145 research outputs found
Elektron transzport molekuláris nanostruktúrákban = Electron transport in molecular nanostructures
Az OTKA K76010 kutatói pályázat keretében nanokontaktusok viselkedését vizsgáltuk, melyekben az áram egyetlen atomon vagy egyetlen molekulán keresztül folyik. A kutatás keretében kifejlesztettünk egy molekulák kontrollált adagolására alkalmas mérőrendszert, mely egyedi molekulák kontaktálását teszi lehetővé folyékony hélium hőmérsékleten. Szupravezető subgap módszerrel karakterizáltunk különböző anyagból készült atomi méretű kontaktusokat és elméleti csoportokkal együttműködve részt vettünk egy vezetőképesség hisztogramok szimulálására alkalmas módszer fejlesztésében, melynek megbízhatóságát a subgap módszer segítségével egyedi vezetési csatornák szintjén ellenőriztük. Kifejlesztettünk egy új statisztikai módszert, melynek segítségével atomi és molekuláris kontaktusokban kialakuló konfigurációk közötti korrelációk vizsgálhatók. Ezen módszer segítségével számos atomi és molekuláris nanovezeték viselkedését sikerült a szokásos vezetőképesség hisztogram technikánál részletesebben feltérképezni. | Within the OTKA K76010 project nano-scale junctions were investigated, in which the current flows along single atoms or molecules. A novel measurement setup was developed which is capable of a controlled dosing of molecules to a liquid helium temperature break junction device so that single molecules can be contacted in a well controlled manner. With the help of superconducting subgap structure measurements various metal atomic sized contacts were characterized. In collaboration with theory groups a novel method was developed to simulate conductance histograms. With the help of subgap structure measurements the reliability of this method was tested on the level of individual channel transmission eigenvalues. Beside, we have introduced a novel statistical analysis method based on the two-dimensional cross-correlation histogram analysis of conductance traces. This method provides new information about the relation of different junction configurations that occur during the formation and evolution of metal and single-molecule junctions. The correlation method was successfully applied to study the behavior a several atomic and single-molecule structures beyond conductance histograms
Strong nonlocal tuning of the current-phase relation of a quantum dot based Andreev molecule
Multiple systems hosting Andreev molecular states have been proposed and
studied, consisting of closely spaced Josephson junctions modeled as ballistic
channels. We show that replacing the ballistic channels in the weak link of the
Josephson junctions with quantum dots (QD), leads to a very exciting, rich
phase diagram. It shows a strong nonlocal Josephson effect: as one junction is
tuned the current-phase relation of the other junction is modified. This
architecture hosts transitions and shows a tunable anomalous
phase-shift , nonlocally controlled in both cases, without relying on
spin-orbit interaction or Zeeman fields. In addition significant
superconducting diode effect can also be observed. The presented non-local
current-phase relation can be used as a signature of the formation of an
Andreev molecular state, as well as to introduce new ways to tune quantum
architectures
Point contacts in encapsulated graphene
We present a novel method to establish inner point contacts on hexagonal
boron nitride (hBN) encapsulated graphene heterostructures with dimensions as
small as 100 nm by pre-patterning the top-hBN in a separate step prior to
dry-stacking. 2 and 4-terminal field effect measurements between different lead
combinations are in qualitative agreement with an electrostatic model assuming
pointlike contacts. The measured contact resistances are 0.5-1.5 k per
contact, which is quite low for such small contacts. By applying a
perpendicular magnetic fields, an insulating behaviour in the quantum Hall
regime was observed, as expected for inner contacts. The fabricated contacts
are compatible with high mobility graphene structures and open up the field for
the realization of several electron optical proposals
Urban Bus Network Electrification
Electric busses are spreading in cities in hope of mitigating local air pollution. Currently, battery electric busses are more expensive and require novel operational methods to optimize their use (e.g., applying daytime charging, and operating trolleybuses). Despite these, the electrification of urban busses is usually ad-hoc, preliminary planning is superficial, and does not consider the relationships among bus lines. This chapter introduces a method regarding charging infrastructure planning, electric bus type selection, and cost estimation. Based on the characteristics of the vehicle, charging infrastructure, bus service (lines, timetable, etc.), and energy consumption, a line-group optimization is introduced, which is the main novelty. The method was applied in a case study considering static terminal and dynamic catenary charging. The results help operators to boost the electrification of the urban bus network
Preconditioning protects the heart in a prolonged uremic condition
Metabolic diseases such as hyperlipidemia and diabetes attenuate the cardioprotective effect of ischemic preconditioning. In the present study, we examined whether another metabolic disease, prolonged uremia, affects ischemia/reperfusion injury and cardioprotection by ischemic preconditioning. Uremia was induced by partial nephrectomy in male Wistar rats. The development of uremia was verified 29 wk after surgery. Transthoracic echocardiography was performed to monitor cardiac function. At week 30, hearts of nephrectomized and sham-operated rats were isolated and subjected to a 30-min coronary occlusion followed by 120 min reperfusion with or without preceding preconditioning induced by three intermittent cycles of brief ischemia and reperfusion. In nephrectomized rats, plasma uric acid, carbamide, and creatinine as well as urine protein levels were increased as compared with sham-operated controls. Systolic anterior and septal wall thicknesses were increased in nephrectomized rats, suggesting the development of a minimal cardiac hypertrophy. Ejection fraction was decreased and isovolumic relaxation time was shortened in nephrectomized rats demonstrating a mild systolic and diastolic dysfunction. Infarct size was not affected significantly by nephrectomy itself. Ischemic preconditioning significantly decreased infarct size from 24.8 ± 5.2% to 6.6 ± 1.3% in the sham-operated group and also in the uremic group from 35.4 ± 9.5% to 11.9 ± 3.1% of the area at risk. Plasma ANG II and nitrotyrosine were significantly increased in the uremic rats. We conclude that although prolonged experimental uremia leads to severe metabolic changes and the development of a mild myocardial dysfunction, the cardioprotective effect of ischemic preconditioning is still preserved
Exfoliation of single layer BiTeI flakes
Spin orbit interaction can be strongly boosted when a heavy element is
embedded into an inversion asymmetric crystal field. A simple structure to
realize this concept in a 2D crystal contains three atomic layers, a middle one
built up from heavy elements generating strong atomic spin-orbit interaction
and two neighboring atomic layers with different electron negativity. BiTeI is
a promising candidate for such a 2D crystal, since it contains heavy Bi layer
between Te and I layers. Recently the bulk form of BiTeI attracted considerable
attention due to its giant Rashba interaction, however, 2D form of this crystal
was not yet created. In this work we report the first exfoliation of single
layer BiTeI using a recently developed exfoliation technique on stripped gold.
Our combined scanning probe studies and first principles calculations show that
SL BiTeI flakes with sizes of 100 m were achieved which are stable at
ambient conditions. The giant Rashba splitting and spin-momentum locking of
this new member of 2D crystals open the way towards novel spintronic
applications and synthetic topological heterostructures.Comment: 20 pages, 5 figure
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