37 research outputs found
Electrically tunable multi-terminal SQUID-on-tip
We present a new nanoscale superconducting quantum interference device
(SQUID) whose interference pattern can be shifted electrically in-situ. The
device consists of a nanoscale four-terminal/four-junction SQUID fabricated at
the apex of a sharp pipette using a self-aligned three-step deposition of Pb.
In contrast to conventional two-terminal/two-junction SQUIDs that display
optimal sensitivity when flux biased to about a quarter of the flux quantum,
the additional terminals and junctions allow optimal sensitivity at arbitrary
applied flux, thus eliminating the magnetic field "blind spots". We demonstrate
spin sensitivity of 5 to 8 over a continuous field
range of 0 to 0.5 T, with promising applications for nanoscale scanning
magnetic imaging
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Nano-sized SQUID-on-tip for scanning probe microscopy
We present a SQUID of novel design, which is fabricated on the tip of a pulled quartz tube in a simple 3-step evaporation process without need for any additional processing, patterning, or lithography. The resulting devices have SQUID loops with typical diameters in the range 75–300 nm. They operate in magnetic fields up to 0.6 T and have flux sensitivity of 1.8 μΦ0/Hz1/2 and magnetic field sensitivity of 10−7 T/Hz1/2, which corresponds to a spin sensitivity of 65 μB/Hz1/2 for aluminum SQUIDs. The shape of the tip and the small area of the SQUID loop, together with its high sensitivity, make our device an excellent tool for scanning SQUID microscopy: With the SQUID-on-tip glued to a tine of a quartz tuning fork, we have succeeded in obtaining magnetic images of a patterned niobium film and of vortices in a superconducting film in a magnetic field.Physic
The mathematical analysis for peristaltic flow of nano fluid in a curved channel with compliant walls
Quantized magnetic vortices driven by electric current determine key electromagnetic
properties of superconductors. While the dynamic behavior of slow vortices has been
thoroughly investigated, the physics of ultrafast vortices under strong currents remains
largely unexplored. Here, we use a nanoscale scanning superconducting quantum
interference device to image vortices penetrating into a superconducting Pb film at rates of
tens of GHz and moving with velocities of up to tens of km/s, which are not only much larger
than the speed of sound but also exceed the pair-breaking speed limit of superconducting
condensate. These experiments reveal formation of mesoscopic vortex channels which
undergo cascades of bifurcations as the current and magnetic field increase. Our
numerical simulations predict metamorphosis of fast Abrikosov vortices into mixed
Abrikosov-Josephson vortices at even higher velocities. This work offers an insight into the
fundamental physics of dynamic vortex states of superconductors at high current densities,
crucial for many applications
Formation of Pd2Si on single-crystalline Si (100) at ultrafast heating rates : an in-situ analysis by nanocalorimetry
The kinetics of intermediate phase formation between ultrathin films of Pd (12 nm) and single-crystalline Si (100) is monitored by in-situ nanocalorimetry at ultrafast heating rates. The heat capacity curves show an exothermic peak related to the formation of Pd2Si. A kinetic model which goes beyond the conventional linear-parabolic growth to consider independent nucleation and lateral growth of Pd2Si along the interface and vertical growth mechanisms is developed to fit the calorimetric curves. The model is used to extract the effective interfacial nucleation/growth and diffusion coefficients at the unusually high temperatures of silicide formation achieved at very fast heating rates
Errors in chromosome segregation during oogenesis and early embryogenesis
Errors in chromosome segregation occurring during human oogenesis and early embryogenesis are very common. Meiotic chromosome development during oogenesis is subdivided into three distinct phases. The crucial events, including meiotic chromosome pairing and recombination, take place from around 11 weeks until birth. Oogenesis is then arrested until ovulation, when the first meiotic division takes place, with the second meiotic division not completed until after fertilization. It is generally accepted that most aneuploid fetal conditions, such as trisomy 21 Down syndrome, are due to maternal chromosome segregation errors. The underlying reasons are not yet fully understood. It is also clear that superimposed on the maternal meiotic chromosome segregation errors, there are a large number of mitotic errors taking place post-zygotically during the first few cell divisions in the embryo. In this chapter, we summarise current knowledge of errors in chromosome segregation during oogenesis and early embryogenesis, with special reference to the clinical implications for successful assisted reproduction
Nanoscale thermal imaging of dissipation in quantum systems
Energy dissipation is a fundamental process governing the dynamics of physical, chemical and biological systems. It is also one of the main characteristics that distinguish quantum from classical phenomena. In particular, in condensed matter physics, scattering mechanisms, loss of quantum information or breakdown of topological protection are deeply rooted in the intricate details of how and where the dissipation occurs. Yet the microscopic behaviour of a system is usually not formulated in terms of dissipation because energy dissipation is not a readily measurable quantity on the micrometre scale. Although nanoscale thermometry has gained much recent interest, existing thermal imaging methods are not sensitive enough for the study of quantum systems and are also unsuitable for the low-temperature operation that is required. Here we report a nano-thermometer based on a superconducting quantum interference device with a diameter of less than 50 nanometres that resides at the apex of a sharp pipette: it provides scanning cryogenic thermal sensing that is four orders of magnitude more sensitive than previous devices-below 1 μKH. This non-contact, non-invasive thermometry allows thermal imaging of very low intensity, nanoscale energy dissipation down to the fundamental Landauer limit of 40 femtowatts for continuous readout of a single qubit at one gigahertz at 4.2 kelvin. These advances enable the observation of changes in dissipation due to single-electron charging of individual quantum dots in carbon nanotubes. They also reveal a dissipation mechanism attributable to resonant localized states in graphene encapsulated within hexagonal boron nitride, opening the door to direct thermal imaging of nanoscale dissipation processes in quantum matter