229,593 research outputs found
Berry Phase in Cuprate Superconductors
Geometrical Berry phase is recognized as having profound implications for the
properties of electronic systems. Over the last decade, Berry phase has been
essential to our understanding of new materials, including graphene and
topological insulators. The Berry phase can be accessed via its contribution to
the phase mismatch in quantum oscillation experiments, where electrons
accumulate a phase as they traverse closed cyclotron orbits in momentum space.
The high-temperature cuprate superconductors are a class of materials where the
Berry phase is thus far unknown despite the large body of existing quantum
oscillations data. In this report we present a systematic Berry phase analysis
of Shubnikov - de Haas measurements on the hole-doped cuprates
YBaCuO, YBaCuO, HgBaCuO, and the
electron-doped cuprate NdCeCuO. For the hole-doped materials, a
trivial Berry phase of 0 mod is systematically observed whereas the
electron-doped NdCeCuO exhibits a significant non-zero Berry
phase. These observations set constraints on the nature of the high-field
normal state of the cuprates and points towards contrasting behaviour between
hole-doped and electron-doped materials. We discuss this difference in light of
recent developments related to charge density-wave and broken time-reversal
symmetry states.Comment: new version with added supplementary informatio
Possible Z2 phase and spin-charge separation in electron doped cuprate superconductors
The SU(2) slave-boson mean-field theory for the tt'J model is analyzed. The
role of next-nearest-neighbor hopping t' on the phase-diagram is studied. We
find a pseudogap phase in hole-doped materials (where t'<0). The pseudo-gap
phase is a U(1) spin liquid (the staggered-flux phase) with a U(1) gauge
interaction and no fractionalization. This agrees with experiments on hole
doped samples. The same calculation also indicates that a positive t' favors a
Z2 state with true spin-charge separation. The Z2 state that exists when t' >
0.5J can be a candidate for the pseudo-gap phase of electron-doped cuprates (if
such a phase exists). The experimental situation in electron-doped materials is
also addressed.Comment: 6 pages, 2 figures, RevTeX4. Homepage http://dao.mit.edu/~wen
Strength of Correlations in electron and hole doped cuprates
High temperature superconductivity was achieved by introducing holes in a
parent compound consisting of copper oxide layers separated by spacer layers.
It is possible to dope some of the parent compounds with electrons, and their
physical properties are bearing some similarities but also significant
differences from the hole doped counterparts. Here, we use a recently developed
first principles method, to study the electron doped cuprates and elucidate the
deep physical reasons why their behavior is so different than the hole doped
materials. We find that electron doped compounds are Slater insulators, e.g. a
material where the insulating behavior is the result of the presence of
magnetic long range order. This is in sharp contrast with the hole doped
materials, where the parent compound is a Mott charge transfer insulator,
namely a material which is insulating due to the strong electronic correlations
but not due to the magnetic order.Comment: submitted to Nature Physic
Theory of non-Fermi liquid and pairing in electron-doped cuprates
We apply the spin-fermion model to study the normal state and pairing
instability in electron-doped cuprates near the antiferromagnetic QCP. Peculiar
frequency dependencies of the normal state properties are shown to emerge from
the self-consistent equations on the fermionic and bosonic self-energies, and
are in agreement with experimentally observed ones. We argue that the pairing
instability is in the channel, as in hole-doped cuprates, but
theoretical is much lower than in the hole-doped case. For the same
hopping integrals and the interaction strength as in hole-doped materials, we
obtain K at the end point of the antiferromagnetic phase. We argue
that a strong reduction of in electron-doped cuprates compared to
hole-doped ones is due to critical role of the Fermi surface curvature for
electron-doped materials. The -pairing gap
is strongly non-monotonic along the Fermi surface.
The position of the gap maxima, however, does not coincide with the hot spots,
as the non-monotonic gap persists even at doping when the hot
spots merge on the Brillouin zone diagonals.Comment: 16 page
On the optical conductivity of Electron-Doped Cuprates I: Mott Physics
The doping and temperature dependent conductivity of electron-doped cuprates
is analysed. The variation of kinetic energy with doping is shown to imply that
the materials are approximately as strongly correlated as the hole-doped
materials. The optical spectrum is fit to a quasiparticle scattering model;
while the model fits the optical data well, gross inconsistencies with
photoemission data are found, implying the presence of a large, strongly doping
dependent Landau parameter
Cholesteric aggregation at the quinoidal-to-diradical border enabled stable n-doped conductor
Resumen de la comunicaciĂłnSemiconductor materials constitute the heart of solar cells since they are responsible of the photovoltaic effect. For this reason, the search of new materials to improve the efficiency and stability of these devices is on the focus of the organic electronics. These semiconductors are typically formed by p-doped materials. Despite the relative high abundance of molecules suitable for photovoltaic purposes, that is, able of absorbing light and allowing the transport of the new created charges through them, n-doped organic semiconductors are not plentiful due to their well-known ambient instability.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tec
Double tungstate lasers: From bulk toward on-chip integrated waveguide devices
It has been recognized that the monoclinic double tungstates , , and possess a high potential as rare-earth-ion-doped solid-state laser materials, partly due to the high absorption and emission cross sections of rare-earth ions when doped into these materials. Besides, their high refractive indexes make these materials potentially suitable for applications that require optical gain and high power in integrated optics, with rather high integration density. We review the recent advances in the field of bulk lasers in these materials and present our work toward the demonstration of waveguide lasers and their integration with other optical structures on a chip
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