Interactions between Sheets of Phonons in Liquid 4He

We have created two sheets of 1 K phonons in liquid 4He at 55 mK such that they intersect each other as they move towards a common point. If the two sheets have a small angle between them, they interact strongly and create a hot line in the liquid helium. This line is continuously fed with energy from the two sheets and loses energy by creating high-energy phonons. If the angle between the sheets is larger than 30 they do not interact but pass through each other. These results give direct evidence for the composition of the sheets: they comprise strongly interacting low-energy phonons which occupy a narrow cone in momentum space

Pseudogap state in slightly doped by aluminium and praseodymium YBa2_2Cu3_3O7−δ_{7-\delta} single crystals with a given topology of plane defects

In present work the conductivity in the basis plane of YBaCuO single crystals slightly doped by Al and Pr with a pre-specified topology of twin boundaries has been investigated. The excess conductivity for the analyzed samples shows dependence like $\Delta\sigma\sim(1-T/T^*)\exp(\Delta_{ab}^*/T)$ in wide temperature range $T_f<T<T^*$, where $T^*$ can be represents as mean field temperature of superconducting transition. The temperature dependence of pseudogap can be satisfactory described in terms of the BCS-BEC crossover theoretical model.Comment: 3 pages, 2 figure

Impact of isovalent doping on the formation of the CiOi(SiI)n defects in silicon

It has been determined that carbon-oxygen-self-interstitial defects in silicon (Si) can influence the operation of devices through the concentration of intrinsic point defects. Doping with larger isovalent dopants such as germanium (Ge) and tin (Sn) can impact the formation, energetics and structure of defect clusters in Si. In the present study we use density functional theory calculations to gain insights on the formation and stability of the CiOi(SiI)n (n = 0, 1, 2) defects in Si doped with Ge or Sn. It is calculated that the CiOi(SiI)n defects will preferentially form away from the oversized dopants. This result for the interstitial clusters is opposite to what is expected for vacancy-containing clusters which strongly associate with oversized dopants.Publisher Statement: NOTICE: this is the author’s version of a work that was accepted for publication in Solid State Communications. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Solid State Communications, [263, (2017)] DOI: 10.1016/j.ssc.2017.06.010© 2017, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0

Evolution of over-conductivity of YВа₂Сu₃О₇-δ single crystals under the exposure of irradiation by high-energy electrons

The evolution of the excess conductivity of YВа₂Сu₃О₇-δ single crystals upon electron irradiation is investigated. It was shown that electron irradiation leads to a significant expansion of the temperature range for the existence of excess conductivity, thereby narrowing the region of the linear dependence of p(Т) in the ab plane. It was found that the excess conductivity Δσ(Т) of YВа₂Сu₃О₇-δ single crystals in a wide temperature range Tf<Т<T⚹ (Тf – the transition temperature from the PG to the FP mode) is subject to exponential temperature dependence. Moreover, the description of excess conductivity using the relation Δσ ⁓ (1-Т/Т⚹)exp(Δ⚹ab/T) (Δ⚹ab – the pseudogap in ab-plane) can be interpreted in terms of the mean-field theory, where T⚹ is presented as the mean-field temperature of the transition to the PG state, and the temperature dependence of the pseudogap is satisfactorily described in the framework of the BCS-BEC crossover theory. In this case, the value of the transverse coherence length ξс(0) increases 1.4 times and the 2D-3D crossover point shifts in temperature.Досліджено еволюцію надлишкової провідності монокристалів YВа₂Сu₃О₇-δ при опроміненні електронами. Показано, що опромінення електронами призводить до значного розширення температурного інтервалу існування надлишкової провідності, тим самим, звужуючи область лінійної залежності p(Т) в ab площині. Встановлено, що надлишкова провідність Δσ(Т) монокристалів YВа₂Сu₃О₇-δ в широкому інтервалі температур Tf<Т<T⚹ підпорядковується експоненційній температурній залежності. При цьому опис надлишкової провідності за допомогою співвідношення Δσ⁓(1–Т/Т⚹)exp(Δ⚹ab/T) може бути інтерпретовано в термінах теорії середнього поля, де Т⚹ представлена, як середньополева температура переходу в ПЩ-стан, а температурна залежність псевдощілини задовільно описується в рамках теорії кросовера БКШ-БЕК. При цьому величина поперечної довжини когерентності ξс(0) збільшується в 1,4 рази, і зміщується по температурі точка 2D-3D кросовера.Исследована эволюция избыточной проводимости монокристаллов YВа₂Сu₃О₇-δ при облучении электронами. Показано, что облучение электронами приводит к значительному расширению температурного интервала существования избыточной проводимости, тем самым, сужая область линейной зависимости p(Т) в ab-плоскости. Установлено, что избыточная проводимость Δσ(Т) монокристаллов YВа₂Сu₃О₇-δ в широком интервале температур Tf<Т<T⚹ подчиняется экспоненциальной температурной зависимости. При этом описание избыточной проводимости с помощью соотношения Δσ⁓(1–Т/Т⚹)exp(Δ⚹ab/T) может быть интерпретировано в терминах теории среднего поля, где Т⚹ представлена, как среднеполевая температура перехода в ПЩ-состояние, а температурная зависимость псевдощели удовлетворительно описывается в рамках теории кроссовера БКШ-БЭК. При этом величина поперечной длины когерентности ξс(0) увеличивается в 1,4, раза и смещается по температуре точка 2D-3D кроссовера