Magneto-Optical Properties Of Graphene In High Magnetic Field Via Terahertz Time Domain Spectroscopy

Terahertz is commonly defined in the region from 0.1 THz to 10 THz in the elec-tromagnetic spectrum.Terahertz time domain spectroscopy(THz-TDS)becomes an increasingly advanced material characterization method,yet it is still difficult to build a high efficient terahertz wave source.In this thesis,chirped pulse amplification(CPA)femtosecond laser,the wavelength is 800nm,is applied to pump lithium niobate crystal to generate terahertz,which can obtain a pulse power as high as 1 micro joule THz pulse.Since few strong terahertz system combined with high magnetic field or low tempera-ture conditions is reported either in China or abroad,we initially build this high magnetic field and low temperature terahertz measurement system,which is able to carry on THz-TDS measurement from 4.2 to 400 Kelvin,and under up to 9 Tesla.Consequently,it allows us to explore various phenomena in such extreme conditions.Graphene is sp2 orbital-hybridization single atom layer belonging to two dimen-sional crystal,whose electronics,optical,mechanical,thermal properties are very unique,and its ratio sphere area is much high.Meanwhile,owning to its excellent electrical transportation property,graphene has a promising potential in terahertz region.For example,terahertz detector based on graphene metamaterial,terahertz emitter based on graphene etc.Especially,as a member of two dimensional gas systems,serious of effects happen in graphene under high magnetic field and low temperature,such as,Quantum hall effects,Shubnikov De Hass ossilation,cyclotron resonance,and so on.However,in traditional electrical test for QHE,an ohmic contact hall bar is necessarily fabricated on graphene surface,which is not that easy task or disable graphene to be reused repeatedly.Hence,it is uniquely beneficial to research magneto-optical proper-ties of graphene via terahertz spectroscopy.There are three chapters in this thesis.First of all,basic physical properties,the fabrication and characterization of graphene are introduced.Meanwhile,the defini-tion,generation and detection of terahertz wave are explained.In the second chapter,it is included the following parts:the structure of CPA laser,the diagram of terahertz generation based on CPA laser and lithrum niabate crystal,the equipment of supercon-ductivity magnet and cryostat,as well as the principles of THz-TDS data analysis;In the third chapter,single layer graphene is grew by chemical vapor deposition(CVD)and its magneto-optical properties are investigated in high magnetic field via THz-TDS.