Fermi surface and many-body enhancement in Pd

Fermi surface is at the heart of our understanding of metals and strongly correlated many-body systems. An abrupt change in the Fermi surface topology, also called Lifshitz transition, can lead to the emergence of fascinating phenomena like colossal magnetoresistance and superconductivity. While Lifshitz transitions have been demonstrated for a broad range of materials by equilibrium tuning of macroscopic parameters such as strain, doping, pressure, and temperature, a nonequilibrium dynamical route toward ultrafast modification of the Fermi surface topology has not been experimentally demonstrated. Combining time-resolved multidimensional photoemission spectroscopy with state-of-the-art TDDFT+U simulations, we introduce a scheme for driving an ultrafast Lifshitz transition in the correlated type-II Weyl semimetal Td-MoTe2. We demonstrate that this nonequilibrium topological electronic transition finds its microscopic origin in the dynamical modification of the effective electronic correlations. These results shed light on a previously unexplored ultrafast scheme for controlling the Fermi surface topology in correlated quantum materials.

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What Can Positrons Contribute to High-Tc Superconductivity?

Zeitschrift für Naturforschung A ◽

10.1515/zna-1993-1-267 ◽

1993 ◽

Vol 48 (1-2) ◽

pp. 390-397 ◽

Cited By ~ 7

Author(s):

M. Peter ◽

T. Jarlborg ◽

A. A. Manuel ◽

B. Barbiellini

Keyword(s):

Fermi Surface ◽

Anderson Localization ◽

Charge Density Waves ◽

Actual Situation ◽

Many Body ◽

Fermi Surfaces ◽

High Tc ◽

Superconducting Oxides ◽

Lifetime Studies ◽

Definition Of

Abstract The positron annihilation technique has made well-known contributions to the study of Fermi surfaces in "classical" superconductors, including A15 phases where the definition of the Fermi surface has been questioned on the grounds of Anderson localization. In the case of the superconducting oxides, even more far out models were proposed, which made the clear imaging of the Fermi surface by positrons desirable. The difficulties due to the predicted weakness of the signal, and the large possibility for trapping have now been surmounted and the Fermi surface has been seen; what more can we learn from positrons?After presenting the actual situation with experiment, we will comment on enhancement and correlation and their effect on ACAR and lifetime studies. Then we explain the picture of Jarlborg and Singh of enhancement, with its recent tests for many substances. We conclude by asking the question of sensitivity of positrons to many-body effects. Ferromagnetism, antiferromagnetism, possibly charge density waves have been seen -superconductors, heavy fermions and spinons-holons would pose a problem.Stephan Berko (1924-1991) was interested in these problems and knew that better machines and better detectors would open new possibilities.

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Quantum chaos on a critical Fermi surface

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1618185114 ◽

2017 ◽

Vol 114 (8) ◽

pp. 1844-1849 ◽

Cited By ~ 80

Author(s):

Aavishkar A. Patel ◽

Subir Sachdev

Keyword(s):

Fermi Surface ◽

Quantum Chaos ◽

Random Phase ◽

Gauge Coupling ◽

High Energy ◽

Fermi Velocity ◽

Coupling Constant ◽

Many Body ◽

Spatial Dimensions ◽

The Relationship

We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory ofNspecies of fermions at nonzero density coupled to aU(1)gauge field in two spatial dimensions and determine the Lyapunov rate and the butterfly velocity in an extended random-phase approximation. The thermal diffusivity is found to be universally related to these chaos parameters; i.e., the relationship is independent ofN, the gauge-coupling constant, the Fermi velocity, the Fermi surface curvature, and high-energy details.

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