomb pseudopotential parameter μ*. The experimental Tc can be reproduced by taking a slightly enhanced μ*=0.176, which leaves little room for the possibility of suppression of superconductivity by disorder.
Ultralight dark matter (ULDM) halos constituted by ultralight axions (ULAs) generate gravitational potentials that oscillate in time. In this paper, I show these potentials interact with gravitational waves, resonantl...
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Ultralight dark matter (ULDM) halos constituted by ultralight axions (ULAs) generate gravitational potentials that oscillate in time. In this paper, I show these potentials interact with gravitational waves, resonantly amplifying them. For all ULA masses considered, the resonance in the solar region is currently negligible, while in a denser dark matter environment, which may arise in different scenarios, it might become significant. The frequency of the amplified gravitational wave is equal to the ULA mass in the case of the first resonance band, which represents the most efficient scenario.
We calculate the baryon number cumulants within acceptance with short-range correlations and global baryon number conservation in terms of cumulants in the whole system without baryon conservation. We extract leading ...
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We calculate the baryon number cumulants within acceptance with short-range correlations and global baryon number conservation in terms of cumulants in the whole system without baryon conservation. We extract leading and next-to-leading order terms of the large baryon number limit approximation. These approximations are checked to be very close to the exact results.
In relativistic heavy-ion collisions, the longitudinal fluctuations of the fireball density caused, e.g., by fluctuations in the number of stopped baryons result in event-by-event modifications of the shape of the pro...
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In relativistic heavy-ion collisions, the longitudinal fluctuations of the fireball density caused, e.g., by fluctuations in the number of stopped baryons result in event-by-event modifications of the shape of the proton rapidity density distribution. The multiparticle rapidity correlation functions due to the varying distribution width of the proton rapidity density in central Au+Au collisions at low energies are derived. The cumulant ratios are calculated and discussed in the context of the recent STAR Collaboration results. We find that for small fluctuations in the width of the proton rapidity distribution, the cumulant ratios are independent of the underlying width distribution. It is also emphasized that the cumulant ratios strongly depend on the size of the rapidity interval.
Uncertainty relations are a fundamental feature of quantum mechanics. How can these relations be found systematically? Here, we develop a semidefinite programming hierarchy for additive uncertainty relations in the va...
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Uncertainty relations are a fundamental feature of quantum mechanics. How can these relations be found systematically? Here, we develop a semidefinite programming hierarchy for additive uncertainty relations in the variances of noncommuting observables. Our hierarchy is built on the state polynomial optimization framework, also known as scalar extension. The hierarchy is complete in the sense that it converges to tight uncertainty relations. We improve upon upper bounds for all 1292 additive uncertainty relations on up to nine operators for which a tight bound is not known. The bounds are dimension-free and depend entirely on the algebraic relations among the operators. The techniques apply to a range of scenarios, including Pauli, Heisenberg-Weyl, and fermionic operators, and generalize to higher order moments and multiplicative uncertainty relations.
Primordial black holes (PBHs) and the violation of the null energy condition (NEC) have significant implications for our understanding of the very early Universe. We present a novel approach to generate PBHs via the N...
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Primordial black holes (PBHs) and the violation of the null energy condition (NEC) have significant implications for our understanding of the very early Universe. We present a novel approach to generate PBHs via the NEC violation in a single-field inflationary scenario. In our scenario, the Universe transitions from a first slow-roll inflation stage with a Hubble parameter H=Hinf1 to a second slow-roll inflation stage with H=Hinf2≫Hinf1, passing through an intermediate stage of NEC violation. The NEC violation naturally enhances the primordial scalar power spectrum at a certain wavelength, leading to the production of PBHs with masses and abundances of observational interest. We also investigate the phenomenological signatures of scalar-induced gravitational waves resulting from the enhanced density perturbations. Our work highlights the potential of utilizing a combination of PBHs, scalar-induced gravitational waves, and primordial gravitational waves as a valuable probe for studying NEC violation during inflation, opening up new avenues for exploring the early Universe.
The paper presents the rotated 3D-printed dielectric lens assembly with an ultra-wideband (UWB) antenna for use in the beam-steering applications. The focus is on achieving beam steering by combining the rotated 3D-pr...
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Rendering high-polygonal models from distant perspectives has certain performance issues related to high density of subpixel triangles, which can be solved by levels of detail, a classical optimization method. Since a...
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