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The Electron-Phonon Interaction and Strong-Coupling Superconductors
Published in R. D. Parks, Superconductivity, 2018
In 1956 Landau (24) suggested a semiphenomenological theory of a Fermi liquid which provides a useful conceptual framework for describing the interacting electron gas. Landau argued that the appropriate normal modes for describing a system of interacting Fermions were quasi-particle excitations. These can be envisioned as reducing in the noninteracting limit to the plane-wave particle states of a free Fermi gas. This implies that the quasi-particles are fermions, and the assumed translational and rotational invariance of the system means that the quasi-particle excitations can be labeled by momentum p and spin s quantum numbers. Then the low-lying excited states of the interacting system are described in terms of the quasi-particle occupation numbers in the same way the noninteracting system is described by the free-particle-state occupation numbers. In particular, the ground state of the interacting system consists of a filled Fermi sea of quasi-particles. The low-lying excited states contain a small number of excited quasi-particles (and quasi-holes). In these states the number of excited quasi-particles is sufficiently low that interactions between them are negligible and an independent-particle picture is obtained.
Skyrmions in blue phases of chiral liquid crystals
Published in Liquid Crystals, 2023
J. Pišljar, M. Marinčič, S. Ghosh, S. Turlapati, Rao Nandiraju, A. Nych, M. Škarabot, A. Mertelj, A. Petelin, A. Pusovnik, M. Ravnik, I. Muševič
It would be very interesting to see whether a phase analogous to BPIII exists in any other physical system. There has been work done by Tewari, Belitz and Kirkpatrick [81] on the phases observed in the pressure-temperature phase diagram of MnSi, which shows some exotic magnetic phases. Much like the phase diagram of Figure 1(a), the phase diagram they studied, exhibits a critical point. At pressures above the critical point, at low enough temperatures, a new phase is observed which exhibits non-Fermi liquid (NFL) behaviour. Within the NFL neutron scattering experiments gave evidence that on a large scale the NFL is disordered but possesses a degree of short-range helical order of magnetic spins. Its structure was considered a mixture between the higher temperature chiral gas and lower temperature chiral spin liquid. In that sense the authors speculated this ‘quantum fog phase’ may be an analogue of BPIII found in LCs. If this were true, measurements of its dynamics should also show a two mode behaviour. A dynamically disordered phase was found in MnSi just above the at an ambient pressure using neutron spin echo spectroscopy [82] and measurements show relaxation times in the order of nanoseconds, most likely a signature of the soft mode relaxation.
Ultrafast Electron–Phonon Coupling at Metal-Dielectric Interface
Published in Heat Transfer Engineering, 2019
Qiaomu Yao, Liang Guo, Vasudevan Iyer, Xianfan Xu
The subscripts i are 0, 1, and 2 for the Drude term and the two Lorentz terms, respectively. For the damping factor in the Drude model Γ0, the coefficient describing electron–electron scattering Aee0 is taken as 1.2 × 107 s−1K−2 which is obtained from the low temperature Fermi liquid theory [20]. Bep0 is chosen as 3.6 × 1011 s−1K−1 which is predicted by matching the experimental results of dielectric constant at room temperature [21]. The electron–electron scattering rate of Lorentzian oscillators Aee1, Aee2 are assumed to be the same as those in the Drude model Aee0. Bep1,Bep2 are determined using room temperature optical constants with Eq. (7) [17]. We also found that a temperature-independent term Yi needs to be included for the Lorentzian oscillators (Y0 is taken to be 0), in order to fit the entire optical response. Y1, Y2 are found to be 7.9 × 1014 rad/s and 1.9 × 1015 rad/s, respectively. All the parameters are listed in Table 1.
Study of the ferromagnetic quantum phase transition in Ce3−x Mg x Co9
Published in Philosophical Magazine, 2020
Tej N. Lamichhane, Valentin Taufour, Andriy Palasyuk, Sergey L. Bud'ko, Paul C. Canfield
Despite being 75% atomic Co, pure CeCo has a Pauli paramagnetic, low-temperature ground state. In polycrystalline samples of CeMgCo, structural and transformation of a Pauli paramagnetic CeCo into a ferromagnetic phase was studied in our earlier work [5]. It is a rhombohedral crystal system with space group R−3m. There are two inequivalent Ce-sites among where 3g sites are partially substituted with Mg. Though the systematic experimental investigation is not done, our speculation of development of itinerant ferromagnetism via tuning the density of states of Co-bands [5] agrees with first-principle calculations [6]. A similar example of doping-induced quantum phase transition of a Pauli paramagnetic to ferromagnetic system is observed in a lightly Fe-doped (CrFe)B system [7]. This system exhibits a quantum phase transition along with a distinct intermediate antiferromagnetic phase and associated non-Fermi liquid behaviours in thermodynamical and transport properties. However, in this study, no intermediate phase and non-Fermi liquid behaviour was not observed in the studied physical properties. For single-phase samples, ferromagnetism was observed for . In mixed-phase samples, signs of magnetic order could be found for but in such samples, magnetism could be influenced by several factors such as defects [8], stress [9], impurities [10], etc. To elucidate the phase transformation in a much cleaner way, the study of magnetism using single-phase, single-crystalline samples is always a better idea. We investigated the magnetic properties, electrical transport and specific heat capacity of selected compositions around 0.35 of single-crystalline CeMgCo samples.