arXiv subjects

R. Settai

Publications and source records attributed to R. Settai.

46 records · Page 3Linked to original sources

arXiv2002

Fermi surface of the heavy fermion superconductor PrOs$_{4}$Sb$_{12}$

We have investigated the de Haas-van Alphen effect in the Pr-based heavy fermion superconductor PrOs$_4$Sb$_{12}$.The topology of Fermi surface is close to the reference compound LaOs$_4$Sb$_{12}$ and well explained by the band structure calculation based on the FLAPW-LDA+U method, where the 4{\it f} electrons are localized. We have confirmed a highly enhanced cyclotron effective mass 2.4$\sim7.6m_{\rm 0}$ which is apparently large compared to the usual Pr-based compounds.

cond-mat.str-el↗

arXiv2002

Exotic Heavy Fermion State in the Filled Skutterudite PrFe$_4$P$_{12}$ Uncovered by the de Haas-van Alphen Effect

We report the de Haas-van Alphen (dHvA) experiment on the filled skutterudite PrFe$_4$P$_{12}$ exhibiting apparent Kondo-like behaviors in the transport and thermal properties. We have found enormously enhanced cyclotron effective mass $m^{\rm \ast}_{\rm c}=81 m_{\rm 0}$ in the high field phase (HFP), which indicates that PrFe$_4$P$_{12}$ is the first Pr-compound in which really heavy mass has been unambiguously confirmed. Also in the low field non-magnetic ordered phase (LOP), we observed the dHvA branch with $m^{\rm \ast}_{\rm c}=10 m_{0}$ that is quite heavy taking into account its small Fermi surface volume (0.15% of the Brillouin zone size). The insensitivity of mass in LOP against the magnetic field suggests that the quadrupolar interaction plays a main role both in the mass renormalization and the LOP formation.

cond-mat.str-el↗

arXiv2002

^{115}In-NQR evidence for unconventional superconductivity in CeIn_3 under pressure

We report evidence for unconventional superconductivity in CeIn_3 at a pressure P = 2.65 GPa above critical pressure (P_c ~ 2.5 GPa) revealed by the measurements of nuclear-spin-lattice-relaxation time (T_1) and ac-susceptibility (ac-chi). Both the measurements of T_1 and ac-chi have pointed to a superconducting transition at T_c = 95 mK, which is much lower than an onset temperature T_{onset} = 0.15 K at zero resistance. The temperature dependence of 1/T_1 shows no coherence peak just below T_c, indicative of an unconventional nature for the superconductivity induced in CeIn_3.

cond-mat.str-el↗

arXiv2002

Coexistence of antiferromagnetism and superconductivity in heavy-fermions systems

We report the novel pressure(P)-temperature(T) phase diagrams of antiferromagnetism (AF) and superconductivity (SC) in CeRhIn$_5$, CeIn$_3$ and CeCu$_2$Si$_2$ revealed by the NQR measurement. In the itinerant helical magnet CeRhIn$_5$, we found that the Néel temperature $T_N$ is reduced at $P \geq$ 1.23 GPa with an emergent pseudogap behavior. The coexistence of AF and SC is found in a narrow P range of 1.63 - 1.75 GPa, followed by the onset of SC with line-node gap over a wide P window 2.1 - 5 GPa. In CeIn$_3$, the localized magnetic character is robust against the application of pressure up to $P \sim$ 1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations. In CeCu$_2$Si$_2$, the SC and AF coexist on a microscopic level once its lattice parameter is expanded. We remark that the underlying marginal antiferromagnetic state is due to collective magnetic excitations in the superconducting state in CeCu$_2$Si$_2$. An interplay between AF and SC is discussed on the SO(5) scenario that unifies AF and SC. We suggest that the SC and AF in CeCu$_2$Si$_2$ have a common mechanism.

cond-mat.str-el↗

arXiv2001

Pressure-Temperature Phase Diagram of Antiferromagnetism and Superconductivity in CeRhIn5 and CeIn3 : In-NQR Study under Pressure

We report the novel pressure($P$) - temperature($T$) phase diagram of antiferromagnetism and superconductivity in CeRhIn$_5$ and CeIn$_3$ revealed by the $^{115}$In nuclear-spin-lattice-relaxation ($T_1$) measurement. In the itinerant magnet CeRhIn$_5$, we found that the Néel temperature $T_N$ is reduced at $P \geq$ 1.23 GPa with an emergent pseudogap behavior. In CeIn$_3$, the localized magnetic character is robust against the application of pressure up to $P \sim$ 1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations.

cond-mat.str-el↗

arXiv2001

Pressure-induced Superconductivity in a Ferromagnet UGe$_2$ -- Resistivity Measurements in Magnetic Field --

The electrical resistivity measurements in the magnetic field are carried out on the pressure-induced superconductor UGe$_2$. The superconductivity is observed from 1.06 to 1.44 GPa. The upper critical field of $H_{C2}$ is anisotropic where $H_{C2}(T)$ exhibits positive curvature for $H//b$ and $c$-axis. The characteristic enhancement of $H_{C2}$ is reconfirmed for $H//a$-axis. In the temperature and field dependence of resistivity at $P > P_{C}$ where the ferromagnetic ordering disappears, it is observed that the application of the external field along the {\it a}-axis increases the coefficient of Fermi liquid behavior $AT^{2}$ correspondingly to the metamagnetic transition.

cond-mat↗

arXiv2001

Heat Capacity of the Pressure-induced Superconductivity in Itinerant Ferromagnet UGe$_2$

Recently co-existence of the ferromagnetism and superconductivity was reported in the high-pressure region (1.0-1.6 GPa) in UGe$_2$. We performed the heat capacity measurement on UGe$_2$ under high pressure. At 1.13 GPa, we found a peak corresponding to the superconducting transition. The superconducting temperature $T_{SC}$ and ${\itΔ} C/(γT_{SC})$ are 0.6 K and 0.25, respectively. The superconducting transition was also confirmed by the appearance of the Meissner effect in the {\it ac} susceptibility. From these results, we confirm a bulk nature of the superconductivity in UGe$_2$. The value of $C/T$ ($\sim$ 95 mJ/moleK$^2$) just above $T_{SC}$ at 1.15 GPa is as much as 3 times larger than that at ambient pressure, which indicates a large mass enhancement of quasiparticles under high pressure.

cond-mat.str-el↗

arXiv2001

Magnetic Properties of a Pressure-induced Superconductor UGe$_2$

We performed the DC-magnetization and neutron scattering experiments under pressure {\it P} for a pressure-induced superconductor UGe$_2$. We found that the magnetic moment is enhanced at a characteristic temperature {\it T}$^{*}$ in the ferromagnetic state, where {\it T}$^{*}$ is smaller than a Curie temperature {\it T}$_{\rm C}$. This enhancement becomes remarkable in the vicinity of {\it P}$_{\rm C}^{*}$ = 1.20 GPa, where {\it T}$^{*}$ becomes 0 K and the superconducting transition temperature {\it T}$_{\rm SC}$ shows a maximum. The characteristic temperature {\it T}$^{*}$, which decreases with increasing pressure, also depends on the magnetic field.

cond-mat.str-el↗

arXiv2001

Angular Position of Nodes in the Superconducting Gap of Quasi-2D Heavy-Fermion Superconductor CeCoIn_5

The thermal conductivity of the heavy-fermion superconductor CeCoIn_5 has been studied in a magnetic field rotating within the 2D planes. A clear fourfold symmetry of the thermal conductivity which is characteristic of a superconducting gap with nodes along the (+-pi,+-pi)-directions is resolved. The thermal conductivity measurement also reveals a first order transition at H_c2, indicating a Pauli limited superconducting state. These results indicate that the symmetry most likely belongs to d_{x^2-y^2}, implying that the anisotropic antiferromagnetic fluctuation is relevant to the superconductivity.

cond-mat.supr-con↗

arXiv2001

Superconducting Gap Structure of Spin-Triplet Superconductor Sr_2RuO_4 Studied by Thermal Conductivity

To clarify the superconducting gap structure of the spin-triplet superconductor Sr_2RuO_4, the in-plane thermal conductivity has been measured as a function of relative orientations of the thermal flow, the crystal axes, and a magnetic field rotating within the 2D RuO_2 planes. The in-plane variation of the thermal conductivity is incompatible with any model with line nodes vertical to the 2D planes and indicates the existence of horizontal nodes. These results place strong constraints on models that attempt to explain the mechanism of the triplet superconductivity.

cond-mat.supr-con↗