日程 : 2024年2月7日(水) 16:00 - 17:00
場所 : 物性研究所6階第5セミナー室（A615）及び ZOOM（Hybrid）
講師 : Toni Helm
所属 : Dresden High Magnetic Field Laboratory, Helmholtz Zentrum Dresden Rossendorf
主催 : 強磁場コラボラトリー
共催 : 学術変革領域研究(A) 1000テスラ科学、学術変革領域研究(A) アシンメトリ量子（第７回アシンメトリ量子セミナー）
世話人 : 宮田敦彦（物性研）、木俣基（東北大）
e-mail : a-miyata@issp.u-tokyo.ac.jp, motoi.kimata.b4@tohoku.ac.jp
In order to uncover and understand the physics of topical quantum materials, experiments are pushed to their limits in terms of setup dimensions and resolution. Challenging conditions, such as very low temperatures, high pulsed-magnetic fields, strong pressures or microscopically small but well-defined sample dimensions are inevitable for successful investigations. We apply focused ion beam (FIB) micro-patterning for the fabrication of micron-scale structures from bulk single crystals suitable for high precision electrical transport experiments. This approach has proven a powerful tool for experiments on various compounds with intriguing transport properties. In particular, Hall effect signals can be optimized by means of reducing the sample thickness to few microns.
In this talk, I will exemplify some of our recent projects that benefited from FIB assisted patterning and uncovered new physics in topical materials [1-4]. In the first examples, I will show how we can contribute to the field of unconventional magnetism. I will present recent results from electrical-transport experiments that we combined with microscopic magneto-sensitive imaging tools. This enabled us to study finite size-effects and reveal the Hall signature, comprised of anomalous and topological contributions, of Antiskyrmions in the Heusler magnet Mn1.4PtSn [1] and that of Skyrmion bubbles in the hard magnet MnBi [2]. We, furthermore, study highly conductive heavy-fermion metals in pulsed magnetic fields up to 70 T. In our recent work on the potential spin-triplet superconductor UTe2, we revealed a correlation between the emergence of reentrant superconductivity in fields above 40 T and the vanishing of the anomalous Hall effect. The vanishing and reemerging of the Hall signature within a particular field-orientation range, hints at a field-induced compensation of magnetic exchange, the so-called Jaccarino-Peter effect, as the potential origin of reentrant high-field superconductivity in UTe2 [3,4].
[1] Winter, M., Goncalves, F.J.T., Soldatov, I., et al.
“Antiskyrmions and their electrical footprint in crystalline mesoscale structures of Mn1.4PtSn.” Commun. Mater. 3, 102 (2022).
[2] He, Y., Schneider, S., Helm, T., et al.
“Topological Hall effect arising from the mesoscopic and microscopic non-coplanar magnetic structure in MnBi.” Acta. Mater. 226, 117619 (2022)
[3] Niu, Q., Knebel, G., Braithwaite, D., Helm, T., et al.
“Evidence of Fermi surface reconstruction at the metamagnetic transition of the strongly correlated superconductor UTe2.” Phys. Rev. Res. 2, 033179 (2020)
[4] Helm, T., Kimata, M., Sudo, K., et al.
“Field-induced compensation of magnetic exchange as the possible origin of reentrant superconductivity in UTe2.” Nat Commun 15, 37 (2024).