This is a supplementary material for
arxiv:1308.3220,
This is a supplementary material for
arxiv:1308.3220.
See also supplementary information
Here.
See the published version in Phys. Rev. Lett.
Introduction
The three-component Ginzburg-Landau
free energy is
\begin{align*}
{\cal F}= \frac{\B^2}{2}
+&\sum_{a=1}^3\frac{1}{2}|\D\psi_a|^2
+ \alpha_a|\psi_a|^2+\frac{1}{2}\beta_a|\psi_a|^4 \\
-&\sum_{a=1}^3\sum_{b>a}^3 \eta_{ab}|\psi_a||\psi_b|\cos(\varphi_b-\varphi_a)
\end{align*}
with the covariant derivative $\D=\Grad+ie\A$ and the magnetic field $\B=\Curl\A$.
The coupling constant $e$ parametrizes the London penetration length
$\lambda=\frac{1}{e\sqrt{\sum_a|\psi_a|^2}}$.
To investigate the magnetization process of a three-band superconductor, in the type-II regime, we simulate the Gibbs free energy ${ \cal G}={\cal F}-\B\cdot {\bf H} $ of the system, on a finite domain in an increasing external field $ {\bs H}=H{\bs e}_z $. Here, the energy is minimized using a nonlinear conjugate gradient algorithm within a finite element formulation provided by Freefem++ library.
Field cooled experiments : There, the Gibbs energy is minimized at $T=T_c+\delta T$, for a given applied field $H$ exceeding the second critical field $H>H_{c2}$. The Gibbs energy is subsequently minimized for decreasing temperatures.
Magnetization process at fixed $ T $ : At a temperature $T<\Tz$, no field is initially applied ($H=0$) and the superconductor is in a uniform Meissner state. Note that in the presence of geometrically stabilized domain-wall, even at $H=0$ the system is not in a uniform Meissner state. Keeping the temperature fixed, the applied field is increased with a step $\delta H$.
To investigate the magnetization process of a three-band superconductor, in the type-II regime, we simulate the Gibbs free energy ${ \cal G}={\cal F}-\B\cdot {\bf H} $ of the system, on a finite domain in an increasing external field $ {\bs H}=H{\bs e}_z $. Here, the energy is minimized using a nonlinear conjugate gradient algorithm within a finite element formulation provided by Freefem++ library.
Field cooled experiments : There, the Gibbs energy is minimized at $T=T_c+\delta T$, for a given applied field $H$ exceeding the second critical field $H>H_{c2}$. The Gibbs energy is subsequently minimized for decreasing temperatures.
Magnetization process at fixed $ T $ : At a temperature $T<\Tz$, no field is initially applied ($H=0$) and the superconductor is in a uniform Meissner state. Note that in the presence of geometrically stabilized domain-wall, even at $H=0$ the system is not in a uniform Meissner state. Keeping the temperature fixed, the applied field is increased with a step $\delta H$.
0. Time-Reversal Symmetry Breaking
The displayed quantity is :
This shows the minimum of the potential energy, as a function
of the the two phase differences $ \varphi_2-\varphi_1 $ and
$ \varphi_3-\varphi_1 $. Potential energy is thus minimized
with respect to densities for a given phase configuration.
The temperature dependence of the parameters is referred in
the paper as Set-I. This is shown for decreasing
temperatures, past $T<\Tz\simeq 0.92$ and the temperature is
given in units of $ T_c$.
Movie 0 -
This shows the potential energy as a function of temperature.
For temperatures above $ \Tz $, the ground state is unique and
the Time Reversal Symmetry is unbroken. For temperatures below
$ \Tz $, the ground state has discrete degeneracy and the Time
Reversal Symmetry is broken.
1. Zero field cooled experiment - Geometric stabilization
The displayed quantities are :
On the first line, the magnetic field $\B$ and the phase differences
$ \varphi_2-\varphi_1 $ and $ \varphi_3-\varphi_1 $. The second line
shows the densities of the superconducting condensates $ |\psi_1|^2 $,
$ |\psi_2|^2 $ and $ |\psi_3|^2 $ respectively. The temperature is
given in the units of $ T_c $.
Movie 2 -
This shows a three-band superconductor being cooled through
the Broken Time-Reversal Symmetry transition, in zero external
field. At temperatures higher than $\Tz$, the system is uniform
Meissner state. At the symmetry breaking temperature $\Tz$,
in different regions the system assumes two different phase
configurations. This leads to the formation of a domain wall.
Here, the domain wall is stabilized by pinning defects.
2. Field cooled experiment
The displayed quantities are :
On the first line, the magnetic field $\B$ and the phase differences
$ \varphi_2-\varphi_1 $ and $ \varphi_3-\varphi_1 $. The second line
shows the densities of the superconducting condensates $ |\psi_1|^2 $,
$ |\psi_2|^2 $ and $ |\psi_3|^2 $ respectively. The temperature is
given in the units of $ T_c $.
Movie 3 -
This shows a three-band superconductor being cooled through
the Broken Time-Reversal Symmetry transition, in external
field $ HS/\Phi_0=70 $. At temperatures higher than $\Tz$,
the system forms simple vortex lattice. At the symmetry
breaking temperature $\Tz$, in different regions the system
assumes two different phase configurations. This leads to the
formation of a domain-wall, which cannot freely decay. The
preexisting vortices stabilize the domain-wall.
3. Magnetization process at fixed T
The displayed quantities are :
On the first line, the magnetic field $\B$ and the phase differences
$ \varphi_2-\varphi_1 $ and $ \varphi_3-\varphi_1 $. The second line
shows the densities of the superconducting condensates $ |\psi_1|^2 $,
$ |\psi_2|^2 $ and $ |\psi_3|^2 $ respectively. $ N $ is the number
of applied flux quanta. The corresponding applied field on a sample of
surface $ S $, is $ H=N\Phi_0/S $.
Movie 4 -
This shows the magnetization process of the same system as in Movie 2.
That is starting at temperature below $\Tz$. The field is then
slowly increased. Because of Bean-Livingston barrier, vortices enter for
applied field above $ H_{c1} $. At the final stages, the step in the
applied field is big enouh to locally push the system to another phase
locking, thus nucleating a domain wall. The later is stabilized by the vortices.
Movie 5 -
This shows the reference magnetization process of the same system as in Movie 1.
That is starting at temperature below $\Tz$, when a domain wall has been
geometrically stabilized by the non-convex geometry. The field is then
slowly increased. Because of depleted densities on the domain-wall,
(fractional) vortices enter on the domain-wall. Vortices enter for
applied field way below $ H_{c1} $, since on the domain wall
the first critical field is effectively smaller.
Movie 6 -
This shows the magnetization process of the same system as in Movie 3.
That is starting at temperature below $\Tz$, when no domain wall has been
geometrically stabilized by the non-convex geometry. The field is then
slowly increased. Because of Bean-Livingston barrier, vortices enter for
applied field above $ H_{c1} $.
References