日本东京大学Satoru Nakatsuji研究团队的一项最新研究揭示了烧绿石晶格上的自旋轨道液态和液-气变磁转变。这一研究成果于2022年12月1日发表在国际顶尖学术期刊《自然—物理学》上。
该研究组展示了在Pr2Zr2O7中的相反情况，由于自旋和轨道之间的相互作用，轨道简并度保持在毫开尔文范围内。Pr2Zr2O7是一种多极自旋冰，具有强烈局域化4f电子，处于偶数组态，产生携带横向四极矩和纵向偶极矩的非Kramers双重态。
他们对Pr2Zr2O7超纯单晶的研究发现了非Kramers双重态自旋-轨道量子动力学增强的全面证据。这种动态Jahn–Teller效应包裹于液体-气体变磁转变，这是自旋冰的特征，伴随着强烈的晶格软化。这些行为表明，在低温和低磁场下，烧绿石晶格上形成了自旋-轨道液态。
研究人员表示，具有简并电子轨道的晶体结构，对于提升简并性的晶格畸变是不稳定的。尽管这些Jahn–Teller畸变对磁性有深远的影响，但由于能量尺度的分离，通常不受磁有序起始的影响。
附：英文原文
Title: Spin–orbital liquid state and liquid–gas metamagnetic transition on a pyrochlore lattice
Author: Tang, Nan, Gritsenko, Yulia, Kimura, Kenta, Bhattacharjee, Subhro, Sakai, Akito, Fu, Mingxuan, Takeda, Hikaru, Man, Huiyuan, Sugawara, Kento, Matsumoto, Yosuke, Shimura, Yasuyuki, Wen, Jiajia, Broholm, Collin, Sawa, Hiroshi, Takigawa, Masashi, Sakakibara, Toshiro, Zherlitsyn, Sergei, Wosnitza, Joachim, Moessner, Roderich, Nakatsuji, Satoru
Issue&Volume: 2022-12-01
Abstract: Crystal structures with degenerate electronic orbitals are unstable towards lattice distortions that lift the degeneracy. Although these Jahn–Teller distortions have profound effects on magnetism, they are typically unaffected by the onset of magnetic ordering because of a separation in energy scales. Here we show the contrary case in Pr2Zr2O7, where orbital degeneracy remains down to the millikelvin range due to an interplay between spins and orbitals. Pr2Zr2O7 is a multipolar spin ice with strongly localized 4f electrons in an even-number configuration, giving rise to a non-Kramers doublet that carries transverse quadrupolar and longitudinal dipolar moments. Our study of ultrapure single crystals of Pr2Zr2O7 finds comprehensive evidence for enhanced spin–orbital quantum dynamics of the non-Kramers doublet. This dynamical Jahn–Teller effect is encapsulated by the liquid–gas metamagnetic transition that is characteristic of spin ice being accompanied by strong lattice softening. This behaviour suggests that a spin–orbital liquid state forms on the pyrochlore lattice at low temperatures and low magnetic fields.
DOI: 10.1038/s41567-022-01816-4
Source: https://www.nature.com/articles/s41567-022-01816-4