Limitations of detecting structural changes and time-reversal symmetry breaking in scanning tunneling microscopy experiments

Abstract

The family of kagome superconductors $A$V$_3$Sb$_5$ ($A$=K, Cs, Rb) is an exciting playground for investigating various density waves, unusual superconductivity and a surprising time-reversal symmetry breaking despite the absence of spin magnetism. The origin of time-reversal symmetry breaking has been of particular interest, and conflicting results have been intensely debated. Scanning tunneling microscopy (STM) provided crucial evidence by the observation that apparent chirality associated with the 2 $\times$ 2 charge density wave (CDW) may be modified by the direction of magnetic field, a phenomenon observed in select sample areas in some experiments, but not others. Related to this, Xing et al. investigated the effects of magnetic and electric fields on the 2 $\times$ 2 CDW state and the lattice structure of kagome superconductor RbV$_3$Sb$_5$. They report a $\sim$ 1% change in the in-plane lattice constants, concomitant with the CDW intensities modification, controlled by the field direction. This was interpreted as a rare case of piezomagnetism. Here we show how the apparent magnetic field induced lattice and CDW intensity change is a consequence of two independent experimental artifacts: reconfiguration of atoms at the STM tip apex that alter the amplitudes of CDW modulations, and piezo creep, hysteresis, and thermal drift that artificially distort STM topographs. We find no evidence supporting that magnetic field leads to intrinsic changes in the sample, which challenges reported piezomagnetism.