Observation of an electronic smectic liquid crystal and its relation with superconductivity in NaAlSi
Christopher Butler1*, Toshiya Ikenobe2, Daigorou Hirai3, Takahiro Yamada4, Hisanori Yamane4, Tetsuo Hanaguri1, Zenji Hiroi2
1CEMS, RIKEN, Wako, Saitama, Japan
2ISSP, University of Tokyo, Tokyo, Japan
3Department of Applied Physics, Nagoya University, Nagoya, Japan
4Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan
* Presenter:Christopher Butler, email:christopher.butler@riken.jp
The compound NaAlSi initially attracted interest because it is a nodal-line semimetal that also exhibits superconductivity. It has an unexpectedly high Tc of about 7 K which, among other properties, fuels speculation that its superconductivity might have an unconventional origin [1,2]. In several prominent unconventional superconductors, the superconductivity is thought to have a strong relationship, either cooperating or competing, with some other order such as magnetic or charge order, or might be enhanced by fluctuations of an underlying order. Using spectroscopic-imaging scanning tunneling microscopy at the cleaved surface of NaAlSi, we discover short-ranged charge stripe order, which would be described as an electronic smectic phase in the language of liquid crystals. We observe some sample-dependence of both the superconductivity and the apparent energy scale of the charge order that suggests a competing relationship between them. We also observe that the superconducting order parameter appears to be spatially modulated by the charge order, and we discuss whether this indicates a Cooper pair density wave state or, perhaps more accurately, a 'Cooper pair liquid crystal'.
[1] H. B. Rhee, S. Banerjee, E. R. Ylvisaker and W. E. Pickett, PRB 81, 245114 (2010).
[2] T. Yamada, D. Hirai, H. Yamane and Z. Hiroi, JPSJ 90, 034710 (2021).
Keywords: Electronic liquid crystals, Superconductivity, Scanning tunneling microscopy