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SUMMARY:Magneto-optical probes shed light on the unconventional transport 
 and magnetism of Eu – based semi-metals - Dr. Veronika Sunko\, Departmen
 t of Physics\, UC Berkeley
DTSTART:20230425T101500Z
DTEND:20230425T113000Z
UID:TALK199846@talks.cam.ac.uk
CONTACT:Malte Grosche
DESCRIPTION:Understanding the mechanisms and consequences of the coupling 
 between disparate degrees of freedom is at the forefront of quantum materi
 als research. A prominent example is coupling between magnetic and electro
 nic degrees of freedom\, offering the exciting opportunity to control the 
 near Fermi level electronic structure and topology by manipulating magneti
 c order. However\, the same coupling may promote a complex magnetic state\
 , which is challenging to identify experimentally.\n\nUsing a series of sy
 mmetry-sensitive optical techniques we investigate two Eu-based semi-metal
 s which recently attracted attention due to theoretical predictions of top
 ologically non-trivial electronic structure\, as well as experimental obse
 rvations of striking transport and magnetic properties. Firstly\, we study
  EuCd2P2 [1]\, a material which stands out due to the unusual temperature 
 dependence of its resistivity: metallic behavior at high temperatures is f
 ollowed by a 100-fold increase of resistivity with decreasing temperature 
 [2]. Remarkably\, resistivity peaks at 18K\, well above the Neel temperatu
 re of 11K. Using a powerful combination of experimental probes\, we reveal
  a far richer picture of EuCd2P2 magnetism than has been previously report
 ed\, helping to resolve this mystery.\n\nFurthermore\, we investigate the 
 magnetic structure and dynamics of EuIn2As2\, a material considered to be 
 an axion insulator candidate. Neutron scattering revealed an onset of a co
 mplex ‘broken helix’ magnetic state at 16K\, preceded by a helical spi
 n order stabilized in a narrow temperature window of 16K-17K [3]. We build
  upon this work to demonstrate that the magnetic structures differ slightl
 y from the ones deduced by past experiments and show how the structures ar
 ise due to frustrated magnetic interactions promoted by itinerant electron
 s. Surprisingly\, those subtle differences in magnetic structure have dras
 tic consequences for symmetry\, resulting in qualitatively different topol
 ogical properties.\n\nTaken together\, our results emphasize the power of 
 sensitive optical techniques in identifying complex magnetic structures\, 
 as well as the rich physics created by the interplay of the conduction ele
 ctrons and the localized moments in low carrier density systems.\n\n[1] Su
 nko\, V.\, Sun\, Y.\, et al.\, 2022\, arXiv\, 2208.05499 \n\n[2] Wang et a
 l.\, 2021\, Adv. Mater. 33(10)\, 2005755\n\n[3] Riberolles\, S. X. M.\, Na
 t Commun 2021\, 12 (1)\, 999
LOCATION:Mott Seminar Room (531)\, Cavendish Laboratory\, Department of Ph
 ysics
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