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CeTe 3 is a unique platform to investigate the itinerant magnetism in a van der Waals (vdW) coupled metal. Despite chemical pressure being a promising route to boost quantum fluctuation in this system, a systematic study on the chemical pressure effect on Ce 3+ (4 f 1 ) states is absent. Here, we report on the successful growth of a series of Se doped single crystals of CeTe 3 . We found a fluctuation driven exotic magnetic rotation from the usual easy-axis ordering to an unusual hard-axis ordering. Unlike in localized magnetic systems, near-critical magnetism can increase itinerancy hand-in-hand with enhancing fluctuation of magnetism. Thus, seemingly unstable hard-axis ordering emerges through kinetic energy gain, with the self-consistent observation of enhanced magnetic fluctuation (disorder). As far as we recognize, this order-by-disorder process in fermionic system is observed for the first time within vdW materials. Our finding opens a unique experimental platform for direct visualization of the rich quasiparticle Fermi surface deformation associated with the Fermionic order-by-disorder process. Also, the search for emergent exotic phases by further tuning of quantum fluctuation is suggested as a promising future challenge.

We construct a \"needle-anvil\" type point-contact spectrometer for spin polarization measurements, which is installed in a 4He-cryostat. Two types of piezo devices are used to control the contact size precisely between a sample ferromagnet and a superconductor. An attocube piezo-based positioner is mounted for coarse movement of the tip, while a stacked-type piezo device is used for fine control of the contact size. This enables to change the contact size between the tip and sample from sub micro-meters to atomic-size contacts continuously. By suppressing thermal flow into the sample space and mechanical vibration, we can keep the contact over hours, enabling the precision measurements. To examine the performance of the spectrometer, we study the spin polarization of polycrystalline SrRuO3 with the point-contact Andreev reflection measurements. The polarization is estimated to be ∼0.59 at the clean limit of the interface, which is consistent with previous study.

We report on hydrogen (H) and deuterium (D) atoms absorption below T = 20 K in metallic palladium (Pd) via quantum tunnelling (QT). When a small bias voltage is applied between Pd nanocontacts that are immersed in liquid H2 (D2), the differential conductance spectra measured by point-contact spectroscopy change enormously. The results indicate H (D) absorption in Pd nanocontacts at the temperature where H (D) absorption due to thermal hopping process is not expected, and can be explained by QT. The QT occurs when the energy level of the potential well trapping the H (D) atom coincides with those not trapping the H (D) atom, and is assisted by phonons induced by ballistic electrons.

To study non-magnetic and magnetic impurity effects at the superconductor-normal metal interfaces, we have measured the differential conductance dI/dV for Josephson contacts made by vanadium (V) nanoconstrictions with a different amount of hydrogen (H) and deuterium (D) impurities, which are prepared by a mechanically controllable break junction (MCBJ) technique at low temperature. Below the superconducting transition temperature TC, we have found distinct peaks within and outside the gap, known as the sub-gap structure and an over-the-gap structure respectively, due to 5% concentration of atomic H and D on V nanocontact. Moreover, the temperature dependence of dI/dV spectra represents that both structures are survived until the critical temperature TC, which is consistent with the prediction of BCS energy gap. On the other hand, a very high concentrating phase (30atom%) behaves as a normal metal.

We report experimental study on low-temperature hydrogen (H) absorption in vanadium (V) and niobium (Nb) nanocontacts below T = 20 K using a point-contact spectroscopy (PCS) technique. When a small bias voltage is applied between both sides of nanocontacts immersed in liquid H2, the differential conductance (dI/dV) and the second derivative (d2I/dV2) are changed from those for pure V and Nb nanocontacts. Further, the spectra approach to those for a high concentrated phase of H with increasing the bias voltage. The results indicate that in-situ investigation of H absorption process from liquid H2 is possible through dI/dV and d2I/dV2 measurements using the PCS technique.

PrAg2In has a non-Kramers doublet Λ3 ground state, which is expected to show a quadrupolar phenomena. Although many studies have been devoted to investigate the novel features of PrAg2In, there is no clear result how to remove the degeneracy of quadrupolar moment because this compound has a Heusler structure, in which the substitution between Pr and In ions is inevitable. We therefore prepare a high quality single crystal of PrAg2In with the residual resistivity ratio of 14, which is much larger than that of the previous samples. We measure the magnetic susceptibility with the SQUID magnetometer down to T 0.4 K and the specific heat in the magnetic fields up to H 8T along [100] crystal direction down to T =0.1 K. The susceptibility is consistent with the CEF calculation. The specific heat shows a sharp peak at around Tp 0.33 K. When the magnetic field is applied, the peak at TP does not move up to H 2.5 T. In contrast, it shifts to higher temperatures with broadening above H 2.5 T. The broad peak above H 2.5 T is well reproduced by the Schottky specific heat due to the splitting of the Λ3 doublet in the magnetic fields. From these results, we conclude that a phase transition related to the r3 doublet occurs at around TP.

The electrical conductance of cobalt (Co) nano-scale contacts prepared by a Mechanically Controllable Break Junction (MCBJ) technique has been studied to understand the origin of Fano resonance in ferromagnetic atomic-sized contacts. In an atomic-scale contacts, the zero-bias anomaly is well-fitted by the Fano formula. The characteristic temperature, which is introduced as the fitting parameter of that formula, exhibits the log-normal distribution. These indicate that the anomaly is likely caused by Kondo effect. Moreover, the zero-bias anomaly is observed in large scale contacts where the bulk ferromagnetic properties should be retained. This suggests the coexistence of Kondo effect and ferromagnetism.

We have measured the specific heat of heavy fermion YbCo2Zn20 down to 0.1 K under magnetic field up to 3 T. At zero-field, the electronic contribution to the specific heat Ce/T shows logarithmic increase with decreasing temperature and tends to saturate at lower temperature, reflecting the Fermi-liquid state. With increasing magnetic field, Ce/T exhibits a power-law divergence at Hm ~ 0.6 T, which corresponds to the critical field of the metamagnetic crossover. The field dependence of Ce/T shows the two peak structure and the local minimum point of this structure coincides with Hm as observed in prototypical metamagnetic compound CeRu2Si2. We will compare the characteristic energy scale relevant to the metamagnetic behavior of YbCo2Zn20 and CeRu2Si2.

We have measured the magnetic field dependence of the specific heat in PrPb3 for H || [001] and [110] up to H = 8T. At H = 0T, a sharp λ-type peak due to antiferro-quadrupolar(AFQ) ordering and a small anomaly appears at TQ = 0.43K and T* = 0.25K, respectively. The field dependence of TQ shows a reentrant behavior and a high-field phase appear above H ~ 6 T in the both field directions. T* shows a large difference between H || [001] and [110], suggesting that the anomaly is related to the anisotropic feature of the quadrupolar moment in magnetic fields. From these results, we describe the T-H phase diagram PrPb3 in H || [001] and [110].