An experimental study on the current shot noise of a quantum point contact with short channel length is reported. The experimentally measured maximum energy level spacing between the ground and the first excited state...An experimental study on the current shot noise of a quantum point contact with short channel length is reported. The experimentally measured maximum energy level spacing between the ground and the first excited state of the device reached up to 7.5meV, probably due to the hard wall confinement by using shallow electron gas and sharp point contact geometry. The two-dimensionM non-equilibrium shot noise contour map shows noise suppression characteristics in a wide range of bias voltage. Fano factor analysis indicates spin-polarized transport through a short quantum point contact.展开更多
Apart from usual quantization steps on the ballistic conductance of quasi-one-dimensional conductor, an additional plateau-like feature appears at a fraction of about 0.7 below the first conductance step in GaAs-based...Apart from usual quantization steps on the ballistic conductance of quasi-one-dimensional conductor, an additional plateau-like feature appears at a fraction of about 0.7 below the first conductance step in GaAs-based quantum point contacts (QPCs). Despite a tremendous amount of research on this anomalous feature, its origin remains still unclear. Here, a unique model of this anomaly is proposed relying on fundamental principles of quantum mechanics. It is noticed that just after opening a quasi-1D conducting channel in the QPC a single electron travels the channel at a time, and such electron can be—in principle—observed. The act of observation destroys superposition of spin states, in which the electron otherwise exists, and this suppresses their quantum interference. It is shown that then the QPC-conductance is reduced by a factor of 0.74. “Visibility” of electron is enhanced if the electron spends some time in the channel due to resonant transmission. Electron’s resonance can also explain an unusual temperature behavior of the anomaly as well as its recently discovered feature: oscillatory modulation as a function of the channel length and electrostatic potential. A recipe for experimental verification of the model is given.展开更多
In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By emp...In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By employing photolithography and wet-etching processes, suspended electrode pairs were patterned and fabricated successfully on Si microchips. Rather than adopting an acid Cu electroplating solution, a novel alkaline electroplating solution was developed and utilized to establish Cu nanocontacts between electrode pairs. Typically, the widths of the as-fabricated Cu nanocontacts were found to be smaller than 18 nm. A large number of Cu quantum point contacts were then produced and characterized by a home-built MCBJ setup. In addition to the conventional histogram, where peaks tend to decrease in amplitude with increasing conductance, an anomalous type of conductance histogram, exhibiting different peak amplitudes, was observed. Through statistical analysis of the maximum allowable bending of the Si microchips, and theoretical calculations, we demonstrated that our alkaline Cu electroplating solution affords Cu nanocontacts that are compatible with subsequent MCBJ operations, which is essential for the fabrication of Cu quantum point contacts. As sophisticated e-beam lithography is not required, the EC-MCBJ method is fast, simple, and cost-effective. Moreover, it is likely to be suitable for the fabrication and characterization of quantum point contacts of various metals from their respective electroplating solutions.展开更多
输运测量是研究物质状态基本性质的重要工具。其中通过量子点接触(Quantum Point Contact)的输运是介观物理学中一个非常有趣的现象。在无相互作用或弱相互作用费米系统中,电导随门电压的变化呈现出量子化的阶梯状,这一现象揭示了物质...输运测量是研究物质状态基本性质的重要工具。其中通过量子点接触(Quantum Point Contact)的输运是介观物理学中一个非常有趣的现象。在无相互作用或弱相互作用费米系统中,电导随门电压的变化呈现出量子化的阶梯状,这一现象揭示了物质的量子特性。近年来,冷原子体系中输运的研究已成为该领域的前沿研究之一冷原子体系具有高度可操控性的特点,也存在许多新奇物态,因此可以在冷原子的输运实验中观测到许多材料物理中无法观测到的新的实验现象。本文将以综述的形式介绍冷原子费米气体通过量子点接触的输运行为的一些前沿实验进展,此外,我们也将介绍处理该体系常用的非平衡场论方法。展开更多
Recent work on magnetic quantum point contacts (QPCs) was discussed. Complete magnetoresistance loops across Co QPCs as small as a single atom was measured. The remarkable feature of these QPCs is the rapid oscillator...Recent work on magnetic quantum point contacts (QPCs) was discussed. Complete magnetoresistance loops across Co QPCs as small as a single atom was measured. The remarkable feature of these QPCs is the rapid oscillatory decay in magnetoresistance with the increase of contact size. In addition, stepwise or quantum magnetoresistance loops are observed, resulting from varying transmission probability of the available discrete conductance channels because the sample is cycled between the ferromagnetic (F) and antiferromagnetic (AF) aligned states. Quantized conductance combined with spin dependent transmission of electron waves gives rise to a multi-channel system with a quantum domain wall acting as a valve, i.e., a quantum spin-valve. Behavior of a few-atom QPC is built on the behavior of a single-atom QPC and hence the summarization of results as ‘single-atom spintronics’. An evolutionary trace of spin-dependent electron transmission from a single atom to bulk is provided, the requisite hallmarks of artefact-free magnetoresistance is established across a QPC – stepwise or quantum magnetoresistance loops and size dependent oscillatory magnetoresistance.展开更多
Preliminary results of a study are reported here investigating mesoscopic tunnel junctions irradiated with coherent low-intensity (-50 to -10 dB) pulsed microwave RF fields at moderately low (LN2) temperatures. Quantu...Preliminary results of a study are reported here investigating mesoscopic tunnel junctions irradiated with coherent low-intensity (-50 to -10 dB) pulsed microwave RF fields at moderately low (LN2) temperatures. Quantum tunneling of electrons was observed through fabricated mesoscale gap junctions as a result of coherent irradiating fields at low temperatures around 77 - 100 K. The tunneling current was seen as a result of applied microwave fields across the junctions, distinguishable from shot noise and resistance effects. The form of tunneling behavior does not lead to any conductance quantization effects which could manifest the junction as a Quantum Point Contact (QPC), hence it is surmised that the phenomenon is purely low intensity RF field-induced tunneling of electrons across the mesoscale junctions at low temperatures.展开更多
基金Supported by the Basic Science Research Program through the National Research Foundation of Korea under Grant No 2011-0004949
文摘An experimental study on the current shot noise of a quantum point contact with short channel length is reported. The experimentally measured maximum energy level spacing between the ground and the first excited state of the device reached up to 7.5meV, probably due to the hard wall confinement by using shallow electron gas and sharp point contact geometry. The two-dimensionM non-equilibrium shot noise contour map shows noise suppression characteristics in a wide range of bias voltage. Fano factor analysis indicates spin-polarized transport through a short quantum point contact.
文摘Apart from usual quantization steps on the ballistic conductance of quasi-one-dimensional conductor, an additional plateau-like feature appears at a fraction of about 0.7 below the first conductance step in GaAs-based quantum point contacts (QPCs). Despite a tremendous amount of research on this anomalous feature, its origin remains still unclear. Here, a unique model of this anomaly is proposed relying on fundamental principles of quantum mechanics. It is noticed that just after opening a quasi-1D conducting channel in the QPC a single electron travels the channel at a time, and such electron can be—in principle—observed. The act of observation destroys superposition of spin states, in which the electron otherwise exists, and this suppresses their quantum interference. It is shown that then the QPC-conductance is reduced by a factor of 0.74. “Visibility” of electron is enhanced if the electron spends some time in the channel due to resonant transmission. Electron’s resonance can also explain an unusual temperature behavior of the anomaly as well as its recently discovered feature: oscillatory modulation as a function of the channel length and electrostatic potential. A recipe for experimental verification of the model is given.
基金Acknowledgements This work was supported by the National Natural Science Foundation of China （Nos. 21503179, 21403181, 61573295, 21522508, 21673195, 21533006, and 61071010）, the National Basic Research Program of China （No. 2015CB932300）, the Natural Science Foundation of Fujian Province （No. 2016J05162）, the Fundamental Research Funds for the Central Universities in China （Xiamen University, Nos. 20720170035 and 20720160092）, and the Young Thousand Talent Project of China.
文摘In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By employing photolithography and wet-etching processes, suspended electrode pairs were patterned and fabricated successfully on Si microchips. Rather than adopting an acid Cu electroplating solution, a novel alkaline electroplating solution was developed and utilized to establish Cu nanocontacts between electrode pairs. Typically, the widths of the as-fabricated Cu nanocontacts were found to be smaller than 18 nm. A large number of Cu quantum point contacts were then produced and characterized by a home-built MCBJ setup. In addition to the conventional histogram, where peaks tend to decrease in amplitude with increasing conductance, an anomalous type of conductance histogram, exhibiting different peak amplitudes, was observed. Through statistical analysis of the maximum allowable bending of the Si microchips, and theoretical calculations, we demonstrated that our alkaline Cu electroplating solution affords Cu nanocontacts that are compatible with subsequent MCBJ operations, which is essential for the fabrication of Cu quantum point contacts. As sophisticated e-beam lithography is not required, the EC-MCBJ method is fast, simple, and cost-effective. Moreover, it is likely to be suitable for the fabrication and characterization of quantum point contacts of various metals from their respective electroplating solutions.
文摘输运测量是研究物质状态基本性质的重要工具。其中通过量子点接触(Quantum Point Contact)的输运是介观物理学中一个非常有趣的现象。在无相互作用或弱相互作用费米系统中,电导随门电压的变化呈现出量子化的阶梯状,这一现象揭示了物质的量子特性。近年来,冷原子体系中输运的研究已成为该领域的前沿研究之一冷原子体系具有高度可操控性的特点,也存在许多新奇物态,因此可以在冷原子的输运实验中观测到许多材料物理中无法观测到的新的实验现象。本文将以综述的形式介绍冷原子费米气体通过量子点接触的输运行为的一些前沿实验进展,此外,我们也将介绍处理该体系常用的非平衡场论方法。
文摘Recent work on magnetic quantum point contacts (QPCs) was discussed. Complete magnetoresistance loops across Co QPCs as small as a single atom was measured. The remarkable feature of these QPCs is the rapid oscillatory decay in magnetoresistance with the increase of contact size. In addition, stepwise or quantum magnetoresistance loops are observed, resulting from varying transmission probability of the available discrete conductance channels because the sample is cycled between the ferromagnetic (F) and antiferromagnetic (AF) aligned states. Quantized conductance combined with spin dependent transmission of electron waves gives rise to a multi-channel system with a quantum domain wall acting as a valve, i.e., a quantum spin-valve. Behavior of a few-atom QPC is built on the behavior of a single-atom QPC and hence the summarization of results as ‘single-atom spintronics’. An evolutionary trace of spin-dependent electron transmission from a single atom to bulk is provided, the requisite hallmarks of artefact-free magnetoresistance is established across a QPC – stepwise or quantum magnetoresistance loops and size dependent oscillatory magnetoresistance.
文摘Preliminary results of a study are reported here investigating mesoscopic tunnel junctions irradiated with coherent low-intensity (-50 to -10 dB) pulsed microwave RF fields at moderately low (LN2) temperatures. Quantum tunneling of electrons was observed through fabricated mesoscale gap junctions as a result of coherent irradiating fields at low temperatures around 77 - 100 K. The tunneling current was seen as a result of applied microwave fields across the junctions, distinguishable from shot noise and resistance effects. The form of tunneling behavior does not lead to any conductance quantization effects which could manifest the junction as a Quantum Point Contact (QPC), hence it is surmised that the phenomenon is purely low intensity RF field-induced tunneling of electrons across the mesoscale junctions at low temperatures.
