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Heavy fermion behavior without magnetism in ThCr2Si2-type KNi2Se2

Event Details

Event Dates: 

Thursday, September 11, 2014 - 12:00pm

Seminar Location: 

  • Duane Physics Room D142

Speaker Name(s): 

Jamie Neilson

Speaker Affiliation(s): 

Colorado State University
Seminar Type/Subject

Scientific Seminar Type: 

  • Condensed Matter Seminar

Event Details & Abstract: 

Materials with the ThCr2Si2-type structure host myriad examples of many-body physics, including high-temperature superconductivity and heavy fermion behavior. In these compounds, the emergence of the collective electronic state frequently occurs near a magnetic instability, suggesting that magnetic fluctuations underlie the electronic phenomena. However, there is evidence for similar many-body physics in the structurally related, but non-magnetic compounds, KN2S2 and KNi2Se2. From the analysis of low-temperature synchrotron X-ray diffraction and neutron total scattering data as well as vibrational spectroscopy, there are spatially aperiodic charge density wave fluctuations that disappear on cooling, in contrast to known charge density wave materials. Along with this unusual increase in local symmetry, there is negative thermal expansion and enhancement of the electronic band mass below T~15 K, with superconductivity emerging below T ~1 K. These findings demonstrate that collective electronic phenomena occur in ThCr2Si2-type materials without a direct proximity to localized magnetism. Furthermore, these results highlight the importance in understanding charge fluctuations and their hybridization in driving the emergence of coherent or many-body electronic states, akin to localized magnetism associated with heavy fermion behavior.