Perovskite Spin Coherence Lasts 2ms at Near Zero

Longitudinal spin relaxation times, or $T_$1, exceeding 2 milliseconds have now been measured in mixed-A-site perovskite crystals using optically detected magnetic resonance. Until now, measurements of $T_$1 in similar perovskite single crystals ranged from tens to hundreds of nanoseconds. This achievement resolves multiple electron and hole spin subensembles, each with varying g-factors, and establishes these crystals as a promising material for quantum information technologies

Rongrong Hu of the TU Dortmund University and colleagues have identified remarkably long spin relaxation times in perovskite crystals, specifically exceeding two milliseconds for holes. Spin relaxation time refers to how long a material can maintain the spin of an electron, a key property for data storage and processing. Resolving multiple distinct spin characteristics within these crystals reveals varied environments for electrons and holes, the charge carriers within the material.

Spin relaxation time is the duration for which a spinning electron, or ‘hole’, maintains its quantum information; imagine a spinning top gradually slowing down and eventually stopping. This property is vital for developing advanced data storage and processing technologies. Rongrong Hu and colleagues resolved multiple distinct spin characteristics within these crystals, revealing that electrons and holes experience varied environments, influenced by tiny, random magnetic fields from atomic nuclei, akin to static on a radio signal disrupting clear reception. These findings establish the crystals as a promising material for quantum applications, but a thorough understanding of the underlying mechanisms is now needed to fully use their potential.

Millisecond spin relaxation and resolved g-factors in mixed-halide perovskite single crystals

Longitudinal spin relaxation times ($T_$1) now exceed 2 milliseconds in mixed-A-site perovskite crystals, representing an improvement of up to three orders of magnitude over previously reported values in similar materials. Prior perovskite single crystal measurements were limited to tens or hundreds of nanoseconds, making millisecond-scale $T_$1 in bulk semiconductors a long-sought achievement. This breakthrough resolves multiple electron and hole spin subensembles, each exhibiting distinct g-factors ranging from 0.5 to 3.6, indicating varied localisation environments within the crystal lattice.

The analysis of magnetic field dependence indicates random nuclear fields of approximately 0.4-0.8 millitesla for electrons and 4-12 millitesla for holes, suggesting carrier hopping between shallow localisation sites occurs over microsecond timescales. These long $T_$1 values, particularly for holes, establish these materials as a promising platform supporting long-lived spin states suitable for quantum information processing and optical spin control. Electron g-factors span 2.9 to 3.6, while hole g-factors range from 0.5 to 1.2, demonstrating a diversity in spin characteristics and varied environments influencing carrier localisation. While these long $T_$1 values demonstrate potential for quantum applications, current measurements are limited to 1.6 Kelvin and do not yet demonstrate sustained coherence at more practical operating temperatures.

Characterising spin dynamics in mixed-halide perovskites via optically detected magnetic resonance

Optically detected magnetic resonance proved key to resolving subtle differences within the perovskite crystals. The technique sensitively measures the spins of electrons and holes, the charge carriers within the material, by detecting their interaction with magnetic fields and light. A laser excites these spins, and the resulting signal is monitored as it responds to applied radio frequencies, revealing information about the spin’s environment and behaviour.

This method allowed the distinction between multiple ‘spin subensembles’, groups of electrons and holes experiencing slightly different conditions within the crystal lattice, and enabled the measurement of their individual properties with high precision. Investigations focused on mixed-cation MAxFA1-xPbI3 single crystals, specifically compositions with x equal to 0.4 and 0.8, utilising this approach. Experiments were conducted at a cryogenic temperature of 1.6 K to enable long spin lifetimes, achieving longitudinal spin relaxation times reaching 2 milliseconds, even for weakly localised carriers.

Millisecond spin coherence mapped within perovskite semiconductor environments

Hybrid perovskite semiconductors are gaining attention as potential building blocks for next-generation quantum devices, offering a unique blend of optical properties and spin characteristics. However, these millisecond-long spin coherence times are currently observed only at extremely low, cryogenic temperatures of 1.6 Kelvin. This reliance on near-absolute zero conditions presents a significant hurdle, as practical quantum technologies demand operation at, or closer to, room temperature.

Achieving millisecond-long spin coherence at 1.6 Kelvin is a valuable step forward, guiding material refinement and optimisation for future quantum technologies. Detailed analysis of electron and hole spins provides a foundation for controlling these materials, even if room-temperature operation remains a distant goal. Mixed-A-site perovskite crystals demonstrate unexpectedly long spin coherence, exceeding previous benchmarks and establishing them as potential materials for quantum technologies. The crystals revealed multiple distinct spin ‘subensembles’, exhibiting varying g-factors, indicating diverse environments influencing electron and hole behaviour. Longitudinal spin relaxation, a measure of how long a spinning electron maintains its quantum information, reached 2 milliseconds at cryogenic temperatures, linked to random nuclear fields and carrier hopping between localised sites.

The research successfully demonstrated millisecond-long spin coherence in mixed-cation MA$x$FA${1-x}$PbI$_3$ single crystals at 1.6 K. This is significant because maintaining spin coherence for extended periods is crucial for processing and storing quantum information. Researchers resolved multiple spin subensembles and measured longitudinal spin relaxation times reaching 2ms, revealing the influence of the material’s environment on spin behaviour. These findings establish these perovskite crystals as a promising platform for exploring solid-state quantum technologies, and further work will focus on optimising the material for improved performance.