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International audience; T he focus of much research on correlated-electron quantum materials is the competition between ordered and disordered electronic states, their tuning via quantum phase transitions and their possible relationship with unconventional superconductivity 1-6. Amongst these materials, URu 2 Si 2 occupies a special place, due to the richness of its quantum electronic properties and the challenge of understanding them 7. Discussions and controversies still exist about the nature of the 'hidden-order' (HO) phase, which is established below the temperature T 0 = 17.5 K. Efforts have been devoted to understand its order parameter, but so far none has been successful in determining it unambiguously. The transition at T 0 leads to strong physical responses, such as a large jump in the heat capacity 8 , an enhancement and a sudden gapping of intersite magnetic fluctuations 9,10 , a boost of the carrier mobility and a modification of the Fermi surface 11-14 and the opening of an electronic gap 15,16. While neutron diffraction experiments 17 showed a small antiferromagnetic (AF) moment below T 0 , most now accept that ambient-pressure antiferromagnetism is an extrinsic property induced by crystal defects and distortions 18. One proposal, motivated by Fermi-surface studies under pressure, is that the HO has the same periodicity of wavevector k 0 = (0 0 1) as the AF phase stabilized under pressure 19. The symmetry of the HO has also been considered: torque 20 and diffrac-tion 21 experiments lead to the proposal of a nematic behaviour in the HO phase. However, this picture faces a series of contradictory diffraction 22,23 , NMR 24 and thermodynamic 25 experiments, and the question of the symmetry remains open. Beyond experiments , many theories have tried to describe the HO within different approaches: localized, itinerant or dual (localized/itinerant) f-electrons, multipolar order, nematicity, spin liquid, 'hastatic' order and so on 26-30. It is difficult to find experimental evidence, in a direct and unambiguous manner, for the order parameters proposed by these models. To reveal the physics of the HO, an alternative route is to study how it can be destabilized by tuning external parameters 5. In the HO state, gapped low-energy magnetic fluctuations peaked at the wavevectors k 0 and k 1 = (0.6 0 0) (refs. 9,10) can be seen as precursors of long-range magnetic ordering with the same wavevectors and indicate nearby quantum phase transitions. In heavy-fermion paramagnets, such intersite magnetic fluctuations often indicate the proximity of a magnetically ordered phase. For instance, in the textbook CeRu 2 Si 2 case quantum magnetic fluctuations with wave-vector k 1 = (0.31 0 0) can be transformed into long-range magnetic order with the same wavevector by La doping 31. As well as doping, pressure and magnetic field are ideal tools to tune the electronic interactions. In URu 2 Si 2 , hydrostatic pressure 32-34 leads to a phase transition from the HO phase towards an AF state, with the wave-vector k 0 and the moments aligned along the c axis of the tetrago-nal crystal. At ambient pressure, under a magnetic field from 35 to 39 T applied along c, the HO is replaced by a spin-density wave (SDW), where the magnetic moments are ordered with the wave-vector k 1 and aligned along c (refs. 35,36). Remarkably, experiments under combined magnetic field and pressure, in the limited ranges 16 T/2 GPa (ref. 37) and 45 T/1 GPa (ref. 38), showed that a magnetic field applied to the pressure-induced AF phase induces a return to the HO phase 37 , and that the SDW phase shrinks and moves to higher fields under pressure 38. The relative stability of these different types of order is clearly complicated, and a full description of how URu 2 Si 2 evolves under combined pressure and magnetic field is needed. Here, we present the three-dimensional (3D) magnetic-field-pressure-temperature phase diagram of URu 2 Si 2. Its magnetoresis-tivity was measured in magnetic fields up to 60 T combined with pressures up to 4 GPa. We find a rich phase diagram indicating a subtle competition between the electronic interactions. The main features are the disappearance of the field-induced SDW phase and a squeezing out of the HO phase under high pressure. We emphasize that many of the boundaries of the 3D phase diagram are controlled by the field and pressure dependences of a single parameter characterizing the electronic correlations. The mystery of the hidden-order phase in the correlated electron paramagnet URu 2 Si 2 is still unsolved. To address this problem, one strategy is to search for clues in the subtle competition between this state and neighbouring magnetically ordered states. It is now well established that long-range antiferromagnetic order can be stabilized in this metal when it is under pressure and that a spin-density wave manifests when a magnetic field is applied along the easy magnetic axis c. However, the full boundaries of the hidden-order phase in the pressure-magnetic-field plane have not been determined so far. Here we present a systematic investigation of URu 2 Si 2 under combined high pressures and intense magnetic fields. The boundaries of the hidden-order, antiferromagnetic and spin-density-wave phases are mapped out, indicating an intricate three-dimensional phase diagram. We show that the field-induced spin-density-wave and hidden-order phases disappear in favour of antiferromagnetism at high pressure. Interestingly, a large number of phase boundaries are controlled by the field and pressure dependences of a single parameter. This gives new constraints for theories that model the electronic correlations and ordered phases in URu 2 Si 2. NAtURe PhySicS | VOL 16 | SEPTEMbER 2020 | 942-948 | www.nature.com/naturephysics 942

We have measured the temperature dependence of resistivity in single-crystalline CeNiGe$_{3}$ under hydrostatic pressure in order to establish the characteristic pressure-temperature phase diagram. The transition temperature to AFM-I phase $T_{\rm N1}$ = 5.5 K at ambient pressure initially increases with increasing pressure and has a maximum at $\sim$ 3.0 GPa. Above 2.3 GPa, a clear zero-resistivity is observed (SC-I phase) and this superconducting (SC) state coexists with AFM-I phase. The SC-I phase suddenly disappears at 3.7 GPa simultaneously with the appearance of an additional kink anomaly corresponding to the phase transition to AFM-II phase. The AFM-II phase is continuously suppressed with further increasing pressure and disappears at $\sim$ 6.5 GPa. In the narrow range near the critical pressure, an SC phase reappears (SC-II phase). A large initial slope of upper critical field $\mu_0H_{\rm c2}$ and non-Fermi liquid behavior indicate that the SC-II phase is mediated by antiferromagnetic fluctuations. On the other hand, the robust coexistence of the SC-I phase and AFM-I phase is unusual on the contrary to superconductivity near a quantum critical point on most of heavy-fermion compounds., Comment: 5 pages, 6 figures

Zeolite LSX (low-silica X) crystals have an aluminosilicate framework with regular supercages and β-cages. They are arrayed in a double diamond structure. The loading density of guest K atoms per supercage (or β cage), n, can be controlled from 0 to ≈ 9. At n 6. These properties are explained by the polaron effect including the electron correlation. Ferrimagnetic properties are observed at n ≈ 9. A remarkable increase in the resistivity is observed at very low temperatures at n ≈ 9, and is discussed in terms of the hypothesis of a Kondo insulator.

Alkali metal nanoclusters can be stabilized in the regular cages of zeolite crystals by the loading of guest alkali metals. Cages are connected by the sharing of windows of the framework, and arrayed in simple cubic, diamond and body centered cubic structures in zeolites A, X and sodalite, respectively. The s-electrons have the localized nature of nanoclusters with magnetic moments, and have mutual interactions through the windows of cages. They show exotic magnetism depending on the structure type of zeolites, the kind of alkali metals and the average loading density of alkali atoms per cage. In zeolite A, potassium clusters are formed in α-cages that have an inside diameter of 11 A. They exhibit ferromagnetic properties explained by the canted antiferromagnetism of the Mott insulator, where the 1p-like degenerate orbitals of clusters play an essential role in the magnetic properties. Na-K alloy clusters generated at supercages and β-cages of low-silica X (LSX) zeolite exhibit Neel’s N-type ferrimagnetism at specific loading densities of alkali metals. Alkali metal clusters in sodalite show the ideal Heisenberg antiferromagnetism of the Mott insulator.

The mineral tetrahedrite Cu$_{12}$Sb$_{4}$S$_{13}$ exhibits a first-order metal--insulator transition (MIT) at $T_{\rm MI}$ = 85 K and ambient pressure. We measured the $^{63}$Cu-NMR at ambient pressure and the resistivity and magnetic susceptibility at high pressures. $^{63}$Cu-NMR results indicate a nonmagnetic insulating ground state in this compound. The MIT is monotonically suppressed by pressure and disappears at $\sim1.0$ GPa. Two other anomalies are observed in the resistivity measurements, and the pressure -- temperature phase diagram of Cu$_{12}$Sb$_{4}$S$_{13}$ is constructed., Comment: 5 pages, 7 figures

We grew single crystals of PrCoIn 5 , PrRhIn 5 , and PrIrIn 5 with the tetragonal crystal structure and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization and de Haas–van Alphen effect. These Pr compounds reveal no magnetic ordering. The topology of the Fermi surfaces is the same as that of a non-4 f reference compound LaRhIn 5 . The cyclotron mass and/or the electronic specific heat coefficient are also approximately the same as those of LaRhIn 5 . The magnetic susceptibility and magnetization are anisotropic, reflecting the crystal structure, which are well explained by the tetragonal crystalline electric field scheme with the singlet ground state.

We report the discovery of new superconducting and novel magnetic phases in CeIn$_3$ on the verge of antiferromagnetism (AFM) under pressure ($P$) through the In-nuclear quadrupole resonance (NQR) measurements. We have found a $P$-induced phase separation of AFM and paramagnetism (PM) without any trace for a quantum phase transition in CeIn$_3$. A new type of superconductivity (SC) was found in $P=2.28-2.5$ GPa to coexist with AFM that is magnetically separated from PM where the heavy fermion SC takes place. We propose that the magnetic excitations such as spin-density fluctuations induced by the first-order magnetic phase transition might mediate attractive interaction to form Cooper pairs.

Magnetic excitations in a single crystal of heavy-fermion superconductor PrOs 4 Sb 12 have been studied by inelastic neutron scattering (INS) at low temperatures under high magnetic fields. The crystal field (CF) excitations at 0.7 meV observed in a previous INS study of a polycrystal sample were confirmed in this study on a single crystal. The observed excitations in the zero magnetic field soften around a wave vector (1,0,0), which is the modulation vector of the field-induced antiferro-quadrupolar ordering, suggesting the presence of quadrupolar instability. The observed field dependence of excitations is better reproduced in a singlet ground-state model rather than in a non-Kramers doublet ground-state model. In a high resolution experiment, furthermore, the change of the excitation spectra at (1,0,0) was observed on passing through the superconducting transition temperature, indicating that the excitation and the superconductivity are closely related in PrOs 4 Sb 12 .

Neutron diffraction experiments on the heavy-fermion superconductor PrOs 4 Sb 12 revealed that a small antiferromagnetic moment, parallel to [010] ( y -direction), is induced in the field-induced phase ( H ∥ z ). The analysis, based on the Γ 1 singlet ground state crystal field model, shows that antiferro-order of O y z -type quadrupole moments of Pr ions is formed in the field-induced phase. This strongly suggests that the crystal field ground-state of Pr ions in PrOs 4 Sb 12 is the Γ 1 singlet and the quadrupolar ordering is induced due to level crossing with an excited state under a magnetic field.

The effects of pressure on antiferromagnetic (AFM) and superconducting phase transitions of 112-type Ca$_{1-x}$La$_{x}$FeAs$_{2}$ were studied, and the in-plane electrical resistivity $\rho_{ab}$ was measured with an indenter-type pressure cell. The AFM phase transition temperatures of $T_{\rm N}$ = 47, 63, and 63 K at ambient pressure for $x$ = 0.18, 0.21, and 0.26 was suppressed by applying pressure $P$, with superconductivity emerging at critical pressures of $P_{\rm c}$ $\simeq$ 0, 1.5, and 3.4 GPa, respectively. Correspondingly, the slope of $T_{\rm N}$ against $P$ decreased as $dT_{\rm N}/P$ $\simeq$ $-$15 and $-$2 K/GPa for $x$ = 0.21 and 0.26, respectively. Thus, although the AFM phase was stabilized with La doping $x$, the AFM phase was suppressed by pressure, and superconductivity eventually emerged., Comment: 4 pages, 2 figures, Note added after publication: We noticed a paper by Yazhou Zhou et al. [Science Bulletin, 62, 857(2017)] reporting the pressure-induced superconductivity in the 112 system

We measured the specific heat, thermal expansion coefficient, magnetization, electrical resistivity, magnetoresistance and de Haas-van Alphen (dHvA) effect in PrSn 3 . The dense Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass of 8–9 m 0 for the main Fermi surface. The magnetic phase diagram was also clarified by the high-field magnetization measurement.

We have studied the magnetic and Fermi surface properties in a ferromagnet UGa 2 . The electrical resistivity, elastic constant, thermal expansion coefficient, thermoelectric power, magnetic susceptibility and Hall coefficient indicate highly anisotropic properties, reflecting the hexagonal structure. The 5 f 2 - and 5 f 3 -CEF schemes, based on the localized 5 f -electron nature, are discussed to understand the magnetic susceptibility and magnetization data. We have also done the magnetoresistance and de Haas-van Alphen (dHvA) experiments to investigate the Fermi surface properties. Both data are very complicated, implying that the Fermi surface is a multiply-connected one. They are explained neither by the localized 5 f 2 - and 5 f 3 -core models nor by the spin-polarized 5 f -itinerant model. The cyclotron mass is, however, rather light, ranging from 0.17 to 6.2 m 0 , which is consistent with the electronic specific heat coefficient of 11 mJ/K 2 ·mol.

We have measured the ac magnetic susceptibility in various fields and thermal expansion of single crystals of the heavy fermion compound ${\mathrm{CeCu}}_{6}$ at temperatures down to $250\ensuremath{\mu}\mathrm{K}$. The susceptibility of ${\mathrm{CeCu}}_{6}$ shows a peak at about 2 mK and has a large anisotropy. We also detected an anomaly of thermal expansion at the same temperature. The observed behaviors of the susceptibility and the thermal expansion in ${\mathrm{CeCu}}_{6}$ indicate the occurrence of an antiferromagnetic order.

We have carried out the de Haas-van Alphen (dHvA) experiments in a valence fluctuating compound CeNi. Forty seven dHvA branches are observed experimentally, which are mainly centered at the symmetrical axes. Most of the dHvA branches are approximately explained by the 4 f -itinerant band model. The cyclotron mass is in the range from 3.0 to 27 m 0 . Branch α, which has the largest cross-sectional area of the Fermi surface in the detected branches along the a -axis, has the cyclotron mass of 27 m 0 . This mass is five times larger than the corresponding band mass of 5.45 m 0 .

We have grown single crystals of CeRh 2 Si 2 and LaRh 2 Si 2 , and measured the temperature dependence of the thermal expansion coefficient. The magnetic component of the thermal coefficient in CeRh 2 Si 2 has been analyzed on the basis of the crystalline electric field. We have also succeeded in observing the de Haas-van Alphen (dHvA) effect of CeRh 2 Si 2 . The detected dHvA branches are small in cross-section and are observed in a narrow angle region centered at the symmetrical axis, reflecting the multiply-connected Fermi surface.

We have grown single crystals of CeRh 2 Si 2 and LaRh 2 Si 2 by the Czochralski pulling method in a tetra-arc furnace. The electrical resistivity and magnetic susceptibility are highly anisotropic, reflecting the tetragonal crystal structure. A metamagnetic transition is found for the magnetic field along the [001] direction at 26 T.

The effects of Ni substitution on Ce(Cu1-xNix)2Si2 have been studied by specific heat and electrical resistivity measurements. The specific heat measurement has revealed that the enhanced quantum fluctuations around an antiferromagnetic quantum critical point are markedly suppressed by Ni substitution, and that the Fermi liquid state recovers in the Nirich region (x > 0.12). The characteristic T-linear dependence of the resistivity has been observed at approximately x ~ 0.10 together with a sign of superconductivity. The variation of n in the form of rho - rho0 = aT^n against Tmax^1, at which the resistivity peaks, coincides with the case of high-pressure experiments on pure CeCu2Si2. The anomalous T-linear behavior appears to occur in the crossover region from the Kondo regime to the valence fluctuation regime rather than in the conventional antiferromagnetic quantum critical region., 11 pages, 5 figures, to be published (J. Phys. Soc. Jpn)

We observed the de Haas–van Alphen (dHvA) oscillations in CeRh 2 Si 2 under pressures up to 1.54 GPa. Three dHvA branches at higher pressure than the critical pressure p c ≃1.06 GPa are well explained by the result of the 4 f -itinerant model. Their cyclotron masses are large, being 24 m 0 , 30 m 0 and 31 m 0 , which are about 4 times larger than the corresponding band masses.

Ca(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ undergoes successive phase transitions with increasing Rh doping in the $T$ $=$ 0 limit. The antiferromagnetic-metal phase with orthorhombic structure at 0.00 $\le$ $x$ $\le$ 0.020 is driven to a superconducting phase with uncollapsed-tetragonal (ucT) structure at 0.020 $\le$ $x$ $\le$ 0.024; a non-superconducting collapsed-tetragonal (cT) phase takes over at $x$ $\geq$ 0.024. The breakdown of Fermi-liquid transport is observed in the ucT phase above $T_{\rm c}$. In the adjacent cT phase, Fermi-liquid transport is restored along with a disappearance of superconductivity. This interplay of superconductivity and Fermi-liquid transport suggests the essential role of magnetic fluctuations in the emergence of superconductivity in doped CaFe$_2$As$_2$., 11 pages, 4 figures

We have studied the pressure dependence of the specific heat in a CeNi single crystal using a clamp-type pressure-cell up to 0.8 GPa. The pressure dependence of the electronic specific heat coefficient is found to exhibit a sharp drop at 0.3–0.4 GPa. The present result indicates the instability of a mixed valence state of 4 f electrons.

The temperature dependence of the Hall coefficient of CeIn3 under high pressure has been investigated. The absolute value of the Hall coefficient shows an anomalous increase below T* ∼ 80 K at ambient pressure. The increase in T* with increasing pressure is similar to the pressure dependence of the characteristic temperature where the resistivity reaches its maximum. The temperature variations below T* at various pressures are well scaled on a single curve that is the formula based on the two-fluid model. No effect of the antiferromagnetic fluctuations observed in CeTIn5 (T = Co, Rh, and Ir) is observed above 2 K even near the critical pressure where antiferromagnetic ordering disappears.

The pressure–temperature–field phase diagram and quantum fluctuation effect were investigated in the itinerant ferromagnet U3P4 by resistivity, ac susceptibility, and Hall effect measurements under high pressure. The zero-temperature ferromagnetic-to-paramagnetic transition is located at Pc ∼ 4.0 GPa. The tricritical point exists at P* = 3.8 GPa and T* = 32 K, where the ferromagnetic transition changes from second- to first-order. As a quantum fluctuation effect, the low-temperature resistivity at Pc follows T5/3 dependence, which was theoretically described in the case of a three-dimensional ferromagnet. This result indicates that the ferromagnetic-to-paramagnetic transition at Pc may be considered as weakly first-order. Another critical behavior, the huge enhancement of ρ0 observed at Pc, cannot be interpreted as the ferromagnetic fluctuation effect. The Hall effect measurements suggest that the magnetic structure in the ordered state changes under high pressure.

We present detailed investigations on the effects of Ni substitution (x) on Ce(Cu1−xNix)2Si2 with x < 0.3, and a pressure (p) study for x = 0.04(2), 0.05(2), and 0.09(2) by resistivity measurements. The Cu–Ni substitution suppresses both antiferromagnetic fluctuations and superconductivity in CeCu2Si2, and leads to a dramatic crossover from the heavy-fermion (HF) regime to the intermediate-valence (IV) regime with progressive Ni doping. The crossover can be characterized by a marked increase in Kondo temperature evaluated from resistivity, specific heat, and susceptibility measurements. In high-pressure resistivity measurements, the Ni-doped system exhibits similar anomalies to those observed in CeCu2Si2, namely, T-linear dependence, an enhancement of residual resistivity, and a marked decrease in the A coefficient of the T2-resistivity. Furthermore, we observed an unexpected upturn anomaly in resistivity in the Ni-doped system under high pressure. By constructing the x–p phase diagram of Ce(Cu1−xNix)2Si2...

The longitudinal magnetoresistance (LMR) of polycrystalline Ce(Cu1−xNix)2Si2 samples is investigated between T = 2 and 15 K up to H = 80 kOe. The application of magnetic field induces anomalous temperature dependence of the resistivity with the power index n 0.03) is observed at 2 K. The negative LMR at 80 kOe is maximized (∼ −4 % at T = 2 K) around x ∼ 0.10 and subsequently disappears at higher Ni concentrations. Disappearance of the positive LMR in lower x region and the negative LMR at higher Ni concentrations implies a collapse of a coherent Kondo lattice state, and a rapid enhancement of Kondo temperature, respectively. Anomalous quantum fluctuations are probably developed around x ∼ 0.10.

EuGa4 and EuAl4 crystallize in the BaAl4-type tetragonal structure. The antiferromagnetic order was observed at 15 and 16.5K in EuGa4 and EuAl4, respectively.1,2) The magnetic susceptibilities in EuGa4 and EuAl4 well follow the Curie–Weiss law with effective moments of 7.97 and 8.02 B, respectively, which are consistent with the theoretical value of 7.94 B for a Eu-divalent electronic state.1,3) In the electrical resistivity and thermoelectric power measurements under pressure, a shoulderlike change was observed below about 100K at 1GPa in EuGa4. Moreover, a similar resistivity hump was observed below TCDW 1⁄4 140K at ambient pressure in EuAl4. The authors in Ref. 2 considered that this transition corresponds to the emergence of a charge density wave (CDW). In this study, we measured the magnetoresistance and Hall effect to clarify whether this is indeed based on CDW transition. Single crystals of EuAl4 were grown by the Al self-flux method. The transverse magnetoresistance and Hall resistivity were measured with an AC resistance bridge. The magnetic field H was applied along the [010] and [001] directions. The electrical current flow J was parallel to the [100] direction. Figure 1 shows a Kohler plot for the transverse magnetoresistance in the configurations of H k 1⁄2001 and J k 1⁄2100 . Kohler’s rule, i.e., = 1⁄2 ðHÞ ð0Þ = ð0Þ 1⁄4 fðH= ð0ÞÞ, holds when the temperature dependences of the scattering relaxation time are the same for all carriers. The = above 150K, namely, at 150, 160, and 200K, is well scaled on a single curve, which indicates that Kohler’s rule is satisfied above TCDW. On the other hand, the = below 140K deviates from Kohler’s rule, indicating that the carrier density and/or the scattering mechanism change below TCDW. In the two-band model, the transverse magnetoresistance and Hall resistivity are expressed as xx 1⁄4 ex hxð ey þ hyÞ þ ð exR 2 h þ hxReÞH ð ex þ hxÞð ey þ hyÞ þ ðRe þ RhÞH2 ; ð1Þ yx 1⁄4 ðRe hx hy þ Rh ex eyÞ þ ReRhðRe þ RhÞH 2 ð ex þ hxÞð ey þ hyÞ þ ðRe þ RhÞH2 H; ð2Þ where ei ( hi) and Re (Rh) are the resistivity along the i 1⁄4 xor y-direction and the Hall coefficient of the electron (hole) band, respectively.4) The Hall coefficient of each band is inversely proportional to the carrier density as Re 1⁄4 1=nee and Rh 1⁄4 1=nhe, where ne and nh are the electron and hole densities, respectively. The resistivity of each band is ei 1⁄4 1=ne eie ( hi 1⁄4 1=nh hie), where ei ( hi) is the mobility of the electron (hole). The transverse magnetoresistance increases quadratically, = H, for a compensated metal (ne 1⁄4 nh) at a high field limit (!c 1), whereas it tends to saturate for an uncompensated metal (ne 61⁄4 nh). Here, !c is the cyclotron frequency and is the scattering relaxation time. !c is roughly estimated using the relation = ð!c Þ2, which is obtained from the free-electron model. There is one EuAl4 unit in a body-centered tetragonal primitive cell. Considering that Eu is divalent, as proved by the magnetic susceptibility data,3) EuAl4 is a compensated metal with an even number of valence electrons. The experimentally obtained H-dependent magnetoresistance of up to = 2:5 10 2 (!c 0:16), shown as the solid curve in Fig. 1, reveals that EuAl4 is a compensated metal above TCDW. On the other hand, the = below TCDW gradually deviates at higher fields from the initial H dependence, as shown by the broken curve in Fig. 1 and the broken line in the inset of Fig. 1, at 100K. The deviation at 100K occurs at = 8 10 3 (!c 0:09). This behavior corresponds to the tendency toward saturation at higher fields, although the high field limit (!c 1) is not satisfied. Therefore, the transverse magnetoresistance indicates that EuAl4 is a compensated metal above TCDW and changes into an uncompensated metal below TCDW. The present experimental result and the hump of μ just below TCDW indicate that ne or nh starts to decrease below TCDW. Figure 2 shows the temperature dependence of the Hall coefficient RH determined at 0 T, shown by solid circles for H k 1⁄2010 and by solid squares for H k 1⁄2001 . The phase transitions at TCDW 1⁄4 140K and TN 1⁄4 14K are well observed. RH is temperature independent and negative above TCDW for both field directions. This means that the anomalous Hall coefficient, which is related to the magnetic susceptibility, is negligible in EuAl4. The negative RH for the compensated metal indicates e > h. The absolute value of RH increases with decreasing temperature below TCDW. The Hall resistivity is proportional to the magnetic field above TCDW, for example, at 200K, as shown in the inset of Fig. 2. On the other hand, the Hall resistivity gradually deviates downward from the linear field dependence with decreasing 0.06

Pressure effects on the rattling and superconductivity in the Einstein solids; AxV2Al20 (Ax = Ga0.2, Al0.3, and Y) are investigated by means of electrical resistivity measurements under high pressure. We observed bumps in resistivity at low temperatures only for Ga0.2 and Al0.3, which can be explained by scattering of conduction electrons by local phonons with Einstein temperatures of 8.5 and 22 K, respectively. The bumps gradually fade out with increasing pressure, and the temperature variations of resistivity for Ga0.2 and Al0.3 approach those of Y. This indicates that the low-energy local phonons in the Ga and Al compounds disappear at high pressures. We also observed \(T^{2}\) behavior with large \(A\) coefficients in the low-temperature limit for Ga and Al compounds, but not for Y. With increasing pressure, the \(A\) coefficient is largely suppressed, while \(H_{\text{c2}}' \equiv |\mathrm{d}H_{\text{c2}}/\mathrm{d}T|_{T_{\text{c}}}\) that also reflects the density of states at Fermi energy decreases...

Heat capacity and ac-susceptibility measurements under high pressure are carried out in SmOs 4 Sb 12 . Application of pressure increases the Curie temperature T C and enhances the heat-capacity jump at T C . On the other hand, the peak value of ac-susceptibility at T C decreases above 1 GPa and then almost vanishes at 3.6 GPa. These experimental facts suggest that the ordered state in SmOs 4 Sb 12 is not simple ferromagnetic state but possibly multipolar ordered state.

We report the results of Hall effect measurements on CeCu 2 Si 2 under high pressures up to 4.8 GPa. The Hall coefficient at ambient pressure increases with decreasing temperature and exhibits maximum at 4 K. The Hall coefficient at temperature higher than the coherent temperature of 10 K is consistent with the anomalous Hall effect. The pressure effect on the temperature dependence of the Hall coefficient is not simple. The pressure dependence of the Hall coefficient shows anomaly from 3.1 to 4.8 GPa, where the superconductivity is enhanced. These results indicate the close relationship between the Hall coefficient and the superconductivity.

A series of ternary compounds RRhIn 5 (R: rare earth) has been grown in the single crystalline form by means of the flux method. The magnetic properties of these compounds were investigated by meas...