scholarly journals Probing charge pumping and relaxation of the chiral anomaly in a Dirac semimetal

2021 ◽  
Vol 7 (16) ◽  
pp. eabg0914
Author(s):  
Bing Cheng ◽  
Timo Schumann ◽  
Susanne Stemmer ◽  
N. P. Armitage
Keyword(s):  
Terahertz Spectroscopy ◽  
Point Group ◽  
Spectral Weight ◽  
Chiral Anomaly ◽  
Group Representations ◽  
Field Independence ◽  
Transport Channel ◽  
Scattering Rate ◽  
Chiral Magnetic Effect ◽  
A Charge

The linear band crossings of 3D Dirac and Weyl semimetals are characterized by a charge chirality, the parallel or antiparallel locking of electron spin to its momentum. These materials are believed to exhibit an E · B chiral magnetic effect that is associated with the near conservation of chiral charge. Here, we use magneto-terahertz spectroscopy to study epitaxial Cd3As2 films and extract their conductivities σ(ω) as a function of E · B. As field is applied, we observe a markedly sharp Drude response that rises out of the broader background. Its appearance is a definitive signature of a new transport channel and consistent with the chiral response, with its spectral weight a measure of the net chiral charge and width a measure of the scattering rate between chiral species. The field independence of the chiral relaxation establishes that it is set by the approximate conservation of the isospin that labels the crystalline point-group representations.

scholarly journals Chirality production with mass effects — Schwinger pair production and the axial Ward identity

2020 ◽  
Vol 35 (28) ◽  
pp. 203005
Author(s):  
Patrick Copinger ◽  
Shi Pu
Keyword(s):  
Ward Identity ◽  
Chiral Condensate ◽  
Magnetic Effect ◽  
Chiral Anomaly ◽  
Expectation Values ◽  
Mass Effects ◽  
Chiral Magnetic Effect ◽  
Time Formalism ◽  
Background Fields ◽  
Schwinger Mechanism

The anomalous generation of chirality with mass effects via the axial Ward identity and its dependence on the Schwinger mechanism is reviewed, utilizing parity violating homogeneous electromagnetic background fields. The role vacuum asymptotic states play on the interpretation of expectation values is examined. It is discussed that observables calculated with an in–out scattering matrix element predict a scenario under Euclidean equilibrium. A notable ramification of which is a vanishing of the chiral anomaly. In contrast, it is discussed observables calculated under an in–in, or real-time, formalism predict a scenario out-of equilibrium, and capture effects of mean produced particle–antiparticle pairs due to the Schwinger mechanism. The out-of equilibrium chiral anomaly is supplemented with exponential quadratic mass suppression as anticipated for the Schwinger mechanism. Similar behavior in and out-of equilibrium is reviewed for applications including the chiral magnetic effect and chiral condensate.

scholarly journals Signatures of a Charge Density Wave Phase and the Chiral Anomaly in the Fermionic Material Cobalt Monosilicide CoSi

2019 ◽  
Vol 6 (2) ◽  
pp. 1900857 ◽  
Author(s):  
Lauritz Schnatmann ◽  
Kevin Geishendorf ◽  
Michaela Lammel ◽  
Christine Damm ◽  
Sergey Novikov ◽  
...  
Keyword(s):  
Charge Density ◽  
Charge Density Wave ◽  
Density Wave ◽  
Chiral Anomaly ◽  
Wave Phase ◽  
Charge Density Wave Phase ◽  
A Charge

Quantum-critical conductivity of the Dirac fluid in graphene

Science ◽  
2019 ◽  
pp. eaat8687 ◽  
Author(s):  
Patrick Gallagher ◽  
Chan-Shan Yang ◽  
Tairu Lyu ◽  
Fanglin Tian ◽  
Rai Kou ◽  
...  
Keyword(s):  
Terahertz Spectroscopy ◽  
Quantum Criticality ◽  
Relativistic Hydrodynamics ◽  
Rapid Rate ◽  
Charge Neutrality ◽  
Scattering Rate ◽  
Rate Characteristic ◽  
Quantum Critical ◽  
On Chip ◽  
Dynamic Excitations

Graphene near charge neutrality is expected to behave like a quantum-critical, relativistic plasma—the “Dirac fluid”—in which massless electrons and holes rapidly collide at a rapid rate. We measure the frequency-dependent optical conductivity of clean, micron-scale graphene at electron temperatures between 77 and 300 K using on-chip terahertz spectroscopy. At charge neutrality, we observe the quantum-critical scattering rate characteristic of the Dirac fluid. At higher doping, we uncover two distinct current-carrying modes with zero and nonzero total momenta, a manifestation of relativistic hydrodynamics. Our work reveals the quantum criticality and unusual dynamic excitations near charge neutrality in graphene.

scholarly journals The pseudogap in La2–xSrxCuO4: A Raman viewpoint

2000 ◽  
Vol 78 (5-6) ◽  
pp. 483-493 ◽  
Author(s):  
J G Naeini ◽  
J C Irwin ◽  
T Sasagawa ◽  
Y Togawa ◽  
K Kishio
Keyword(s):  
Fermi Surface ◽  
Normal State ◽  
Low Temperatures ◽  
Spectral Weight ◽  
Energy Scale ◽  
Low Energy ◽  
Scattering Rate ◽  
Low Energies ◽  
Consistent Picture ◽  
Rate Suppression

We report the results of Raman scattering experiments on single crystals of La2–xSrxCuO4 (La214) as a function of temperature and doping. In underdoped compounds low-energy B1g spectral weight is depleted in association with the opening of a pseudogap on regions of the Fermi surface located near (±π, 0) and (0, ±π).The magnitude of the depletion increases with decreasing doping, and in the most underdoped samples, with decreasing temperature.The spectral weight that is lost at low energies (ω [Formula: see text] 800 cm–1) is transferred to the higher energy region normally occupied by multimagnon scattering. From the normal-state B2g spectra we have determined the scattering rate Γ(ω,T) of qausiparticles located near the diagonal directions in k-space. In underdoped compounds, Γ(ω,T) is suppressed at low temperatures for energies less than Eg(x) [Formula: see text] 800 cm–1. The doping dependence of both the two-magnon scattering and the scattering rate suppression suggest that the pseudogap is characterized by an energy scale Eg ~ J, where J is the antiferromagnetic super-exchange energy. Comparison with the results from other techniques provides a consistent picture of the pseudogap in La214.PACS Nos.: 74.25.Gz, 74.72.Dn, 78.30.Er

scholarly journals ON d+id DENSITY WAVE AND SUPERCONDUCTING ORDERINGS IN HOLE-DOPED CUPRATES

2013 ◽  
Vol 27 (13) ◽  
pp. 1330008
Author(s):  
PARTHA GOSWAMI ◽  
AJAY PRATAP SINGH GAHLOT ◽  
PANKAJ SINGH
Keyword(s):  
Chemical Potential ◽  
Density Wave ◽  
Mean Field ◽  
Spectral Weight ◽  
Quasi Particle ◽  
Scattering Rate ◽  
Consistent Manner ◽  
Single Particle Excitation ◽  
The Mean ◽  
Competing Orders

The d+id-density wave (chiral DDW) order, at the anti-ferromagnetic wave vector Q = (π, π), is assumed to represent the pseudo-gap (PG) state of a hole-doped cuprate superconductor. The pairing interaction U(k, k′) required for d+id ordering comprises of (Ux2-y2(k, k′), Uxy(k, k′)), where [Formula: see text] and [Formula: see text] with U1 > U2. The d-wave superconductivity (DSC), driven by an assumed attractive interaction of the form [Formula: see text] where V1 is a model parameter, is discussed within the mean-field framework together with the d+id ordering. The single-particle excitation spectrum in the CDDW + DSC state is characterized by the Bogoluibov quasi-particle bands — a characteristic feature of SC state. The coupled gap equations are solved self-consistently together with the equation to determine the chemical potential (μ). With the pinning of the van Hove-singularities close to μ, one is able to calculate the thermodynamic and transport properties of the under-doped cuprates in a consistent manner. The electron specific heat displays non-Fermi liquid feature in the CDDW state. The CDDW and DSC are found to represent two competing orders as the former brings about a depletion of the spectral weight (and Raman response function density) available for pairing in the anti-nodal region of momentum space. It is also shown that the depletion of the spectral weight below Tc at energies larger than the gap amplitude occurs. This is an indication of the strong-coupling superconductivity in cuprates. The calculation of the ratio of the quasi-particle thermal conductivity αxx and temperature in the superconducting phase is found to be constant in the limit of near-zero quasi-particle scattering rate.

scholarly journals A semiclassical formulation of the chiral magnetic effect and chiral anomaly in even d + 1 dimensions

2016 ◽  
Vol 31 (13) ◽  
pp. 1650074 ◽  
Author(s):  
Ömer F. Dayi ◽  
Mahmut Elbistan
Keyword(s):  
Symplectic Form ◽  
Magnetic Effect ◽  
Chiral Anomaly ◽  
Simple Method ◽  
New Approach ◽  
Chiral Magnetic Effect ◽  
Integral Measure ◽  
The Matrix ◽  
External Electromagnetic Fields ◽  
Definition Of

In terms of the matrix valued Berry gauge field strength for the Weyl Hamiltonian in any even space–time dimensions a symplectic form whose elements are matrices in spin indices is introduced. Definition of the volume form is modified appropriately. A simple method of finding the path integral measure and the chiral current in the presence of external electromagnetic fields is presented. It is shown that within this new approach the chiral magnetic effect as well as the chiral anomaly in even [Formula: see text] dimensions are accomplished straightforwardly.

scholarly journals Far from equilibrium Chiral Magnetic Effect in Strong Magnetic Fields from Holography

2022 ◽  
Vol 258 ◽  
pp. 10007
Author(s):  
Sebastian Grieninger ◽  
Sergio Morales-Tejera
Keyword(s):  
Heavy Ion ◽  
Magnetic Effect ◽  
Chiral Anomaly ◽  
Equilibration Time ◽  
Strong Magnetic Fields ◽  
Strongly Coupled ◽  
Anomalous Field ◽  
Ion Collisions ◽  
Chiral Magnetic Effect ◽  
Far From Equilibrium

We study the real time evolution of the chiral magnetic effect out-ofequilibrium in strongly coupled anomalous field theories. We match the parameters of our model to QCD parameters and draw lessons of possible relevance for the realization of the chiral magnetic effect in heavy ion collisions. In particular, we find an equilibration time of about ~ 0:35 fm/c in presence of the chiral anomaly for plasma temperatures of order T ~ 300 - 400 MeV.

scholarly journals Fermi surface instabilities in electronic Raman scattering of the metallic kagome lattice CsV3Sb5

2021 ◽  
Author(s):  
Dirk Wulferding ◽  
Seungyeol Lee ◽  
YoungSu Choi ◽  
Qiangwei Yin ◽  
Zhijun Tu ◽  
...  
Keyword(s):  
Fermi Surface ◽  
Charge Density ◽  
Density Wave ◽  
Spectral Weight ◽  
Superconducting Transition ◽  
Electronic Raman Scattering ◽  
Charge Correlations ◽  
Surface Fluctuations ◽  
Out Of Plane ◽  
A Charge

Abstract Understanding the link between a charge density wave (CDW) instability and superconductivity is a central theme of the 2D metallic kagome compounds AV3Sb5 (A=K, Rb, and Cs). Using polarization-resolved electronic Raman spectroscopy, we shed light on Fermi surface fluctuations and electronic instabilities. We observe a quasielastic peak (QEP) whose spectral weight is progressively enhanced towards the superconducting transition. The QEP temperature-dependence reveals a steep increase in coherent in-plane charge correlations within the charge-density phase. In contrast, out-of-plane charge fluctuations remain strongly incoherent across the investigated temperature range. In-plane phonon anomalies appear at T* ≈ 50 K in addition to right below TCDW ≈ 95 K, while showing no apparent evidence of reduced symmetry at low temperatures. In conjunction with the consecutive phonon anomalies within the CDW state, our electronic Raman data unveil additional electronic instabilities that persist down to the superconducting phase, thereby offering a superconducting mechanism.

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