Study Of EuCd₂As₂/NbFeTe₂/NbC By Scanning Tunneling Microscopy/Spectroscopy

Scanning tunneling microscopy/spectroscopy（STM/S）is an indispensable experimental method in modern condensed matter physics research.It can acquire not only the real-space atomically-resolved topography but also the local density of states（LDOS）.We are building an ultrahigh-energy resolution STM/S working in extreme conditions combined with angle-resolved photoemission spectroscopy（ARPES）,oxide molecular beam epitaxy（OMBE）,and pulsed laser deposition（PLD）in ultrahigh vacuum（UHV）.This instrument will help us realize the growth and in-situ measurement of artificially fabricated materials.This dissertation briefly introduces the working principle of STM at first,and then demonstrates our design details of STM/S,and illustrates our study of the antiferromagnetic materials and superconductor using STM/S:1.We endeavor to develop an ultra-high-resolution real-space/momentum-space in-situ spectroscopy measuring system.We aim to build an STM/S,of which energy resolution can reach a dozen micro electron volts.For this target,we put forward a series of sophisticated designs and comprehensive plans,and some details are listed as follows:To isolate vibration,we build an isolated concrete base and set up an active vibration cancellation.To eliminate radio frequency noise,we build an electromagnetic interference shielding room with acoustic isolation.To cancel line noise,we use an isolated power supply for all measurement instruments.To achieve extreme conditions,we use an 18 T magnet and a dilution refrigerator.To prepare and modify the tip and sample,we design a set of multifunctional UHV chambers.To realize the sample transfer among STM,ARPES,PLD,OMBE,we design a UHV connecting chamber system which is about 6 meters.2.The influence of magnetism on the topological properties of materials is a key branch of condensed matter physics.Whilst EuCd₂As₂ is an A-type antiferromagnetic material,which is suggested to be with fertile topological properties by many theories.We studied A-type antiferromagnetic EuCd₂As₂ and NbFeTe₂ by STM/S:（1）We acquired the topography image of the cleaving surface with atomic resolution.（2）We observed the magnetostriction with the metamagnetic transition.Appling external magnetic filed,EuCd₂As₂ contracts along the c axis without obvious hysteresis behavior.However,NbFeTe₂ extends along the b axis in the external field and has hysteresis behavior.（3）Below Néel temperature,the DOS variations of EuCd₂As₂ with the magnetic field are probably related to the metamagnetic transition.3.A brief report on several superconductor material studies,which were studied together with my groupmates.Mainly discuss the physics properties of NbC in external magnetic fields:（1）The magnetic vortex of NbC with magnetic fields perpendicular to the sample surface;（2）The evolution of magnetic vortex of NbC and surface superconductivity critical field Hc₃ with the angleθbetween the field direction and the sample surface.