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The search for quantum materials and their manipulation is a paradigm shift in contemporary condensed matter research. This particular research direction requires the access of microscopic interactions between charge, lattice, spin and orbital degrees of freedom, and their subsequent selective control towards desired macroscopic quantum states, e.g. high-Tc superconductivity, room-temperature ferromagnet, quantum and anomalous Hall effects. In this talk, I will first highlight my PhD work based on magnetic proximity effects in oxide-based superconductor/ferromagnet (SC/FM) heterostructures. In particular, with x-ray magnetic circular dichroism technique, I will show how we can tune interaction between Cu and Mn ions at the interface of YBa2Cu3O7/La2/3Ca1/3MnO3 (SC/FM) heterostructures [1]. On the other hand, Raman spectroscopy is an ideal tool to simultaneously probe lattice (phonon), spin (magnon) and charge dynamics in correlated systems. This in return allows us to determine fundamental interactions, such as spin-phonon coupling, electron-phonon coupling and electron-electron correlation. In my talk, I will demonstrate how we exploited Raman spectroscopy to uncover strong spin-phonon coupling in CrAs single crystals [2] and complex charge dynamics in SrIrO3 thin films [3]. CrAs exhibit a first-order magneto-structural phase transition at TN= 265 K, below which the magnetic moments of Cr form an incommensurate helical magnetic structure and the unit-cell volume abruptly expands. Whereas, SrIrO3 has been proposed as a candidate to realize the so-called ‘topological semimetal’ phase due to its strong spin-orbit coupling (0.4 eV) and electron-electron correlations (0.3 eV). We identified that the charge dynamics both in hole- and electron-pockets in its semi-metallic Fermi surface are marginal Fermi-liquid like. We have further developed a memory function formalism for marginal Fermi-liquid to extract scattering rate and mass enhancement factor of both charge carriers in dynamic, as well as in static limit. Finally, I will mention my recent work on momentum-resolved phonons in antiferromagnetic oxides Sr2IrO4 and Sr3Ir2O7 using inelastic x-ray scattering [4].
References:
[1] X-ray absorption study of the ferromagnetic Cu moment at the YBa2Cu3O7 / La2/3Ca1/3MnO3 interface and the variation of its exchange interaction with the Mn moment, K. Sen, E. Perret, A. Alberca, M. A. Uribe-Laverde, I. Marozau, M. Yazdi-Rizi, B.P.P. Mallett, P. Marsik, C. Piamonteze, Y. Khaydukov, M. Döbeli, T. Keller, N. Biškup, M. Varela, J. Vašátko, D.Munzar and C. Bernhard
Phys. Rev. B 93, 205131 (2016).
[2] Raman scattering study of lattice and magnetic excitations in CrAs, K. Sen, Y. Yao, R. Heid, A. Omoumi, F. Hardy, K. Willa, M. Merz, A. A. Haghighirad, and M. Le Tacon Phys. Rev. B 100, 104301 (2019)
[3] Strange semimetal dynamics in SrIrO3, K. Sen, D. Fuchs, R. Heid, K. Kleindienst, K. Wolff, J. Schmalian, and M. Le Tacon, Nat. Commun. 11, 4270 (2020)
[4] Absence of temperature-dependent phonon anomalies in Sr2IrO4 and Sr3Ir2O7, K. Sen, R. Heid, S. M. Souliou, D. Boll, A. Bosak, N. H. Sung, J. Bertinshaw, H. Gretarsson, B. J. Kim, F. Weber, and M. Le Tacon, arXiv:2111.04081 (2021)
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