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[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

日本物理学会誌及びJournal of the Physical Society of Japanの月刊について

Physical Review B

This review discusses instabilities of the Fermi-liquid state of conduction electrons in metals with particular emphasis on magnetic quantum critical points. Both the existing theoretical concepts and experimental data on selected materials are presented; with the aim of assessing the validity of presently available theory. After briefly recalling the fundamentals of Fermi-liquid theory, the local Fermi-liquid state in quantum impurity models and their lattice versions is described. Next, the scaling concepts applicable to quantum phase transitions are presented. The Hertz-Millis-Moriya theory of quantum phase transitions is described in detail. The breakdown of the latter is analyzed in several examples. In the final part experimental data on heavy-fermion materials and transition-metal alloys are reviewed and confronted with existing theory.

http://export.arxiv.org/pdf/cond-mat/0606317

Fermi-liquid instabilities at magnetic quantum phase transitions

We report the observation of heavy-fermion superconducitivity in CeCoIn5 at Tc =2.3 K. When compared to the pressure-induced Tc of its cubic relative CeIn3 (Tc ~200 mK), the Tc of CeCoIn5 is remarkably high. We suggest that this difference may arise from magnetically mediated superconductivity in the layered crystal structure of CeCoIn5 .

Heavy-fermion superconductivity in CeCoIn5 at 2.3K

We report specific heat measurements of the heavy fermion superconductor ${\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_{5}$ in the vicinity of the superconducting critical field ${H}_{c2}$, with magnetic fields in the [110], [100], and [001] directions, and at temperatures down to 50 mK. The superconducting phase transition changes from second to first order for fields above 10 T for $H\ensuremath{\parallel}[110]$ and $H\ensuremath{\parallel}[100]$. In the same range of magnetic fields, we observe a second specific heat anomaly within the superconducting state. We interpret this anomaly as a signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. We obtain similar results for $H\ensuremath{\parallel}[001]$, with the FFLO state occupying a smaller part of the phase diagram.

https://arxiv.org/pdf/cond-mat/0304420.pdf

Possible Fulde-Ferrell-Larkin-Ovchinnikov superconducting state in CeCoIn5.

CeIrIn5 is a member of a new family of heavy-fermion compounds and has a Sommerfeld specific heat coefficient of 720 mJ/mol-K2. It exhibits a bulk, thermodynamic transition to a superconducting state at Tc=0.40 K, below which the specific heat decreases as T2 to a small residual T-linear value. Surprisingly, the electrical resistivity drops below instrumental resolution at a much higher temperature T0=1.2 K. These behaviors are highly reproducible and field-dependent studies indicate that T0 and Tc arise from the same underlying electronic structure. The layered crystal structure of CeIrIn5 suggests a possible analogy to the cuprates in which spin/charge pair correlations develop well above Tc.

A New Heavy-Fermion Superconductor CeIrIn5: Relative of the Cuprates?

Raman spectra of ZnO and Co substituted Zn1-xCoxO (ZCO) were carried out using the Raman microprobe system with an p.,+ ion laser source of 514.5 nm wavelength. The shift towards the lower frequency side of the nonpolar E210w mode and the broadening due to Co substitution in ZnO were analyzed using the phonon confinement model. The magnetic measurements showed ferromagnetic behavior with the maximum saturation magnetization (1.2micron Beta/ErCo) for 10% Co substitution, which decreased wi th at further increase in Co concentrations. The intensities of E1(LO) at 584 cm-1 and multiphonon modes at 540 cm-1 were increased with an increase in Co substitution. The additional Raman modes in ceramic targets of ZCO spectra for higher concentration of Co substitution (x=15%-20%) were identified to be due to the spinel ZnCo2O4 secondary phase.

Raman Scattering Studies in Dilute Magnetic Semiconductor Zn(1-x)Co(x)O

We report a new family of Ce-based heavy-fermion compounds whose electronic specific heat coefficients range from about 400 to over 700 mJ/mole Ce-K2. Crystal in this family form as CenTmIn3n+2m, where T=Rh or Ir, n=1 or 2, and m=1, with a tetragonal structure that can be viewed as n-layers of CeIn3 units stacked sequentially along the c-axis with intervening m-layers of TIn2. Ambient and high pressure studies show that the quasi-2D layers of CeIn3 produce unconventional superconducting and magnetic ground states. This family should enable new understanding of the relationship between magnetism and superconductivity in heavy-fermion materials and more generally of why heavy-fermion superconductivity prefers to develop in one structure type and not another.

/pdf/superconductivity-and-magnetism-in-a-new-class-of-heavy-18yzdu18tw.pdf

P. G. Pagliuso

Papers

Heavy-fermion superconductivity in CeCoIn5 at 2.3K

Possible Fulde-Ferrell-Larkin-Ovchinnikov superconducting state in CeCoIn5.

A New Heavy-Fermion Superconductor CeIrIn5: Relative of the Cuprates?

Raman Scattering Studies in Dilute Magnetic Semiconductor Zn(1-x)Co(x)O

Superconductivity and Magnetism in a New Class of Heavy-Fermion Materials