10 research outputs found
Gate-defined electron-hole double dots in bilayer graphene
We present gate-controlled single, double, and triple dot operation in
electrostatically gapped bilayer graphene. Thanks to the recent advancements in
sample fabrication, which include the encapsulation of bilayer graphene in
hexagonal boron nitride and the use of graphite gates, it has become possible
to electrostatically confine carriers in bilayer graphene and to completely
pinch-off current through quantum dot devices. Here, we discuss the operation
and characterization of electron-hole double dots. We show a remarkable degree
of control of our device, which allows the implementation of two different
gate-defined electron-hole double-dot systems with very similar energy scales.
In the single dot regime, we extract excited state energies and investigate
their evolution in a parallel magnetic field, which is in agreement with a
Zeeman-spin-splitting expected for a g-factor of two.Comment: 5 pages, 5 figure
AZT resistance of simian foamy virus reverse transcriptase is based on the excision of AZTMP in the presence of ATP
Azidothymidine (AZT, zidovudine) is one of the few nucleoside inhibitors known to inhibit foamy virus replication. We have shown previously that up to four mutations in the reverse transcriptase gene of simian foamy virus from macaque (SFVmac) are necessary to confer high resistance against AZT. To characterize the mechanism of AZT resistance we expressed two recombinant reverse transcriptases of highly AZT-resistant SFVmac in Escherichia coli harboring three (K211I, S345T, E350K) or four mutations (K211I, I224T, S345T, E350K) in the reverse transcriptase gene. Our analyses show that the polymerization activity of these mutants is impaired. In contrast to the AZT-resistant reverse transcriptase of HIV-1, the AZT resistant enzymes of SFVmac reveal differences in their kinetic properties. The SFVmac enzymes exhibit lower specific activities on poly(rA)/oligo(dT) and higher KM-values for polymerization but no change in KD-values for DNA/DNA or RNA/DNA substrates. The AZT resistance of the mutant enzymes is based on the excision of the incorporated inhibitor in the presence of ATP. The additional amino acid change of the quadruple mutant appears to be important for regaining polymerization efficiency
Tuning the supercurrent distribution in parallel ballistic graphene Josephson junctions
We report on a ballistic and fully tunable Josephson-junction system consisting of two parallel ribbons of graphene in contact with superconducting molybdenum-rhenium. By electrostatic gating of the two individual graphene ribbons, we gain control over the real-space distribution of the superconducting current density, which can be continuously tuned between the two ribbons. We extract the respective gate-dependent spatial distributions of the real-space current density by employing Fourier and Hilbert transformations of the magnetic-field-induced modulation of the critical current. This approach is fast and does not rely on a symmetric current profile. It is therefore a universally applicable tool, potentially useful for carefully adjusting Josephson junctions
Dissertatio Inauguralis De Sponsalibus
Quam ... In Alam Et Perantiqua Universitate Coloniensi Ordinario Sub Praesidio ... D. Joannis Jacobi Caardauns J.U.D. Professoris publici & ordinarii, Facultatis Juridicae Dictatoris, Nec Non D. Joannis Benedicti Wilmes J.U.D. Professoris publici & ordinarii, ejusdemque Facultatis Fisci, ... Publicae Disquisitioni Submittit Henricus Frohn ex Friesheim, Archidiaconalis Ecclesiae ad S. Severinum Canonicus & Pastor S. Joannis Baptistae. Die [] Mensis [] 1791. Horis locoque consuetisAutopsie nach Ex. der ULB DüsseldorfVorlageform der Veröffentlichungsangabe: Coloniae Ex Typographia UniversitatisDatumsangabe fehlt im DruckUniversität Köln, Dissertation, 29. Aug. 179
TiN nanobridge Josephson junctions and nanoSQUIDs on SiN-buffered Si
We report the fabrication and properties of titanium nitride (TiN) nanobridge Josephson junctions (nJJs) and nanoscale superconducting quantum interference devices (nanoSQUIDs) on SiN-buffered Si substrates. The superior corrosion resistance, large coherence length, suitable superconducting transition temperature and highly selective reactive ion etching (RIE) of TiN compared to e-beam resists and the SiN buffer layer allow for reproducible preparation and result in long-term stability of the TiN nJJs. High-resolution transmission electron microscopy reveals a columnar structure of the TiN film on an amorphous SiN buffer layer. High-resolution scanning electron microscopy reveals the variable thickness shape of the nJJs. A combination of wet etching in 20% potassium hydroxide and RIE is used for bulk nanomachining of nanoSQUID cantilevers. More than 20 oscillations of the V(B) dependence of the nanoSQUIDs with a period of ∼6 mT and hysteresis-free I(V) characteristics (CVCs) of the all-TiN nJJs are observed at 4.2 K. CVCs of the low-Ic all-TiN nJJs follow theoretical predictions for dirty superconductors down to ∼10 mK, with the critical current saturated below ∼0.6 K. These results pave the way for superconducting electronics based on nJJs operating non-hysteretically at 4.2 K, as well as for all-TiN qubits operating at sub-100 mK temperatures
Supporting data for "Tuning the supercurrent distribution in parallel ballistic graphene Josephson junctions"
<p>Supporting data and analysis scripts for all figures in the article "Tuning the supercurrent distribution in parallel ballistic graphene Josephson junctions".</p>
<p>The files are sorted according to the figures/panels in the publication.</p>
<p>For the data evaluation Matlab (version R2022b) has been used.</p>
Anomalous temperature dependence of multiple Andreev reflections in a topological insulator Josephson junction
As a promising platform for unconventional superconductivity, Josephson junctions (JJs) of tetradymite topological insulators (TIs) and s-wave superconductors have been investigated in recent years. This family of TI materials, however, often suffers from spurious bulk transport, which hampers the observation of the exotic physics of their topological surface states. Thus, disentangling the transport mechanism of bulk and surface contributions in TI JJs is of high importance when investigating proximity induced superconductivity in those crystals. In this work, we add to the insights regarding these contributions by studying the temperature-dependent behaviour of a Bi2Te3-based JJ with transparent interfaces. In electrical transport measurements, we investigate differential conductance spectra of multiple Andreev reflections (MARs) and find a qualitative temperature-dependent change from peak features at low temperatures to dip features at higher ones. The observation of both kind of MAR patterns in a single JJ suggests contributions of diffusive bulk and ballistic surface states and links to a similar finding in the temperature dependence of the critical current. Our work advances the research of induced superconductivity in TIs and offers new avenues to study the induced superconductivity in the topological surface states of these materials