scholarly journals Electron-momentum dependence of electron-phonon coupling underlies dramatic phonon renormalization in YNi2B2C

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Philipp Kurzhals ◽  
Geoffroy Kremer ◽  
Thomas Jaouen ◽  
Christopher W. Nicholson ◽  
Rolf Heid ◽  
...  
Keyword(s):  
Fermi Surface ◽  
Inelastic Neutron Scattering ◽  
Density Wave ◽  
Momentum Dependence ◽  
Phonon Coupling ◽  
Electronic Band ◽  
Electron Momentum ◽  
Electron Phonon Coupling ◽  
Wide Range ◽  
Fermi Surface Nesting

AbstractElectron-phonon coupling, i.e., the scattering of lattice vibrations by electrons and vice versa, is ubiquitous in solids and can lead to emergent ground states such as superconductivity and charge-density wave order. A broad spectral phonon line shape is often interpreted as a marker of strong electron-phonon coupling associated with Fermi surface nesting, i.e., parallel sections of the Fermi surface connected by the phonon momentum. Alternatively broad phonons are known to arise from strong atomic lattice anharmonicity. Here, we show that strong phonon broadening can occur in the absence of both Fermi surface nesting and lattice anharmonicity, if electron-phonon coupling is strongly enhanced for specific values of electron-momentum, k. We use inelastic neutron scattering, soft x-ray angle-resolved photoemission spectroscopy measurements and ab-initio lattice dynamical and electronic band structure calculations to demonstrate this scenario in the highly anisotropic tetragonal electron-phonon superconductor YNi2B2C. This new scenario likely applies to a wide range of compounds.

scholarly journals Electronic nature of charge density wave and electron-phonon coupling in kagome superconductor KV3Sb5

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Hailan Luo ◽  
Qiang Gao ◽  
Hongxiong Liu ◽  
Yuhao Gu ◽  
Dingsong Wu ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Fermi Surface ◽  
Charge Density ◽  
Charge Density Wave ◽  
Density Wave ◽  
Phonon Coupling ◽  
Electronic Nature ◽  
Electron Phonon Coupling ◽  
Gap Opening ◽  
Fermi Surface Reconstruction

AbstractThe Kagome superconductors AV3Sb5 (A = K, Rb, Cs) have received enormous attention due to their nontrivial topological electronic structure, anomalous physical properties and superconductivity. Unconventional charge density wave (CDW) has been detected in AV3Sb5. High-precision electronic structure determination is essential to understand its origin. Here we unveil electronic nature of the CDW phase in our high-resolution angle-resolved photoemission measurements on KV3Sb5. We have observed CDW-induced Fermi surface reconstruction and the associated band folding. The CDW-induced band splitting and the associated gap opening have been revealed at the boundary of the pristine and reconstructed Brillouin zones. The Fermi surface- and momentum-dependent CDW gap is measured and the strongly anisotropic CDW gap is observed for all the V-derived Fermi surface. In particular, we have observed signatures of the electron-phonon coupling in KV3Sb5. These results provide key insights in understanding the nature of the CDW state and its interplay with superconductivity in AV3Sb5 superconductors.

Lattice-distortion-enhanced electron-phonon coupling and Fermi surface nesting in1T−TaS2

2006 ◽  
Vol 74 (15) ◽  
Author(s):  
F. Clerc ◽  
C. Battaglia ◽  
M. Bovet ◽  
L. Despont ◽  
C. Monney ◽  
...  
Keyword(s):  
Fermi Surface ◽  
Lattice Distortion ◽  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Fermi Surface Nesting

scholarly journals Electronic Nature of Charge Density Wave and Electron-Phonon Coupling in Kagome Superconductor KV3Sb5

2021 ◽  
Author(s):  
Xingjiang Zhou ◽  
Hai-Lan Luo ◽  
Qiang Gao ◽  
Hongxiong Liu ◽  
Yuhao Gu ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Fermi Surface ◽  
Charge Density ◽  
Charge Density Wave ◽  
Density Wave ◽  
Anomalous Hall Effect ◽  
Phonon Coupling ◽  
Electronic Nature ◽  
Electron Phonon Coupling ◽  
The Impact

Abstract The Kagome superconductors AV3Sb5 (A=K, Rb, Cs) have received enormous attention due to their nontrivial topological electronic structure, anomalous physical properties and superconductivity. Unconventional charge density wave (CDW) has been detected in AV3Sb5 that is found to be intimately intertwined with the anomalous Hall effect and superconductivity. High-precision electronic structure determination is essential to understand the origin of the CDW transition and its interplay with electron correlation, topology and superconductivity, yet, little evidence has been found about the impact of the CDW state on the electronic structure in AV3Sb5. Here we unveil electronic nature of the CDW phase in our high-resolution angle-resolved photoemission (ARPES) measurements on KV3Sb5. We have observed CDW-induced Fermi surface reconstruction and the associated band structure folding. The CDW-induced band splitting and the associated gap opening have been revealed at the boundary of the pristine and reconstructed Brillouin zone. The Fermi surface- and momentum-dependent CDW gap is measured for the first time and the strongly anisotropic CDW gap is observed for all the V-derived Fermi surface sheets. In particular, we have observed signatures of the electron-phonon coupling for all the V-derived bands. These results provide key insights in understanding the nature of the CDW state and its interplay with superconductivity in AV3Sb5 superconductors.

scholarly journals Classification of charge density waves based on their nature

2015 ◽  
Vol 112 (8) ◽  
pp. 2367-2371 ◽  
Author(s):  
Xuetao Zhu ◽  
Yanwei Cao ◽  
Jiandi Zhang ◽  
E. W. Plummer ◽  
Jiandong Guo
Keyword(s):  
Matrix Element ◽  
Charge Density ◽  
Density Wave ◽  
Charge Density Waves ◽  
Dimensional System ◽  
Momentum Dependence ◽  
Density Waves ◽  
Electronic Band ◽  
Electron Phonon Coupling ◽  
A Charge

The concept of a charge density wave (CDW) permeates much of condensed matter physics and chemistry. CDWs have their origin rooted in the instability of a one-dimensional system described by Peierls. The extension of this concept to reduced dimensional systems has led to the concept of Fermi surface nesting (FSN), which dictates the wave vector(q→CDW)of the CDW and the corresponding lattice distortion. The idea is that segments of the Fermi contours are connected byq→CDW, resulting in the effective screening of phonons inducing Kohn anomalies in their dispersion atq→CDW, driving a lattice restructuring at low temperatures. There is growing theoretical and experimental evidence that this picture fails in many real systems and in fact it is the momentum dependence of the electron–phonon coupling (EPC) matrix element that determines the characteristic of the CDW phase. Based on the published results for the prototypical CDW system 2H-NbSe2, we show how well theq→-dependent EPC matrix element, but not the FSN, can describe the origin of the CDW. We further demonstrate a procedure of combing electronic band and phonon measurements to extract the EPC matrix element, allowing the electronic states involved in the EPC to be identified. Thus, we show that a large EPC does not necessarily induce the CDW phase, with Bi2Sr2CaCu2O8+δas the example, and the charge-ordered phenomena observed in various cuprates are not driven by FSN or EPC. To experimentally resolve the microscopic picture of EPC will lead to a fundamental change in the way we think about, write about, and classify charge density waves.

scholarly journals Atomic-scale strain manipulation of a charge density wave

2018 ◽  
Vol 115 (27) ◽  
pp. 6986-6990 ◽  
Author(s):  
Shang Gao ◽  
Felix Flicker ◽  
Raman Sankar ◽  
He Zhao ◽  
Zheng Ren ◽  
...  
Keyword(s):  
Fermi Surface ◽  
Charge Density ◽  
Charge Density Wave ◽  
Density Wave ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Electronic Band ◽  
Simple Method ◽  
Wide Range ◽  
A Charge

A charge density wave (CDW) is one of the fundamental instabilities of the Fermi surface occurring in a wide range of quantum materials. In dimensions higher than one, where Fermi surface nesting can play only a limited role, the selection of the particular wavevector and geometry of an emerging CDW should in principle be susceptible to controllable manipulation. In this work, we implement a simple method for straining materials compatible with low-temperature scanning tunneling microscopy/spectroscopy (STM/S), and use it to strain-engineer CDWs in 2H-NbSe2. Our STM/S measurements, combined with theory, reveal how small strain-induced changes in the electronic band structure and phonon dispersion lead to dramatic changes in the CDW ordering wavevector and geometry. Our work unveils the microscopic mechanism of a CDW formation in this system, and can serve as a general tool compatible with a range of spectroscopic techniques to engineer electronic states in any material where local strain or lattice symmetry breaking plays a role.

scholarly journals Mechanisms of electron-phonon coupling unraveled in momentum and time: The case of soft phonons in TiSe2

2021 ◽  
Vol 7 (20) ◽  
pp. eabf2810
Author(s):  
Martin R. Otto ◽  
Jan-Hendrik Pöhls ◽  
Laurent P. René de Cotret ◽  
Mark J. Stern ◽  
Mark Sutton ◽  
...  
Keyword(s):  
Wave Vector ◽  
Density Wave ◽  
Phonon Coupling ◽  
Many Body ◽  
Soft Zone ◽  
Electron Phonon Coupling ◽  
Underlying Mechanisms ◽  
The Many ◽  
Coupling Phenomena ◽  
Electron Pocket

The complex coupling between charge carriers and phonons is responsible for diverse phenomena in condensed matter. We apply ultrafast electron diffuse scattering to unravel electron-phonon coupling phenomena in 1T-TiSe2 in both momentum and time. We are able to distinguish effects due to the real part of the many-body bare electronic susceptibility, R[χ0(q)], from those due to the electron-phonon coupling vertex, gq, by following the response of semimetallic (normal-phase) 1T-TiSe2 to the selective photo-doping of carriers into the electron pocket at the Fermi level. Quasi-impulsive and wave vector–specific renormalization of soft zone-boundary phonon frequencies (stiffening) is observed, followed by wave vector–independent electron-phonon equilibration. These results unravel the underlying mechanisms driving the phonon softening that is associated with the charge density wave transition at lower temperatures.

scholarly journals Ultrafast electron calorimetry uncovers a new long-lived metastable state in 1T-TaSe2 mediated by mode-selective electron-phonon coupling

2019 ◽  
Vol 5 (3) ◽  
pp. eaav4449 ◽  
Author(s):  
Xun Shi ◽  
Wenjing You ◽  
Yingchao Zhang ◽  
Zhensheng Tao ◽  
Peter M. Oppeneer ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Metastable State ◽  
Density Wave ◽  
Charge Order ◽  
Phonon Coupling ◽  
Phonon Modes ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Quantum Matter ◽  
Electron Phonon Coupling ◽  
Equilibrium Phases

Quantum materials represent one of the most promising frontiers in the quest for faster, lightweight, energy-efficient technologies. However, their inherent complexity and rich phase landscape make them challenging to understand or manipulate. Here, we present a new ultrafast electron calorimetry technique that can systematically uncover new phases of quantum matter. Using time- and angle-resolved photoemission spectroscopy, we measure the dynamic electron temperature, band structure, and heat capacity. This approach allows us to uncover a new long-lived metastable state in the charge density wave material 1T-TaSe2, which is distinct from all the known equilibrium phases: It is characterized by a substantially reduced effective total heat capacity that is only 30% of the normal value, because of selective electron-phonon coupling to a subset of phonon modes. As a result, less energy is required to melt the charge order and transform the state of the material than under thermal equilibrium conditions.

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