We report on the itinerant ferromagnetic superconductor UGe2 through 73 Ge-NQR measurements under pressure (P ). The P dependence of the NQR spectrum signals a first-order transition from the low-temperature (T ) and low-P ferromagnetic phase (FM2) to high-T and high-P one (FM1) around a critical pressure of Px ∼ 1.2 GPa. The superconductivity exhibiting a maximum value of Tsc = 0.7 K at Px ∼ 1.2 GPa, was found to take place in connection with the P -induced first-order transition. The nuclear spin-lattice relaxation rate 1/T1 has probed the ferromagnetic transition, exhibiting a peak at the Curie temperature as well as a decrease without the coherence peak below Tsc. These results reveal the uniformly coexistent phase of ferromagnetism and unconventional superconductivity with a line-node gap. We remark on an intimate interplay between the onset of superconductivity and the underlying electronic state for the ferromagnetic phases.PACS numbers:

We report that a novel type of superconducting order parameter has been realized in the ferromagnetic states in UGe2 via 73 Ge nuclear-quadrupole-resonance (NQR) experiments performed under pressure (P ). Measurements of the nuclear spin-lattice relaxation rate (1/T1) have revealed an unconventional nature of superconductivity such that the up-spin band is gapped with line nodes, but the down-spin band remains gapless at the Fermi level. This result is consistent with that of a ferromagnetic spin-pairing model in which Cooper pairs are formed among ferromagnetically polarized electrons. The present experiment has shed new light on a possible origin of ferromagnetic superconductivity, which is mediated by ferromagnetic spin-density fluctuations relevant to the first-order transition inside the ferromagnetic states.The coexistence of magnetism and superconductivity (SC) has recently become an important topic in condensed-matter physics. The recent discovery of SC in ferromagnets UGe 2 [1, 2] and URhGe [3] has been a great surprise because the Cooper pairs are influenced by a non-vanishing internal field due to the onset of ferromagnetism (FM), which is believed to prevent the onset of SC. In the ferromagnet UGe 2 with a Curie temperature T Curie = 52 K at ambient pressure (P = 0), the emergence of P -induced SC has observed in the P range of 1.0 -1.6 GPa [1,2]. It is noteworthy that the SC in UGe 2 disappears above P c ∼ 1.6 GPa, beyond which FM is suppressed. The SC and FM in this compound have been shown to be cooperative phenomena [4]. The superconducting transition temperature (T sc ) is the highest at P x ∼ 1.2 GPa, where a first-order transition occurs from FM2 to FM1 as P increases. Here, it should be noted that ferromagnetic moments are increased in the first-order transition from FM1 to FM2 as functions of temperature and pressure, as shown in Fig. 1(a) [5,6,7]. The P -induced SC in UGe 2 coexists with FM1 and FM2 exhibiting the large magnetization of an order 1 µ B /U even for the case of T Curie ∼ 30 K [6]. Therefore, the onset of SC is proposed to be suitable for the formation of a spin-triplet pairing state rather than a spin-singlet pairing state [2]. However, there are few reports that address the type of order parameter is realized in FM1 and FM2. In a previous study, an unconventional nature of the SC has been suggested from the measurement of the 73 Ge-NQR nuclear spin-lattice relaxation rate 1/T 1 [6]. However, it has not been well understood whether the presence of the residual density of states (RDOS) at the Fermi level in the SC state is intrinsic or not, suggesting the occurrence of a possible extrinsic effect due to the presence of any impurity and/or imperfection in the sample [6]. In particular, it is unclear why SC emerges with the highest T sc when the first-order transition occurs from FM1 to FM2 at P x ∼ 1.2 GPa. In order to gain insight into this issue, further experiments are required for understanding a P -induced evolution in the FM states and a novel order-parameter symmetry emer...

We report on a cooperative phenomenon of ferromagnetism and unconventional superconductivity (SC) in UGe2 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 Pc ∼ 1.5 GPa, pointing to a first-order transition. The measurements of nuclear-spin-lattice-relaxation-rate 1/T1 revealed that SC emerges under the background of ferromagnetism, but not of the paramagnetic phase.KEYWORDS: itinerant ferromagnetism, unconventional superconductivity, UGe2, NQR under pressure, first-order phase transitionRecently, superconductivity (SC) has been observed under a background of ferromagnetism (FM) in UGe 2 1, 2 and URhGe.3 Since FM and SC have been generally believed to be exclusive from each other, the coexsistence of FM and SC in these compounds is a great surprise. Figure 1(a) shows the pressure (P ) versus temperature (T ) phase diagram of UGe 2 established from various measurements.1, 2, 4, 5, 7, 8 The ferromagnetic transition temperature T Curie at ambient pressure (P = 0) decreases monotonically from T Curie = 52 K with increasing P and seems to suddenly vanish around P c ∼ 1.5 GPa. SC was discovered in the range of P = 1 to 1.5 GPa, exhibiting the highest transition temperature T sc ∼ 0.7 K at P x ∼ 1.2 GPa. Upon cooling below T x , ferromagnetic moments increase markedly.1, 2, 5 The high-P -T and the low-P -T phases are denoted as FM1 and FM2 respectively, as indicated in the phase diagram. At P x , the first-order transition from FM2 to FM1 emerges as a function of P and at T x as a function of T in the case of P < P x . Here, P x is a terminal point of the first-order transition. 8, 11By contrast, it should be noted that both SC and FM1 are simultaneously suppressed at a ferromagnetic critical pressure P c . This suggests that SC and FM in UGe 2 are cooperative phenomena. Indeed, the 73 Ge-NQR measurements have revealed that both FM1 and FM2 coexist uniformly with the unconventional SC with a line nodegap in the vicinity of P x .9-11 It is surprising that the 5f electrons of uranium contribute to the onset of the uniform coexistent phase of FM and SC. This phenomenon is difficult to understand in terms of the spin-singlet pairing framework for the Cooper pairs. Therefore, this fact * Present address: Department of Physics, Faculty of Science, Okayama University, Okayama 700-8530, Japan suggests that SC in UGe 2 may be in a spin-triplet pairing state under the background of FM. In order to address the intimate interplay between FM and SC in UGe 2 near P c ∼ 1.5 GPa where FM seems to collapse, we here report on the microscopic characteristics of FM and SC near and over P c revealed by the measurements of nuclearquadrupole-resonance (NQR) of enriched 73 Ge under P at zero magnetic field (H = 0) . A polycrystalline sample enriched with 73 Ge was prepared and crushed into powder to allow a maximal penetration of oscillating magnetic field into the sample. The NQR experiment was per...

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Pancreatic fat content measured by computed tomography was significantly associated with IPMN. These results suggest that IPMN may develop secondary to pancreatic steatosis that could be an overlapping risk factor for PDAC and IPMN.