Search results for "quantum phase"
showing 10 items of 127 documents
New state of matter: heavy-fermion systems, quantum spin liquids, quasicrystals, cold gases, and high temperature superconductors
2018
We report on a new state of matter manifested by strongly correlated Fermi systems including various heavy-fermion (HF) metals, two-dimensional quantum liquids such as $\rm ^3He$ films, certain quasicrystals, and systems behaving as quantum spin liquids. Generically, these systems can be viewed as HF systems or HF compounds, in that they exhibit typical behavior of HF metals. At zero temperature, such systems can experience a so-called fermion-condensation quantum phase transition (FCQPT). Combining analytical considerations with arguments based entirely on experimental grounds we argue and demonstrate that the class of HF systems is characterized by universal scaling behavior of their ther…
Quantum Criticality in a Bosonic Josephson Junction
2011
In this paper we consider a bosonic Josephson junction described by a two-mode Bose-Hubbard model, and we thoroughly analyze a quantum phase transition occurring in the system in the limit of infinite bosonic population. We discuss the relation between this quantum phase transition and the dynamical bifurcation occurring in the spectrum of the Discrete Self Trapping equations describing the system at the semiclassical level. In particular, we identify five regimes depending on the strength of the effective interaction among bosons, and study the finite-size effects arising from the finiteness of the bosonic population. We devote a special attention to the critical regime which reduces to th…
Photon Production from the Vacuum Close to the Superradiant Transition: Linking the Dynamical Casimir Effect to the Kibble-Zurek Mechanism
2012
The dynamical Casimir effect (DCE) predicts the generation of photons from the vacuum due to the parametric amplification of the quantum fluctuations of an electromagnetic field. The verification of such an effect is still elusive in optical systems due to the very demanding requirements of its experimental implementation. We show that an ensemble of two-level atoms collectively coupled to the electromagnetic field of a cavity, driven at low frequencies and close to a quantum phase transition, stimulates the production of photons from the vacuum. This paves the way to an effective simulation of the DCE through a mechanism that has recently found experimental demonstration. The spectral prop…
Universal Behavior of Quantum Spin Liquid and Optical Conductivity in the Insulator Herbertsmithite
2018
We analyze optical conductivity with the goal to demonstrate experimental manifestation of a new state of matter, the so-called fermion condensate. Fermion condensates are realized in quantum spin liquids, exhibiting typical behavior of heavy fermion metals. Measurements of the low-frequency optical conductivity collected on the geometrically frustrated insulator herbertsmithite provide important experimental evidence of the nature of its quantum spin liquid composed of spinons. To analyze recent measurements of the herbertsmithite optical conductivity at different temperatures, we employ a model of strongly correlated quantum spin liquid located near the fermion condensation phase transiti…
Pressure-induced phase transition and bandgap collapse in the wide-bandgap semiconductor InTaO4
2016
A pressure-induced phase transition, associated with an increase of the coordination number of In and Ta, is detected beyond 13 GPa in InTaO4 by combining synchrotron x-ray diffraction and Raman measurements in a diamond-anvil cell with ab initio calculations. High-pressure optical-absorption measurements were also carried out. The high-pressure phase has a monoclinic structure that shares the same space group with the low-pressure phase (P2/c). The structure of the high-pressure phase can be considered as a slight distortion of an orthorhombic structure described by space group Pcna. The phase transition occurs together with a unit-cell volume collapse and an electronic band-gap collapse o…
Two-dimensional model colloids and nano wires: phase transitions, effects of external potentials and quantum effects
2005
Abstract Quantum effects, structures and phase transitions in Nano-systems have been analyzed. An overview is given on the results of our computations on structural and elastic properties of model colloids, on phase transitions of model colloids in external fields, and on structural and electronic properties of stretched atomic wires.
Dynamics of Phase Transition in 0.4NBT-0.4ST-0.2PT Solid Solution
2012
In this paper we present dielectric spectroscopy results of NBT-(0.6-x)ST-xPT with x = 0.2 solid solution. Dielectric investigations clearly showed a relaxor—normal ferroelectric phase transition at TPT = 419 K and low temperature and low frequency dispersion similar to coexistence of dipolar glass and ferroelectric phase. The mean relaxation time above the phase transition follows Vogel—Fulcher law with following parameters: E A = 0.179 eV, τ 0 = 3.39·10−14 s, T VF = 223 K.
Ordering phenomena and phase transitions in the physisorbed quantum systems H2, HD and D2
1991
Abstract Recent experimental results of H2, HD and D2 films physisorbed on graphite are briefly reviewed. In particular, the monolayer phase diagrams, the order-disorder transition of the commensurate (C) phase and the commensurate-incommensurate (C-IC) transition are discussed. It will be shown that the melting transition of the C phase belongs to the three-state Potts universality class, and that the C-IC transition occurs via a series of novel intermediate phase, which could be identified as density-modulated phases characterized by striped and hexagonal patterns of domain walls. Due to this rich variety of phenomena, the hydrogen isotopes can be considered as model systems for two-dimen…
Uhlmann curvature in dissipative phase transitions
2018
We study the mean Uhlmann curvature in fermionic systems undergoing a dissipative driven phase transition. We consider a paradigmatic class of lattice fermion systems in non-equilibrium steady-state of an open system with local reservoirs, which are characterised by a Gaussian fermionic steady state. In the thermodynamical limit, in systems with translational invariance we show that a singular behaviour of the Uhlmann curvature represents a sufficient criterion for criticalities, in the sense of diverging correlation length, and it is not otherwise sensitive to the closure of the Liouvillian dissipative gap. In finite size systems, we show that the scaling behaviour of the mean Uhlmann curv…
Violation of the Time-Reversal and Particle-Hole Symmetries in Strongly Correlated Fermi Systems: A Review
2020
In this review, we consider the time reversal T and particle-antiparticle C symmetries that, being most fundamental, can be violated at microscopic level by a weak interaction. The notable example here is from condensed matter, where strongly correlated Fermi systems like heavy-fermion metals and high Tc superconductors exhibit C and T symmetries violation due to so-called non-Fermi liquid (NFL) behavior. In these systems, tunneling differential conductivity (or resistivity) is a very sensitive tool to experimentally test the above symmetry break. When a strongly correlated Fermi system turns out to be near the topological fermion condensation quantum phase transition (FCQPT), it exhibits t…