Abstract
Recent findings of anomalous superlinear scaling of low-temperature penetration depth (PD) in several nodal superconductors near putative quantum critical points suggest that the low-temperature PD can be a useful probe of quantum critical fluctuations in a superconductor. On the other hand, cuprates, which are poster child nodal superconductors, have not shown any such anomalous scaling of PD, despite growing evidence of quantum critical points (QCP). Then it is natural to ask when and how can quantum critical fluctuations cause anomalous scaling of PD? Carrying out the renormalization group calculation for the problem of two-dimensional superconductors with point nodes, we show that quantum critical fluctuations associated with a point group symmetry reduction result in nonuniversal logarithmic corrections to the dependence of the PD. The resulting apparent power law depends on the bare velocity anisotropy ratio. We then compare our results to data sets from two distinct nodal superconductors: and . Considering all symmetry-lowering possibilities of the point group of interest, , we find our results to be remarkably consistent with being near a vertical nematic QCP and being near a diagonal nematic QCP. Our results motivate a search for diagonal nematic fluctuations in .
- Received 20 October 2014
- Revised 15 June 2015
DOI:https://doi.org/10.1103/PhysRevB.92.035112
©2015 American Physical Society