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동경대학교의 Matsumoto 박사님초청하여 아래와 같이 세미나를 개최합니다.

학과 구성원 여러분의 많은 참석을 부탁 드립니다


     1. 일시: 2015 4 21(화) 오전 11

     2. 장소: 삼성학술정보관 7층 Creative Learning Room

     3. 초청연사: Dr. Yosuke Matsumoto (Institute for Solid State Physics, University of Tokyo, Japan)

     4. 제목: Novel quantum criticality beyond Doniach phase diagram

     5. Abstract: Novel quantum phases formed in the vicinity of a quantum critical point (QCP) is one of the most important topics for strongly correlated electron systems. So far, quantum criticality (QC) in heavy fermion systems has been studied mainly for Kondo lattice systems with integer valence. In this case, QC is usually related to magnetism and is understood by so called Doniach phase diagram. Here, we would like to discuss two examples of novel QC which are beyond this picture. The one is the novel QC found in the mixed valent YbAlB4 systems. The first Yb-based heavy fermion superconductor -YbAlB4 [1,2] exhibits QC without tuning any control parameter, indicating formation of a strange metal phase [3]. Recent resistivity measurements under pressure have revealed indeed that a non-Fermi liquid phase extends over a finite pressure range up to ~ 0.4 GPa [4]. We will further discuss a sharp valence crossover induced by a chemical substitution in -YbAlB4, which is an isostructural polymorph of -YbAlB4. Interestingly, we observed a pronounced NFL behavior as a possible evidence of a quantum valence criticality [5]. Another example is a possibility of quantum criticality arising from orbital degrees of freedom. Our recent studies revealed that PrT2Al20 (T = Ti, V) are ideal systems to study such possibilities. The both systems have the nonmagnetic cubic 3 crystal electric field doublet [6]. In addition, the hybridization is strong as is evident in many physical properties [6]. We would like to discuss heavy fermion superconductivity observed inside the multipole ordering phases [7-9].

[1] S. Nakatsuji et al., Nature Phys. 4, 603 (2008).
[2] K. Kuga et al., Phys. Rev. Lett. 101, 137004 (2008).
[3] Y. Matsumoto et al., Science 331, 316 (2011). References therein.
[4] T. Tomita, K. Kuga, Y. Uwatoko, P. Coleman, and S. Nakatsuji, preprint (2015).
[5] K. Kuga et al., preprint (2015).
[6] A. Sakai, and S. Nakatsuji, JPSJ 80, 063701 (2011). References therein.
[7] A. Sakai et al., JPSJ 81, 083702 (2012).
[8] K. Matsubayashi et al., PRL 109, 187004 (2012).
[9] M. Tsujimoto et al., PRL 113, 267001 (2014). References therein.

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