scholarly journals RECENT ADVANCES IN UNCONVENTIONAL DENSITY WAVES

2004 ◽  
Vol 18 (09) ◽  
pp. 327-344 ◽  
Author(s):  
BALÁZS DÓRA ◽  
KAZUMI MAKI ◽  
ATTILA VIROSZTEK
Keyword(s):  
Cuprate Superconductors ◽  
Mean Field Theory ◽  
Density Wave ◽  
Mean Field ◽  
Temperature Phase ◽  
Pseudogap Phase ◽  
Excitonic Insulator ◽  
Quasiparticle Motion ◽  
Low Temperature Phase ◽  
Electronic Ground

The unconventional density wave (UDW) was speculated on as a possible electronic ground state in the excitonic insulator in 1968. The recent surge of interest in UDW's is partly due to the proposal that the pseudogap phase in high Tc cuprate superconductors is a d-wave density wave (d-DW). Here we review our recent works on UDW's within the framework of mean field theory. In particular, we have shown that many properties of the low temperature phase (LTP) in α-( BEDT-TTF )2 MHg ( SCN )4, with M = K , Rb and Tl , are well characterized in terms of the unconventional charge density wave (UCDW). In this identification the Landau quantization of the quasiparticle motion in a magnetic field (the Nersesyan effect) plays the crucial role. Indeed, the angle-dependent magnetoresistance and the negative giant Nernst effect are two hallmarks of UDW's.

scholarly journals CRITICAL BEHAVIOR OF TARGET SPACE MEAN FIELD THEORY

1993 ◽  
Vol 08 (28) ◽  
pp. 2703-2713 ◽  
Author(s):  
MARK WEXLER
Keyword(s):  
Free Energy ◽  
Low Temperature ◽  
Matrix Model ◽  
Mean Field Theory ◽  
Mean Field ◽  
Target Space ◽  
Temperature Phase ◽  
Critical Curves ◽  
Baby Universes ◽  
Low Temperature Phase

Recently, the free energy of the target space mean field (TSMF) matrix model has been calculated in the low temperature phase, order-by-order in a low temperature expansion. The TSMF model is a matrix model whose discrete target space has an infinite coordination number, and whose free energy assumes a universal form, corresponding to baby universes joined into a tree. Here the free energy is summed to all orders, and expressed through a transcendental algebraic equation, using which we analyze the critical phenomena that occur in the TSMF model. There are two critical curves, at which the matter and the geometry become critical, and for which the critical exponents are [Formula: see text] and [Formula: see text], respectively. There is a bi-critical point where the curves meet, at which [Formula: see text].

Brave new world of unconventional density waves

2002 ◽  
Vol 12 (9) ◽  
pp. 49-52
Author(s):  
K. Maki ◽  
B. Dora ◽  
B. Korin-Hamzic ◽  
M. Basletic ◽  
A. Virosztek ◽  
...  
Keyword(s):  
Paradigm Shift ◽  
Glassy Phase ◽  
Density Wave ◽  
Organic Superconductor ◽  
Temperature Phase ◽  
Density Waves ◽  
Pseudogap Phase ◽  
Brave New World ◽  
2D And 3D ◽  
Low Temperature Phase

Recently many people discuss unconventional density wave (i.e. UCDW and USDW). Unlike in conventional density waves, the quasiparticle excitations in these systems are gapless. The appearence of these systems suggests paradigm shift from quasi ID system to quasi 2D and 3D systems. Here we limit ourselves to the angular dependent magnetoresistance (ADMR) observed in the low temperature phase (LTP) of α-(BEDT-TTF)2KHg(SCN)4. Here we show that UCDW describes successfully many features of ADMR as manifestation of the Landau quantization of the quasiparticle spectrum in magnetic field. Indeed ADMR will provide a unique window to access UDW like the AF phase in URu2Si2, the pseudogap phase in high Tc cuprates and the glassy phase in organic superconductor κ-(ET)2 salts.

scholarly journals Direct observation of excitonic instability in Ta2NiSe5

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kwangrae Kim ◽  
Hoon Kim ◽  
Jonghwan Kim ◽  
Changil Kwon ◽  
Jun Sung Kim ◽  
...  
Keyword(s):  
Phase Transition ◽  
Direct Observation ◽  
Structural Phase ◽  
Temperature Phase ◽  
Phonon Coupling ◽  
Strong Electron ◽  
Weiss Temperature ◽  
Excitonic Insulator ◽  
Electron Phonon Coupling ◽  
Low Temperature Phase

AbstractCoulomb attraction between electrons and holes in a narrow-gap semiconductor or a semimetal is predicted to lead to an elusive phase of matter dubbed excitonic insulator. However, direct observation of such electronic instability remains extremely rare. Here, we report the observation of incipient divergence in the static excitonic susceptibility of the candidate material Ta2NiSe5 using Raman spectroscopy. Critical fluctuations of the excitonic order parameter give rise to quasi-elastic scattering of B2g symmetry, whose intensity grows inversely with temperature toward the Weiss temperature of TW ≈ 237 K, which is arrested by a structural phase transition driven by an acoustic phonon of the same symmetry at TC = 325 K. Concurrently, a B2g optical phonon becomes heavily damped to the extent that its trace is almost invisible around TC, which manifests a strong electron-phonon coupling that has obscured the identification of the low-temperature phase as an excitonic insulator for more than a decade. Our results unambiguously reveal the electronic origin of the phase transition.

CHARGE-FLUX DENSITY WAVES: ANYONS IN A PERIODIC POTENTIAL

1991 ◽  
Vol 05 (21) ◽  
pp. 1431-1438
Author(s):  
D. M. Gaitonde ◽  
Sumathi Rao
Keyword(s):  
Flux Density ◽  
Periodic Potential ◽  
Mean Field Theory ◽  
Density Wave ◽  
Mean Field ◽  
Landau Levels ◽  
Filling Fraction ◽  
Lattice Periodicity ◽  
Magnetic Length ◽  
A Charge

We show that the lattice periodicity which causes a modulation of the charge density by a wave vector q also leads to a modulation of the flux density if the charged particles are anyons. Within mean field theory, we obtain a charge and flux density wave (CFDW) where the degenerate Landau levels of a constant magnetic field split into bands. For a weak periodic flux superimposed on a strong constant flux, anyon superconductivity at integer filling of Landau levels (corresponding to a statistics parameter of θ = π(1 − 1/ν) with ν = n = integer ) is not affected. However, at statistics corresponding to non-integer filling of Landau levels, for certain commensurability conditions between the lattice length (a), the magnetic length (l) and the filling fraction (ν), gaps open up at the Fermi level and convert an anyon metal into an anyon insulator.

The anomalous electronic structure of electron-doped cuprate superconductors by considering the next higher harmonics of the superconducting gap

2021 ◽  
pp. 2150256
Author(s):  
Jihong Qin
Keyword(s):  
Electron Spectrum ◽  
Cuprate Superconductors ◽  
Mean Field Theory ◽  
Mean Field ◽  
Anomalous Behavior ◽  
Momentum Dependence ◽  
Higher Harmonics ◽  
Critical Strength ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Energy And Momentum

Based on the self-consistent mean field theory by considering the next higher harmonics of the superconducting (SC) gap, we discuss the energy and momentum dependence of the electron spectrum in electron-doped cuprate superconductors. By calculation of the electron spectral function, it is shown that the weight of the electron spectrum at the Fermi energy is strongly redistributed by the next higher harmonics of the SC gap in electron-doped cuprate superconductors, especially for the antinodal region. At the antinodal region, the weight of the electron spectrum at the Fermi surface increases with the increase of next higher harmonics term, reaches the maximum at a critical strength, then decreases when the next higher harmonics is larger. Our theoretical results show that the variation of the SC gap with the next higher harmonics can explain the anomalous behavior of the electron spectrum and different angle-resolved photoemission spectroscopy experimental results of different samples of electron-doped cuprate superconductors. Moreover, the magnitude of the SC gap can be suppressed by the next higher harmonics, which may be one of the reasons for the smaller SC gap in electron-doped cuprate superconductors. Obvious topological change happens in the SC gap at a critical strength of the next higher harmonics.

INTERACTING BOSONIC ATOMS WITH RANDOM POTENTIAL IN OPTICAL LATTICES

2009 ◽  
Vol 23 (11) ◽  
pp. 1391-1404
Author(s):  
WEI LIU ◽  
JIAN-YANG ZHU
Keyword(s):  
Optical Lattice ◽  
Optical Lattices ◽  
Mean Field Theory ◽  
Mean Field ◽  
Temperature Phase ◽  
Optical Parameters ◽  
Xxz Model ◽  
Bose Glass ◽  
The Mean ◽  
Bosonic Atoms

In this paper, we study the ultracold atoms in optical lattice with a weak random external potential by an extended Bose–Hubbard model. When the on-site interaction is strong enough, the model can be mapped to the XXZ model. Then the mean-field theory is applied and we get the zero- and finite-temperature phase diagrams in different optical parameters. The differences between the systems with and without disorder were found, and the Bose-glass phase may exist in the system with disorder.

scholarly journals Vanishing nematic order beyond the pseudogap phase in overdoped cuprate superconductors

2021 ◽  
Vol 118 (34) ◽  
pp. e2106881118
Author(s):  
Naman K. Gupta ◽  
Christopher McMahon ◽  
Ronny Sutarto ◽  
Tianyu Shi ◽  
Rantong Gong ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Symmetry Breaking ◽  
Cuprate Superconductors ◽  
Rotational Symmetry ◽  
Density Wave ◽  
Charge Order ◽  
Pseudogap Phase ◽  
Correlated Electron ◽  
The Relationship ◽  
Electronic Nematicity

During the last decade, translational and rotational symmetry-breaking phases—density wave order and electronic nematicity—have been established as generic and distinct features of many correlated electron systems, including pnictide and cuprate superconductors. However, in cuprates, the relationship between these electronic symmetry-breaking phases and the enigmatic pseudogap phase remains unclear. Here, we employ resonant X-ray scattering in a cuprate high-temperature superconductor La1.6−xNd0.4SrxCuO4 (Nd-LSCO) to navigate the cuprate phase diagram, probing the relationship between electronic nematicity of the Cu 3d orbitals, charge order, and the pseudogap phase as a function of doping. We find evidence for a considerable decrease in electronic nematicity beyond the pseudogap phase, either by raising the temperature through the pseudogap onset temperature T* or increasing doping through the pseudogap critical point, p*. These results establish a clear link between electronic nematicity, the pseudogap, and its associated quantum criticality in overdoped cuprates. Our findings anticipate that electronic nematicity may play a larger role in understanding the cuprate phase diagram than previously recognized, possibly having a crucial role in the phenomenology of the pseudogap phase.

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