Studies On Low Temperature Transport Properties Of Semimetal MoTe₂ Thin Film

Transition Metal Dichalcogenides?TMDs?,often collectively called as MX₂,are a group of compounds composed of group VIA and group VIB atoms.These materials have two stable crystal structures atroom temperature,being sem iconductor and semimetal,respectively.The MX₂ have layered structure,and the van der Waals'force between layers make these compounds easy to be cleaved into thin sheets of a few atom layers.In ultra-thin sam ples the band structures and transport properties will be different form bulk samples.Among the TMDs,the band structure of semimetal MoTe₂ shows an indirect band overlap,and is expected to be a typ e-II Weyl semimetal.Novel properties,such as superconductivity,Giant magnetoresistance,etc.,has been observed on the sem imetal MoTe₂.In this thesis we measured the transport properties of MoT e₂ down to cryogenic temperatures.On bulk sam ples,as earlier reported in the literature,we observed the1T'-phase to Td-phase transition hysteresis at near 250K,however,for sample that cleaved to about 70nm,the hysteresis charact erizing the phase transition disappears.In much thinner sam ples,we observed a res istance increase that follows a ln?T?relation at cryogenic temperat ures,and in m agneto transport we also observed the anti-weak localization behavior typical to systems with strong spin-orbital interaction.We also observed a cu rrent heating effect at low tem perature,with an elevated electron temperature roughly proportional to the squre root of the heating current.Moreover,the superconductivity of semimetal MoTe₂ were studied in our smaples.In bulk sam ple,we observed superconductivity with much higher onset temperature than form er reports.In com parison with earlier reports and our bulk sample,the onset tem perature and that of zero resistivity are both lower in a 70nm thick sample,indicating a suppression onthe superconductivity by the sam ple cleavage.And in sam ples that cleaved to few nanometers,the superconductivity no longer exists.In summary,we m easured and analyzed the transport pro perties of s emimetal MoTe₂ at low tem peratures.Through the wo rk,useful understandings on sem imetal MoTe₂ have been gained that is importantfor further investigations on sim ilar materials of the TMDs.