标题： 时间反演对称性破缺在微米级单晶 Sr$_2$RuO$_4$器件中的研究 显示英文标题

标题： Time-reversal symmetry breaking in microscopic single-crystal Sr$_2$RuO$_4$ devices

摘要： 时间反演对称性破缺的超导态是一种典型的非常规量子态。 在约瑟夫森结中，时间反演对称性破缺会体现在超电流干涉图样中，表现为临界电流在输运方向和磁场方向同时反转时保持不变，即 $I_\text{c+}(H) = I_\text{c-}(-H)$。 到目前为止，此类系统已在通过外部磁场和静电门控精心调节的弱连接介质中实现，其中超导性被注入到人为构建的弱连接介质中。 在这项工作中，我们报告了在自发形成的无故意构建弱连接的约瑟夫森结中观察到的时间反演对称性破缺现象。 这在 Sr$_2$RuO$_4$的超高纯度单晶微结构中得以实现，这是一种具有多分量序参量的非常规超导体。 在这里，约瑟夫森效应在超导畴壁处内在地出现，此时简并态部分重叠。 除了违反 $I_\text{c+}(H) = I_\text{c-}(-H)$之外，我们还发现了丰富的奇异输运现象，包括在整个干涉图样中呈现的超电流二极管效应、偏离 $\Phi_0$ 的双通道临界电流振荡、分数阶夏皮罗步及具有高度不对称临界电流的可切换双稳态。 我们的发现直接证明了未应变 Sr$_2$RuO$_4$中的 TRSB，并揭示了畴壁约瑟夫森结的潜力，这种结可以在任何配对对称性由多分量序参量描述的超导体中自发出现。 显示英文摘要

摘要： Time-reversal symmetry breaking superconductivity is a quintessential unconventional quantum state. In Josephson junctions, time-reversal symmetry breaking manifests itself in the supercurrent interference pattern as the invariance of the critical current under the reversal of both transport and magnetic field directions, i.e., $I_\text{c+}(H) = I_\text{c-}(-H)$. So far, such systems have been realized in devices where superconductivity is injected into a deliberately constructed weak link medium, usually carefully tuned by external magnetic fields and electrostatic gating. In this work, we report time-reversal symmetry breaking in spontaneously emerging Josephson junctions without intentionally constructed weak links. This is realized in ultra-pure single-crystal microstructures of Sr$_2$RuO$_4$, an unconventional superconductor with a multi-component order parameter. Here, the Josephson effect emerges intrinsically at the superconducting domain wall, where the degenerate states partially overlap. In addition to violating $I_\text{c+}(H) = I_\text{c-}(-H)$, we find a rich variety of exotic transport phenomena, including a supercurrent diode effect present in the entire interference pattern, two-channel critical current oscillations with a period that deviates from $\Phi_0$, fractional Shapiro steps, and current-switchable bistable states with highly asymmetric critical currents. Our findings provide direct evidence of TRSB in unstrained Sr$_2$RuO$_4$ and reveal the potential of domain wall Josephson junctions, which can emerge in any superconductor where the pairing symmetry is described by a multi-component order parameter.