Mechanisms of high-Tc superconductivity in low-dimensional materials

1987 ◽  
Vol 2 (6) ◽  
pp. 793-799 ◽  
Author(s):  
Vladimir Z. Kresin
Keyword(s):  
Proximity Effect ◽  
Coherence Length ◽  
Two Dimensional ◽  
Phonon Coupling ◽  
Strong Electron ◽  
High Tc ◽  
Electron Phonon Coupling ◽  
Low Dimensionality ◽  
Low Dimensional ◽  
Low Dimensional Materials

High-Tc superconductivity is due to the action of two mechanisms: (1) plasmon mechanism, i.e., exchange of two-dimensional (2-D) plasmons and (2) strong electron-phonon coupling. The low dimensionality and the small value of the carrier concentration make the plasmon mechanism favorable. The small value of the coherence length leads to a unique opportunity to observe a multigap structure. The proximity effect can be used in order to increase Tc of A-15 compounds.

scholarly journals Observation of the polaronic character of excitons in a two-dimensional semiconducting magnet CrI3

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Wencan Jin ◽  
Hyun Ho Kim ◽  
Zhipeng Ye ◽  
Gaihua Ye ◽  
Laura Rojas ◽  
...  
Keyword(s):  
Magnetic Semiconductors ◽  
Longitudinal Optical ◽  
Longitudinal Optical Phonon ◽  
Two Dimensional ◽  
Phonon Coupling ◽  
Temperature Dependent ◽  
Strong Electron ◽  
Range Magnetic Order ◽  
Electron Phonon Coupling ◽  
Long Range Magnetic Order

Abstract Exciton dynamics can be strongly affected by lattice vibrations through electron-phonon coupling. This is rarely explored in two-dimensional magnetic semiconductors. Focusing on bilayer CrI3, we first show the presence of strong electron-phonon coupling through temperature-dependent photoluminescence and absorption spectroscopy. We then report the observation of periodic broad modes up to the 8th order in Raman spectra, attributed to the polaronic character of excitons. We establish that this polaronic character is dominated by the coupling between the charge-transfer exciton at 1.96 eV and a longitudinal optical phonon at 120.6 cm−1. We further show that the emergence of long-range magnetic order enhances the electron-phonon coupling strength by ~50% and that the transition from layered antiferromagnetic to ferromagnetic order tunes the spectral intensity of the periodic broad modes, suggesting a strong coupling among the lattice, charge and spin in two-dimensional CrI3. Our study opens opportunities for tailoring light-matter interactions in two-dimensional magnetic semiconductors.

VAN HOVE SINGULARITIES AND HIGH-Tc SUPERCONDUCTIVITY: A REVIEW

1991 ◽  
Vol 05 (12) ◽  
pp. 2037-2071 ◽  
Author(s):  
R. S. MARKIEWICZ
Keyword(s):  
Electronic System ◽  
Structural Instability ◽  
Hole Doping ◽  
Phonon Coupling ◽  
Van Hove Singularity ◽  
Strong Electron ◽  
High Tc ◽  
Electron Phonon Coupling ◽  
Half Filling ◽  
Fluctuation Effects

This review describes a Fermi liquid picture of high-T c superconductivity. A density-of-states (dos) peak associated with the CuO 2-plane van Hove singularity causes a peak in T c as a function of hole doping. Strong correlation effects drive a Mott transition at half filling. For intermediate doping, the electronic system is unstable against phase separation, with one phase near the insulating state, the other near the T c peak. The large dos leads to competition between superconductivity and structural instability, in analogy with the A15 compounds. The superconductivity appears to be driven by strong electron-phonon coupling, enhanced by fluctuation effects.

Thermopower of low-dimensional structures: The effect of electron–phonon coupling

2017 ◽  
Author(s):  
M. Tsaousidou
Keyword(s):  
Quantum Wires ◽  
Single Wall Carbon Nanotubes ◽  
Two Dimensional ◽  
Phonon Drag ◽  
Phonon Coupling ◽  
Electron Gases ◽  
Theoretical Approaches ◽  
Electron Phonon Coupling ◽  
Low Dimensional

This article examines the effect of electron-phonon coupling on the thermopower of low-dimensional structures. It begins with a review of the theoretical approaches and the basic concepts regarding phonon drag under different transport regimes in two- and one-dimensional systems. It then considers the thermopower of two-dimensional semiconductor structures, focusing on phonon drag in semi-classical two-dimensional electron gases confined in semiconductor nanostructures. It also analyzes the influence of phonon drag on the thermopower of semiconductor quantum wires and describes the phonon-drag thermopower of doped single-wall carbon nanotubes. The article compares theory and experiment in order to demonstrate the role of phonon-drag and electron-phonon coupling in the thermopower in two and one dimensions.

THEORETICAL AND EXPERIMENTAL EVIDENCES FOR A STRONG ELECTRON-PHONON COUPLING IN HIGH-Tc OXIDES

1993 ◽  
Vol 07 (01n03) ◽  
pp. 103-108
Author(s):  
ROLAND ZEYHER
Keyword(s):  
Experimental Data ◽  
Heat Conductivity ◽  
Present Status ◽  
Compelling Evidence ◽  
Coupling Constant ◽  
Phonon Coupling ◽  
Ionic Model ◽  
Strong Electron ◽  
High Tc ◽  
Electron Phonon Coupling

The present status of superconductivity-induced lattice properties and electron-phonon effects in electronic properties is discussed. It is argued that most of the experimental data can be understood if the dimensionless electron-phonon coupling constant λ is between 1 and 3 and the corresponding transport constant around λtr 1. An analysis of the temperature dependence of the heat conductivity based on the screened ionic model reveals that both the observed maximum below Tc as well as the change in slope at Tc are compatible with a strong electron-phonon coupling in contrast to previous conclusions. It is also pointed out that the presently available resistivity data in stochiometric high-Tc oxides can be understood as phonon-limited resistivities and yield no compelling evidence for exotic scattering mechanisms.

scholarly journals Structural phase transition and superconductivity hierarchy in 1T-TaS2 under pressure up to 100 GPa

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Qing Dong ◽  
Quanjun Li ◽  
Shujia Li ◽  
Xuhan Shi ◽  
Shifeng Niu ◽  
...  
Keyword(s):  
Structural Phase ◽  
Transition Metal Dichalcogenides ◽  
Phonon Coupling ◽  
Structural Phase Transitions ◽  
Strong Electron ◽  
Electron Phonon Coupling ◽  
Increasing Trend ◽  
Metal Dichalcogenides ◽  
Dome Shape ◽  
Enhanced Superconductivity

AbstractThe adoption of high pressure not only reinforces the comprehension of the structure and exotic electronic states of transition metal dichalcogenides (TMDs) but also promotes the discovery of intriguing phenomena. Here, 1T-TaS2 was investigated up to 100 GPa, and re-enhanced superconductivity was found with structural phase transitions. The discovered I4/mmm TaS2 presents strong electron–phonon coupling, revealing a good superconductivity of the nonlayered structure. The P–T phase diagram shows a dome shape centered at ~20 GPa, which is attributed to the distortion of the 1T structure. Accompanied by the transition to nonlayered structure above 44.5 GPa, the superconducting critical temperature shows an increasing trend and reaches ~7 K at the highest studied pressure, presenting superior superconductivity compared to the original layered structure. It is unexpected that the pressure-induced re-enhanced superconductivity was observed in TMDs, and the transition from a superconductor with complicated electron-pairing mechanism to a phonon-mediated superconductor would expand the field of pressure-modified superconductivity.

scholarly journals Direct observation of excitonic instability in Ta2NiSe5

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kwangrae Kim ◽  
Hoon Kim ◽  
Jonghwan Kim ◽  
Changil Kwon ◽  
Jun Sung Kim ◽  
...  
Keyword(s):  
Phase Transition ◽  
Direct Observation ◽  
Structural Phase ◽  
Temperature Phase ◽  
Phonon Coupling ◽  
Strong Electron ◽  
Weiss Temperature ◽  
Excitonic Insulator ◽  
Electron Phonon Coupling ◽  
Low Temperature Phase

AbstractCoulomb attraction between electrons and holes in a narrow-gap semiconductor or a semimetal is predicted to lead to an elusive phase of matter dubbed excitonic insulator. However, direct observation of such electronic instability remains extremely rare. Here, we report the observation of incipient divergence in the static excitonic susceptibility of the candidate material Ta2NiSe5 using Raman spectroscopy. Critical fluctuations of the excitonic order parameter give rise to quasi-elastic scattering of B2g symmetry, whose intensity grows inversely with temperature toward the Weiss temperature of TW ≈ 237 K, which is arrested by a structural phase transition driven by an acoustic phonon of the same symmetry at TC = 325 K. Concurrently, a B2g optical phonon becomes heavily damped to the extent that its trace is almost invisible around TC, which manifests a strong electron-phonon coupling that has obscured the identification of the low-temperature phase as an excitonic insulator for more than a decade. Our results unambiguously reveal the electronic origin of the phase transition.

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