Bound polaron in a spherical quantum dot: Strong electron-phonon coupling case

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.

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Direct observation of excitonic instability in Ta2NiSe5

Nature Communications ◽

10.1038/s41467-021-22133-z ◽

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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TRANSITION FREQUENCY OF STRONG-COUPLING IMPURITY BOUND POLARON IN AN ASYMMETRIC QUANTUM DOT

International Journal of Nanoscience ◽

10.1142/s0219581x12500263 ◽

2012 ◽

Vol 11 (03) ◽

pp. 1250026 ◽

Cited By ~ 4

Author(s):

CHENG-SHUN WANG ◽

YU-FANG CHEN ◽

JING-JIN XIAO

Keyword(s):

Excited State ◽

Coupling Strength ◽

State Energy ◽

Transition Frequency ◽

Phonon Coupling ◽

Excited State Energy ◽

Bound Polaron ◽

Asymmetric Quantum Dot ◽

Asymmetric Quantum ◽

Electron Phonon Coupling

Properties of the excited state of strong-coupling impurity bound polaron in an asymmetric quantum dot are studied by using linear combination operator and unitary transformation methods. The first internal excited state energy, the excitation energy and the transition frequency between the first internal excited and the ground states of the impurity bound polaron as functions of the transverse and the longitudinal effective confinement lengths of the dot, the electron–phonon coupling strength and the Coulomb bound potential were derived. Our numerical results show that they will increase with decreasing the effective confinement lengths, due to interesting quantum size confining effects. But they are an increasing functions of the Coulomb bound potential. The first internal excited state energy is a decreasing function of the electron–phonon coupling strength whereas the transition frequency and the excitation energy are an increasing one of the electron–phonon coupling strength.

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