Max-Planck-Institute for Chemical Physics of Solids, Dresden, Germany

报告地点：物理所M楼255会议室

报告摘要：

Materials in which the structural, electronic and magnetic degrees of freedom are entangled can exhibit unexpected or even spectacular physical phenomena like superconductivity or colossal magnetoresistance (CMR). A hallmark of such coupled degrees of freedom is the appearance of distinct electronic phases, along with phase separation and pattern formation. One particular case of electronic inhomogeneity often observed in Eu-containing compounds are magnetic polarons, within which conduction electrons are localized via strong exchange interaction with the Eu 4f  moments. Here,  Eu²⁺ is of particular interest due to its vanishing orbital angular momentum L = 0. Here, we report on our investigations on three different compounds, all of which exhibit a large CMR effect. The ferromagnetic material EuB₆ is presented as a benchmark case for which polaron formation is well established [1]. We then focus on the antiferro-magnetic Zintl compound Eu₅In₂Sb₆ which crystallizes in the non-symmorphic space group Pbam and hence, non-trivial topological properties can be expected. We find a record CMR and strong evidence for the occurrence of polarons in this low-carrier density material[2]. Thermal expansion and magnetostriction measurements indicate that Eu₅In₂Sb₆ is a rare example where ferromagnetic polarons can exist in an antiferromagnetic environment [3]. The calculated band structures and resultant DOS for the considered antiferromagnetic and ferromagnetic spin structures in Eu₅In₂Sb₆. nicely illustrate how the difference in spin configuration can lead to a reorganization of the small band contributions near the Fermi level E_F[4]. At present neither our band structure calculations nor the low-temperature STS results provide any indication for a nontrivial band topology of Eu₅In₂Sb₆. 

Also, EuCd₂P₂ exhibits an enormous CMR of up to 10⁵ %. We, again, combined locally resolved investigations by Scanning Tunneling Spectroscopy with bulk measurements of the magnetic, thermodynamic and electronic transport properties and find a complex interplay of ferro- and antiferromagnetic interactions at work. The implications of inhomogeneous states in relation to possible scenarios for CMR will be discussed.

* In collaboration with M. V. Ale Crivillero, H. Dawczak-Dębicki, S. Krebber, J. Müller, C. Krellner, K. Kliemt, P. F. S. Rosa and U. K. Rößler 

References：

1. M. Pohlit et al., Phys. Rev. Lett. 120, 257201 (2018). 

2. M. V. Ale Crivillero et al., Sci. Rep. 13, 1597 (2023). 

3. H. Dawczak-Dębicki et al., to be published. 

4. M. V. Ale Crivillero et al., Phys. Rev. B 106, 035124 (2022)

报告人简介： 

Dr. Steffen Wirth received his Ph.D. degree in Physics at Technical University Dresden, Germany in 1995. Then he did his postdoctoral research at Trinity College during 1995-1996 and Florida State University during 1996-2000, when he received the Feodor Lynen fellowship from the Humboldt-foundation. In 2010, he became a scientific staff member at Max Planck Institute (MPI) for Chemical Physics of Solids, Dresden. He worked as a visiting professor at the University Gottingen in 2009-2010. In 2010, he became an associate professor and research group leader at MPI for Chemical Physics of Solids. He was elected to be a fellow of American Physical Society in 2017.

Dr. Wirth is an expert in scanning tunneling microscopy, magnetization and electronic transport measurements at low temperatures and high magnetic fields. His research interest covers a broad range of topics in condensed matter physics, including magnetic materials, strongly correlated electron systems including heavy fermion metals, quantum criticality, superconductivity, electronic transport properties, Kondo insulators, topological materials, manganites, chalcogenides and magnetic nanoparticles. 

联系人：刘恩克 研究员(82649085，ekliu@iphy.ac.cn)

        李永庆 研究员(82649557，yqli@iphy.ac.cn)