物理学教室 談話会（7月12日）
コロキウム・談話会 2023/06/30
【日 時】2023年7月１2日(水)１5時00分～16時30分
【講演者】Prof. Natalia Drichko
（The Johns Hopkins University, Baltimore, USA）
【場 所】理学部4号館 1220号室
【タイトル】フラストレーション磁気と電子バンドトポロジーの出会い:Nd2Ir2O7の場合。
| Pyrochlore iridates present a unique interplay of magnetic frustration, electron correlations, and spin orbit coupling [1]. Weyl semimetal state was suggested in these materials when the quadratic band touching splits into Weyl nodes as a result of time reversal symmetry breaking by the all-in-all-out (AIAO) ordering of the Ir moments [2]. We show [3,4] that not only Nd2Ir2O7 is the best candidate to live up to these theoretical expectations, but due to both A (Nd) and B (Ir) sites of the pyrochlore lattice of this material being magnetic, it demonstrates a unique way to enhance magnetic interactions in the Nd pyrochlore lattice. Using polarized Raman scattering spectroscopy we can separate electronic and magnetic contributions to the spectral response, and follow their temperature dependence down to 7 K through the ordering of Ir moments at TN(Ir)= 33 K and Nd moments ordering at about 14 K. We detect Gamma-point magnon excitations of the AIAO order of Ir moments. A step-like decrease of the electronic scattering at TN(Ir)= 33 K is interpreted as a signature for the splitting of quadratic band touching into Weyl nodes. We show that the presence of Ir results in the renormalization of magnetic interactions between Nd moments: Below TN(Ir)= 33 K spin ice fluctuations of Nd magnetic moments are detected through an observation of a collective mode at 15 meV which disappears when Nd moments order in AIAO below 14 K. Phonons evolution through these magnetic ordering transitions evidence for the weak distortion of the lattice at low temperatures. |
References:
1. D. Pesin and L. Balents, Nature Physics 6, 376 (2010).
2. X. Wan, A. M. Turner, A. Vishwanath, and S. Y. Savrasov. Physical Review B 83, 205101 (2011).
3. Y. Xu, Y. Yang, J. Teyssier, T. Ohtsuki, Y. Qiu, S. Nakatsuji, D. van der Marel, N. Perkins, N. Drichko. arXiv:2302.00579 (2023).
4. P. Nikolic, Y. Xu, T. Ohtsuki, S. Nakatsuji, N. Drichko. arXiv:2204.13722 (2022).
