Using Uniaxial Stress to Probe the Relationship between Competing Superconducting States in a Cuprate with Spin-stripe Order

We report muon spin rotation and magnetic susceptibility experiments on in-plane stress effects on the static spin-stripe order and superconductivity in the cuprate system ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x{\mathrm{CuO}}_4$ with $x=0.115$. An extremely low uniaxial stress of $\sim 0.1\mathrm{GPa}$ induces a substantial decrease in the magnetic volume fraction and a dramatic rise in the onset of 3D superconductivity, from $\sim 10$ to 32 K; however, the onset of at-least-2D superconductivity is much less sensitive to stress. These results show not only that large-volume-fraction spin-stripe order is anticorrelated with 3D superconducting coherence but also that these states are energetically very finely balanced. Moreover, the onset temperatures of 3D superconductivity and spin-stripe order are very similar in the large stress regime. These results strongly suggest a similar pairing mechanism for spin-stripe order and the spatially modulated 2D and uniform 3D superconducting orders, imposing an important constraint on theoretical models.

Figure 1

(a) The schematic temperature-doping phase diagram of ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x{\mathrm{CuO}}_4$. The arrow indicates the present doping value. The inset illustrates the orthogonal stripe directions between neighboring layers. The various phases in the phase diagram are denoted as follows: charge-stripe order (CO), low-temperature orthorhombic (LTO), low-temperature tetragonal (LTT), spin-stripe order (SO), and 3D superconductivity (SC). (b) Illustration of a domain of spin-stripe and charge-stripe orders for a layer of LBCO, indicating the periods of the charge (4a) and spin (8a) modulations. (c) The temperature dependence of the zero-field-cooled magnetic susceptibility for ${\mathrm{La}}_{1.885}{\mathrm{Ba}}_{0.115}{\mathrm{CuO}}_4$. (d) The uniaxial stress sample holder used for the $\mu \mathrm{SR}$ experiments.

Figure 2

(a) The temperature dependence of the (dia)magnetic susceptibility for ${\mathrm{La}}_{1.885}{\mathrm{Ba}}_{0.115}{\mathrm{CuO}}_4$ recorded at ambient (left axis) and under various degrees of compressive stress (right axis). Arrows mark the onset temperature $T_{c,\mathrm{ons}}$ and the temperature $T_{c,\mathrm{mid}}$ at which ${\chi }_{\mathrm{dc}}=-0.5$. (b) The temperature dependence of the in-plane resistivity (without stress). Electrodes and contacts were placed on the sample as schematically shown in the inset. (c) Schematic temperature-doping phase diagram, indicating the enhancement of 3D SC critical temperature $T_{c,3\mathrm{D}}$ under stress for the LBCO $x=0.115$ sample. The value of the $T_{c,3\mathrm{D}}$ under maximum stress is quite similar to the optimal value of SC critical temperature observed in LBCO. The dashed line represents the hypothetical SC phase boundary expected under applied stress in the broader region around $1/8$ doping.

Figure 3

(a) The weak-TF $\mu \mathrm{SR}$ spectra recorded for ${\mathrm{La}}_{1.885}{\mathrm{Ba}}_{0.115}{\mathrm{CuO}}_4$ at the base temperature $T=3\mathrm{K}$ under various degrees of compressive stress. (b) The zero-field $\mu \mathrm{SR}$ spectra recorded at the base temperature under various stresses. (c) The temperature dependence of the magnetically ordered volume fraction recorded under various stresses, as deduced from the TF $\mu \mathrm{SR}$ data shown in panel (a).

Figure 4

(a) The compressive stress dependence of the SC transition temperatures and of static spin-stripe order temperature $T_{\mathrm{so}}$ in LBCO $x=0.115$. Black arrow marks the critical stress value ${\sigma }_{\mathrm{cr}}$, above which a sharp 3D SC transition is established. (b) The stress dependence of the base-$T$ value ($T=3\mathrm{K}$) of the magnetically ordered fraction $V_m$ and the value of the internal magnetic field $B_{\mathrm{int}}$. The SC fraction is only schematic.