No observation of chiral flux current in the topological kagome metal ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$

Compounds with kagome lattice usually host many exotic quantum states, including the quantum spin liquid, non-trivial topological Dirac bands and a strongly renormalized flat band, etc. Recently an interesting vanadium based kagome family $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ $(A=\mathrm{K},\mathrm{Rb},\text{or}\mathrm{Cs})$ was discovered, and these materials exhibit multiple interesting properties, including unconventional saddle-point driving charge density wave (CDW) state, superconductivity, etc. Furthermore, some experiments show the anomalous Hall effect which inspires us to believe that there might be some chiral flux current states. Here we report scanning tunneling measurements by using spin-polarized tips. Although we have observed clearly the $2a_0\times 2a_0$ CDW and $4a_0$ stripe orders, the well-designed experiments with refined spin-polarized tips do not reveal any trace of the chiral flux current phase in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ within the limits of experimental accuracy. No observation of the local magnetic moment in our experiments may put an upper bound constraint on the magnitude of magnetic moments induced by the possible chiral loop current which has a time-reversal symmetry breaking along $c$ axis in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$.

Figure 1

(a) Schematic illustration of the spin-polarized STM measurements. (b) Atomically resolved topography of the top Sb surface ($V_{\mathrm{set}}=20$ mV, $I_{\mathrm{set}}=100$ pA). (c) Enlarged view of the topography in the area of black square in (b). The theoretically proposed hexagonal current loops are shown by blue disks, while the triangular current loops are marked by red disks. (d) Fourier transform of the topography in (b). The Bragg peaks are marked by circles; spots for the $2\times 2$ CDW order are marked by dashed circles.

Figure 2

(a),(b) Topography of the top Sb surface measured in the same area and under the field of $+0.3$ and $-0.3$ T; the tip has been polarized by the magnetic fields of $+2$ ($\uparrow$) and $-2$ T ($\downarrow$), respectively ($V_{\mathrm{set}}=30$ mV, $I_{\mathrm{set}}=100$ pA). (c) Spin-difference topography between the topographies shown in (a) and (b). (d),(e) Tunneling spectra taken at the centers of hexagonal holes marked by dots in (a) and (b), respectively ($V_{\mathrm{set}}=30$ mV, $I_{\mathrm{set}}=100$ pA). (f) Spin-difference spectra between the tunneling spectra taken at the same positions but with different tip spin directions and under different magnetic fields. The curves in (d) to (f) are offset for clarity.

Figure 3

(a)–(c) Differential conductance mappings measured at $E=20$ meV in the same area ($V_{\mathrm{set}}=50$ mV, $I_{\mathrm{set}}=100$ pA). The magnetic field and the spin polarization of the tips are different in these configurations. (d) to (f) FT patterns of the differential conductance mappings in (a) to (c), respectively. (g),(h) Spin-difference differential conductance mappings derived by the subtraction of (b) from (a) and (c) from (b), respectively. (i),(j) FT patterns of spin-difference differential conductance mappings in (g) and (h), respectively. (k) Intensities of scattering spots corresponding to the $2\times 2$ CDW order in the FT pattern shown in (d) to (f).

Figure 4

(a),(b) Differential conductance mappings measured at $E=20$ meV in the same area ($V_{\mathrm{set}}=30$ mV, $I_{\mathrm{set}}=100$ pA). The magnetic field and the spin polarization of the tips are different in these configurations. (c) Spin-difference differential conductance mapping derived by the subtraction of (b) from (a). (d),(e) FT patterns of the differential conductance mappings in (a) and (b), respectively. (f) Intensities of the FT patterns of the $2\times 2$ CDW order shown in (d) and (e).