Self-organized magnon condensation in quasi-one-dimensional edge-shared cuprates without external magnetic field

Multimagnon bound states were predicted nearly a century ago and have since been a key topic in condensed matter physics due to their intriguing quantum properties. However, their realization in natural materials remains elusive, especially in low-dimensional quantum magnets, where stabilizing them is particularly challenging due to the traditionally required extremely high external magnetic fields near or below presently available experimentally achieved fields using pulsed techniques in spite of corresponding resolution problems. However, these difficulties may be circumvented considering the much easier and convenient experimental case of ambient external magnetic fields. Therefore, we introduce a mechanism that enables the stabilization of multimagnon bound states in quasi-one-dimensional edge-shared cuprates. Our theoretical framework, supported by numerical simulations and experimental data, demonstrates that small antiferromagnetic interchain couplings act as effective internal magnetic fields, promoting a collinear antiferromagnetic order and enabling magnon condensation even at zero external field. This intrinsic stabilization mechanism eliminates the need for high external fields, offering a platform that is more accessible for experimental realization. We validate this concept by applying it to representative materials such as <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>Li</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi>CuO</a:mi><a:mn>2</a:mn></a:msub></a:mrow><a:mo>,</a:mo><a:mo> </a:mo><a:mrow><a:msub><a:mi>Ca</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi mathvariant="normal">Y</a:mi><a:mn>2</a:mn></a:msub><a:mi>Cu</a:mi><a:msub><a:mrow/><a:mn>5</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mn>10</a:mn></a:msub></a:mrow><a:mo>,</a:mo><a:mo> </a:mo><a:msub><a:mi>LiCuSbO</a:mi><a:mn>4</a:mn></a:msub></a:math>, and <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:msub><d:mi>PbCuSO</d:mi><d:mn>4</d:mn></d:msub></d:math>(<e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:msub><e:mrow><e:mi>OH</e:mi><e:mo>)</e:mo></e:mrow><e:mn>2</e:mn></e:msub></e:math>. Beyond its experimental feasibility, this mechanism could drive advancements in magnon-based quantum computing, low-power spintronic devices, and high-speed magnonic circuits. Moreover, our findings reveal that small interchain and/or interlayer couplings can generally unlock previously overlooked magnetic phenomena, redefining the nature of magnetically ordered states and expanding the frontiers of quantum magnetism.