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arXiv 1306.5073cond-mat.mes-hallcond-mat.dis-nn
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声子强耦合引起的隧穿缺陷对称性约化

Symmetry reduction for tunneling defects due to strong couplings to phonons

P. Nalbach, M. Schechter

摘要:

在非晶态固体中,双能级系统是普遍存在的,并且在诸如纳米机械振荡器、单电子晶体管和超导量子比特的系统中形成主要的噪声源。尽管缺陷与声子耦合,但缺陷隧穿的不稳定性被认为是弱缺陷-声子耦合的标志。这是因为与声子的强耦合导致显著的声子修整,并有效地抑制了二能级隧穿缺陷中的隧穿。在这里,我们确定的动态晶体隧道缺陷强烈耦合到声子纳入我们的描述中的完整的3D几何形状。我们发现,反转对称隧穿是不打扮的声子,而其他隧穿路径打扮的声子,因此,被强烈的缺陷声子耦合抑制。我们提供了晶体隧穿缺陷的线性声学和介电响应函数的强缺陷声子耦合。这允许直接实验测定的缺陷声子耦合。在单个隧穿缺陷中的反转对称隧穿态的挑选是对它们在强无序固体中的低能量激发的主导地位的补充,这是由于大缺陷浓度的缺陷间相互作用的结果。这表明反转对称二能级系统在无序固体的低能性质中起着独特的作用。

英文摘要:

Tunneling two-level systems are ubiquitous in amorphous solids, and form a major source of noise in systems such as nano-mechanical oscillators, single electron transistors, and superconducting qubits. Occurance of defect tunneling despite their coupling to phonons is viewed as a hallmark of weak defect-phonon coupling. This is since strong coupling to phonons results in significant phonon dressing and suppresses tunneling in two-level tunneling defects effectively. Here we determine the dynamics of a crystalline tunnelling defect strongly coupled to phonons incorporating the full 3D geometry in our description. We find that inversion symmetric tunnelling is not dressed by phonons whereas other tunnelling pathways are dressed by phonons and, thus, are suppressed by strong defect-phonon coupling. We provide the linear acoustic and dielectric response functions for a crystalline tunnelling defect for strong defect-phonon coupling. This allows direct experimental determination of the defect-phonon coupling. The singling out of inversion-symmetric tunneling states in single tunneling defects is complementary to their dominance of the low energy excitations in strongly disordered solids as a result of inter-defect interactions for large defect concentrations. This suggests that inversion symmetric two-level systems play a unique role in the low energy properties of disordered solids.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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