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Phase separation and suppression of critical dynamics at quantum phase transitions of MnSi and (Sr1−xCax)RuO3

Abstract

Quantum phase transitions (QPTs) at zero temperature are generally studied by means of pressure or composition tuning. Volume-integrated probes such as neutron and magnetization measurements, as well as pressure uncertainties in NMR studies using powder specimens, however, have limited the characterization of magnetism and detection of discontinuous changes at QPTs. Overcoming these limitations, we carried out muon spin relaxation measurements that have a unique sensitivity to volume fractions of magnetically ordered and paramagnetic regions, and studied QPTs from itinerant helimagnet or ferromagnet to paramagnet transitions in MnSi (single crystal; varying pressure) and (Sr1−xCax)RuO3 (ceramic specimens; varying x). Our results provide the first clear evidence that both cases are associated with phase separation and suppression of dynamic critical behaviour, reveal slow dynamics of the ‘partial order’ diffuse spin correlations in MnSi above the critical pressure and suggest the possibility that a majority of QPTs in correlated electron systems involve first-order transitions and/or phase separation.

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Figure 1: Temperature–pressure phase diagram and envelope of μSR oscillation spectra of MnSi.
Figure 2: μSR results on the volume fraction, relaxation rate and spin precession frequency in MnSi.
Figure 3: ZF μSR and magnetization results in (Sr1−xCax)RuO3.
Figure 4: Free-energy profile for the first- and second-order phase transitions.

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Acknowledgements

We acknowledge financial support from NSF DMR-05-02706 (Material World Network, Inter-American Materials Collaboration program) at Columbia and Kentucky, NSF DMR-01-02752 and CHE-01-11752 at Columbia, NSERC and CIAR (Canada) at McMaster, Brazilian grant CIAM-CNPq 49.2674/2004-3 at CBPF and CIAM-CONICET project 509/20-04-05 at CAB Bariloche, Argentina; technical support from S.R. Kreitzman and K. Satoh and scientific discussions with B. Binz, M. Continentino, S.R. Julian and A.J. Millis.

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Uemura, Y., Goko, T., Gat-Malureanu, I. et al. Phase separation and suppression of critical dynamics at quantum phase transitions of MnSi and (Sr1−xCax)RuO3. Nature Phys 3, 29–35 (2007). https://doi.org/10.1038/nphys488

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