1may 4 related paper la alo 3/ktao 3( 1 1) electric field control of interface superconductivity (electric field control laalo3/ktao3 (11) interface superconductivity). The first authors of this thesis are Chen Zheng, Liu Yuan, Ph.D. students of Physics Department of Zhejiang University, and Zhang Hui, postdoctoral fellow of Beihang University. The authors of the correspondence are Xie, Sun and Zhou Yi, researchers from the Physics Department of Zhejiang University. This discovery provides a new vision for people to explore low-temperature quantum phenomena, and also provides a new idea for the research and development of superconducting devices.
The potential of "returning waves"
Laalo _ 3/KTAO _ 3 interfacial superconductivity just appeared in Science magazine in February this year. It is the second member of the oxide interface superconductivity family. The 1 th member appeared in 2007. Professor Triscone of the University of Geneva in Switzerland and others first discovered the superconductivity of LaAlO3/SrTiO3 interface, which marked the birth of a new superconducting system: oxide interface superconductivity.
Triscone used a bunch of Lego bricks to describe the wonder of this field: different oxides can produce ever-changing combinations, and each combination may contain unknown novel properties. Subsequent research found that the superconductivity of LaAlO3/SrTiO3 can be turned on or off by voltage, just like the well-known semiconductor transistor. This can't help but make people imagine that maybe one day we can make superconducting devices that can be precisely controlled like semiconductors.
More than a year ago, the performance of LaAlO3/KTaO3, the "new student" of Argonne Laboratory in the United States, seemed to be more eye-catching. The paper published in the journal Science in February this year pointed out that "the superconducting transition temperature of LaAlO3/KTaO3 can reach 2.2 K, which is a whole order of magnitude higher than that of Qianlang's 0.3 K". So, what novel properties will it have? Can its superconducting properties also be regulated? What is the value of studying superconducting mechanism? The mysterious "back wave" attracts Xie and his partners to find out.
New regulations and new mechanisms
Regulation is the most important means and content of experimental scientific research. In this study, the research team found a new regulation mechanism, which realized the continuous regulation of the conductivity of LaAlO3/KTaO3, and the device showed a continuous transition from superconducting to insulator with the change of voltage.
Doctoral students Chen Zheng and Liu Yuan are preparing samples in the laboratory.
Xie introduced that at low temperature, conductive electrons form superconductivity in pairs. There are many known superconducting systems, but few of them can be controlled by electric field. The essence of our control method is to control the spatial distribution of electron formation and make them close to or away from the interface. When a large number of electrons move near the oxide interface, they will be affected by lattice defects (also known as disorder). "It's like driving into an obstacle." Xie said that this "disorder" is denser as it gets closer to the interface, and thinner as it gets farther away from the interface. Based on this understanding, the research team put forward the idea of changing the spatial distribution of electrons. "If more electrons are close to the interface, on the whole, they will encounter more' obstacles', which will significantly affect the motion behavior of electrons and superconducting Cooper pairs."
There are 80 trillion electrons moving in the interface channel per square centimeter, and the gate voltage affects the interface conductivity by changing their "formation". The shape of "mountain" indicates disordered distribution.
In this experiment, the researchers tested the conductivity of the interface when the gate voltage was between -200V and150 V. "The conductivity can be continuously adjusted whether it is above or below the superconducting transition temperature." Chen Zheng said, "We also directly measured the changes in the spatial distribution of electron' formation' in this voltage range. When the conductive channel is 6 nm, LaAlO3/KTaO3 looks like a good superconductor, but when the channel is adjusted to 2 nm, it becomes an insulator. "
When different gate voltages are applied in the range of -200V to150 V, the surface resistance (Rsheet) of LaAlO3/KTaO3 interface changes with temperature (t).
"On the surface, we use the traditional method to adjust the gate voltage, but the adjustment mechanism behind it is completely new." Sun Jirong said that the traditional methods, whether semiconductor transistors or LaAlO _ 3/SrTiO _ 3, adjust the conductivity by changing the electron concentration, which requires a premise: low electron concentration. "In contrast, the electron concentration of LaAlO3/KTaO3 interface is very high, which can not meet the traditional regulation mechanism, so it is necessary to explore new regulation mechanisms." Sun said that the new regulation still works like a transistor, but it essentially breaks the limit of electron concentration.
Quantum metal state
Doctoral students Chen Zheng and Liu Yuan participated in the sample preparation and testing. Chen Zheng said that the most unforgettable thing in the research process was the day when the superconductivity of LaAlO3/KTaO3 was first measured. "This shows that we have mastered the method of preparing this new interfacial superconducting system and can start our regulation research!" With the advancement of the experiment, more and more data surfaced. When they put them together, they were surprised to find that there is a horizontal line at low temperature, that is to say, no matter how the temperature changes in the range of 0~ 1K, the resistance of LaAlO3/KTaO3 interface is almost always constant. "Quantum metal is a novel quantum state of matter, which has both partial superconductivity and metallic characteristics and is a typical quantum metal state." Zhou Yi said, "The known quantum metal state is only at a certain quantum critical point. This system can be controlled continuously, and quantum metal exists as a phase on the phase diagram. This new discovery makes us extremely excited. "
Physical photos of the equipment. The bridging part of the intermediate core is 20 microns wide and 100 microns long.
Critics of Science magazine gave a very positive response to this research. They think that this completely tunable superconductivity is a fascinating breakthrough, and the research is deep enough to cover almost all the knowledge gained in LaAlO3/SrTiO3 system in the past 65,438+00 years.
Xie said that the study of new materials mainly comes from two aspects: on the one hand, I want to discover new physical phenomena and gain more scientific insights through the study of new materials; On the other hand, it also tries to provide useful clues for developing new equipment. "Our research in LaAlO _ 3/KTAO _ 3 system can provide brand-new materials for understanding superconducting mechanism, especially in high temperature superconductivity, and also provide a new vision for developing superconducting devices in the future."
The team members of this research also include Sun He, a Ph.D. student from the Physics Department of Zhejiang University, and Professor Tian He and Dr. Liu Zhongran from the School of Materials Science of Zhejiang University.
The research has received all-round support from colleagues in the Quantum Crossing Center of Zhejiang University in terms of technology and equipment, as well as the special funds for the construction of "double first-class" in Zhejiang University, the national key R&D plan, the National Natural Science Foundation, and the key R&D plan in Zhejiang Province.
Xie Yanwu, Department of Physics, Zhejiang University
Paper doi:10.1126/science.abb3848.
(The original title is "Zhejiang University Team Science Post Again! Decryption how to control oxide interface superconductivity with electric field. Editor Zhang Zhongwen)