Theme 3 colloquium by dr. Christoph Meingast (Karlsruhe Institute of Technology, Germany): 'The fate of superconductivity and charge order in underdoped YBCO under high magnetic fields' (Lecture)

Due to the small coherence lengths, large anisotropies and high critical temperatures cuprate superconductors exhibit extremely strong superconducting fluctuations. High-resolution capacitance dilatometry on YBCO has proven to be particularly useful in studying these fluctuation effects due to large thermal expansion signals compared to the phonon background [1-3].   The superconducting transition at optimal doping was shown to be very well described by 3D-XY phase ordering transition (analogous to the lambda transition in superfluid 4He) [1,2].  For underdoped crystals fluctuations increase and were attributed to anisotropic 3D-XY behavior [3].

Here, we use magnetostriction measurements up to 30 T to investigate how large a magnetic field is necessary to suppress the superconducting transition.  For an oxygen content of x = 6.7 we find that 30 T is far from sufficient to fully suppress the transition.  This is in seemingly stark contrast to previous work claiming an Hc2 of roughly 20-25 T for this doping [4,5].  Further, we see little thermodynamic evidence in the magnetostriction data at 10 K for a field-induced charge-ordering transition [6], suggesting that the entropy associated with charge ordering is small.  Our results are discussed in light of recent report of an unconventional quantum vortex matter ground state surviving to fields beyond 40 T [7].

[1] V. Pasler et al., Phys. Rev. Lett. 81, 1094 (1998).
[2] R. Lortz et al., Phys. Rev. Lett. 91, 207001 (2003).
[3] C. Meingast et al., Phys. Rev. Lett. 86, 1606 (2001).
[4] G. Grissonnanche et al., Nat. Comm. 5, 3280 (2014).
[5] C. Marcenat et al., Nature Comm. 6, 7927 (2015).
[6] J. Chang et al., Nat. Comm. 5, 3280 (2014).
[7] Yu-Te Hsu et al., PNAS (2021) Vol. 118 No. 7 e2021216118.