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Title (deu)
Multipole orders in 5d transition metal double perovskites and pyrochlores
Speaker / Lecturer
Daigorou Hirai
Nagoya U
Description (deu)

This talk was part of the Workshop on "Spin-Orbit Entangled Quantum Magnetism" held at the ESI September 23 -- 27, 2024.

Multipolar orders have been studied mainly in f-electron systems; however, 4d and 5d electron systems with strong spin-orbit interactions (SOIs) have become the focus of research as novel platforms for multipole physics in recent years [1,2]. Double perovskite, a variant of perovskite with cations ordered in a rock salt manner, provides a very good platform for studying multipole properties. For octahedrally coordinated transition metal ions with d1 electron counts, the combination of a high symmetry crystal field and strong SOIs stabilizes a J = 3/2 quartet as ground states. The multipolar degrees of freedom of J = 3/2 state is expected to give rise to orders of quadrupole and octupole moments [3].

We searched for a model system that shows multipolar order of d electrons among and found an ideal compound hosting a quadrupolar order, Ba2MgReO6, in which the Re6+ ions with 5d1 electronic configuration form an FCC lattice. Detailed physical property measurements using high quality single crystals of Ba2MgReO6 revealed a spin-orbit-entangled J = 3/2 state and two phase transitions: a quadrupolar order at Tq = 33 K and a magnetic order at Tm = 18 K [4]. Then, our synchrotron x-ray diffraction measurements revealed that the quadrupolar order is composed of antiferroically arranged Qx2–y2 and ferroically arranged Q3z2–r2 moments [5]. In the presentation, the response of the quadrupolar and magnetic orders to the external field and electronic orders in related Re-based double perovskites will also be discussed.

Multipole order can be formed not only in 5d-based insulators but also in metals. Metals whose Fermi surfaces are unstable due to strong spin-orbit interactions are proposed as "spin-orbit coupled metals," in which the spatial inversion symmetry is spontaneously broken and a unique odd-parity electronic order is formed [6]. The pyrochlore oxide Cd2Re2O7 is one of the few examples of spin-orbit coupled metals, and it is the first superconductor (Tc = 1.0 K) found in pyrochlore oxides. Cd2Re2O7 undergoes a structural phase transition with inversion symmetry breaking at 200 K, resulting in a significant change in the resistivity and magnetic susceptibility [7]. This phase transition is proposed to originate from the formation of an odd-parity itinerant multipole order [8]. We have revealed complex structural phase transitions that have been overlooked so far, and proposed that they are related to the switching of order parameters [9]. In the presentation, we will also introduce the phase transition of the analogous pyrochlore Pb2Re2O7 [10] and discuss the differences between the two.

[1] W. Witczak-Krempa et al., Annu. Rev. Condens. Matter Phys. 5, 57 (2014).
[2] T. Takayama et al., J. Phys. Soc. Jpn. 90, 062001 (2021).
[3] Chen, R. Pereira, and L. Balents, Phys. Rev. B 82, 174440 (2010).
[4] D. Hirai and Z. Hiroi, J. Phys. Soc. Jpn. 88, 064712 (2019).
[5] D. Hirai et al., Phys. Rev. Res. 2, 022063(R) (2020).
[6] L. Fu, Phys. Rev Lett. 115, 026401 (2015).
[7] Z. Hiroi et al., J. Phys. Soc. Jpn. 87, 024702 (2018).
[8] S. Hayami et al., Phys. Rev Lett. 112, 147026401 (2015).
[9] D. Hirai et al., J. Phys.: Condens. Matter 51, 035403 (2023).
[10] Y. Nakayama et al., Phys. Rev Mater. 8, 055001

Keywords (deu)
solid-state magnetismESIcondensed matter physics
Subject (eng)
ÖFOS 2012 -- 103 -- Physics, Astronomy
Type (eng)
Language
[eng]
Persistent identifier
https://phaidra.univie.ac.at/o:2094137
Date created
2024-09-26
Place of creation (eng)
ESI
Duration
39 minutes 37 seconds
Content
Details
Object type
Video
Format
video/mp4
Created
26.09.2024 03:53:00
Metadata