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SignificanceThe 3D nodal points in Dirac and/or Weyl semimetals are in the vanguard of quantum materials research. A hallmark of these systems is the linear band dispersion. This latter electronic stricture gives rise to unconventional transport and optical phenomena. Here, we demonstrate that solids with dispersive nodal lines in the electronic structure share many common aspects with the response of 3D nodal-points systems. We investigated NbAs2 using a combination of optical and magneto-optical techniques and have identified electromagnetic signature of dispersive nodal lines. This particular compound has allowed us to inquire the impact of spin-orbit coupling on the universal characteristic of nodal metals. Using polarized optical and magneto-optical spectroscopy, we have demonstrated universal aspects of electrodynamics associated with Dirac nodal lines that are found in several classes of unconventional intermetallic compounds. We investigated anisotropic electrodynamics of NbAs2 where the spin-orbit coupling (SOC) triggers energy gaps along the nodal lines. These gaps manifest as sharp steps in the optical conductivity spectra σ1(ω). This behavior is followed by the linear power-law scaling of σ1(ω) at higher frequencies, consistent with our theoretical analysis for dispersive Dirac nodal lines. Magneto-optics data affirm the dominant role of nodal lines in the electrodynamics of NbAs2.

Fermi showed that, as a result of their quantum nature, electrons form a gas of particles whose temperature and density follow the so-called Fermi distribution. As shown by Landau, in a metal the electrons continue to act like free quantum mechanical particles with enhanced masses, despite their strong Coulomb interaction with each other and the positive background ions. This state of matter, the Landau-Fermi liquid, is recognized experimentally by an electrical resistivity that is proportional to the square of the absolute temperature plus a term proportional to the square of the frequency of the applied field. Calculations show that, if electron-electron scattering dominates the resistivity in a Landau-Fermi liquid, the ratio of the two terms, b, has the universal value of b = 4. We find that in the normal state of the heavy Fermion metal URu₂Si₂, instead of the Fermi liquid value of 4, the coefficient b = 1 ± 0.1. This unexpected result implies that the electrons in this material are experiencing a unique scattering process. This scattering is intrinsic and we suggest that the uranium f electrons do not hybridize to form a coherent Fermi liquid but instead act like a dense array of elastic impurities, interacting incoherently with the charge carriers. This behavior is not restricted to URu₂Si₂. Fermi liquid-like states with b ≠ 4 have been observed in a number of disparate systems, but the significance of this result has not been recognized.

The 3D nodal points in Dirac and/or Weyl semimetals are in the vanguard of quantum materials research. A hallmark of these systems is the linear band dispersion. This latter electronic stricture gives rise to unconventional transport and optical phenomena. Here, we demonstrate that solids with dispersive nodal lines in the electronic structure share many common aspects with the response of 3D nodal-points systems. We investigated N b A s 2 using a combination of optical and magneto-optical techniques and have identified electromagnetic signature of dispersive nodal lines. This particular compound has allowed us to inquire the impact of spin-orbit coupling on the universal characteristic of nodal metals. Using polarized optical and magneto-optical spectroscopy, we have demonstrated universal aspects of electrodynamics associated with Dirac nodal lines that are found in several classes of unconventional intermetallic compounds. We investigated anisotropic electrodynamics of N b A s 2 where the spin-orbit coupling (SOC) triggers energy gaps along the nodal lines. These gaps manifest as sharp steps in the optical conductivity spectra σ 1 ( ω ) . This behavior is followed by the linear power-law scaling of σ 1 ( ω ) at higher frequencies, consistent with our theoretical analysis for dispersive Dirac nodal lines. Magneto-optics data affirm the dominant role of nodal lines in the electrodynamics of N b A s 2 .

Using polarized optical and magneto-optical spectroscopy, we have demonstrated universal aspects of electrodynamics associated with Dirac nodal lines that are found in several classes of unconventional intermetallic compounds. We investigated anisotropic electrodynamics of NbAs₂ where the spin-orbit coupling (SOC) triggers energy gaps along the nodal lines. These gaps manifest as sharp steps in the optical conductivity spectra σ₁(ω). This behavior is followed by the linear power-law scaling of σ₁(ω) at higher frequencies, consistent with our theoretical analysis for dispersive Dirac nodal lines. Magneto-optics data affirm the dominant role of nodal lines in the electrodynamics of NbAs₂.

Using polarized optical and magneto-optical spectroscopy, we have demonstrated universal aspects of electrodynamics associated with Dirac nodal lines that are found in several classes of unconventional intermetallic compounds. We investigated anisotropic electrodynamics of NbAs2NbAs2 where the spin-orbit coupling (SOC) triggers energy gaps along the nodal lines. These gaps manifest as sharp steps in the optical conductivity spectra σ1(ω)σ1(ω). This behavior is followed by the linear power-law scaling of σ1(ω)σ1(ω) at higher frequencies, consistent with our theoretical analysis for dispersive Dirac nodal lines. Magneto-optics data affirm the dominant role of nodal lines in the electrodynamics of NbAs2NbAs2.

Using polarized optical and magneto-optical spectroscopy, we have demonstrated universal aspects of electrodynamics associated with Dirac nodal lines that are found in several classes of unconventional intermetallic compounds. We investigated anisotropic electrodynamics of N b A s 2 where the spin-orbit coupling (SOC) triggers energy gaps along the nodal lines. These gaps manifest as sharp steps in the optical conductivity spectra σ 1 ( ω ) . This behavior is followed by the linear power-law scaling of σ 1 ( ω ) at higher frequencies, consistent with our theoretical analysis for dispersive Dirac nodal lines. Magneto-optics data affirm the dominant role of nodal lines in the electrodynamics of N b A s 2 .

Fermi showed that, as a result of their quantum nature, electrons form a gas of particles whose temperature and density follow the so-called Fermi distribution. As shown by Landau, in a metal the electrons continue to act like free quantum mechanical particles with enhanced masses, despite their strong Coulomb interaction with each other and the positive background ions. This state of matter, the Landau–Fermi liquid, is recognized experimentally by an electrical resistivity that is proportional to the square of the absolute temperature plus a term proportional to the square of the frequency of the applied field. Calculations show that, if electron-electron scattering dominates the resistivity in a Landau–Fermi liquid, the ratio of the two terms, b , has the universal value of b = 4. We find that in the normal state of the heavy Fermion metal URu 2 Si 2 , instead of the Fermi liquid value of 4, the coefficient b = 1 ± 0.1. This unexpected result implies that the electrons in this material are experiencing a unique scattering process. This scattering is intrinsic and we suggest that the uranium f electrons do not hybridize to form a coherent Fermi liquid but instead act like a dense array of elastic impurities, interacting incoherently with the charge carriers. This behavior is not restricted to URu 2 Si 2 . Fermi liquid-like states with b ≠ 4 have been observed in a number of disparate systems, but the significance of this result has not been recognized.

Fermi showed that, as a result of their quantum nature, electrons form a gas of particles whose temperature and density follow the so-called Fermi distribution. As shown by Landau, in a metal the electrons continue to act like free quantum mechanical particles with enhanced masses, despite their strong Coulomb interaction with each other and the positive background ions. This state of matter, the Landau-Fermi liquid, is recognized experimentally by an electrical resistivity that is proportional to the square of the absolute temperature plus a term proportional to the square of the frequency of the applied field. Calculations show that, if electron-electron scattering dominates the resistivity in a Landau-Fermi liquid, the ratio of the two terms, b, has the universal value of b = 4. We find that in the normal state of the heavy Fermion metal ..., instead of the Fermi liquid value of 4, the coefficient b = 1 ± 0.1. This unexpected result implies that the electrons in this material are experiencing a unique scattering process. This scattering is intrinsic and we suggest that the uranium f electrons do not hybridize to form a coherent Fermi liquid but instead act like a dense array of elastic impurities, interacting incoherently with the charge carriers. This behavior is not restricted to ... Fermi liquid-like states with b ... 4 have been observed in a number of disparate systems, but the significance of this result has not been recognized. (ProQuest: ... denotes formulae/symbols omitted.)

Arising from: J. Lee et al . Nature442, 546–550 (2006)10.1038/nature04973 The study of bosonic modes that couple to the charge carriers is a key element in understanding superconductivity. Using atomic-resolution scanning-tunnelling microscopy (STM) to extract the spectrum of these modes in the high-temperature superconductor Bi 2 Sr 2 CaCu 2 O 8+δ , Lee et al . 1 find a mode whose frequency does not depend on doping but that changes on isotopic substitution of 16 O with 18 O. From this, they infer a role for lattice modes (phonons). However, examination of their data reveals a weaker, but distinct, feature that has all the characteristics of the magnetic excitation identified as the bosonic mode in other competing experiments 2 , 3 , 4 . We therefore suggest that the lattice mode seen by Lee et al . 1 is not relevant to superconductivity and is due to inelastic tunnelling through the insulating oxide layer 5 .

Hwang et al. reply - Our optical technique has the advantage of being a bulk probe, which is less subject to uncertainties in the doping level and in the quality of the surface than ARPES. It is also capable of higher energy resolution and the overall noise level is lower. The disadvantage is that it gives momentum-averaged properties.