arXiv subjects

M. R. Norman

Publications and source records attributed to M. R. Norman.

At least 127 records · Page 7Linked to original sources

arXiv2003

Hall Effect in Nested Antiferromagnets Near the Quantum Critical Point

We investigate the behavior of the Hall coefficient in the case of antiferromagnetism driven by Fermi surface nesting, and find that the Hall coefficient should abruptly increase with the onset of magnetism, as recently observed in vanadium doped chromium. This effect is due to the sudden removal of flat portions of the Fermi surface upon magnetic ordering. Within this picture, the Hall coefficient should scale as the square of the residual resistivity divided by the impurity concentration, which is consistent with available data.

cond-mat.str-el↗

arXiv2003

The Electronic Nature of High Temperature Cuprate Superconductors

We review the field of high temperature cuprate superconductors, with an emphasis on the nature of their electronic properties. After a general overview of experiment and theory, we concentrate on recent results obtained by angle resolved photoemission, inelastic neutron scattering, and optical conductivity, along with various proposed explanations for these results. We conclude by reviewing efforts which attempt to identify the energy savings involved in the formation of the superconducting ground state.

cond-mat.supr-con↗

arXiv2002

The neutron resonance in the cuprates and its effect on fermionic excitations

We argue that the exciton scenario for the magnetic resonance in the cuprate superconductors yields a small spectral weight of the resonance, in agreement with experiment. We show that the small weight is related to its concentration in a small region of momentum and energy. Despite this, we find that a large fermionic self-energy can indeed be generated by a resonance with such properties, i.e., the scattering from the resonance substantially affects the electronic properties of the cuprates below $T_c$.

cond-mat.supr-con↗

arXiv2002

Crossover from coherent to incoherent electronic excitations in the normal state of Bi2Sr2CaCu2O8

Angle resolved photoemission spectroscopy (ARPES) and resistivity measurements are used to explore the overdoped region of the high temperature superconductor Bi2Sr2CaCu2O8+delta. We find evidence for a new crossover line in the phase diagram between a coherent metal phase for lower temperatures and higher doping, and an incoherent metal phase for higher temperatures and lower doping. The former is characterized by two well-defined spectral peaks in ARPES due to coherent bilayer splitting and superlinear behavior in the resistivity, whereas the latter is characterized by a single broad spectral feature in ARPES and a linear temperature dependence of the resistivity.

cond-mat.supr-con↗

arXiv2002

Photoemission in the High Tc Superconductors

We review angle resolved photoemission spectroscopy (ARPES) results on the high Tc superconductors, focusing primarily on results obtained on the quasi-two dimensional cuprate Bi2Sr2CaCu2O8 and its single layer counterpart Bi2Sr2CuO6. The topics treated include the basics of photoemission and methodologies for analyzing spectra, normal state electronic structure including the Fermi surface, the superconducting energy gap, the normal state pseudogap, and the electron self-energy as determined from photoemission lineshapes.

cond-mat.supr-con↗

arXiv2002

Dispersion Anomalies in Bilayer Cuprates and the Odd Symmetry of the Magnetic Resonance

We present a theoretical model which accounts for recent angle resolved photoemission data in bilayer cuprate superconductors. Lineshapes and dispersions of the various bonding and antibonding features in the spectra are quantitatively reproduced. The observed dispersion anomalies are consistent with the interaction of electrons with a bosonic mode which is odd with respect to the layer indices, a unique property of the magnetic resonance observed by inelastic neutron scattering.

cond-mat.supr-con↗

arXiv2002

Quasiparticle Formation and Optical Sum Rule Violation in Cuprate Superconductors

Using a simple model for the frequency dependent scattering rate, we evaluate the in-plane optical integral for cuprate superconductors in the normal and superconducting states. In the overdoped region, this integral is conserved. In the optimal and underdoped region, though, the optical integrals differ, implying a lowering of the in-plane kinetic energy in the superconducting state. This sum rule violation, due to the difference of the non Fermi liquid normal state and the superconducting Fermi liquid state, has a magnitude comparable to recent experimental results.

cond-mat.supr-con↗

arXiv2001

Momentum Distribution Curves in the Superconducting State

We demonstrate that the E vs. k dispersion in the superconducting state extracted from momentum distribution curves differs qualitatively from the traditional dispersion extracted from energy distribution curves. This occurs because of a combination of many-body effects and the presence of an energy gap, along with the associated coherence factors. Analysis of such MDC dispersions can give important information on the microscopics of high temperature superconductors.

cond-mat.supr-con↗

arXiv2001

Influence of vortices on the magnetic resonance in cuprate superconductors

We investigate several theoretical possibilities for the suppression in a c-axis magnetic field of the magnetic resonance recently observed in inelastic neutron scattering experiments on YBCO_{6.6}. We find that neither the Doppler shift of the quasiparticle states caused by supercurrents outside the vortex core, nor an assumed spatially uniform suppression of the coherence factors or spectral gap due to the applied field, can account for the observed effect. In contrast, suppressing the gap or the coherence factors in the vortex core to zero is consistent with the data. We demonstrate that an even simpler description of the data can be achieved by assuming that the resonance is not supported within an effective radius xi_{eff} around each vortex, where xi_{eff} is the sum of the superconducting and spin-spin correlation lengths. We use this simple idea to predict the doping dependence of the field suppression.

cond-mat.supr-con↗

arXiv2001

On the determination of the Fermi surface in high-Tc superconductors by angle-resolved photoemission spectroscopy

We study the normal state electronic excitations probed by angle resolved photoemission spectroscopy (ARPES) in Bi2201 and Bi2212. Our main goal is to establish explicit criteria for determining the Fermi surface from ARPES data on strongly interacting systems where sharply defined quasiparticles do not exist and the dispersion is very weak in parts of the Brillouin zone. Additional complications arise from strong matrix element variations within the zone. We present detailed results as a function of incident photon energy, and show simple experimental tests to distinguish between an intensity drop due to matrix element effects and spectral weight loss due to a Fermi crossing. We reiterate the use of polarization selection rules in disentangling the effect of umklapps due to the BiO superlattice in Bi2212. We conclude that, despite all the complications, the Fermi surface can be determined unambiguously: it is a single large hole barrel centered about (pi,pi) in both materials.

cond-mat.supr-con↗

arXiv2001

Magnetic Resonance, Electronic spectra and Bilayer Splitting in Underdoped Bi2212

We report the first inelastic neutron scattering (INS) experiments of the resonance in the underdoped regime of Bi2Sr2CaCu2O8+d. The energy of the resonance is found to be 34 meV and the temperature dependence shows a smooth evolution through Tc with a remnant persisting in the pseudogap state. Besides the INS data, we present also angle resolved photoemission (ARPES) spectra taken on the same crystals. As a function of temperature, the neutron intensity scales with the square of the ARPES gap estimated by the leading-edge midpoint at (pi,0). We also show that the energy of the collective mode inferred from the peak-dip-hump structure compares well with the energy of the resonance. Based on kinematics, we argue that the correlation of these two energies is consistent with the absence of bilayer splitting in the electronic dispersion.

cond-mat.supr-con↗

arXiv2000

The Temperature Evolution of the Spectral Peak in High Temperature Superconductors

Recent photoemission data in the high temperature cuprate superconductor Bi2212 have been interpreted in terms of a sharp spectral peak with a temperature independent lifetime, whose weight strongly decreases upon heating. By a detailed analysis of the data, we are able to extract the temperature dependence of the electron self-energy, and demonstrate that this intepretation is misleading. Rather, the spectral peak loses its integrity above Tc due to a large reduction in the electron lifetime.

cond-mat.supr-con↗

arXiv2000

Magnetic Collective Mode Dispersion in High Temperature Superconductors

Recent neutron scattering experiments in the superconducting state of YBCO have been interpreted in terms of a magnetic collective mode whose dispersion relative to the commensurate wavevector has a curvature opposite in sign to a conventional magnon dispersion. The purpose of this article is to demonstrate that simple linear response calculations are in support of a collective mode interpretation, and to explain why the dispersion has the curvature it does.

cond-mat.supr-con↗

arXiv2000

Where is the pi particle?

We discuss the interplay of particle-particle and particle-hole spin-triplet channels in high-T_c superconductors using a quasiparticle dispersion motivated by angle-resolved photoemission. Within a generalized RPA, we find a well defined antibound state of two holes, the pi resonance of Demler and Zhang, as well as a bound state of a particle and a hole, the spin exciton. We show that the energy of the pi resonance always exceeds 2 Delta, twice the maximum d-wave gap, therefore the neutron resonance observed in the cuprates around energy Delta is most likely a spin exciton. At the same time, we speculate that the pi particle can exist at higher energies and might be observed in neutron scattering around 100 meV.

cond-mat.supr-con↗

arXiv2000

Renormalization of spectral lineshape and dispersion below Tc in Bi2Sr2CaCu2O8+d

Angle-resolved photoemission (ARPES) data in the superconducting state of Bi2Sr2CaCu2O8+d show a kink in the dispersion along the zone diagonal, which is related via a Kramers-Kronig analysis to a drop in the low-energy scattering rate. As one moves towards (pi,0), this kink evolves into a spectral dip. The occurrence of these anomalies in the dispersion and lineshape throughout the zone indicate the presence of a new energy scale in the superconducting state.

cond-mat.supr-con↗

arXiv2000

The neutron resonance: modeling photoemission and tunneling data in the superconducting state of Bi_2Sr_2CaCu_2O_{8+d}

Motivated by neutron scattering data, we develop a model of electrons interacting with a magnetic resonance and use it to analyze angle resolved photoemission (ARPES) and tunneling data in the superconducting state of Bi_2Sr_2CaCu_2O_{8+d}. We not only can explain the peak-dip-hump structure observed near the (pi,0) point, and its particle-hole asymmetry as seen in SIN tunneling spectra, but also its evolution throughout the Brillouin zone, including a velocity `kink' near the d-wave node.

cond-mat.supr-con↗

arXiv2000

Photoemission and the Origin of High Temperature Superconductivity

The condensation energy can be shown to be a moment of the change in the occupied part of the spectral function when going from the normal to the superconducting state. As a consequence, there is a one to one correspondence between the energy gain associated with forming the superconducting ground state, and the dramatic changes seen in angle resolved photoemission spectra. Some implications this observation has are offered.

cond-mat.supr-con↗

arXiv1999

The Relation of Neutron Incommensurability to Electronic Structure in High Temperature Superconductors

The relation between the incommensurability observed in neutron scattering experiments in bilayer cuprate superconductors and the electronic structure is investigated. It is found that the observed incommesurability pattern, as well as its dependence on energy, can be well reproduced by electronic dispersions motivated by angle resolved photoemission data. The commensurate resonance and its contribution to the superconducting condensation energy are discussed in the context of these calculations.

cond-mat.supr-con↗