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We study phase transitions in uniformly frustrated SU(N)-symmetric $(2+epsilon)$-dimensional lattice models describing type-II superconductors near the upper critical magnetic field $H_{c2}(T)$. The low-temperature renormalization-group approach is employed for calculating the beta-function $beta(T,f)$ with $f$ an arbitrary rational magnetic frustration. The phase-boundary line $H_{c2}(T)$ is the ultraviolet-stable fixed point found from the equation $beta(T,f)=0$, the corresponding critical exponents being identical to those of the non-frustrated continuum system. The critical properties of the SU(N)-symmetric complex Ginzburg-Landau (GL) model are then examined in $(4+epsilon)$ dimensions. The possibility of a continuous phase transition into the mixed state in such a model is suggested.
Orbital degrees of freedom of a Cooper pair play an important role in the unconventional superconductivity. To elucidate the orbital effect in the Kondo problem, we investigated a single magnetic impurity coupled to Cooper pairs with a $p_x +i p_y$ (
In iron selenide superconductors only electron-like Fermi pockets survive, challenging the $S^{pm}$ pairing based on the quasi-nesting between the electron and hole Fermi pockets (as in iron arsenides). By functional renormalization group study we sh
A universal phase diagram for weakly pinned low-T$_c$ type-II superconductors is revisited and extended with new proposals. The low-temperature ``Bragg glass phase is argued to transform first into a disordered, glassy phase upon heating. This glassy
A review is given on the theory of vortex-glass phases in impure type-II superconductors in an external field. We begin with a brief discussion of the effects of thermal fluctuations on the spontaneously broken U(1) and translation symmetries, on the
We present a detailed study of the quasiparticle contribution to the low-temperature specific heat of an extreme type-II superconductor at high magnetic fields. Within a T-matrix approximation for the self-energies in the mixed state of a homogeneous