scholarly journals The pseudogap in La2–xSrxCuO4: A Raman viewpoint

2000 ◽  
Vol 78 (5-6) ◽  
pp. 483-493 ◽  
Author(s):  
J G Naeini ◽  
J C Irwin ◽  
T Sasagawa ◽  
Y Togawa ◽  
K Kishio
Keyword(s):  
Fermi Surface ◽  
Normal State ◽  
Low Temperatures ◽  
Spectral Weight ◽  
Energy Scale ◽  
Low Energy ◽  
Scattering Rate ◽  
Low Energies ◽  
Consistent Picture ◽  
Rate Suppression

We report the results of Raman scattering experiments on single crystals of La2–xSrxCuO4 (La214) as a function of temperature and doping. In underdoped compounds low-energy B1g spectral weight is depleted in association with the opening of a pseudogap on regions of the Fermi surface located near (±π, 0) and (0, ±π).The magnitude of the depletion increases with decreasing doping, and in the most underdoped samples, with decreasing temperature.The spectral weight that is lost at low energies (ω [Formula: see text] 800 cm–1) is transferred to the higher energy region normally occupied by multimagnon scattering. From the normal-state B2g spectra we have determined the scattering rate Γ(ω,T) of qausiparticles located near the diagonal directions in k-space. In underdoped compounds, Γ(ω,T) is suppressed at low temperatures for energies less than Eg(x) [Formula: see text] 800 cm–1. The doping dependence of both the two-magnon scattering and the scattering rate suppression suggest that the pseudogap is characterized by an energy scale Eg ~ J, where J is the antiferromagnetic super-exchange energy. Comparison with the results from other techniques provides a consistent picture of the pseudogap in La214.PACS Nos.: 74.25.Gz, 74.72.Dn, 78.30.Er

scholarly journals U(1)×SU(2) Gauge Theory of Underdoped Cuprate Superconductors

1998 ◽  
Vol 12 (05) ◽  
pp. 173-180 ◽  
Author(s):  
P. A. Marchetti ◽  
Zhao-Bin Su ◽  
Lu Yu
Keyword(s):  
Gauge Theory ◽  
Fermi Surface ◽  
Transport Properties ◽  
Gauge Field ◽  
Spectral Function ◽  
Normal State ◽  
Doping Concentration ◽  
Cuprate Superconductors ◽  
Low Energy ◽  
Chern Simons

The U(1)×SU(2) Chern–Simons gauge theory is applied to study the 2D t–J model describing the normal state of underdoped cuprate superconductors. The U(1) field produces a flux phase for holons converting them into Dirac-like fermions, while the SU(2) field, due to the coupling to holons gives rise to a gap for spinons. An effective low-energy action involving holons, spinons and a self-generated U(1) gauge field is derived. The Fermi surface and electron spectral function obtained are consistent with photoemission experiments. The theory predicts a minimal gap proportional to doping concentration. It also explains anomalous transport properties.

Spectral-weight transfer: Breakdown of low-energy-scale sum rules in correlated systems

1993 ◽  
Vol 48 (6) ◽  
pp. 3916-3926 ◽  
Author(s):  
M. B. J. Meinders ◽  
H. Eskes ◽  
G. A. Sawatzky
Keyword(s):  
Sum Rules ◽  
Spectral Weight ◽  
Energy Scale ◽  
Low Energy ◽  
Correlated Systems ◽  
Weight Transfer

scholarly journals Electronic Properties of Quasi-One-Dimensional Semiconductor Nanostructures: Plasmons and Exchange-Correlation Effects in Quantum Wires

1993 ◽  
Vol 46 (3) ◽  
pp. 359
Author(s):  
S Das Sarma ◽  
Ben Yu-Kuang Hu
Keyword(s):  
Fermi Surface ◽  
Finite Temperature ◽  
Quantum Wire ◽  
Impurity Scattering ◽  
Low Energy ◽  
One Dimensional ◽  
Exchange Correlation ◽  
Self Energy ◽  
Scattering Rate ◽  
Emission Threshold

We review the many-body exchange-correlation properties of electrons confined to the lowest sub-band of a quantum wire, including effects of impurity scattering. Without impurity scattering, the virtual excitations of arbitrarily low energy one-dimensional plasmons destroy the Fermi surface of the electrons, whereas the presence of impurity scattering damps out the low energy plasmons and restores the Fermi surface. The electron inelastic scattering rate r in the absence of scattering is zero below a critical wavevector kc corresponding to the plasmon emission threshold, above which r diverges as (k - kc )-1/2 for k -t kc. For typical wire widths and electron densities currently available, the calculated bandgap renormalisation is found to be on the order of 10-20 meV. We also calculate the finite-temperature inelastic scattering rates and mean free paths of electrons injected into a quantum wire containing a quasi-one-dimensional electron gas. We show that there is a very sharp increase in the electron scattering rate at the one-dimensional plasmon emission threshold. Based on these results, we suggest the possibility of a one-dimensional hot-electron device which possesses an I - V curve with a sharp onset of a large negative differential resistance. We also present a general method for obtaining expressions for the analytic continuation of finite-temperature self-energies which are suitable for use in numerical computations. In the case of the GW approximation for the self-energy, this method gives the finite-temperature generalisation of the zero-temperature 'line and pole' decomposition. This formalism is used to calculate the finite-temperature self-energy and bandgap renormalisation of electrons in the extreme quantum limit of a quantum wire. A brief review of the experimental and theoretical status of plasmons in quantum wire structures is given.

Electrical Damage Due to Low Energy Plasma Processing of GaAs Structures

1991 ◽  
Vol 223 ◽  
Author(s):  
Hans P. Zappe ◽  
Gudrun Kaufel
Keyword(s):  
Chemical Processes ◽  
Low Energy ◽  
Electrical Behavior ◽  
Rapid Thermal Anneal ◽  
High Temperature Anneal ◽  
Significant Damage ◽  
Low Energies ◽  
Long Time ◽  
Physical Plasma

ABSTRACTThe effect of numerous plasma reative ion etch and physical milling processes on the electrical behavior of GaAs bulk substrates has been investigated by means of electric microwave absorption. It was seen that plasma treatments at quite low energies may significantly affect the electrical quality of the etched semiconductor. Predominantly physical plasma etchants (Ar) were seen to create significant damage at very low energies. Chemical processes (involving Cl or F), while somewhat less pernicious, also gave rise to electrical substrate damage, the effect greater for hydrogenic ambients. Whereas rapid thermal anneal treatments tend to worsen the electrical integrity, some substrates respond positively to long-time high temperature anneal steps.

STABLE hc/e VORTICES IN SUPERCONDUCTORS WITH SPIN-CHARGE SEPARATION

1992 ◽  
Vol 06 (05n06) ◽  
pp. 509-526
Author(s):  
Subir Sachdev
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Normal State ◽  
Phenomenological Model ◽  
Charge Separation ◽  
Cuprate Superconductors ◽  
Superconducting Phase ◽  
Low Energy ◽  
Large N ◽  
Normal State Properties

A phenomenological model, F, of the superconducting phase of systems with spin-charge separation and antiferromagnetically induced pairing is studied. Above Hc1, magnetic flux can always pierce the superconductor in vortices with flux hc/2e, but regimes are found in which vortices with flux hc/e are preferred. Little-Park and other experiments, which examine periodicities with a varying magnetic field, always observe a period of hc/2e. The low energy properties of a symplectic large-N expansion of a model of the cuprate superconductors are argued to be well described by F. This analysis and some normal state properties of the cuprates suggest that hc/e vortices should be stable at the lowest dopings away from the insulating state at which superconductivity first occurs.

scholarly journals Probing charge pumping and relaxation of the chiral anomaly in a Dirac semimetal

2021 ◽  
Vol 7 (16) ◽  
pp. eabg0914
Author(s):  
Bing Cheng ◽  
Timo Schumann ◽  
Susanne Stemmer ◽  
N. P. Armitage
Keyword(s):  
Terahertz Spectroscopy ◽  
Point Group ◽  
Spectral Weight ◽  
Chiral Anomaly ◽  
Group Representations ◽  
Field Independence ◽  
Transport Channel ◽  
Scattering Rate ◽  
Chiral Magnetic Effect ◽  
A Charge

The linear band crossings of 3D Dirac and Weyl semimetals are characterized by a charge chirality, the parallel or antiparallel locking of electron spin to its momentum. These materials are believed to exhibit an E · B chiral magnetic effect that is associated with the near conservation of chiral charge. Here, we use magneto-terahertz spectroscopy to study epitaxial Cd3As2 films and extract their conductivities σ(ω) as a function of E · B. As field is applied, we observe a markedly sharp Drude response that rises out of the broader background. Its appearance is a definitive signature of a new transport channel and consistent with the chiral response, with its spectral weight a measure of the net chiral charge and width a measure of the scattering rate between chiral species. The field independence of the chiral relaxation establishes that it is set by the approximate conservation of the isospin that labels the crystalline point-group representations.

Inelastic collisions at low energies

1969 ◽  
Vol 47 (10) ◽  
pp. 1723-1729 ◽  
Author(s):  
A. Dalgarno
Keyword(s):  
Energy Loss ◽  
Cross Sections ◽  
Low Energy ◽  
Inelastic Collisions ◽  
Low Energies ◽  
Low Energy Electrons ◽  
The Cross ◽  
Loss Rates

A summary is presented of the processes by which low energy electrons lose energy in moving through the atmosphere and estimates are given of the cross sections and energy loss rates. The mechanisms by which thermal electrons cool are described and the cooling efficiencies are listed.

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