共查询到20条相似文献,搜索用时 15 毫秒
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Kaoru Iwano 《Phase Transitions》2013,86(1-2):129-173
A theoretical framework for photoinduced structural transitions (PSPTs) is described with low-dimensional charge-density-wave (CDW) systems as typical examples. Our point of view is based on the concept of domain formation, which is expected to have the structure of a hetero-phase sandwiched between two domain walls. Common to all the cases here, we assume that the initial states are stable or metastable with an appreciable energy barrier so that a thermal phase transition cannot occur. Contrary to such stationarity in the ground states, there are various possibilities in photo-excited states, depending on system conditions. In this article, we focus on one of the most basic conditions, namely, the dimensionality or the geometry of the system and survey the expected features. Based on such a basic consideration, we review the work on MX-chains, which are typical quasi-one-dimensional materials. Since their two ground states in the half-filling case are identical except for a phase difference, the “photoinduced structural transition” in those systems are considered as a soliton-pair formation in the analogy of polyacetylene or mathematical models as φ4- and Sine-Gordon models. Next, we mention other CDW systems. Although they are rather theoretical, they convey two important concepts in cooperative PSPT: nonlinearity in the converted fraction as a function of the absorbed photon density, and aggregation of excitations. 相似文献
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We consider the problem of sliding motion of a charge-density-wave subject to static disorder within an elastic medium model. Starting with a field-theoretical formulation, which allows exact disorder averaging, we propose a self-consistent approximation scheme to obtain results beyond the standard large-velocity expansion. Explicit calculations are carried out in three spatial dimensions. For the conductivity, we find a strong-coupling regime at electrical fields just above the pinning threshold. Phase and velocity correlation functions scale differently from the high-field regime, and static phase correlations converge to the pinned-phase behaviour. The sliding charge-density-wave is accompanied by narrow-band noise. 相似文献
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Phenomena analogous to ground state quantum phase transitions have recently been noted to occur among states throughout the excitation spectra of certain many-body models. These excited state phase transitions are manifested as simultaneous singularities in the eigenvalue spectrum (including the gap or level density), order parameters, and wave function properties. In this article, the characteristics of excited state quantum phase transitions are investigated. The finite-size scaling behavior is determined at the mean-field level. It is found that excited state quantum phase transitions are universal to two-level bosonic and fermionic models with pairing interactions. 相似文献
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Spin interaction Hamiltonians are obtained from the unitary Yang-Baxter -matrix. Based on which, we study Berry phase and quantum criticality in the Yang-Baxter systems. 相似文献
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Feldman DE 《Physical review letters》2005,95(17):177201
We study the effect of the voltage bias on the ferromagnetic phase transition in a one-dimensional itinerant electron system. The applied voltage drives the system into a nonequilibrium steady state with a nonzero electric current. The bias changes the universality class of the second order ferromagnetic transition. While the equilibrium transition belongs to the universality class of the uniaxial ferroelectric, we find the mean-field behavior near the nonequilibrium critical point. 相似文献
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Ye J 《Physical review letters》2006,97(23):236803
We extend the composite boson theory to study slightly imbalanced bilayer quantum Hall systems. In the global U(1) symmetry breaking excitonic superfluid side, as the imbalance increases, the system supports continuously changing fractional charges. In the translational symmetry breaking pseudospin density wave (PSDW) side, there are two quantum phase transitions from the commensurate PSDW to an incommensurate PSDW and then to the excitonic superfluid state. We compare our theory with experimental data and also the previous microscopic calculations. 相似文献
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G. De Chiara A. Łoziński G. M. Palma 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):179-183
The evolution of a two level system with a slowly varying Hamiltonian, modeled as a spin 1/2 in a slowly varying magnetic
field, and interacting with a quantum environment, modeled as a bath of harmonic oscillators is analyzed using a quantum Langevin
approach. This allows to easily obtain the dissipation time and the correction to the Berry phase in the case of an adiabatic
cyclic evolution. 相似文献
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A theoretical model with electron-phonon and anharmonic interactions is proposed to explain the two-phonon mode observed in
the Raman spectra of layered transition metal dichalcogenides, which exhibit charge density wave (cdw) phase transition. The phonon self-energy, which involves the electron response function and the two-phonon Green’s function,
is calculated using the double-time Green’s function formalism. It is shown that in these low-dimensional systems there exists
an anharmonicity-mediated two-phonon mode in the phonon spectral function both in the normal and in thecdw phases. In the normal phase since the phonon Raman scattering proceeds through a single optic phonon the calculations are
carried out for zero wave vector and hence the contribution of the electron response function to the self-energy vanishes.
On the other hand explicit evaluation of the two-phonon Green’s function shows that the frequency of the two-phonon mode is
twice that of the Kohn anomaly phonon and decreases with decreasing temperature. The strength of two-phonon peak is found
to be comparable to that of the original optic phonon. In thecdw phase the phonon which enters into the Raman scattering is taken to be the one with thecdw wave vectorQ, which when zone-folded becomes equivalent to zero wave vector. The evaluation of the electron response function in this
phase generates a phonon corresponding to thecdw-amplitude mode. The two-phonon Green’s function is assumed to be of similar form as in the normal phase. The spectral function
evaluated at zero temperature shows a weak two-phonon peak besides the prominentcdw-amplitude mode. Numerical results are presented for the system 2H-NbSe2 and are found to be in qualitative agreement with the experimental data. 相似文献
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A model where phase transitions between the Peierls and periodic soliton wall superlattice (SWS) charge-density-wave phases
occur in a magnetic field is proposed. The model accounts for the peculiarities of the electron spectrum in a quasi-one-dimensional
conductor (Per)2Pt(mnt)2. Possible experimental investigations of the theoretically predicted phase transitions in (Per)2Pt(mnt)2 to discover a unique SWS phase are discussed.
The text was submitted by the authors in English. 相似文献
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《中国物理 B》2019,(5)
Charge-density-wave(CDW) materials with strongly correlated electrons have broadband light absorption and ultrafast response to light irradiation, and hence hold great potential in photodetection. 1 T-TaS2 is a typical CDW material with various thermodynamically CDW ground states at different temperatures and fertile out-of-equilibrium intermediate/hidden states. In particular, the light pulses can trigger melting of CDW ordering and also forms hidden states, which exhibits strikingly different electrical conductivity compared to the ground phase. Here, we review the recent research on phase transitions in 1 T-TaS2 and their potential applications in photodetection. We also discuss the ultrafast melting of CDW ordering by ultrafast laser irradiation and the out-of-equilibrium intermediate/hidden states by optical/electrical pulse. For photodetection, demonstrations of photoconductors and bolometers are introduced. Finally, we discuss some of the challenges that remain. 相似文献
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J. Ginibre 《Communications in Mathematical Physics》1969,14(3):205-234
We prove that the following lattice systems:
- anisotropic Heisenberg model,
- Ising model with transverse magnetic field,
- quantum lattice gas with hard cores extending over nearest neighbours,