60 research outputs found
Observation of a superconducting glass state in granular superconducting diamond
The magnetic field dependence of the superconductivity in nanocrystalline
boron doped diamond thin films is reported. Evidence of a glass state in the
phase diagram is presented, as demonstrated by electrical resistance and
magnetic relaxation measurements. The position of the phase boundary in the H-T
plane is determined from resistance data by detailed fitting to
zero-dimensional fluctuation conductivity theory. This allows determination of
the boundary between resistive and non-resistive behavior to be made with
greater precision than the standard ad hoc onset/midpoint/offset criterion
Fluctuation spectroscopy as a probe of granular superconducting diamond films
We present resistance versus temperature data for a series of boron-doped
nanocrystalline diamond films whose grain size is varied by changing the film
thickness. Upon extracting the fluctuation conductivity near to the critical
temperature we observe three distinct scaling regions -- 3D intragrain,
quasi-0D, and 3D intergrain -- in confirmation of the prediction of Lerner,
Varlamov and Vinokur. The location of the dimensional crossovers between these
scaling regions allows us to determine the tunnelling energy and the Thouless
energy for each film. This is a demonstration of the use of \emph{fluctuation
spectroscopy} to determine the properties of a superconducting granular system
Design and development of a low temperature, inductance based high frequency ac susceptometer
We report on the development of an induction based low temperature high
frequency ac susceptometer capable of measuring at frequencies up to 3.5 MHz
and at temperatures between 2 K and 300 K. Careful balancing of the detection
coils and calibration have allowed a sample magnetic moment resolution of
at 1 MHz. We will discuss the design and
characterization of the susceptometer, and explain the calibration process. We
also include some example measurements on the spin ice material CdErS
and iron oxide based nanoparticles to illustrate functionality
A continuous dry 300 mK cooler for THz sensing applications
We describe and demonstrate the automated operation of a novel cryostat design that is capable of maintaining an unloaded base temperature of less than 300 mK continuously, without the need to recycle the gases within the final cold head, as is the case for conventional single shot sorption pumped 3He cooling systems. This closed dry system uses only 5 l of 3He gas, making this an economical alternative to traditional systems where a long hold time is required. During testing, a temperature of 365 mK was maintained with a constant 20 μW load, simulating the cooling requirement of a far infrared camera
Fluctuation spectroscopy in granular superconductors with application to boron-doped nanocrystalline diamond
We perform a detailed calculation of the various contributions to the fluctuation conductivity of a granular metal close to its superconducting transition. We find three distinct regions of power law behavior in reduced temperature,
η
=
(
T
−
T
c
)
/
T
c
, with crossovers at
Γ
/
T
c
and
E
Th
/
T
c
, where
Γ
is the electron tunneling rate, and
E
Th
is the Thouless energy of a grain. The calculation includes both intergrain and intragrain degrees of freedom. This complete theory of the fluctuation region in granular superconductors is then compared to experimental results from boron-doped nanocrystalline diamond, using the assumption of a constant phase breaking rate
Ï„
−
1
Ï•
. We find a semiquantitative agreement between the theoretical and experimental results only in the case of large phase breaking. We argue that there may be a phase breaking mechanism in granular metals worthy of further experimental and theoretical investigation
Experimental measurement of the isolated magnetic susceptibility
The isolated susceptibility may be defined as a
(non-thermodynamic) average over the canonical ensemble, but while it has often
been discussed in the literature, it has not been clearly measured. Here, we
demonstrate an unambiguous measurement of at avoided
nuclear-electronic level crossings in a dilute spin ice system, containing
well-separated holmium ions. We show that quantifies the
superposition of quasi-classical spin states at these points, and is a direct
measure of state concurrence and populations.Comment: 9 pages, & figure
Quantitative analysis of the interaction between a dc SQUID and an integrated micromechanical doubly clamped cantilever
We provide simulations to quantitatively describe the interaction between a dc superconducting quantum interference device (SQUID) and an integrated doubly clamped cantilever. The simulations have been performed using the SQUID equations described by the resistively and capacitively shunted junction model coupled to the equation of motion of a damped harmonic oscillator. We have chosen to investigate an existing experimental configuration and have explored the motion of the cantilever configuration and the reaction of the SQUID as a function of the voltage flux V(Φ)
V(Φ)
characteristics. We clearly observe the Lorentz force back-action interaction and demonstrate how a sharp transition state drives the system into a nonlinear-like regime and modulates the cantilever displacement amplitude, simply by tuning the SQUID parameters
Observation of a superconducting glass state in granular superconducting diamond
The magnetic field dependence of the superconductivity in nanocrystalline boron doped diamond thin films is reported. Evidence of a superconducting glass state is presented, as demonstrated by the observation of a quasi de Almeida-Thouless line in the phase diagram and a logarithmic time dependence of the magnetism. The position of the phase boundary in the H-T plane is determined from electrical transport data by detailed fitting to quasi-zero-dimensional fluctuation conductivity theory. This allows determination of the boundary between resistive and non-resistive behaviour to be made with greater precision than the standard ad hoc onset/midpoint/offset criterion. We attribute the glassy superconductivity to the morphological granularity of the diamond films
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