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تسجيل مستخدم جديدConvergence of the enhancement of the effective mass under pressure and magnetic field in heavy-fermion compounds: CeRu2Si2, CeRh2Si2, and CeIn3
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Emphasis is given on the observation of a convergence to a critical value of the effective mass of a heavy fermion compound by tuning it through a quantum instability either by applying pressure or magnetic field from an antiferromagnetic (AF) to a paramagnetic (PM) ground state. Macroscopic and microscopic results are discussed and the main message is to rush to the discovery of an ideal material whose Fermi surface could be fully observed on both sides of each quantum phase transition.
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The effect of uniaxial pressure (P_u) on the magnetic susceptibility (X), magnetization (M), and magnetoresistance (MR) of the heavy-fermion metamagnet CeRu2Si2 has been investigated. For the magnetic field along the tetragonal c axis, it is found th
at characteristic physical quantities, i.e., the temperature of the susceptibility maximum (T_max), the pagamagnetic Weiss temperature (Q_p), 1/X at 2 K, and the magnetic field of the metamagnetic anomaly (H_M), scale approximately linearly with P_u, indicating that all the quantities are related to the same energy scale, probably of the Kondo temperature. The increase (decrease) of the quantities for P_u || c axis (P_u || a axis) can be attributed to a decrease (increase) in the nearest Ce-Ru distance. Consistently in MR and X, we observed a sign that the anisotropic nature of the hybridization, which is believed to play an important role in the metamagnetic anomaly, can be controlled by applying the uniaxial pressure. PACS numbers: 75.20.Hr, 71.27.+a, 74.62.Fj
We report on the pressure-induced unconventional superconductivity in the heavy-fermion antiferromagnet CeIn3 by means of nuclear-quadrupole-resonance (NQR) studies conducted under a high pressure. The temperature and pressure dependences of the NQR
spectra have revealed a first-order quantum-phase transition (QPT) from an AFM to PM at a critical pressure Pc=2.46 GPa. Despite the lack of an AFM quantum critical point in the P-T phase diagram, we highlight the fact that the unconventional SC occurs in both phases of the AFM and PM. The nuclear spin-lattice relaxation rate 1/T1 in the AFM phase have provided evidence for the uniformly coexisting AFM+SC phase. In the HF-PM phase where AFM fluctuations are not developed, 1/T1 decreases without the coherence peak just below Tc, followed by a power-law like T dependence that indicates an unconventional SC with a line-node gap. Remarkably, Tc has a peak around Pc in the HF-PM phase as well as in the AFM phase. In other words, an SC dome exists with a maximum value of Tc = 230 mK around Pc, indicating that the origin of the pressure-induced HF SC in CeIn3 is not relevant to AFM spin fluctuations but to the emergence of the first-order QPT in CeIn3. When the AFM critical temperature is suppressed at the termination point of the first-order QPT, Pc = 2.46 GPa, the diverging AFM spin-density fluctuations emerge at the critical point from the AFM to PM. The results with CeIn3 leading to a new type of quantum criticality deserve further theoretical investigations.
We studied the anisotropy of the superconducting upper critical field $H_{rm c2}$ in the heavy-fermion superconductor UTe$_2$ under hydrostatic pressure by magnetoresistivity measurements. In agreement with previous experiments we confirm that superc
onductivity disappears near a critical pressure $p_{rm c} approx 1.5$~GPa, and a magnetically ordered state appears. The unusual $H_{rm c2}(T)$ at low temperatures for $H parallel a$ suggests that the multiple superconducting phases which appear under pressure have quite different $H_{rm c2}$. For a field applied along the hard magnetization $b$ axis $H_{rm c2} (0)$ is glued to the metamagnetic transition $H_{rm m}$ which is suppressed near $p_{rm c}$. The suppression of $H_{rm m}$ with pressure follows the decrease of temperature $T_{chi}^{rm max}$, at the maximum in the susceptibility along $b$. The strong reinforcement of $H_{rm c2}$ at ambient pressure for $H parallel b$ above 16~T is rapidly suppressed under pressure due to the increase of $T_{rm sc}$ and the decrease of $H_{rm m}$. The change in the hierarchy of the anisotropy of $H_{rm c2}(0)$ on approaching $p_{rm c}$ points out that the $c$ axis becomes the hard magnetization axis.
We present thermoelectric power (TEP) studies under pressure and high magnetic field in the antiferromagnet CeRh2Si2 at low temperature. Under magnetic field, large quantum oscillations are observed in the TEP, S(H), in the antiferromagnetic phase. T
hey suddenly disappear when entering in the polarized paramagnetic (PPM) state at Hc pointing out an important reconstruction of the Fermi surface (FS). Under pressure, S/T increases strongly of at low temperature near the critical pressure Pc, where the AF order is suppressed, implying the interplay of a FS change and low energy excitations driven by spin and valence fluctuations. The difference between the TEP signal in the PPM state above Hc and in the paramagnetic state (PM) above Pc can be explained by different FS. Band structure calculations at P = 0 stress that in the AF phase the 4f contribution at the Fermi level (EF) is weak while it is the main contribution in the PM domain. By analogy to previous work on CeRu2Si2, in the PPM phase of CeRh2Si2 the 4f contribution at EF will drop.
We have performed magnetization measurements at high magnetic fields of up to 53 T on single crystals of a uranium heavy-fermion compound U$_2$Zn$_{17}$ grown by the Bridgman method. In the antiferromagnetic state below the N{e}el temperature $T_{rm
N}$ = 9.7 K, a metamagnetic transition is found at $H_c$ $simeq$ 32 T for the field along the [11$bar{2}$0] direction ($a$-axis). The magnetic phase diagram for the field along the [11$bar{2}$0] direction is given. The magnetization curve shows a nonlinear increase at $H_m$ $simeq$ 35 T in the paramagnetic state above $T_{rm N}$ up to a characteristic temperature $T_{{chi}{rm max}}$ where the magnetic susceptibility or electrical resistivity shows a maximum value. This metamagnetic behavior of the magnetization at $H_m$ is discussed in comparison with the metamagnetic magnetism of the heavy-fermion superconductors UPt$_3$, URu$_2$Si$_2$, and UPd$_2$Al$_3$. We have also carried out high-pressure resistivity measurement on U$_2$Zn$_{17}$ using a diamond anvil cell up to 8.7 GPa. Noble gas argon was used as a pressure-transmitting medium to ensure a good hydrostatic environment. The N{e}el temperature $T_{rm N}$ is almost pressure-independent up to 4.7 GPa and starts to increase in the higher-pressure region. The pressure dependences of the coefficient of the $T^2$ term in the electrical resistivity $A$, the antiferromagnetic gap $Delta$, and the characteristic temperature $T_{{rho}{rm max}}$ are discussed. It is found that the effect of pressure on the electronic states in U$_2$Zn$_{17}$ is weak compared with those in the other heavy fermion compounds.
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