arXiv subjects

Etsuji Yamamoto

Publications and source records attributed to Etsuji Yamamoto.

41 records · Page 3Linked to original sources

arXiv2007

High pressure study on the strong-coupling superconductivity in non-centrosymmetric compound CeIrSi_3

We have carried out high pressure experiment on the pressure-induced superconductor CeIrSi$_3$ without inversion center. The electrical resistivity and ac heat capacity were measured in the same run for the same sample. The critical pressure of the antiferromagnetic state was determined to be $P_{\rm c}$ = 2.25 GPa. The heat capacity $C_{\rm ac}$ shows both antiferromagnetic and superconducting transitions at pressures close to $P_{\rm c}$. The superconducting transition temperature $T_{\rm sc}$ shows a maximum value of 1.6 K around $2.5-2.7$ GPa. At 2.58 GPa, a large heat capacity anomaly was observed at $T_{\rm sc}$ = 1.59 K. The jump of the heat capacity in the form of $Δ{C_{\rm ac}}/C_{\rm ac}(T_{\rm sc})$ is 5.7 $\pm$ 0.1. This is the largest value observed among all superconductors studied previously, suggesting the strong-coupling superconductivity in CeIrSi$_3$. The large magnitude and anisotropy of the upper critical field $B_{\rm c2}$ at 2.65 GPa is discussed from view points of the strong-coupling superconductivity and the reduced paramagnetic effect in the non-centrosymmetric superconductor. Above $P_{\rm c}$, the electrical resistivity shows the anomalous $T$-linear dependence in the wide temperature region from $T_{\rm sc}$ to 30 K, which is different from the Fermi liquid theory. Meanwhile, the heat capacity $C_{\rm ac}/T$ shows a simple temperature dependence in the normal state above $T_{\rm sc}$. These features do not seem to be explained simply by the spin fluctuation theory. The electronic specific heat coefficient at $T_{\rm sc}$ is approximately unchanged as a function of pressure, even at $P_{\rm c}$.

cond-mat.supr-con↗

arXiv2007

Strong-Coupling Superconductivity of CeIrSi$_3$ with the Non-centrosymmetric Crystal Structure

We studied the pressure-induced superconductor CeIrSi$_3$ with the non-centrosymmetric tetragonal structure under high pressure. The electrical resistivity and ac heat capacity were measured in the same run for the same sample. The critical pressure was determined to be $P_{\rm c}$ = 2.25 GPa, where the antiferromagnetic state disappears. The heat capacity $C_{\rm ac}$ shows both antiferromagnetic and superconducting transitions at pressures close to $P_{\rm c}$. On the other hand, the superconducting region is extended to high pressures of up to about 3.5 GPa, with the maximum transition temperature $T_{\rm sc}$ = 1.6 K around $2.5-2.7$ GPa. At 2.58 GPa, a large heat capacity anomaly was observed at $T_{\rm sc}$ = 1.59 K. The jump of the heat capacity in the form of $Δ{C_{\rm ac}}/C_{\rm ac}(T_{\rm sc})$ is 5.7 $\pm$ 0.1. This is the largest observed value among previously reported superconductors, indicating the strong-coupling superconductivity. The electronic specific heat coefficient at $T_{\rm sc}$ is, however, approximately unchanged as a function of pressure, even at $P_{\rm c}$.

cond-mat.str-el↗

arXiv2007

Itinerant to localized transition of f electrons in antiferromagnetic superconductor UPd2Al3

Electrons in solids have been conventionally classified as either band-like itinerant ones or atomic-like localized ones depending on their properties. For heavy Fermion (HF) compounds, however, the f electrons show both itinerant and localized behaviours depending on temperature. Above the characteristic temperature T*, which is typically of the order of few K to few tens K, their magnetic properties are well described by the ionic f-electron models, suggesting that the f-electrons behave as 'localized' electrons. On the other hand, well below T*, their Fermi surfaces (FS's) have been observed by magneto-oscillatory techniques, and generally they can be explained well by the 'itinerant' f-electron model. These two models assume totally different natures of felectrons, and how they transform between localized and itinerant state as a function of temperatures has never been understood on the level of their electronic structures. Here we have studied the band structure of the HF antiferromagnetic superconductor UPd2Al3 well below and above T* by angle-resolved photoelectron spectroscopy (ARPES), and revealed the temperature dependence of the electronic structure. We have found that the f-bands, which form the FS's at low temperatures are excluded from FS's at high temperatures. The present results demonstrate how the same f-electrons show both itinerant and localized behaviours on the level of electronic structure, and provide an important information for the unified description of the localized and itinerant nature of HF compounds.

cond-mat.str-el↗

arXiv2006

Itinerant U 5f band states in the layered compound UFeGa5 observed by soft X-ray angle-resolved photoemission spectroscopy

We have performed angle-resolved photoemission spectroscopy (ARPES) experiments on paramagnetic UFeGa5 using soft X-ray synchrotron radiation (hn=500eV) and derived the bulk- and U 5f-sensitive electronic structure of UFeGa5. Although the agreement between the experimental band structure and the LDA calculation treating U 5f electrons as being itinerant is qualitative, the morphology of the Fermi surface is well explained by the calculation, suggesting that the U 5f states can be essentially understood within the itinerant-electron model.

cond-mat.str-el↗

arXiv2005

Cooperative Phenomenon of Ferromagnetism and Unconventional Superconductivity in UGe$_2$: A ^73^Ge-NQR Study under Pressure

We report on a cooperative phenomenon of ferromagnetism and unconventional superconductivity (SC) in UGe$_2$ through the measurements of $^{73}$Ge nuclear-quadrupole-resonance (NQR) under pressure ($P$). The NQR spectra evidenced phase separation into ferromagnetic and paramagnetic phases in the vicinity of $P_c\sim 1.5$ GPa, pointing to a first-order transition. The measurements of nuclear-spin-lattice-relaxation-rate $1/T_1$ revealed that SC emerges under the background of ferromagnetism, but not of the paramagnetic phase.

cond-mat.str-el↗