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SUMMARY:Magnetotransport of pyrochlore spin ice Sm2Ir2O7 across the pressu
 re-induced quantum-critical phase boundary - Dr. Matthew Coak\, London Cen
 tre for Nanotechnology\, University College London
DTSTART:20221123T111500Z
DTEND:20221123T123000Z
UID:TALK193019@talks.cam.ac.uk
CONTACT:Malte Grosche
DESCRIPTION:The family of rare-earth pyrochlore iridates Ln2Ir2O7 comprise
  an ideal environment for investigating fundamental magnetism and correlat
 ed-electron physics. In addition to the all-in-all-out (AIAO) magnetism of
  the Ir ions\, and associated metal-insulator transition\, the rare-earth 
 sublattice in these materials may also show interesting and correlated beh
 avior. In Dy2Ir2O7 and Ho2Ir2O7\, the large rare-earth Ising moments are c
 onstrained along their local [111] axes and are coupled ferromagnetically 
 via dipolar interactions\, promoting spin-ice physics and the appearance o
 f magnetic monopole quasiparticles. I will first discuss our ambient-press
 ure measurements of magnetotransport under different orientations at Warwi
 ck\, and their explanation in terms of a magnetic monopole density\, befor
 e moving on to discuss the Samarium compound.\nWe have measured the transp
 ort and magnetotransport properties of single-crystal Sm2Ir2O7 for the fir
 st time\, then tuned them up to and beyond the pressure-induced quantum cr
 itical point for AIAO Ir order suppression at pc = 63 kbar previously iden
 tified by resonant X-ray scattering. Contrary to prior predictions\, we do
  not find a crossover from insulating to metallic behavior at low temperat
 ures above pc.\nInstead\, the metal-insulator transition temperature\, whi
 ch tracks the decrease in the AIAO ordering temperature for pressures up t
 o 30 kbar\, begins to increase under further application of pressure\, poi
 nting to the presence of an additional localization mechanism. The behavio
 r of magnetotransport does track the Ir magnetism\, however\, with a stron
 g hysteresis observed only within the AIAO phase boundary\, similar to tha
 t found for Ho2Ir2O7 and attributed to plastic deformation of Ir domains.\
 nAround pc a new type of electronic behavior emerges\, characterized by ne
 gative magnetoresistance with small hysteresis at the lowest temperatures\
 , and hysteresis-free positive magnetoresistance above 5 K. The results ar
 e discussed in light of the Weyl semimetal and quadratic-band-touching pha
 ses predicted to occur in the vicinity of the quantum critical point.\n
LOCATION:Mott Seminar Room (531)\, Cavendish Laboratory\, Department of Ph
 ysics
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