458 research outputs found
CeCoIn5 - a quantum critical superfluid
We have made the first complete measurements of the London penetration depth
of CeCoIn5, a quantum-critical metal where superconductivity
arises from a non-Fermi-liquid normal state. Using a novel tunnel diode
oscillator designed to avoid spurious contributions to , we have
established the existence of intrinsic and anomalous power-law behaviour at low
temperature. A systematic analysis raises the possibility that the unusual
observations are due to an extension of quantum criticality into the
superconducting state.Comment: 5 pages, 3 figure
Weak spin-orbit interactions induce exponentially flat mini-bands in magnetic metals without inversion symmetry
In metallic magnets like MnSi the interplay of two very weak spin-orbit
coupling effects can strongly modify the Fermi surface. In the absence of
inversion symmetry even a very small Dzyaloshinsky-Moriya interaction of
strength delta<<1 distorts a ferromagnetic state into a chiral helix with a
long pitch of order 1/delta. We show that additional small spin-orbit coupling
terms of order delta in the band structure lead to the formation of
exponentially flat minibands with a bandwidth of order exp(-1/sqrt(delta))
parallel to the direction of the helix. These flat minibands cover a rather
broad belt of width sqrt(delta) on the Fermi surface where electron motion
parallel to the helix practically stops. We argue that these peculiar
band-structure effects lead to pronounced features in the anomalous skin
effect.Comment: 7 pages, minor corrections, references adde
On the occurrence of Berezinskii-Kosterlitz-Thouless behavior in highly anisotropic cuprate superconductors
The conflicting observations in the highly anisotropic Bi2Sr2CaCu2O8+x,
vidence for BKT behavior emerging from magnetization data and smeared 3D-xy
behavior, stemming form the temperature dependence of the magnetic in-plane
penetration depth are traced back to the rather small ratio, gsic+/gsic-=0.45,
between the c-axis correlation length probed above (+) and below (-) Tc, and
the comparatively large anisotropy. The latter leads to critical amplitudes
gsic0+,-which are substantially smaller than the distance between two CuO2
double layers. In combination with gsic+/gsic-=0.45 and in contrast to the
situation below Tc the c-axis correlation length gsic exceeds the distance
between two CuO2 double layers very close to Tc only. Below this narrow
temperature regime where 3D-xy fluctuations dominate, there is then an extended
temperature regime where the units with two CuO2 double layers are nearly
uncoupled so that 2D thermal fluctuations dominate and BKT features are
observable.Comment: 4 pages, 4 figure
Superfluid Density in a Highly Underdoped YBCO Superconductor
The superfluid density rho_s(T) = 1/lambda^2(T) has been measured at 2.64 GHz
in highly underdoped YBCO, at 37 dopings with T_c between 3 K and 17 K. Within
limits set by the transition width Delta T_c ~ 0.4 K, rho_s(T) shows no
evidence of critical fluctuations as T goes to T_c, with a mean-field-like
transition and no indication of vortex unbinding. Instead, we propose that
rho_s displays the behaviour expected for a quantum phase transition in the (3
+ 1)-dimensional XY universality class, with rho_s0 ~ (p - p_c), T_c ~ (p -
p_c)^1/2 and rho_s(T) ~ (T_c - T)^1 as T goes to T_c.Comment: 4 pages, 5 figures; final version of pape
Coastal rehabilitation manual
Provides an overview of the coastal environment to ensure that the natural environment and coastal processes are considered properly. Describes how to develop a successful coastal rehabilitation strategy and detail rehabilitation techniques applicable to Western Australia. Lists sources of further advice and information.https://researchlibrary.agric.wa.gov.au/bulletins/1210/thumbnail.jp
Bolometric technique for high-resolution broadband microwave spectroscopy of ultra-low-loss samples
A novel low temperature bolometric method has been devised and implemented
for high-precision measurements of the microwave surface resistance of small
single-crystal platelet samples having very low absorption, as a continuous
function of frequency. The key to the success of this non-resonant method is
the in-situ use of a normal metal reference sample that calibrates the absolute
rf field strength. The sample temperature can be controlled independently of
the 1.2 K liquid helium bath, allowing for measurements of the temperature
evolution of the absorption. However, the instrument's sensitivity decreases at
higher temperatures, placing a limit on the useful temperature range. Using
this method, the minimum detectable power at 1.3 K is 1.5 pW, corresponding to
a surface resistance sensitivity of 1 for a typical 1
mm1 mm platelet sample.Comment: 13 pages, 12 figures, submitted to Review of Scientific Instrument
Apparatus for high resolution microwave spectroscopy in strong magnetic fields
We have developed a low temperature, high-resolution microwave surface
impedance probe that is able to operate in high static magnetic fields. Surface
impedance is measured by cavity perturbation of dielectric resonators, with
sufficient sensitivity to resolve the microwave absorption of sub-mm-sized
superconducting samples. The resonators are constructed from high permittivity
single-crystal rutile (TiO2) and have quality factors in excess of 10^6.
Resonators with such high performance have traditionally required the use of
superconducting materials, making them incompatible with large magnetic fields
and subject to problems associated with aging and power-dependent response.
Rutile resonators avoid these problems while retaining comparable sensitivity
to surface impedance. Our cylindrical rutile resonators have a hollow bore and
are excited in TE_01(n-d) modes, providing homogeneous microwave fields at the
center of the resonator where the sample is positioned. Using a sapphire
hot-finger technique, measurements can be made at sample temperatures in the
range 1.1 K to 200 K, while the probe itself remains immersed in a liquid
helium bath at 4.2 K. The novel apparatus described in this article is an
extremely robust and versatile system for microwave spectroscopy, integrating
several important features into a single system. These include: operation at
high magnetic fields; multiple measurement frequencies between 2.64 GHz and
14.0 GHz in a single resonator; excellent frequency stability, with typical
drifts < 1 Hz per hour; the ability to withdraw the sample from the resonator
for background calibration; and a small pot of liquid helium separate from the
external bath that provides a sample base temperature of 1.1 K.Comment: 10 pages, 5 figure
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