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- Structure of
C8K, a typical stage 1 intercalation compound. Stage n
means that n layers of graphite are present between each pair of
intercalant layers.[67] a) The layer
structure. The lattice constant along the direction perpendicular to
the planes is called Ic in GIC's. b) Three common in-plane
structures. C8K has the (2 × 2)R0°
structure.
- Evidence for dimensionality crossover in a Nb/Ge
superlattice.[208] Solid lines are fits to the KLB
theory.[131] The direction marked ``||'' means _|_ ^c in the vernacular of GIC's and the direction marked ``_|_''
is || ^c in GIC terms. The Hc2 data marked
_|_ is almost unaffected by the dimensionality crossover. The Hc2 data marked || covers the range from the fully 3D regime
(45 Å/ 7 Å specimen) to the fully 2D regime (45 Å/ 50
Å specimen). The intermediate 65 Å/35 Å specimen shows a crossover from 3D to
2D character as the temperature is lowered.
- Hc2(t) data on Nb/Ta superlattices
showing two low-temperature critical field discontinuities. From
Ref. [30]. The discontinuity in slope at t 0.8-0.9
is the 3D-2D coupling change. The identity of the lower transition at t = 0.49 has
not been definitely determined.
- Hc2(theta) data on Nb/Ta superlattices from
Ref. [29]. The data is for three samples at a
reduced temperature t = 0.9. Lambda is the bilayer period, which
corresponds to Ic in the GIC case. Data in the trace marked 3D are
fit with Eqn.
, while data in the traces marked 2D are fit
with Eqn.
.
- Tc
vs layer thickness in Nb/Cu superlattices. From
Ref. [14]. The decrease of Tc with decreasing
thickness of the superconducting component is predicted by
proximity-effect theories.[49,54] The predictions of
the standard proximity-effect theories is indicated by the solid line. The
proximity effect calculation modified to allow a thickness-dependent Tc for the Nb layers is indicated by the dashed line.
- Hc2(theta) for a high- Tc superconductor. From
Ref. [118]. Each set of symbols corresponds to a different
definition of Hc2. For example, the curve labeled 0.7 R N was
obtained by plotting versus theta the values of H that satisfy
R(H,theta) = 0.7 RN. Each curve is also labeled in parentheses
with the magnitude of the anisotropy parameter 1/epsilon that was used
for the fit to Eqn.
.
- Phase
diagrams of the K-Hg and Cs-Bi binary alloys.[103]
- Range of
compositions of the starting alloy which will produce a given stage GIC in
the K-Hg and Cs-Bi binary systems. From Ref. [145]. Upper, K-Hg
system. In region (1), C8K is produced; in region (2), C4KHg; in region (3), C8KHg; in region (4), C12KHg; in
region (5), higher-stage binary compounds, or no reaction. Lower, Cs-Bi
system. In region (1), C8Cs is produced; in (2), C4CsBi; in
region (3), no reaction.
- (00l)
x-ray scans for pink and gold C4KHg. The large peak near
22° in each scan is from the copper sample holder. The broad hump
from about 6° to 14° is due to the glass tube that the
sample holder is in. a) Ic = (10.22 ± 0.03) Å pink
sample. Tc = 1.53 K. b) Ic = (10.18 ± 0.03) Å gold
sample. Tc = 0.95 K.
- (00l) x-ray scans before and after hydrogenation for a gold
C4KHg sample. The broad hump from about 6° to
14° is due to the glass tube that the sample is in. Before: Tc = 0.84 K gold C4KHg sample. Ic = (10.24 ± 0.03)
Å. After: Same sample as in ``Before'' picture, only after exposure to
200 torr hydrogen gas. Tc = 1.535 K. Ic = (10.24 ± 0.03)
Å.
- (00l) x-ray scans for alpha-phase stage 1 CsBi-GIC's. The broad hump
from about 6° to 14° is due to the glass tube that the
sample holder is in. a) Ic = (10.61 ± 0.03) Å alpha-phase
sample. b) Similar (00l) scan taken by
Bendriss-Rerhrhaye.[17] In b), theta is increasing from
right to left, whereas in a) 2theta is increasing from left to right.
- Raman spectra on gold and pink C4KHg. a) Spectrum of a
Tc = 0.719 K gold sample with a single Ic value = 10.14 Å.
The peak frequency is 1597.1 cm-1 and the HWHM is 13.2 cm-1. b)
Spectrum of a Tc = 1.53 K pink sample with a single Ic value
= 10.22 Å. The peak frequency is 1593.9 cm-1 and the HWHM is 15.5
cm-1.
- X-ray and neutron diffraction (00l) spectra of a gold C4KHg specimen. The beta-phase peaks are marked with downarrow.
a) Only the Ic = 10.24 Å alpha phase is clearly visible using
x-rays. The small bump to the left of the (002) may be the beta-phase
(002) peak. b) With neutrons, both the Ic = 10.24 Å alpha
phase and the Ic = 10.83 Å beta phase show well-defined
peaks.
- Neutron diffraction spectra
of a gold C4KHg specimen with hydrogen and a pink specimen without
hydrogen. Note the lack of beta phase in either sample. a) Spectrum of
a gold sample whose Tc was 0.84 K before hydrogenation and 1.54 K
afterward. b) Spectrum of a pink C4KHg sample.
- Definition of the distances zi used in the fits
to the neutron diffraction data (from Ref. [272]). The distances
are measured from the center of the sandwich, halfway between the mercury
layers. Deltaz, the Hg layer splitting, is twice the distance of the Hg
layers from z = 0.
- Real-space structure of the majority phase of C4KHg along
the c-axis as calculated from the Fourier transform of the extended neutron
diffraction data. All plots were scaled to a carbon peak height of 1.0.
a) Plot of nuclear scattering intensity versus distance along the graphite
c-axis for a pink sample (*) and a gold sample (circ). b) A
similar plot comparing the structure of the MIT pink sample (*) to a
structure (circ) calculated from fit parameters reported by Yang et
al.[272]
- Experimental definition of
Tc.
- a) dc magnetization
versus field for ideal type I and type II superconductors. Hc1 is
the lower critical field, Hc is the thermodynamic critical field,
and Hc2 is the upper critical field. kappa < 1/sqrt2
indicates type I superconductivity; kappa 0.8 indicates
weak type II behavior; kappa 2 indicates strongly type II
behavior. b) ac susceptibility versus field for ideal type II
superconductor with kappa 0.8. Adapted from
Ref. [252].
- A sketch of the sample holder used in the critical field
measurements. The dimension d of the metal piece was chosen to be the
inner diameter of the sample tube so that the holder would be centered and
fixed inside the tube. A careful effort was made to orient the carbon
(graphene) planes parallel to the holder's surface. The GIC's were affixed
to the metal pieces with Apiezon N grease.
- A schematic drawing of the inductance bridge.
The sample capsule was placed inside the primary coil. The windings were
made from 38 gauge magnet wire. There were 20 complete layers of winding
in the secondary coils and 2 complete layers of winding in the primary.
- A schematic of the data acquisition system. For zero-field temperature
sweeps, the thermometer voltage was attached to the x-input of the flatbed
plotter. For fixed-temperature magnetic field sweeps, the dc output of a
stepping motor on the magnet power supply was attached to the x-input of
the plotter.
- Illustration of how a sample which is only
partially superconducting can mimic full superconductivity in an inductive
transition.
- a) Definition of the angle theta, the angle between the applied
magnetic field and the graphite c-axis. This angle is the complement to
that usually used in the thin-film superconductivity literature, but
corresponds to customary usage in the GIC literature. b) A sketch showing
how Hc2 is determined graphically from raw susceptibility versus
magnetic field data. Note the similarity of this trace to
Figure
b).
- a)
Superconducting transitions with the magnetic field applied parallel and
perpendicular to the graphite c-axis for a typical C4KHg sample.
Notice how much broader the transition is in the vecH_|_ ^c
case. b) Similar data from Iye and Tanuma, Ref.[120], Figure 2.
- Critical field Hc2 as a function of
the angle theta for 4 C4KHg GIC's at T 0.4 K. Fits
(dotted lines) were calculated using Equation
. a) Data for
an MIT C4KHg sample with Tc = 0.95 K (circ) and also
for a Tc = 0.73 K sample (bullet) from Ref. [240]. For
Tc = 0.95 K sample, 1/epsilon = 10.0 and Hc2(0°)
= 24 Oe with a residual cal R = 0.29. For data of Ref. [240],
1/epsilon = 11.3, Hc2(0°) = 26 Oe, and cal R = 0.090.
b) Data for two C4KHg samples with Tc 1.5 K.
(circ), Tc = 1.53 K with 1/epsilon = 10.2, Hc2(0°) = 46 Oe, and cal R = 0.73; bullet, Tc = 1.54
K with 1/epsilon = 9.5, Hc2(0°) = 47 Oe, and cal R
= 1.18.
- Why a tilted
sample affects the shape of Hc2(theta). The notation ( vecH cdot ^x)^x signifies the projection of vecH
along ^x. a) The aligned case. Rotations of the sample around
the vertical ^z allow theta to be varied all the way from
( vecH||^c) to ( vecH_|_^c) ( vecH_|_^c = vecH|| ^a). b) The
misaligned case. Hc2,_|_^c can still be measured
correctly, but instead of the true value of Hc2||^c
one will get Hc2,||^c/sqrtcos2ø + epsilon2sin2ø.
- The effect of
sample tilt on Hc2(theta). The three curves in this picture were
calculated using the parameters Hc2,|| ^c = 42 Oe,
anisotropy == 1/epsilon = 15 and the following values for the tilt
angle: (circ) ø = 0°; (bullet) ø =
10°; (diamond) ø = 40°. The ø = 0°
curve corresponds to one of the fits shown in Figure
b).
Note that the curves for ø = 10° and for ø = 0°
are almost indistinguishable.
- The effect of
mosaic spread on Hc2(theta), calculated using
Equation
. The same parameters were used as in
Figure
, except that here the mosaic spread, Delta, is
varied: (circ) Delta = 0°; (bullet) Delta =
3°; (diamond) Delta = 10°.
- Comparison of the effect of the two definitions of
Hc2 on Hc2(theta). circ, tangent definition;
diamond, 90% definition. Data are for a Tc = 1.53 K sample at
T/T c = 0.29. The 90% method tends to produce slightly higher
critical fields, but there is only a small difference between the shapes
of the curves for the two analysis methods. Use of the 90% definition
does not improve agreement with Eqn.
.
- Hc2(theta) for
C8K, from Ref. [141]. The fields are labeled Hc2
in the type II region and Hc3 and Hc in the type I region.
- Hc2(theta)
curves for TaN showing a transition from type I to type II character as a
function of field direction. From Ref. [259]. TaN is the only bulk superconductor besides
C8K (and possibly C4KHg) known to display this variability.
The temperatures at which the curves were taken and the thermodynamic
critical fields are indicated. Note that at 1.65 K, the sample is entirely
type II, but that at 2.4 K it is entirely type I.
- Anisotropic Ginzburg-Landau model fits (dotted curves) to
Hc2(theta) data as a function of temperature. All fits were
produced with the parameters tilt = 0° and mosaic spread =
0°. a) t = 0.29, Hc2,||^c = 47 Oe,
anisotropy (1/epsilon) = 9.5, and residual parameter cal R = 1.18.
b) t = 0.57, Hc2, ||^c = 33 Oe, anisotropy (1/epsilon) = 5.5, and cal R = 1.25. c) t
= 0.78, Hc2,||^c = 23.1 Oe, anisotropy (1/epsilon)
= 4.5, and cal R = 1.43.
- Anisotropic Ginzburg-Landau model fits
(dotted curves) to Hc2(theta) data as a function of temperature,
taking into account the possibility of type I behavior. All fits were
produced with the parameters tilt = 0° and mosaic spread =
0°. a) t = 0.29, Hc2,||^c = 35 Oe,
anisotropy (1/epsilon) = 14, Hc = 65 Oe, and residual parameter
cal R = 0.39. b) t = 0.57, Hc2, ||^c = 19 Oe, anisotropy (1/epsilon) = 15.5, Hc = 43 Oe, and cal R = 0.84. c) t = 0.78, Hc2,||^c = 14.5 Oe, anisotropy (1/ epsilon) = 12.5, Hc = 24.5 Oe, and cal R = 1.11.
- Comparison of field sweeps between type II and possible type
I transitions. The vertical direction is the inductive voltage, while the
horizontal direction is field. All traces taken at about 0.4 K. a)
Transitions with vecH _|_ ^c and vecH || ^c for a Tc = 0.95 K sample. For both
orientations the transitions appear smooth. b) Transitions with vecH _|_ ^c
and vecH || ^c for a Tc = 1.5 K sample. For vecH _|_ ^c, the transition looks smooth, consistent with
its expected type II character. For vecH || ^c, on
the other hand, there is a small discontinuity in the susceptibility near
the upper critical field which is indicated by an arrow. This feature was
seen consistently in Tc = 1.5 K samples.
- Thermodynamic critical fields obtained from Hc2(theta) fits versus temperature for Tc = 1.5 K C4KHg
specimens. The numbers plotted here are the same as in
Table
. (bigtriangleup), data for a Tc = 1.53 K
sample; (circ), data for a Tc = 1.54 K sample; (diamond), a
linear fit to the data with Hc(0) = 85.2 g; (circ), a quadratic fit
to the data with Hc(0) = 66.5 g; (×), Hc(t) calculated
using the specific heat data of Alexander et al.,[8]
which gives Hc(0) = 112 Oe.
- Comparison
of the Tinkham formula and AGL theory fits to Hc2(theta) data on
a Tc = 1.5 K C4KHg-GIC. bullet, data at t = 0.55.
circ, AGL fit with Hc2(0°) = 19 Oe, 1/epsilon = 15.5,
and a residual cal R = 0.84. diamond, TF fit with Hc2(0°) = 23 Oe, 1/epsilon = 13, Hc = 41 Oe, and cal R = 0.47. Below, a plot of the errors of each fit versus theta. The
same symbols are used.
- Critical field Hc2 as a function of reduced
temperature for C4KHg. Dotted curves are least-squares line fits to
the data. Fit parameters are given in Table
. a) Data
for a C4KHg with Tc = 0.95 K: (circ), vecH _|_ ^c. (bullet), vecH || ^c
Data for a Tc = 0.73 K sample from Ref. [240]:
(diamond), vecH _|_ ^c. (×), vecH || ^c. b) Data for two C4KHg-GIC's with Tc 1.5 K. Tc = 1.53 K sample: (circ), vecH _|_ ^c. (bullet), vecH || ^c. Tc = 1.54
K sample: diamond, vecH _|_ ^c. ×, vecH || ^c.
- Critical fields with vecH || ^c for Tc 1.5 K C4KHg samples. Uparrow marks the value of Tc
found using a zero-field temperature sweep. a) (bullet), data for a Tc = 1.53 K sample; (diamond), a linear fit to the data with Hc2(0) = 89.7 Oe, Tc = 1.65 K and cal R = 6.25e-3; (.), a
quadratic fit to the data with Hc2(0) = 64.0 Oe, Tc = 1.55 K
and cal R = 1.2e-2. b) (bullet), data for a Tc = 1.54 K sample;
(diamond), a linear fit to the data with Hc2(0) = 85.8 Oe, Tc = 1.62 K and cal R = 1.62e-3; (.), a quadratic fit to the data
with Hc2(0) = 62.8 Oe, Tc = 1.51 K and cal R = 4.7e-2.
- Comparison of WHH and linear fits to Hc2(T)
data taken on a Tc = 1.54 K sample. a) (bullet), data for vecH _|_ ^c. (.), linear fit with Hc2(0) = 748 Oe, Tc = 1.52 K, and cal R = 6.9e-3. (circ), WHH fit with Hc2(0) = 518 Oe, Tc = 1.53 K, and cal R = 1.6e-2. b)
(bullet), data with vecH || ^c. (.), linear fit
with Hc2(0) = 85.8 Oe, Tc = 1.62 K, and cal R =
1.6e-3. (circ), WHH fit with Hc2(0) = 59.76 Oe, Tc =
1.63 K, and cal R = 1.2e-2.
- Summary of all Hc2 data, both _|_ and ||
to the c-axis. The dimensionless quantities plotted are reduced field
( h*) versus reduced temperature (t). (bullet), 143 data points
taken on 5 different GIC's. (circ), best 2-parameter WHH fit to the
data with cal R = 1.7e-2. (.), best linear fit to the data with cal R = 1.3e-2. Both fits have fracdh*dt = -1 at t = 1.
- Demonstration of the temperature dependence of
the anisotropy parameter epsilon in C4KHg, where 1/epsilon == Hc2(90°)/Hc2(0°). Data are for a Tc =
1.54 K C4KHg sample. (circ), t = 0.29. (bullet), t = 0.55.
(×), t = 0.76. All Hc2(0°) values were determined
from the data, not the fits, so that this plot is model-independent. Fits
to this data are shown in Figure
.
- Temperature-dependent anisotropy in C8KHg is demonstrated
by a plot of Hc2(theta)/Hc2(0°) versus theta, just
as in Figure
. All data from Iye and Tanuma,
Ref. [240] on a Tc = 1.94 K sample. (×), data at t
= 0.23. Fit, (diamond), with 1/epsilon = 17.6 and cal R = 6.8e-3.
(bullet), data at t = 0.81. (circ), fit with 1/epsilon = 21.6 and
cal R = 5.3e-3.
- Positive
curvature of Hc2(T) in C8RbHg. Data are taken from Iye and
Tanuma, Ref. [120]. (circ), Hc2, _|_ ^c.
(bullet), Hc2, || ^c. Parameters for the line
fits: for vecH _|_ ^c, Hc2(0) = 3078 Oe, Tc
= 1.36 K, and cal R = 0.56; for vecH || ^c, Hc2(0) = 89.0 Oe, Tc = 1.37 K, and cal R = 3.02e-2.
Zero-field Tc for this sample was 1.4 K.[120]
- Theoretical demonstration of dimensional
crossover in Josephson-coupled superlattices from the work of Klemm,
Luther and Beasley.[131]. r is the parameter which characterizes
the dimensionality of coupling. alpha, tauSO, and H P
== 4 kB Tc/ pi mu are parameters which characterize the
degree of Pauli-limiting (Pauli-limiting is discussed in
Section
). The inset shows a plot of T*/ Tc
(where T* is the dimensionality crossover temperature) versus r.
- Tc versus normal-layer thickness for S/N bilayers.
Figure taken from Ref. [261] Here D N and D S are the
thicknesses of the normal and superconducting layers, and T cS is
the bulk Tc of the superconducting component. Approximately T/ TcS = (1 - t(DN -> infty))(1 - exp-2DN/xi), where xi is the dirty-limit Pippard coherence length.
- Extended critical field linearity due to
small-scale sample inhomogeneity. From a calculation by Carter and
colleagues.[34] The plots are of reduced field versus reduced
temperature for several different normalized diffusivity distribution
functions Q(y). Q(y) == DaveP(D), where P(D) is the
distribution function for diffusivity, Dave is the average
diffusivity, and y == D/D ave. In the lower plot, a P(D)
skewed to lower diffusivities produces an even greater critical field
enhancement at low temperatures. The index n refers to the power of the
linear factor used to skew the symmetric distribution.
- Illustration of how v_|_ vecH (vecq) changes as
a function of wavevector vecq for an ellipsoidal Fermi surface.
vecq is the coordinate of a point on the Fermi surface. B is Dalrymple's
anisotropy parameter, which is equivalent to epsilon in the AGL
model.[50]
- Enhanced linearity of h*(t) calculated from Butler's equations[33] using an
ellipsoidal FS model. Taken from Ref. [50]. Dalrymple's
parameter B is equivalent to 1/epsilon in the AGL model. The B = 1.0
curve is for a spherical Fermi Surface, and so is equivalent to the WHH
theory.
- Butler-model[33] fit of NbSe2 Hc2(t) data.
Figures taken from Dalrymple's thesis.[50] a) Hc2, _|_ = Hc2, || ^c. An excellent fit is obtained by
using the Wexler-Woolley Fermi Surface model[263] plus an additional ellipsoid.
b) Hc2, || = Hc2, _|_ ^c. The
Wexler-Woolley-plus-ellipsoid model produces the correct shape, but needs
to be multiplied by an additional factor of 2.1 to account for mean-free-path
anisotropy.
- Two-band model fit to anomalous Hc2(t) of Cs0.1WO2.9F0.1 from Ref. [81]. The
plot is of h* versus t. The curve labeled (4) is the
Helfand-Werthamer isotropic theory. The crosses, circles and squares are
experimental data for three different crystallographic orientations (the
orientations are not specified). Curve (1) is the two-band model with no
interband-scattering, whereas (2) and (3) correspond to increasing
interband-scattering. The parameters of these fits are too numerous to
list here, but may be found in Ref. [81].
- Fermi surface computed for C4KHg by Holzwarth and
colleagues.[112] The basic structure of the Fermi surface is
similar to that of NbSe2[51] in that both have pieces of
nearly cylindrical symmetry at the corner of a hexagonal Brillouin zone,
and both have higher masses for transport along kz than in the layer
planes. The hexagonal solid line is the Brillouin zone; the roughly
triangular pieces drawn with a solid line at the corners of the BZ are the
graphitic pi bands. The pieces drawn with a dotted line are due to
mercury bands. The small circular zone-center part is from Hg 6s holes;
the hexagonal portion is from Hg 6ppi electron carriers; and the
trigonal pieces at the zone corner are derived from H 6psigma bands.
- Comparison of Hc2(T) in C8K and C6K, one of
its high-pressure phases. a) Data on a Tc = 134 mK C8K
sample taken by Koike and Tanuma.[141] Note the marked positive
curvature of the critical fields. Hsc|| is a supercooling
field. b) Data on a Tc = 1.5 K sample of C6K from
Ref. [13]. (circ), Hc2, _|_ ^c;
(bigtriangleup), Hc2, || ^c. Note the enhanced
linearity of the critical fields.
- Hydrogen stoichiometry dependence of the
superconducting transition temperature Tc, Debye temperature
thetaD, the Einstein temperature TE, and the linear specific
heat coefficient Gamma in C8KHx and C8RbHx. From
Ref. [78]. The label F(x)/F(0) indicates that each of the
quantities is plotted normalized to 1.0 at x = 0.
- Schematic density-of-states for a) C8K and b) C8KH0.55. From Ref. [171]. Note the very small hole band
near EF in b).
- Tc increase in TaS2 induced by a) hydrogenation and b)
pressure. a) From Ref. [179]. The error bars represent the
transition width, while the circles are the volume % superconducting.
This experiment was performed on a powder sample. At a hydrogen
concentration ofu.87, Tc ;SPMlt; 0.5 K (not shown). b) From
Ref. [90]. TCDW is the CDW onset temperature, while
Tc is the usual superconducting transition temperature. 4H b and 2H are TaS2 polytypes with different crystal structures.
- In-plane resistivity discontinuities in TaSe2 associated with
CDW formation. From Ref. [264]. 1T- and 2H- refer to different
polytypes (crystal structures). The CDW transitions occur at 473 K in
1T-TaSe2 and at 117 K in 2H-TaSe2, respectively. Notice that
1T-TaSe2 has a higher resistivity below its transition, whereas
the resistivity of 2H-TaSe2 decreases at its transition.
- Superconducting transitions before and after hydrogenation in
three types of C4KHg samples. a) A gold sample. Tc
increases from 0.88 K to 1.54 K, and Delta Tc/ Tc decreases
from 7.3× 10-2 to 7.8× 10-2. b) A pink sample. Tc is almost constant; Delta Tc/ Tc decreases from
4.7× 10-2 to 2.2× 10-2. c) A copper-colored sample.
Tc increase from 1.32 K to 1.50 K; Delta Tc/ Tc
decreases from 0.138 to 6.47× 10-2.
- Pressure
dependence of Tc in KHg-GIC's. From Ref. [55]. a)
Pressure-induced transition narrowing in C4KHg. Notice that the
application of a small pressure, 0.8 kbar, increases Tc to 1.5 K,
while application of further pressure decreases Tc at a rate
dTc/dP = -5×10-5 K/bar. b) Monotonic decline of Tc
with pressure in C8KHg. dTc/dP = -6.5×10-5
K/bar.
- Possible
Fermi surface nesting wave vector in C8K. From
Ref. [115]. The horizontal cross-section of the FS in the
Gamma-K-M plane is shown. The arrow indicates the proposed nesting wave
vector near the M point.
- Temperature dependence of the resistivity
and susceptibility in the alkali-metal mercury GIC's. From
Ref. [72]. a) Temperature dependence of the resisitivity.
Curves (1) and (2) are for C4RbHg; (3) is for C4KHg; (4) is
for C8RbHg; and (5) is for C8KHg. b) Temperature dependence
of the susceptibility. Curves (1) and (2) are for C4KHg; (3) is for
C8RbHg; (4) is for C4K0.5Rb0.5Hg; (5) is for C4RbHg, and (6) is for C8KHg.
- An
electron micrograph showing intercalant inclusions (bright regions) in a C4CsBix alpha + beta-phase polycrystal grown here at MIT. The
magnification for this micrograph is indicated by the 100 nm scale bar.
[Micrograph prepared by J. Speck, MIT.]
- A plot of superconducting transition temperature Tc for
C4CsBix versus starting alloy Bi/Cs ratio. bigotimes, MIT
data from Ref. [36]; bigtriangleup, University of Kentucky data
from Ref. [270]; and bigcirc, Freie Universität Berlin data
from Ref. [223]. The X are alloy (not GIC) data from the
CRC Handbook. The presence of downarrow means that the nearest point
represents an upper bound on Tc. Data from the University of Nancy
is not included because precise starting alloy compositions are not given
for their samples.
- The transverse magnetoresistance of a C4CsBi0.6
(stage 1, alpha-phase) sample at 1.2 K with a current of 1 mA. The
current is applied in the graphite planes; the magnetic field is along the
graphite c-axis.
- a) Fourier transform of the data in Figure
. Most
reproducible frequency is (1120 ± 110) T, although other frequencies
sometimes occur. b) Comparison of the data from Figure
with a
simulated trace calculated using Equation
and parameters
obtained from the Fourier transform of the data. The calculated curve is
offset from the data for clarity.
- (3root13 X 8)R(15°,0°) in-plane unit cell
proposed for C4CsBi0.6 by A. Bendriss-Rerhrhaye.[17].
- a) Softening
of the elastic constant C33 as a function of composition in the
C8K(1-x)Rbx system. From Ref. [183]. The elastic
constant was obtained from a fit to the acoustic branch of the phonon
system. The phonons were observed using inelastic neutron scattering.
Similar softening of the M-point optic modes has been seen using Raman
scattering.[219] b) Tc versus x in the C8K(1-x)Rbx system. Only the endpoint compounds have been
characterized.
- Coherence lengths
of a uniaxial superconductor. As pointed out by Morris et
al.,[175] the coherence length of a uniaxial superconductor is
the length of a vector from the center of a biaxial ellipsoid to its edge.
a) The case of an aligned sample, which is described by Eqn.
.
(See Figure
a).) The ellipsoid has two radii of length xia and one of length epsilon xia. b) The case where the sample is tilted by an angle
ø, which is described by Eqn.
. Now the ellipsoid is
triaxial, with one of the coherence lengths of size xia from a)
being replaced by one of size xia sqrtcos2 ø + epsilon2 sin2 ø.
- Cross-section of the flux quantum in a uniaxial
superconductor. In all cases, the magnetic field is directed out of the
paper. a) The aligned case. For vecH || ^c, the
cross-section of the flux quantum along the field direction is circular.
b) The tilted case. Now that the ellipsoid that determines xi(theta)
is triaxial, the cross-section of the flux quantum is non-circular for all
field orientations.
alchaiken@gmail.com (Alison Chaiken)
Wed Oct 11 22:59:57 PDT 1995