Experimental signature of the attractive Coulomb force between positive and negative magnetic monopoles in spin ice
Experimental signature of the attractive Coulomb force between positive and negative magnetic monopoles in spin ice
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DOI：
10.1038/nphys3704
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发表时间：
2016-07-01
期刊：
影响因子：
19.6
通讯作者：
Bramwell, S. T.
中科院分区：
文献类型：
--
作者：
Paulsen, C.;Giblin, S. R.;Bramwell, S. T.
随着外加电场的平方根呈指数增长的非欧姆电流在热离子场发射（肖特基效应）(1)、电解质（第二维恩效应）(2)和半导体（普尔-弗伦克尔效应）(3)中众所周知。这是正电荷和负电荷之间的吸引库仑力的普遍特征，当电荷被施加的电场的力驱动到相反的方向时，就会显示出来。在这里，我们将热淬(4)应用于自旋冰（5-11），以制备毫开尔文温度下正、负涌现磁单极子（12-16）束缚对的亚稳居群。我们发现磁场的应用导致磁电流的普遍指数根场增长，从而证实了磁单极子准粒子之间的微观库仑力，并建立了普尔-弗伦克尔效应的磁模拟。在300 mK以上的温度下，动力学单极平衡的逐渐恢复导致非欧姆电流平滑地演变为磁单极子的高场维恩效应(2)，这一点通过与最近关于自旋冰维恩效应的严格理论的比较得到了证实（17,18）。我们的结果将指数根场形式的普遍性扩展到磁性中，并说明了涌现粒子动力学在描述复杂系统中的远平衡响应方面的能力。
A non-Ohmic current that grows exponentially with the square root of applied electric field is well known from thermionic field emission (the Schottky effect)(1), electrolytes (the second Wien effect)(2) and semiconductors (the Poole-Frenkel effect)(3). It is a universal signature of the attractive Coulomb force between positive and negative electrical charges, which is revealed as the charges are driven in opposite directions by the force of an applied electric field. Here we apply thermal quenches(4) to spin ice(5-11) to prepare metastable populations of bound pairs of positive and negative emergent magnetic monopoles(12-16) at millikelvin temperatures. We find that the application of a magnetic field results in a universal exponential-root field growth of magnetic current, thus confirming the microscopic Coulomb force between the magnetic monopole quasiparticles and establishing a magnetic analogue of the Poole-Frenkel effect. At temperatures above 300 mK, gradual restoration of kinetic monopole equilibria causes the non-Ohmic current to smoothly evolve into the high-field Wien effect(2) for magnetic monopoles, as confirmed by comparison to a recent and rigorous theory of the Wien effect in spin ice(17,18). Our results extend the universality of the exponential-root field form into magnetism and illustrate the power of emergent particle kinetics to describe far-from-equilibrium response in complex systems.