Uniaxial stress study of spin and charge stripes in La${}_{1.875}$Ba${}_{0.125}$CuO${}_4$ by ${}^{139}$La NMR and ${}^{63}$Cu NQR

We study the response of spin and charge order in single crystals of La${}_{1.875}$Ba${}_{0.125}$CuO${}_4$ to uniaxial stress, through ${}^{139}$La nuclear magnetic resonance (NMR) and ${}^{63}$Cu nuclear quadrupole resonance (NQR), respectively. In unstressed La${}_{1.875}$Ba${}_{0.125}$CuO${}_4$, the low-temperature tetragonal structure onsets below $T_{\text{LTT}}=57$K, while the charge order and the spin order transition temperatures are $T_{\text{CO}}=54$K and $T_{\text{SO}}=37$K, respectively. We find that uniaxial stress along the [110] lattice direction strongly suppresses $T_{\text{CO}}$ and $T_{\text{SO}}$, but has little effect on $T_{\text{LTT}}$. In other words, under stress along [110] a large splitting ($\approx 21$K) opens between $T_{\text{CO}}$ and $T_{\text{LTT}}$, showing that these transitions are not tightly linked. On the other hand, stress along [100] causes a slight suppression of $T_{\text{LTT}}$ but has essentially no effect on $T_{\text{CO}}$ and $T_{\text{SO}}$. Magnetic field $H$ along [110] stabilizes the spin order: the suppression of $T_{\text{SO}}$ under stress along [110] is slower under $H\parallel [110]$ than $H\parallel [001]$. We develop a Landau free energy model and interpret our findings as an interplay of symmetry breaking terms driven by the orientation of spins.