Contrasting c-axis and in-plane uniaxial stress effects on superconductivity and stripe order in La1.885Ba0.115CuO4

Abstract

The cuprate superconductor La_2-x Ba _x CuO₄ (LBCO) near x = 0.125 is a striking example of intertwined electronic orders, where 3D superconductivity is anomalously suppressed, allowing spin and charge stripe order to develop. Understanding this interplay remains a key challenge in cuprates, highlighting the necessity of external tuning for deeper insight. While in-plane uniaxial stress enhances superconductivity and suppresses stripe order, the effects of c-axis compression remains largely unexplored. Here, we use muon spin rotation (μSR) and AC susceptibility with an in situ piezoelectric stress device to investigate the spin-stripe order and superconductivity in LBCO-0.115 under c-axis compression. The measurements reveal a gradual suppression of the superconducting transition temperature (T _c) with increasing c-axis stress, in stark contrast to the strong enhancement observed under in-plane stress. We further show that while in-plane stress rapidly reduces both the magnetic volume fraction (V _m) and the spin-stripe ordering temperature (T _so), c-axis compression has no effect, with V _m and T _so exhibiting an almost unchanged behavior up to the highest applied stress of 0.21 GPa. These findings demonstrate a strong anisotropy in stress response.

Keywords: Magnetic properties and materials; Superconducting properties and materials.

Fig. 1. Experimental schematic and anisotropic response to uniaxial stress.

a Schematic representation of stripe order stacking along the c-axis in LBCO, showing charge and spin stripe modulation within CuO₂ layers and their alternating 90^∘ rotation between adjacent layers. The blue and green arrows indicate the in-plane (at an angle of 30^∘ to the Cu-O bond direction, denoted as a-axis) and c-axis compressive stress, respectively. b The uniaxial stress sample holder used for the μSR experiments. Backside view of the sample showing the AC susceptibility coil and the Cernox temperature sensors (left panel). View from the direction of the incoming muon beam (right panel). Hematite pieces masking the holder frame exposed to the muon beam. c–e c-axis (hollow symbols) and in-plane (solid symbols) uniaxial stress dependence of 3D superconducting transition temperatures T_c,3D (c) derived from AC susceptibility measurements, spin-stripe ordering temperatures (T_so) (d) derived from weak transverse field μSR experiments and the magnetically ordered fraction V_m at base-T ≃ 0.7 K (e) derived from zero-field μSR experiments for La_1.885Ba_0.115CuO₄. The results for the in-plane strain are taken from our previous work ref. . Error bars represent the uncertainty from temperature resolution in T_c,3D and T_so, and fitting uncertainty in V_m. The small difference in zero-stress T_c,3D and T_so between the in-plane and c-axis datasets arises from measurements on two separate LBCO crystals with nominally the same doping (x = 0.115), but likely differing slightly in actual Ba content – a known sensitivity near the 1/8-anomaly.

Fig. 2. Superconducting response under c-axis stress.

a The temperature dependence of the AC diamagnetic susceptibility (${\chi }_{\mathrm{AC}}^{\prime }$) for La_1.885Ba₀. 115CuO₄ under varying c-axis compressive stress. The arrow indicates the bulk 3D superconducting transition temperature (T_c,3D), defined as the point where ${\chi }_{\mathrm{AC}}^{\prime }=-0.5$. b Schematic temperature-doping (x) phase diagram of LBCO near x = 0.125, illustrating the contrasting effects of uniaxial stress on superconductivity. The suppression of T_c,3D under c-axis compression is shown for LBCO-0.115, while the pronounced enhancement of T_c,3D under in-plane stress is depicted for both LBCO-0.115 and LBCO-0.135. The dashed line represents the anticipated superconducting phase boundary under in-plane stress, shown as a qualitative guide, based on the experimental data on x = 0.115, 0.135^,.

Fig. 3. Spin-stripe order under c-axis stress.

a Weak transverse field μSR spectra of La_1.885Ba_0.115CuO₄ at 40 K under zero stress and at base-T ≃ 0.7 K under varying c-axis compressive stress. The error bars are the standard error of the mean (s.e.m.) in about 10⁶ events. b Temperature dependence of the magnetically ordered fraction (V_m) under different stresses, extracted from weak transverse field μSR data in (a). The error bars represent the standard deviation of the fit parameters. c Zero-field μSR spectra at 50 K under zero stress and T ≃ 0.7 K under different c-axis stresses. The error bars are the standard error of the mean (s.e.m.) in about 10⁶ events. d Temperature dependence of internal fields under various stresses, derived from zero-field μSR data. Solid and empty symbols indicate the values extracted for forward-backward and left-right detector sets (see the Supplementary Note 1 and the Supplementary Fig. S1), respectively.

Fig. 4. Stress-strain curve for LBCO-0.115.

The force sensor output is proportional to stress, while the displacement sensor reading is proportional to strain. The dashed lines represent linear fits to the data across the entire applied stress region. The inset shows the distorted CuO₆ octahedron in the low-temperature tetragonal structure.