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Register a new userDesign of opposed-anvil-type high-pressure cell for precision magnetometry and its application to quantum magnetism
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We have developed a much sensitve technique to conduct magnetometry under ultrahigh pressures up to 6.3~GPa, which can detect a weak volume susceptibilities as small as $sim 10^{-4}$. An opposed-anvil-type high-pressure cell is designed by numerical analysis to give nearly zero magnetic response, in a commercial SQUID magnetometer. We introduced procedures for subtracting background contributions from a high-pressure cell by taking displacements of the cell parts into account, and found a way of resolving tiny magnetism of a sample from given magnetometer response curves. A non-magnetic material, binderless tungsten carbide ceramic, is employed. To increase sample-signal-to-background ratio further, a conical shaped gasket and cupped anvils are introduced, yielding nearly ten times better space efficiency. The new set-up and analysis are applied to measure the paramagnetic susceptibilities of spin orbit entangled moment under pressures.
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We have developed a new type of opposed-anvil high pressure cell with substantially improved space efficiency. The clamp cell and the gasket are made of non-magnetic Ni-Cr-Al alloy. Non-magnetic tungsten carbide (NMWC) is used for the anvils. The assembled cell with the dimension phi 29mm times 41mm is capable of generating pressure up to 9 GPa over a relatively large volume of 7 mm3. Our cell is particularly suitable for those experiments which require large sample space to achieve good signal-to-noise ratio, such as the nuclear magnetic resonance (NMR) experiment. Argon is used as the pressure transmitting medium to obtain good hydrostaticity. The pressure was calibrated in situ by measuring the fluorescence from ruby through a transparent moissanite (6H-SiC) window. We have measured the pressure and temperature dependences of the 63Cu nuclear-quadrupole-resonance (NQR) frequency of Cu2O, the in-plane Knight shift of metallic tin, and the Knight shift of platinum. These quantities can be used as reliable manometers to determine the pressure values in situ during the NMR/NQR experiments up to 9 GPa.
We propose an analytical approach to high-harmonic generation (HHG) for nonperturbative low-frequency and high-intensity fields based on the (Jeffreys-)Wentzel-Kramers-Brillouin (WKB) approximation. By properly taking into account Stokes phenomena of WKB solutions, we obtain wavefunctions that systematically include repetitive dynamics of production and acceleration of electron-hole pairs and quantum interference due to phase accumulation between different pair production times (St{u}ckelberg phase). Using the obtained wavefunctions without relying on any phenomenological assumptions, we explicitly compute electric current (including intra- and inter-band contributions) as the source of HHG for a massive Dirac system in (1+1)-dimensions under an ac electric field. We demonstrate that the WKB approximation agrees well with numerical results obtained by solving the time-dependent Schr{o}dinger equation and point out that the quantum interference is important in HHG. We also predict in the deep nonperturbative regime that (1) harmonic intensities oscillate with respect to electric-field amplitude and frequency, with a period determined by the St{u}ckelberg phase; (2) cutoff order of HHG is determined by the Keldysh parameter; and that (3) non-integer harmonics, controlled by the St{u}ckelberg phase, appear as a transient effect.
CeRhIn$_5$ provides a textbook example of quantum criticality in a heavy fermion system: Pressure suppresses local-moment antiferromagnetic (AFM) order and induces superconductivity in a dome around the associated quantum critical point (QCP) near $p_{c} approx 23,$kbar. Strong magnetic fields also suppress the AFM order at a field-induced QCP at $B_{rm c}approx 50,$T. In its vicinity, a nematic phase at $B^*approx 28,$T characterized by a large in-plane resistivity anisotropy emerges. Here, we directly investigate the interrelation between these phenomena via magnetoresistivity measurements under high pressure. As pressure increases, the nematic transition shifts to higher fields, until it vanishes just below $p_{rm c}$. While pressure suppresses magnetic order in zero field as $p_{rm c}$ is approached, we find magnetism to strengthen under strong magnetic fields due to suppression of the Kondo effect. We reveal a strongly non-mean-field-like phase diagram, much richer than the common local-moment description of CeRhIn$_5$ would suggest.
We have developed an approach to control the carrier density in various material under high pressure by the combination of an electric double layer transistor (EDLT) with a diamond anvil cell (DAC). In this study, this EDLT-DAC was applied to a Bi thin film, and here we report the field-effect under high pressure in the material. Our EDLT-DAC is a promising device for exploring unknown physical phenomena such as high transition-temperature superconductivity (HTS).
Neutron-scattering and specific-heat measurements of the heavy-fermion superconductor URu2Si2 under hydrostatic pressure and with Rh-doping [U(Ru{0.98}Rh{0.02})2Si2] show the existence of two magnetic phase transitions. At the second-order phase transition Tm ≈ 17.5 K, a tiny ordered moment is established, while at TM < Tm, a first-order phase transition (under pressure or doping) gives rise to a large moment. The results can be understood in terms of a hidden OP Psi coupled to the ordered moment m, where m and Psi have the same symmetry.
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