Flux tubes and the type-I/type-II transition in a superconductor coupled to a superfluid
Flux tubes and the type-I/type-II transition in a superconductor coupled to a superfluid
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与超流体耦合的超导体中的通量管和 I 型/II 型转变
DOI：
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发表时间：
2007
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通讯作者：
G. Good
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作者：
M. Alford;G. Good
我们分析了超导体中零温度的磁通管，该超导体通过密度和梯度(“夹带”)相互作用与超流体耦合。我们脑海中的例子是高密度核物质，它是质子超导体和中子超流，但我们的处理是一般和简单的，将相互作用建模为带有四个费米子耦合的金兹堡-朗道有效理论，只包括$S波对。我们数值求解了具有任意多个通量量子的通量管场方程，并比较了它们的能量。这使我们能够映射超导体中的I型/II型转变，如果凝聚体是非耦合的，那么这种转变发生在传统的$ensuremath{kappa}ensuremath{equiv}ensuremath{lambda}/ensuremath{xi}=1/sqrt{2}$中。我们发现，凝聚体之间的密度耦合提高了临界的{kappa}，并且，对于足够高的中子密度，将I/II类跃迁线分解成与``$ext{type-II}(N)$‘相对应的无限多个带，其中$n$是所青睐的通量管中的量子数，从1递增到无穷大。对于较低的中子密度，耦合在I型/II型边界周围创建了旋节区，在这些区域中亚稳态通量配置是可能的。我们发现凝聚体之间的梯度耦合降低了临界的$ensureath{kappa}$，并产生了调幅节点区。这些奇异现象可能不会出现在核物质中，核物质被认为位于第二类区域的深处，但可能在凝聚态物质系统中观察到。
We analyze magnetic-flux tubes at zero temperature in a superconductor that is coupled to a superfluid via both density and gradient (``entrainment') interactions. The example we have in mind is high-density nuclear matter, which is a proton superconductor and a neutron superfluid, but our treatment is general and simple, modeling the interactions as a Ginzburg-Landau effective theory with four-fermion couplings, including only $s$-wave pairing. We numerically solve the field equations for flux tubes with an arbitrary number of flux quanta and compare their energies. This allows us to map the type-I/type-II transition in the superconductor, which occurs at the conventional $ensuremath{kappa}ensuremath{equiv}ensuremath{lambda}/ensuremath{xi}=1/sqrt{2}$ if the condensates are uncoupled. We find that a density coupling between the condensates raises the critical $ensuremath{kappa}$ and, for a sufficiently high neutron density, resolves the type-I/type-II transition line into an infinite number of bands corresponding to ``$ ext{type-II}(n)$' phases, in which $n$, the number of quanta in the favored flux tube, steps from 1 to infinity. For lower neutron density, the coupling creates spinodal regions around the type-I/type-II boundary, in which metastable flux configurations are possible. We find that a gradient coupling between the condensates lowers the critical $ensuremath{kappa}$ and creates spinodal regions. These exotic phenomena may not occur in nuclear matter, which is thought to be deep in the type-II region but might be observed in condensed-matter systems.