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Effect of chemical doping on heterostructured Fe-based superconductor Sr2VO3FeAs
옥종목,나세웅,김준성 한국초전도.저온공학회 2018 한국초전도저온공학회논문지 Vol.20 No.1
Phase diagrams of electron- and hole-doped Sr2VO3FeAs are investigated using Co and Mn substitution at Fe site. Metallic nature survives only for Co (electron) doping, not for Mn (hole) doping. The conductivity of Sr2VO3(Fe,M)As (M=Mn,Co) is sensitive to the structural modification of FeAs microstructure rather than carrier doping. This finding implies that the FeAs layer plays a dominant role on the charge conduction, thus the SrVO3 layers should be considered as an insulating block. Also, we found that the superconductivity is rapidly suppressed by both dopants. This result is different from the conventional behavior that superconductivity is induced by doping in the most of Fe pnictides. Our finding strongly supports the uniqueness of Sr2VO3FeAs among the Fe pnictide superconductors.
Anisotropic superconductivity of high quality FeSe1-x Single crystal
권창일,옥종목,김준성 한국초전도.저온공학회 2014 한국초전도저온공학회논문지 Vol.16 No.4
We investigate the upper critical field anisotropy ΓH and the magnetic penetration depth anisotropy Γλ of a high-quality FeSe1-xsingle crystal using angular dependent resistivity and torque magnetometry up to 14 T. High quality single crystals of FeSe1-x weresuccessfully grown using KCl-AlCl3 flux method, which shows a sharp superconducting transition at TC ~ 9 K and a high residualresistivity ratio of ~ 25. We found that the anisotropy ΓH near TC is a factor of two larger than found in the poor-quality crystals,indicating anisotropic 3D superconductivity of FeSe1-x. Similar to the 1111-type Fe pnictides, the anisotropies Γλ and ΓH showdistinct temperature dependence; ΓH decreases but Γλ increases with lowering temperature. These behaviors can be attributed tomulti-band superconductivity, but different from the case of MgB2. Our findings suggest that the opposite temperature dependenceof Γλ and ΓH is the common properties of Fe-based superconductors.
토크 마그네토메트리를 이용한 박막 이종구조의 양자자성 관측 가능성
공민식,옥종목,손창희 한국자기학회 2022 韓國磁氣學會誌 Vol.32 No.6
Quantum spin liquid (QSL) is an intriguing quantum phenomenon caused by quantum superposition and entanglement of spins and has attracted much attention because of the occurrence of unconventional ground states with high potential for applications in quantum computing. In particular, the realization of QSL in the thin film heterostructure provides a lot of possibility, however it has not been intensively studied due to the lack of measurement technique for magnetic properties of thin film heterostructure. In this paper, we discuss the possibility of observing the QSL states in the thin film heterostructure using torque magnetometry.
아크 융해로를 이용한 β-Ti<SUB>3</SUB>O<SUB>5</SUB> 및 λ-AlxTi<SUB>3-x</SUB>O<SUB>5</SUB>의 합성
공민식(Minsik Kong),김서희(Seohee Kim),김민재(Min Jae Kim),강명준(Myeongjun Kang),지광철(Gwangcheol Ji),박성욱(Seonguk Park),이지성(Jisung Lee),손영준(Yeongjun Son),박성균(Sungkyun Park),옥종목(Jong Mok Ok) 한국물리학회 2024 새물리 Vol.74 No.1
마그넬리(Magneli)상 티타늄 산화물인 Ti₃O<SUB>5</SUB>는 514 K에서 β상에서 λ상으로 변화하며 절연체에서 도체로 변화하는 금속-절연체 전이(metal-insulator transition; MIT)를 보인다. Ti<SUB>5</SUB>O<SUB>5</SUB>의 MIT는 큰 저항 변화와 높은 열에너지 저장 특성을 동반하는 것으로 알려져있어 높은 응용성을 가지고 있다. 이러한 Ti₃O<SUB>5</SUB>의 전기적 혹은 열적 특성을 활용하기 위해선 균일한 시료의 합성과 상전이 온도의 제어가 우선되어야 한다. 본 연구에서는 아크 융해로(arc melting furnace)를 이용한 티타늄 환원법으로 Ti₃O<SUB>5</SUB>를 합성하였고, 그 구조를 탄소 환원법으로 제조한 Ti₃O<SUB>5</SUB>와 비교하였다. 또한, 티타늄 환원법을 이용해 Al이 도핑된 AlxTi₃−xO<SUB>5</SUB>를 합성하고 Al 도핑 비율에 따른 구조, 상전이 온도 및 잠열량을 확인함을 통해 아크 융해법이 Ti₃O<SUB>5</SUB>를 합성하고 상전이를 온도를 제어하는데 효과적인 합성법임을 확인하였다. Ti₃O<SUB>5</SUB> exhibits a metal-insulator transition (MIT) accompanied by a structural change from β- phase to λ-phase at 514 K. During the transition, Ti₃O<SUB>5</SUB> demonstrates significant resistance changes and high thermal energy storage characteristics. To harness the beneficial characteristics of Ti₃O<SUB>5</SUB>, it is essential to develop a growth method that yields homogeneous samples and to control the phase transition temperature. In this study, we successfully synthesized high-quality β-Ti₃O<SUB>5</SUB> and λ-AlxTi₃−xO5 polycrystalline samples using an arc melting method. Furthermore, the structural and physical properties of β-Ti₃O<SUB>5</SUB> and λ-AlxTi₃−xO<SUB>5</SUB> were investigated as a function of the Al doping ratio. Our results suggest that the arc melting method provides an effective way to synthesize high-quality Ti₃O<SUB>5</SUB> and control the transition temperature of the MIT.