The electrical conductivity and Raman spectroscopy measurements have been performed on MoS2 at high pressures up to 90 GPa and variable temperatures down to 5 K. We find that the temperature dependence of the resistance in a metallic 2H a phase has an anomaly (a hump) which shifts with pressure to higher temperature. Concomitantly, a new Raman phonon mode appears in the metallic state suggesting that the electrical resistance anomaly may be related to a structural transformation. We suggest that this anomalous behavior is due to a charge density wave state, the presence of which is indicative for a possibility for an emergence of superconductivity at higher pressures. PACS numbers: 73.90.+f, 71.30.+h, 71.45.Lr Two-dimensional (2D) materials are characterized by a strong anisotropy of the intra-versus inter-layer bonding. This remarkable difference brings up unique notions such as 2D materials which can be exploited for practical applications [1]. One of the most exposed materials of such a kind is graphene [1,2], which also brought the interests to inorganic materials with unique electronic [3], optical [4] attributes and high mobility [5]. However, graphene is a gapless (semimetallic) material which restricts its possible applications. In contrast, the transition-metal dichalcogenides (TMDs), quasi-2D material with distinct structures and unique physical properties [6-10], possess a non-zero band gap that could also be tuned. Therefore, TMDs are currently attracted enormous research interests. MoS 2 is one of the most extensively investigated member of TMDs, and it can be prepared as a 2D material via mechanical exfoliation [4,11]. By varying the number of layers, MoS 2 can be transformed from an indirect band-gap semiconductor to a direct band-gap semiconductor [11]. Monolayer MoS 2 has mechanical properties almost as good as graphene, but unlike graphene, possesses a direct bandgap. Thus, MoS 2 shows an excellent potential to replace graphene in the next generation nanoelectronics applications [12][13][14][15][16]. Furthermore, doping of 2D MoS 2 has been shown to change the electronic and structural properties dramatically that results to metallization, formation of the charge density wave (CDW) [17] and eventually superconducting states [18,19]. Similar structural effects related to 2H to 1T transition (from trigonal to octahedral TM coordination) have been found in other doped TMDs (MoTe 2 ), confirmed by Raman spectroscopy measurements [20] including the case when 1T phase has been stabilized by pressure and superconductivity appears accordingly [21].The application of external pressure is an alternative (to doping) way to tune the electronic as well as crystal structure. MoS 2 transforms from 2H c to 2H a phase (through a sliding of the layers) above 20 GPa along with a metallization [22,23]. However, the resistivity measurements show that the temperature dependence of the resistivity is not monotonous in both semiconducting and metallic regimes revealing a pressure dependent hump in the resistivity−te...
The solid‐state‐based thermoelectric (TE) materials have attracted considerable interest for their potential application in energy conversion. In general, high‐frequency optical phonon modes are always thought to have a negligible contribution to thermal transport due to their short mean free path. Herein, the optical phonons effect in bulk molybdenum diselenide (MoSe2) is studied using advanced low‐wavenumber Raman spectroscopy with a wide temperature range. It is found that the cubic anharmonicity is dominant at low temperatures, and quartic anharmonicity becomes gradually stronger with increasing temperature. The obtained normalE2g1 mode is the most susceptible to the anharmonicity effect and has high phonon density of states (DOS). This is an effect that cannot be explained by previous TE models and, therefore, offers new insight into the nature of phonon transport in 2D materials. The results reveal that the thermal transport can be regulated via high‐frequency phonon scattering.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.