A5058613150- Physics of Superconductivity and Magnetism
- Quantum and electron transport phenomena
- Magnetic properties of thin films
- Magnetic and transport properties of perovskites and related materials
- Cold Atom Physics and Bose-Einstein Condensates
- Electronic and Structural Properties of Oxides
- Advanced Condensed Matter Physics
- Atomic and Subatomic Physics Research
- Iron-based superconductors research
- Semiconductor Quantum Structures and Devices
- Superconducting and THz Device Technology
- Mechanical and Optical Resonators
- Magneto-Optical Properties and Applications
- Terahertz technology and applications
- stochastic dynamics and bifurcation
- Superconductivity in MgB2 and Alloys
- Nonlinear Dynamics and Pattern Formation
- Advanced Electrical Measurement Techniques
- Surface and Thin Film Phenomena
- Theoretical and Computational Physics
- Acoustic Wave Resonator Technologies
- Magnetic Field Sensors Techniques
- Quantum Information and Cryptography
- Advanced Memory and Neural Computing
- Advanced NMR Techniques and Applications
University of Tübingen
2015-2024
TH Bingen University of Applied Sciences
2023-2024
Quantum Science Center
2016-2020
National Institute of Advanced Industrial Science and Technology
2015
National Institute for Materials Science
2015
Nanjing University
2015
Center for Integrated Quantum Science and Technology
2013
Universität Ulm
2013
Biotherapy of Genetic Diseases, Inflammatory Disorders and Cancers
2009
Iowa State University
2006
The advent of high-${T}_{c}$ superconductors gave great impetus to the development thin-film superconducting quantum interference devices (SQUIDs) for operation at temperatures up boiling point liquid nitrogen, 77 K. spectral density white flux noise can be calculated analytically rf SQUIDs and by computer simulation dc SQUIDs; however, observed densities are typically an order magnitude higher. Low-frequency $1/f$ from thermally activated vortex motion is a much bigger issue in K than...
Superconducting quantum interference devices (SQUIDs) are sensitive detectors of magnetic flux. A SQUID consists a superconducting loop interrupted by either one or two Josephson junctions for the RF dc SQUID, respectively. Low transition temperature (T/sub c/) SQUIDs fabricated from thin films niobium. Immersed in liquid helium at 4.2 K, their flux noise is typically 10/sup -6//spl Phi//sub 0/ Hz/sup -1/2/, where /spl 0//spl equiv/h/2e quantum. High-T/sub c/ YBa/sub 2/Cu/sub 3/O/sub 7-x/,...
We report on THz emission measurements and low temperature scanning laser imaging of Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks. Coherent is observed at large dc input power, where a hot spot standing wave, formed in the "cold" part stack, coexist. By varying size cavity resonance frequency emitted radiation can be tuned. The linewidth much smaller than expected from quality factor mode excited. Thus, an additional mechanism synchronization seems to play role, possibly arising...
Recently, it has been shown that large stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2O8 emit synchronous THz radiation, the synchronization presumably triggered by a cavity resonance. To investigate this effect we use low temperature scanning laser microscopy to image electric field distributions. We verify appearance modes at bias and high input-power regime find standing-wave patterns are created through interactions with hot spot, possibly pointing new mode generating synchronized...
We fabricated high quality $\mathrm{Nb}/{\mathrm{Al}}_{2}{\mathrm{O}}_{3}/{\mathrm{Ni}}_{0.6}{\mathrm{Cu}}_{0.4}/\mathrm{Nb}$ superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions. Using a ferromagnetic layer with steplike thickness, we obtain $0\mathrm{\text{\ensuremath{-}}}\ensuremath{\pi}$ junction, equal lengths and critical currents of 0 $\ensuremath{\pi}$ parts. The ground state our $330\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$...
Several recent experiments revealed a change of the sign first harmonic in current-phase relation Josephson junctions (JJs) based on, e.g., $d$-wave superconductors or JJs with ferromagnetic barrier. In this situation, role second can become dominant; case, it determines scenario $0\text{\ensuremath{-}}\ensuremath{\pi}$ transition. We discuss different mechanisms generation and its sign. If is positive changes as function any control parameter, temperature, ground state phase abruptly...
We demonstrate experimentally the existence of Josephson junctions having a doubly degenerate ground state with an average phase $\ensuremath{\psi}=\ifmmode\pm\else\textpm\fi{}\ensuremath{\varphi}$. The value $\ensuremath{\varphi}$ can be chosen by design in interval $0<\ensuremath{\varphi}<\ensuremath{\pi}$. used our experiments are fabricated as 0-$\ensuremath{\pi}$ moderate normalized length asymmetric 0 and $\ensuremath{\pi}$ regions. show that (a) these have two critical currents,...
The focused ion beam (FIB) is a powerful tool for fabrication, modification, and characterization of materials down to the nanoscale. Starting with gallium FIB, which was originally intended photomask repair in semiconductor industry, there are now many different types FIB that commercially available. These instruments use range species applied broadly science, physics, chemistry, biology, medicine, even archaeology. goal this roadmap provide an overview instrumentation, theory, techniques,...
We report the levitation of a superconducting lead-tin sphere with $100\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{m}$ diameter (corresponding to mass $5.6\text{ }\mathrm{\ensuremath{\mu}}\mathrm{g}$) in static magnetic trap formed by two coils an anti-Helmholtz configuration, adjustable resonance frequencies up 240 Hz. The center-of-mass motion is monitored magnetically using dc quantum interference device as well optically and exhibits quality factors...
The controllable fabrication of reliable HTS Josephson junctions with sufficiently small spread their characteristic parameters has not yet been achieved and prevents the successful use in complex integrated circuits. problems junction certainly are related to specific properties cuprate superconductors, which make high quality interfaces employing artificial barrier layers extremely difficult. Therefore, several types so-called intrinsic originating from grain boundaries or layer structure...
We fabricated high quality $\Nb/\Al_2\O_3/\Ni_{0.6}\Cu_{0.4}/\Nb$ superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions. Depending on the thickness of ferromagnetic $\Ni_{0.6}\Cu_{0.4}$ layer and ambient temperature, junctions were in 0 or $\pi$ ground state. All have homogeneous interfaces showing almost perfect Fraunhofer patterns. The $\Al_2\O_3$ barrier allows to achieve rather low damping, which is desired for many experiments especially quantum domain. McCumber...
By extending scanning electron microscopy to the temperature regime of liquid helium and nitrogen a powerful technique for imaging local properties superconducting thin films Josephson junctions is obtained. Low (LTSEM) allows one both investigate interesting physical phenomena in film samples with spatial resolution about 1 mu m perform functional test devices circuits at their operation temperature. We discuss technical background LTSEM including optical cryogenic requirements, interaction...
At high enough input power in stacks of Bi_2Sr_2CaCu_2O8 intrinsic Josephson junctions a hot spot (a region heated to above the superconducting transition temperature) coexists with regions still state. In ``cold'' cavity resonances can occur, synchronizing ac currents and giving rise strong coherent THz emission. We investigate interplay spots standing electromagnetic waves by low temperature scanning laser microscopy emission measurements, using various geometries. For rectangular...
We have combined a stand-alone Bi2Sr2CaCu2O8 intrinsic Josephson junction stack, emitting terahertz radiation, with YBa2Cu3O7 grain boundary acting as detector. The detector is mounted on lens, positioned 1.2 cm away from the emitter similar lens. With radiating at 0.5 THz, we observed up to 7 Shapiro steps current-voltage characteristic of ac current induced in this was 0.9 mA, and dissipated power 1.8 μW. setup, although far being optimized, may be considered first step towards an...
We report on measurements of the linewidth $\ensuremath{\Delta}f$ terahertz radiation emitted from intrinsic Josephson junction stacks, using a Nb/AlN/NbN integrated receiver for detection. Previous resolution-limited indicated that may be below 1 GHz---much smaller than expected purely cavity-induced synchronization. While at low bias we found to not $\ensuremath{\sim}$500 MHz, high bias, where hot spot coexists with regions which are still superconducting, turned out as narrow 23 MHz....
We consider an asymmetric 0-pi Josephson junction consisting of 0 and pi regions different lengths L_0 L_pi. As predicted earlier this system can be described by effective sine-Gordon equation for the spatially averaged phase psi so that current-phase relation includes a \emph{negative} second harmonic ~sin(2 psi). If its amplitude is large enough, ground state doubly degenerate psi=\pmvarphi, where varphi depends on amplitudes first harmonics. study behavior such in applied magnetic field H...
The φ Josephson junction has a doubly degenerate ground state with the phases ±φ. We demonstrate use of such as memory cell (classical bit), where writing is done by applying magnetic field and reading bias current. In “store” state, does not require any or field, but just needs to stay cooled for permanent storage logical bit. Straightforward integration rapid single flux quantum logic possible.
The current-phase relation (CPR) of a Josephson junction (JJ) determines how the supercurrent evolves with superconducting phase difference across junction. Knowledge CPR is essential in order to understand response JJ various external parameters. Despite rising interest ultra-clean encapsulated graphene JJs, such junctions remains unknown. Here, we use fully gate-tunable quantum intereference device (SQUID) determine ballistic JJs. Each two JJs SQUID made hexagonal boron nitride. By...
We demonstrate coupling of magnetically trapped ultracold $^87$Rb ground state atoms to a coherently driven superconducting coplanar resonator on an integrated atom chip. measure the microwave field strength in cavity through observation AC shift hyperfine transition frequency when is off-resonance from atomic transition. The measured shifts are used reconstruct resonator, close agreement with transmission measurements cavity, giving proof between and resonator. When driving resonance atoms,...
To fabricate high-${T}_{c}$ Josephson junctions, YBa${}_{2}$Cu${}_{3}$O${}_{7}$ (YBCO) bicrystal grain-boundary junction technology is used most frequently, as it simple and yields junctions of reasonable quality. This technique only allows placement along a single line on chip, though. The authors instead use focused helium-ion beam (He-FIB) to ``draw'' anywhere the chip. High FIB doses can also produce highly resistive walls that be circuit boundaries, avoiding extra lithography. A SQUID...
We examined the temporal evolution of Josephson and resistive barriers created by a 30-keV focused helium ion beam in microbridges epitaxially grown single-crystal ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ thin films. Repeated electric transport measurements at 4.2 K within 300 days after irradiation revealed an increase critical current density ${j}_{\mathrm{c}}$ for devices stored room temperature under nitrogen atmosphere. This behavior can be...
We have fabricated magnetometers patterned in a single layer of YBa2Cu3O7−x involving dc superconducting quantum interference devices (SQUIDs) with bicrystalline grain boundary junctions. The consist either SQUID large area square washer or turn pickup loop coupled directly to the body small SQUID. found that transfer function falls off increasing inductance much more rapidly than predicted; implications for magnetometer performance are discussed. When operated at 77 K bias reversal...
We propose a type of Josephson vortex ratchet. In this system moves in periodic asymmetric potential under the action deterministic or random force with zero time average. For some implementations amplitude can be controlled during experiment, thus allowing us to tune performance and build rocking as well flashing ratchets. discuss differences between conventional ratchets present model describing dynamics fluxon such system. show numerical simulation results that predict rectification...