| With the development of micro-nano fabrication technologies,the processing accuracy of integrated circuit can reach the level of 7 nanometer.Along with the reduction of device size more and more problems are brought to our attention,one of which is that as the device size decreases to mesoscopic scale,the classical theory cannot be applied.In order to solve these problems,mesoscopic physics needs to be developed.In recent decades,mesoscopic physics has developed rapidly.Various functional micro-nano devices such as quantum dots,quantum wires,superconducting josephson junctions and other devices have been fabricated in different laboratories all over the world.With the development of cryogenic dilution refrigeration technology,more and more quantum phenomena which cannot be observed at room temperature have been observed at low temperatures.For example,fractional quantum hall states,quantum point contacts and so on are observed in the two-dimensional electron gas system at ultra-low temperatures.At present,the research of quantum computers,such as those based on Josephson junctions and semiconductor quantum dots,is closely related to mesoscopic physics.Traditionally,electrical noise is considered as an interference source to low level measurements.However,since Schottky discovered shot noise while studying vacuum tubes in 1918,people have gained a close view of shot noise in mesoscopic physics.Shot noise is the current fluctuation caused by the discreteness of electrons.In mesoscopic system,shot noise is sensitive to the interaction between charge carriers.Shot noise measurement can provide the information of quantum fluctuations,which cannot be measured with traditional transport measurement.In recent years,with the rise of quantum computing and quantum information research,researchers urgently need to discover and study new quantum materials.By the means of numerical calculation,the behavior of shot noise in Dirac semi-metal,Weyl semi-metal,Topological insulator and the bound state of Majorana in topological quantum computation have been theoretically analyzed and predicted by researchers.In addition,in the current field of quantum computing research,quantum noise has a tremendous impact on the operation of quantum systems.Noise measurement of mesoscopic physical systems has become an important research direction and a tool in condensed matter physics.This thesis takes the basic theory of mesoscopic physics as a starting point and introduces the different basic characteristic sizes of mesoscopic physics.With these basic concepts,we know how to distinguish between diffusion transport and ballistic transport.Landauer-Buttiker conductance formula,which is an important formula in shot noise and mesoscopic physics.By introducing the concept of noise power spectral density,the principle of noise correlation measurement and the origin of different types of noise,our understanding of noise will be changed.Electrical noise is sensitive to the interaction of charge carriers and can reflect the fundamental laws of physics in microsystem.In the second chapter,we introduce the basic theory of the shot noise of tunneling junctions,quantum point contact,quantum dots,diffusive metal conductors,superconductor-normal metal interface,fractional quantum hall effect and so on.The application of shot noise measurement is widely used in condensed matter physics.Shot noise is closely related to the transmission of the interface and the mechanisms of interaction in mesoscopic physical systems.As the formula of shot noise is 2eFI,we can design a device with well-known Fano factor F,then we can measure the shot noise of this device to calculate the quasi-particle effective charge e.Taking fractional quantum hall system as an example,quantum point contact is designed in this system to measure its quasi-particle effective charge e.In the third chapter,the concept of noise figure is first introduced,which can explain why the cryogenic preamplifier should be used as the first stage amplification in the field of weak noise signal measurement system.Furthermore,the related technical details of the development of our homemade low-noise cryogenic preamplifiers are introduced,including the selection of transistors used in the amplifiers,the method of how to select static operating point of transistor,the electrical circuit structure of amplifier,the manufacture of low-noise power supply and so on.During the process of practice,it was found that the commercial high electron mobility transistor was relatively high in 1/f noise compared with the HEMT provided by Jin Yong's group in France's National Science Center.Yong's HEMTs are optimized for low frequency noise.All these devices can be used for noise measurement with frequency domain from 100kHz to 20MHz.Finally,we developed a series of ultra-low noise cryogenic preamplifiers with integrated design.All the electronic components of the amplifier are packaged in a shielding box,which makes the installation of the cryogenic amplifier on the 4K stage of dry dilution refrigerator more convenient.The power consumption of these homemade cryogenic amplifiers are 700?W to 3.5mW.The bandwidth of the amplifier is 10Hz to 20MHz and the background voltage noise spectrum density is 0.17nV/?Hz to 0.45nV/?Hz.We also tried our best to design cryogenic amplifiers with power consumption near 1?W which can work at mK temperature.The last part of this chapter introduces the operating characteristics of HEMT and SiGe transistors at mK temperature.On the basis of the low-noise cryogenic preamplifiers developed in the third chapter,the fourth chapter will firstly introduce several room temperature homemade amplifiers used for shot noise measurement system.The low-temperature shot noise measurement system in the Oxford Triton 200 dilution refrigerator with single-channel and two-stage amplifiers is introduced.LC resonant circuit is used in this shot noise measurement system to improve the signal-to-noise ratio.Since the inductance L can be regarded as short circuit ground at low frequency,it is possible for us to measure the differential resistance of sample at low frequency while measuring its shot noise at high frequency.In this chapter,the noise source and model of the shot noise measurement system are introduced in detail.The method of how to extract shot noise signal data from measured power spectrum density also introduced in this chapter.Due to the importance of circuit ground of weak signal measurement system,the way of how to reduce background noise by grounding with personal experience is also given in this chapter.After the shot noise measurement system was constructed,the method of measuring the electronic temperature of the system by measuring the thermal noise of the resistance in our shot noise measurement system is introduced in the fifth chapter.The amplification of the system is calibrated by the thermal noise measurement of a two-value composite resistance network composed by the film resistances of tantalum-nitride and nickel-chromium materials.Because the tunneling junction and quantum point contact are standard shot noise systems,they can be used to verify reliability of the shot noise measurement system.In this thesis,the performance of the system is demonstrated by a shot noise measurement of an Al/AlOx/Al tunneling junction at various temperatures.Above the superconducting transition temperature of aluminum,the measured Fano factor of the system is very close to 1,which is in a good agreement with the theory prediction.Finally,the noise behavior related to the device structure of the topological insulator Bi2Se3 nanowire was measured in this shot noise measurement system.Due to the lack of experimental research in the field of ultra-low temperature shot noise measurement of mesoscopic physics system in China,it is hoped that this thesis will provide some reference value for experimental shot noise research by our series work.In the future,correlation noise reduction technology can be carried out in the field of shot noise measurement. |
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