Related papers: Superconductivity and Quantum Phase Transitions in…
The quantum phase transition in clean itinerant ferromagnets is analyzed. It is shown that soft particle-hole modes invalidate Hertz's mean-field theory for $d \leq 3$. A renormalized mean-field theory predicts a fluctuation-induced first…
The effects of the charging energy in the superconducting transition of granular materials or Josephson junction arrays is investigated using a pseudospin one model. Within a mean-field renormalization-group approach, we obtain the phase…
Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom…
The nature of the quantum valence transition is studied in the one-dimensional periodic Anderson model with Coulomb repulsion between f and conduction electrons by the density-matrix renormalization group method. It is found that the…
Superconductivity is a quantum phenomenon caused by bound pairs of electrons. In diverse families of strongly correlated electron systems, the electron pairs are not bound together by phonon exchange but instead by some other kind of…
The tricritical point, which separates first and second order phase transitions in three-dimensional superconductors, is studied in the four-dimensional Coleman-Weinberg model, and the similarities as well as the differences with respect to…
The universal behaviour of superconductors near the phase transition is described by the three-dimensional field theory of scalar quantum electrodynamics. We approximately solve the model with the help of non-perturbative flow equations. A…
Vortex matter in layered high-$T_c$ superconductors, including iron-pnictides, undergo several thermodynamic phase transitions due to the complex interplay of pinning energy, thermal energy and elastic energy. Moreover, the presence of…
A new critical behavior in unconventional superconductors and superfluids is established and described by the Wilson-Fisher renormalization-group method. For certain symmetries of order a new type of fluctuation-driven first order phase…
The magnetic field (H) - temperature (T) phase diagram of a superconductor is significantly altered when domains are present in an underlying ferromagnet with perpendicular magnetic anisotropy. When the domains have a band-like shape, the…
The upper critical magnetic field H_{c2} in thin-film FSF trilayer spin-valve cores is studied experimentally and theoretically in geometries perpendicular and parallel to the heterostructure surface. The series of samples with variable…
We resolve the nature of the quantum phase transition between a N\'eel antiferromagnet and a valence-bond solid in two-dimensional spin-1/2 magnets. We study a class of $J$-$Q$ models, in which Heisenberg exchange $J$ competes with…
Echoes of quantum phase transitions (QPTs) at finite temperatures are theoretically and experimentally challenging and unexplored topics. Particularly in metallic quantum ferromagnets the experimental investigations are hampered by an…
We analyze the anomalies of superconducting state (both s- and d-wave pairing) in the model of the pseudogap state induced by Heisenberg spin fluctuations of antiferromagnetic short-range order, and based on the scenario of strong…
Exchange interactions between $S=\frac{1}{2}$ sites in piperazinium hexachlorodicuprate produce a frustrated bilayer magnet with a singlet ground state. We have determined the field-temperature phase diagram by high field magnetization and…
Recently co-existence of the ferromagnetism and superconductivity was reported in the high-pressure region (1.0-1.6 GPa) in UGe$_2$. We performed the heat capacity measurement on UGe$_2$ under high pressure. At 1.13 GPa, we found a peak…
We investigate the impact of quantum and thermal phase fluctuations on the suppression of superconducting order in two-dimensional systems. Within the two-dimensional quantum XY model in the phase representation, where on-site interaction…
Bilayer nickelates exhibit high-temperature superconductivity under proper hydrostatic pressure or epitaxial strain, signifying the emergence of quantum phase transitions whose physical mechanisms remain unclear. Using a minimal bilayer…
We propose a thermodynamic model of free energy expansion up to eighth order of magnetisation to describe the complex magnetic phase transitions in ferromagnetic superconductor UGe$_2$. The model successfully describes transitions between…
We study the temperature dependence of the conductivity due to quantum interference processes for a two-dimensional disordered itinerant electron system close to a ferromagnetic quantum critical point. Near the quantum critical point, the…