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SUMMARY:Larmor diffraction from antiferromagnetic and hidden order in URu2
 Si2 - Philipp Niklowitz\, Royal Holloway
DTSTART:20081126T111500Z
DTEND:20081126T121500Z
UID:TALK13511@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:Following the border of antiferrmagnetism to zero temperature 
 often turned out to be a promising route to unconventional metallic and su
 perconducting phases. Even the simple d-electron system NiS2 revealed an e
 xtended non-Fermi-liquid regime dominated by spin-fluctuations above the q
 uantum phase transition.[1] In the latter case\, measurements of the elect
 rical resistivity measurements were done in the framework of the clean and
  highly controlled technique of pressure tuning. The range of further quan
 titative experimental probes\, which can be realised in a high-pressure en
 vironment is limited. However\, advances have recently been made in neutro
 n scattering\, where elliptically shaped neutron guides can now increase t
 he beam intensity sent to mm size sample for high pressure studies.[2] Neu
 tron scattering also allows highly accurate measurements of the thermal ex
 pansion via the Larmor diffraction technique\, which proved extremely usef
 ul in studying the high-pressure phase diagram of the itinerant helimagnet
  MnSi.[3] We now combined Larmor diffraction with conventional diffraction
  measurements to investigate the pressure-temperature phase diagram of URu
 2Si2 up to 20 kbar. URu2Si2 offers a further spectacular example for the p
 resence of unconventional phases in the vicinity of antiferromagnetism. In
  this compound\, antiferromagnetism (AF) is replaced below approximately 5
  kbar by the mysterious “hidden order” (HO) and unconventional superco
 nductivity. Our measurements allow the simultaneous observation of magneti
 c order and changes in the a- and c-axis lattice constants across the phas
 e transitions. The results contain clear indications of a first-order tran
 sition and strong differences between the AF phase and the HO phase in the
  coupling to the lattice\, questioning simple models of coupled order para
 meters.\n\n\n[1] P. G. Niklowitz et al.\; Phys. Rev. B 77\, 115135 (2008)\
 n[2] S. Mühlbauer\, P. G. Niklowitz\, et al.\; Nucl. Inst & Methods in Ph
 ys. Res. A 586\, 77 (2008)\n[3] C. Pfleiderer\, P. Böni\, T. Keller\, U. 
 K. Rößler\, and A. Rosch\; Science 316\, 1871 (2007)\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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