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Recent experiments on quantum criticality in the Ge-substituted heavy-electron material YbRh2Si2 under magnetic field have revealed a possible non-Fermi liquid (NFL) strange metal (SM) state over a finite range of fields at low…
The main features of fermion condensation quantum phase transition (FCQPT), which are distinctive in several aspects from that of conventional quantum phase transition (CQPT), are considered. We show that in contrast to CQPT, whose physics…
A quantum phase transition (QPT) in a heavy-fermion (HF) compound may destroy the Fermi liquid groundstate. However, the conditions for this breakdown have remained obscure. We report the first direct investigation of heavy quasiparticle…
This article is aimed at a pedagogical introduction to the physics of quantum phase transitions that is unique to metallic systems. It has been recognized for some time that quantum criticality can result in a breakdown of Landau's Fermi…
Unconventional quantum critical phenomena observed in Yb-based periodic crystals such as YbRh$_2$Si$_2$ and $\beta$-YbAlB$_4$ have been one of the central issues in strongly correlated electron systems. The common criticality has been…
In strongly correlated systems, interactions give rise to critical fluctuations surrounding the quantum critical point (QCP) of a quantum phase transition. Quasicrystals allow the study of quantum critical phenomena in aperiodic systems…
The nature of quantum criticality in CeCoIn$_5$ is studied by low-temperature thermal expansion $\alpha(T)$. At the field-induced quantum critical point at H=5 T a crossover scale $T^\star\approx 0.3$ K is observed, separating…
We show that spatially local, yet low-energy, fluctuations can play an essential role in the physics of strongly correlated electron systems tuned to a quantum critical point. A detailed microscopic analysis of the Kondo lattice model is…
How ground states of quantum matter transform between one another reveals deep insights into the mechanisms stabilizing them. Correspondingly, quantum phase transitions are explored in numerous materials classes, with heavy fermion…
Quantum phase transitions arise in many-body systems due to competing interactions that promote rivaling ground states. Recent years have seen the identification of continuous quantum phase transitions, or quantum critical points, in a host…
Quantum phase transitions of metals involve changes in the Fermi surface, and can be divided into three categories. The first two categories involve symmetry breaking, and lead to a deformation or reconstruction of the Fermi surface. The…
Quantum critical points (QCPs) are widely accepted as a source of a diverse set of collective quantum phases of matter. A central question is how the order parameters of phases near a QCP interact and determine the fundamental character of…
We study electron correlation effects on quantum criticalities of Lifshitz transitions at zero temperature, using the mean-field theory based on a preexisting symmetry-broken order, in two-dimensional systems. In the presence of…
We solve the 3D periodic Anderson model via two impurity DMFT. We obtain the temperature v.s. hybridization phase diagram. In approaching the quantum critical point (QCP) both the Neel and lattice Kondo temperatures decrease and they do not…
Metallic quantum critical phenomena are believed to play a key role in many strongly correlated materials, including high temperature superconductors. Theoretically, the problem of quantum criticality in the presence of a Fermi surface has…
Considerable efforts have been made in recent years to theoretically understand quantum phase transitions in Kondo lattice systems. A particular focus is on Kondo destruction, which leads to quantum criticality that goes beyond the Landau…
We consider two-dimensional Fermi systems with quadratic band touching and $C_3$ symmetry, as realizable in Bernal-stacked honeycomb bilayers. Within a renormalization-group analysis, we demonstrate the existence of a quantum critical point…
Recent studies of the global phase diagram of quantum-critical heavy-fermion metals prompt consideration of the interplay between the Kondo interactions and quantum fluctuations of the local moments alone. Toward this goal, we study a…
When a second-order magnetic phase transition is tuned to zero temperature by a non-thermal parameter, quantum fluctuations are critically enhanced, often leading to the emergence of unconventional superconductivity. In these `quantum…
Quantum criticality, being important as an indicator of new quantum matters emerging, is known to occur only at zero or low temperature. We find that a quantum probe, if its coherence time is long, can detect quantum criticality at…