Spintronic devices, by harnessing the spin degree of freedom, are expected to outperform charge-based devices in terms of energy efficiency and speed of operation. The use of an electric field to control spin at room temperature has been pursued for decades. A major hurdle that has contributed to the slow progress in this regard is the dilemma between effective control and strong spin relaxation. For example, in a Rashba/Dresselhaus material with strong spin–orbit coupling, although the internal magnetic field could be substantial enough to effectively control spin precession, often, the spin-relaxation time becomes extremely short as a consequence of Dyakonov–Perel scattering. To address this, a persistent spin helix has been proposed in systems with SU(2) symmetry. Here we show the discovery of the persistent spin helix in an organic–inorganic hybrid ferroelectric halide perovskite whose layered nature makes it intrinsically like a quantum well. We demonstrate that the spin-polarized band structure is switchable at room temperature via an intrinsic ferroelectric field. We reveal valley–spin coupling through a circular photogalvanic effect in single-crystalline bulk crystals. The favoured short spin helix wavelength (three orders of magnitude shorter than in III–V materials), room-temperature operation and non-volatility make the hybrid perovskite an ideal platform for understanding symmetry-tuned spin dynamics, towards designing practical spintronic materials and devices that can resolve the control-relaxation dilemma.

自旋电子器件通过利用自旋自由度，有望在能源效率和运行速度方面优于基于电荷的器件。几十年来，人们一直在追求使用电场来控制室温下的自旋。导致这方面进展缓慢的一个主要障碍是有效控制和强自旋松弛之间的困境。例如，在具有强自旋-轨道耦合的 Rashba/Dresselhaus 材料中，虽然内部磁场可能足够大以有效控制自旋进动，但由于 Dyakonov-Perel 散射，自旋弛豫时间通常会变得非常短。为了解决这个问题，已经在具有 SU(2) 对称性的系统中提出了一个持久的自旋螺旋。在这里，我们展示了在有机-无机杂化铁电卤化物钙钛矿中发现的持久自旋螺旋，其层状性质使其本质上类似于量子阱。我们证明了自旋极化能带结构在室温下可通过本征铁电场进行切换。我们通过单晶块状晶体中的圆形光电效应揭示了谷-自旋耦合。受青睐的短自旋螺旋波长（比 III-V 材料短三个数量级）、室温操作和非挥发性使混合钙钛矿成为理解对称调谐自旋动力学、设计实用自旋电子材料和器件的理想平台这可以解决控制松弛困境。