Enhanced Electron-Phonon Interaction in Multivalley Materials

Sohier, Thibault; Ponomarev, Evgeniy; Gibertini, Marco; Berger, H.; Marzari, Nicola; Ubrig, Nicolas; Morpurgo, Alberto F.

doi:10.1103/physrevx.9.031019

Cited by 73 publications

(135 citation statements)

References 85 publications

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“…The observed strain and doping are among the highest observed to date. 9 , 12 , 14 , 15 , 18 , 23 − 25 Several previous studies of the MoS 2 /Au heterostructure report the Raman spectra. Upshifts of both the E′/E 2g 1 and A 1 ′/A 1g modes with the MoS 2 thickness were observed using a low-resolution spectrometer, 3 , 10 consistent with Figure 1 c if heavily averaged spectra are considered.…”

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confidence: 99%

“…The n-doping of 1L MoS 2 in contact with Au, proven by XPS, UPS, and KPFM, corroborates that it is the increased electron concentration which is responsible for the A 1 ′(L) downshift, in line with electrochemically gated MoS 2 experiments. 14 , 15 , 18 Nevertheless, one could envisage alternative explanations. The strong binding in MoS 2 –Au heterostructures with a clean interface could cause softening of the Mo–S bonds, 26 instead of the stiffening seen for the contaminated MoS 2 –Au interface.…”

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confidence: 99%

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Strain and Charge Doping Fingerprints of the Strong Interaction between Monolayer MoS₂ and Gold

Velický

Rodríguez

Bouša

et al. 2020

J. Phys. Chem. Lett.

147

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Gold-mediated exfoliation of MoS 2 has recently attracted considerable interest. The strong interaction between MoS 2 and Au facilitates preferential production of centimeter-sized monolayer MoS 2 with near-unity yield and provides a heterostructure system noteworthy from a fundamental standpoint. However, little is known about the detailed nature of the MoS 2 –Au interaction and its evolution with the MoS 2 thickness. Here, we identify the specific vibrational and binding energy fingerprints of this interaction using Raman and X-ray photoelectron spectroscopy, which indicate substantial strain and charge doping in monolayer MoS 2 . Tip-enhanced Raman spectroscopy reveals heterogeneity of the MoS 2 –Au interaction at the nanoscale, reflecting the spatial nonconformity between the two materials. Micro-Raman spectroscopy shows that this interaction is strongly affected by the roughness and cleanliness of the underlying Au. Our results elucidate the nature of the MoS 2 –Au interaction and guide strain and charge doping engineering of MoS 2 .

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confidence: 99%

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confidence: 99%

Strain and Charge Doping Fingerprints of the Strong Interaction between Monolayer MoS₂ and Gold

Velický

Rodríguez

Bouša

et al. 2020

J. Phys. Chem. Lett.

147

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“…WS 2 would be more difficult and MoS 2 the most difficult. This trend of multivalley population was previously identified to account for Raman softening, which is a signature of strengthened electron-phonon coupling62 . Now it is again verified by the more robust superconductivity in WSe 2 than WS 2 and MoS 2 , albeit the detailed phonons involved in Raman and superconductivity may not be the same.…”

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confidence: 52%

Probing the nature of an emergent insulator in ionic gated monolayer transition metal dichalcogenides

Qin¹,

Ding²,

Li³

et al. 2020

Preprint

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Electronic correlation in a flat band has been a longstanding interest because of emergent phenomena such as Mott insulator and superconductivity. Besides recent Moiré superlattice, transition metal dichalcogenides (TMDs) may directly, e.g. by forming a charge density wave in 1T-TaS2, reconstruct a narrow band that exhibits a correlated insulator. Here we report an emergent insulator in electron doped monolayer WSe2, a prototypical TMDs with direct bandgaps. By detailed mapping a cascade of phases “band insulator-superconductor-emergent insulator-metal”, we can identify, besides the superconducting dome, a narrow miniband split from the conduction band, half filling of which coincides with the insulating state. The correlation picture is supported by a density wave that possesses an isolated flat band. Finally, through evolutionary changes within the same class of materials, multivalley population is suggested to account for enhanced superconductivity and the insulator. Our finding provides new opportunities to explore correlated physics within traditionally non-correlated materials.

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“…Before applying the BCS theory to further discuss the unusual 'high T c ' for Cu 0.09 Bi 2 Se 3 , we have examined if the adiabatic limit satisfies or not in Cu x Bi 2 Se 3 . The BCS solution is only a good description for the systems in the adiabatic limit [68,69], which requires the phonon energy ω must be much smaller than the carrier relaxation rate /τ , namely, ωτ 1. To make such an estimation, taking the highest phonon frequency A 2 1g mode 175.4 cm −1 at 3 K for Bi 2 Se 3 [70] and the scattering time τ = 5.2 × 10 −14 s for Cu 0.25 Bi 2 Se 3 [2], we obtain ωτ = 0.27 as an upper bound.…”

Section: Discussionmentioning

confidence: 99%

Unconventional superconductivity in Cu_xBi₂Se₃ from magnetic susceptibility and electrical transport

Fang

You

2020

New J. Phys.

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Although the Cu doped Bi 2 Se 3 topological insulator was discovered and intensively studied for almost a decade, its electrical and magnetic properties in normal state, and the mechanism of 'high-T c ' superconductivity regarding the relatively low-carrier density are still not addressed yet. In this work, we report a systematic investigation of magnetic susceptibility, critical fields, and electrical transport on the nominal Cu 0.20 Bi 2 Se 3 single crystals with T onset c = 4.18 K, the highest so far. The composition analysis yields the Cu stoichiometry of x = 0.09(1). The magnetic susceptibility shows considerable anisotropy and an obvious kink at around 96 K was observed in the magnetic susceptibility for H c, which indicates a charge density anomaly. The electrical transport measurements indicate the two-dimensional (2D) Fermi liquid behavior at low temperatures with a high Kadowaki-Woods ratio, A/γ 2 = 30.3a 0 . The lower critical field at 0 K limit was extracted to be 6.0 Oe for H ab. In the clean limit, the ratio of energy gap to T c was determined to be Δ 0 /k B T c = 2.029 ± 0.124 exceeding the standard BCS value 1.764, suggesting Cu 0.09 Bi 2 Se 3 is a strong-coupling superconductor. The in-plane penetration depth at 0 K was calculated to be 1541.57 nm, resulting in an unprecedented high ratio of T c /λ −2 (0) ∼ = 9.86. Moreover, the ratio of T c to Fermi temperature is estimated to be T c /T 2D F = 0.034. Both ratios fall into the region of unconventional superconductivity according to Uemura's regime, supporting the unconventional superconducting mechanism in Cu x Bi 2 Se 3 . Finally, the enhanced T c value higher than 4 K is proposed to arise from the increased density of states at Fermi energy and strong electron-phonon interaction induced by the charge density instability. 1 K, such as SrTiO 3 (T c ∼ 0.05-0.29 K, n e = 0.65 to 42.4 × 10 20 cm −3 ) [3,4], GeTe (T c ∼ 0.07-0.3 K, n e = 8.6 to 15.2 × 10 20 cm −3 ) [5], and SnTe (T c ∼ 0.034-0.214 K, n p = 7.5 to 20.0 × 10 20 cm −3 ) [6]. To compare with these systems, the T c value of Cu x Bi 2 Se 3 is relatively 'high' given it is a highly doped narrow semiconductor with lower carrier density. However, the mechanism of such anomalous enhanced T c phenomenon remains unclear despite nearly a decade of extensive research. © 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft New J. Phys. 22 (2020) 053026 Y Fang et alThe emergence and enhancement of superconductivity may occur in various cases by tailoring the ground states of quantum materials. For example, suppression of charge density wave (CDW) by chemical doping or pressure is observed in many systems [7-10], including low dimensional layered Cu x TiSe 2 and three dimensional (3D) alloys Lu(Pt 1−x Pd x ) 2 In and (Sr, Ca) 3 Ir 4 Sn 13 , 3D oxides Ba 1−x K x BiO 3 . Similarly, the magnetic ordering or spin density wave (SDW) have also been suppressed in strongly correlated heavy fermions materials, high-T c cuprates and i...

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Enhanced Electron-Phonon Interaction in Multivalley Materials

Cited by 73 publications

References 85 publications

Strain and Charge Doping Fingerprints of the Strong Interaction between Monolayer MoS₂ and Gold

Strain and Charge Doping Fingerprints of the Strong Interaction between Monolayer MoS₂ and Gold

Probing the nature of an emergent insulator in ionic gated monolayer transition metal dichalcogenides

Unconventional superconductivity in Cu_xBi₂Se₃ from magnetic susceptibility and electrical transport

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Enhanced Electron-Phonon Interaction in Multivalley Materials

Cited by 73 publications

References 85 publications

Strain and Charge Doping Fingerprints of the Strong Interaction between Monolayer MoS2 and Gold

Strain and Charge Doping Fingerprints of the Strong Interaction between Monolayer MoS2 and Gold

Probing the nature of an emergent insulator in ionic gated monolayer transition metal dichalcogenides

Unconventional superconductivity in CuxBi2Se3 from magnetic susceptibility and electrical transport

Contact Info

Product

Resources

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Strain and Charge Doping Fingerprints of the Strong Interaction between Monolayer MoS₂ and Gold

Strain and Charge Doping Fingerprints of the Strong Interaction between Monolayer MoS₂ and Gold

Unconventional superconductivity in Cu_xBi₂Se₃ from magnetic susceptibility and electrical transport