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Ubiquitous V-shape density of states in mixed state of clean limit type II superconductors; STM experiment and theory

N. Nakai·P. Miranovic·M. Ichioka·H. F. Hess·K. Uchiyama·H. Nishimori·S. Kaneko·N. Nishida·K. Machida
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Abstract

It is demonstrated theoretically and experimentally that the low energy density of states $N(E)$ is described by a singular V-shape form $N(E)=N_0(H)+α|E|+O(E^2)$ for all clean superconductors in a vortex state, irrespective of the underlying gap structure. The linear term $α|E|$ which has been not recognized so far is obtained by exactly evaluating the vortex contribution. Based on microscopic Eilenberger theory $N(E)$ is evaluated for isotropic gap, line and point node gaps to yield a V-shape $N(E)$. STS-STM experiments on NbSe$_2$ and YNi$_2$B$_2$C give direct evidence for this. We provide arguments on significance of this finding and on relevance to other experiments.

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N. Nakai, P. Miranovic, M. Ichioka, H. F. Hess, K. Uchiyama, H. Nishimori, S. Kaneko, N. Nishida, K. Machida. 2006-10-10. Ubiquitous V-shape density of states in mixed state of clean limit type II superconductors; STM experiment and theory. https://doi.org/10.1103/physrevlett.97.147001

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