Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India.
ISC-CNR and Department of Physics, Sapienza University of Rome, Piazzale Aldo Moro, 5, 00185 Rome, Italy.
Phys Rev Lett. 2019 Feb 1;122(4):047001. doi: 10.1103/PhysRevLett.122.047001.
The hexatic fluid refers to a phase in between a solid and a liquid that has short-range positional order but quasi-long-range orientational order. In the celebrated theory of Berezinskii, Kosterlitz, and Thouless and subsequently refined by Halperin, Nelson, and Young, it was predicted that a two-dimensional hexagonal solid can melt in two steps: first, through a transformation from a solid to a hexatic fluid, which retains quasi-long-range orientational order; and then from a hexatic fluid to an isotropic liquid. In this Letter, using a combination of real space imaging and transport measurements, we show that the two-dimensional vortex lattice in an a-MoGe thin film follows this sequence of melting as the magnetic field is increased. Identifying the signatures of various transitions on the bulk transport properties of the superconductor, we construct a vortex phase diagram for a two-dimensional superconductor.
六方流体是指介于固体和液体之间的一种相态，它具有短程位置序但具有准长程取向序。在著名的 Berezinskii、Kosterlitz 和 Thouless 理论以及后来由 Halperin、Nelson 和 Young 所做的改进理论中，人们预测二维六方固体可以分两步熔融：首先，从固体转变为保留准长程取向序的六方流体；然后再从六方流体转变为各向同性液体。在这篇快报中，我们使用实空间成像和输运测量的组合方法，证明了随着磁场的增加，a-MoGe 薄膜中的二维涡旋晶格遵循这种熔融顺序。通过识别超导体体输运性质上各种转变的特征，我们为二维超导体构建了一个涡旋相图。
