High-temperature superconductors (HTSC) and heavy-fermion (HF) metals exhibit extraordinary properties. They are so unusual that the traditional Landau paradigm of quasiparticles does not apply. It is widely believed that utterly new concepts are required to describe the underlying physics. There is a fundamental question: how many concepts do we need to describe the above physical mechanisms? This cannot be answered on purely experimental or theoretical grounds. Rather, we have to use both of them. Recently, in HTSC, the new and exciting measurements have been performed, demonstrating a puzzling magnetic field induced transition from non-Fermi liquid to Landau Fermi liquid behavior. We show, that in spite of very different microscopic nature of HTSC and HF metals, the behavior of HTSC is similar to that observed in HF compounds. We employ a theory, based on fermion condensation quantum phase transition which is able to resolve the above puzzles.
Comment on "Spectroscopic Evidence for Multiple Order Parameters in the Heavy Fermion Superconductor CeCoIn5"
这是对Rourke等人最近发表的题为“Spectroscopic Evidence for Multiple序参量Parameters in the Heavy Fermion Superconductor CeCoIn 5”（cond-mat/0409562 v1 22 Sep 2004）的论文的评论。我们认为，洛克等人观察到的功能。这是因为它们的接触不在弹道极限内。
Majorana fermions cannot be found in nature as a free fundamental particle. Nevertheless, in condensed matter systems, they can emerge as a collective excitation. In this work, using functional integration techniques, we calculated the effective potential for emergent Majorana fermions in the Kitaev chain. In this case, we have shown how the superconductor parameter behaves as a function of temperature. Furthermore, we considered surface-induced superconductivity in a Topological Insulator and calculated the effective potential for emergent Majorana fermions in this system. In the case of an s…
Landau levels (LL) have been predicted to emerge in systems with Dirac nodal points under applied non-uniform strain. We consider 2D, $d_{xy}$ singlet (2D-S) and 3D $p \pm i p$ equal-spin triplet (3D-T) superconductors (SCs). We demonstrate the spinful Majorana nature of the bulk gapless zeroth-LLs. Strain along certain directions can induce two topologically distinct phases in the bulk, with zeroth LLs localized at the the interface. These modes are unstable toward ferromagnetism for 2D-S cases. Emergent real-space Majorana fermions in 3D-T allow for more exotic possibilities.
In heavy-fermion superconductors, it is widely believed that the superconducting gap function has sign-reversal due to the strong electron correlation. However, recently discovered fully-gapped s-wave superconductivity in CeCu2Si2 has clarified that strong attractive pairing interaction can appear even in heavy-fermion systems. To understand the origin of attractive force, we develop the multipole fluctuation theory by focusing on the inter-multipole many-body interaction called the vertex corrections. By analyzing the periodic Anderson model for CeCu2Si2, we find that hexadecapole fluctuation…
Nuclear quadrupole resonance (NQR) measurements were performed on the heavy fermion superconductor Ce3PtIn11 with Tc = 0.32 K. The temperature dependence of both spin-lattice relaxation rate 1/T1 and NQR spectra evidences the occurrence of two successive magnetic transitions with TN1 = 2.2 K and TN2 = 2.0 K. In successive magnetic transitions, even though the magnetic moment at the Ce(2) site plays a major role, the magnetic moment at the Ce(1) site also contributes to some extent. While a commensurate antiferromagnetic ordered state appears for TN2 < T < TN1, a partially incommensurate antife…
Motivated by recent London penetration depth measurement [H. Kim et al. Phys. Rev. Lett. \textbf{114}, 027003 (2015)] and novel composite pairing scenario [O. Erten, R. Flint and P. Coleman, Phys. Rev. Lett. \textbf{114}, 027002 (2015)] on Yb-doped heavy fermion superconductor CeCoIn$_{5}$, we revisit the issue of superfluid response in microscopic heavy fermion lattice model. However, it is found that in literature explicit expression of superfluid response function in heavy fermion superconductor is rare. In this paper, we make a contribution to this issue by investigating superfluid density…
Enhancement of Superconducting Transition Temperature due to the strong Antiferromagnetic Spin Fluctuations in Non-centrosymmetric Heavy-fermion Superconductor CeIrSi3 :A 29Si-NMR Study under Pressure
Anomalous metallic behavior, marked by a saturating finite resistivity much lower than the Drude estimate, has been observed in a wide range of two-dimensional superconductors. Utilizing the electrostatically gated LaAlO3/SrTiO3 interface as a versatile platform for superconductor-metal quantum phase transitions, we probe variations in the gate, magnetic field, and temperature to construct a phase diagram crossing from superconductor, anomalous metal, vortex liquid, to Drude metal states, combining longitudinal and Hall resistivity measurements. We find that the anomalous metal phases induced …
Topological superconductors are novel classes of quantum condensed phases, characterized by topologically nontrivial structures of Cooper pairing states. On the surfaces of samples and in vortex cores of topological superconductors, Majorana fermions, which are particles identified with their own anti-particles, appear as Bogoliubov quasiparticles. The existence and stability of Majorana fermions are ensured by bulk topological invariants constrained by the symmetries of the systems. Majorana fermions in topological superconductors obey a new type of quantum statistics referred to as non-Abeli…
We report a systematic study of temperature- and field-dependent charge ($\boldsymbolρ$) and entropy ($\mathbf{S}$) transport in the heavy-fermion superconductor CeIrIn$_5$. Its large positive thermopower $S_{xx}$ is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal $S_{xy}$. By separating the off-diagonal Peltier coefficient $α_{xy}$ from $S_{xy}$, we find that $α_{xy}$ becomes positive and greatly enhanced at temperatures well above the bulk $T_c$. Compared with the non-magnetic analog LaIrIn$_5$, these results…
Recently, Majorana Fermions (MFs) have attracted intensive attention due to their exotic statistics and possible applications in topological quantum computation (TQC). They are proposed to exist in various two-dimensional (2D) topological systems, such as px+ipy topological superconductor and nanowire-superconducting hybridization system. In this paper, two types of Majorana Fermions with different polygon sign rules are pointed out. A "smoking gun" numerical evidence to identify MF's classification is presented through looking for the signature of a first order topological quantum phase trans…
Through a systematic symmetry and topology analysis we establish that three-dimensional chiral superconductors with strong spin-orbit coupling and odd-parity pairing generically host low-energy nodal quasiparticles that are spin-non-degenerate and realize Majorana fermions in three dimensions. By examining all types of chiral Cooper pairs with total angular momentum $J$ formed by Bloch electrons with angular momentum $j$ in crystals, we obtain a comprehensive classification of gapless Majorana quasiparticles in terms of energy-momentum relation and location on the Fermi surface. We show that t…
