105 research outputs found
Evolution of the Fermi surface of BaFe_2(As_{1-x}P_x)_2 on entering the superconducting dome
Using the de Haas-van Alphen effect we have measured the evolution of the
Fermi surface of BaFe_2(As_{1-x}P_x)_2 as function of isoelectric substitution
(As/P) for 0.41<x<1 (T_c up to 25 K). We find that the volume of electron and
hole Fermi surfaces shrink linearly with decreasing x. This shrinking is
accompanied by a strong increase in the quasiparticle effective mass as x is
tuned toward the maximum T_c. It is likely that these trends originate from the
many-body interaction which give rise to superconductivity, rather than the
underlying one-electron bandstructure.Comment: 4 page
Superconductivity and Pseudogap in Quasi-Two-Dimensional Metals around the Antiferromagnetic Quantum Critical Point
Spin fluctuations (SF) and SF-mediated superconductivity (SC) in
quasi-two-dimensional metals around the antiferrromagnetic (AF) quantum
critical point (QCP) are investigated by using the self-consistent
renormalization theory for SF and the strong coupling theory for SC. We
introduce a parameter y0 as a measure for the distance from the AFQCP which is
approximately proportional to (x-xc), x being the electron (e) or hole (h)
doping concentration to the half-filled band and xc being the value at the
AFQCP. We present phase diagrams in the T-y0 plane including contour maps of
the AF correlation length and AF and SC transition temperatures TN and Tc,
respectively. The Tc curve is dome-shaped with a maximum at around the AFQCP.
The calculated one-electron spectral density shows a pseudogap in the
high-density-of-states region near (pi,0) below around a certain temperature T*
and gives a contour map at the Fermi energy reminiscent of the Fermi arc. These
results are discussed in comparison with e- and h-doped high-Tc cuprates.Comment: 5 pages, 3 figure
The fermi arc and fermi pocket in cuprates in a short-range diagonal stripe phase
In this paper we studied the fermi arc and the fermi pocket in cuprates in a
short-range diagonal stripe phase with wave vectors , which
reproduce with a high accuracy the positions and sizes of the fermi arc and
fermi pocket and the superstructure in cuprates observed by Meng et
al\cite{Meng}. The low-energy spectral function indicates that the fermi pocket
results from the main band and the shadow band at the fermi energy. Above the
fermi energy the shadow band gradually departs away from the main band, leaving
a fermi arc. Thus we conclude that the fermi arc and fermi pocket can be fully
attributed to the stripe phase but has nothing to do with pairing.
Incorporating a d-wave pairing potential in the stripe phase the spectral
weight in the antinodal region is removed, leaving a clean fermi pocket in the
nodal region.Comment: 5 pages, 6 figure
Advances in single crystal growth and annealing treatment of electron-doped HTSC
High quality electron-doped HTSC single crystals of and have been
successfully grown by the container-free traveling solvent floating zone
technique. The optimally doped and crystals have transition temperatures
of \,K and \,K, respectively, with a transition width of less than
\,K. We found a strong dependence of the optimal growth parameters on the Ce
content . We discuss the optimization of the post-growth annealing treatment
of the samples, the doping extension of the superconducting dome for both
compounds as well as the role of excess oxygen. The absolute oxygen content of
the as-grown crystals is determined from thermogravimetric experiments and is
found to be . This oxygen surplus is nearly completely removed by a
post-growth annealing treatment. The reduction process is reversible as
demonstrated by magnetization measurements. In as-grown samples the excess
oxygen resides on the apical site O(3). This apical oxygen has nearly no doping
effect, but rather influences the evolution of superconductivity by inducing
additional disorder in the CuO layers. The very high crystal quality of
is particularly manifest in magnetic quantum
oscillations observed on several samples at different doping levels. They
provide a unique opportunity of studying the Fermi surface and its dependence
on the carrier concentration in the bulk of the crystals.Comment: 19 pages, 7 figures, submitted to Eur. Phys. J.
Doing Biopolitics Differently? Radical Potential in the Post-2015 MDG and SDG Debates
Post print On institutional repository or subject-based repository after a 18 months embargo, withdraw
13C NMR study of superconductivity near charge instability realized in beta"-(BEDT-TTF)4[(H3O)Ga(C2O4)3]C6H5NO2
To investigate the superconducting (SC) state near a charge instability, we
performed ^{13}C NMR experiments on the molecular superconductor
beta"-(BEDT-TTF)_{4}[(H_{3}O)Ga(C_{2}O_{4})_{3}]C_{6}H_{5}NO_{2}, which
exhibits a charge anomaly at 100 K. The Knight shift which we measured in the
SC state down to 1.5 K demonstrates that Cooper pairs are in spin-singlet
state. Measurements of the nuclear spin-lattice relaxation time reveal strong
electron-electron correlations in the normal state. The resistivity increase
observed below 10 K indicates that the enhanced fluctuation has an electric
origin. We discuss the possibility of charge-fluctuation-induced
superconductivity.Comment: 5 pages, 4 figure
From high temperature supercondutivity to quantum spin liquid: progress in strong correlation physics
This review gives a rather general discussion of high temperature
superconductors as an example of a strongly correlated material. The argument
is made that in view of the many examples of unconventional superconductors
discovered in the past twenty years, we should no longer be surprised that
superconductivity emerges as a highly competitive ground state in systems where
Coulomb repulsion plays a dominant role. The physics of the cuprates is
discussed, emphasizing the unusual pseudogap phase in the underdoped region. It
is argued that the resonating valence bond (RVB) picture, as formulated using
gauge theory with fermionic and bosonic matter fields, gives an adequate
physical understanding, even though many details are beyond the powers of
current calculational tools. The recent discovery of quantum oscillations in a
high magnetic field is discussed in this context. Meanwhile, the problem of the
quantum spin liquid (a spin system with antiferromagnetic coupling which
refuses to order even at zero temperature) is a somewhat simpler version of the
high problem where significant progress has been made recently. It is
understood that the existence of matter fields can lead to de-confinement of
the U(1) gauge theory in 2+1 dimensions, and novel new particles (called
fractionalized particles), such as fermionic spinons which carry spin and no charge, and gapless gauge bosons can emerge to create a new critical
state at low energies. We even have a couple of real materials where such a
scenario may be realized experimentally. The article ends with answers to
questions such as: what limits if pairing is driven by an electronic
energy scale? why is the high problem hard? why is there no consensus?
and why is the high problem important?Comment: Submitted as "Key Issue" essay for Report of Progress in Physics; v2:
References are added and typos correcte
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