Specific heat at the transition in a superconductor with fluctuating magnetic moments

In the heavy-fermion materials CeCoIn$_5$ and UBe$_{13}$, the superconducting order parameter is coupled to flucutating magnetization of the uncompensated part of the localized $f$-moments. We find that this coupling decreases the superconducting transition temperature and increases the jump of the specific-heat coefficient, which indicates entropy transfer from the magnetic to the superconducting degree of freedom at the transition temperature. Below the transition, we find that the magnetic fluctuations are suppressed. We discuss the relation of our results to experiments on CeCoIn$_5$ under pressure.Comment: 4 pages, 1 figur

Free Energy of an Inhomogeneous Superconductor: a Wave Function Approach

A new method for calculating the free energy of an inhomogeneous superconductor is presented. This method is based on the quasiclassical limit (or Andreev approximation) of the Bogoliubov-de Gennes (or wave function) formulation of the theory of weakly coupled superconductors. The method is applicable to any pure bulk superconductor described by a pair potential with arbitrary spatial dependence, in the presence of supercurrents and external magnetic field. We find that both the local density of states and the free energy density of an inhomogeneous superconductor can be expressed in terms of the diagonal resolvent of the corresponding Andreev Hamiltonian, resolvent which obeys the so-called Gelfand-Dikii equation. Also, the connection between the well known Eilenberger equation for the quasiclassical Green's function and the less known Gelfand-Dikii equation for the diagonal resolvent of the Andreev Hamiltonian is established. These results are used to construct a general algorithm for calculating the (gauge invariant) gradient expansion of the free energy density of an inhomogeneous superconductor at arbitrary temperatures.Comment: REVTeX, 28 page

Supertvrdé kovové povlaky

Článek popisuje povrchové vytvrzení měkkého objemového kovu ochranným povlakem z téhož kovu s tvrdostí až 6 krát vyšší. Proces je předveden na příkladu pokrytí titanového substrátu o nízké tvrdosti asi 5 GPa povlakem o vysoké tvrdosti asi 30 GPa a tloušťce 1200 nm. Povlaky byly naneseny novou technikou využívající vysokých tlaků nad 1000 GPa, vysokých teplot nad teplotou tání a vysokou chladící rychlost nad 10^10 K/s. Princip této techniky provedené na atomové úrovni je detailně popsán.The letter reports on the surface hardening of bulk soft metal materials by protective coatings made of the same metal as bulk but with up to 6 times higher hardness than that of the bulk material. This surface hardening is demonstrated by covering of the Ti substrate with a low hardness Hbulk ≈ 5 GPa by a 1200 nm thick Ti coating with a high hardness Hcoating ≈ 30 GPa. The protective hard Ti coatings were sputtered by a new sputtering technology based on extremely high pressures (≥ 1000 GPa), high temperatures exceeding the melting temperature Tm of the coating material and extremely high cooling rate of the created coating (≥ 10^10 K/s). The principle of this technology realized at an atomic level is described in detail

Tvrdé slitinové vrstvy se zvýšenou odolností vůči vzniku trhlin

Článek pojednává o mechanických vlastnostech slitinových vrstev připravených magnetronovým naprašováním. Vznik trhlin je velkým nedostatkem slitinových vrstev, protože silně omezuje mnoho z jejich praktických využití. Je ukázáno, že tvrdé slitinové vrstvy musí být superelastické a vykazovat vysoký poměr H/E* ≥ 0.1, H je tvrdost a E* efektivní Youngův modul vrstvy. Mechanické vlastnosti tvrdých slitinových vrstev s obsahem Si se zvýšenou odolností vůči vzniku trhlin jsou ukázány jako příklady. Dále je vysvětlen vliv přidání Si a N do Mg vrstev na mechanické vlastnosti a je studován jejich vztah ke změnám homologické teploty materiálu.The article reports on the mechanical properties of alloy films prepared by magnetron sputtering. Cracking is a great drawback of alloy films because it strongly limits many of their practical applications. It is shown that hard alloy films resistant to cracking must be superelastic and exhibit a high ratio H/E* ≥ 0.1; here H is the hardness and E* is the effective Young's modulus of the film. As examples, mechanical properties of the Si-based hard alloy films with enhanced resistance to cracking are given. Furthermore, the effect of the addition of Si and N into single element Mg films on the film mechanical properties and its relation to the changes of the material homologous temperature is investigated

Povlaky nadstechiometrických přechodových kovových nitridů (TMNx (x > 1)) připravené magnetronovým naprašováním

Článek pojednává o přípravě silně nadstechiometrických povlaků ZrNx>1 a Ti(Al,V)Nx>1 reaktivním magnetronovým naprašováním. Jsou diskutovány problémy přípravy nadstechiometrických povlaků a možnosti, jak vytvořit silně nadstechiometrické TMNx>1 nitridové povlaky až s TMNx=2, TM jsou přechodové kovy jako Ti, Zr, Mo, Ta, Nb, W, atd. Stechiometrie povlaku x = N/TM silně ovlivňuje jeho elektrické a mechanické vlastnosti. Byla zkoumána příprava a vlastnosti reaktivně naprášených ZrNx povlaků. Bylo zjištěno, že (1) rezistivita ZrNx povlaků se mění s rostoucím x od velmi elektricky vodivých s x ≤ 1 přes polovodivé vrstvy s x mezi 1 a 1,26 na nevodivé s x ≥ 1,3, což potvrzuje, že stechiometrie x je důležitý parametr, který dovoluje kontrolovat elektrickou vodivost povlaku v širokém rozsahu, (2) elektricky vodivé povlaky s x ≤ 1 jsou tvrdší než polovodivé a elektricky nevodivé povlaky a (3) ZrN2 vrstvy nemohou být připraveny, protože vznikající Zr3N4 fáze má vyšší formovací entalpii než ZrN2 fáze. Dále je ukázáno, že hlavním problémem při přípravě silně nadstechiometrických povlaků TMNx>1 a dinitridů TMN2 je potřeba velkého zvýšení ionizace rozprašovacího plynu dusíku k dosažení nezbytného vysokého poměru N/TM > 1.This article reports on the formation of strongly overstoichiometric ZrNx>1 and Ti(Al, V)Nx>1 coatings by reactive magnetron sputtering. Problems in the formation of overstoichiometric coatings and possible ways to form strongly overstoichiometric TMNx>1 nitride coatings up to TMNx=2 dinitride coatings are discussed; here, TM are transition metals such as Ti, Zr, Mo, Ta, Nb, W, etc. The coating stoichiometry x = N/TM strongly influences its electrical and mechanical properties. The creation and properties of reactively sputtered ZrNx coatings were investigated. It was found that (1) the electrical resistivity of the ZrNx coating varies with increasing x from well electrically conducting films with x ≤ 1 through semi-conducting films with x ranging from 1 to ≤ 1.26 to non-conductive with x ≥ 1.3, showing that the stoichiometry x is a strong parameter which enables to control an electric conductivity of the coating in a wide range, (2) electrically conductive coatings with x ≤ 1 are harder than the semiconducting and electrically insulating coatings, and (3) the ZrN2 dinitride film cannot be created due to the formation of a Zr3N4 phase whose formation enthalpy is greater than that of a ZrN2 phase. Further, it is shown that the main problem in the formation of strongly overstoichiometric TMNx>1 and dinitride TMN2 coatings is a strong increase of ionization of the nitrogen sputtering gas to achieve a necessary high ratio N/TM > 1. Trends enabling the mastery of formation of the TMN2 dinitride coatings are briefly outlined

FTIR microscopy reveals distinct biomolecular profile of crustacean digestive glands upon subtoxic exposure to ZnO nanoparticles

<p>Biomolecular profiling with Fourier-Transform InfraRed Microscopy was performed to distinguish the Zn²⁺-mediated effects on the crustacean (<i>Porcellio scaber</i>) digestive glands from the ones elicited by the ZnO nanoparticles (NPs). The exposure to ZnO NPs or ZnCl₂ (1500 and 4000 µg Zn/g of dry food) activated different types of metabolic pathways: some were found in the case of both substances, some only in the case of ZnCl₂, and some only upon exposure to ZnO NPs. Both the ZnO NPs and the ZnCl₂ increased the protein (∼1312 cm⁻¹; 1720–1485 cm⁻¹/3000–2830 cm⁻¹) and RNA concentration (∼1115 cm⁻¹). At the highest exposure concentration of ZnCl₂, where the effects occurred also at the organismal level, some additional changes were found that were not detected upon the ZnO NP exposure. These included changed carbohydrate (most likely glycogen) concentrations (∼1043 cm⁻¹) and the desaturation of cell membrane lipids (∼3014 cm⁻¹). The activation of novel metabolic pathways, as evidenced by changed proteins’ structure (at 1274 cm⁻¹), was found only in the case of ZnO NPs. This proves that Zn²⁺ are not the only inducers of the response to ZnO NPs. Low bioavailable fraction of Zn²⁺ in the digestive glands exposed to ZnO NPs further supports the role of particles in the ZnO NP-generated effects. This study provides the evidence that ZnO NPs induce their own metabolic responses in the subtoxic range.</p