5 research outputs found
Metastable states and hidden phase slips in nanobridge SQUIDs
We fabricated an asymmetric nanoscale SQUID consisting of one nanobridge weak
link and one Dayem bridge weak link. The current phase relation of these
particular weak links is characterized by multivaluedness and linearity. While
the latter is responsible for a particular magnetic field dependence of the
critical current (so-called vorticity diamonds), the former enables the
possibility of different vorticity states (phase winding numbers) existing at
one magnetic field value. In experiments the observed critical current value is
stochastic in nature, does not necessarily coincide with the current associated
with the lowest energy state and critically depends on the measurement
conditions. In this work, we unravel the origin of the observed metastability
as a result of the phase dynamics happening during the freezing process and
while sweeping the current. Moreover, we employ special measurement protocols
to prepare the desired vorticity state and identify the (hidden) phase slip
dynamics ruling the detected state of these nanodevices. In order to gain
insights into the dynamics of the condensate and, more specifically the hidden
phase slips, we performed time-dependent Ginzburg-Landau simulations.Comment: 10 pages, 4 figures, 1 supplementary vide
Identifying Native Point Defects in the Topological Insulator Bi2Te3
We successfully identified native point defects that occur in Bi2Te3 crystals by combining high-resolution bias-dependent scanning tunneling microscopy and density functional theory based calculations. As-grown Bi2Te3 crystals contain vacancies, antisites, and interstitial defects that may result in bulk conductivity and therefore may change the insulating bulk character. Here, we demonstrate the interplay between the growth conditions and the density of different types of native near-surface defects. In particular, scanning tunneling spectroscopy reveals the dependence on not only the local atomic environment but also on the growth kinetics and the resulting sample doping from n-type toward intrinsic crystals with the Fermi level positioned inside the energy gap. Our results establish a bias-dependent STM signature of the Bi2Te3 native defects and shed light on the link between the native defects and the electronic properties of Bi2Te3, which is relevant for the synthesis of topological insulator materials and the related functional properties.status: publishe
Catastrophic magnetic flux avalanches in NbTiN superconducting resonators
Abstract Macroscopic superconducting components are an important building block of various quantum circuits. Since several of the envisioned applications require exposure to magnetic fields, it is of utmost importance to explore the impact of magnetic fields on their performance. Here we explore the complex pattern of magnetic field penetration and identify its impact on the resonance frequency of NbTiN superconducting resonators by combining magneto-optical imaging and high-frequency measurements. At temperatures below approximately half of the superconducting critical temperature, the development of magnetic flux avalanches manifests itself as a noisy response in the field-dependent resonance frequency. Magneto-optical imaging reveals different regimes and distinguishes the impact of avalanches in the ground plane and resonator. Our findings demonstrate that superconducting resonators represent a valuable tool to investigate magnetic flux dynamics. Moreover, the current blooming of niobium-based superconducting radio-frequency devices makes this report timely by unveiling the severe implications of magnetic flux dynamics