Deconfinement of vortices with continuously variable fractions of the unit flux quanta in two-gap superconductors

Abstract

Abstract. -We propose a new stage of confiment-decofinment transition, which can be observed in laboratory. In two-gap superconductors (SCs), two kinds of vortex exist and each of them carries a continuously variable fraction of the unit flux quanta Φ0 = hc/2e. The confined state of these two is a usual vortex and stable in the low temperature region of the system under a certain magnetic field above Hc1. We see an analogy to quarks in a charged pion. An entropy gain causes two fractional vortices to be deconfined above a certain temperature.Introduction. -Topological defects furnish fascinating problems in physics, and keep attracting a lot of concerns. In general, they lead the quantization of physical quantities. Vortex is one of the most important example of topological defects [1]. It is well known that in superconductors (SCs), the requirement that the order parameter is a single-valued function guarantees the quantization of the magnetic flux of a vortex in the unit of Φ 0 = hc/2e.The fractionalization of topologically quantized numbers have also been researched extensively in many different contexts [2]. Vortices with fractional fluxes have been discussed in p-wave superfluid Here we discuss vortex state in two-gap SCs [6] which has two superconducting gaps on two separate Fermi surfaces. The two-gap superconductivity can be seen in a lot of SCs in solid state and has been paid special attention. MgB 2 is a recent typical textbook [7]. The possibility of the two-gap superconducting state is also pointed out in 2H-NbSe 2 [8], PrOs 4 Sb 12 [9], Y 2 C 3 [10], Ca-doped YBCO [11], and liquid hydrogen [12]. The fractionalization of the flux quanta has also been discussed in two-gap SCs [13,14]. Tanaka considered a wire ring and showed that a trapped flux in the ring can be an arbitrary fraction of Φ 0 [13]. Babaev considered a planer geometry and dis-

Disappearance of Meissner Effect and Specific Heat Jump in a Multiband Superconductor, Ba0.2K0.8Fe2As2

“…Figure 4 illustrates these situations. According to Goryo, the phase difference soliton is thermally activated just below T c [7]. This mechanism can work regardless of whether there is a vortex [9].…”

“…The soliton, in which the relative phase between two order parameters rotates 2π , can emerge [3,4,7] when there are two order parameters (or two components). Owing to the phase difference soliton, the quantum phase texture tends to be invoked for the film sample [3,7,9].…”

“…Owing to the phase difference soliton, the quantum phase texture tends to be invoked for the film sample [3,7,9]. The small grains can also satisfy the necessary criterion.…”

“…Its rotation of 2π results in a soliton (intercomponent phase difference soliton) [2], which makes a phase texture [3,4]. These hierarchical structures exhibit rich physical phenomena and potential applications [5], which some researchers are seeking in the two-band superconductor [5][6][7][8][9].…”

Baryonic Bound State of Vortices in Multicomponent Superconductors

“…On the other hand, two half-quantized vortices winding around two different gap functions are connected by a domain wall (sine-Gordon kink) [4,5] when the interband Josephson coupling is considered. The domain wall provides an attractive potential linearly depending on the distance between the two vortices [6]; this bound state resembles a meson in QCD. In fact, confinement/deconfinement phase transition occurs at finite temperature, similar to the case in QCD, in which fluctuations of the domain wall contribute to entropy [6].…”