Kitaoka lab Itohara Keita Antiferromagnetic order induced by an applied magnetic field in a high-temperature superconductor Kitaoka lab Itohara Keita My name is Keita Itohara. I am a member of Kitaoka laboratory. Today,I will talk about “Antiferromagnetic order induced by an applied magnetic field in a high-temperature superconductor”

Contents ・Introduction Meissner effect TypeⅠand TypeⅡsuperconductor La2-xSrxCuO4 Experimental method Magnetic neutron diffraction ・Experimental data and discussions ・Summary This is the contents of my presentation. Firstly,I’ll introduce you the brief of Meissner effect. Next,what the difference between type1 and type2 superconductor is. And I’ll show you the crystal structure of LaSrCuO,which is the sample of this study and explain its features. Then, I’ll talk about how authors did their jobs using magnetic neutron diffraction. This is the main subject in my presentation, experimental data and discussions. Finally I’ll summarize my presentation.

Meissner effect B=M+H=0 Magnetic field H As you know, superconductor has a characteristic feature, the electric resistivity suddenly dropped to zero below transition temperature Tc. And this is another important feature, it called “Meissner effect” The Meissner effect is the expulsion of a magnetic field from a superconductor. It is not surprising that this effect occurs below Tc. This phenomenon is applied to a linear motor car floating. Right figure shows the brief model of “Meissner effect” If we give the external magnetic field H, superconductors in the Meissner state exhibit perfect diamagnetism, such that their magnetization M=-H Diamagnetism is defined as the generation of a spontaneous magnetization of a material which directly opposes the direction of an applied field. Magnetic field H

TypeⅠand typeⅡsuperconductor Perfect diamagnetism Perfect diamagnetism Magnetic field H Vortex state There are two type of superconductors. The one is called Type1 superconductor and the other called Type2. If there is no magnetic field , both of them show perfect diamagnetism. And no flux can penetrate inside it. That’s because I showed you on the previous page. In stronger field, in type2 a little flux can penetrate though type1 is still perfect diamagnetism. In this state, partially, superconductivity has broken by field penetrating On this picture, a partial colored with black means normal state, and with gray means supreconductivity. And this state, coexisting normal state and superconductivity,is called “Vortex state” Then in much stronger field, type 1 suddenly changes normal state. And in type2, much more flux can penetrate than lower field, but it still shows vortex state. As you can see in a last row,finally, type2 also has broken their superconductivity completely. Normal state Normal state

underdoped La2-xSrxCuO4 0.1 0.2 0.3 50 100 150 200 250 300 350 Temperature[K] Sr doping　(x) Antiferromagnetism Spin glass superconductivity Here shows the crystal structure of LaSrCuO. There exists Cu atom on the yellow ball, O on the gray, La on the blue one. This material has one CuO2 plane. And we can put carriers into it by chemical substitution,La3+ ions to Sr2+ ions. The right side of this slide,this is the phase diagram. The non-doped compound is an insulating antiferromagnet. Introduction of charge carriers via Sr doping reduces the ordered moment until it vanishes at x<0.13 LaSrCuO becomes a superconductor for Sr doping of 0.06<x<0.25. In this study, authors used single crystals of underdoped(x=0.1) compound. Use single crystals of 　underdoped La2-xSrxCuO4

Neutron diffraction Bragg’s law 2dsinθ= nλ Neutron diffraction is closely related to X-ray powder diffraction Merit ・Neutrons have stronger penetration than X-ray and interact directly with the nucleus of the atom →Samples sizes are relatively 　 large compared to those used 　 in X-ray diffraction

Magnetic neutron diffraction Neutrons are uncharged, they carry a spin interact with magnetic moments reveal the microscopic magnetic structure of a material

Experimental data (1) Superconductivity characterized T(K) Superconductivity characterized by zero-resistivity at the much lower temperature →Tc=29K

Experimental data (2) The applied field that imposes antiferromagnetism The applied field that imposes the vortex lattice also induces antiferromagnetic order superconductivity and antiferro coexist throughout the bulk of the material

Experimental data (3) The order increases rapidly with small fields, reflecting the linear dependence of vortex density on field Vortex core

130Å av 500Å H=1T H=14.5T Magnetic correlation length →ζ>400Å Superconducting coherent length →ξ〜20Å 130Å av 500Å H=1T H=14.5T

Summary ・In the high-temperature superconductivity, La2-xSrxCuO4(x=0.10),there is the field-induced antiferromagnetism ・The field-induced antiferromagnetism is intrinsic ・And superconductivity and antiferromagnetism coexist throughout the bulk of the material 0.1 0.2 0.3 50 100 150 200 250 300 350 Temperature[K] Sr doping　(x) he Antiferromagnetism Spin glass superconductivity