一維反鐵磁海森堡自旋鏈上spinon的安德森局域化最終報告

李世燕

摘 要：安德森局域化是物理學中的一個基本現象，最初是安德森提出在晶體中電子受到雜質散射由于散射路徑的相干導致電導完全消失，這完全來源于電子的波動特性，后來在其他各種波，如，光、微波、超聲波，甚至是冷原子體系中都觀察到安德森局域化現象。在晶體中，除電子外，還可能存在各種各樣的磁激發準粒子，但是對于這些磁性準粒子的安德森局域化研究幾乎沒有。我們測量了苯甲酸銅Cu（C6H5COO）2·3H2O這個一維反鐵磁海森堡鏈單晶的極低溫比熱和熱導率，發現一直到50 mK的極低溫，spinon磁性準粒子對比熱都有一個恒定的線性貢獻項Cs/T，但是其熱導率的線性貢獻項ks/T只保持不變到300 mK。在300 mK以下，ks/T迅速減小，到100 mK以下就基本消失了。實驗結果是spinon安德森局域化的一個較強的證據，為在凝聚態物理中研究安德森局域化現象開辟了一個新的窗口。

關鍵詞：反鐵磁自旋鏈 自旋子 熱導率 安德森局域化

Abstract：Anderson localization is a general phenomenon of wave physics， which stems from the interference between multiple scattering paths. It was originally proposed for electrons in a crystal， but later was also observed for light， microwaves， ultrasound， and ultracold atoms. Actually， in a crystal， besides electrons there may exist other quasiparticles such as magnons and spinons. However the search for Anderson localization of these magnetic excitations is very rare so far. Here we report the first observation of spinon localization in copper benzoate， an ideal compound of spin-1/2 antiferromagnetic Heisenberg chain， by ultra-low-temperature thermal conductivity and specific heat measurements. We find that the spinons thermal conductivity ks manifests linear temperature dependence down to 300 mK. Below 300 mK， ks/T decreases rapidly and vanishes at about 100 mK， while the spinon specific heat Cs displays linear temperature dependence all the way down to 50 mK. This result is a clear evidence for Anderson localization of spinons in one-dimensional spin chain. Our finding opens a new window for studying such a fundamental phenomenon in condensed matter physics.

Key Words：Anitferromagnetic spin chain； Spinon； Thermal conductivity； Anderson localization

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