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3 Interfaces
Published in Jiabao Yi, Sean Li, Functional Materials and Electronics, 2018
Zhiqi Liu, Anil Annadi, Ariando
Shalom et al. [75] found that the MR of the 2DEG is strongly anisotropic. The out-of-plane MR is positive, while the in-plane parallel MR is negative up to more than 60% (Fig. 2.28). The positive MR can be understood by the orbital effect. The relevant mechanisms that can produce negative MR are 2D weak localization, magnetic impurities, and the magnetic order itself. The weak localization effect is typically small, of the order of few percent. The magnetic impurity effect is usually isotropic, which is hard to coincide with the strongly anisotropic MR here. Finally, it was concluded that the large negative MR is due to the magnetic order formed at the interface. In addition, MR measurements by Seri and Klein [76] revealed that the out-of-plane MR has an antisymmetric term [namely R(H) ± R(-H)] which increases with decreasing temperature and increasing field. It was suggested that nonuniform field-induced magnetization exists at the interface. These pioneering studies largely stimulated magnetic investigations on the 2DEG at the LAO/STO interface later.
Superfluid and Ginzburg–Landau behaviour in the cuprates
Published in J. R. Waldram, Superconductivity of Metals and Cuprates, 2017
Unfortunately, though the form (15.8) is plausible it has not proved easy to justify the relaxation-time approximation involved. In microscopic terms, departures from the equilibrium state may be described as suitable linear combinations of single-particle excitations, any one of which is usually long-lived and has a time dependence of the form e−iEkt/ℏ relative to the ground state. When the excitations concerned are spread over a range of energies E, they get out of phase with one another in a time of order ħ/E, and the order parameter does indeed decay approximately exponentially with this relaxation time. This is a good approximation in, for instance, a superconductor made gapless by magnetic impurity scattering. However, in a bcs superconductor with its sharp density of states, many of the important excitations have almost the same energy, and fluctuations tend to oscillate at the gap frequency Δ/ħ while decaying more gradually with several different significant relaxation times (Section 11.3). We shall ignore this complication, and assume that
Transport in Quantum Dots
Published in Jian-Bai Xia, Duan-Yang Liu, Wei-Dong Sheng, Quantum Waveguide in Microcircuits, 2017
Jian-Bai Xia, Duan-Yang Liu, Wei-Dong Sheng
When the temperature is lower than TK, the mobile electrons in the host metal tend to screen the non‐zero total spin of the electrons in the magnetic impurity atom. In the simplest Anderson model of a magnetic impurity there is only one electron level with energy 80 and the impurity spin is 1/2. The exchange processes can effectively flip the impurity spin while simultaneously creating a spin excitation in the Fermi sea. When many such processes are added coherently, a new state—the Kondo resonance—is generated with the same energy as the Fermi level. Such resonance is very effective at scattering electrons with energies close to the Fermi level. The strong scattering contributes greatly to the resistance. The whole system, that is, the magnetic impurity atom plus its surrounding electrons, forms a spin singlet. The energy scale for this singlet state is the Kondo temperature.
Persistent currents in the presence of the radial electric fields of charged rods and off-centre positively and negatively charged impurities
Published in Philosophical Magazine, 2021
H. K. Salehani, Davood Haji Taghi Tehrani, M. Solaimani
Persistent currents in different systems, such as multichannel rings or cylinders [20] and two-dimensional quantum dot arrays [17], coupled quantum rings [21], superconducting thin-walled cylinder [22], superconductor/quantum dot ring/superconductor [23], quantum rings with tunnel barriers [24], distorted quantum rings [25], twisted quantum rings [26], helical structures [27], polymer rings [28], ferromagnetic Heisenberg ring [29], ferrimagnetic spin rings [30], metal rings by correlated disorder [31], quantum ring coupled to a quantum wire [32], Mobius ladder [33], elliptical quantum rings [34], a ring of topological insulator thin film [35], two-terminal double quantum ring [36], MoS2 quantum rings [37], zigzag hexagonal graphene ring [38], crossed double rings [39], p-wave disordered superconducting rings [40], a ring with Aubry–André–Harper model [41] and the semiconducting mesoscopic device [42] have been considered. Besides, the effects of magnetic impurity [43], Rashba spin–orbit coupling [44], electron–electron interaction [45], dissipation [46], electron–phonon interaction [47] and quantum dot curvature [48] on the persistent current have so far been explored. The effect of the radial magnetic field on the persistent current of a quantum ring has previously been studied [49]. However, although the effect of external electric fields on the persistent currents [50], has till now been studied, the effect of the radial electric field of charged rods has not yet been investigated.
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
Figure 2 shows the zero-field cooled (ZFC) temperature-dependent magnetisation for . Although CeCo was identified as a Pauli paramagnetic compound long ago [17], there has been some room for the question because of the presence of a low-temperature upturn in temperature-dependent magnetisation [5]. Moreover, recent density functional calculation showed CeCo could order ferromagnetically at low temperature [6]. With of Mg addition, the low-temperature magnetisation remains temperature independent and manifests Pauli paramagnetism as shown in the inset of Figure 2. These temperature independent magnetisation data for x = 0.01, 0.16, and 0.24 confirm that for these x-values, CeMgCo is Pauli paramagnetic system. Since x = 0.01 sample is Pauli paramagnetic down to 2 K, this suggests that pure CeCo may also be a Pauli paramagnetic. The low temperature upturn [5] is most likely associated with magnetism of impurity ions or traces of extrinsic magnetic impurity.
Magnetic phase transitions around room temperature in Cu
Published in Phase Transitions, 2019
Annette Setzer, Pablo D. Esquinazi, Lukas Botsch, Oliver Baehre, Eti Teblum, Anat Itzhak, Olga Girshevitz, Gilbert Daniel Nessim
Apart from the magnetic impurity analysis described above, we have checked the influence of magnetic impurities in the magnetization of our samples by measuring magnetic field loops at 300 K. The magnetic moment m was measured following the field sequence (all values in kOe). Figure 2(a) shows the field loops of the magnetic moment of the Cu source sample at 300 K and one CuS bulk sample at two different temperatures. The observed differences in the diamagnetic response of the CuS sample at the same temperature indicate that the crystalline phase of the sample depends on the previous temperature cycle, as it will become clear in the next section. Note also that the susceptibility at 300 K of CuS is slightly paramagnetic (after reaching 300 K from low temperatures).