Cu/Fe High Temperatue Superconductors
In collaboration with Prof. P. Canfield - AMES- National Institute of Advanced Industrial Science and Technology (AIST), Japan &
Novel 'electronic liquid crystal' phases have long been predicted for correlated electronic materials, especially those where the intense correlations generate the highest temperature superconductivity. By using direct atomic-scale visualization we have discovered several of these phases including the smectic (DW) state in CuHTS (Science 295, 466 (2002); Nature 430 , 1001 (2004); Science 315, 1380 (2007)); the nematic phase in CuHTS (Nature 466, 374 (2010); Science 333, 426 (2011)); the famous nematic phase of FeHTS (Science 327, 181 (2010); Science 357, 75 (2017)) the Cooper-Pair Density Wave (PDW) state in CuHTS (Nature 532, 343 (2016)).
Fig. 5 A,B The characteristic DW observed in virtually all CuHTS system has very short correlation lengths and appears to be lattice commensurate and 4a0 period.
Having established the existence of these broken-symmetry electronic liquid crystal states, the challenge now is to understand their relationship to the HTS.
a) Recently the effects of quenched disorder on such a two-dimensional DW state have been discovered. While long range order of a unidirectional incommensurate DW cannot exist in the presence of quenched disorder, its short-range remnant survives up to a certain critical disorder strength but in the form of a Q=0 broken rotational-symmetry state. This state was dubbed a vestigial nematic (VN). We plan to search for the VN state by determining if energy scale of nematic state is the same as that of the DW state throughout phase diagram.
b) Intense theoretical interest has emerged in whether a PDW state is actually the competing phase to superconductivity in CuHTS. Thus, we plan to test if the reported charge modulation phenomenology is actually a secondary effect of a fundamental PDW state. We will image conventional density-of-states N(r,E) of charge modulations, simultaneously with imaging of Josephson IC(r) to visualize the PDW. Comparison between the first ever such pairs of N(r,E):IC(r) images will be highly revealing as to which state is fundamental.