Research: Quadrupole Order and Fluctuations

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		Ferroquadrupole order, in which local atomic sites develop identically-oriented spontaneous quadrupole moments, provides a specific realization of electronic nematic order. Materials that harbor quadrupolar order can therefore provide deep insights to open questions about the roles played by nematic fluctuations in a wide range of strongly correlated quantum materials, including effects arising from interactions with the lattice, with conduction electrons, and with the disorder that is implicit in chemically-substituted materials. By identifying suitable longitudinal and transverse effective fields for such quadrupole ordered states, we can measure the quadrupole susceptibility, and, via application of the transverse fields, drive such systems through a quantum phase transition. The divergence of the quadrupole strain susceptibility also provides possibilities for interesting applications. Figure illustrates the crystal structure of TmVO4, an architypal material that undergoes such a ferroquadrupolar phase transition. The Tm ions (purple spheres) develop a spontaneous quadrupole moment (projected onto basal plane) below 2.15 K. (Figure courtesy Yuntian Li.)
Publications
Key publications:
Realization of giant elastocaloric cooling at cryogenic temperatures in TmVO4 via a strain load/unload technique Giant elastocaloric effect at low temperatures in TmVO4 and implications for cryogenic cooling Disorder-induced local strain distribution in Y-substituted TmVO4 The nematic susceptibility of the ferroquadrupolar metal TmAg2 measured via the elastocaloric effect Elastocaloric signatures of symmetric and antisymmetric strain-tuning of quadrupolar and magnetic phases in DyB2C2 Field-tuned ferroquadrupolar quantum phase transition in the insulator TmVO4
Additional publications:
Role of magnetic ions in the thermal Hall effect of the paramagnetic insulator TmVO4 Nuclear magnetic resonance studies in a model transverse field Ising system Spin Echo, Fidelity, and the Quantum Critical Fan in TmVO4 Second order Zeeman interaction and ferroquadrupolar order in TmVO4 Anisotropic nematic fluctuations above the ferroquadrupolar transition in TmVO4 Lattice dynamics, crystal-field excitations, and quadrupolar fluctuations of YbRu2Ge2 Divergence of the quadrupole-strain susceptibility of the electronic nematic system YbRu2Ge2 Electronic structure of the quadrupolar ordered heavy-fermion compound YbRu2Ge2 measured by angle-resolved photoemission
PhD Theses
Elliot Rosenberg: Multipolar order and fluctuations in TmAg2 and YbRu2Ge2 Matthew Sorensen: Measurement of electric quadrupole and magnetic octupole susceptibilities of certain cubic praesodymium-containing compounds
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Fisher Research Group Geballe Laboratory for Advanced Materials Dept. of Applied Physics Stanford University CA 94305-4045

Last Updated: Nov 24th 2024

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