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青木 大*; Taupin, M.*; Paulsen, C.*; Hardy, F.*; Taufour, V.*; 小手川 恒*; Hassinger, E.*; Malone, L.*; 松田 達磨; 三宅 厚志*; et al.
Journal of the Physical Society of Japan, 81(Suppl.B), p.SB002_1 - SB002_6, 2012/12
被引用回数：3 パーセンタイル：26.98(Physics, Multidisciplinary)We review our recent studies on ferromagnetic superconductors, UGe2, URhGe, and UCoGe. We focus on experimental results of URhGe and UCoGe in which the superconductivity occurs already at ambient pressure. The huge upper critical field 
on UCoGe for the field along the hard magnetization axis (
-axis) is confirmed by the AC susceptibility measurements by the fine tuning of field angle. Contrary to the huge along the hard-magnetization axis, along the easy-magnetization axis (
-axis) is relatively small in value. However, the initial slope of , namely 
/
(
0) both in UCoGe and in URhGe indicates the large value, which can be explained by the magnetic domain effect detected in the magnetization measurements. The specific heat measurements using a high quality single crystal of UCoGe demonstrate the bulk superconductivity, which is extended under magnetic field for the field along -axis.
Si青木 大*; Knebel, G.*; Sheikin, I.*; Hassinger, E.*; Malone, L.*; 松田 達磨; Flouquet, J.*
Journal of the Physical Society of Japan, 81(7), p.074715_1 - 074715_6, 2012/07
被引用回数：24 パーセンタイル：74.76(Physics, Multidisciplinary)We performed the Shubnikov-de Haas (SdH) experiments of the low-carrier heavy-fermion compound URuSi at high fields up to 34T and at low temperatures down to 30 mK. All main SdH branches named 
and 
and were observed for all the measured field-directions, indicating that they are attributed to the closed Fermi surfaces with nearly spherical shapes. An anomalous split of branch 
was detected for the field along the basal plane; the split immediately disappeared by tilting the field to [001] direction, implying a fingerprint of the hidden order state. High-field experiments reveal the complicated field-dependence of the SdH frequencies and the cyclotron masses due to the Zeeman spin-splitting associated with the Fermi surface reconstruction in the hidden order state with small carrier numbers. A new SdH branch named 
with a large cyclotron mass of 25 
was detected at high fields above 23T close to hidden order instabilities.
SiMalone, L.*; 松田 達磨; Antunes, A.*; Knebel, G.*; Taufour, V.*; 青木 大*; Behnia, K.*; Proust, C.*; Flouquet, J.*
Physical Review B, 83(24), p.245117_1 - 245117_5, 2011/06
被引用回数：16 パーセンタイル：56.29(Materials Science, Multidisciplinary)Measurements of the thermoelectric coefficients of URuSi in a high magnetic field could imply topological Fermi surface changes even deep inside the hidden order state. A change is observed in the thermopower as a function of the field applied parallel to the easy axis of magnetization, which could signify a change in the Fermi surface characteristics. The maximum of the thermopower coincides with previously measured anomalies in resistivity at 
= 23T. We analyze our results in terms of a Lifshitz transition in URuSi originating from the hidden order Pauli depairing on a given subband.
Si青木 大*; Paulsen, C.*; 松田 達磨; Malone, L.*; Knebel, G.*; Haen, P.*; Lejay, P.*; 摂待 力生*; 大貫 惇睦; Flouquet, J.*
Journal of the Physical Society of Japan, 80(5), p.053702_1 - 053702_4, 2011/05
被引用回数：17 パーセンタイル：68.41(Physics, Multidisciplinary)Resistivity measurements performed under pressure in the paramagnetic ground state of CeRuSi are reported. They demonstrate that the relative change of effective mass through the pseudo metamagnetic transition is invariant under pressure. The results are compared with the first order metamagnetic transition due to the antiferromagnetism of Ce
La
RuSi which corresponds to the "negative" pressure of CeRuSi by volume expansion. Finally, we describe the link between the spin-depairing of quasiparticles on CeRuSi and that of Cooper pairs on the unconventional heavy fermion superconductor CeCoIn
.
