Center for Correlated Electron Systems

Seminar

Itinerant multipolar orders in the spin–orbit coupled metal Cd2Re2O7

May 28, 2019l Hit 378
Date : June 8, 2019 10:00 ~ 11:30
Speaker : Prof. Zenji Hiroi(Institute for Solid State Physics, University of Tokyo)
Location : Bldg. 19, Rm. 210

The superconducting pyrochlore oxide Cd 2 Re 2 O 7 has drawn attention as the only superconductor (T c = 1.0 K) that has been found in the family of α -pyrochlore oxides since its discovery in 2001 [ 1 ]. Moreover, it exhibits two characteristic structural transitions from the cubic pyrochlore structure, with the inversion symmetry broken at the first one at 200 K [ 2 ]. Recently, it has attracted increasing attention as a candidate spin-orbit coupled metal (SOCM), in which specific Fermi liquid instability leads to an odd-parity order with spontaneous inversion-symmetry breaking [ 3 ] and parity-mixing superconductivity [ 4 , 5 ]. More recent theoretical classification based on the crystal symmetry reveals that the two parity-breaking phases are described by unconventional multipoles, electric toroidal quadrupoles (ETQs) with different components, x 2 y 2 and 3z 2 r 2 , in the pyrochlore tetrahedral unit [ 6 ]. These ETQs are unique as they are extended cluster multipoles, distinguished from conventional atomic multipoles realized in f-electron systems [ 7 ].

We have been performing various experiments using high-quality single crystals of Cd 2 Re 2 O 7 in order to clarify the nature of the low-temperature phases. Particularly interesting would be to observe possible spin-split Fermi surfaces which may cause unusual magneto-electric effects such as the Edelstein effect [ 7 ]. For this, however, one has to control the domain formation across the phase transitions: twin domains arising from the tetragonal distortions and parity domains associated with the electronic chirality. Here we report on our recent experimental progress such as controlling the twin domains by stress [ 8-10 ] and review the present understanding of the SOCM Cd 2 Re 2 O 7 .

                  

 

 

Figure 1: Resistivity of Cd 2 Re 2 O 7 .

 

[1]       M. Hanawa, Y. Muraoka, T. Tayama et al., Phys. Rev. Lett. 87 , 187001 (2001).

[2]       Z. Hiroi, J. Yamaura, T. C. Kobayashi et al., J. Phys. Soc. Jpn. 87 , 024702 (2018).

[3]       L. Fu, Phys. Rev. Lett. 115 , 026401 (2015).

[4]       V. Kozii and L. Fu, Phys. Rev. Lett. 115 , 207002 (2015).

[5]       Y. Wang, G. Y. Cho, T. L. Hughes et al., Phys. Rev. B 93 , 134512 (2016).

[6]       S. Hayami, Y. Yanagi, H. Kusunose et al., Phys. Rev. Lett. 122 , 147602 (2019).

[7]       S. Hayami, M. Yatsushiro, Y. Yanagi et al., Phys. Rev. B 98 , 165110 (2018).

[8]       Y. Matsubayashi, D. Hirai, M. Tokunaga et al., J. Phys. Soc. Jpn. 87 , 104604 (2018).

[9]       Y. Matsubayashi, K. Sugii, H. T. Hirose et al., J. Phys. Soc. Jpn. 87 , 053702 (2018).

[10]     Y. Matsubayashi, T. Hasegawa, N. Ogita et al., Physica B 536 , 600 (2018).

 

 

 

Host: Prof. Tae Won Noh