159 research outputs found
Personal history of my engagement with cuprate superconductivity, 1986-2010
Six months ago I was asked to write a personal history of my engagement with
the high-Tc problem of the cuprate superconductors, in rather informal and
autobiographical style. As the work proceeded I realized that it was impossible
and would have been dishonest to separate out my rather amusing but seminal
early fumblings from the complete restructuring of the problem which I have
achieved during the past decade. But the result became considerably too long,
by over half, for its intended recipient. The assignment had left me with no
obligation to deal with all the fascinating but irrelevant phenomenology which
I had more or less instinctively ignored on my way, but that feature also fails
to endear the article to any conceivable editorial board containing
knowledgeable experts on the subject. Also, their purpose was for it to serve
as a (quote) introduction to the more technical debates, but its message is
that almost all of these are not relevant. They are not, on the whole, focused
on achieving understanding of the crucial experimental anomalies, many, if not
most, of which are now understood. The key to the problem is a new method of
dealing with the constrained Hilbert space which follows from the necessity of
Gutzwiller projection
Evolution of Hall coefficient in two-dimensional heavy fermion CeCoIn
We report on the pressure dependence of the Hall coefficient in
quasi-2D heavy fermion CeCoIn. At ambient pressure, below a temperature
associated with the emergence of non-Fermi liquid properties, is
anomalously enhanced. We found that the restoration of the Fermi liquid state
with applied pressure leads to a gradual suppression of this dramatic
enhancement. Moreover, the enhancement in was found to be confined to an
intermediate temperature window, where inelastic electron-electron scattering
is dominant. Our results strongly support the presence of cold and hot spots on
the Fermi surface probably due to anisotropic scattering by antiferromagnetic
fluctuations, which may also prove relevant for the debate on the anomalous
normal-state properties of high- cuprates.Comment: 9 pages, 5 fiqures, to be published in J. Phys. Soc. Jp
Quasi-linear magnetoresistance in an almost 2D band structure
We present a theoretical study of the orbital magnetoresistance in a unixial
anisotropic metal within the relaxation-time approximation. The appearance of a
new dimensionless scale, delta=4t_perp/epsilon_F, allows the possibility of a
new region at intermediate fields where the magnetoresistance is linear in
applied magnetic field for currents flowing along the unixial direction. (Here,
t_perp characterizes the bandwidth along the unixial direction.) In the limit
of large anisotropy (small delta), corresponding to a quasi-two-dimensional
metal made up of weakly coupled layers, we obtain an analytic expression for
the magnetoresistance valid for all magnetic fields. We test our analytic
results numerically and we compare our expressions with the c-axis
magnetoresistance of Sr_2RuO_4.Comment: 7 pages Latex (revtex4 and epsf) 4 postscript figures included.
Replaced with published version which includes more details and a fit to dat
Breakdown of Fermi-liquid theory in a cuprate superconductor
The behaviour of electrons in solids is remarkably well described by Landau's
Fermi-liquid theory, which says that even though electrons in a metal interact
they can still be treated as well-defined fermions, called ``quasiparticles''.
At low temperature, the ability of quasiparticles to transport heat is strictly
given by their ability to transport charge, via a universal relation known as
the Wiedemann-Franz law, which no material in nature has been known to violate.
High-temperature superconductors have long been thought to fall outside the
realm of Fermi-liquid theory, as suggested by several anomalous properties, but
this has yet to be shown conclusively. Here we report on the first experimental
test of the Wiedemann-Franz law in a cuprate superconductor,
(Pr,Ce)CuO. Our study reveals a clear departure from the universal law
and provides compelling evidence for the breakdown of Fermi-liquid theory in
high-temperature superconductors.Comment: 7 pages, 3 figure
Recommended from our members
Visual responsiveness in sensorimotor cortex is increased following amputation and reduced after mirror therapy
Phantom limb pain (PLP) following amputation, which is experienced by the vast majority of amputees, has been reported to be relieved with daily sessions of mirror therapy. During each session, a mirror is used to view the reflected image of the intact limb moving, providing visual feedback consistent with the movement of the missing/phantom limb. To investigate potential neural correlates of the treatment effect, we measured brain responses in volunteers with unilateral leg amputation using functional magnetic resonance imaging (fMRI) during a four-week course of mirror therapy. Mirror therapy commenced immediately following baseline scans, which were repeated after approximately two and four week intervals. We focused on responses in the region of sensorimotor cortex corresponding to primary somatosensory and motor representations of the missing leg. At baseline, prior to starting therapy, we found a strong and unexpected response in sensorimotor cortex of amputees to visually presented images of limbs. This response was stronger for images of feet compared to hands and there was no such response in matched controls. Further, this response to visually presented limbs was no longer present at the end of the four week mirror therapy treatment, when perceived phantom limb pain was also reduced. A similar pattern of results was also observed in extrastriate and parietal regions typically responsive to viewing hand actions, but not in regions corresponding to secondary somatosensory cortex. Finally, there was a significant correlation between initial visual responsiveness in sensorimotor cortex and reduction in PLP suggesting a potential marker for predicting efficacy of mirror therapy. Thus, enhanced visual responsiveness in sensorimotor cortex is associated with PLP and modulated over the course of mirror therapy
Evolution of the resistivity anisotropy in Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} single crystals for a wide range of hole doping
To elucidate how the temperature dependence of the resistivity anisotropy of
the cuprate superconductors changes with hole doping, both the in-plane and the
out-of-plane resistivities (\rho_{ab} and \rho_{c}) are measured in a series of
high-quality Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} (BSLCO) single crystals for a
wide range of x (x = 0.23 - 1.02), which corresponds to the hole doping per Cu,
p, of 0.03 - 0.18. The anisotropy ratio, \rho_{c}/\rho_{ab}, shows a systematic
increase with decreasing p at moderate temperatures, except for the most
underdoped composition where the localization effect enhances \rho_{ab} and
thus lowers \rho_{c}/\rho_{ab}. The exact p dependence of \rho_{c}/\rho_{ab} at
a fixed temperature is found to be quite peculiar, which is discussed to be due
to the effect of the pseudogap that causes \rho_{c}/\rho_{ab} to be
increasingly more enhanced as p is reduced. The pseudogap also causes a rapid
growth of \rho_{c}/\rho_{ab} with decreasing temperature, and, as a result, the
\rho_{c}/\rho_{ab} value almost reaches 10^6 in underdoped samples just above
T_c. Furthermore, it is found that the temperature dependence of \rho_{c} of
underdoped samples show two distinct temperature regions in the pseudogap
phase, which suggests that the divergence of \rho_{c} below the pseudogap
temperature is governed by two different mechanisms.Comment: 10 pages, 10 figures, revised version. Discussions are expanded with
a new analysis of the T-dependence of \rho_{c} and the resulting new phase
diagra
Genomic catastrophes frequently arise in esophageal adenocarcinoma and drive tumorigenesis
Oesophageal adenocarcinoma (EAC) incidence is rapidly increasing in Western countries. A better understanding of EAC underpins efforts to improve early detection and treatment outcomes. While large EAC exome sequencing efforts to date have found recurrent loss-offunction mutations, oncogenic driving events have been underrepresented. Here we use a combination of whole-genome sequencing (WGS) and single-nucleotide polymorphism-array profiling to show that genomic catastrophes are frequent in EAC, with almost a third (32%, n¼40/123) undergoing chromothriptic events. WGS of 22 EAC cases show that catastrophes may lead to oncogene amplification through chromothripsis-derived double-minute chromosome formation (MYC and MDM2) or breakage-fusion-bridge (KRAS, MDM2 and RFC3). Telomere shortening is more prominent in EACs bearing localized complex rearrangements. Mutational signature analysis also confirms that extreme genomic instability in EAC can be driven by somatic BRCA2 mutations. These findings suggest that genomic catastrophes have a significant role in the malignant transformation of EAC
Comparison of coherent and weakly incoherent transport models for the interlayer magnetoresistance of layered Fermi liquids
The interlayer magnetoresistance of layered metals in a tilted magnetic field
is calculated for two distinct models for the interlayer transport. The first
model involves coherent interlayer transport and makes use of results of
semi-classical or Bloch-Boltzmann transport theory. The second model involves
weakly incoherent interlayer transport where the electron is scattered many
times within a layer before tunneling into the next layer. The results are
relevant to the interpretation of experiments on angular-dependent
magnetoresistance oscillations (AMRO) in quasi-one- and quasi-two-dimensional
metals. We find that the dependence of the magnetoresistance on the direction
of the magnetic field is identical for both models except when the field is
almost parallel to the layers. An important implication of this result is that
a three-dimensional Fermi surface is not necessary for the observation of the
Yamaji and Danner oscillations seen in quasi-two- and quasi-one-dimensional
metals, respectively. A universal expression is given for the dependence of the
resistance at AMRO maxima and minima on the magnetic field and scattering time
(and thus the temperature). We point out three distinctive features of coherent
interlayer transport: (i) a beat frequency in the magnetic oscillations of
quasi-two-dimensional systems, (ii) a peak in the angular-dependent
magnetoresistance when the field is sufficiently large and parallel to the
layers, and (iii) a crossover from a linear to a quadratic field dependence for
the magnetoresistance when the field is parallel to the layers. Properties (i)
and (ii) are compared with published experimental data for a range of
quasi-two-dimensional organic metals and for Sr2RuO4.Comment: 21 pages, RevTeX + epsf, 4 figures. Published version. Subsection
added. References update
Measuring anisotropic scattering in the cuprates
A simple model of anisotropic scattering in a quasi two-dimensional metal is
studied. Its simplicity allows an analytic calculation of transport properties
using the Boltzmann equation and relaxation time approximation. We argue that
the c-axis magnetoresistance provides the key test of this model of transport.
We compare this model with experiments on overdoped Tl-2201 and find reasonable
agreement using only weak scattering anisotropy. We argue that optimally doped
Tl-2201 should show strong angular-dependent magnetoresistance within this
model and would provide a robust way of determining the in-plane scattering
anisotropy in the cuprates.Comment: 12 pages, 8 figures, typset in REVTeX 4. Version 2; added references
and corrected typo
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